Engineered Stability: The History of Composite Materials in the 19th and 20th Centuries 3658414073, 9783658414078

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Andreas T. Haka

Engineered Stability The History of Composite Materials in the 19th and 20th Centuries

Engineered Stability

Andreas T. Haka

Engineered Stability The History of Composite Materials in the 19th and 20th Centuries

Andreas T. Haka Section for the History of Science and Technology University of Stuttgart Stuttgart, Germany

ISBN 978-3-658-41407-8 ISBN 978-3-658-41408-5 (eBook) https://doi.org/10.1007/978-3-658-41408-5 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Fachmedien Wiesbaden GmbH, part of Springer Nature 2023 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Fachmedien Wiesbaden GmbH, part of Springer Nature. The registered company address is: Abraham-Lincoln-Str. 46, 65189 Wiesbaden, Germany

Foreword

Andreas Haka’s book is mainly devoted to laminate and fibre-composite materials research and its history in Germany—as reflected in developments around the world. In fact, almost all relevant materials are composites, and the origins of very many new composites in all fields of application lie in Germany. Ranging from automotive design to aerospace, shipbuilding, mechanical engineering and electrical engineering, their emergence was partly driven by industry, partly by far-sighted institute foundings at polytechnics now mostly redesignated as universities. These academic institutes were often transformed into institutions in their own right, which in most cases were so successful that they not only continue to exist today, but experience an ongoing fascinating adaptation to the respective requirements of the day in terms of content and personnel. This proves how effective the appointment practices at our universities have been in the past in many cases, and the significance it has on interactions with industry. In the present grippingly written study, Mr. Haka considers both the practical aspects of composite materials development in German institutions and companies as well as the integration of innovative demands in history and their satisfaction by suitable framing conditions and effective hiring in the respective cases considered. Thereby he moves easily and ably between historical and political boundaries to reveal the connections between the people involved, the material requirements as well as the industrial challenges of the period. This allows the reader to absorb the interactions and logical trains of thought quickly and effortlessly. The contemporary sources document the interdependencies among the players, if not their independence, as well as the pioneering spirit of personalities who by virtue of their skill and ability staked out the essential course, some of the lasting effects of which we can only marvel at today. Many examples meticulously retrace how certain developments which elicit admiration and demand abroad became possible at all in the first place. One example is the recent creation of the hardwood technical centre Technikum Laubholz as a spin-off of the German Institutes of Textile and Fibre Research Deutsche Institute für Textil- und Faserforschung (DITF Denkendorf) with state funding. The aim was to promote broadly and consolidate the production of C-fibres from wood on a commercial scale, which was in principle successful at the parent institute. Similar isolated efforts do v

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exist worldwide to exploit the potential of wood beyond the applications of that classical composite material. Nevertheless, this development is unique for the comprehensive and scientifically sustainable manner in which it had been envisaged, and probably will remain so for a very long time. Of greatest merit in Mr. Haka’s investigations is his identification of the intellectual precursors to such and other innovative developments, especially the ones located at the interface between academia and commerce, since they are often not so readily visible to either the layman or the specialist. Museums might be most likely to attempt to highlight such connections for the interested viewer by means of select images and citations. However, that insight is often reserved to specialists, as in the case of more recent company museums, such as for the firms Eberspächer in Esslingen or Mahle in Stuttgart. Otherwise the level is reduced to cater to a general lay public or to schoolchildren without any ambition to place the connections within any larger context. Mr. Haka’s survey of these interrelations treats not only the directly involved parties and their institutions but also the historical processes underway in parallel, which mostly reveal the demands and true specifications for sought advances, such as army requirements for lightweight composite materials or, at that time, for Zeppelin technology, as well as for current-day low cost wood-derived C-fibre production. Glass fibre development illustrates particularly vividly the involvement of the leading industrial institutions of the day with the polytechnics in Dresden, Darmstadt, Aachen and Stuttgart, as well as the lightweight construction requirements of the aircraft industry and their ties to the important institutions of the time, even the Materials Testing Office in Dresden. Assuming the commercial aspect, the company Römmler AG in Spremberg in Upper Lusatia, which is associated with the composite material resopal, repeatedly appears, just to mention one representative example from the book. The technical requirements of these new materials dictated that the underlying theory be developed as well, so technical engineering, including fracture mechanics and design technology, benefited in particular, alongside materials science proper. As a consequence, the innovative power of composite materials development extended even further to include thermodynamics and—due to its utilization in aircraft construction—even fluid mechanics. The trend towards reinforced presstoff materials, which was gathering strength from these developments, led to a counter-reaction to the all-metal aircraft equipment pursued by the German Association of Engineers (VDI) and the triumphant advance of duraluminium. Interwoven into this exciting story about the development of composite materials are a number of more personal strands in which people such as Udet, the Horten brothers, Junkers or Rommel figure, as well as institutions such as the then German Aviation Research Institution (DVL) in Berlin, the Army Experimental Station (Heeresversuchsanstalt) in Peenemünde or the Kaiser Wilhelm Institute of Fluid Dynamics Research in Göttingen. It is interesting to note in this context that GFRPs were developed and used in Germany much earlier than in the USA.

Foreword

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In the matter of composite materials, besides resopal such famous brands as aramide or kevlar also appear, which made a name for themselves in the USA, as well as a number of other well-known materials such as GRP, balsa wood, bakelite, pressboard, GLARE® , CFRP and the CMCs, MMCs, PNCs, to name but a few and to preempt their mention here. Andreas Haka, with whom I had the pleasure of offering the lecture History and Practice of Materials Testing to interested students, broached the essential stages in the development of composites guided by five topics and seven phases in the scientific development of materials. It is fair to say that following this scheme his exposition has persuasively succeeded. June 2021

Prof. Dr. Dr. h.c. Siegfried Schmauder Stuttgart University Institute for Materials Testing, Materials Science and Strength of Materials Lenningen, Germany

Preface

Composite materials are ubiquitous today even though people are generally unaware of this. Many users still have the classical material categories too much in mind, such as steel, aluminium, wood and concrete. The range of applications that composites with their “adjustable” properties have conquered is becoming ever broader and multifarious. This is a crucial characteristic of composites that sets them apart, besides many other parameters in their favour as materials, especially nowadays when urgent issues about resources and sustainability are waiting to be solved. Thus far, little is known about the historical and by no means unidirectional development of composite materials. Although individual episodes recur in the relevant literature in a fragmentary fashion, as a rule composites are only contextualized within the framework of performance parameters in materials technology, as a means toward a specific end. Any focus on the material itself rarely takes place. This inquiry within the history of materials science presents for the first time the research strategies employed in 19th and 20th-century technology in designing hybrid materials. Numerous facts are established that evidence a back-and-forth between applied engineering and technological probings of such “building-block” materials. The development of composite materials proves to have followed a highly interdisciplinary path. In this area multiple fields are interwoven since the outset. The present analysis initially outlines the early history of composites in order to show that composites are not an invention of modern times. However, the focus of this book is on the developments from the nineteenth and twentieth centuries, which were initially flanked and driven by industrialization. Composite materials are used in a wide variety of fields, such as aerospace, vehicle construction, boat- and shipbuilding, mechanical engineering, construction, electrical engineering and recreational sports, among others. Retracing the development in all these areas would have overtaxed this research project. Thus, the concentration is on important stages of development, with the materials involved always placed centre stage. The idea to write this book was inspired by the interdisciplinary lectures I held at the University of Stuttgart on the history and practice of materials science (with the topic clusters: materials testing, liquid crystals and superconductivity) and on the history and ix

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practice of research technologies (with the topic clusters: electron microscopy, laser technology, thermography and fibre-composite technology). The extensive researches carried out within this context, also pertaining to the fibre-composite technology cluster, laid the groundwork in the writing of this book, along with my own experiences in industry and non-academic research as an engineer in the field of composite materials development. As a result of these lecture cycles and the associated research, I also realized how little current knowledge is communicated in particular about the focal subjects of fibre-composite technology and materials testing—indeed also about already established knowledge in materials technology—or how few insights are conveyed within a given specialty and even beyond disciplinary boundaries. Surveyal of older findings in the literature is almost always omitted. As a result, many materials, techniques and technical terms are forgotten, and subsequently much research is repeated and even patented as a result of such ignorance. The reasons for this are complex. However, the fact that it is worthwhile to reactivate or reprocess “outdated” or even historical knowledge is suggested by the large number of current enquiries which I receive, for example, from the aerospace and automotive industries. Materials such as various magnesium alloys, titanium and different ceramics are experiencing a renaissance within the context of lightweight construction design, which is based not least on knowledge dating back to the 1930s and 1940s and in some cases even much earlier. The primary aim of this work is to present the genesis and significance of composite materials within historical context. This book therefore addresses historians of science and technology as well as engineers, architects, scientists and the interested layperson. Dresden, Germany June 2021

Andreas T. Haka

Preface to the English Edition

Among the extensive and positive responses to the German edition from fellow colleagues and from other interested parties in Germany—but above all, also from abroad—I have received many requests that my book also appear in English. Many of the developments covered in it are unknown or suit other subject areas well, such as the histories of materials science or of textiles, material culture, or the immediate and early developments of glassfibre-reinforced plastics. Likewise, as regards the ambivalent development of the Horten brothers’ flying wing or composite materials development in the GDR. These wishes for a broader readership I seek to meet with the present translation. The decision to publish the book in English also gave me the opportunity to include a number of current research findings which I had not yet concluded by the editorial deadline of the German edition, and to highlight new areas of interest for stimulating discourse. This involves, for example, my research dealing with the convoluted interrelationships between: the Holig homogeneous wood factory and the Research and Design Association of the headquarters of the Reich Labour Service as well as the German Timber-Construction Convention (FOKORAD) and the company Christoph & Unmack. Also involved are findings on the early serial and standardized production of wood and wood-derived materials, starting with machine-tooled furniture or buildings fabricated by Deutsche Werkstätten Hellerau. My focus here is specifically on the afore-mentioned FOKORAD, about which I would like to present initial results, such as their work during the National socialist era on a project designing disassemblable barracks, for instance, as stabling for the Army High Command, which were ultimately utilized by the SS so terribly in concentration camps like Auschwitz to intern people and thus became a defining symbol of the exterminations of the Holocaust. In addition, it was only after the editorial deadline had elapsed that I gained access to documentation on the design project Hütter Hü 211, a fibre-aligned lightweight wooden long-range reconnaissance plane from 1943. This material, which had hitherto been supposed lost, is among the papers left by Wolfgang Hütter. In the interim, I was able to evaluate this estate and incorporate initial findings in the present book. The aircraft

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developed by Hütter, which never took to the skies, is worth mentioning because the concept he used for the materials concerned can be considered an interesting offshoot in the development of composites. Furthermore, I have made minor additions to a number of chapters and supplemented suitable illustrations. I hope to have thus found a suitable introduction to a range of topics, the presentation or historical reflection upon which has only just begun. Dresden, Germany October 2022

Andreas T. Haka

Acknowledgements

My special thanks go foremost to Prof. Dr. Klaus Hentschel (Director of the Section for History of Science and Technology, University of Stuttgart), who generously supported and encouraged this work. I would also like to express my sincere gratitude to my colleagues from the Arbeitskreis Faserverbund-Leichtbau of the reference manual Luftfahrttechnisches Handbuch (LTH) for their kind support of my work. In particular, I would like to thank the following members of this LTH working group (in alphabetical order): Prof. Dr. Wilfried Becker (Head of Structural Mechanics Department, TU Darmstadt), Dr. Stefan Carosella (Institute of Aircraft Design, University of Stuttgart), Dipl.-Ing. Ulrich Denecke (Airbus Helicopters, Donauwörth), Dipl.-Ing. Ralf Herrmann (Airbus Operations, Bremen), Dipl.Ing. Paul Kächele (formerly Pilatus Aircraft Ltd, Stans, Switzerland), Dipl.-Ing. Frank Kocian (German Aerospace Centre, Institute of Propulsion Technology, Köln), Dipl.-Ing. Holger Orawetz (Qpoint Composite, Dresden), Dipl.-Ing. Jan-Uwe Roth (Dornier Seawings, Wessling), Dipl.-Ing. Joachim Scharringhausen (formerly MT Aerospace, Augsburg), Dipl.-Ing. Hans-Peter Wentzel (formerly Airbus Operations, Bremen), all of whom discussed with me fibre-composite developments during numerous working group meetings in recent years. I am especially indebted to Dipl.-Ing. Peter F. Selinger (Stuttgart). He gave me a number of insights into his conversations with Reimar Horten and his collaboration with him. I would also like to thank him for his permission to assess and use the documents in his private possession and for the photographic material on the aircraft builders Reimar and Walter-Max Horten and their flying wing models, as well as on Wolfgang Hütter. I would like to thank Dr. Elsa Nickel (Bonn), Mr. Klaus W. Horten (Bonn) and the retired vice admiral Dirk Horten (Hamburg) for their willingness to talk to me and allow me to use photographs and texts from their family collections. I am grateful to Dr. Evelyn Crellin of the National Air and Space Museum—Smithsonian Institution, Aeronautics Department (Washington D.C, USA), for the discussions and exchanges on the Horten Model H IX and for pin-pointing the relationship between the Horten brothers and the pilot Hanna Reitsch.

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Ms. Lauren Anne Horelick, M.A. of the American Institute for Conservation of Historic and Artistic Works (Washington D.C., USA) made available to me the material analysis of the Horten IX V3. Special thanks go to Dr. Hans Jürgen Kärcher and Dipl.-Ing. Dieter Muser for their willingness to tell me about their work on the SOFIA project and for leaving at my disposal a large number of documents and photographic material. Prof. Stephen W. Tsai, research emeritus, aeronautics and astronautics, Stanford University, California, USA had numerous discussions and kind exchanges with me about the development of the theoretical approaches to composite materials, for which I am grateful. I would like to thank Prof. em. Dr. Helmut Schürmann (Technische Universität Darmstadt) for turning my attention to the studies by Alfred Puck and Zvi Hashin and consulting me on questions of technical terminology in the context of FRP. Prof. em. Dr. Ralf Cuntze (formerly MAN-Technologie, head of the Department of Structural and Thermal Analysis) offered helpful explanations on the topic of failure criteria for FRP besides information about his own work in this context. I had the opportunity to discuss the work by Wilhelm Thielemann and the fundamentals of classical laminate theory with Prof. Dr. Klaus Rohwer (formerly of the German Aerospace Centre (DLR), Institute of Composite Structures and Adaptive Systems, Braunschweig), and I thank him for this. I am endebted to Prof. Dr. Walter Sauer of the Max Himmelheber-Stiftung for his kind support of my work and for providing the Foundation’s historical specimen for technical material analysis. I would also like to sincerely thank Dr. Jessika Wichner, the head of the Central Archive of the German Aerospace Centre in Göttingen, for her interest in my work and her support on aspects within the context of German aeronautical research. All the staff at the numerous university, state and company archives in which I conducted research must also be thanked for their support of my research endeavours. I must also express my gratitude to my colleagues Dr. Josef Webel (Mörlenbach) and Dr. Tino Kühn (scientific director at the Chair for the Development and Assembly of Textile Products, Technical University, Dresden), with whom I was able to discuss my work and the topic of hybrid materials. My exceptional thanks go to Mrs. Ann M. Hentschel, B.A. (Stuttgart) for her meticulous translation work, which ensured that the content in this edition could be rendered in accurate linguistic form. Last but not least, my gratitude goes to my wife Susann and my family, who supported me throughout all the phases leading to the appearance of this volume.

Contents

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Content of This Study and Guiding Questions . . . . . . . . . . . . . . . . . . . . . . . 1.2 Temporal and Spatial Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 State of the Art in Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4 Overview of Important Primary and Secondary Sources . . . . . . . . . . . . . . . 1.5 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5.1 Network Analysis of Primary and Secondary Sources . . . . . . . . . . 1.5.2 Stoffgeschichte and Product-Line Analysis . . . . . . . . . . . . . . . . . . . . 1.5.3 Material Culture (Studies) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5.4 Biographical Facets, Institutional and Corporate History . . . . . . . . 1.5.5 Eyewitness Interviews . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5.6 My Own Methodological Approach—Typology . . . . . . . . . . . . . . . . 1.6 Structure of the Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.7 Terms and Definitions of Composite Materials . . . . . . . . . . . . . . . . . . . . . . . 1.8 Terminology—Material Versus Hybrid Material . . . . . . . . . . . . . . . . . . . . . .

1 4 6 6 26 31 31 33 37 41 43 46 48 51 55

2 Early Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 Unique Piece from the Stone Age . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 First Reproducible Composite Materials—Fibre-Reinforced Bricks . . . . . 2.3 First Weapons—Composite Bows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4 Papier-Mâché—Composite Material from the Middle Ages . . . . . . . . . . . .

61 61 62 66 69

3 The Development of Composite Materials Within the Context of 19th-Century Industrialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 The Plastic Masses Versus Presstoff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.1 Materials Design of the Plastic Masses . . . . . . . . . . . . . . . . . . . . . . . 3.1.2 The Development of Vulcanized Fibre, an Early Laminate Around 1850 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Wood as a Fibre Composite and the Development of Industrially Manufactured Wooden Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.1 Veneer Wood Versus Plywood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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3.2.2 Fibreboard and Chipboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.2.1 Standardization and Norms—The Holig Homogenholzwerke, from Aircraft Flooring to Prisoner Barracks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 Machine Elements—Early Designs with Hybrid Materials . . . . . . . . . . . . . 3.3.1 Early Presstoff and Layered Materials From the 1880s to the Turn of the Century . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Composites in 20th-Century Polymer Chemistry . . . . . . . . . . . . . . . . . . . . . . . . 4.1 Between Aesthetics and Functionality—Bakelite, The First Years Until 1930 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.1 Bakelite “A-Wing” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.2 “Old” Materials in Early Lightweight Designs the Productive 1920s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.2.1 John Dudley North . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.2.2 Albin Kasper Longren . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 A High-Performance Material Matrix From Polymer Chemistry in the Early 1920s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.1 “Engineered Stability”—Layered Presstoff, a Modern Fibre Composite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.2 Machine Elements as “Fibre-Composite Pioneers”—the Development Between 1925 and 1945 . . . . . . . . . . 4.2.3 First German Presstoff Plain-Bearings Research in Darmstadt and Dresden . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Römmler AG Versus Dynamit Nobel AG . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.1 Presstoff, an Emancipated “Substitute Material”? . . . . . . . . . . . . . . 4.3.2 Top-Secret Order on “Presstoff”—Compressed Thermoplastic in Armaments Research and Production in the 1930s and 1940s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.2.1 Competency Disputes About Where to Apply the Materials Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.2.2 Specialized Navy and Army Orders for Römmler AG . . . 4.4 Between Professional and Political Ambivalence—Fibre Research from 1920 to 1945 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.1 Friedrich Tobler—Botanist, Fibre Researcher, Raw Materials Expert . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.1.1 Glass-Fibre-Reinforced Plastic—A Secret Serial Product for the Luftwaffe from the 1940s . . . . . . . . . . . . . 4.4.2 Institute of Materials Research at the DVL—New Materials and Conventional Knowledge—Researches Between 1930 and 1945 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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95 108 108 113 113 121 127 127 130 134 135 138 141 146 150

153 156 160 165 172 177

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4.4.2.1 Uncharted Academic Territory Far Removed From University Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.3 Fibre Research—The Institute of Materials Research at the DVL and the Graf Zeppelin Research Institute . . . . . . . . . . . 4.5 Aviation Case Study I: Fibre-Aligned Wood Construction. Developing an Aircraft that Never Flew—The Hütter Hü 211 . . . . . . . . . . 4.5.1 Preamble to the Reconnaissance Aeroplane Hütter Hü 211 . . . . . . 4.5.2 Fibre-Aligned Lightweight Wood Construction and Conventional Moulded-Wood Production . . . . . . . . . . . . . . . . . . 4.5.3 Testing of Construction Methods and Materials to Underpin Design Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.4 Moulded Wood Versus Shell Fabrication . . . . . . . . . . . . . . . . . . . . . . 4.5.5 Foreign and Forced Labour for the Hü 211 . . . . . . . . . . . . . . . . . . . . 4.6 Aviation Case Study II: New Load Horizons for Aircraft—the Horton Brothers’ Fibre-Composite Flying Wing from 1935 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6.2 The Horten Brothers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6.3 The Horten Flying Wing Model H V-a Made of Layered Presstoff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6.4 The “Composite” Flying Wing IX V2/V3 by the Horten Brothers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6.5 Composite Materials and Their Applications in Foreign Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Development of Hybrid Material Systems in the Second Half of the Twentieth Century . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1 The Bridge to the Future—Glass-Fibre-Reinforced Plastic and the Akafliegs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 New Load Horizons from “Black Gold”—Early 1970 . . . . . . . . . . . . . . . . . 5.2.1 Student Involvement Leads to Serially Produced CFRP . . . . . . . . . 5.2.2 A New “Era in Materials Engineering” for Civil Aviation . . . . . . . 5.3 Research with Limited Prospects—GDR Composite Materials Development, 1954 to 1980 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.1 The “Reinvention” of Lightweight Design . . . . . . . . . . . . . . . . . . . . 5.3.2 From Garland to Lightweight “Honeycomb” in Aviation . . . . . . . . 5.3.3 Composite Materials Development Compared—FRG and GDR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4 Beast of Burden for the Ether—The SOFIA Project, 1985 to 2009 . . . . . 5.4.1 First Steps and Historical Obstacles . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.2 “Black” Decision and New Ways Along Old Paths . . . . . . . . . . . . . 5.4.3 The “Black-Frame” View into the Past and Future . . . . . . . . . . . . .

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187 194 197 198 201 205 210 215

218 218 221 231 241 251 257 257 260 260 272 281 282 288 293 300 302 305 308

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5.5 Hybrid Materials with Other Matrices and Reinforcing Materials . . . . . . .

312

6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

315

Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

343

List of Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

345

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

355

Name Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

393

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

397

Abbreviations1

AEG AFRP AFTUD

AHA AIC AK Akaflieg APS AVA BASF BFRP BLHA BMFT BMVg BMW BWB

Allgemeine Elektricitäts-Gesellschaft, electrical combine in Berlin/ Frankfurt am Main Aramide-fibre-reinforced plastic (AFK in German) Archiv des Vereins zur Förderung von Studierenden der Technischen Universität Dresden e. V., archive of the association for the promotion of students at TU Dresden Allgemeines Heeresamt, General Office of the Army American Institute for Conservation of Historic and Artistic Works, Washington D.C Arbeitskreis, working group Akademische Fliegergruppe, aircraft design association, Braunschweig Archive of Peter F. Selinger, Stuttgart Aerodynamische Versuchsanstalt, Aerodynamic Testing Station, Göttingen Badische Anilin- & Soda-Fabrik, chemical company, Ludwigshafen Boron-fibre-reinforced plastic (BFK in German) Brandenburgisches Landeshauptarchiv, Main Archive of the Province of Brandenburg Bundesministerium für Forschung und Technologie, German Federal Ministry of Research and Technology Bundesministerium der Verteidigung, German Federal Ministry of Defence Bayerische Motoren Werke Aktiengesellschaft, automotive company Bundesamt für Wehrtechnik und Beschaffung, German Federal Office of Defence Technology and Procurement, integrated in 2012 into the newly established higher federal authority: Bundesamt für Ausrüstung, Informationstechnik und Nutzung der Bundeswehr, Federal

1 German abbreviations not normally used in this translation are rendered parenthetically in italics.

xix

xx

CFRP CMC CMEA DAG DARA DFL

DFVLR

DIN DKW DLR DSH DSI DVL Eff ETH FCM FDJ FEM FGZ FOKORAD

FRG FRP FZL

Abbreviations

Office of Army Equipment, Information Technology and In-Service Support (BAAINBw) Carbon-fibre-reinforced plastic (CFK in German) Ceramic matrix composites Council for Mutual Economic Assistance (Comecon) Dynamit-Actien-Gesellschaft (stock company), formerly Alfred Nobel & Co. Deutsche Agentur für Raumfahrtangelegenheiten, German Agency for Spacecraft Affairs Deutsche Forschungsanstalt für Luftfahrt, German Aeronautical Research Institute, Braunschweig (a.k.a. Luftfahrtforschungsanstalt Hermann Göring 1938–45) Deutsche Forschungs- und Versuchsanstalt für Luft- und Raumfahrt, German Research and Testing Institute of Aeronautics and Astronautics German industrial standard Dampf-Kraft-Wagen, a vehicle model by Auto Union AG Deutsches Zentrum für Luft- und Raumfahrt, German Aerospace Centre Deutsche Studiengemeinschaft Hubschrauber, German Study Group on Helicopters in Stuttgart Deutsches SOFIA Institut, Stuttgart Deutsche Versuchsanstalt für Luftfahrt e.V., German Aviation Research Institute, Berlin Material stressing effort, stress exposure Eidgenössisch-Technische Hochschule, Swiss Federal Institute of Technology, Zurich Fibre composite material (FVW in German) Freie Deutsche Jugend, German youth association Finite element method Forschungsanstalt Graf Zeppelin, Graf Zeppelin Research Institute, Stuttgart Forschungs- und Konstruktionsgemeinschaft der Reichsleitung des Reichsarbeitsdienstes und der Deutschen Holzbau-Konvention, Research and Design Association of the Reich Labour Service and the German Timber-Construction Convention Federal Republic of Germany (Bundesrepublik Deutschland, BRD) Fibre-reinforced polymer or plastic (FVK in German) Forschungszentrum der Luftfahrtindustrie der DDR, Research Centre of the Aviation Industry in the GDR

Abbreviations

GDR GFP GFRP GNT

GST HMS I.G. Farben IAND IFF IMF IRAM KAO KEL KWG KWI LEWH LFU LTH MAN GHH MAN SE MBB MKN MPA MPBD NASA NASM NATO NESC

xxi

German Democratic Republic (Deutsche Demokratische Republik DDR, former East Germany) Glasfaserverstärkte Plaste, term used in East Germany for its variant of GFRP Glass-fibre-reinforced plastic (GFK in German) Geschichte der Naturwissenschaften und der Technik, Section for History of Science and Technology, History Department, University of Stuttgart Gesellschaft für Sport und Technik, Sports and Technology Association, East Germany Hybrid material systems (HWS in German) Interessengemeinschaft Farbenindustrie AG, chemical trust, Frankfurt am Main Institut für angewandte Naturwissenschaften, Institute of Applied Natural Sciences Dresden Inter-fibre failure Interview with Manfred Flemming Institut de Radioastronomie Millimétrique, Grenoble Kuiper Airborne Observatory, California Komponenten- und Experimentalprogramm, research programme Kaiser-Wilhelm-Gesellschaft, Kaiser Wilhelm Society Kaiser-Wilhelm-Institut, Kaiser Wilhelm Institute Lebenserinnerungen by Walter Horten, notes and memoirs (see Primary Sources) Leichtflugtechnik Union, Union of Lightweight-Flight Engineers Luftfahrttechnisches Handbuch, standard aviation reference, editorial offices, Ottobrunn MAN Gute Hoffnungs-Hütte AG, metallurgical and mechanical engineering enterprise Maschinenfabrik Augsburg-Nürnberg, Societas Europaea, Munich Messerschmitt-Bölkow-Blohm GmbH, aviation company in Ottobrunn “Memorandum”, unpublished memoirs of Prof. Dr. Karl Nickel (see Primary Sources) Materialprüfungsanstalt, Materials Testing Institute, Stuttgart Materialprüfungsamt Berlin-Dahlem, Materials Testing Office National Aeronautics and Space Administration, Washington D.C. National Air and Space Museum—Smithsonian Institution, Washington D.C. North Atlantic Treaty Organization, Brussels NASA Engineering and Safety Center, Hampton, Virginia

xxii

NFRP NLR NSBDT NSDAP NSFK NSLB NVA OHG OKH OKM OKW PDM

PfL PNC PRONAOS PVC RAD RF RFR RLM RTM RWS RWTH S.A.Z. SED SOFIA TH TNL

Abbreviations

Natural-fibre-reinforced plastic (NFK in German) Nationaal Lucht- en Ruimtevaartlaboratorium, National Aerospace Laboratory, Delft Nationalsozialistischer Bund Deutscher Technik, National Socialist League of German Technology Nationalsozialistische Deutsche Arbeiterpartei, Nazi German Workers’ Party Nationalsozialistische Fliegerkorps, Nazi Flying Corps Nationalsozialistischer Lehrerbund, National Socialist Teachers League Nationale Volksarmee, East-German People’s Army Offene Handesgesellschaft, general partnership (commerce) Oberkommando des Heeres, High Command of the German Army Oberkommando der Marine, High Command of the German Navy Oberkommando der Wehrmacht, High Command of the German Armed Forces Prosopographische Datenbank von Maschinenbauern an deutschen Hochschulen und außeruniversitären Forschungseinrichtungen des 19.und 20.Jahrhunderts: Haka (2014b) Prüfstelle für Luftfahrtgeräte der DDR, East-German aircraft testing station, Dresden Polymer nanocomposites Programme National d’Observations Submillimétriques Polyvinyl chloride Reichsarbeitsdienst, Reich Labour Service Reserve factor Reichsforschungsrat, Reich Research Council Reichsluftfahrtministerium, Reich Ministry of Aviation Resin transfer moulding Rheinisch-Westfälische Sprengstoff AG, explosives manufacturer Rheinisch-Westfälische Technische Hochschule, polytechnic in Aachen Schwachstellenauswertungszentrum des Heereswaffenamtes, vulnerability assessment centre of the German Army Ordnance Office Sozialistische Einheitspartei Deutschlands, Socialist Unity Party of (East) Germany Stratospheric Observatory For Infrared Astronomy Technische Hochschule, polytechnic, academic institute of technology Technische Norm Luftfahrt, technical standard of the East-German aviation industry

Abbreviations

TU UA TUD UD USSR VDE VDI VEB VFW VVB Wa Abn Wa Chef Ing 1 WA Chef Ing 3/Hz Wa J Rü Mun 2 WA Prüf 1 Wa Prüf 2 Wa Prüf 4 Wa Prüf 5 Wa Prüf 6 Wa Prüf 7 Wa Z 5

WWFE ZTL

xxiii

Technische Universität, technical university University Archive, Technische Universität Dresden Unidirectional Union of Soviet Socialist Republics Verband Deutscher Elektrotechniker, German Electrotechnical Association Verein Deutscher Ingenieure, Association of German Engineers Volkseigener Betrieb, publicly-owned enterprise in GDR Vereinigte Flugtechnische Werke GmbH, aerospace manufacturer, Bremen Vereinigung Volkseigener Betriebe, federation of publicly-owned enterprises in GDR Heereswaffenamt, Amtsgruppe Abnahme, German Army Ordnance, inspections division Heereswaffenamt, Chefkonstrukteur, German Army Ordnance, chief designer Heereswaffenamt, Abt. Halbzeuge, German Army Ordnance, semifinished products department Heereswaffenamt, Munitionsabteilung, German Army Ordnance, ammunitions department Heereswaffenamt, Ballistische und Munitionsabteilung, German Army Ordnance, ballistics and ammunition department Infanterieabteilung, German Army Ordnance infantry department Artillerieabteilung, German Army Ordnance artillery department Pionier-und Eisenbahnpionier-Abteilung, pioneers and railway pioneers department Abteilung Panzer-und Motorisierung, Ordnance tanks and motorization department Heereswaffenamt, Nachrichtenabteilung, Army Ordnance, communications department Zentrale Amtsgruppe des Heereswaffenamtes, Abteilung technisches Regelwerk, Army Ordnance central office group, technical control department World-wide failure exercise “Zukunft—Technik—Luft”, research programme “Future—Technology—Air”

List of Figures

Fig. 1.1

Fig. 1.2

Fig. 1.3 Fig. 1.4

Fig. 1.5

Fig. 2.1

Fibre composite, here a simple fibre composite in which the fibres run in a single direction in accordance with the load. Other fibre composites have their fibres arranged at other angles (resp. to one another) depending on the requirements of the given component (CAD model: A. Haka) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Laminate composite in which the individual layers can be arranged to have different fibre alignments respective to one another (CAD model: A. Haka) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Particle or particulate composite (CAD model: A. Haka) . . . . . . . . . . . Google Ngram Viewer query on the usage of the terms Verbundwerkstoff (blue line) and Hybridwerkstoff (lower red line). This shows that the former evidently is used synonimously in the German-speaking world for composite materials. The latter term has been in use only haltingly since 1994. Obviously, this term is only used among specialists. Source Google Ngram Viewer, retrieved 21 Nov. 2020 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Google Ngram Viewer query on the technical terms “composite material”, “hybrid material” and “layered material”. Usage of the technical term composite material in English begins to rise in the 1960s with the appearance of glass-fibre-reinforced plastic and later carbon-fibre-reinforced plastic. Occurrences of “layered composite” and “hybrid material” here for comparison . . . . . . . . . . . . . Straw-reinforced bricks from the labourer settlement of Deirel-Medina, which is located on the west bank of Thebes, south-east of the Valley of the Kings in Egypt. It was inhabited from about 1520–1069 BC by the workers who constructed the pharaonic rock tombs. Photo Courtesy of Klaus Hentschel, 18 Feb. 2020, Deirel-Medina, Egypt . . . . . . . . . . . . . . . . . . . . . . . . . . . .

52

54 54

56

60

63

xxv

xxvi

Fig. 2.2

Fig. 2.3

Fig. 2.4 Fig. 2.5

Fig. 3.1

Fig. 3.2

Fig. 3.3

Fig. 3.4

Fig. 3.5

List of Figures

Excerpt from the mural of the vizier Rekhmire showing the production of Nile mud bricks. Left: mud extraction in and on the banks of the Nile; lower centre: mud and straw compounding, and upper centre: brick production; right: measurement and computation of the quantity of building materials. Source Myers (1897, p. 13) . . . . . . . . . . . . . . . . . . . . . . . . . . . The bow described by Henry Balfour; from the left, the whole length of the bow, in cross-section, and the prominent incisions on the bow shaft. Source Balfour (1897, p. 221) . . . . . . . . . . . . . . . . . . Cross-section showing the structure of the composite material of a composite bow. Source Balfour (1897, p. 213) . . . . . . . . . . . . . . . . The altar-piece painted on Ludwigslust carton in the choir room of the former Ludwigslust castle church, which is currently the Evangelical Lutheran church for the town of Ludwigslust. Source Postcard (1930) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Excerpt from the patent by J. W. Hyatt. The manufacture and structure of the balls can be clearly seen in the fifth sketch (Fig. 1.5). The longitudinal section shows how individual cellulose ring layers are stacked upon one another and later pressed together to thereby obtain its precisely spherical shape. The ring holes facilitate precise alignment of the layers by inserting a pin to row them up like a string of beads. Source Patent—John Wesley Hyatt, US Patent No. 50,359 from 1865 . . . . . . . Diagram of the most important early plastics, which were developed by modifying natural materials, along with example products made of them (Compilation: A. Haka) . . . . . . . . . . . . . . . . . . . On the left: Suitcase made of vulcanized fibre from 1926. Right: company logo of WICO Görlitz, which manufactured such travel suitcases, among other products. Photos A. Haka, 28 Aug. 2019 . . . . Chest made of cedar wood, veneered with ebony and ivory, from the tomb of Tutankhamun. Source Knight and Wulpi (1930), p. 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-section of a plywood board—the light and dark individual layers of wood clearly show the laminate structure and the hybrid character of the material. The grain layers are arranged alternately at an angle of 90º and pressed together to form a uniform board by means of an adhesive. Photo A. Haka, 6 Sep. 2019 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

64

68 68

71

77

79

83

86

87

List of Figures

Fig. 3.6

Fig. 3.7 Fig. 3.8

Fig. 3.9 Fig. 3.10

Fig. 3.11

Fig. 3.12

View of the cross-section of a fibrous felt-like fibreboard of medium density, the fine fibres of which have been compressed under pressure and heat to form a tight fleece, and which here serve as the support material for the lighter-coloured furniture veneer on top. Photo A. Haka, 6 Sep. 2019 . . . . . . . . . . . . . . . . . . . . . . These patent drawings from 1901 illustrate the hybrid material structure of early chipboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Section through a chipboard according to DIN EN 309, in which the chips in the upper and lower layers were compacted more by the pressing process than in the core area of the board, which is essentially because of the differing chip sizes in the middle and surface layers. Photo A. Haka, 6 Sep. 2019 . . . . . . . . . . . . . . . . . . Max Himmelheber (1904–2000), as a first lieutenant in the Luftwaffe in 1943. Source Himmelheber-Stiftung . . . . . . . . . . . . Experimental aircraft trim tab for the model Me 109 made of foam wood (spruce) coated with a resin-impregnated sateen fabric. This composite material was manufactured by the homogeneous-wood process at “Holig”. Homogenholzwerke GmbH Görlitz 1944. Source Himmelheber-Stiftung, Photo: A. Haka, 10 June 2022 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Barracks blueprint by Holig-Werke using the designation “foreigners’ accommodations” for the forced-labourer barracks at the Holig Homogenholzwerke branch plant in Neustrelitz. It was part of the funding application submitted to the construction planning office of the Reichsminister der Luftfahrt und Oberbefehlshaber der Luftwaffe. Source Attachment 5 of the application, BArch R8121/508 Bl. 166 . . . . . . . . . . . . . . . . . . . . . Barracks by Christoph and Unmack, which was patented in 1933 and based on the Doecker standard barracks design by the Danish officer Johann Doecker. Source Patent Christoph and Unmack, Reichspatentamt, Patent No. 659 123, published 1938 . . . . . . . . . . . . .

xxvii

90 92

93 97

99

101

103

xxviii

Fig. 3.13

Fig. 3.14

Fig. 3.15

Fig. 3.16

Fig. 4.1 Fig. 4.2

Fig. 4.3

List of Figures

The barracks building at Neuhofer Strasse 4–6 in Niesky in 2021, which were the headquarters of FOKORAD until 1945. This inconspicuous building, currently a materials warehouse, was the place of origin of the barracks design used in the concentration camps of the nazi system, in which millions of people were forced to live under inhumane conditions and very often lost their lives. (Photo A. Haka, 11 Oct. 2021) The letterhead logo of FOKORAD is superimposed indicating the branch office in Niesky, where these barracks had been designed. (Compiled by A. Haka from documents at Barch RH 9/301 and Staatsarchiv Sachsen, Standort Chemnitz, Bestand 31,111, Signature 136) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Blueprint of the horse stables of Army High Command of type 260/9 (OKH). This design was used by the SS at Auschwitz and elsewhere to accommodate prisoners . . . . . . . . . . . . . . . . . . . . . . . . Section through the bearing with shaft; the layered structure of pressed parchment paper, which rests against the shaft from above and below, is clearly visible. Source German patent specification, No. 23837, 1883 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Patent drawings of a reaction propeller, an early form of water-jet turbine. This design is of an inland vessel with two “paddle-wheel turbines” designed to force water through flow piping to propel the vessel in the water by recoil. Source German patent specification, No. 2370, 1882 . . . . . . . . . . . . . . . . . . . . . . . . . . . . Leo Hendrik Baekeland, inventor and eponym of the plastic bakelite. Source Time Magazine, Vol. IV, No. 12, 1924 . . . . . . . . . . . . . A new 2500-ton ten-platen press of the company WUMAG Görlitz in the production hall of Römmler AG in 1926. Each level accommodated a material plate for individual pressing. Source Weigel (1942), p. 19 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Desk lamp from 1930 made of bakelite, manufactured by Römmler AG in Spremberg after a design by Christian Dell. Photo A. Haka, 3 May 2019 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

105

105

109

110 114

119

120

List of Figures

Fig. 4.4

Fig. 4.5

Fig. 4.6

Fig. 4.7

Fig. 4.8

Fig. 4.9

Fig. 4.10

Details of a patent filed by Robert Kemp in 1916. Figure 1.2 provides the key to the aircraft components that can be made of early fibre-composite material. Figure 1.6 shows the material types. No. 39 represents plate material showing layerings of paper impregnated with phenol and formaldehyde. No. 40 indicates plate material containing fabric tapes as a reinforcing agent. No. 41 shows material with wood-fibre reinforcement and number 42 shows impregnated wood. Source Patent—Kemp, 1916, US Patent No. 1,435,244 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Excerpt from the patent by Kemp and Johnson, in which they describe a new composite material for use in aeroplane construction. Source Patent—Kemp and Johnson, 1916, US Patent No. 1,414,419 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Advertising leaflet on the camera Autographic Kodak Special No. 1A from 1917. Its housing is made of the composite material micarta. Source Packaging insert for the model Autographic Kodak Special No. 1A from 1917 by Eastman Kodak Co., Rochester, N.Y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Excerpt from Robert Kemp’s patent from 1918. Figures 1.1 and 1.2 show two interlocked pipes encased in fibre-reinforced plastic (5 and 7). Source Patent—Robert Kemp, 1923, US Patent No. 1,447,361 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Excerpt from Robert Kemp’s patent from 1919, which deals primarily with technical joining aspects for connecting fibre-composite structures to metallic structures. Source Patent—Robert Kemp, 1923, US Patent No. 1,469,220 . . . . . . . . . . . . . A cross-section detail of a closed two-part mould (3 and 4). Via an inflow tube (8 and 9) which is integrated into the mould, a hot liquid enters and increasingly presses movable small non-meltable spherical bodies (11) against the fibre sheets (2) lining the inside of the mould, thus forming two fibre-composite shells. Kemp asserts that fibre-composite structures for an aeroplane or boat could be fashioned in this way. Source Patent—Robert Kemp, 1926, US Patent No. 1,572,936 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . John Dudley North (1893–1968), the first aeronautical designer and later director of the British manufacturer Boulton & Paul Aircraft, in 1919. Source Flight. The Aircraft Engineer and Airships, 1919, No. 49, Vol. XI, p. 547 . . . . . . . . . . . . . . . . . . . . . .

xxix

122

123

124

125

126

127

128

xxx

Fig. 4.11

Fig. 4.12

Fig. 4.13

Fig. 4.14

Fig. 4.15

Fig. 4.16

List of Figures

The Boulton and Paul P.10 at the Parisian Salon de l’Aéronautique 1919. The tail, wings and part of the fuselage had not been planked in order to reveal the structure. The P.10 was the first British all-metal aircraft and probably the first practical application of fibre-reinforced plastic in aircraft design. Source Flight. The Aircraft Engineer & Airships, 1919, No. 1, Vol. XII, p. 12 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Excerpt from the patent by Albin Longren from 1922, which shows in Fig. 1.1 the basic structure of the Longren AK. In Fig. 1.2 Longren describes, on one hand, the stressed-skin structure of the fuselage and, on the other hand, that the semimonocoques should be made of vulcanized fibre in a single piece. Source Patent specification Albin Longren, 1922, US Patent No. 1,541,976 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Excerpt from Albin Longren’s second patent from 1922, in which he describes the manufacture of fuselage semimonocoques by means of a preformed shell mould. Regarding Fig. 1.2, he indicates that a thin rotary-cut veneer is first placed inside the mould, three layers of vulcanized fibre mats are placed on top of it, and these are then covered with a face veneer. Under pressure and heat, this hybrid material construction is then compressed into stable fuselage semimonocoques for the aeroplane, as shown in Fig. 1.3. Source Albin Longren patent specification, 1922, US Patent No. 1,471,906 . . . . . . . . . . . . . . . View into the dining room of the rigid airship LZ 127 Graf Zeppelin, the interior walls of which were made of layered presstoff. These pressed panels were wallpapered for decorative reasons. Source Postcard 1929, Graphic Department of Luftschiffbau Zeppelin GmbH . . . . . . . . . . . . . . . . . . . . Bearing bushings and shells made of presstoff (i.e. phenoplast, with wound fibrous tape as filler, brand name Gerohlex GR) by Römmler AG for use in mechanical engineering. Source Handbuch der Römmler Presstoffe, Römmler AG 1938, p. 142 . . . . . . Enno Heidebroek, mechanical engineer and holder of the chair for fundamental mechanical engineering and transport technology at the polytechnic in Dresden (photograph: Heeresversuchsanstalt Peenemünde 1940). Heidebroek established the Laboratory for Bearings and Lubrication Research, which was later transformed into the Institute of Lubrication and Bearings Research. Source Enno Heidebroek papers, AFTUD . . . . . . . . . . . . . . .

129

132

133

138

139

142

List of Figures

Fig. 4.17

Fig. 4.18

Fig. 4.19

Fig. 4.20

Fig. 4.21

The first of three presstoff plain bearings testing machines developed by Enno Heidebroek in 1934 in the Laboratory for Bearings and Lubrication Research at the Dresden polytechnic. It was used to investigate the stress limits of presstoff plain bearings. All three of these models by Enno Heidebroek were dismantled by the Red Army shortly after its arrival in Dresden in 1945, as reparations. Source Enno Heidebroek papers, AFTUD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The assistant to Prof. Heidebroek, Dipl.-Ing. Rudolf Scheiner, examining materials for presstoff bearings in 1943 in the chemical laboratory affiliated with the Dresden chair. Source Enno Heidebroek papers, AFTUD . . . . . . . . . . . . . . . . . . . . . . . . Presstoff inspection seal for Römmler AG. The stylized letters M and D in the seal logo stand for Materialprüfungsamt Berlin-Dahlem. The number 32 is the manufacturer’s identification number, in this case Römmler AG. The letter S stands for the simplest type of such compressed thermoplastics: phenolic resin with a wood-flour filler. Source Prüfprotokolle, Rep. 75 Chem. Werke Römmler; BLHA . . . . . . . . . . . . . . . . . . . . . . . . . Prototype of a car door made of the laminate presstoff DYNAL for the model DKW F-8, a vehicle for the German army manufactured by Dynamit AG in 1938. Source Mehdorn 1939, p. 191 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-section of a production mould (no. 1 in the patent drawing) onto which the prepreg cellulose tape (no. 11) is laminated with a hand roller (no. 12). The manufacturer Auto-Union in Chemnitz applied for the patent in 1936, which was granted in 1940. Source Patent—Auto-Union Chemnitz, Patent No. 684981, 1940 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

xxxi

145

146

147

152

152

xxxii

Fig. 4.22

Fig. 4.23

Fig. 4.24

Fig. 4.25

Fig. 4.26

Fig. 4.27

List of Figures

Network of the most important German compressed thermoplastics manufacturers, their expert bodies, testing and trials facilities, in the context of German armaments production in the year 1940/1941. The products were: Presstoff plain bearings, presstoff bushings and laminate presstoff panels. Reinforcement materials: hard woven fabric and hard paper (bearings, bushings and plates), glass-fibre fabric (plates), resin matrix: cresol-resol, phenol-resol, aniline-formaldehyde and from 1944 on also lignite phenol as a substitute resin. (Thick connecting lines = production supply, thin lines = information flow). This network diagram (excerpted) was compiled on the basis of correspondence from and to Römmler AG (Brandenburgisches Landeshauptarchiv) and from E. Heidebroek found at the Bundesarchiv, the Archives of TU Dresden, Sächsisches Hauptstaatsarchiv and AFTUD. Diagram by the author. See the List of Abbreviations for the designations of the Army Ordnance Office (Heereswaffenamt) resp. the Heeresamt (AHA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The information sheet Von der Front für die Front with the rhyming dialogue about the proper maintenance of presstoff bushings. Source Zentrum für Militärgeschichte und Sozialwissenschaften der Bundeswehr . . . . . . . . . . . . . . . . . . . . . . . . . . . Title page of the book by Georg Rudolf Böhmer on the “Technical History of Plants” from 1794. Source Sächsische Landesbibliothek—Staats-und Universitätsbibliothek (SULB), Dresden, Technol. A.311–1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . Silhouette portrait of Georg Rudolf Böhmer from around 1771/ 1800, brush, woodcut, unknown artist. Source LWL Museum für Kunst und Kultur, Westfälisches Landesmuseum, Münster, Diepenbroick Portrait Archive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Friedrich Tobler as an “Alter Herr”, an alumnus member of the student fraternity Sängerschaft Erato at the Dresden polytechnic in 1934. He is wearing his fraternity’s ribbon colours on his lapel. Source Enno Heidebroek papers, AFTUD . . . . . . . . . . . . . Klaus Menzel (1907–1995), doctoral student of Friedrich Tobler and later head of the bast fibre research department at the Institute of Fibre Technology at the Dresden polytechnic. Here as an alumnus wearing the tricolour sash of his student fraternity and a “Biertönnchen” cap, 1993. Photo Helmuth Schierig, Schierig papers AFTUD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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List of Figures

Fig. 4.28

Fig. 4.29

Fig. 4.30

Fig. 4.31

Fig. 4.32

Fig. 4.33

Paul-August Koch (1905–1998), from 1939 the joint holder of the chair for fibrous materials science and the extraordinary professorship on textile and paper technology at the Dresden polytechnic. (Photo undated, probably taken as professor of fibrous materials science). Source Courtesy of the University Archive of TU Dresden . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Günther Satlow (1914–1979), assistant to the chair for fibrous science at the Dresden polytechnic, from 1954 deputy director of the German Wool Research Institute at the Aachen polytechnic. The picture shows him as an alumnus of the student fraternity Corps Altsachsen, donning the fraternity cap. Source Schierig papers, AFTUD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Structure and dimensions of a synthetic-resin spar. A prototype flange spar for structural application in aircraft construction, diagramme from the DVL’s textile department 1937. Basically, two presstoff U-profiles made of cellulose (paper) tapes with phenol–formaldehyde resin as the supporting matrix and a birch veneer (cross pieces: fivefold plywood with fabric outer layers, pressed together with synthetic-resin glue and screws). Source DVL research report 1937, Riechers (1937), p. 58, Fig. 3.6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . View of a rudder-unit shell made of laminate presstoff by the DVL, with cellulose tape as reinforcement material for the lightweight bomber plane Heinkel He 45 from 1934. Source Küch, Riechers 1941, p. 16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Characteristic values of prototypical armed presstoff containing raw-fibre inlays with orientated strengths determined at the DVL’s textiles department in 1935. It indicates the yarns in normal, twisted and stretched states for their tensile, compressive, flexural and impact strengths, along with their elasticity moduli and specific weights. Source excerpt from the DVL report by Kurt Riechers, 1937, p. 50, original Fig. 2.4 . . . . . . . . . . . . . . . . . . . Stephen W. Tsai in 2020, research professor emeritus, aeronautics and astronautics, Stanford University. Photo Courtesy of Stephen W. Tsai, 1 July 2020 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Fig. 4.34

Fig. 4.35 Fig. 4.36

Fig. 4.37

Fig. 4.38 Fig. 4.39

Fig. 4.40

Fig. 4.41

List of Figures

Cross-section diagram of the instrument for parachute-fabric burst testing developed by the DVL in Berlin in 1938. A fabric sample is clamped firmly and air-tight between two rings. Pressurized air is fed underneath the rubber membrane from below, causing it to bulge upwards. The bursting process of the fabric above it is observable under the pressure hood through a viewing window. A sensor (from above) with a gauge record the time and load exerted on the sample. Source Riechers (1938a) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wolfgang Hütter (1909–1990), photograph taken in 1942. Source Frits Ruth papers via Peter F. Selinger . . . . . . . . . . . . . . . . . . . . . . . . . . Construction of the pressing facility in the summer of 1943 for the manufacture of the shell wing of Hütter model Hü 211. Source APS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Model of the Hü 211, which had probably been made in Nabern or Kirchheim unter Teck. The photographer was probably Gisela Ruth (née Remy), the wife of Frits Ruth, who worked for Wolfgang Hütter as a foreign worker in the 1940s. Source APS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-section drawing by Wolfgang Hütter of the structure of the Hü 211 aerofoil. Source APS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Specification of the fibre-alignments of the shell veneers for the Hü 211 wing. Taken from the production instructions by Hütter GmbH from 1945. It lists the veneer compositions by the enumerated shell bodies (|| for longitudinally, // for diagonally aligned veneer fibres, the dot indicates “Polystahl” or P600 adhesive layers; the columns on the right indicate their thicknesses, number of veneers in total, followed by longitudinal and diagonal ones, and their proportional %). Source APS . . . . . . . . . . Shell-body veneers of a wing design illustrating the defined fibre orientations of the plywood layers for the upper and lower shells of Hü 211. Excerpt from patent specification A 20,029 “Haupttragende Flügelschalenkörper insbesondere für Flugzeuge aus verleimten Holzfurnieren oder Kunststoffplatten”. This fiber architecture is comparable to a modern multi-axial non-crimp fabric.Source APS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Experimental mould for shaping the layered veneer shell at Wolf-Hirth, the manufacturer of Wolfgang Hütter’s shell bodies for testing purposes. The stepped stack of veneer layers constituting the shell body are clearly visible on the left-hand side. Photo undated, probably 1943. Source APS . . . . . . . . . . . . . . . . . .

196 198

199

200 201

203

204

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List of Figures

Fig. 4.42

Fig. 4.43

Fig. 4.44

Fig. 4.45

Fig. 4.46 Fig. 4.47

Fig. 4.48

Fig. 4.49

Fig. 4.50

Fig. 4.51

Construction method tests on rib and shell curvature and web dimensioning of the shell for Hü 211 from 1943 at Hütter GmbH. Source APS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bending test with and without load as part of the shell tests for the Hü 211. A sample shell of about 5 m length (above) was loaded to failure (below). The test took place on 20 March 1943 at the MPA in Stuttgart under the direction of Otto Graf. Collection of photos on materials testing as part of the preliminary investigations into the dimensions of the wing of the Hü 211. Source APS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Analysis on shell construction with fibre alignment. The stability fracture of a shell specimen of 10 mm thickness with a veneer proportion of 18% in diagonal orientation, made of quality grade I beech and a fibre-alignment positioned at 45º. Dated 22 June 1943 as part of the preliminary investigations for the Hü 211 wing dimensions at the Materials Testing Institute in Stuttgart. Source APS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Showroom of the Erwin Behr firm in Wendlingen am Neckar displaying aircraft parts made of moulded wood for the aeroplane type Me 109 built by Messerschmitt AG. Moulded wood components from Erwin Behr were also used in the models Me 110, Me 210 and Me 309. The sign defines Formholz as “chipless reshaped pressed layered wood”. Source APS . . . . . . . . . . Press for the upper and lower shells of the wings for the aeroplane model Hü 211 shortly before completion in 1944. Source APS . . . . . . Hütter GmbH employees inserting glass tubes with heater wires into one of the concrete blocks of the press for the Hü 211 in 1944. Source APS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wing dummy with engine and landing gear segment for developing a prototype of model Hü 211 at Schempp-Hirth, 1944. Source APS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Staff assembly in the factory hall at Schempp-Hirth, presumably in 1943 or 1944. The speakers and participants at this meeting could not be identified. Photo by Gisela Ruth. Source APS . . . . . . . . . Helmut Horten (1908–1987), the department-store entrepreneur who supported Walter Horten after World War II. Source Reproduced by courtesy of Gräfin Goëss-Horten . . . . . . . . . . . . . . . . . . Ursula and Wolfram Horten in the year of their wedding. Source Archiv D. Horten . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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211 212

213

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222 223

xxxvi

Fig. 4.52

Fig. 4.53 Fig. 4.54

Fig. 4.55

Fig. 4.56

Fig. 4.57

List of Figures

Walter-Max Horten as a flying officer (Oberleutnant) in the Luftwaffe in 1939. Source Horten family archive; Klaus W. Horten . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reimar Horten as a non-commissioned officer (Unteroffizier) in the Luftwaffe in 1936. Source APS . . . . . . . . . . . . . . . . . . . . . . . . . . . Illustration of the Zanonia seed leaf (lat. Alsomitra macrocarpa), a tropical gourd-bearing plant. There are transparent wing-like areas to the right and left of the seed—shown here in yellow. The Zanonia is native to Malaysia, Indonesia, Thailand and New Guinea. The German zoologist and physicist Friedrich Ahlborn (1858–1937) first described the flight characteristics of this seed in detail in 1897 in a paper “On the stability of flying apparatus” (Über die Stabilität der Flugapparate), which was later used by the aircraft designer Ignaz “Igo” Etrich (1879–1967) as a model for the first flying wing built. Source Ahlborn (1897) p. 1 f., Samenflug im Pflanzen Reich from 1934, Liebig-Sammelbilder series no. 1091 . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sabine von der Groeben next to her superior Ernst Udet on a private excursion in June 1937. At this time Ernst Udet held the rank of major general. The position of Generalflugzeugmeister was assigned to him by Hermann Göring in 1939. Source By courtesy of Klaus W. Horten . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Prototype wing of the glider Hol’s der Teufel, which was built by Reimar and Walter Horten and their staff at Dynamit Nobel A. G. The complete strut mechanism is built according to classical wooden construction, but layered presstoff was applied here. The smooth and shiny polymer surface of this material can be seen on the right-hand side along the leading edge of the airfoil, which has already been planked. The rest of the wing was later covered in fabric. Source Willy Radinger. Reproduced by courtesy of Peter F. Selinger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Advertisement for the TROLITAX brand of laminated presstoff produced by Dynamit Nobel A. G. in 1937 but manufactured by Römmler AG in Spremberg and distributed by Venditor Kunststoff-Verkaufsgesellschaft m.b.H. Source Courtesy of Verein Kunststoff-Museum Troisdorf (Museumsverein) e.V . . . . . .

224 224

226

230

234

235

List of Figures

Fig. 4.58

Fig. 4.59

Fig. 4.60

Fig. 4.61

Fig. 4.62

Fig. 4.63

Fig. 4.64

The Horten V-a under construction in the DAG workshop in Troisdorf, 1936. The visible skeletal structure consisted of steel tubes. The shiny plane areas on the right and left are clearly discernable; they are already planked with the layered presstoff TROLITAX SUPRA with inlaid hard paper. Source Reimar Horten, courtesy of Peter F. Selinger . . . . . . . . . . . . . . . . . . . . . Sandbags were used to weigh down the glued surfaces of the H V-a wing panelling, which is made of laminated presstoff, in order to avoid possible de-gluing. Source Walter Horten, courtesy of Peter F. Selinger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The completed Horten V-a in the DAG workshop in Troisdorf, as it was presumably presented to the participants of the Lilienthal Society meeting in January 1937. The shiny fuselage planking of layered presstoff, TROLITAX, is clearly visible. The panels have been butt-jointed to the supporting frame by means of a double row of rivets. The steel-tube framework is also visible through the transparent ASTRALON panes into the cockpit as well as the two Hirth engines with hardwood propellers at the tail end. Source Walter Horten, courtesy of Peter F. Selinger . . . Beginning to mount a Jumo 004 engine into the structural frame of the Horten IX V2 in the maintenance workshop of the Göttingen Autobahn. Some elements of what would be the wooden engine housing are also visible in the tubular skeleton. Source Reimar Horten, courtesy of Peter F. Selinger . . . . . . . The landing of the Horten IX V1 after landing with a brake chute (a ribbon parachute) in the snow in March 1944. Photo H. Zübert, APS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The braking chute of the Horten IX V1. This ribbon parachute was developed at the Graf Zeppelin Research Institute in Stuttgart under Theodor Knacke. Photo Walter Horten, APS . . . . . . . . . . . . . . . . Visit by Ludwig Prandtl (director of the Kaiser Wilhelm Institute of Fluid Dynamics Research in Göttingen) on the Göttingen airfield in 1943. From the left: Robert Wichard Pohl (1884–1976) (director of the 1st Physics Institute at the University of Göttingen and doctoral advisor of the physicist and inventor of the jet engine Hans Joachim Pabst von Ohain), Walter Horten, Ludwig Prandtl, Eduard Hildenbrand and Reimar Horten. Source Courtesy of the DLR Archive, Göttingen . . . . . . . . . . . . . . . . . . . . . . . .

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241

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xxxviii

Fig. 4.65

Fig. 4.66

Fig. 4.67

Fig. 4.68

Fig. 5.1

List of Figures

Detail drawing 9 of the massive wing nose (section G–H in the drawing) made of plywood for Horten model IX V2. In order to be able to lay the inner layers with the appropriate radius curvature, the two inner converging plywood layers were scarf jointed (red arrow) in the common fashion employed by carpenters. Source Detail drawing 9; constructional drawing of the Horten IX V2; APS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-section of the plywood panelling of the Horten model IX V3 from the material analysis at the American Institute for Conservation of Historic and Artistic Works. Numbers 1–5 on the image show the fivefold layering of laminate panels, which are glued together with an amber-coloured adhesive. Each panel layer consists of approximately 20 layers of veneer. The white arrow points to one of the layers of adhesive bonding together the 5-ply plywood packages. No carbon film applied as radar shielding could be detected here. Nor could the particle analysis detect any carbon residues, only dirt particles presumably from the parting agent used in the press at that time. Source Courtesy of Lauren Horelick via E. Crellin . . . . . Fuselage section of the Horten IX V3 in the workshop of the National Air and Space Museum—Smithsonian Institution in 2017. The swastika and identification number had been painted on after its arrival in the U.S. in 1945 to distinguish it as nazi technology. Source Courtesy of Peter F. Selinger . . . . . . . . . . . Detail from the patent by Henry Ford and Eugene Gregorie. The detail shows part of the basic structure of the vehicle. The patent does not contain any information about the materials used, neither that it was a hybrid material, nor that a special supporting matrix was planned, only the indication that the overall structure of the car was considerably lighter than previous vehicular structures. Source Patent H. Ford, E. Gregorie, 1942 . . . . . . . . . . . . . . . Reconstruction of the network of clients, developers and testers for the commissioning of the world’s first serial component made of CFRP in aircraft design: the manoeuvring air brake for the Alpha Jet light fighter-bomber (1968–1972). This network flow chart is based on the interview with Prof. Manfred Flemming and worksheets from the Luftfahrttechnisches Handbuch (LTH) by Arbeitskreis Faserverbund-Leichtbau . . . . . . . . . .

247

249

250

254

263

List of Figures

Fig. 5.2

Fig. 5.3

Fig. 5.4

Fig. 5.5

Fig. 5.6

Fig. 5.7

Fig. 5.8 Fig. 5.9

Fig. 5.10

Fig. 5.11

The SB 10 glider by Akaflieg Braunschweig, the first civil aircraft in the world whose wings were made of carbon-fibre-reinforced plastic, here as a single-seater with a wing-span of 29 m. The maiden flight occurred in 1972. Source Courtesy of Akaflieg Braunschweig . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Manfred Flemming (1930–2015) next to the CFRP brake flap he had developed for the Alpha Jet. This air-brake, mounted on a marble base, was an original that he had received as a gift from his employees at Dornier and was displayed in his front garden. Photo A. Haka, 22 June 2011, Markdorf . . . . . . . . . . . . . . . . . . Ulrich Hütter, from 1965 director of the Institute of Aircraft Design at TH Stuttgart and director of the Institute of Construction Methods and Design Research at the DFVLR. Photo Dangl family, courtesy of Peter F. Selinger . . . . . . . . . . . . . . . . . Alpha Jet with installed CFRP air-brake version III (deployed). Source LTH. Arbeitsblatt, Conen, FL 25 400–05. Courtesy of Arbeitskreis Faserverbund-Leichtbau des LTH . . . . . . . . . . . . . . . . . . Verall view of the CFRP spoiler and its installation locations on the Airbus A 300 B2/B4. Source LTH—Arbeitsblatt FL 25.400–30, p. 7. Arbeitskreis Faserverbund-Leichtbau des LTH . . . . . . Glass-fibre reinforced aluminium = Glare (acronym for Glass Laminate Aluminium Reinforced Epoxy), shown here in various material thicknesses. The matchstick indicates how thin the glass-fibre-reinforced laminates between the aluminium sheets are designed to be. Photo A. Haka, 21 Sep. 2017 . . . . . . . . . . . Alfred Puck (1927–2021). Foto Courtesy of Hannelore Puck . . . . . . . . Internal structure of the CFRP slat, where textile technology and electrical engineering meet. This material design is based on the tailored fibre placement technology developed at the Institut für Polymerforschung in Dresden. Source Courtesy of Qpoint Dresden . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Prototype of a CFRP slat by Airbus Germany and Qpoint Composite in Dresden, here fixed on a stand as a demonstration object. Source Courtesy of Qpoint Dresden . . . . . . . . . . . . . . . . . . . . . . Cover of the 96-page technical description and specifications of the improved prototype of the GDR’s jet turbine airliner 152 II V4. Source VEB Flugzeugwerke Dresden (ed.), 1959. Technische Beschreibung. Strahlturbinen-Verkehrsflugzeug152 II. Dresden . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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274 276

279

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xl

Fig. 5.12

Fig. 5.13

Fig. 5.14

Fig. 5.15

Fig. 5.16

Fig. 5.17

Fig. 5.18

Fig. 5.19

List of Figures

Component parts of a wedge-shaped honeycomb core system (hexagonal) with a GFRP coating (matrix: polyester resin) for the auxiliary rudder of the soviet commercial airliner Ilyushin Il-14P, which was built in 1959 at VEB Apparatebau in Lommatzsch. Source Courtesy of the University Archive of TU Dresden, 94–2-11_6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Female employees of VEB Apparatebau in Lommatzsch stretching honeycombs for the aviation industry. A metal pin was used to “stretch” glued honeycomb chambers, into which the adhesive (“Plastacol”, a pure phenolic resin from VEB Plasta Kunstharz- und Pressmassewerk in Espenhain) had penetrated, and the material was then mounted on an immersion frame for resin impregnation. Source Courtesy of the University Archive of TU Dresden, 94–2-10_5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Female employees of the production department of VEB Apparatebau in Lommatzsch laying out a honeycomb mat for the tank compartment panels, a sandwich composite with glass-fibre face sheets on either side and used in the jet-turbine airliner 152-II V4. Source Courtesy of the University Archive of TU Dresden, 94–2-10_7 . . . . . . . . . . . . . . Experimental house as a honeycomb structure by VEB Flugzeugwerke in Dresden, which was tested out by employees in Graal-Müritz in the Rostock Heath on the Baltic Sea. Source Courtesy of the University Archive of TU Dresden, 94–2-11_8 . . . . . . Comparison of the classical honeycomb shape (left) and the custom reshapable honeycomb (right) with no cell deformation when in a cylindrical curve. Source Courtesy of the University Archive of TU Dresden, 94-2-14_15 . . . . . . . . . . . . . Hermann Landmann (1898–1977), director of the Institute of Aircraft Design and holder of the chair for lightweight construction at the Dresden polytechnic. Source Courtesy of the Archive at TU Dresden . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Landmann La 16 V2 “Heidelerche”, which Hermann Landmann had developed together with students as holder of the chair for lightweight construction at TH Dresden in 1957. This motor glider was built as a wood-GFRP mixed structure. Source Flieger-Jahrbuch, 1961, p. 91 . . . . . . . . . . . . . . . . . . . . . . . . . . . Central part of the wing of the model FL 60 with a shell made of glass-fibre-reinforced plastic and wood as a mixed construction. Source Kautschuk und Plaste, 1963, p. 497 . . . . . . . . . . .

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293

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296

List of Figures

Fig. 5.20 Fig. 5.21

Fig. 5.22

Fig. 5.23

Fig. 5.24

Fig. 5.25

Fig. 5.26

Initial structure of the SOFIA project 1987 (compiled by A. Haka) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . First system concept for the installation of the telescope in the Boeing 747 from 1987, which envisaged that it be positioned directly behind the cockpit. Source Document No, PD-2001, APSK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . One of the seven antenna units with a mirror diameter of 15 m at IRAM Observatory, on Plateau de Bure at 2,550 m altitude in the French Alps. Astronomers there observe interstellar molecules and cosmic dust, or else are on the lookout for “black holes”. Mounted on rails, these telescope antennae can change their position relative to one another or can be moved into a maintenance hangar. The photo on the left shows an antenna in front of such a hangar. The photo on the right shows an antenna inside the maintenance hangar with the mirrors and paneling removed; the black CFRP supporting frame is visible. Source APSK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cross-sectional view of a fuselage section of the Boeing 747 of the SOFIA project, showing the subdivisioning of the aircraft into the cockpit, visitor’s area, working area of the researching astronomers along with their scientific equipment, the separating aircraft bulkhead and the telescope cabin with the telescope behind it. Source CAD drawing: MAN Technologie, APSK . . . . . . . . . Later mirror version of the reflector telescope. The dumbbell shape can be seen with its “handlebar” embedded in the bulkhead of the aeroplane structure. The right-hand part of the telescope is incorporated into a light truss-type structure. The counterweights and the control units for operating the telescope can be seen on the left-hand side behind the bulkhead where the scientific staff is also located along with suitable IT recording equipment. Source CAD drawing, telescope design by H. J. Kärcher, APSK . . . . . SOFIA, the Boeing 747 with its hatch open during flight. The telescope mirror is protected from direct sunlight by a special textile tarpaulin without, however, impairing the mirror quality. Source APSK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Meeting between the past and future of astronomical research, in two senses. This photo depicts astronomers of the SOFIA project at the rear of the cabin section of the SOFIA Boeing, standing right next to the counterweight of the telescope, in conversation with the second man to have walked on the Moon, astronaut Buzz Aldrin (centre, in a red shirt). Source APSK . . . . . . . .

xli

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304

307

309

310

311

312

List of Tables

Table 1.1

Table 4.1

Table 4.2

Table 4.3

Table 4.4 Table 5.1

The thematic focus of material culture studies contrasted against the focal points examined within the context of the genesis of composite materials as well as their overlapping points (The arrows indicate the shifts in emphasis and issues treated.) . . . . . . . . . . A selective list of plastic products offered on the German market, broken down by sector, type of application and plastic (as of 1930). Compiled from the journal Kunststoffe covering the period 1925–1930 (no claim to completeness) . . . . . . . . . . . . . . . . . Römmler AG product range at the beginning of the 1930s in the field of synthetic-resin plain bearings. Author’s compilation (on the basis of Römmler AG 1938, p. 138 f.) . . . . . . . . . Commissioned fibre-research projects at the Dresden polytechnic, conducted at the Institute of Botany there between 1937 and 1945 by and under Friedrich Tobler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Commissioned research at the chair for fibrous materials science of the Dresden polytechnic between 1939 and 1945 . . . . . . . . . . . . . . . Members of the Materials Working Group, subordinated under the central Working Group on Research and Technology in Aircraft Design in the Research Centre of the Aviation Industry (FZL). The meeting place was Pirna-Sonnenstein. The status in 1958 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

40

118

139

176 181

286

xliii

1

Introduction

Workable materials have always played a central role in the lives of people and their earliest activities, such as the crafting of weaponry for hunting or of religious artefacts. They are the basis of handmade and technical products, the subject of scientific research—indeed the very expression of cultural activity. Research on the genesis of the materials sciences with a focus on malleable materials especially in connection with technical developments is still in its infancy.1 Up to now, closer attention has mainly been paid to metallurgy as well as to a few other special materials, such as glass, porcelain, wood, paper or plastics.2

1 The results and findings from the present study are becoming generally available in a database

on the historical development of materials (Datenbank zur Historischen Entwicklung von Werkstoffen), as the quintessence of my interdisciplinary teaching. It provides a key to materials used in production, sorted by characteristic value, processing, technical actors, era, related materials, etc. The database will be published in German only. It grants the layperson as well as the expert the means to explore by various search options the technical knowledge of materials spanning an application period of four centuries. The database will be accessible on the website hosted by the section for the history of science (GNT) of the University of Stuttgart. The basic principles governing this database and its development have been presented in Haka (2021). 2 This already manifests the diversity of manufacturing materials (Werkstoffe). For better orientation at a deeper level it is thus advisable to categorize them, for example, as metallic and non-metallic materials or as natural materials, such as wood or graphite. This categorization underlies this study as well, although materials could also be classified otherwise, for example, into structural and construction materials as opposed to functional materials. The current state of the art in research on the genesis of materials appears in Sect. 1.3. In addition, Sect. 1.7 on terms and definitions of composite materials, subdivides polymer materials, which count among the non-metallic materials and often serve as a bearing matrix in hybrid materials.

© The Author(s), under exclusive license to Springer Fachmedien Wiesbaden GmbH, part of Springer Nature 2023 A. T. Haka, Engineered Stability, https://doi.org/10.1007/978-3-658-41408-5_1

1

2

1 Introduction

Metallic materials, for example, were of decisive importance to humanity within the context of the Industrial Revolution up to the end of modernity.3 Thanks to modern machine technology, their utilization or transformation in diverse ways has forever changed all aspects of societal life. The multifarious abundance of materials in innumerable areas of modern industrial society stems almost exclusively from the findings made by materials science, which has set itself the task of exploring the kaleidoscope of workable materials and continues to process and broaden the spectrum of technical materials on an almost daily basis. The demand of our technological world is constantly on the rise and continues to drive research at university and non-academic establishments to develop and produce more and more new materials. This sought multiplicity of products and, in addition, the research-induced quest for new fields of application are the motor driving this exploration of the performance potential of materials technology. The broad array of composite materials has already attracted special attention for some time now, causing researchers, manufacturers and users alike to focus on this area. These material systems are geometrically defined “constructions” of several materials fused together, the components of which interact physically with one another. This is in contrast to alloys, for example, for which the mutual interactions between their components are within the realm of chemistry. The physical interactions in composite materials, primarily guided by natural structures, have undergone a number of evolutionary stages leading to a mechanical optimum. These material systems have thus found a closer approximation to the mechanical material principles of nature than virtually any other product over the course of their development and implementation by designers and engineers. Hence, the man-made fibre composite should be viewed primarily as a bionic structure that marries biology with the technical requirements in the design of a component part which applies the appropriate statics to exploit the lines of flow of the active forces according to the principles of nature. The guiding performance parameters are: generating high strength and high rigidity at low overall weight, which ultimately leads to lower consumption of energy. The finite resource pool makes this currently one of the most important product goals in the context of product life-cycle management. Developed materials design that exploits the statics after models observed in nature can almost attain the technical optimum for a given product. One of the best-known applications from bionics are the upwardly curved winglets at the tips of modern aeroplane wings. Both wings and winglets are made of fibre-reinforced plastics, whereby—thanks to the reference to active principles of naturally grown fibre structures—a significantly 3 In terms of materials the Industrial Revolution initiated in Great Britain in the eighteenth century

was driven by iron and steel. In particular, new ways of producing steel generated cheaper products from this material. The greatest quantities of these “new” materials were used in railway construction and for rolling stock, but tool quality was also greatly influenced by these metallic working materials. König (1997), p. 330, Wengenroth (1993), p. 103, Benad-Wagenhoff et al. (1993), p. 189 f., id. 329 f., id. (1991), p. 279, Spur (1991), p. 127 f., Brooke (1986), p. 18 f., Warren (1970), Carr (1962).

1 Introduction

3

higher degree of mechanical load-bearing capacity is achieved. Winglets are modelled on the wings of large birds, such as the condor, golden eagle or stork, whose wing tips also curve upwards during flight.4 If one considers that bones, as found in the human body just as in the wings of a bird, are also built of fibrous structures, it becomes apparent how close an approximation to nature the designer has come with this application. The effective statics and lightweight construction are the technical advantages of wings made of fibre-reinforced plastics. In the field of mechanics and its sub-disciplines, such as fracture mechanics, a comprehensive catalogue of issues has arisen in connection with composite materials. This is particularly evident in the case of fibre-reinforced composite materials (FCM), which belong to the class of composite materials. Since most designers and engineers were still accustomed to isotropic material behaviour from metallic materials, henceforth a rethinking needed to occur. Developers first had to familiarize themselves with the strength anisotropy of many FCMs and how to join FCMs with metallic or other materials. It was a matter of avoiding direct confrontation between different material structures, surfaces and differing chemical potentials coming from the individual materials, while at the same time in many cases adjusting to varying material parameters. Further problems involved stress concentrations or the finicky business of introducing the load into a component part. Comprehensive solutions in connection with FCMs were—and still are—being sought in chemical and mechanical joining technology. In addition, the topic of fatigue5 in the case of FCMs under static and dynamic loads is currently the subject of intensive investigations. The mental path from isotropic construction materials to anisotropic FCMs was a lengthy process for designers, engineers and scientists that should not be underestimated, as they had to rethink traditional concepts about workable materials or acquire new ones in this context. The historical treatment and development of composite materials has just begun. Although they are mentioned in quite a number of publications, they are generally only mentioned within the context of technical developments and mainly figure as performance parameters in materials technology, as a means to an end. Any focus on the material itself is rare. As a rule, related works are limited to a brief explanation of the design principles of composite materials with a reference to the fact that these principles were already in use during antiquity. As visionary as various approaches to the use of composites have been, little is known about the historical development of these composites. The present work is intended to take a first step towards closing this research gap.

4 There is already very early documentation about the adaptation of wings and it has been a recurring

topic among researchers and technicians for several centuries. The Italian universal scholar Leonardo da Vinci (1452–1519), who attempted to transfer aspects of avian flight to machines, is often cited as a pioneer in the field of bionics. See Oertel (2008), Dickens (2006), Nicholl (2006). 5 On the aspect of fatigue/fatigue resistance, see Cuntze (2019), p. 24.

4

1 Introduction

This book is therefore devoted to examining the burgeoning diversity of these “building-block materials”, which is becoming increasingly complex owing to this permanent differentiation brought on by further advances and product-specific adaptations. It intends to retrace the important stages in the development of this wealth of facets. Not only will light be shed on the specifics of the individual materials and material systems as well as their subdivisions, but their roots will also be identified and ordered. Besides the search for the origins of composite materials, the intention is to explore the early principles of material reinforcement, including fibre reinforcement. In addition, the ways in which such materials were received both culturally and technically will also be examined. The technical-materials knowledge base, which ultimately underlies many modern material constructions, is illuminated to bring about a wider understanding of how it is obtained, appropriated and utilized in products. At the same time, the motivations of technologist actors in devising these materials must be viewed within their temporal context and the attendant social and political framing conditions explicated. Only thus does it ultimately become possible to come to grips with the broad array of materials used in manufacturing and to present the associated gain in knowledge. Only by incorporating the foregoing stages of knowledge in the development of materials technology as well as the intended schemes conceived by the forerunning actors can future potentials and lines of development in materials technology be properly assessed.

1.1

Content of This Study and Guiding Questions

The aim of this research project is to investigate the strategies employed in technical research and development on hybrid materials in the nineteenth and twentieth centuries and to shed light on the early search for suitable fields of application for these “buildingblock materials”. The emancipation efforts of designers, engineers and scientists, who tried early on to establish composite materials as a new group of materials in technicalproduct design, will also be compared. To this end, an extensive search of the scientific literature was undertaken and relevant dossiers perused at a number of university, state and company archives. In particular, the estate of the mechanical engineer and university lecturer Enno Heidebroek (1876–1955), comprising his research in Darmstadt and Dresden, was viewed in its entirety for the first time. He was one of the central players in the Association of German Engineers (Verein Deutscher Ingenieure, VDI) of the Weimar period and beyond, as a member of the technical boards; and his participation in preparing one of the most important DIN standards for early composite materials was of great importance. His plain-bearing research is closely associated with the establishment of composite materials in mechanical engineering. Furthermore, the estates of the brothers Walter-Max Horten (1913–1998) and Reimar Horten (1915–1994) were assessed. Their pioneering work on applying the first highperformance composite materials in combination with a sophisticated and pioneering

1.1

Content of This Study and Guiding Questions

5

design of flying-wing aircraft represented a turning point in this segment of the industry. These papers were therefore a valuable source in defining the performance parameters of the materials of this period. In this context guided interviews with members of their family were able to supplement many aspects of the brothers’ personal histories and their technical ambitions. The interview with Manfred Flemming (1930–2015), one of the central developers at Dornier involved in designing the German fighter aircraft Alpha Jet, provided decisive insights into the development of the first serial component part made of carbon-fibrereinforced plastic (CFRP) for this model. He not only granted these insights but also supplied important information about the network of participating actors. One essential aspect on the topic of industry-led applications of composite materials with aircraft at the focus arose from a comprehensive survey of the supporting material for the volume on fibre-reinforced composites in lightweight construction (FaserverbundLeichtbau) of the standard reference work Luftfahrttechnisches Handbuch (LTH), issued by the oldest interest group in this field in Germany. The minutes, guide-lines and handling regulations supplied valuable contrasting data with regard to the handling of composite materials not found elsewhere in the regular technical literature. The LTH is not a stand-alone volume of articles, but an ongoing collection of technical application regulations and recommendations involving the handling of composite material systems. Its contributing members do not try to continually update or replace outdated articles. They rather intend to document and archive snapshots of the time. Close connections to defence-related issues revealed a whole series of early application fields and problems posed by composite materials. A comprehensive collection of documents and images relating to the German SOFIA project could be consulted from amongst the files of the retired chief designer of that project’s telescope, Hans Jürgen Kärcher from the firm Maschinenfabrik AugsburgNürnberg (MAN). These dossiers were of central importance, since this forward-looking project had not been archived by the company itself. Therefore, these archival papers, which also include most of the internal correspondence of the project, and the additional interview about the utilization of composite materials in the context of the design must be regarded as an important information source. This also includes the interviews conducted with him and with the chief developer of fibre-composite structures in this project, Mr. Dieter Muser. The afore-mentioned documents and images do not reveal either the industrial development of composite materials, or when and in what time periods this occurred, nor which actors or groups of actors initiated and shaped this process. Thus, the following guiding questions arose: • When and where were composite materials first developed and utilized with industrial application as the specific purpose in order to attain new performance thresholds especially as lightweight or high-performance structural materials?

6

1 Introduction

• Is it possible to identify central players in this context who drove the development process forward as key figures? • How did developers and engineers treat composite materials within the context of the processes of design and application? • How do the developments of hybrid materials in the two German states—the Federal Republic of Germany (FRG) and the German Democratic Republic (GDR)—compare with each other? • Are key stages in the development of composites or hybrid material systems identifiable?

1.2

Temporal and Spatial Scope

The main period of investigation of the present work is the nineteenth and twentieth centuries. The analysis revealed that composite materials, and especially fibre composite materials (FCM) as the currently most prominent class of composites, had been purposefully developed as “building-block materials” during the twentieth century and became established as new high-performance materials in engineering. The modern developments in materials science and design of the twentieth century are based on the growing refinement and expansion of chemical analysis and processing methods going back to the late eighteenth century, foremost ones from the beginning of the nineteenth century and from the period of accelerated industrialization, to which the many developments in mechanical engineering and process technology are included. The temporal focus has been placed on the nineteenth and twentieth centuries in order to be able to illuminate the first flush of developments in materials science and the many foundations of composite materials as we know them today and to place them into context. The basic ideas and developments in materials design, such as the central principle of fibre reinforcement, are much older, however. In order to be able to contextualize the roots of the working principles and constructive applications, it was therefore necessary for my investigation to reach back even further in time.

1.3

State of the Art in Research

The history of materials science, i.e. the history of materials and its research, was for a long time a topic pursued predominantly by figures themselves active in that field of science and was otherwise marginalized by historiography. In the history of metallic materials, for example, Cyril S. Smith (1903–1992) put forward important contributions.6 In 6 Smith (1988), id. (1968), id. (1966).

1.3

State of the Art in Research

7

particular, Smith’s book A History of Metallography should be mentioned, which examines the structure of metals and alloys and their properties. This treatise can be seen as a fundamental work in the history of metallography. In it, Smith sheds light on a whole range of craftsmen and artisans who had intensely studied metallic materials and had also worked practically with them, such as Descartes, Brinell and Biringuccio. Smith describes the development of a modern scientific understanding of materials and focuses on the interplay between practice, theory and aesthetic aspects within the context of metalworking. For the history of materials science as a whole, contributions have notably been made by Robert W. Cahn (1924–2007), Ronald Frank Tylecote (1916–1990) as well as Merton C. Flemings (*1929) from the internalist perspective of the materials scientist specialized in metallurgy.7 The latter should also be mentioned in the context of archaeometallurgy, which deals with the metallurgy of archaeological finds, of which they are among the co-founders. The work of Tylecote deserves particular mention, who began to teach archaeometallurgy in the late 1970s as a university lecturer at the Institute of Archaeology, University College London.8 A more detailed survey of the historiography is provided by Klaus Hentschel in his essay bearing the rubric:”from materials investigations to Materials Science”.9 In all of these histories of materials science, composite materials and especially fibre composites play only a minor role, while metallic materials take the foreground. Analogously, material classes such as glass,10 ceramics11 or plastics12 have also received vivid portrayals of their histories from the perspective of a specialist scientist. Publications in the history of science and technology Only in the last twenty years or so has the history of materials science been studied more intensely by professional historians of science and technology. Among these, Bernadette Bensaude-Vincent and Tim Palucka, Helmut Maier and Klaus Hentschel may be mentioned, furthermore Ursula Klein and Wolfgang Lefèvre. The former studied the disciplinary genesis of materials science in the USA, which had evidently taken the lead in materials research for a long time after the World War. Klaus Hentschel extended this to include Germany and other countries where similar developments took place with some lag in time. Helmut Maier preferred to devote himself to metallic materials in the twentieth century. Klein and Lefèvre devoted special attention to historical ontology in

7 Cahn (2001), Tylecote (1992). 8 Tylecote (1987), id. (1962). 9 Hentschel (2011), p. 5 f. 10 Musgraves et al. (2019), McCray and Kingery (1998). 11 Chavarria (1994), Nelson (1984). 12 Crespy et al. (2008), Kohlepp (2005), Rosato (1982).

8

1 Introduction

the eighteenth century, inspired by the philosopher Ian Hacking’s book from 2002 which transcends the bounds set by period and discipline.13 Although my investigation also presents early case studies of composite materials, which go back to antiquity and beyond, the emphasis is on the nineteenth and twentieth centuries. For this reason, I also prefer to limit this exposition of the state of the art in the scientific literature to works whose period of investigation is situated within the bounds covered by the principal part of this study.14 Pioneering work with regard to the representation of the genesis of composite materials was provided by Bernadette Bensaude-Vincent and Tim Palucka. The latter has also addressed composites in two other papers, among others. In the online publication from 2002, the authors Palucka and Bensaude-Vincent discuss for the first time the emergence of composite materials, various applications and implementation phases. They present a four-phase model (1. glass-fibre-reinforced composites, 2. high-performance composites in the post-Sputnik era, 3. the search for new markets and synergies, 4. hybrid materials, nanocomposites and biomimetic strategies). The individual phases are presented in a keyword-like fashion and in short episodes. They broadly retrace the development of composites with the USA in focus. The developmental stages of specific composites in the USA outlined by these authors, such as the development of glass-fibre-reinforced plastic (GFRP), will be compared in the present book with the developments that occurred in Germany and, where appropriate, other countries. In this context, the authors’ phase model will be taken up again in my evaluation of my research findings, and its coherence critically scrutinized on the basis of my investigations. I don’t want to forget BensaudeVincent anthologies Between Nature and Society. Biographies of Materials, which focuses in particular on a number of materials and addresses their interface between nature and society.15 For an account of early plastics, the British author from the Science Museum London, Susan Mossman, should be mentioned. This author has already presented several papers on the early development of plastics in the nineteenth century, pin-pointing the design of everyday items made of celluloid and some initial bakelite products.16 She also traces the latter to the 1930s in the USA and Great Britain. This author concentrates on design, functionality and everyday utensils made of these materials, and she also scrutinizes how those still novel products were advertised and sold on the arts market.17 She does not, however, shed light on the development of these materials in the technical or industrial sense, nor

13 See Hentschel and Webel (2016), Hentschel (2011), Hentschel and Reinhardt (2011), Klein

(2019), Klein and Lefèvre (2007), Hacking (2002), Palucka and Bensaude-Vincent (2002), Bensaude-Vincent (2001a), id. (2001b). 14 See here, among others, Lattermann (2003), Braun and Collin (2001), Mossman (1994). 15 Bensaude-Vincent (2022). 16 Mossman (2017), id. (2002), id. (1994). 17 Mossman (2017), p. 20 f.

1.3

State of the Art in Research

9

does she mention the most important players, with the exception of Leo Hendrik Baekeland (1863–1963). My work, by contrast, specifically chooses industrial processes and technical development of composite materials as its object of analysis. Within the general field of plastics18 the work by Günter Lattermann is exemplary for the German-speaking realm, which extends its scope to describing restoration research on historical plastics.19 For the present book, his essay from 2017 on the first semisynthetic plastic, galalith, a casein-formaldehyde resin, is relevant. Lattermann retraces the appropriation of natural polymers whose exploitation during antiquity has already been demonstrated. The author focuses on casein which was often used as a binder material, for example in paints. Its ultimate industrial usage in the nineteenth century is covered by the author following the path taken by the Swiss industrialist Adolf Spitteler (1846–1940), who shared the first basic galalith patent of 1897 with Wilhelm Krische (1859–1909). Lattermann discusses economic aspects, technical processing and patenting and describes the early years of the production of this plastic. Starting from Lattermann’s account of galalith, the present study examines and presents as another important material the second plastic of this generation, celluloid, which nowadays is more commonly associated with the cinematographic film medium. The work of the US-American chemist and physicist Gary Patterson should also be mentioned. His two books, A Prehistory of Polymer Science and Polymer Science from 1935–1953, first deal with the prehistory and then with the establishment of polymer science.20 In his first account, he discusses, among other things, natural rubber, polysaccharides or the first plastic mass bakelite which paved the way for the polymer chemistry of Hermann Staudinger. Although various assessments, e.g. of Staudinger, are not always cogently presented, the study traces a whole range of topics in the early history of plastics, with its particular focus on the USA. The depiction of the Faraday Society and its involvement in polymer science is interesting. On the basis of their meetings, which convened between 1907 and 1935, and the debates held in this context, which broached among other things osmosis, colloids and polyreactions, the insights into the professional discourse of the time come alive. Patterson’s second volume follows on directly from this and deals with the debates about polymerization in the Faraday Society, taking a close look at the people who were active there and their public opinions, as well as the professional currents that emerged from them. The books by Dietrich Braun in the field of plastics have come to be regarded as standard works, especially his “brief history of plastics”, in which he presents short episodes 18 For an overview and general information, a number of Internet presentations are available on the

development of plastics; see among others: https://www.thoughtco.com/history-of-plastics-199232 or https://www.plasticsindustry.org/history-plastics. Commenting on the wide range of relevant sites in detail would exceed the scope of this introduction. An initial review of the facts there should in any case be followed by more in-depth research on individual aspects, to ensure proper verification. 19 Lattermann (2017), id. (2013), id. (2003). 20 Patterson (2014), id. (2012).

10

1 Introduction

of the most important stages in the development of plastics. His book on “recognizing plastics—qualitative plastics analysis by simple means” is very similarly disposed and provides interesting insights, particularly as regards the evaluation or historical classification of plastics.21 Its description of different analytical procedures and testing methods provides a good overview of older or historical types of plastics. The short chapter added to the 5th edition, which discusses historical plastic objects, is gripping. Its guidance on how to identify early plastics and natural resins without executing methods of chemical testing is an important addition, especially for museum applications or even for the private collector. The centennial volume by Matthias Dederichs providing a survey of plastics originating from Troisdorf, which appeared in 2008 in the series published by the archive of that city, begins at the year 1905.22 On some 190 loosely bound pages rather resembling a seminar report, the author traces the rise of Dynamit Nobel AG to one of the most important German plastics producers, which had its beginnings at the Troisdorf site under the company name Rheinisch-Westfälische-Sprengstoff AG. The study, interspersed with many visual illustrations and relying on numerous sources, describes the varied and eventful history of this plastics location. Important players, product developments and manufacturing processes are described over the course of time, whose influence—interjected by the two world wars—continues to be felt until now at the existing company and far beyond. If the natural composite known as wood or other wood-derived materials are drawn into view, the book by Joachim Radkau on the subject, recounting “how a natural material wrote history”, is indispensable as a basis but also for its informative details.23 The work, conceived as a cultural history of wood, skilfully illuminates the many facets of wood as a renewable resource, a material and a commodity in its interplay with the human consumer. The author temporally spans the Stone Age up to current events, globalization and the destruction of forests. It delves deeply and extensively into many problematic touching points between the human being, that eternal consumer, and wood as a finite natural material. In the context of the present investigation, it can be ascertained that an account of the developments of fibreboard, chipboard, plywood and veneer is duly made, but in parts only in rough overview—which does not, however, speak unfavorably against the book considering its scope.24 Many episodes and strands of development concerning the wood-derived materials just mentioned are not to be found in Radkau, though. In the present context, my study examines these materials more thoroughly and, in particular, takes a closer look at their development or, as the case may be, specifies it more precisely.

21 Dietrich (2013), id. (2012). 22 Dederichs (2008). 23 The first edition of the book was entitled Holz. Ein Naturstoff in der Technikgeschichte and was

written in collaboration with Ingrid Schäfer (1987), the new edition was retitled: Holz—Wie ein Naturstoff Geschichte schreibt, Radkau (2012). 24 Radkau (2012), p. 240 f.

1.3

State of the Art in Research

11

The studies by the historian of science Klaus Hentschel of relevance to this study appeared in 2011 and 2016. In the former publication, the author25 explores the question of whether the historical roots of metallurgy, solid state physics, physical chemistry and polymer chemistry should be classified under a new type of materials science. From this discourse a specific aspect was picked out for the present investigation, which Hentschel had indirectly broached and which figures importantly especially with respect to the approach taken in my own study. The author demonstrated that from the mid-1970s onwards, a change in the self-perception of materials science occurred as a result of the increasing complexity and entanglements with the subject matter of materials technology. This was reflected in an eventual renaming of the discipline or its institutions, which for a time appeared under the label Materials Science and Engineering.26 The point in time of this change in the discipline identified by me here can be linked to the increased use of engineering design for one of the most important composite materials to date, carbonfibre-reinforced plastic (CFRP). The aspect of drafting or constructive designing—or viewed differently—the engineered design of this composite material sets it apart from the conventional ones within the portfolio of materials science. Composite materials have fundamentally changed materials science, not only in terms of new, more efficient load horizons. Of relevance to the present investigation was the book by J. E. Gordon The Science of Structures and Materials from 1988.27 The author of this book takes a look at a wide range of material structures subjected to various stresses. They range from the architectures of biological plants and buildings from different eras to various vehicle structures. He presents a wide range of materials including manufacturing materials. The chapter on new synthetic materials was of particular interest to my study, whereby the focus was primarily on exemplary applications in Great Britain and the USA. He gives a brief overview of standard material characteristics as well as the historical developments in the most important composite materials and manufacturing processes. Gordon’s work was mainly consulted to cross-check my own research and to supplement composite developments from abroad. At the time of publication of the work in the late 1980s, composites were only just beginning to be studied or scrutinized in greater detail. In the field of materials science, the work of Helmut Maier should also be mentioned.28 In his article from 2010 on “rescue metals”, plastics pioneers and the West German postwar “economic miracle”, Maier focuses on the development of scientific associations in the field of materials science. The account starts prior to World War I and postulates that the scientification of materials research stood on three supporting pillars. In particular, the essay emphasizes the founding of associations, federations, and expert committees in 25 Hentschel and Reinhardt (2011), p. 1 f., here also briefly together with Carsten Reinhardt. 26 Hentschel (2011), p. 6 f., and Hentschel and Webel (2016), p. 16 f., contain the 2011 article with

minor changes and additions, cf. the classification of “composites” as depicted in two charts. 27 Gordon (1988), id. (1989). 28 Maier (2010), id. (2015).

12

1 Introduction

this context. The author assigns a key function or hybrid character to these bodies, whose heterogeneous composition interlinked government with industry and science. Different associations, the intentions underlying their foundations and their interests are examined, with the focus on metallic materials. Chapter 3, which concentrates on plastics research, was of particular interest to the present study. The most important associations are highlighted, in particular the association of German chemists Verein Deutscher Chemiker and the association of German engineers (VDI). What specific tasks and materials the respective actors or expert committees they steered actually focused on is left out. It also remains unmentioned that the change that materials technology experienced since the mid-1930s away from the classic moulding material bakelite, to which fillers were added, to presstoff, in which fibres or fibre fabrics were introduced for reinforcement, is also left unmentioned.29 The conclusion of Helmut Maier’s article is the section on the communal effort leading to the western post-war economic boom known as the “Wirtschaftswunder”.30 Maier’s paper only briefly alludes to East Germany, however, with scant mention of the founding of the Kammer der Technik, the eastern equivalent of the VDI, which was active in the later German Democratic Republic. The present book intends to close this and other interpretational gaps through a more detailed consideration of the technical terms and actors operating within the engineering context as well as their integration into diverse networks, including those in the former GDR. With his monograph on “chemists in the ‘Third Reich’—the German Chemical Society and the Association of German Chemists under the nazi regime”, Helmut Maier presented another work of relevance to the present study.31 The volume, commissioned by the Gesellschaft der Deutschen Chemiker, sheds light on its origins and evolution citing 29 See Haka (2011), p. 73. (Since the focus of Maier’s work is on the associations in technical

science, gaps in the content require further explanation. For example, today the term “plastic” can be considered as generally understood, but only those aware of the technical terms of the time can comprehend what is meant by pressed materials (presstoff) or synthetic-resin compression moulded parts. A brief introduction would have been useful here, in order to understand that a kaleidoscope of materials existed under such designations at that time already. A general presentation contextualizing materials familiar today would have afforded the interested reader worthwhile comparison. Likewise, an explicatory presentation of the “success story” of plastics utilization within the framework of the war economy—this author contends—would have been necessary at this point, in order to understand that “plastics utilization” must be disproportionately understood as applications of presstoff materials and that only to a limited degree can their developmental specifics in terms of materials technology be depicted or situated in the context of substitute materials). 30 For more details on Enno Heidebroek and the founding of the Kammer der Technik, see: Haka (2014a), p. 307 f.; and on the researches of the firm Römmler AG, see: Haka (2011), p. 75 f. (In Maier’s volume, a comparison with the development of plastics and compression moulding materials, resp. the corresponding boards inside the young GDR would have been desirable here. For example, the founding president of the Kammer der Technik, the Dresden mechanical engineer Enno Heidebroek, was a key player in university and industrial research into applications of presstoff during the nazi period and in the early GDR. One of the most important and innovative manufacturers of presstoff of that time, Römmler AG, was also located within the borders of the former GDR). 31 Maier (2015).

1.3

State of the Art in Research

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numerous sources. The main portion of the volume deals with that society’s complicity in the nazi system and its various agencies. The author elaborates further on a number of his remarks in the 2010 article just cited.32 In accordance with the focus of that work, various boards and actors are named without further details about the individuals, their intentions or even facts relevant to materials being offered. Incorporating many new sources, the author draws a multifaceted picture of the society within the nazi system. One thematic strand which is merely alluded to as a matter of fact and which is of interest in the present investigation is the working group of the Technical Committee on Plastics and Presstoff of the Association of German Engineers (VDI) and its head Gerhard Lucas, who from 1943 onwards also acted as head of the related Hauptring Kunst- und Preßstoffe from 1943 onwards.33 Setting out from this state of affairs, the present study will take a closer look at the latter board of experts as well as the embedding of Gerhard Lucas in the network of technical panels, industrial companies and military authorities. A similarly written work by Helmut Maier takes the format of a documentation to cover “one hundred years of the German Society of Materials Science 1919–2019”.34 We can state about this work too that its multitude of sources is impressive and that it presents the evolution of the Deutsche Gesellschaft für Materialkunde (DGM) in considerable detail. It is regrettable, though—something upon which Maier could have no influence—that the presentation of the society’s development from 2009 onwards could only rest on existing publications for copyright reasons, whereas the front portion of the account is based on primary sources. The resulting rupture in the narrative is apparent but has only a limited affect on the comprehensiveness of this documentation. Nonetheless, this is the first comprehensive account of the development of this society over the course of a century and it provides interesting insights not only into said society, but primarily also into the development of materials science in Germany. Among other things, the author pays tribute to a number of members of the society, including the mechanical engineer Paul Albert Brenner (1897–1973), who assumed the presidency of the society in 1953. In his emphatically benevolent biographical sketch, the author states that Brenner’s career “reflects the virtually ideal model of the contemporary development of metallurgy and the industrial use of light metals from the 1920s onwards”.35 The only key biographical points before 1945 are that Brenner joined the Deutsche Versuchsanstalt für Luftfahrt (DVL) in 1923 and, from 1936 onwards, took up a post as head of the industrial research institute of the Vereinte Leichtmetall-Werke in Hanover. It is therefore not surprising, the author concludes, that Brenner was recruited by the victorious powers after World War II.36 This 32 Ibid., p. 313, Maier (2010), p. 161. 33 Maier (2015), pp. 292, 298. 34 Maier (2019). 35 Ibid., p. 111 f. 36 The documentation does not note that Brenner was by no means an industrial researcher focused

on the specialty, as is presented in the biographical sketch. Brenner had not just positioned himself politically early on, he had also participated as a Freikorps fighter in the suppression of the Weimar

14

1 Introduction

interest by the victorious powers was probably due not only to Brenner’s expertise in the field of light metals but also to the fact that Brenner had been more than a mere employee during his time at the DVL. Paul Brenner37 controlled the research interests of the DVL in materials science for ten years as head of the Institute of Materials Research (Institut für Werkstofforschung) there and was thus involved with development in military aviation in Germany.38 This is relevant to my question insofar as Brenner innovatively advanced materials research in one of the five departments at his DVL institute in the field of nonmetallic materials during the afore-mentioned period. Therefore, Brenner’s work is the subject of the present study, especially with regard to the researches conducted at the DVL’s Institute of Materials Research. Chapter 5 should also be mentioned here, which presents the technical committees operating within the DGM. For the present study, the Composite Materials committee, founded in 1969, and the Hybrid Materials and Structures expert panel were considered relevant. Only the committee established in 1969 was useful for this inquiry, as the other committee was established in 2012 and therefore no longer lies within the period covered by this study. For my investigation it was interesting to find out how the treatment of topics about composites coming from the classical materials disciplines was handled in the society; which representatives were sent to the composites committee; and that they did not come directly from the field of composites as was the case in other expert committees. As a result, it was obviously not until the 1990s that fibre-reinforced composites were entrusted with their own working group, although they had already gained considerable importance in industry at the beginning of the 1970s.39 If one considers that a permanent working group for fibre-reinforced plastics (FRP) was established in the aerospace industry as early as the beginning of the 1970s, it is clear that the DGM was very sluggish in reacting to this trend in materials technology. This did not change until the 2000s. Günther Luxbacher is another author to mention who has dealt primarily with questions involving raw materials and the German efforts to achieve autarky as well as with materials testing and its institutionalization.40 His essay from 2004 examines the scientific organization of textile raw materials and materials science in Germany in the first half of Räterepublik. See: UA Hannover [hereafter UAH]: Sign./Akz. Best. 5, Nr. 3292, PA Paul Albert Brenner, Best. 5, Nr. 3292. 37 The year of death of Paul August Brenner as indicated by Maier is not correct (Maier 2019, p. 111.). He died in Switzerland on 20 Mar. 1973, a good ten years later than the documentation indicates. See UAH, Personalakte Paul Brenner, Todesanzeige Prof. Dr. Paul Brenner. 38 Brenner (1937), p. I 580. The period from 1926 to 1936, which Maier does not address in his biographical outline, would certainly have been of interest in the account about the society. However, Maier does present some of these biographical facts about Paul Brenner in his earlier publications from 2002, p. 381 and 2007 (vol. 1, p. 414 f). It can therefore only be assumed that in his documentation the author wanted to direct the image of Paul Brenner, as a formative figure of the DGM in the post-war period, primarily toward his engineering achievements. 39 Maier (2019), p. 495. 40 Luxbacher (2018), id. (2011), id. (2010), id. (2004).

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the twentieth century and their objectives from the perspective of the Kaiser-WilhelmGesellschaft (KWG).41 Within the context of early propagation of Technical Botany, the author addresses German efforts to institutionalize fibre research between 1914 and 1938, taking as his example the research and development conducted at the Kaiser Wilhelm Institute of Bast Fibre Research. This institute was one of the cores of German fibre research and is particularly relevant to this study, as it dealt with one of the base materials of fibre composites. The analysis briefly discusses the botanist and natural-fibre researcher Friedrich Tobler (1879–1957), but rather in the context of his role as director. Luxbacher states that Tobler was “amongst the best-known fibre (substitute-material) researchers and propagandists in both the world wars.”42 Despite Tobler’s central position within German fibre research, he remains a rather marginal figure in Luxbacher’s book. The present study intends to fill this gap by taking a closer look at Friedrich Tobler and his work as a fibre-materials expert. In the fourth volume of the series on the history of the German Research Foundation (Deutsche Forschungsgemeinschaft), Luxbacher examines substitute materials and the research efforts pursued principally with institutional funding at various times within the period from 1920 to 1970, placing his focus entirely on metallic materials. The early coupling between demand for materials and applied research, which was primarily industry-driven, takes centre stage here.43 The author aptly differentiates between research on substitute materials and forms of technically induced alterations to materials.44 This central aspect will be further specified in the present study particularly respecting composite materials and as they relate to substitutes, taking pressed materials into view. Attached to this, the term “substitute-materials culture” (Ersatzstoffkultur) will also be discussed and the concept “economy of materials” (Stoffökonomie) examined within the context of the actions taken by German industrial enterprises in following their design ambitions and their quest for efficient materials.45 In the process, the original assumption that Germany manifested special behavioural patterns as regards substitute materials is abandoned. German intentions within the context of the two wars gain special focus in this subject area. In his essay on the research practice in German explorations for metal substitutes during its autarkic phases of the twentieth century, Luxbacher (2011) returns again to the topic of substitute materials with the focus on metallic materials during the National socialist era.46 He takes up in particular the interplay between design demands and realistic materials engineering and discusses the complexity of this sphere of problems. In my earlier book, I was able to demonstrate the topic of complexity in particular in presenting 41 Luxbacher (2004). 42 Ibid., p. 24. 43 Luxbacher (2011), p. 44, Haka (2011), p. 74 f. 44 Luxbacher (2010), p. 166, Haka (2012), p. 6, id. (2011), p. 80 f. 45 Luxbacher (2010), p. 167. 46 Luxbacher (2011).

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1 Introduction

the Schnellaktion Schweinfurt.47 The depiction of the Dresden mechanical engineer Enno Heidebroek and his multi-layered research within the context of his material-technical research intentions on early composite materials is elaborated further in the present volume. I had examined the aforesaid mechanical engineer earlier in some detail already, including a number of aspects of his research on bearings.48 The focus there had been on Heidebroek’s social networks, which developed over some forty years of networked research; and his work on bearings machine elements and their special fundamental character in mechanical engineering turned out to be a fruitful field of investigation. The examination of Heidebroek’s research and development on composite materials undertaken for this study represents a new and important facet. It sheds new light on both early composites and Heidebroek’s innovative research practices and the way he dealt with the German mechanical engineering community which was highly design-oriented and professionally conservative.49 In my preceding book, I investigated German mechanical engineering and the active players in that field. It compiles the biographical records of about 4000 mechanical engineers and, by the method of network analysis, 19 university lecturers were filtered out from this total and their research activities examined in more detail.50 One of these was the above-mentioned engineer, Enno Heidebroek, who pursued research topics far beyond the boundaries of his specialty, only a small excerpt of which I had been able to present in my earlier book. The present book, however, will take a look at the development of the large group of materials known as composite materials from the nineteenth and twentieth centuries. Different manufacturing materials and material composites will be examined in detail and the related design and manufacturing processes illuminated. In this context,

47 Haka (2014a), p. 251 f. One of the protagonists there, the Dresden mechanical engineer Enno Hei-

debroek, is also briefly mentioned by Luxbacher as regards his research on bearings employing an early presstoff material, but the composite material itself and its thematization within the context of substitute materials science is lacking. On the basis of more extensive research on Dresden mechanical engineers, I can show here that Luxbacher’s account of Heidebroek’s interpretation of liquid friction is inaccurate. Design and lubrication—the latter with reference to liquid friction—certainly were central aspects for Heidebroek in designing bearing systems. But his many years of industrial research into materials optimization for such systems clearly show that the materials issue was of equal importance to him. Luxbacher’s interpretation that Heidebroek subordinated the given material to design is therefore not correct. Günther Luxbacher and I both addressed this aspect of Enno Heidebroek’s research on bearings in the same issue of the journal NTM (1/2011), whereas I discussed Heidebroek’s research as it directly relates to pressed materials or fibre composites. Cf. Haka (2011), p. 78 f. 48 Haka (2014a), p. 192 f. 49 The state of research on Enno Heidebroek and an analysis of the papers in his estate will be discussed in more detail in the next section on primary sources (Sect. 1.4). 50 Haka (2014a), p. 18 f., see here in particular on the aspect of data collection and the selection of a large number of relevant mechanical engineers as representatives of different generations in the engineering sector.

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the strategies used to develop various composite materials, the actors involved and their networking will also be addressed. Another book by Günther Luxbacher that counts as part of the history of materials science of relevance here appeared in 2018. This history of the German Society for NonDestructive Testing covering the period from 1933 to 2018 bears the title Durchleuchten und Durchschallen, which translates roughly as: “penetration by light and sound”.51 It is devoted to a field that had hitherto received little attention although it occupies an outstanding position in the area of the development of materials diagnostics. This work represents an interesting preliminary study on diagnostics of composite materials, since among the methods used in non-destructive examinations of composites in use today, we have thermography and X-ray techniques. The author begins his study with a brief history of non-destructive materials testing and describes very clearly the implementation of these materials-testing methods in industry. Unfortunately, his investigation focuses only on the X-ray technique although alternatives already existed at that time, such as the Förster probe or thermography mentioned above.52 In addition to naming a number of actors in the field, the author also sheds light on one of the German figureheads of non-destructive testing, the mineralogist and scientist Ernst Schiebold (1894–1963), who became particularly interested in materials testing. Unfortunately, the author hardly mentions the network around Schiebold at the Materials Testing Station in the Dresden polytechnic and his work there as head of the Leipzig section of non-destructive testing (Abteilung Leipzig für zerstörungsfreie Prüfung) or as associate professor of roentgenology and materials testing there.53 This would have been desirable, though, because there are a number of overlaps in staffing and professional interests, and these former networks were important for his later research in the GDR in particular. Precisely this work at the college of heavy machinery design, Hochschule für Schwermaschinenbau, the later Magdeburg polytechnic, is discussed only cursorily. However, this book with its abundant sources offers multifaceted insights into communications between the individual institutions and their actors, which paints an interesting picture of this still relatively young specialist community. The habilitation thesis by Günther Luxbacher on substitute materials and new materials in metals technology and the research policy in 20th-century Germany,54 which was submitted to the Technical University of Berlin in 2013, was unfortunately inaccessible

51 Luxbacher (2018). 52 See also my own work on the history of thermography, a special method of non-destructive mate-

rial testing, which became established in industry around twenty years ago, particularly in the field of composite materials, and whose roots go back to the beginning of the twentieth century, as well as partially even further. On this, see Haka (2020b), p. 539 f., id. (2020c), p. 116 f. 53 See the embedding of his personnel in the network and structure of the materials testing station at the TH Dresden, Haka (2014a), p. 246. 54 Luxbacher (2020).

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1 Introduction

to scholarship until recently for legal reasons.55 The topic of presstoff materials, a central point of particular relevance to the present study, was only marginally addressed by Luxbacher.56 On the whole, though, Luxbacher’s and my research projects emphasize different thematic areas. Luxbacher focuses primarily on substitute materials, whereas my research emphasizes the group of composite materials taking fibre composites specially into account. One important field of application for composite materials early on was aircraft design. In this context, the dissertation by Philipp Hassinger, entitled “between evolution and revolution—the transformation of materials in aircraft design” from 2013, focuses in particular on the development of materials in this industry.57 The author screens a number of publications in materials engineering for characteristic values and design details for a range of aviatic equipment. This evaluation is flanked by issues of the periodical Flight. He indicated that his review covers the period from 1909 to 2004.58 The book remains regrettably one-sided throughout, mainly comprising mere extracts from the source publications rarely going beyond the naming of aircraft models, material specifications, and technical details of manufacture, with metallic materials occupying the bulk of the work. But the occasional quotation from various articles interrupts these expositions.59 For the period after 1945, the group of composite materials of importance to the present investigation, is named for the first time as a crossroads in aeronautical development, here specifically the use of GFRP or later CFRP in a glider design by students. The author’s account seems to take the replacement of GFRP by CFRP as a matter of course. The fact that lengthy materials testing with boron fibres performed in student and commercial laboratories preceded the application of CFRP, and that those student investigations were largely funded by the German Ministry of Defence, remains unmentioned in this 55 Note in the catalogue of the University Library of TU Berlin—last accessed on 1 July 2020. 56 My own publications, in particular my book from 2014 on social networks in mechanical engi-

neering at German universities and non-academic research institutions between 1920 and 1970, and my article on the development of fibre composites and pressed materials from 2011, alluding to those “wings made of black gold”, are not taken sufficiently into account in Luxbacher’s published edition from 2020, merely citing the latter in a footnote. That footnote cites a factual assertion that does not appear in my 2011 publication. It alleges that “nets” made of glass fibres were tested during the 1940s. From the point of view of materials technology, this statement is incorrect in substance, as “nets” never were used to reinforce pressed materials, not even later in fibre composites. Cf. Luxbacher (2020), p. 378, footnote 207. Likewise, not insignificant overlaps exist in Luxbacher’s publication with my book from 2014 and my article from 2011, such as on Enno Heidebroek, Hugo Wögerbauer, August Thum, the firm Dynamit Nobel AG in Troisdorf and the research on plain bearings, which, however, were not considered. 57 Hassinger (2013). 58 This refers to: Flight—A Journal Devoted to the Interests, Practice, and Progress of Aerial Locomotion and Transport. 59 University archives, private collections, archives of aviation companies, museums and technical reference works had yet to be surveyed. An early introduction or guide to the broad field of composite materials would have been possible and desirable.

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fleeting account, even though this has been a known fact for a while already in the science.60 Scholarship has hitherto neglected to treat the contemporary developers of the first lightweight aircraft made of GFRP along with their immediate environments. The present investigation intends to close this gap. Apart from alluding to aircraft types and their component materials, Hassinger provides hardly any further information about these important stages of modern composite materials. The evidently appended chapter on automotive engineering and its clumsy introduction to fibre composites does not improve this. Even though composites were not the sole focus of Hassinger’s investigation, significant gaps still exist in the work, both in terms of important key technical points in aeronautics and in terms of the materials utilized in that field. Classical lignocellulosic materials, such as chipboard, are only granted scant mention. Lightweight design and its materials have been a key issue in the aircraft construction sector from the very beginning. The question of the usage of composite materials or magnesium is now being raised more and more frequently especially for interior structures, particularly from the perspective of preliminary research, resp. the search for suitable technologies. The parallels to composite materials are therefore an important aspect for the present investigation. In this context, the book by Günter Matter from 2019 should be mentioned, which is specifically dedicated to magnesium metallurgies. That work pays particular attention to the activities of the chemist and engineer Adolf Beck (1892–1949) and the Bitterfeld industrial region.61 Among other things, the book sheds light on the beginnings of electrometallurgy and traces the material brand name “electron”. The author takes a look at the development of the industrial region of Bitterfeld, which he presents not quite gaplessly up to post-1998. This richly illustrated work deals, among other things, with the lightweight construction potential of metallic materials.62 The expositions are dominated by detailed aspects of aircraft models and their characteristics. Although design issues are also discussed to some extent and early bionic approaches to bird flight are alluded to, the chapter remains entrenched in the performance data of aircraft models. A broader comparison of lightweight materials discussed at the time, such as hardwood versus duraluminium, or innovative design approaches, would have put the work on a broader footing. The one sentence mentioning the Horten all-wing aircraft or its American successor does not salvage the latter aspect either.63 One of the other chapters by Matter deals specifically with electron metal in aircraft and airship design.64 The author goes down a list of aircraft manufacturers who chose to apply electron metal to their models, for which parts specifically it was taken and how much, along with the context

60 On the subject of the student “materials pioneers” after 1945 within the context of GFRP and

CFRP in aircraft construction, see Haka (2011), p. 84 f., id. (2012), p. 16 f. 61 Matter (2019). 62 Ibid., p. 75 f., see there in particular the investigations by Hugo Junkers. 63 Matter (2019), p. 237. 64 Ibid., p. 153 f., 175.

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1 Introduction

of these products. The book presents an interesting overview of the development of magnesium alloys and draws a multifaceted picture of the industrial Bitterfeld region, but it remains largely fixated on the performance parameters of a single group of materials and their product applications. Finally, a brief review of the book “Alles aus Plaste”.65 This account by the Documentation Centre for Everyday Culture in the GDR in Eisenhüttenstadt traces the development of mainly everyday objects out of plastic—referred to as “Plaste” on that side of the iron curtain as opposed to the western designation “Kunststoff ”). The book is based on an exhibition sharing the same title: “Everything out of plaste—its promises and uses in the GDR” from 2013. It begins after 1945 and describes the findings obtained by the GDR chemical programme of 1958 which led to the introduction of various plastics into the cycle of everyday products in the GDR. The brief introduction to the “material” also includes a review of early composite materials, such as bakelite or vulcanized fibre. However, the quarter-page fact sheets about each material merely offer encyclopaedic knowledge to acquaint the reader thematically. This publication was irrelevant to the present investigation. Technical publications Technical publications dealing with the historical development of composites or directly with the main topics of this study should not remain unacknowledged. One of the first comprehensive publications on composite materials, especially as regards fibre composites, dates from 1934 and was written by the senior engineer Walter Mehdorn.66 The second and third editions of his book appeared in 1939 and 1949. In the technical terminology of the time,67 these materials were called Kunstharzpreßstoffe, i.e. synthetic-resin pressed compounds, which also became the main title of the three editions of his book. In his first edition, Mehdorn addresses the reader as a practical working technician to the customer or end user. He presents the current state of the art and points out the performance limits of the given materials, also taking a large number of technical details into account. The 1939 edition is almost identically worded but has an addendum about new areas of application, products and more powerful presstoff technology. In his post-war edition, Mehdorn sums up German pressed materials development in the introduction and also compares the more advanced product assortment developed in the US.68 This book was a good overview for the present study, both in terms of the material and in terms of technical aspects of manufacturing for the examined period from 1930 to 1950. The early use of composite materials in mechanical engineering established itself primarily in the form of presstoff bearing shells in plain bearing systems at the end of the 65 Böhme and Ludwig (2012). 66 Mehdorn (1934), id. (1939), id. (1949). 67 For the technical terminology, see Sect. 1.8 on the terminology, comparing manufacturing mate-

rials against hybrid materials. 68 Mehdorn (1949), p. 1 f.

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1930s. Little is known about their development and use, which is why these two points are treated by the present work.69 In this context, the book on materials for plain bearings, Werkstoffe für Gleitlager, should be mentioned. It was edited in 1939 by Reinhold Kühnel (1887–1983), then member of the German railway council, later serving as the Reichbahn’s senior councillor. 70 This anthology documents the technical status of bearing systems in 1939 in accordance with the intentions of Kühnel, who was intensely preoccupied with materials testing issues.71 As a member of the railway’s central office, he was particularly interested in bearing systems, a crucial component of locomotives. Chapter A on non-metallic materials (plastics) and synthetic-resin presstoff bearings is of relevance to the present study. The authors of this section are the Darmstadt university lecturer and director of the local materials testing office August Thum (1881–1957) and his co-worker Rudolf Strohauer. The article written by Thum and Strohauer appears as a special section inserted after an introduction to plain bearing systems and a presentation of conventional materials of which they are made. In the introduction, the authors state that synthetic-resin presstoff were first used in mechanical engineering for plain bearings. University research, industrial companies and, above all, the Technical Committee on Plastics and Presstoff of the Association of German Engineers (VDI) contributed toward their establishment. The longstanding head of the VDI “working group on testing of presstoff bearings”, who initiated the VDI working group on bearings and gears also mentioned there, was the mechanical engineer Enno Heidebroek, whose early publications on presstoff in plain bearings are also cited by Thum and Strohauer several times.72 It can be assumed that this section was prepared in close consultation with Enno Heidebroek. Heidebroek’s network should be drawn into account here.73 Heidebroek and Thum had known each other since the 1920s from a trip to Scandinavia that lasted several weeks. Heidebroek was also a member of the appointment committee that called August Thum to Darmstadt polytechnic. Although Heidebroek left Darmstadt in the early 1930s, this academic friendship persisted into the post-1945 period. It was also a close professional cooperation dominated by Enno Heidebroek insofar as machine elements are concerned. It is therefore not surprising that Heidebroek should write a favourable affidavit (Persilschein) about his friend August Thum when he was compelled to leave the polytechnic in 1945 for having been a member of the NSDAP.74 69 On synthetic-resin pressed materials in plain bearings, see the brief mention within the context of

Enno Heiderbroek’s researches in Haka (2011), p. 78 f. For detailed information on plain bearing research with metallic bearing shells in the 1920 and 1930s, see Haka (2014a), p. 219 f. 70 Kühnel (1939). 71 For further information on Reinhold Kühnel, see Luxbacher (2018), p. 91 f. 72 See, inter alia, Heidebroek (1937b), id. (1937d). 73 On the acquaintance between Heidebroek and Thum, see Haka (2014a), p. 263 f. for more details. 74 See main and special report on the appointment of August Thum or correspondence between Enno Heidebroek and the rector of the TH Darmstadt, Erich Reuleaux dated 6 Feb. and 22 Feb.1946 and

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1 Introduction

The second edition of Kühnel’s book was published in 1952 and only slightly exceeds the contents of the first edition.75 This also applies to Thum’s chapter on presstoff. As in that chapter of the first edition, it almost exclusively cites publications from the time before 1945, with Enno Heidebroek being quoted most frequently. The book Gleitlager on plain bearings can therefore only be used for comparative purposes respecting the development of synthetic-resin presstoff, since it only documents the technical status of 1939 without going into any stages of development. How this status was attained was hitherto unknown and is investigated in this study. In this context, one reference work is worth particular mention, the Römmler-Buch. Handbuch der Römmler-Presstoffe, with the subtitle: “their proper applications as manufacturing materials of the Four-Year Plan.76 It was conceived by Römmler AG in 1938 as a showcase of that company’s achievements and contains an impressive number of technical details. It presents the extensive product range of the company, specifies numerous characteristic properties of various types of presstoff, goes into technical details of production and explains the first DIN standard for such compressed materials. The publication shows how tightly the company was bound into nazi economic policy. The network in which the company operated is examined in more detail in the present study. The book also contains a brief historical outline of the company and the development of synthetic resins. An extension to this is the book Kunstharzpreßstoffe im Maschinenbau published in 1942 by Wolfgang Weigel who headed the physical testing field of Römmler AG in Spremberg.77 This book is aimed at a specialist audience and focuses on applications of synthetic-resin presstoff in mechanical engineering, with the emphasis placed on the various types of presstoff and the manufacture of machine elements. Other fields of application are also discussed in addition and the book closes with a discussion of the state of materials testing of presstoff and finished products. Both the Römmler handbook and the volume by Wolfgang Weigel were good sources with regard to the technical details about materials and various fields of application. The post-war publication Gleitlager co-authored by the physicist Erich Schmid (1896– 1983), director of the Second Institute of Physics at the University of Vienna and former head of the metals laboratory at the concern Metallgesellschaft AG in Frankfurt, together with his colleague there, Richard Weber, deals specifically with the machine element plain bearings.78 Like Kühnel’s publication from 1939, this book is a representation of the state of the art in that technology. It notes hardly any major changes and is primarily supported by references to research conducted between 1940 and 1945. A closer examination reveals that not only are a great many topics by the German pioneer in plain-bearing research, with the Military Government Darmstadt dated 6 Feb.1946 (Personalakte August Thum, Universitätsarchiv der TU Darmstadt). 75 Kühnel (1952). 76 Römmler (1938). 77 Weigel (1942). 78 Schmid and Weber (1953).

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Enno Heidebroek, presented and cited. It is also conspicuous that the majority of his colleagues are cited there, whom he had integrated into his network in 1944/1945 within the framework of the project Schnellaktion Schweinfurt to coordinate the substitution of rolling bearings with plain bearings on military equipment for the German Wehrmacht.79 This book by Schmid and Weber almost exclusively documents the technical status of plain bearings shortly before the end of World War II. Only a few additions regarding application examples venture beyond this representation. Thus, this publication as well as the book by Kühnel was only useful to the present study for comparative consultation.80 Of far greater interest is the volume on plain bearings (Gleitlager) in the series on friction, lubrication and wear co-authored by Edgar Pietsch (1913–1987) and Stefan Fronius (1913–1984), students of Enno Heidebroek and later university lecturers at the Dresden polytechnic and the technical college for mechanical engineering in Karl-Marx-Stadt (Chemnitz).81 There we find a reference to the fact that during the 1950s research on presstoff bearings was actively pursued at the Dresden polytechnic as well as a revision was made of their application guide-lines. This research is explicitly cited as having emanated from the work of the research director, Enno Heidebroek, who in 1950 had published his guide-lines for the replacement of rolling bearings with plain bearings, the most up-to-date exposition on the subject at that time in Germany.82 I have already been able to shed light on bearing research in the GDR in my earlier book, where I also briefly discussed the research into presstoff and the actors and institutions involved in it.83 With the above-mentioned volume and the publication by Pietsch and Fronius, it was possible for the present study to compare with profit the network actors and the substance of the subject matter for various areas of composite-materials research within the GDR that had previously escaped closer attention. Another post-war book is the technical volume Low-pressure Laminating of Plastics from 1947.84 Its authors are Joseph Skean Hicks, technical director of the Owens-Corning Fiberglas Corporation (Toledo, Ohio, USA), and Richard Francis, a chemical engineer from the same company. This publication was conceived primarily as a kind of performance showcase within a young industrial sector in the United States. The book provides interesting insight into the technical status of the development of glass-fibre-reinforced plastics shortly after World War II in the company in question and partly also in various other American supplier companies. The focus is on the technical performance of the 79 For more information on the network involving this “rapid-action” programme Schnellaktion

Schweinfurt and its technical and political actors, see Haka (2014a), p. 251 f. 80 Schmid and Weber (1953). 81 Peitsch and Fronius (1953). For more on Enno Heidebroek’s student network, see Haka (2014a),

p. 298 f., for an in-depth discussion. 82 On the extraordinariness of this publication, see Heidebroek (1950), p. 36. The national and inter-

national influence of this publication led to the award of the National Prize of the GDR to Enno Heidebroek; for more details, see Haka (2014a), p. 288 f. 83 For details on networks in bearings research in the GDR, see Haka (2014a), p. 286. 84 Hicks and Francis (1947).

24

1 Introduction

products, economic advantages in utilizing the materials, and details of technical processing. Patents and publications are cited as sources, almost all of which date from the years 1944–1946. This also applies to all its illustrations. This suggests that technical developments in the USA was still in its infancy. Among the products discussed we mainly find piping systems and panels. High-quality products are almost without exception referred to as prototypes, such as facing for an aircraft, a sports vessel and container systems. Basically, it can be stated that a very young industrial sector was endeavouring to present itself advantageously. The noteworthy thing is, however, that this is a presentation in an area of manufacturing, specifically a presentation of the vacuum process, which today is one of the standard processes for the manufacture of fibre composites. In this process, the fibre composite is wrapped inside a plastic film and the component is compressed upon application of a vacuum. At that time, the process must have been very complex and costly and could only be used for the production of small parts. This leads to the conclusion that although serial production was suggested, hand laminating was the routine order of the day. Many of the processes and design potentials of this material euphorically alluded to in the book, were preferentially tied to manufactory work, which was to be automated, a process that continues to this day. For the present investigation, this book is the point of departure, in particular to scrutinize the state of developments in glass-fibre-reinforced plastics in the USA during and after World War II and to compare it with the developments in Germany and other industrialized countries. The publication by Brian Parkyn is of a very similar nature, who wrote the first book on glass-fibre-reinforced plastics in Great Britain in 1963, which briefly describes the development of the material in the preface.85 The author mentions in outline military aircraft construction in the USA and dates the first aircraft components to 1942. However, he does not indicate any sources, nor does he give any further details about any component parts. Parkyn also sees the early application of glass-fibre-reinforced plastic in boat building as occurring after 1945, which was also taken up by Great Britain in 1947. He postulates this to be the beginning of industrial utilization of that material, which led to the foundation of the British Plastic Federation in 1952.86 The technical state-of-the-art of the composites presented in the book differs only insignificantly from the one presented in 1956 by Harro Hagen in his book Glasfaserverstärkte Kunststoffe.87 Another book on glass-fibre-reinforced plastics appeared in East Germany in the same year as Brian Parkyn’s under the title Glasfaserverstärkte Plaste by the authors Alfred Wende, Wolfgang Moebes and Heinz Marten.88 The short historical sketch of composite materials which precedes the main arguments of the book starts with the Baekeland patent of 1908, which will be discussed later on. This account then jumps directly to the period of the young GDR and points briefly to the early development of the Trabant automobile 85 Parkyn (1963), p. 3 f. 86 Parkyn (1963). 87 Hagen (1956). 88 Wende et al. (1963).

1.3

State of the Art in Research

25

with its main body made out of a cotton fleece-phenolic resin composite. Then reference is made to powerful technical developments in the GDR but without being specific. The level of development shown in the book is comparable to that in the study by Harro Hagen from 1956. Especially as regards the development in the GDR, this publication is the point of departure in following the development of composite materials in that sector of Germany. Among other things, the question of how research evolved in both German states and what levels of development were attained and what knowledge gained is to be examined here. Another author in the field of composite materials is Helmut Schürmann, now emeritus university lecturer from Darmstadt, to whom we shall return in the discussion about technical-term usage. His book from 2007 on constructing composites out of fibrereinforced plastic offers a ten-page introduction to the diverse uses of such composites for the interested reader. Short sections report on the successful application of this group of materials in a variety of technical industries. The quasi-historical outline thus created provides an interesting, fast-paced survey of the subject in aircraft design, shipbuilding, apparatus and pipeline construction, the building industry, electrical engineering, etc.89 Such a brief sketch of this subject is also provided by Gottfried W. Ehrenstein in his book Faserverbund-Kunststoffe, where he presents a 50-year timeline of historical stages on one-and-a-half pages, but omits source citations.90 Also included in this series is the book by Jack Vinson and Robert Sierakowski, who present on a single page stages in the development of composite materials that they deem to be important. Their focus is on the USA.91 This also applies to the essay by Ernst Hirschel from 2007, in which he mentions hybrid materials within the context of the development strategies of the German aviation industry.92 For the building industry, the two dissertations by Elke Genzel and Pamela Voigt should be mentioned. Both these authors discuss composite materials insofar as they specifically concern questions of structural design and material reinforcement used up to that point, resp. applications of composite materials in architecture in the second half of the twentieth century. Their analyses deal almost exclusively with existing buildings without addressing developments in materials technology.93 My own preliminary research in the area of the history of composites was published between 2011 and 2020. Various aspects from these articles are taken up again, reconsidered in depth and discussed in this study. In addition, I have looked at the development of aluminium foil as an insulating material within the context of the history of materials

89 Schürmann (2007). 90 Ehrenstein (2006). 91 Vinson and Sierakowski (2002). 92 Hirschel (2007), p. 316 f. 93 Voigt (2007), Genzel (2006).

26

1 Introduction

science.94 Likewise, questions about the development of materials testing were also pursued; in particular I have treated the developments of thermography, outdoor-weathering and climatic-chamber testing of materials. The latter two topics found entry into the Encyclopedia of the Development and History of Materials Science edited by Joseph D. Martin and Cyrus Mody.95

1.4

Overview of Important Primary and Secondary Sources

Primary Sources In addition to technical documentary materials, specialist articles and books, patent specifications and photographic material, two privately held collections of personal papers from the first half of the twentieth century could be located. For the analysis of the development of the world’s first fibre-composite plain-bearing systems, which began in the mid-1920s, the papers of the mechanical engineer Enno Heidebroek (1876–1955) were examined regarding this special machine element for the first time. He had developed and extensively tested it at the polytechnics of Darmstadt and later, jointly with his industrial partners, Dresden. A small number of the documents in this estate had already figured in my earlier book although the question it explored was his social network. Now that the indexing of these papers is complete, which had been in private hands amongst different members of his family at different locations, they could be assembled and have meanwhile been transferred to Dresden. The size of this estate called for a more extensive and comprehensive assessment. Therefore, the evaluation of the Heidebroek estate relating to the present investigation of the early use of composite-material bearings or, more generally, to research by Enno Heidebroek on materials technology, constitutes an independent analysis; whereby it should be noted here that this comprises but a part of Enno Heidebroek’s research work. The presentation of his research work on natural and synthetic lubricants remains unaffected and is only touched upon with regard to individual aspects of plain-bearing systems. At the family’s request, this estate has been handed over for scientific processing to the archive of Förderverein der Technischen Universität Dresden; Enno Heidebroek himself had been a supporting member of the predecessor association for the furtherance of that university. The estate includes scientific correspondence and publications, private and official records, as well as numerous private and professional photographs and a previously unpublished autobiography, which covers the period from 1895 to 1950. Both on the basis of the latter records and by means of a number of documents, reports and photographic material, it has been possible to document the development of the above-mentioned machine elements and to verify it largely with further archival material. 94 Haka (2017), id. (2016), id. (2012), id. (2011). 95 Haka (2020a), p. 227 f., id. (2020b), p. 539 f.

1.4

Overview of Important Primary and Secondary Sources

27

A further basic source is the estate of the brothers Wolfram Horten (1912–1940), Walter-Max Horten (1913–1998) and Reimar Horten (1915–1994), which became accessible over a longer period by following up the various branches of this family. This estate made it possible to trace the activities of these German flying-wing pioneers for the first time, particularly in its focus area from the 1930 and 1940s. It thus became possible to examine here their pioneering research in applying fibre-reinforced plastics and the associated flying-wing aircraft design. The results of my evaluation of this estate also show how closely technical decisions about materials and structures were linked to the economic and political circumstances. Private documents and a large amount of scientific correspondence and graphic material were looked at. Furthermore, this compilation of source material contains an unpublished autobiography of First Lieutenant WalterMax Horten (1913–1998), as well as a memorandum by his brother-in-law Prof. Dr. Karl Nickel (1924–2009), director of the Institute of Applied Mathematics at the University of Freiburg. These various accounts provide unique insight into the developmental stages not only of aircraft construction under national socialism but also later in post-war Germany. In particular, the representations and contextualization by Karl Nickel, who was involved in the development of the Horten brothers’ aircraft as a budding mathematician in his student days, provide a knowledgeable and precise understanding of the scientific intentions of the acting individuals involved. This enabled further investigations with regard to the appreciation of how they considered the technology at that time as opposed to now. Karl Nickel’s reminiscences, Memorandum. Die Horten-Nurflügel-Flugzeuge. Erinnerungen von Karl Nickel, initially proved difficult to handle. Owing to many very private, as well as difficult constellations among the actors recorded in this memorandum of over 400 pages, Nickel had left strict conditions for its use. Gaining access to the memorandum was therefore not easy; however, it was ultimately granted by the family for the present study. Furthermore, the interview with Wolfram Horten’s son, Dirk Horten, was particularly valuable, not only with regard to the Horten family but also to the work by the Horten brothers in flying-wing technology during the nazi era and within the context of military strategy. Dirk Horten headed the German Navy as commander-in-chief with the rank of vice admiral from 1995 to 2000 and previously also served as department director on the staff of the representative of the German military on the NATO Military Committee in Brussels for the Federal Republic of Germany. His military reflections contributed significantly toward evaluating the various weapons systems of a modern army or their structures. Another important source on the subject of the Horten flying wing is Dipl.-Ing. Peter F. Selinger, who co-published a history of this “Nurflügel” covering the period 1933–1960 together with Reimar Horten in 1983. As co-author, Selinger concentrated on the subject of Horten flying-wing models and evaluated a large number of documents which Reimar and Walter Horten, as well as their brother-in-law Karl Nickel, had entrusted to him on the subject. Based on a whole set of conversations and notes taken with the afore-mentioned, it was possible for him to verify or critically scrutinize a large number of aspects that

28

1 Introduction

not only included technical points related to the development of the Horten flying-wing aircraft but also biographical points concerning the brothers personally. For the historical evaluation of the materials constituting the Horten flying wing, the last surviving prototype of the Horten 8–229 model (the first jet-propelled flying wing as a mixed plywood-steel construction), could be examined and a technical analysis of the materials by the Aeronautics Department of the National Air and Space Museum—Smithsonian Institution consulted. In addition, discussions with that department, in particular with Evelyn Crellin, provided the opportunity to explore not only aspects concerning technical restoration issues as far as the materials of the Horten 8–229 were concerned, but also the role of the German pilot Hanna Reitsch (1912–1979) and her interrelationships with the Horten brothers and decision-makers at the Reich Ministry of Aviation. As an aviation historian, Peter F. Selinger also opened the way to further material involving the development of the Hütter Hü 211 based on the original files from the estate of Wolfgang Hütter. Although the interview with Wolfgang Hütter himself about his life planned by Peter F. Selinger could not be realized, as Hütter died shortly before the scheduled meeting, a large number of technical aspects about his developmental work and biographical key points could be recorded by Peter F. Selinger in numerous conversations and notes in preparation for that interview. The conversations with Peter F. Selinger according to the prescriptions of “oral history” and the evaluation of the documents from the estate of Wolfgang Hütter, formed the basis of Sect. 4.5 on “Fibre-aligned wood construction: The development of an aircraft that never flew—the Hütter Hü 211”. Essential observations about the development and first-time use of fibre-composite structures in aircraft design could be gained from the interview with the now deceased mechanical engineer Manfred Flemming (1930–2015). As head of the department of structural calculation, structural testing and acoustics at the aerospace company Dornier and later as holder of the chair for design and structural engineering at the Swiss Federal Institute of Technology (ETH) Zurich, he was able to impart decisive views on the development of fibre-composite materials for the period from 1960 to 1980. The original documents provided by Flemming on the approval of the world’s first serially produced component part made of carbon fibre in the fighter aircraft Alpha Jet gave far-reaching insights into research and development efforts between an industrial company and the Federal Ministry of Defence. Quite a number of the sources consulted were subject to various restrictions, as they documented the development and use of composite materials involving defence systems. In particular, this applied to materials applications for the Alpha Jet light fighter bomber, the Panavia 200 Tornado multi-role combat aircraft, the military transporter helicopter NATO Helicopter 90 (NH 90) and the Airbus A400 M Atlas. Publication approval was not granted for some of the documents and images on the above-mentioned military aircraft, which therefore could not be drawn into account. For the exposition on the technical developments of materials within the scope of the German-American research project SOFIA, which has integrated a telescope into a Boeing 747 aircraft for astronomical observation in the infrared and sub-millimetre wavelength

1.4

Overview of Important Primary and Secondary Sources

29

range, it was possible to access a stock of sources in the private possession of the former technical construction director for the SOFIA project at MAN Gutehoffnungshütte AG, now affiliated with the MAN SE Group. The source material examined here consists exclusively of internal company documents and images relating to the SOFIA project. Archival accessioning of this comprehensive developmental research, which was commenced in 1986, was not completed due to the lack of archival guide-lines. The documents on the SOFIA project available in the MAN company archives in Augsburg only comprise a series of public lectures mostly at the level of popular science or statistical charts for the company’s annual report, none of which were of any relevance for the present study and were hence not incorporated into the subsequent argumentation. The interviews with the chief designer of the SOFIA telescope, Hans Jürgen Kärcher (MAN Gute HoffnungsHütte), and the leading development engineer of the fibre-composite structures of the SOFIA project, Dieter Muser (MAN Technologie, now called MT Aerospace Augsburg), were an essential extension and provided helpful pointers for the surveyal of Hans Jürgen Kärcher’s private archive. His archive comprises about 200 files averaging 50 pages each and about 100 photos from different periods of the SOFIA project. Finally, brief mention must be made of patent specifications, which may be regarded as technical documentation or specialist literature. Although a whole series of patents have been evaluated for this study and are also incorporated into it in a number of instances, they can only be seen as weak indicators of the state of the art in development. On the one hand, they often merely document the conclusion of a procedure involving a given idea,96 which due to the nature of patent specifications must be disclosed in order to establish its legal basis. On the other hand, the patent filer has no interest in disclosing economically relevant and often monetarily lucrative knowledge in its entirety. Based on this dichotomy, products and processes documented by patent law must often be regarded as historically weak sources and can only give a rough impression of the respective technical zeitgeist. In any case, patent specifications and their implementations must be compared, in order to be able to make a realistic assessment of whether they are the procedural documentation of a technical idea or whether they convey the actual state of the art.97 For this study, documents and image sources from a total of 24 archives were evaluated and incorporated in the analysis. Secondary sources Since hardly any historical studies exist about almost all of the topics covered in this book, it was necessary to evaluate a large number of secondary sources in order to obtain a comprehensive picture of the development of composite materials.

96 See here the patent by Robert Kemp. 97 The patent by Robert Kemp in Sect. 4.1.1 was in all probability merely an idea floated for fur-

ther study without ever being implemented. Albin Kasper Longren’s situation in Sect. 4.1.2.2 was entirely different, as his patent submissions were implemented technically almost immediately.

30

1 Introduction

One of these secondary sources was Klepzig’s Textil-Zeitschrift, albeit this periodical was only evaluated selectively for the years 1939 to 1943. From Paul-August Koch’s research notes it was evident that funding bodies wanted to disseminate research results in the textile industry more widely among association members by having such articles published in this journal. A more extensive review of the journal was therefore not undertaken here. The journal Modern Plastics was sampled for relevant articles. The matter at hand regarding the technical status of composite materials in the USA and Europe dictated that the review be carried out for the issues from 1930 and 1940, but hardly any noteworthy contributions could be identified. The series Holz-Zentralblatt was likewise sampled for any articles clarifying questions concerning the development of wood-derived materials, as well as to find biographical information and relevant projects in the respective time periods. This perusal was carried out for the issues spanning the periods from 1930 to 1943 and from 1946 to 1960. From the periodical Kunststoffe, subtitled “for the production and application of refined or chemically produced materials”, later renamed Kunststoffe vereinigt mit KunststoffTechnik und -Anwendung, the volumes from 1911 to 1943 were systematically screened mainly for clarification of the term Kunststoff (plastics) as it related to the developments within the context of polymer chemistry, resp. the carrier matrix for fibre composites, whereupon just a few relevant contributions could be identified. Deutsche Luftwacht—Luftwissen was reviewed with regard to articles about applications of composite materials, especially fibre-reinforced composites, confining this search to the volumes from 1934 to 1944. There, too, few technical articles related to the topic of this inquiry could be identified. The volumes from 1920 to 1945 of Zeitschrift des Vereins Deutscher Ingenieure were scanned for anything related to the question treated in this study. With regard to the use of presstoff in mechanical engineering, contributions were found, in particular, on material applications in plain bearing systems. Likewise, the internal research reports by the German Aviation Research Institute, Forschungsberichte der Deutschen Versuchsanstalt für Luftfahrt e.V., were reviewed with respect to developments at its Institute of Materials Research for the years 1934 to 1944. The relevant research articles could be incorporated into the present investigation. The series Plaste und Kautschuk (initially appearing with the subtitle “technical scientific journal for the manufacture, application and finishing of plastics and rubber”, later altered to “plastics and rubber including the professional division coatings)” was founded in 1954 in the GDR with the aim of serving as a “link between the intelligentsia and the working class, between manufacturers and consumer circles”.98 The volumes from 1954 to 1958 were checked for the present study. The series appeared monthly and contained technical articles, book and press reviews, patent displays and political statements. Surface technology and dyes were added to it later. Already in its first years, there was a strong 98 Selbmann (1954).

1.5

Methodology

31

shift away from technical contributions towards basic research and materials analysis. The relevant technical articles on composites were initially focused on glass-fibre-reinforced plastics from 1956 onwards; in 1962 that was given its own independent focal section. For the most part, the articles were limited to fundamental topics, material analysis and, in individual cases, production examples and simple applications. In the mid-1960s, representative applications were also presented in individual instances, such as the glider FL 6099 by the Dresden lightweight designer Willi Felde or the RS 1000 sports car100 by the “master of sports” Heinz Melkus (1928–2005), which had structural components made of glass-fibre-reinforced plastic. This sports car served as a political showcase on the occasion of the 20th anniversary of the German Democratic Republic. For the present investigation, however, relevant contributions from this series could only be used for comparison or supplemental purposes. Most of these articles appeared as abridged excerpts from book publications, such as, for instance, Glasfaserverstärkte Plaste,101 the article on metal bonding and GFRPs in engineering102 and on GFRPs again103 or else in the form of an outline of topics treated at a conference. A far more productive series of publications from the GDR was the series Verstärkte Plaste—i.e. reinforced plastics. This series, which having been conceived as an anthology appeared at irregular intervals, reproduced the relevant content of the symposium series under the same name, at which research on fibre-reinforced plastics was the exclusive topic of the discussions. This conference also hosted international participation, albeit this reference only applying to friendly socialist states.104 The first edition was published in 1973, the last in 1990. The papers documented there have been looked at and present the state of research and knowledge about fibre-reinforced composites in the GDR and the other states of the Eastern Bloc.

1.5

Methodology

1.5.1

Network Analysis of Primary and Secondary Sources

The primary sources and parts of the secondary sources identified in the present research project were also subjected to network analysis. Network analytical methods were used to yield social characteristics like centrality and prestige.105 These serve to identify network 99 Felde (1963), p. 495 f. 100 Zimmermann (1970), p. 117 f. 101 Wende et al. (1963). 102 Schwarz and Schlegel (1966). 103 Hintersdorf (1969). 104 The participants at these conferences came from the USSR, Poland, Romania, Bulgaria, Hungary and Czechoslovakia. 105 Cf. Mutschke (2010), p. 365 f., Jansen (2003), p. 127 f.

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1 Introduction

stars106 and to probe their standing within a given group of actors and to determine their positions within an institution.107 In this study, such positional definitions were applied, for example, to the researchers Paul-August Koch and Friedrich Tobler as well as to the Horten brothers, Manfred Flemming and Ulrich Hütter. Closeness centrality, another measure of centrality, was applied to investigate the established networks.108 Applying a theoretical approach based on graphical representation, the distance of a node to all others in that network is measured.109 In the present study, for instance, the Horten brothers and Ulrich Hütter were regarded as central. Closeness was used in this study primarily to assess the interactions in research federations, committees or in the network of German presstoff manufacturers. Another measure of centrality used in this study was betweenness centrality.110 This examines nodes in a network to determine how frequently they are employed as an intermediary by others. If a high betweenness measure is ascertained when a node frequently acts as a bridge between two others, that node is considered central. As with other measures, betweenness centrality has different variants that can be used to explore in detail specific aspects of the network, which will not be discussed in detail here.111 In the present study, the betweenness measure was used not only to determine centrality but also as a control measure to assess the extent to which central actors exerted a direct regulatory influence on others. The network relationships of frontline maintenance personnel were likewise examined in this context—in particular, how well their subjective reports about experiences with the success or failure of products made of presstoff used in an active unit under combat conditions were perceived and assimilated. The network of the Horten brothers, for example, was presented in this study as an egocentric network. That means, their environment is represented from the perspective of the network stars Reimar and Walter Horten. Various qualitative and quantitative methods were also combined (mixed-method design) in order to be able to do justice to the dynamic character of the networks over the large spans of time involved, as well as with regard to the inhomogeneity of the available source material.112

106 A “network star” in the context of network analysis is a dominant actor within a community. See here in particular Haka (2014a), p. 18 f. (the section on “methodology—historical network analysis”). 107 See here Haka (2014a), p. 18 f. and in particular p. 23 f. 108 See Mutschke (2010), Jansen (2003), Koschützki et al. (2005), Valente and Foreman (1998), Freeman (1979), Beauchamp (1965), Bavelas (1950). 109 The methods of network analysis are described in more detail in an earlier book of mine (Haka 2014a), used there also to investigate actors and groups of actors in different scientific communities. In the present study, network analytical methods only play a minor role. 110 Cf. Mutschke (2010), Jansen (2003), Freeman (1977), Shimbel (1953), Bavelas (1948). 111 Cf. Borgatti and Everett (2006), Trappmann et al. (2005), Freemann et al. (1980). 112 On ego-centric networks or mixed-method design, see Hollstein (2010), p. 459 f., Jansen (2003), p. 104 f.

1.5

Methodology

33

Going beyond the actual analysis of network relationships, the visualization of such networks is an important means to clarify the usually complex interwoven interlinkages between actors, groups or institutions, which are often difficult to convey, especially in the case of larger networks.113 This form of presentation was chosen here, for example, to illustrate the network of the leading German manufacturers of presstoff, their evaluation experts, testing stations and proving grounds within the context of German armaments production for the year 1940/1941.

1.5.2

Stoffgeschichte and Product-Line Analysis

Stoffgeschichte Owing to the abundance of variants and overlapping developments, the historical evolution of composite materials requires a complex approach. Therefore, in thinking about how to present this broad subject area, it was obvious to first consider Stoffgeschichte—that history of materials which follows the life cycle of a given material, so to speak.114 This concept satisfies a broader perception of materials, enriched and complemented by environmental science. Stoffgeschichte is understood by its pioneers as a heuristic that pursues the basic aspects of a material as regards its composition, structure, utilization and environmental impact.115 Above all, however, it attempts to reflect the diversity of the interplay between materials and society, with the particular focus placed on pointing out the historical connections. Some approaches of this concept are compatible with the intentions of the present study. However, a closer look reveals that the present object of investigation is incommensurable with such representational notions. The focus of such a history of materials seeking a more extensive form of analysis, in particular the transfer of materials by society or the consumer, taking material and environmental factors into account, does not suit the case of composite materials. In the subject of my investigation, composite materials, the attempt so self-explanatory elsewhere to localize a specific recipient social group, is largely futile; it remains undefined. What is the reason for this? Access to composite materials is only granted to a subset of technical experts. But even amongst this circle only some of the actors can gain access to the underlying principles of the construction and design of this multivariable material, especially fibre composites. The cause of this is probably to be found, among other things, in the persistence of technical principles and conveyed knowledge in the practical usage of materials. 113 Krempel (2010), Strauss (2010). 114 Summaries of this Stoffgeschichte include Hahn & Soentgen (2016), p. 93 f., Weber (2015), p. 76

f., id. (2013), p. 5 f., Schmidt (2014), p. 167 f., Wahrig (2013), Reller et al., eds. (2013), Reller and Soentgen (2012), p. 1, Klein and Spary (2010), Marschall (2008). 115 Heßler (2016), p. 543 f., Espahangizi and Orland (2014), p. 11 f., Soentgen (2013), p. 195 f., Böschen et al. (2004), p. 19 f.

34

1 Introduction

Composite materials were not officially recognized in fact by the German government at the level of economic policy until 2020, as part of its raw materials strategy.116 A fact sheet printed by the German Bundestag stated that the government regards composites as key materials in future developments in lightweight construction projects and materials production. This strategy is flanked by the establishment of expert committees for a coordinating staff unit at the federal level and the promotion of networks in this field. Only now is the presentation of this complex group of materials at a national level beginning. In some cases, cooperations are being sought at the international level. Industrial companies have been working with composite materials for years, of course, but on the basis of expert cooperations, which can scarcely be interpreted as national or societal awareness. Already here we see that the black-box system of composites is not yet understood. The transformation with regard to an understanding of composite materials, away from the materials-black-box systems of the technical expert and towards the consumer, has only just begun. The fact that there is a need for this is also evident from the way in which simple consumers have dealt with composite materials to date. Hitherto the perception has been limited to a few spotlights in the media, such as the presentation of the wide-body Airbus 380 or the Megacity Vehicle of the automobile manufacturer BMW, both of which are renowned technical products with a high proportion of composite materials.117 The Handelsblatt, for example, tried to introduce to its readers one of the most important composite materials, namely carbon-fibre-reinforced plastic (CFRP) under the headline: “Carbon—black magic”, and to explain the technical specifics of the material.118 This introduction for laymen, which basically presented fundamental design principles of these material constructions in the form of a transformed version of the classical laminate theory,119 fell flat and consumers immediately relegated that model back to the black-box category. The afore-mentioned change from expert knowledge to generally understandable principles of design and effect is a fundamental prerequisite to understanding this group of materials, which cannot be achieved by the methodological approach of Stoffgeschichte. Thus, my topic and investigation is barred from this approach. Few overlaps in the argumentations of the technical experts allow any leeway to make such a life history of materials useful as the methodological approach for this study via social reflection. Let me point out here the lack of any precise definition of the methodological approach followed in Stoffgeschichte. In view of the multivariable character of the group of materials under study, the room for interpretation that inevitably results from such a gap would also make any such account largely unusable.

116 Deutscher Bundestag (2020), p. 20. 117 Eickenbusch and Krauss (2013), p. 7. 118 https://www.handelsblatt.com/auto/test-technik/auto-leichtbau-karbon-die-schwarze-magie/387

2664.html, author Franz Rother, last accessed 9 May 2020. 119 On the complexity of the classical laminate theory, see Mittelstedt and Becker (2016), p. 144 f.

1.5

Methodology

35

To underscore this point let me mention that any attempt to approach this group of materials solely by means of an assessment of the material or technical processes within the framework of Stoffgeschichte is bound to fail. It would moreover leave the impression of a methodologically one-sided approach to the subject under study, or could even be interpreted as an attempt to revive an outdated historiography. Due to the technical specifics of the materials and processes of the group in question, this approach would quickly reach the limits of technical reality. Similar to the social approach, in a purely technical approach to the materials there would also be overlaps, but they are by no means sufficient to enable a well-founded analysis and thus mark out a methodological way forward. In this connection, it must be argued that in the present investigation considerable interpretational difficulties would arise particularly from a contextualization of the environmentally relevant aspects, which are considered an essential component of Stoffgeschichte.120 In the approach to materials sought here, among other things via scientific technical structures employing forms of representation such as those used in life-cycle assessment, it is precisely the diversity of types that is of interest, and the basic technical concepts of construction of the material, which stand in the way for composite-material systems. This investigation is not oriented towards the natural material, neither does it measure its environmental footprint, but rather sees composite materials primarily as a product with a wide range of variants, each of which obtains its individuality from the manufacturing procedure, the processing and not least from the design of the semi-finished product as well as the end product. Particularly in the case of environmentally relevant factors, which are often used as parameters in Stoffgeschichte, an investigation is not easy to carry out, especially in the case of the critical product life-cycle management of manufacturing materials that are subsumed within the group of composite materials. The diversity of composite materials makes it impossible to describe them in a generally valid way either as a material or as a processed material based on, for example, an analysis of the chipping process used. The design aspect in particular must be evaluated, both with regard to the composition of the (manufacturing) material and the intended use dependent thereon, in the sense of the future structural requirements of a product. It becomes apparent from this that composite materials and, in particular, fibre-reinforced plastics, can be conceived among other things as semi-finished products (prepregs),121 i.e. as a prefabricated “structure”, which can then serve as a base material and design basis for technical systems.122 It is not only for this reason that the investigation and exposition of the development of composite materials by means of the concept of Stoffgeschichte should fail. The orientations of elicited lines of development, product groups, concepts of design and manufacturing as well as fields 120 Böschen (2012), p. 194 f. 121 On textile Halbzeuge, see Cuntze (2019), p. 32 f., prepreg = semi-finished fibre products pre-

impregnated with reactive resins, also ibid., p. 45 or Flemming et al. (1999), p. 42 f. 122 Cf. Lengsfeld et al. (2014), p. 20 f., Distel and Hausding (2011), p. 381 f.

36

1 Introduction

of application for this group of materials and the interacting actors and groups of actors would be reduced to aspects of relevance to the material, and to isolated marginal topics. A description of the web of scientific, social, political and industry-relevant factors would thus only be possible to a limited extent. In view of this state of knowledge, a differentiated analysis of a social reflection on the subject of composite materials is only conceivable in the future, or rather when a clear definition for Stoffgeschichte is put forward that can cope with the afore-mentioned barring specifics of hybrid materials. Product-line analysis Another methodological approach that was examined with a view to investigating the development of composite materials was product-line analysis. The possibility of representing a large number of individual products appeared to be particularly promising here, as it proved to be a viable solution, for example, in Anne Sudrow’s study about “the shoe under national socialism”.123 As Sudrow notes, however, she did not apply product-line analysis in full but rather chose to use the historical explanatory options of this approach selectively.124 The analysis as modified by that author, which she defines as historical product-line analysis,125 intersects with the pure concept of product-line analysis in certain areas. The original analysis, which emerged from various aims of the anti-nuclear power movement of the 1980s and the resulting focus, among other things, on ecological accounting in technology and business, pursues the goal of assessing full ranges of products. The product is assessed over its life cycle according to the dimensions: nature, society and economy.126 The aim of product-line analysis is to describe the requirements and criteria to be set for products in this mesh of relationships. True product-line analysis thus has a different analytical purpose. It was possible for Sudrow to subdivide her product under investigation, which is manufactured in a variety of ways, into three basic elements. Firstly, its construction; secondly, the material; and thirdly, its form.127 Thus a number of defined courses of action for her analysis worked. If an attempt is made to apply these three specific basic product elements to composite materials, it becomes apparent that they collide with the defined principles both of historical product-line analysis as well as with its original version. Anne Sudrow identifies construction as a basic element of a product defined by the mechanical and technical material design of a shoe. In the case of composites, construction can be understood as the layering, alignment, or interweaving (in special cases, three-dimensionally) 123 Sudrow (2013), p. 34 f. 124 Ibid, p. 37. 125 Ibid, p. 34. 126 Nohe (1999), p. 37, Klöpffer and Walter (1991), p. 114 f., Projektgr. Ökologisches Wirtschaften

(1990), p. 2 f. 127 Sudrow (2013), p. 37 f.

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Methodology

37

of the reinforcing material of the actual composite. Construction can likewise mean that the composite material is employed constructively in combination with other materials or on its own, without referring to the variety of possible end products. The second basic element material could be regarded from certain points of view as a compatible quantity for comparison if the composite itself is seen as a finished product. If, however, the composite material is regarded from the point of view of engineered materials—combining structure with technical manufacture, on one hand as a reinforcing material, and on the other as a supporting matrix (or in the case of a hybrid design, with additions)—then material, as Sudrow defines it as an elementary characteristic, is not applicable to composites either. The situation is quite similar with form as a basic element.128 For Sudrow, the shoe is fixed as the end product, even though it is manufactured in a variety of ways. In the case of composites, form/final form can be used to define both the manufactured composite material itself and a product that is made out of a composite material, whereby a large number of additional options from hybrid materials can still arise here affecting the shape of the final product. The fact that in Anne Sudrow’s case study the various self-defined salient points for interpreting the product: “a shoe under national socialism” resulted in a coherent approach, is entirely due to the chosen product, the shoe. The extent to which another product can be suitably captured and depicted thus as well has yet to be verified. The criteria described above on their own quickly led to the exclusion of the aforementioned methodological approaches, not only of historical product-line analysis, but also of pure product-line analysis, for a study on composite materials.

1.5.3

Material Culture (Studies)

Coming to terms with things, objects, artefacts etc. has been the topic of research in a whole range of disciplines, which has produced a kaleidoscope of discipline-specific approaches and viewpoints.129 This is presumably also the reason why the boundaries in this area of material culture studies are often fluid. The British archaeologist Viktor Buchli has noted the following: It has never really been a discipline—it is effectively an intervention within and between disciplines, translations from one realm into another.130

In the context of this trend, there is much talk of material turns, especially in the field of history. The debates about the extent to which this term is accurate are ongoing.131 128 Ibid. 129 Samida et al. (2014), p. 1 f., Soentgen (2014), p. 226 f., Braid (2004), p. 113 f., 145 f., 170 f. 130 Buchli (2002), p. 13. 131 Reckwitz (2013), p. 13, Hicks (2010), p. 25 f., Bennett and Joyce (2010), p. 7 f.

38

1 Introduction

These controversies about the range of subjects involving material cultures rather seem to be moving in the direction of seeking subject-specific definitions, in order to be able to connect artefacts, things or indeed materiality with cultural viewpoints or, resp. to represent one’s own field of research in a manner more broadly centred on objects. This approach proves to be difficult, however, since a convolution of terms is employed in this discourse, which have to be differentiated according to the specific discipline, and the final definitions of such terms are partly still pending.132 Archaeology, ethnology and often also anthropology are pioneers here, as their research on the field has always concentrated on artefacts, objects and materiality. These disciplines continue to dominate the discourse in material culture studies. Meanwhile, a number of other disciplines are also participating in their approaches and theories. The history of science and technology is among these, especially the history of scientific instruments.133 These moves towards the examination of material things are probably primarily owed to the transition from an industrial and labour society to a consumer society, which has led since the 1990s to the development of the history of consumption.134 The standardized values attached to objects and the associated processes assigned by society as a result have essentially paved the way. Not just for the history of science and technology did their integration into this thematic field give rise to a wide range of topics and questions in the history of society and the everyday, especially as relates to the utilization of goods in the household, for leisure and in everyday life.135 However, these topics require critical scrutiny by each discipline. The present study must settle the question of whether there are any methodological points of contact or parameters of action that would allow a more in-depth analysis in the context of the genesis of composite materials. A number of technology studies come to the fore, which look at the interaction between humans and a given material, the material itself and the associated design or manufacturing techniques, as well as social attributions.136 It is assumed that people create and shape artefacts, engage with objects and are, in turn, influenced by these interactions.137 A number of these authors establish that the methods and theoretical approaches used to assess the dynamic relationships between human society, behavioural options in the context of material design and technology should be gauged by different parameters and on an individual basis.

132 On the subject of “terminology”, see Samida et al. (2014), p. 169 f. for an in-depth discussion. 133 Braid (2004), p. 1 f., 89 f., 189 f., Buchli (2002), p. 2 f. 134 Haupt and Torp (2009), p. 9 f. 135 Heßler (2012). 136 Kuhn (2004), Killick (2004), Lubar and Kingery (1993), Lemonnier (1993), Schiffer (2004), id. (2001), id. (1992). 137 Miller (2005), id. (1998), Meskell (2005), DeMarrais et al. (2004).

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Methodology

39

One of these approaches is proposed by the sociologists MacKenzie and Wajcman,138 the archaeologist Schiffer and the anthropologist Skibo.139 They envisage a three-dimensional approach. Thus, technology and materiality can be observed (1) by examining physical objects or artefacts, (2) by human activities or processes, and (3) by examining the human factor in the active context of technology and materiality. Among the parameters, performance characteristics are examined which can be defined by means of objects indicating specific behavioural capabilities within the context of interactions and activities.140 Performance characteristics can relate to mechanical and chemical interactions or to economic variables such as the costs of acquisition, use and maintenance. The study of performance characteristics as such was introduced into material culture studies by the archaeologist David Braun in 1983 and in his view are synonymous with material properties of artefacts.141 Another research approach is the life history approach, which focuses on the interactions and activities that an artefact undergoes throughout its existence or lifetime.142 In this approach, the process begins with the procurement of the raw materials, moves through the production and utilization, and ends with the artefact situated at its destination, also incorporating the maintenance and reuse practices. A very similar approach known as chaîne opératoire was introduced back in the 1940s by the archaeologist André Leroi-Gourhan (1911–1986) and shares a number of parallel elements with the product lifecycle management now familiar to us.143 This approach retraces the techniques and design processes that are employed, starting from the raw material up to the final product, also looking at the interplay between the natural constraints and the technological decisions reached. What does this signify for the genesis of composite materials? How is this to be evaluated in the context of material culture studies? As already stated above, the latter studies are primarily engaged in questions involving artefacts and material cultures at the focus of archaeological and ethnological research. To what extent can the present study be integrated here? Where can their points in common or their discrepancies be situated for an industrially made product? To find this out, a rough orientation was called for in the form of a simple sampling in material culture studies— without claiming to have thereby obtained a complete picture of the focal emphases of such studies. This check list (Table 1.1) shows that the genesis of composite materials is difficult to integrate into the research discourse of material culture studies, even though overlaps 138 MacKenzie and Wajcman (1985), p. 3 f. 139 Schiffer and Skibo (1987), p. 595, very similar to Schiffer’s approach with Hollenback: Hollen-

back and Schiffer (2010), p. 314 f. 140 Schiffer and Miller (1999), p. 16 f., Schiffer and Skibo (1997), p. 27 f. 141 Brown (1983), p. 107 f. 142 LaMotta and Schiffer (2001), p. 21. 143 Cf. Lemonnier (1986), p. 181, id. (1976), p. 6 f.

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1 Introduction

Table 1.1 The thematic focus of material culture studies contrasted against the focal points examined within the context of the genesis of composite materials as well as their overlapping points (The arrows indicate the shifts in emphasis and issues treated.)144 Focus of material culture studies Artefact (focal points grouped together)

Topics of the genesis of composite materials Material specimen (focal points grouped together)

Archaeology Anthropology Ethnology

Technology Materials science Materials analysis

Ascriptions of meaning Design Consumption Culture Curiosities Museums Metaphors Advertising leaflets and posters External economical practices Objects of prestige Product design Marketing Collections and collectible items Trophies Social distinction Language of things Speaking about things Visual cultures

Manufacture Utensils Industry Technology Processes, schemes Technical handbooks Internal, intrascientific practices Important material specimens Registered utility model/prototypes Registered utility model contexts Materials testing Limiting values/load horizons (significance) Utility/purposes Depiction/description Scientific/technical cultures

were identifiable, as was the case with the history of materials and (historical) productline analysis. One instance of common ground in this comparison is the specimen in engineering or materials science of the 19th or twentieth centuries, resp., and the usually vaguely defined artefact or object in archaeology, anthropology and ethnology. Likewise, parallels can be found in the examination of various specimens or artefact-related practices, particularly in terms of design, the working, and the ultimate attribution of value. It should be noted about this comparison that there are few overlapping points between the topics treated by material culture studies and the present investigation, and that many focal points and issues are displaced.

144 This table is based on three relevant publications, which reflect a wide range of topics in material culture studies. They are: Handbuch Materielle Kultur, Samida et al. (2014); The Oxford Handbook

1.5

Methodology

1.5.4

41

Biographical Facets, Institutional and Corporate History

Although this work focuses on the history of a class of materials, it is also important to consider the people, institutions and companies that were centrally involved in their development and production. Therefore, my utilization of these standard methods of historical scholarship must also be discussed here briefly. Biographical facets In the humanities and social sciences, biographical research has become firmly established and methodologically and thematically specialized.145 The presentation of biographical facts or even a whole biography can be done in different ways. For the present study I have used two different approaches, on the one hand, the chronological approach and, on the other hand, the life history approach.146 The chronological approach was used in the present study for persons who are no longer alive. Biographical research based on primary and secondary sources was conducted with the aim of achieving the greatest possible factual detail on the documented stages in the individual’s life. The chronological approach is also frequently followed to draft a complete biography within the framework of an interview. The interviewee is questioned about the stages in his or her career moving along a time scale, in order to obtain as detailed an account of the respective stages of that person’s life as possible. For the present study, the evaluation of primary and secondary sources by the chronological approach was applied, e.g. to the biographies of Enno Heidebroek, Paul Brenner, August Thum, John Dudley North, Albin Kasper Longren, Max Himmelheber, and Christian Dell, among others. The selection of actors whose biographies were to be examined in greater depth was made in particular by means of network analysis. As has already been explained in the description of the primary sources, the determination of degree centrality was purely exploratory in character. The filtering process carried out in this way made it possible to select significant actors and their work, in order subsequently to be able to classify the developmental process of composite materials in materials technology. This classification is described in detail in Sect. 1.5.6 on typology. The life history approach was used for biographical data collection in the interviews with contemporary witnesses, which were conducted by the methodological approach of oral history, which will be discussed separately in Sect. 1.5.5 on eyewitness interviews. The life story determined in this way is recounted in fits and starts, hence unlike the chronological approach it is not staked out with distinctive temporal demarcations and thus suits the flow of normal narrative. Mentions of the years involved do, of course, of Material Culture Studies, Hicks and Beaudry (2010); and The Material Culture Reader, Buchli (2002). 145 Cf. inter alia Dressel (2000), p. 13 f., Faulstich-Wieland (1996), p. 116 f., Blaumeiser et al. (1988), p. 472 f. 146 Faulstich-Wieland (1996), p. 117 f., Blaumeiser (1994), p. 11 f., Müller (1993), p. 1 f.

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1 Introduction

find their way in as markers, but they are not chronologically ordered. The almost natural narrational style, which the oral history approach in particular follows, was of central importance to the present study. The section on eyewitness interviews will present this in greater detail. Facets of institutional history It is possible to record and distinguish the developments of long-standing institutions with some success. It is precisely in the examination of developments over long periods of time that a variety of insights arise, especially from the point of view of network analysis, since institutions usually serve as intersections (nodes)147 ; they become meeting points between individual persons and other institutions. At the same time, practices and procedures can often be identified that are frequently of an enduring nature and reflect long-term developments. Institution is meant here in the narrower sense, as set forth by Rahel Jaeggi in her publication on the “core understanding of the term institution”. This means institutions such as universities, research establishments, etc. Jaeggi sees here the point of origin of multiple strands of interwoven histories, at which discourses, practices, epistemic and technical things meet, where material cultures clash with classificatory systems and structural arrangements, and where the actors, whether or not human, interact with one another.148 These facets of institutional history came to bear in the present investigation and were the premise for actions taken, e.g. at the Institute of Materials Research of the German Aviation Research Institute (DVL), the Research Centre of the Aviation Industry of the GDR, and the professorial chairs resp. the academic institutes of Paul-August Koch and Friedrich Tobler. Facets of corporate history Parallels and sometimes overlaps with the institutions just described can be found in commercial enterprises, i.e. in economically independent organisational units, without attempting to describe in any detail the company structures and their peculiarities.149 The study of companies is a broad field and is of central importance, particularly in the case of materials used in manufacture. In this context, Berghoff denotes commercial firms firstly, as the economic engine of history; secondly, as a social field of action or as culturecreating institutions; thirdly, as crystallization points of values and norms; and fourthly, as important political actors.150 These key points can also be identified in the present study. In addition to the aspects of design and production mentioned above, Berghoff’s corporate

147 In network analysis, such intersections are referred to as “nodes”; see Jansen (2003), p. 53 f. 148 See Jaeggi (2009), p. 528 f., Malich (2018), p. 395 f., Priddat (2004), North (1990), p. 11 f. 149 Pierenkemper (2000), p. 13 f. 150 Berghoff (2004).

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Methodology

43

markers can be applied in particular to such companies as Römmler AG, Dynamit Nobel AG or other manufacturers of early composite materials. Römmler AG serves as a particularly apt illustration of such markers. This corporation was a technical trend-setter for a long time, owing its privileged position particularly to its special phenol–formaldehyde condensation process. Römmler AG was thus able to compete on an equal footing with Bakelite Gesellschaft in Germany and abroad, both technically and in terms of its product range. It was able to take the first steps in the world of plastics for decades, relying on solid in-house and university research into products and chains of processing and distribution. Starting with the design of the desk lamp by the Bauhaus master craftsman, Christian Dell, functional and timeless utensils were created which continue to fascinate people to this day. Their representatives were instrumental in the creation of the first DIN standard for composite materials and acted as mediators in the broad arenas frequented by other companies, users and policy-makers. In the context of German armaments production, the company was also an important player in the manufacture of machine elements all the way up to finished weapons technology, and thus enjoyed considerable economic and personal freedoms. However, biographical, institutional and corporate history as well as network analysis stay in the background as tools of my methodological approach. This also applies to the methodological comparison made in Sect. 5.3.3.151 As an elaborated method of the historical sciences, as Kaelble has noted, among others, this form of investigation serves toward understanding other things. In the end, these tools tend to lead to a typology of composite materials, to which I turn in Sect. 1.5.6.

1.5.5

Eyewitness Interviews

As already mentioned in Sect. 1.4, unavoidable gaps in the written documentation were preferentially supplemented by interviews with eyewitnesses and experts, in order to validate various developmental processes of the composites under discussion to thus arrive at a better description of them. The interviews were conducted according to the methodological approach called oral history.152 In this method, the contemporary witness is given the opportunity to report freely about his or her experiences from a personal point of view. The way to begin an interview, in particular, allows room for a positive account without erecting potential narrational hurdles at the beat of a strict chronology. Critical follow-up questions about difficult periods in that life could be asked more easily as the conversation advanced on the basis of a level of trust that had been gained up to that point. However, how well this should succeed in a given situation cannot be guaranteed with absolute certainty. A 151 On the subject of history and comparison, see, among others, Kaelble (1999), Haupt and Kocka (1996). 152 Cf. Schöpfer and Egger (2013), p. 19 f., Abrams (2010), p. 2 f., Geppert (1994), p. 320 f.

44

1 Introduction

whole series of subjective framing conditions play a not negligible role here, such as the physical constitution of the interlocutors on the day of the interview, the level of sympathy, conversational skill and mutual respect that may arise. This form of narrational and autobiographical dialogue seeks to record and depict the individual experience horizon of the contemporary witness.153 In this context it is also referred to as Erfahrungsgeschichte, history of experiences. The method of oral history originates from the USA and is frequently enough regarded among historians as not easy to apply and difficult to evaluate as well.154 Discrepancies between theory and method are often discussed in specialist discourse, which lead to differences of opinion being formed, e.g. with regard to the subjectivity or reliability of an interviewee’s memory.155 This evidently also came into play in the present study, for example, in the interview with Manfred Flemming (1930–2015), the main department head of the section on structural calculation, structure testing and acoustics at the Dornier company and later professor of design and construction technology at the Swiss Federal Institute of Technology in Zurich (ETH). Upon reviewing the transcript and attempting to put things into chronological order, it became apparent that he had made a mistake with regard to the period and location of research projects he had supervised.156 It was only afterwards, during this evaluation that the contemporary witness conceded, upon being presented with the respective project reports, that he had in fact worked much later on two research topics than had been alleged during the interview. The named projects on the development of carbon-fibre winding techniques could thus be situated in his period of service at the ETH in Zurich and were not, as originally asserted, attributable to his research at Dornier. The corrections just mentioned were essential in Manfred Flemming’s case in adjusting the time line for those research projects and clearly demonstrate the difficulties encountered in evaluating interviews taken by the oral history method. One of the strengths of the method, however, is that it lets the eyewitnesses speak freely. Not infrequently, this opens up new research approaches and reveals new sources,157 as, for example, in the case of the interview with Klaus Horten, the son of the flying-wing pilot and designer Walter Horten (1913–1998). Klaus Horten reported about conversations he had had with his mother, in which she told him a lot about his father’s activities in the period before and after 1945. A number of the facts mentioned by his mother, such as a serious accident that one flying-wing pilot had suffered during a test flight in the final phase of World War II, clearly contradicted now known or official accounts in the literature.

153 Küster (2009). 154 See Thompson (2006), p. 2 f., Henke-Bockschatz (2000), p. 18 f., Haefeli (1995), p. 134 f.,

Vorländer (1990), p. 7 f. 155 Brüggemeier (1987), p. 145 f. 156 Cf. interview with Prof. Dr Manfred Flemming (2010). 157 Cf. interview with Horten (2018).

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Methodology

45

In verifying his recollections, Klaus Horten introduced an autobiographical account of nearly one hundred pages length written by his father, which revealed very important aspects about the development of the Horten all-wing aircraft and described Walter-Max Horten’s personal views about his encounters with many people from science, the military and politics in the 1930 and 1940s. These two examples document in particular how very sensitive the method of oral history is and how cautiously it should be treated within historiography, since it is not easy to apply and its results are not easy to assess.158 However, the special merit of the method lies not least in the fact that new research orientations and sources can be revealed or obtained, thus giving this methodological approach its own added value. Critique of the oral history method often voiced in this context is launched almost exclusively against the interviewing technique or method as such. Here, however, it is taken as an opportunity to question the value of written sources by comparison against the results of an interview.159 It should be pointed out here that oral history must of course be subjected to the same rigorous verification procedures as any other written source. In addition, a number of facts obtained from these interviews formed the basis upon which to conduct a closer examination of a number of actor constellations using the research tool of social network analysis. Its exploratory method of degree centrality was applied, similar to the investigation of primary sources, to investigate the immediate proximity of dominant actors (network stars). The peculiarities and difficulties arising from the choice of this methodological approach for the present investigation were recognized and have been assessed accordingly. As already mentioned, it served almost exclusively to verify incomplete technical documentation and to supplement incomplete sources or facts not documented within the framework of technical courses of events. It should be noted that although the interviews conducted for this investigation played an important role, they did not constitute the basis of this analysis. Critical assessment and evaluation of events and data described in the interviews is called for where corroboration by other documentary evidence or contemporary testimony is lacking. The facts presented during an interview which can be situated within the context of a well-founded state of scientific knowledge, may be evaluated as valuable eyewitness evidence. Provided the interviewing according to the precepts of oral history and its authorized findings are handled responsibly, they can be equated with any other written source.160 The prerequisite for success or for valuable facts ascertained in this way is appropriate preparation. Central framing conditions include sufficient familiarity with

158 Thompson (2006), p. 26 f., Haefeli (1995), p. 132 f., Stöckle (1993), p. 132 f. 159 Cf. Schöpfer and Egger (2013), p. 56 f., Henke-Bockschatz (2000), p. 18, Vorländer (1990), p. 15

f., Grele (1980), p. 146. On oral history interviews, especially on its strengths, weaknesses and risks, see te Heesen (2018), p. 7 f. 160 Cf. Henke-Bockschatz (2000), p. 22, Geppert (1994), p. 309 f.

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1 Introduction

the biography of the respective interviewee or contemporary witness as well as the establishment of a suitable base of knowledge and trust, so that the interviewee can offer his or her reminiscences and feel understood by the interviewer.161 Certainly, the interviewee’s accounts must be classified as subjective, i.e. coloured. A comparison against other sources or contemporary reports where possible is therefore inevitable. In order to corroborate statements made in the interviews with contemporary witnesses and experts, a number of additional documents were reviewed and assessed, including ones among the holdings of the Brandenburg State Archives, the Federal Archives in Berlin and Freiburg, the university archives in Braunschweig, Berlin, Dresden and Hanover, the archives of the association for the promotion of students at the TU in Dresden as well as private family collections. A detailed list of the archives consulted can be found at the end of this volume in the List of Sources. Furthermore, topicrelated literature, patents and personal documents of my interview counterparts were also analysed.

1.5.6

My Own Methodological Approach—Typology

Methodologically, the present study comprises a mixture of historical approaches on materials and objects, personal biographies, institutions, society and the economy; it essentially distills down to the history of materials, corporate history and biography. Based on the previous arguments and the specific interpretation of composites, a different methodological approach was sought for the present study. If the focus is directly set on the composite material and thus an approach via engineering characteristics is chosen, the suspicion might arise that the present investigation perhaps ventures away from the current research discourse. At the same time, the current discourse in material culture studies shows that just such an approach as the three-dimensional one presented above can be regarded as up to date. What is specifically meant for the present study is an approach via physical objects or artefacts and their interpretation. Shouldn’t such an access also to be considered necessary if the findings contribute toward a fundamental understanding of the object of study? The legitimacy of this avenue also derives from the fact that otherwise one runs the risk of not being able to treat the topic at all because of the specifics of the studied object, or else of being stifled by compulsory conformity to a current research trend. Precisely this individual and problem-oriented approach and interpretation, according to the recommendations in the above-mentioned studies on technology and materiality, must therefore to be seen as legitimate for a fundamental interpretation of the group of composite materials. The knowledge acquired through such an approach makes it easier to contextualize the object of study, which means that the study of human activities or processes, resp. the human factor, can be illuminated in the effective context of technology and materiality. The latter arguments are also in line with the authors cited above. 161 Cf. Sypher et al. (1994), p. 47 f.

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Methodology

47

Therefore, the genesis of composite materials is comprehensively derived here for the first time from the available technical context on the basis of the written and pictorial sources, followed by findings from interviews with contemporary witnesses and experts. Within a source-critical exposition, the origins are then situated within their entangled socio-economic and socio-political contexts. The change in perspective from the technical source material to a general presentation of hybrid material systems within the context of the history of science, will be effectuated in order to examine and describe developments spanning decades, such as, the multifaceted abundance of composites respecting the numerous matrix and fibre-reinforced materials, retracing their stages from prototype to release onto the market. The attention devoted to the interaction between the human being and technology, embedded in a study going into the technical specifics of the materials, is a novelty in the history of materials science.162 The variety of types of materials involved, including semi-finished products and constructed material systems, taking the conditions of manufacture into account and the structural concepts and design notions as they evolved over the course of time, requires an organizing framework for their depiction. The surveyal and classification of the above-mentioned (manufacturing) materials and material systems by a research method called typology permits the identification and contextualization of the many chosen materials in an analytical and ordering fashion, taking their characteristic features and properties into account.163 Such distinguishing characteristics include the mechanical, physico-chemical, structural and processing properties or a combination of these for the materials construed here.164 It must also be kept in mind that not all the materials of an identified type within the context of the present investigation manifest exactly the same characteristic qualities. In particular, a large number of smooth transitions can be observed, e.g. in the case of bakelite, where fillers such as wood flour were initially incorporated into the matrix system for stability. Without managing to date it more precisely, this material then made a smooth transition to a new composite material which, with regard to its mechanical, structural and processing properties, had transformed into a complex material system. Starting with the embedding of shredded paper, it ended up as a new hybrid composite whose carrier matrix still consisted of the bakelite resin but its stabilizing ingredients had evolved away from snippets towards proper layers of paper. The transition from a stabilizing ingredient to a material with a specific purpose as reinforcement requires an entirely new characterization as a material, with respect to its mechanical and processing parameters. 162 See, inter alia, Radkau (2012), Bensaude-Vincent (2001 b), Haka (2017), id. (2016), id. (2012),

id. (2011), Hentschel and Webel (2016), Hentschel (2011), Hentschel and Reinhardt (2011), Klein (2017), Klein and Lefèvre (2007), Lattermann (2017), Luxbacher (2011), id. (2004), Maier (2017), id. (2007). 163 Cf. on typology: Burzan (2018), p. 2 f., Zifonun (2018), p. 79 f., Kelle and Kluge (2010), p. 85 f., Kluge (1999), p. 34 f., McKinney (1966), p. 33 f. 164 Cf. Ilschner and Singer (2016), p. 16 f., Bailey (1994), p. 1 f., Haupert (1991), p. 240 f.

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1 Introduction

Although the fuzzy boundaries seem to pose a problem, this aspect is ultimately countered by the combination of characteristic properties leading thus to unambiguous identification.165 Likewise, these fuzzy borders represent an essential demarcation from the ordering scheme of classification, where defined criteria either apply or do not apply to the objects of the classified set. This approach, borrowed from the social sciences, is effective with regard to the technical differentiation among materials required here, for example, in identifying layered presstoff, where the differentiation is not made by the plastic matrix or the fact of having layered inserts, but the composite material is rather determined by the material inserts and their arrangement. It is precisely in connection with the differentiation of fibre composites in the first half of the twentieth century that the method of type determination comes into its own and, through the multi-layered design and manufacturing processes, shows their entanglement in a socio-economic and socio-political context. An example of this is the increasingly multifaceted production of plastic masses and bakelite in particular during this period. The demand for everyday consumer goods, but also for technical product applications, which rose with growing urbanization, led to a rapid development in pressing techniques as well as in the design of processing chains connected with manufacturing.166 Consumer behaviour and the demand for inexpensive and robust products made of plastic, which were seen as a novel quality in everyday life and an expression of modernity, contributed decisively towards the establishment of this group of materials.

1.6

Structure of the Work

The content of this book is structured chronologically and is arranged into four main ranges of interest. The introductory part contains a historical guide into the subject, with evidence of the early appearance of composites, in particular fibre composites. The introductory part glances at the development of early composite materials. In particular, the straw-reinforced Nile mud brick is discussed, which was used to build many structures in antiquity and can be seen as the first typical representative of serially produced fibre-reinforced materials. This historical lead-in to the actual topic—namely, industrially manufactured composites of the nineteenth and twentieth centuries—is supplemented by three further early areas of application of composites. First of all, they were used in the fields of hunting and war weaponry in the form of the composite bow. They were then also employed in the devotional trade or decorative construction. This chapter also intends to show in a special way that the principle behind composite materials is not an invention of the industrial age but was discovered far earlier and was already being applied widely. 165 Kluge (1999), p. 32 f.; with regard to the expression of characteristics, see Sect. 1.7. 166 On the subject of urbanization, see, among others, Lenger and Tenfelde (2006), Teuteberg

(1983).

1.6

Structure of the Work

49

The second main part is subdivided into three topics and highlights the most important developments of composite materials in the nineteenth century. It demonstrates that the growing shortages in colonial products encouraged the search for alternative materials, particularly for everyday products. The early chemical industry is elucidated with the focus set on composite materials. Some of the products developed there were the socalled plastic masses. Pursuant to the selected methodological approach of typology, the first subdivision on characteristic values and design in materials technology of the plastic masses evaluates exemplary basic products, which are modifications of natural materials, and their fields of application and categorizes them. Semi-synthetic and wholly synthetic plastics are then also scrutinized and an overview of the developing chemical industry is presented. In this context, one of the commercially most important early plastics out of cellulose is introduced, the composite material called vulcanized fibre. The second subdivision also follows the methodological approach of typology and is devoted to the development of derived timber products, the base material of which is wood. In its natural form, wood embodies the basic design principle of a composite material. This circumstance justified a closer look at the development and industrial upswing experienced by the most important derived timber products. This analysis focuses on veneer and plywood as well as fibreboard and chipboard. The emphasis here is on the invention of homogeneous wood or the early chipboard by Alfred Schmid and Max Himmelheber. The work by Max Himmelheber, who pushed forward the development of the early chipboard as reich commissioner on homogeneous wood during the nazi period, is also included. Likewise, cooperations, such as with the company Christoph & Unmack, focusing on their design of disassemblable barracks. There then follows a retrospective on antiquity and the early applications of lignocellulose materials. The early furniture and construction industry is examined more closely as well with its focus on aspects of the first lightweight designs. The third subdivision discusses a sample patent from this period, which reflects the early use of a composite material in mechanical engineering and shows that such a material had already attracted the attention of individual developers at this time. The material in question was a composite for a plain bearing system that was part of a prototype water-turbine driving mechanism for use in inland waters. The third main part covers the development of composite materials in the first half of the twentieth century up to the break in 1945. The starting point is the development of bakelite. Then, two pioneers of aeronautical materials technology are examined as case studies: John Dudley North and Albin Kasper Longren. These cases are intended to demonstrate that composite materials had already found their way into technical practice as structural materials and that early approaches to lightweight construction were present in this still young industrial sector. The ground-breaking development of polymer chemistry by Hermann Staudinger and the rapidly developing chemical industry world wide is treated, which played a decisive role in the development of the polymer matrix, in particular in fibre-reinforced plastics.

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This chronological survey then looks at the early use of composite materials in a machine element, the bearing. The network of university and non-academic researchers in industry and the military is illuminated along with its active members. German fibre research is examined more closely. Future developments in high-performance composites are also discussed, selecting glass-fibre-reinforced plastics as a sample case in abidance by the methodical approach of typology. Likewise, the guiding questions posed at the outset are mentioned with regard to the identification of central actors in the development of composite materials during the first half of the twentieth century on the basis of a network analysis. Two case studies form the conclusion of this part, which are intended to illustrate that the innovative implementation of the potential of composites in materials technology occurred at that time already on a product of sophisticated design. The first case study is about the fibre-aligned wooden shell construction method, which the aircraft manufacturer Wolfgang Hütter applied between 1943 and 1945, on commission of the Reich Aviation Ministry. Although Hütter was unable to complete the work before the end of World War II, this development is an interesting branch-off within composite materials development, which starts out from classical timber construction, moves on to plywood and finally leads to a focus on fibre orientations in moulded wood production that ends up as a modern fibre-reinforced composite which is referred to as a fibre-aligned lightweight wood composite. The second case study is an account about the active circles around the flying-wing developers Reimar and Walter Horten. These brothers were driven by technical ambition and partly by egoistical motives. Embedded in military structures and guided by political authorities, a flying wing emerged that consisted almost exclusively of composite materials and can be counted as a technical novelty for its time. It is noteworthy, however, that the decision to use a composite material for this aircraft was not the outcome of a well-considered development in design but of a test run for a commercial product. This was a cheap material available to the developers at a time when technical materials were in short supply. Thus, newly developed composite materials were used, which enabled them to explore new avenues in structural aircraft design. The fourth main part elucidates the development of composite materials in the second half of the twentieth century. The prelude here is the utilization of knowledge in materials engineering from the nazi era, which led to the establishment of glass-fibre-reinforced plastics as a material for structural elements, for example, in aircraft construction. The technical limitations of the material then led to the search for an alternative material, which can be exemplified by the student glider model and the development of the Alpha Jet fighter plane. This part places special emphasis on the developmental investigations of composite materials in the GDR, especially fibre-reinforced plastics. The involvement of this group of materials in the development of flying devices is examined in more detail. This section

1.7 Terms and Definitions of Composite Materials

51

ends with a comparison of the applications and state of knowledge about these materials in the two German states. In accordance with the central question formulated at the outset, the central players in the second half of the twentieth century are studied by means of network analysis. The book concludes with a case study about the development of the SOFIA project— the Stratospheric Observatory For Infrared Astronomy. This illustrates the importance that the use of composite materials can have today in projects with demanding material requirements. In the case of SOFIA, composite materials made it feasible to integrate a telescope into an aircraft. This would not have been possible with conventional structural materials due to the limitations of their load horizons.

1.7

Terms and Definitions of Composite Materials

The kaleidoscope of hybrid materials has meanwhile become unwieldy and calls for closer examination and explanation. Thereby we have the opportunity to convey an impression of how the individual components of a hybrid composite interact with one another. First of all, materials are generally broken down into groups.167 For instance, a rough distinction is made between: • metallic materials – e.g. steel, iron • non-metallic materials – natural products e.g. vegetable matter: wood, cotton or animal materials: leather, wool – artificial substances e.g. glass, ceramics, plastics for instance, plastics are divided into the following groups: thermoplastic and thermoset materials and elastomers. The combination of materials from two or more material groups is called a composite material. This is a man-made “engineered” product. One must distinguish between composite materials and the term material composite.168 This type of composite is further

167 Ilschner and Singer (2016), p. 14 f. 168 Kroll and Nestler (2019), p. 12 f., Nestler (2014), p. 27 f.

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Fig. 1.1 Fibre composite, here a simple fibre composite in which the fibres run in a single direction in accordance with the load. Other fibre composites have their fibres arranged at other angles (resp. to one another) depending on the requirements of the given component (CAD model: A. Haka)

subdivided into compound composites (Mischverbunde, i.e. mixed methods of construction)169 or hybrid composites.170 Material composites will not be discussed here further; solely composite materials will be looked at more closely. Whereas metallic and non-metallic materials can be easily distinguished and separated from each other conceptually, problems often arise with the term composite material. This term is used sweepingly both in common oral usage and in a large number of publications merely to indicate that a classical material such as steel or aluminium isn’t involved. Composite materials can also be broken down in terms of the spatial arrangement of the components in the composite. This results in a number of variants, three of the most important of which are presented here. Fibre-composite material. This composite is the most commonly used. The most prominent representative of fibre composites is fibre-reinforced plastic or polymer (FRP, see Fig. 1.1). A fibre composite is defined by its fibre, which in this case is surrounded by a polymer matrix as a carrier, for example, glass-fibre-reinforced plastic (GFRP). In the German Democratic Republic this was referred to as glass-fibre-reinforced Plaste (GFP in German). Apart from the term “fibre-reinforced plastic” (Faserverstärkter Kunststoff , FVK) there is also another term in use: “fibre-plastic composite” (Faser-Kunststoff-Verbund, FKV ). It had been defined by an advisory panel of the plastics technology branch of the Association of German Engineers (VDI), which around 1983 revised the guide-line VDI 2013 on glass-fibre-reinforced plastics. The successor guide-line on three pages has since 169 Cf. Hornbogen and Warlimont (2001), p. 225 f., p. 330 f.; mixed construction (Mischbau) is a

composite of at least two material components which have been joined by a joining process with a joining element or an additive material. 170 Hybrid composites = materials are joined together without a joining element or additive (such as by reshaping).

1.7 Terms and Definitions of Composite Materials

53

appeared as VDI 2014, with page 3 on the “determination” being the most important part. This panel indicated that a new term was necessary in order to make clear that in fibre-reinforced composites the plastic is not the bearing material but rather the fibrous network, which imparts the rigidity and load-bearing structure.171 In this context, the old term faserverstärkter Kunststoff (FVK in German) was considered ambiguous and was replaced by the abbreviation FKV (Faser-Kunststoff-Verbund). The aim was to formulate with equal emphasis the different but equally important tasks of the fibres and the matrix, by placing the components side by side—separated by hyphens.172 However, this change in the German terminology never really took hold; neither has a resolution on this matter been passed by any DIN standards committee. It is a recommendation which, however, often causes confusion, especially in practical applications. The academic meaning and technical terminology introduced by the VDI panel can only really be verified beyond doubt in practical applications via materials diagnostics, e.g. with regard to the proportionate volume of fibre or the orientation of the fibres. The aeronautical handbook Luftfahrttechnische Handbuch (LTH), whose technical committee on the standardization and rationalization of fibre composite materials for aircraft is the oldest in Germany, has therefore rejected this change as inappropriate and continues to use the abbreviation FVK in German for fibre-reinforced plastics. Layered or laminate composite. This composite is made up of layers (laminates) of different materials, which are usually joined with resin or a special adhesive.The term laminate composite (Fig. 1.2) is also used for sandwich structures which usually consist of one core material and two face materials. However, materials in which a fabric is inserted are also referred to as laminate composites. This fabric can consist of glass, carbon or aramide fibres, for example. Hard paper is likewise possible as a layer (ply). The mentioned woven fabrics or hard paper can also be designed, by weaving technique or fibre alignment, to be able to accommodate the load. Typical representatives of laminate composites are the material Glare® (glass-fibre-aluminium laminate composite) or a carbon-fibre laminate. Particle or particulate composite (Fig. 1.3). Particles (of one or various types) are introduced into this composite and usually bonded with a resin. The particles mostly serve to stabilize the material or generate various other properties such as elasticity or magnetism. Bakelite was a typical representative of a particle composite into which wood flour or crushed shells were added for stability. 171 The Arbeitskreis Faserverbund-Leichtbau des Luftfahrttechnischen Handuches was established in 1974. The founding members were: VFW-Fokker GmbH in Bremen, MBB company division of rotorcraft in Ottobrunn, Dornier Luftfahrt GmbH in Immenstaad, DFVLR Institut für Bauweisen und Konstruktionsforschung in Stuttgart. AK-FL (2009). 172 This explanation of the development of the German technical terms FVK/FKV is by Helmut Schürmann dated 23 May 2022. The English abbreviation FRP is preferentially used in the present volume; see the List of Abbreviations.

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1 Introduction

Fig. 1.2 Laminate composite in which the individual layers can be arranged to have different fibre alignments respective to one another (CAD model: A. Haka)

Fig. 1.3 Particle or particulate composite (CAD model: A. Haka)

Other supporting matrix materials exist besides plastic. For example, a fibre composite can also have a ceramic bearing matrix, so-called CMC materials (ceramic matrix composites). If these have a fibre reinforcement they are referred to as fibre-reinforced ceramics. It would be beyond the scope of this study to list the many variants in detail.173

173 Cf. Neitzel (2014).

1.8 Terminology—Material Versus Hybrid Material

1.8

55

Terminology—Material Versus Hybrid Material

Usage of the term for manufacturing material in the German-speaking world is verifiably recorded in a dictionary as early as 1811. There it is defined as follows: “Werkstoff , the material for a piece of work, for a job more specific than the material”.174 Here, Werkstoff was primarily used as a synonym for material, following the Latin word, which translates as material, mother (material) or (building) timber.175 Today, the term material is understood in a broader context and is situatible in particular as an integral component in the subject area of production and manufacturing processes. The conceptual path from simple material to composite material took about 60 years and emerged with the dynamics of industrialization. Another 70 years or so elapsed before the term hybrid material (Hybridwerkstoff ) emerged. In terms of its systematics, however, this term is not historically equatable with that of composite material and has only been in use in Germany since around 1995 (see Fig. 1.4). A precise definition has yet to be put forward. However, the term hybrid material is now preferably in use in connection with high-performance materials, whereby primarily a specially designed property is associated with it and not exclusively an application horizon in materials technology, such as a high-performance structural material. The term hybrid material system is also used for such a material composite in its entirety. This encompasses all aspects of the design of the material, which is usually developed for a specific context. The use of the term hybrid material in the present work draws into account the respective understanding of the time, whereby its beginnings are to be sought in the early industrial utilization of materials and even further back in time. The first composite materials (Verbundwerkstoff ), i.e. the combination of at least two identical or different substances which form a new material with very specific new properties not inherent in the two initial materials, can be traced back to 1868 in terms of patent law.176 Terminologically, it has only been in use since about 1925 (see Fig. 1.4). Both metallic and non-metallic composites were developed. Patents and technical publications were examined to determine the temporal occurrence of the term. To this day, current technical terms can mostly be found in patents and thus indicate technical innovations, also serving as a kind of yardstick. It is in the nature of patents, and in the special interest of the respective patent class, to define new technical boundaries verbally in order to stand out against the prior technical state of the art. Paradoxically, established terms are used for this purpose in patents in order to be able to define them in a clear and universally understandable manner. It is only in the patent claim, the conclusion of a patent, that new technical terms are often found which purport to be “entering” into new technical territory, in order thus to legitimize patentability as well. 174 “Werkstoff, der Stoff zu einem Werke, zu einer Arbeit, bestimmter als der Stoff.” Campe (1811),

p. 686. 175 Langenscheidt Editorial (1999), p. 326. 176 Judge (1868).

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56 1 Introduction

1.8 Terminology—Material Versus Hybrid Material

57

The just referenced patent by the US-American, Edward Judge, clearly shows that at that time the use of a composite material consisting of conventional materials and additives based on paper fibre on an industrial scale was seen as a central innovation in materials technology and was patented. The patent defines a maché material, which is presented as a composite with new material properties. At the same time, however, it points in the direction of the plastic masses, the established technical term for this type of material at the time. The technical and conceptual transition from the composite material papier-mâché to plastic masses,177 which first found mention in patent law in 1887, took about two decades.178 After a relatively short period of usage of the term ‘plastic masses’ at the end of the nineteenth century, a remarkable turnaround occurred with bakelite, especially with regard to the technical term. Although the material bakelite, a resin system with admixtures, can in fact be counted among the plastic masses, bakelite occupies a special place in the long series of advances in composites. It is not only the world’s first bulk plastic. The extensive use of the material after its development also led to bakelite becoming synonymous with the world’s first everyday plastic.179 Bakelite thus promptly superseded the technical term plastic mass. The superordinate term ‘composite material’, as we understand it today, remained unaffected and is still in use today. It appeared increasingly at the beginning of the 1920s as a term in materials technology. Occasionally it was defined more precisely with respect to the term ‘plastic mass’.180 Its differentiation from among the plastic masses took place almost at the same time, in 1922 with the creation of a new class in patenting whose carrier matrix consisted of synthetic resin. The growing variety of products led to a further type category in 1928. Finally, in 1932, these so-called presstoff materials found their way into the series of composite materials. The conceptual transition had taken place just a few years earlier and was based on the terminology of the associated production process of moulding and was essentially minted by Römmler AG, because it called its products Preßmassen, no longer “plastic masses”. This term for “pressed mass” can be regarded as established by the 1920s at the latest. The products made from them were called Preßstoffe. The change in terminology was closely linked to the manufacturing process and changes in compression technology. The early forms of presstoff types were still composed of undefined amounts of hard-paper pieces or bits of fabric as the core material, which were coated with a synthetic resin supporting matrix. The first standardized technical definition of presstoff was laid down in 1936 in DIN 7701. This DIN standard is described in more detail later in this study, in Sect. 3.2.2 on fibreboard and chipboard. The first patent on presstoff materials was granted in 1934, for a lavatory lid with inserts by a company from Essen. This was a composite material in two senses. It not only 177 Papier-mâché and plastic masses are presented in more detail in Sect. 2.4 on Papier-mâché—

composite material from the Middle Ages and Sect. 3.1 on The plastic masses versus presstoff in this study. 178 Coughlin (1887). 179 This period also produced the definition of the word “plastic” (Kunststoff ) by Ernst Richard Escales (1863–1924), which is addressed in greater detail in this study in Sect. 4.1 on bakelite. 180 Bürgel (1934), p. 519 f.

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1 Introduction

consisted of a fibre composite, but also had metal bolts embedded in its material structure, which connected the lavatory seat to the lid.181 DIN 7701, released by the Technical Committee on Plastics and Presstoff, established in December 1935, of the Association of German Engineers (VDI), defined the aspect of composite materials within the context of presstoff materials.182 One year later, the term composite material (Verbundwerkstoff ) appeared for the first time in patent proceedings, and similar to the presstoff instance, also involved a composite metallic material.183 In the patent a core material is described which is enveloped in another material, whereby both form a material connection with each other. The technical term composite material was thus brought to light for the first time by a patent in the mid-1930s. It became established relatively quickly in specialist circles and is still an integral part of the terminology in materials engineering today. The differentiation of presstoff in materials technology led to a reorganization and expansion of DIN 7701. One of the follow-up standards, DIN 7706 on hard paper and woven-fabric based laminates (Hartgewebe), dealt for the first time with the chemical composition and positioning of the core material with respect to static aspects, which was the outcome of academic influence.184 This focus will be elaborated on later under Sect. 4.4.2.1 “Uncharted academic territory far removed from university research”. One central aspect was, to define hard paper or laminate presstoff in terms of their layered structure from the point of view of material mechanics and to design them specifically according to a requirements profile. This gave rise to the concept of laminate or layered materials (Schichtwerkstoff ) or, in more precise terms, reinforced presstoff / reinforced laminate presstoff at the end of the 1930s.185 Closely linked to this was the technical aspect of optimizing material strength by the presstoff regime of manufacture. Because laminate materials tended to be used in technically sensitive areas such as aircraft construction or military applications,186 this technical term only appeared in two patents by Auto Union Chemnitz. Both patents were related to the development of an off-road vehicle for the Wehrmacht and were not available to the public until after 1945. One of them was the patent “On preshaping hollow bodies of fibrous layers soaked in synthetic resin”,187 and the other regarded motor vehicle boxes made of laminate plastic panels.188 The latter patent was filed with the Reich Patent Office in 1939, but wasn’t issued as a 181 Presswerk (1934). 182 Anon. (1935), p. 319. 183 DIN 7706: Hartpapier und Hartgewebe, Brenner and Roth (1940). 184 Nitzsche (1943), p. 232. 185 Reinforced presstoff (bewehrte Preßstoffe) designated “armed” presstoff materials with unidi-

rectionally inserted fibrous materials/fibre rovings (borrowing the idea from the French armement in military technology), see also Bürgel (1937), p. 91 f. 186 There mostly in military applications. 187 “Zum Vorformen von Hohlkörpern aus mit Kunstharz getränkten Faserstoffschichten.” This patent is mentioned again in this study within the context of the cooperation between Römmler AG and Auto Union. 188 “Kraftwagenkasten aus Kunstharzschichtstoff-Wänden”, Werner et al. (1952), Auto-Union A.G. (1940).

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patent until 1952 by the Office for Inventions and Patents of the GDR. The inventors, including Wilhelm Endres (former head of research at Auto Union Chemnitz) or William Werner (former member of the board of directors for the technical division of Auto Union Chemitz), were correctly identified in the patent, but the holder of the patent was changed to: “property of the nation” because the assets and technical know-how of Auto Union had been confiscated by the GDR, hence also a whole series of patents. The technical term Schichtwerkstoff for laminate materials could be found not only in the afore-mentioned patents from the automobile industry, but also in internal research documents of the German Aviation Research Institute (Deutsche Versuchsanstalt für Luftfahrt, DVL), where such materials were intensely researched at their Institute of Materials Research.189 Thanks to the non-public research on laminate materials, that technical term initially did not find its way into the jargon of materials science. It was not until the materials scientist Franz Bollenrath from Aachen published excerpts of the hitherto secret research from the national socialist era in his paper on synthetic resin laminates with glass fibres in 1946, that the technical term Schichtwerkstoff was introduced into the specialist world of the post-war period. As the former chief editor of the Ringbuch der Luftfahrttechnik in the 1940s, Bollenrath had full access to the secret research results from that period. He used this among other things, to establish himself as a university lecturer in Aachen in the field of materials science.190 It was not until the development work on the Alpha Jet fighter aircraft in the midto-late 1960s that the technical term presstoff was finally abandoned and replaced by the more precise technical term fibre-reinforced plastic.191 They are subdivided into fibre composites and laminate composites.192 The term Hybridwerkstoff (Fig. 1.4) was first mentioned in 1991.193 However, the use of this term is not limited to fibre composites but is also applied to other composite materials. Quite similar to in the German-speaking world, the term most widely used among English speakers is composite material (Fig. 1.5) and is probably used as a synonym for materials composed of multiple parts. The distinction between ‘layered composite’ or ‘hybrid material’ is obviously used much less. It is conceivable that this technical term is used among specialist circles.

189 Küch (1940a), id. (1940 b). 190 Bollenrath (1946); on Bollenrath and his activity as an chief editor in this field, see in greater

depth Haka (2011), p. 85. 191 For more about the development of the “Alpha Jet” fighter plane, see Haka (2011), p. 86 f. 192 Grüninger (1971); see also the detailed description of fibre-reinforced plastics in Sect. 1.7 “Terms and definition of composite materials”. 193 Vleuten (1991).

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2

Early Composites

Before I devote Chaps. 3–5 to the development of composites in the nineteenth and twentieth centuries, I would like to make a brief retrospective here on the much earlier history of this class of materials. The reason for this is that, as outlined earlier in Sect. 1.7 on terms and definitions of composite materials, today’s forms of composites were produced by humans much earlier and are not inventions of the 19th or twentieth centuries. Particulate composites can be found from as early as the Upper Palaeolithic, as well as fibre and layered composites from the Neolithic and Final Neolithic. Although the early forms of these composite materials are not comparable with their counterparts today, they nevertheless show that the “building-block” approach, i.e. combining materials in order to unite better material properties in a newly created material, was already known to the first “modern humans”, Homo sapiens, who worked with flint tools.1

2.1

Unique Piece from the Stone Age

The Venus of Vˇestonice, a Stone Age rudimentary female sculpture, named after its discovery site Dolní Vˇestonice in southern Moravia in the Czech Republic, consists of a simple composite material.2 It was made of clay, reinforced with animal bone meal as a simple stabilizer and then fired. Its age is now estimated at around 29,000 years ago. This means that this sculpture is made of what may be the earliest known primitive composite material created by the human hand. The principle of stabilizing or specifically reinforcing a material by incorporating another material was therefore already known to humanity at a very early stage, albeit the Venus of Vˇestonice is a unique find which cannot be regarded as exhibiting the “standard” technically produced material for its time. 1 Trinkaus (2003), p. 255 f. 2 Králík et al. (2002), p. 107 f., Hummel (1998), p. 7, 288 f.

© The Author(s), under exclusive license to Springer Fachmedien Wiesbaden GmbH, part of Springer Nature 2023 A. T. Haka, Engineered Stability, https://doi.org/10.1007/978-3-658-41408-5_2

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2.2

2 Early Composites

First Reproducible Composite Materials—Fibre-Reinforced Bricks

One of the earliest multiply reproduced composite materials may well be the Egyptian Nile mud brick—as it were, one of the first mass-produced products in the building trade—with its admixture of cut straw for mechanical reinforcement. A very considerable span of time and development lies between the Venus of Vˇestonice, dating from the Upper Paleolithic, and the Egyptian mud brick from the Neolithic. Owing to the current source situation, the intervening stages of development of early composite or fibre-reinforced materials remain opaque. However, the development and success of the Nile mud brick, which falls within the reign of the Egyptian pharaohs, can be illuminated much better. This Nile mud brick, which was used, among other things, for the construction of pyramids, tombs, enclosure walls and even simple houses as well as paving for construction roads and pathways, was produced between around 3000 and 2700 BC.3 It can be seen as an important technical step in materials science within the building trade. The defined manufacture of these bricks also indicates a complex understanding of construction and reveals some architechtonic flexibility between design and material at that time. Upon closer examination of the production process of Egyptian mud bricks, distinct parallels to basic working principles of fibre reinforcement become apparent, which are still found today in modern fibre-reinforced materials. The specific choice of matrix material, the fibre ratio and pertinent surface activation for a good fibre-matrix bond all show that a not inconsiderable amount of attention was devoted to the quality of the building material in the Egyptian pharaonic kingdom. For example, not just any mud or pure clay was used for the Nile mud bricks. Quite the contrary: the brick base material was extracted from particularly moist clay layers in the Nile bed. This mud with its high clay content was mixed with sand, stored (air-dried) and finally processed.4 In order to increase the firmness of the bricks, the cut straw was moistened (Fig. 2.1). Here already, precepts defining the position and length of the straw bundles were followed and the latter were put in a wooden moulding box in order to be able to specifically influence the final stability, albeit only in simple form. Besides reinforcing the brick, the moistened chopped straw fulfilled important technical aspects of their manufacture, which had an influence on the brick quality. The moistened straw bonded better with the clay and thus created a special homogeneity among the components. Moist straw also prevents the formation of cracks during the drying process. If the straw had been added in a dry state, the fibre-matrix bond would only have partly set. In this context, it was also possible to identify a number of different brick qualities suited to their respective intended purposes. It seems probable that each building

3 Cf. Müller-Römer (2011), p. 51 f., Klemm and Klemm (1993), p. 10. 4 Cf. Arnold (1997), p. 282, Goyon (1979), p. 87 f., Spencer (1979), p. 3 f., 140 f.; on mud-brick

architecture and ancient building forms in particular, see Minke (2009), Damluji (1993).

2.2

First Reproducible Composite Materials—Fibre-Reinforced Bricks

63

Fig. 2.1 Straw-reinforced bricks from the labourer settlement of Deirel-Medina, which is located on the west bank of Thebes, south-east of the Valley of the Kings in Egypt. It was inhabited from about 1520–1069 BC by the workers who constructed the pharaonic rock tombs. Photo Courtesy of Klaus Hentschel, 18 Feb. 2020, Deirel-Medina, Egypt

project demanded its own building-material quality and that the bricks had to be sorted in advance—an early form of quality control, so to speak. Very similar framing conditions can be found in the production of modern compositematerials, such as components made of carbon-fibre-reinforced plastic (CFRP) or even glass-fibre-reinforced plastic (GFRP), although moisture is not utilized. For better bonding of a carbon fibre to a polymer matrix, for example, the fibres are furnished with a so-called sizing,5 which increases the adhesiveness at the interface between fibre and matrix.6 It appears that with a high degree of probability the connection between the load-bearing capacity of Nile mud bricks and the quality of both the stabilizing fibrous straw material and the surrounding matrix was known. This knowledge was present in the form of simple craft tradition and eventually led to the production of high-quality bricks which made complex structures feasible. It is not surprising that not only fortresses, fortifications or temple complexes could be built in ancient Egypt with such building materials. The high strength of this highquality building material for the time was also made use of for transportation routes and

5 Sizing = a fibre coating which acts as a bonding agent between the fibre and the matrix. Depending

on the type of fibre, the sizing can consist of synthetic or natural materials. It also protects the fibre from mechanical stresses. 6 Park (2015), Morgan (2005), Flemming and Roth (2003), Flemming et al. (1996).

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Fig. 2.2 Excerpt from the mural of the vizier Rekhmire showing the production of Nile mud bricks. Left: mud extraction in and on the banks of the Nile; lower centre: mud and straw compounding, and upper centre: brick production; right: measurement and computation of the quantity of building materials. Source Myers (1897, p. 13)

construction ramps for other buildings as well.7 One can only surmise at the quality of such bricks when one considers that construction projects and hence also the access roadways or ramps at a pyramid or temple had to withstand daily continuous operation for years, if not decades. Further parallels in materials technology between Egyptian fibre-reinforced building materials and modern fibre composites can be found in the ancient Egyptian city of Tanis in the north-eastern Nile delta, where, for example, 14 m-thick brick walls can be found with incorporated layers of reed matting as horizontal reinforcement.8 This simple material design can be found all over the world today in only slightly modified form. The reed mats have long since been replaced by steel reinforcement, carbon fibre or technical textiles in concrete,9 or resp., a laid web or woven fabric in modern fibre-reinforced plastic.10 However, the basic intent of improving the strength of existing materials through the targeted use of stabilizing materials and thus opening up new load horizons has not changed. That the brick in question was indeed a very early “serial product” is shown by a mural (Fig. 2.2) in the tomb of the vizier Rekhmire from the New Kingdom (fifteenth century B.C.). In his day he was the most powerful official under Pharaoh Thutmose III (1486–1425 B.C.).11 This mural mirrors the vizier’s professional achievements and his duties, e.g. the supervision of building projects for the pharaoh. However, it is also a representation of performance and power, which in the pharaonic realm was primarily defined by the size and quality of buildings. In this context, illustrating brick production is also presenting architectonic skill and reproducing the technical know-how of the time. 7 Cf. Arnold (1997), p. 282. 8 Cf. Wilkinson (2000), p. 37, 155 f. 9 On the subject of fibre-reinforced concrete, see Wietek (2017), id. (2008). 10 Cf. Parra-Montesinos et al. (2012), Flemming et al. (1996). 11 Cf. Wachsmann (1987), p. 45, Davies (1943), p. 63.

2.2

First Reproducible Composite Materials—Fibre-Reinforced Bricks

65

An analysis of the image and the inscriptions in the vizier’s tomb shows not only the extraction of Nile mud and the admixture of cut straw, but also that instead of one standard brick being produced, there were different variants with deviating straw admixtures. This means that the building material was individually adapted to the strength requirements of the respective building project. Consequently, the principle of material reinforcement or the brick production as such played a crucial role. The mural also represents the building boom under Pharaoh Thutmose III, probably the most powerful pharaoh in the history of Egypt. Pharaoh Thutmose III was, according to our knowledge today, not only a brilliant general, strategist and religious leader, but also a prudent and innovative builder.12 One reason for this is certainly that, unlike many other pharaohs, he had an exceptional education. When his father, Pharaoh Thutmose II (c. 1510–1479 B.C.), died, the future ruler was only about seven years old. But unlike some of his predecessors Thutmose III did not have to act as child ruler. That task was taken on by his ambitious stepmother Hatshepsut (1495–1457 B.C.), who crowned herself as pharaoh and ruled autonomously.13 As an adolescent, Thutmose III did not rebel against his stepmother who officially designated him as co-regent. Thutmose III spent almost 20 years as co-regent without making an official appearance as pharaoh until the death of his stepmother. He put this time to very good use, though, and received a well-rounded education for the time, in the areas of military training, commerce, art and architecture. He finally acceded to the throne after the death of his stepmother and skilfully managed to expand the Egyptian realm as no other pharaoh either before or after him. During this period, as already mentioned, he headed a large number of building projects, many of which he inspected himself and in which he also intervened in a corrective manner about the design or building technique during the construction phase. Given the depiction of brick-making in the tomb of his most important official, it is highly probable that Thutmose III also considered, or even decisively influenced, details involving the production of the building material. This assumption can be considered realistic if one considers his botanical garden, in which he cultivated rare plants that had come back with him from his campaigns or that had been given to him as gifts. On the one hand, it is astonishing that no pharaoh before him had such a garden laid out, and on the other hand, that there is also evidence of a whole series of native grains and fibre plants in addition to the exotic plants, which almost seem to be out of place next to them.14 The supposition that Thutmose III also had fibrous cultivars planted there for experimental purposes as reinforcement material for construction also supports this proposition that Thutmose III had some influence on brick design and production. The fact that craftsmen and designers had been concerned with brick making since as early as the 1st dynasty of the Egyptian 12 Cf. Widmaier (2009), p. 78 f., Dormann (2006), p. 41 f., Kühn (2001), p. 37 f., Höber-Kamel

(2001), p. 12 f., Beaux (1990), p. 316 f. 13 Helck (1994), p. 38 f. 14 Beaux (1990), p. 40 f.

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kings (c. 3000 B.C.), i.e. well before Thutmose III, who belonged to the 18th dynasty, should also be borne in mind. Another source that addresses brick making and its reinforcement with straw is the Bible. Although the Bible was compiled over generations from a number of writings into a largely unified work, many aspects are based on descriptions of actual events, while other texts are allegorical towards a better understanding of the faith or of the Bible in general. The making of bricks is the subject of the Second Book of Moses, which describes the budding conflict between the Israelites and Egyptians and can also be regarded as a thoroughly realistic description of the servitude of the Israelites in Egypt. Among other things, it includes a description of the manufacture of straw-reinforced bricks. For example, the Second Book of Moses, Chap. 5, beginning at verses 6 and 7, states: And Pharaoh commanded the same day the taskmasters of the people, and their officers, saying, Ye shall no more give the people straw to make brick, as heretofore: let them go and gather straw for themselves.15

It is noteworthy that the task of gathering straw for the production of bricks was considered a menial task and was performed in servitude to the pharaoh. This suggests that very many people were obliged to produce mud bricks, presumably to satisfay the enormous demand for brick material, which was a permanent condition in Egypt throughout the extensive building projects of the pharaoh. Historical biblical research, which seeks to underpin the Bible with historical facts, specifically locates the emigration of the Israelites from Egypt, as described in the Second Book of Moses, during the reigns of the 18th to 20th dynasties of the Egyptian pharaohs.16 This would mean that with regard to the brick making depicted on the mural in the vizier’s tomb, a direct bridge leads to Pharaoh Thutmose III (as member of the 18th dynasty), which affords it a broader basis. Likewise, biblical researchers deem the living conditions of the Israelites described in the Bible to be realistic. The production of bricks can therefore at least be assigned to a certain segment of the population, although slaves or possibly day labourers also performed this task.

2.3

First Weapons—Composite Bows

The need to defend oneself against enemies or defeat them if not just to distinguish oneself as a successful hunter was a driving force for mankind to develop and constantly improve weaponry very early on. The quest for more powerful mechanisms was almost always coupled with a search for better materials to satisfy new performance parameters. 15 Sächsische Hauptbibelgesellschaft (1915), p. 58, this translation taken from the King James

authorized version of the Church of England, Exodus ch. 5, v. 6–7. 16 Hoffmeier (1999), Davies (1992), Loewenstamm (1992).

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First Weapons—Composite Bows

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One of the earliest weapons of humankind to replace the thrusting lance and throwing spear as a long-range weapon was the bow which made it possible to shoot repeatedly at targets from a greater distance away. The bow is a good example of early, and indeed, of a more complex development of composites, which transferred simple natural load-bearing principles to weapons technology. Although regionally varied, the bow spread rapidly and widely. The first bows were made of simple wood but were relatively quickly replaced by ones out of composite materials (composite bows),17 which had greater ranges, were more accurate and more stable.18 Such bows were made in a sandwich construction19 in order to generate greater tension and stability. The composite material used in composite bows was first described and analysed in the late nineteenth century by the ethnologist Herny Balfour (1863–1939), curator of the Pitt Rivers Museum in Oxford.20 His detailed account of the composite bow in the museum’s collection provides good insight into the weapon’s structure. It had been found in Egypt and dates from the time of Ramesses II (1303–1213 B.C.)—although the bow itself is thought to have originated from what is now Syria and had eventually come to Egypt by warfare. This particular bow not only reveals how it works but also permits further material analyses which, in turn, allows conclusions to be drawn about its workmanship. According to Balfour, the bow (Fig. 2.3), which had probably been made by an experienced bowyer in Syria, belonged to a soldier. The cross-section sketch of the bow (Fig. 2.4) shows the complex structure. The central core piece is the wooden core “a”, which consists of hardwood. Attached to it on either side is another separate supporting piece of hardwood “b”. The immediate elasticity was achieved by the addition of layers of animal horn to the core piece (the layers “c” and “d”), which gave the bow high tensile strength. Another stabilizing horn layer “e” served as a safeguard and prevented compression. Various bands of animal sinews (the layers “f1 ” and “f2 ”) were glued on as additional external reinforcement. They not only increased flexibility but also protected the bow from being overstretched. The outermost layer of the composite structure was layer “g”, which consisted of bark to protect the composite from water or from ungluing. Balfour’s analysis remains regrettably open in terms of materials, in that he does not identify the exact type either of the wood, the sinew or the bark.21

17 “Composite bows” are still made today, both in the traditional way and using modern high-

performance materials. 18 See Loades and Dennis (2016), p. 23 f., De Waele (2005), p. 154 f., Knecht (1997), p. 152 f.,

Steguweit (2009), p. 10 f., Eckhardt (1996), p. 54 f. 19 Sandwich construction characterizes a component or semi-finished product which is made up of

several layers, often of different materials, and usually has a core layer and a covering layer (above and below). 20 Balfour (1897), p. 210 f. 21 Steguweit (2009), De Waele (2005), Knecht (1997).

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Fig. 2.3 The bow described by Henry Balfour; from the left, the whole length of the bow, in cross-section, and the prominent incisions on the bow shaft. Source Balfour (1897, p. 221)

Fig. 2.4 Cross-section showing the structure of the composite material of a composite bow. Source Balfour (1897, p. 213)

Gluten glue was used almost exclusively as the adhesive, which was produced by boiling animal waste, such as bones, fish bones or fish bladders. The horn pieces could have originated from deer antlers or rib segments of large animals such as a whale, depending on the region. The sinew layer was taken from game, such as a stag, worked in a number of ways and then dried. The alignment of the sinews, which were gathered together in bands and processed in conformance with the direction of tension of the bow, shows again how strong the parallels are with the production of modern fibre composites, as has already been seen in the case of the fibre-reinforced brick from Egypt. The

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Papier-Mâché—Composite Material from the Middle Ages

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bands of sinews can easily be compared with modern filaments,22 which are gathered together into a roving23 and arranged in a unidirectional layer (UD layer)24 in modern fibre-reinforced plastic. In most cases, the composite bow was finally spirally wrapped in glue-impregnated birch bark as a moisture-proof protective layer. The composite bow can hence be regarded as an early form of a sophisticated composite-material product. The knowledge about its working principle can be traced all the way back to the early Neolithic period, that is, about 5000 years ago, as early murals from this period in Spain demonstrate.25 The earliest verifiable composite bow dates back to the late Neolithic (ca. 2800 B.C.) and was found in the Pribaikalia region near Lake Baikal. The later medieval bows from England also deserve mention here, their limbs were also constructed of layers of different types of wood and specially prepared animal hide.26

2.4

Papier-Mâché—Composite Material from the Middle Ages

Papier-mâché, and even more so the much more robust variant using cardboard pulp, was already in use early on in bookbinding for making book covers; and the handicrafts and the building trade adapted this technique for their own purposes as well.27 In 16thcentury Italy, for example, devotional crafts attributable to the region of Apulia produced and finished cardboard pulp as a material for sculptures and decorative elements. This material was already being modified with admixtures of substances to stabilize the mass to meet specific load requirements. Whereas nowadays the proportionate material components are precisely defined numerically in modern composite materials, these early composites could rather be referred to as “material mixes” combined according to some “cooking recipe” which moreover depended strongly on the respective industrial enterprise. Calling this material a “mâché” is very apt28 and infers the process of manufacture. The first step in the production process is to shred the paper or cardboard into small pieces. In most cases the paper or cardboard was torn to bits by hand and soaked in water, then stirred into a paper pulp in a mixing and kneading process and subsequently boiled. This process varied greatly from region to region and from place to place, which brought about fluctuations in quality and quantity. At the end of the cooking process, the paper or board had disintegrated, releasing the lignocellulosic fibres in the pulp and allowing the 22 Filament = designation of a single fibre of a fibre-composite material. 23 Roving = a bundle of a certain number of individual fibres for the production of fibre composites. 24 UD layer = unidirectional layer of a fibre-reinforced plastic with all its fibres oriented in a single

direction. 25 Steguweit (2009), p. 10 f. 26 Loades and Dennis (2016), p. 4 f., Green (2006), p. 323 f., Gray (2002), Riesch (2002). 27 Schmidt-Bachem (2011), p. 662, Grünebaum (1993), p. 15 f., 220 f. 28 Papier mâché = French “chewed paper”.

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fibres to reorientate themselves or rebind. The addition of gelatine or similar early natural gluing agents created a new mouldable mass. After the modelling and subsequent drying process, a permanent final shape was formed which had wood-like properties and could be worked. A closer study of old papier-mâché manufacturing processes reveals that this was an early form of materials recycling. Although many papier-mâché manufacturers even advertised that they used high-quality paper to make their maché, material analyses of some products revealed that, for cost reasons, old paper and old cardboard were preferentially used as the raw material.29 Similar to modern composites, some “adjustment screws” can be found with which the technical parameters of the matrix and reinforcement materials could be adjusted according to the requirement profile, such as water quality, the shredding process, kneading and stirring intensity, material quantity, binder, the selection of additives, among others. The material “recipes” of the different local and regional papier-mâché workshops and later of the manufactories show that this “tuning process” was sufficiently well known and was applied in many ways. However, it is not yet possible to speak of a hybrid material design according to today’s standards. The manufacture of papier-mâché is probably as old as paper itself. From antiquity until well into the eighteenth century, papier-mâché was also used as a building material, not least because the “recipes” and refinements of new material mixtures produced increasingly stable machés. One instance is Ludwigslust castle, the main residence of the Dukes of Mecklenburg-Schwerin, which was built in 1763 and today houses the Staatliches Museum Schwerin. Papier-mâché was especially adapted to its specific requirements, leading to the invention of Ludwigsluster carton.30 This papier-mâché with individualized additives could serve as a substitute for expensive marble and then-costly wooden and inlay panelling. But papier-mâché was used not only for cladding and decorative material in Ludwigslust, but also as a building material in the form of nonload-bearing round arches in the castle church, which is now used as the town church. The altar-piece on the south wall of the church, which covers an area of 350 m2 , is painted entirely on Ludwigsluster carton (Fig. 2.5). The image depicts the angel Gabriel heralding the birth of Christ from on high to the shepherds. In addition to the pictorial aspects, the arrangement of the painted papiermâché segments of the altar-piece generates the effect of spatial depth. The extraordinary colouring and shaping possibilities of the maché material play a special role here, making possible, for example, a thickening and tapering of the material where needed and thus permitting individual spatial perspectives without presenting a problem in the statics. The illusion that the viewer is looking into a corridor of clouds is largely achieved by means of the design options available with papier-mâché. The extent to which parallels exist with modern composite materials is apparent in the respective modelling processes 29 Grünebaum (1993), p. 21 f. 30 Staatliches Museum Schwerin ed. (1997), p. 35 f.

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Fig. 2.5 The altar-piece painted on Ludwigslust carton in the choir room of the former Ludwigslust castle church, which is currently the Evangelical Lutheran church for the town of Ludwigslust. Source Postcard (1930)

used in draping by hand or machine with papier-mâché and modern fibre-reinforced plastic, respectively31 Modelling with papier-mâché just as with FRP is often carried out with semi-finished products,32 which are attached to the relevant surfaces. By drying the papier-mâché, or in the case of FRP by hardening in an autoclave33 (or by the appropriate compressing process), their final fixing and hardening occurs. The more recent applications of technical textiles and their ability to be designed freely by means of knitting processes almost without posing any problem, constitutes a new step in the development of modern FRP in the direction of sophisticated spatial structures. Ludwigsluster carton remained an exception for a long time, since its inventor Johann Georg Bachmann (1738–1816) never disclosed his “secret” recipe, and so the production of this “carton” remained temporally and regionally limited. It was not until the turn of the 18th into the nineteenth centuries that the admixture of wood flour, clay, chalk or other

31 The affixing of semi-finished products onto a moulded surface. 32 Halbzeug = prefabricated raw materials and semi-finished products. 33 Autoclave = a sealable pressurized vessel which is used, among other things, for the production

of FRP and in which FRP are allowed to harden or cure under the application of heat and pressure, see Flemming et al. (1999), p. 40 f.

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materials, variously applied according to the particular need, or the usage of thinner or thicker paper strips in the manufacture of papier-mâché, could be viewed as established.34 This is also where the decisive step in the development is ascertainable: The defined “adjustability” of papier-mâché used as the material together with others, even though their technical strength was moderate, makes it possible for the first time to speak of a technically determined hybrid material system, not least also because hybrid papiermâché had transformed from a more-or-less individually produced devotional object into a genuine industrial product. The company owned by the Briton Henry Clay (1738–1812), who took out a patent on “paper ware” in 1772, serves as a good case in point.35 Clay mainly produced small pieces of furniture in the “Japanese style” made of papier-mâché and cardboard pulp, such as sideboards, chests of drawers or writing-desks. His patented technique consisted in gluing together different types of papier-mâché and pulp sheets into several layers, some of which also contained stabilizing additives, and then machining them.36 The layered structure applied in this process is comparable to the basic principles of plywood production in use today. These principles had already been applied to furniture for the Egyptian pharaohs of the first to fourth dynasties, but then got forgotten and were only rediscovered in the nineteenth century.37 Working with papier-mâché and cardboard pulp was always a matter of working with fibres, in search of new and more profitable fibrous materials suitable for paper production in particular. Even when the first paper mills opened business in the fourteenth century, the raw material forming the basis of early paper manufacturing—namely, rags—was already in short supply.38 These were preferably old or used linen fabrics, consisting of hemp or flax fibres. This scarcity quickly led to the restriction, rationing and smuggle of rags and textile scraps of all kinds. Regional licensing in the rag trade was strictly supervised and formed a separate sector situated between the crafts and commerce. Although there were repeated efforts to find alternative fibrous materials to replace rags for paper production, they were doomed to failure either because they were half-hearted attempts or for lack of funding and, not least, because of the papermills’ operating standards. The search for a viable alternative took almost four hundred years. One of the most committed in this search was the practically inclined Protestant senior minister of Regensburg, Superintendent Jakob Christian Schäfer (1718–1790), who was interested in a variety of topics as a natural scientist and inventor. Among other things, he investigated natural fibres with regard to their utility in paper production, such as poplar wool, nettles, straw or milkweed.39 He furthermore experimented with wood, the most important 34 Schmidt-Bachem (2011), p. 663. 35 Inkster, ed. (2012), p. 126, Rivers and Umney (2003), p. 206, Toller (1962), pp. 19, 26, 62 f. 36 Beard and Gilbert (1986), p. 176. 37 Scott (1965), p. 130, Sellers (1985), p. 7 f. 38 Schmidt (2013), p. 50 f., Sandermann (1988), p. 138 f. 39 Roloff (2012), p. 159 f.

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natural fibrous material, and produced paper samples from it. He not only examined a whole range of wood species, but also included wood shavings and wood flour in his considerations, thus pointing the way to how paper is made today. His efforts failed, however, against the opposition of conventional notions about how to produce paper and the economic interests of paper manufacturers and their suppliers. Although the idea of using wood or wood shavings for paper production was not new, the invention of mechanical wood pulp paper was an independent development by the Saxon master weaver Friedrich Gottlob Keller (1816–1895), who thus laid the foundation for modern-day paper production.40 This not only led to an expansion of timber research, which until then had been limited almost exclusively to the construction sector, but also led to an expansion of research into fibrous materials, which had hitherto concentrated primarily on textile application horizons. Papier-mâché and cardboard pulp, which had undergone a variety of transformations, especially during the eighteenth and nineteenth centuries, ultimately allowed fibrereinforced mâché to become a genuinely new manufacturing material with a defined portfolio in materials technology. This material plays a key role in this investigation into the development of composite materials; it becomes, as it were, the development hub of endeavours in materials engineering in the quest for new areas of application and load horizons. By the end of the nineteenth century at the latest, pulp production had not just become the signboard of an industrial branch, but was also at the forefront of a completely new class of materials based on cellulose products modified by means of materials technology.41 A wide array of products reflect this advance, ranging, for instance, from clothing, writing utensils, containers, etc. to sanitary products. But further new, entirely independent lines of development can also be traced, which emerged out of cardboardpulp production and led, for example, to applications in the building trade or the electrical industry. One example is carton pierre or statuary pasteboard, which was introduced into the construction industry and whose basic material is papier-mâché. The enrichment of clay, whiting and cement created a new composite material. A high proportion of whiting chalk yielded a particularly high strength and thus a resistant material for roofing had been developed.42 A much earlier advance in cardboard pulp for building purposes was patented in 1788 by the Briton Lewis Charles although there is no evidence of it having been introduced as any marketable products of his.43 A high point in this field was the utilization of building paper made of cardboard pulp reinforced with preprinted waste

40 Schlieder (1977). 41 Cf. Andrés (1896), p. V f. 42 Rühlmann (1858). 43 Ohlingmüller and Schachnter (2001), p. 222.

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paper and straw.44 A series of small homes was erected using this application on a large scale in the USA by the Western Paper Company in Chicago in 1870.45 The development of hard paper, which was an off-shoot of cardboard pulp production, represents the closest link to the novel industrially manufactured composite materials. Hard paper, reinforced with heavy paper materials, was initially coated with natural resin as a supporting matrix. From 1910 onwards, bakelite resin was applied instead, a duroplastic synthetic plastic out of phenol formaldehyde, which will be discussed more later on.46 Hard paper became well known as a material under the brand name pertinax, which the entrepreneur and patron of the arts Max Meirowsky (1866–1949) registered under his name.47 Papier-mâché can therefore be regarded as the link between the early nature-based industrial products, whose roots go back to the beginnings of paper making and the first semi-synthetic products made of cellulose. Their chemical trajectory via synthetic resins, which were also referred to as “cellulosic plastics”, leading to modern polymer chemistry, traces a line of development which ends at modern fibre-reinforced plastic.48

44 Makulatur = waste paper consisting of discarded printed sheets. 45 White (1983), p. 373. 46 Mannel (1923), p. 497. 47 Ohlingmüller and Schachnter (2001), p. 66, Wessel (1992), p. 130 f. 48 Eyerer et al. (2005), p. 43 f.

3

The Development of Composite Materials Within the Context of 19th-Century Industrialization

3.1

The Plastic Masses Versus Presstoff

The development of the first industrially manufactured composite materials in the middle of the nineteenth century was primarily driven by the fact that high-quality natural products, such as tortoiseshell and ivory, had become exorbitantly costly and the supply remained limited despite extensive colonial trade. The search for alternatives for everyday commodities led to the development of chemically modified materials which were initially based on natural materials such as cellulose.1 The increasing refinement and expansion of methods in chemical analysis and operations in the late eighteenth century and the onset of industrialization, which began to accelerate at the beginning of the nineteenth century, made this development possible, bringing with it numerous technical advances in engineering and processing.2 In this context, a new type of material was developed in the nineteenth century which first emerged from chemically modified natural products, such as natural resins, waxes or cellulose, and later evolved into semi-synthetic, and subsequently wholly synthetic plastics within the budding chemical industry. Starting out from the physical characteristics of these materials, the key points can be established as: chemical modification, plastic consistency, and final technical moulding under pressure and heat. That is why they were integrated within materials technology under the category known as the plastic masses3 — a designation which continued to be in use well into the twentieth century and was not

1 Sommerfeld (1934), p. 1 f. 2 See Benzler (1998), Wetzel (1991), and Henseling and Salinger (1990). 3 Kausch (1931).

© The Author(s), under exclusive license to Springer Fachmedien Wiesbaden GmbH, part of Springer Nature 2023 A. T. Haka, Engineered Stability, https://doi.org/10.1007/978-3-658-41408-5_3

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replaced until the end of the 1930s, mainly due to the differentiation of presstoff (moulding) materials resp. the later research into substitute materials.4 The assignment of these early synthetics amongst the group of plastic masses significantly extended the range of this class which already included the classical working materials cement, ceramics and glass. Two of the most important early plastics developed in this way were, on one hand, the first semi-synthetic polymeric plastic, celluloid, which was based on the natural material cellulose and, on the other hand, casein formaldehyde resin, which was marketed under the brand name galalith.5 Although the inventor of celluloid, the metallurgist Alexander Parkes (1813–1890), patented this under the name parkesine, he was ultimately unable to produce a plastic of stable quality.6 The products he made using parkesine, such as knife hafts, combs or insulators, deformed because inferior cotton flocks significantly impaired the quality. One reason for these manufacturing problems was that Parkes was primarily an inventor and model maker but had no business acumen and did not monitor his production or distribution. Although he was able to win much acclaim with parkesine at the Third World Exhibition in London in 1862, it was the American John Wesley Hyatt (1837–1920), who took up the material compound that Parkes had revealed at the World Fair, modified it and patented it profitably. Together with his brother, Hyatt founded the Albany Billiard Ball Company in the USA in 1868. He supplied the market with cheap billiard balls, which had previously been made of expensive ivory. Upon patenting his billiard ball (Fig. 3.1) and renaming the material from parkesine to celluloid, his firm was also renamed Celluloid Manufacturing Company. Hyatt had chosen the brand name “celluloid” after the base material cellulose. Hyatt’s patented billiard ball is the world’s first industrially produced plastic composite material,7 not only because the balls are a layered composite, but also because Hyatt added bone meal to the celluloid to stabilize it and ivory dust for colour matching, and then pressed everything together to form a ball. Latest by the turn of the 19th into the twentieth centuries, both plastics found wide fields of application. In the early days, celluloid was used not only for the production of billiard balls but also of gearwheels, plain bearings and glasses frames. Nowadays, though, celluloid is primarily known as the material out of which cinematographic reels of film are made, although they only started being developed at the end of the nineteenth century.

4 Cf. Luxbacher (2011), id. (2004), Flachowsky (2008), Maier (2007a), Wengenroth (2002) and

Marsch (2000). 5 Lattermann (2017), p. 29 f. 6 Mossman (2017), p. 15 f., id. (2002), p. 128 f. and Meikle (1995), p. 11. 7 Hyatt (1865).

3.1 The Plastic Masses Versus Presstoff

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◄Fig. 3.1 Excerpt from the patent by J. W. Hyatt. The manufacture and structure of the balls can be clearly seen in the fifth sketch (Fig. 1.5). The longitudinal section shows how individual cellulose ring layers are stacked upon one another and later pressed together to thereby obtain its precisely spherical shape. The ring holes facilitate precise alignment of the layers by inserting a pin to row them up like a string of beads. Source Patent—John Wesley Hyatt, US Patent No. 50,359 from 1865

The other plastic, galalith,8 was also known as “milk stone” or artificial horn. The latter derivation goes back to the widespread use of galalith in button making. Galalith is a by-product of milk processing, in which casein is extracted and after drying and purefication is available as a granulate powder. After soaking this substance in water and subsequent kneading, it was formed into a strand by passing the mass through an extruder, then pressed into shape and finally cured in a formaldehyde solution. Buttons out of animal horn, which had become a widespread accessory by that time, could thus be produced more cheaply with galalith and in consistent quality. Galalith was also used in the manufacture of knitting needles, toy blocks, knife hafts and insulating material.9 Besides the name galalith, which was the best-known brand, this material was also advertised under other trademarks, such as akalit, ergolith or modelith. This canon also includes natural rubber products which, just like celluloid and galalith, were developed in the nineteenth century to address increasing material shortages, particularly for industrial applications or as substitutes for materials in limited supply. Some, such as natural rubber, underwent further development and chemical modification. Natural rubber, which is drawn from the milky sap of various rubber plants, first found mention in 1521 in the writings of Pietro Martire d’Anghiera (1457–1526) about the New World.10 Colonial trade eventually brought natural rubber to Europe and various applications were found for it there. Because of its elasticity and above all its insensitivity to moisture, rubber was a widely used insulating material, both in the area of electrical equipment and the impregnation of textiles. One of the applications developed during this period within the context of waterproofing was the mackintosh raincoat, which is still a well-known brand name for rainproof clothing. As with celluloid, this early industrially manufactured product made with natural rubber can be identified as a composite material. Its inventor Charles Macintosh (1766–1843) produced his raincoats by coating the two sheets with a rubber-benzene solution and then pressing the two sheets together under pressure and heat to form a water-repellent laminate.11 The technical production parameters were particularly decisive here, although no proper pressing regimes had yet been developed that would later 8 Galalith = milk stone, from the Greek: gala—milk, lithos—stone. 9 Glaser (2008a), p. 12 and von Seherr-Thoss (1965), p. 368 f. 10 D’anghiera (ed. Mazzacane) 2005, Baumann and Ismeier (1998), cf. in excerpt also Heim (2013),

p. 59 f., id. (2003), p. 125 f. 11 Sommerfeld (1934), p. 119 f.

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79

shellac

pitch

animal proteins

cellulose

primary acetyl cellulose

converted cellulose

secondary acetyl cellulose

nitrate cellulose

"vulcanized

"celluloid" plate

sheeting,

"cellon"

"trolit"

"galalith"

pipe fittings,

fibre" plating

material, piping

film,

plate

injection-

(artificial

plate material,

artificial

material,

moulding

horn)

piping

silk

piping

masses, rods

material, rods

Fig. 3.2 Diagram of the most important early plastics, which were developed by modifying natural materials, along with example products made of them (Compilation: A. Haka)

have a decisive influence on the quality and quantity of hybrid presstoff materials. In Germany, the chemist Fritz Hofmann (1866–1956) developed the first synthetic rubber in the Elberfelder Farbenfabriken, dye laboratories formerly under the name Friedrich Bayer & Co. and was later replaced by buna rubber and was far more profitable.12

3.1.1

Materials Design of the Plastic Masses

With the development of the chemical industry and the resulting improved safety in handling chemical processes latest by the middle of the nineteenth century, a large number of the plastic masses (Plastische Massen) were produced, which led to a subdivisioning of these early plastics into natural and artificial plastic masses (Fig. 3.2). For lack of space, a comprehensive description of these developments during this period is not possible here—nor are all such masses definable as composite materials.13 Following the methodological approach of typology, the largest group of early plastics, i.e. plastic masses made of cellulose, will be discussed here and arranged in an ordering system. Wood and cotton were then, as now, the most important cellulose sources, along with a number of other plants. Based on their origins, a distinction is made between, among others, lignocelluloses (from wood and plant fibres), pectocelluloses (linen and flax fibres),

12 Burghard (2004) and Heim (2003). 13 Kausch (1931).

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adipocelluloses and cutocelluloses (from cork and cotton).14 In order to be able to process cellulose productively, the so-called incrustations, i.e. deposits in the cell walls of the respective plants, must first be removed. This was an aspect which became increasingly important in the mid-nineteenth century. Advances were also made in processing, procedures and engineering in this area. The reason was that the quality of the cellulose products made available for processing had hitherto been less than satisfactory, which had a decisive influence on the success of the plastic masses and without which no quantitative satisfaction of the huge market demand for their products could have been achieved. Although timber was a familiar material for humans to work with, it was mainly used in construction and as fuel, and cotton likewise, for textiles. Further chemical exploitation and applications of these materials was uncharted territory. In 1838 the French chemist Anselme Payen (1795–1871) succeeded in isolating a substance within the context of his investigations of wood by applying nitric acid and caustic soda. He called this substance les cellules—cellulose,15 the raw material of the plastic masses, and his process formed the foundation of their production. By the 1920s, cellulose-based plastics were being developed and these plastics were covered by a number of patents world wide. A large number of early plastic masses can be identified in terms of their technical material structure primarily by the components used—matrix, fibre and filler. Thus, they are identifiable as composite materials. Both the quality and the anticipated quantity could be derived from the individual material components. This opened up the possibility for companies to develop and produce individually designable plastic products. Most of the matrix materials used at that time came from natural products. They were subdivided into vegetable materials, such as resins, desiccate oils and rubber, or into materials of animal origin, such as shellac and proteins (casein, albumines or blood). Furthermore, mineral matrix materials, such as pitch, were also used in the plastic masses. Representatives of the classical members of this group of matrix materials within this context are, e.g., cement, lime or alumina. The present analysis of composites developed during the nineteenth century will not explore these classical materials further. Until the beginning of the twentieth century, plastic matrix materials were generally brittle in their cured state.16 More elastic matrix materials only began to appear on the market with phenol–formaldehyde resins and later on with the foundation of polymer chemistry by Hermann Staudinger (1881–1965) and the development of thermoplastics in the mid-1920s. However, they did not become established in composite materials until the 1950s with the spread of GFRP.17

14 Cf. Thatcher (2011), p. 74, Franck and Collin (1968), Schwalbe (1911), p. 160 f. 15 Fisher (1989). 16 Sommerfeld (1934), p. 4 f. 17 On the founding of polymer chemistry, see Mülhaupt (2004), Lechner et al. (2003).

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In order to minimize the fracturing behaviour of brittle plastic products, recourse was taken to additives.18 Fibres were stirred into the plastic masses as coarse admixtures. Only short fibres were used and their integration is comparable to modern-day milledfibre composites, although the products of that time are hardly comparable in terms of their strength.19 The fibres preferably used were ground wood pulp, cotton, linen and jute. Here, too, a subdivisioning into vegetable, animal and mineral materials can be made. The animal fibres were wool and silk and the mineral fibres asbestos, although the danger to humans posed by asbestos fibres was not officially recognized as such in Germany until the mid-1930s, in contrast to Austria and Switzerland, which were much earlier.20 The most common fibres used in the plastic masses in the mid-to-late nineteenth century were vegetable fibres, mainly wood pulp, cotton and linen, which also had economic reasons. Another reason for adding fibres was that it added mass to the plastic. Under the motto: only objects with substance are worth anything, the additional weight helped convince the regular buyer of the value of plastic products. There was another reason for the admixture of fibre as well—namely, the use of inexpensive fibre saved on expensive artificial material. The load-oriented integration of fibre so important in modern fibre composites did not play any role yet in the plastic masses from the close of the nineteenth century. Furthermore, a filler, as another potential additive, could be introduced into a plastic mass for reasons that applied equally to fibres. Apart from enriching the mass, a filler also had the task of producing some optical effect. By means of a filler attempts could be made to design the tint and surface of the final material. The fillers used included stone dust, marble and slate flour, baryte and kaolin. The development of the plastic masses in the nineteenth century, which was initially characterized by the search for substitute materials, quickly oriented itself towards new products in response to progress made in the chemical industry. The materials used theretofore were modified and provided with new usage horizons. In this context, high-quality industrially produced composite materials are already identifiable from the mid-nineteenth century and particularly by the end of that century, not least due to further advances in mechanical engineering, particularly in press technology and processing. With the incorporation of fibres and fillers into the plastic masses—although not yet added with an eye to the statics—the naturally based matrix materials in particular mark the beginning of the development of modern, chemically designed and industrially manufactured composites, most notably fibre-reinforced plastics. By the end of the nineteenth century, around twenty basic substances from which plastic masses were produced had been identified, which in turn had given rise to up to forty chemically modified special products marketed under a wide variety of brand names 18 Kausch (1931), p. 18 f. 19 Cf. Flemming and Roth (2003), p. 157 f. and Flemming et al. (1999), p. 210. 20 Höper (2008), p. 149 f.

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related to the base substance.21 Around the turn of that century, the patent office registered around 1000 patents on plastic masses.

3.1.2

The Development of Vulcanized Fibre, an Early Laminate Around 1850

One of the economically most important early plastics made of cellulose was the composite material vulcanized fibre. The starting point or precursor to this material was parchment paper. In search of a material suitable as a writing surface, the French researchers J. A. Poumarède and L. Figuier in 1847 exposed paper to concentrated sulphuric acid which produced a substance resembling vellum.22 With the same intention of finding a useful parchment substitute, the British chemist W. E. Gaine filed a patent promising higher quality paper treated with sulphuric acid. This idea was taken up a short time later by the British entrepreneur Thomas Taylor, who varied Gaine’s parchmentization method by replacing the sulphuric acid treatment with a dilute zinc chloride solution and patented it.23 This solution caused the mass to swell and form hydrate cellulose. At first, old cotton rags were employed as the paper base, later cellulose was used that had been specially produced for this purpose. The fibre tapes, affixed to large rollers, were then compressed under heat and pressure, which led to an entangling of the fibres and thus cross-linked the individual layers to form a layered composite material. Material thicknesses of up to 50 mm could be produced. After the cleansing process, a zinc chloride leaching, a rubber-like mass was initially produced which was transformed during the drying process into a tough, hard material. Within the framework of the manufacturing process, there was also an initial surge of technical improvements in pressing technology, which gained new momentum in the 1920s with the development of laminate pressed materials. Taylor’s patent, registered in the United States and Europe, led to mass production for a variety of applications, such as plates, seals, bearings, bearing shells, handles, pivots and gearwheels.24 Initially, however, only the American market was supplied; in Germany major production did not commence until after World War I. One of the best-known products is the vulcanized fibre suitcase (Fig. 3.3), which was manufactured by various companies. In addition to their high stability and resistance to moisture, the low weight of vulcanized fibre suitcases particularly stimulated demand. In some places the material was therefore also known as “suitcase fibre” (Kofferfiber).

21 Kausch (1931), p. 271 f. 22 Elias (1985), p. 8 f. and Hoyer (1939). 23 Utracki (1998), p. 10, Stark and Wicht (1998), p. 141 f., Braun (2013), p. 137, Bürgel (1937),

p. 125 and Taylor (1871). 24 Rule (1930), p. 242 and Anon (1860).

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Fig. 3.3 On the left: Suitcase made of vulcanized fibre from 1926. Right: company logo of WICO Görlitz, which manufactured such travel suitcases, among other products. Photos A. Haka, 28 Aug. 2019

The earliest application in mechanical engineering can be traced back to 1911 when the patent for a bearing shell made of vulcanized fibre was registered byVereinigte Walz- und Röhrenwerke AG, a roller and piping factory in Hohenlimburg. These bearing shells were made of solid vulcanized fibre and were bent into a bearing shell to fit the shaft crosssection.25 A short time later, a roller bearing was patented with steel rollers encased in vulcanized fibre.26 This laminate composite also gained military relevance in the early 1930s when the Reichswehr, together with the Kaiser Wilhelm Institute of Occupational Physiology, tested the wearability of new gas masks and steel helmets.27 The new Gasmaske 24 had a number of design flaws at the time, and wearing it caused adverse health effects. In this context, new steel helmets were tested which were supposed to be adapted to the new gas masks. These steel helmets were actually prototypes not made of steel but of vulcanized fibre. They were later distributed to the army but only in small quantities and were soon replaced again in 1935 by the M35 Stahlhelm model. Vulcanized fibre helmets were preferentially used in parades. The fact that vulcanized fibre was even used as a structural material is demonstrated in the case study to follow later on about early composite materials used in aircraft construction by the technical autodidact Albin Kasper Longren.

25 Vereinigte Walz-und Röhrenwerke (1913). 26 Franz Halfman in Foche-Solingen (1916). 27 Kaiser-Wilhelm-Institut für Arbeitsphysiologie. Schmaltz (2005), p. 231 f.

84

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3 The Development of Composite Materials Within the Context …

Wood as a Fibre Composite and the Development of Industrially Manufactured Wooden Composites

On a macroscopic level, wood is a fibre-composite material, and as with other composites, dissimilar elements combine in such a way that their combination produces better properties than those exhibited by the individual components.28 The characteristics of a composite material can be traced in wood all the way down to its nanocomposite structure. At the same time, on the chemical level wood can be interpreted as a biocomposite polymer. The structural substances of wood are the polymers cellulose, hemicellulose and lignin. In addition, a number of other ingredients, attendant and extra substances are found, which thus represent a variety of different cross-linkages at different levels, from the macrostructure to the nanostructure, and form a hybrid composite. Wood has been in use as a raw material for building by people since the Palaeolithic Age, besides also serving as a source of energy in the sense of fuel, as a utensil and a weapon.29 In antiquity, wood was already studied more closely, for example by the Greek Theophrastus of Eresos (371–287 B.C.). This student of Aristotle (384–322 B.C.) mentioned timber in his book Historia plantarum and tried to decipher its structures. In his studies he defined the main tissue as the flesh of wood, its fibres and resin canals were described by him as its veins.30 In the Middle Ages, timber as a simple material not only became a commercial commodity supplying many areas, but also became a scarce good for the first time. Foremost, the emerging mining and metallurgical industry needed it as its energy source, which led to the limitation and regulation of wood as a resource.31 In addition to its importance as a fuel in private households, timber became more and more the material object of architects and builders, who explored wood constructively in new ways and, using sophisticated carpentry techniques, transformed construction with wood lastingly.32 In this context, half-timbering in architecture is not only an aesthetic and structural technique, but also signals the esteem of the rising middle class, which set standards and knew how to represent itself with filigree wooden constructions. The combination of stone, clay and wood in half-timbered structures opened a new era in building as regards sophisticated timber-construction design and eventually replaced massive building forms. However, this form of building also became a wood-saving method and hence was an early form of “lightweight construction” through mixed construction using different materials, based on a new understanding of material properties and the resulting options available. An extensive advance in the study of wood as a material took place with the invention of the microscope in the sixteenth century. Whereas until then the wood chip was the 28 Faix (2018), p. 47 f. and Wagenführ (1999), p. 20 f. 29 Radkau (2012), p. 22 f. 30 French (1994) and Scarborough (1978). 31 Radkau (2012), p. 5 f. 32 Stiewe (2007).

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smallest defined quantity in the anatomy of timber, the new perspectives offered by optics made the structure of wood more plastic. In 1695, for example, the Dutch draper and naturalist Antoni van Leeuwenhoek (1632–1723) used his home-made microscope to identify speck-like vessels and intercellular gaps in wood. His descriptions contributed, among other things, towards understanding the microcosm of wood and its internal properties.33

3.2.1

Veneer Wood Versus Plywood

The oldest known wooden composites originate from Egypt. They are veneer woodwork in which one layer of wood was stuck to another one usually of higher quality with glue, such as a chest (Fig. 3.4) from the tomb of Pharaoh Tutankhamun shows, who reigned from about 1332–1323 B.C. In that era veneer wood served exclusively for decorative purposes. It was not until the seventeenth and eighteenth centuries that it was also used with other purposes in mind. It was during this period that veneers began to be used for finishing timber products and for stiffening large wooden surfaces, such as a table top, as well as for concealing machining marks.34 Until then, the production of veneer wood was hand made, utilizing little else than a saw. It was not until 1834 that the first veneer slicing machine for the industrial processing of veneers was developed and patented by the Frenchman Charles Picot.35 The demand for high-quality furniture rose rapidly with increasing urbanization.36 In Germany, the first peeling machine for veneer sheets was produced in 1866. However, furniture made of solid wood or laminated veneer in that period had a fault. They were subject to the hygroscopic properties of the wood used, which became manifest in degluing and not infrequently warping of the material, since the climatic conditions of domestic life at the time still fluctuated greatly. The invention of plywood addressed these problematic reactive hygroscopic properties of wood. The Thuringian entrepreneur Carl Wittkowsky can be considered a pioneer of industrial plywood production, who registered the first patent for Sperrholz in 1894.37 Plywood also marked the transition from veneer wood, applied as a thin layer with the grain matched with that of the carrier wood, to a true composite material with alternating grain patterns. Wood layers of different species were combined not only for optical reasons but also in response to structural considerations. Plywood thus solved two problems related to materials almost at once. On one hand, the fibres of each layer of wood were alternately arranged to run at an angle of 90º, making its ply straddle or “block” the grain of its immediate neighbors and thereby 33 Cf. Webel (2020), p. 174 f., Leeuwenhoek (1939), Cremer (1985), p. 31. 34 Cf. Kollmann (1962), p. 2 f. and Knight and Wulpi (1930), p. 5 f. 35 Cf. Schindler (2009), p. 174 and Kollmann et al. (1975), p. 154 f. 36 Newton, ed. (1835), p. 366. 37 Cf. Niemz and Wagenführ (2018), p. 140 f., Doffiné (1958a), p. 1723 f., id. (1958b), p. 1861 f.,

id. (1958c), p. 1889 and Wittkowsky (1894).

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Fig. 3.4 Chest made of cedar wood, veneered with ebony and ivory, from the tomb of Tutankhamun. Source Knight and Wulpi (1930), p. 5

counteract the various hygroscopic properties of the wood (Fig. 3.5). This barring pressure of the layers incidentally explains the material’s designation as ply-wood. On the other hand, this special layered structure and the associated courses of the fibres made possible far higher static load horizons because the tensile strength could be brought to bear multidimensionally. Completely new product applications were thereby generated.38 One adaptation of plywood was star plywood, which was developed at the same time. Its layers were arranged to have the grain of each layer form a star shape at angles of 15 and 45º, which thus also afforded the corresponding fibre-load angles.39 Thus a new stability was constructed by combining two materials, which could not otherwise have been achieved by those materials on their own. This was not yet as consciously worked out as in present-day composites, however. Modern fibre composites of the type of multiaxial non-crimp fabrics are “engineered” according to this principle. Wittkowsky developed a pressing regime that was specially designed for plywood, which pressed the wood layers together with a casein glue that he produced in-house in his own firm. In this way, he was able to offer the novel material plywood as a highquality product from a single source, which he additionally secured with a large family of patents.40 The base material of this plywood was beech timber which was available in 38 Cf. Radkau (2012), p. 247 and Kollmann (1962), p. 3 f. Sperrholz literally means “blocking” wood. 39 Berthold (1990), p. 716. 40 Wittkowsky (1907), id. (1896).

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Fig. 3.5 Cross-section of a plywood board—the light and dark individual layers of wood clearly show the laminate structure and the hybrid character of the material. The grain layers are arranged alternately at an angle of 90º and pressed together to form a uniform board by means of an adhesive. Photo A. Haka, 6 Sep. 2019

Germany at that time in sufficient quantities and at a reasonable price as well as offering the necessary wood quality. Plywood also formed one of the foundations for the world’s first mass-produced furniture, referred to as machined furniture,41 originally conceived in 1903 by the architect and designer Richard Riemerschmid (1868–1957) for the Schmidt & Müller company in Dresden-Striesen. Just a little while later, in 1907, this small firm renamed itself Deutsche Werkstätten Hellerau near Dresden after reorganizing itself and its shareholders.42 The new company constellation granted Riemerschmid room to fully develop all his skills. As an architect, he also played a major role in the planning of Germany’s first garden city in what is now Dresden-Hellerau, and in 1910 he designed the factory facilities of Deutsche Werkstätten Hellerau. The production of this machined furniture, which could be taken apart, utilized plywood for the first time as a functional composite material with the technical requirements of industrial processing and as a lightweight material that could bear static loads and be predetermined—a novelty in materials technology. That company’s furniture programme, promoting “the inexpensive flat” (Die billige Wohnung), attained by means of the composite material plywood a new quality of constructed stability. It is also 41 On the standardized manufacture of wood and wood-derived materials in Deutsche Werkstätten

Hellerau for “machined furniture” (Maschinenmöbel), and even housing (Maschinenhäuser), see the next subsection on standardization and norms. 42 Cf. Selle (2007), p. 99 f. and Arnold (1993), p. 180 f.

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the prelude to a trend-setting design of functional industrially produced serial furniture. It should be noted here that the phenol–formaldehyde resin used as the new bonding agent,43 which replaced previous binders such as casein, serum albumin or ground wet wood, was already being critically questioned in this context because of its odor and adverse effect on the respiratory tracts, which evaporates from furniture and wood-derived materials in general. By World War I, a large plywood industry had developed in Germany, which mainly supplied furniture makers and the building industry with its products.44 During World War I, high-quality plywood materials were produced primarily in aviation. Some companies specialized in this, such as Schütte-Lanz Holzwerk AG in Seckenheim in the Rhine-Neckar triangle, headed by the shipbuilding engineer and university lecturer Johann Schütte (1873–1940) and the engineer Karl Lanz (1873–1921).45 The construction of the rigid airship Schütte-Lanz SL 1, which was 131 m in length and about 18 m in diameter, took place as early as 1909. Unlike the Zeppelin airship designs, which were primarily made of duralumin, the Schütte-Lanz SL 1 had a rhombic inner frame of glued plywood trusses.46 Schütte-Lanz also designed biplane fighters, but these plywood structures were still under testing during the war. Other aircraft manufacturers increasingly began to use plywood construction as well, such as Albatros Flugzeugwerke GmbH in Berlin-Johannisthal. Their model Albatros D II, the German standard fighter plane of the years 1916 and 1917, which among others the German fighter pilot Manfred von Richthofen (1892–1918) primarily flew, had a plywood fuselage. After the war, the Schütte-Lanz factories were dismantled by the victorious powers. It was not until 1933 that the Interest Group of German Plywood Factories (Interessengemeinschaft Deutscher Sperrholzfabriken) was formed, which was able to place its products in military aircraft and mechanical engineering again during World War II.47 After 1945, the main customers for plywood were again the furniture and construction industries. In the process, a standardization of the material was achieved, which was the prerequisite for today’s mass-production of plywood.

43 “Die billige Wohnung”. In 1902, a patent application was filed for phenol–formaldehyde resin

by the Louis Blumer company (the patent was granted in 1906), as a resinous condensation product similar to shellac. For information on its use in wood-derived materials, see also Berthold (1990), p. 541 f. 44 Hassinger (2013), p. 51 f. 45 Cf. Haka (2018), p. 190 and Lehmann (1999), p. 458 f. 46 Boeyng (2014), p. 18. 47 Küch (1939).

3.2 Wood as a Fibre Composite and the Development of Industrially …

3.2.2

89

Fibreboard and Chipboard

Two further hybrid materials, fibreboard and chipboard, have their origins in the closing nineteenth century. They serve as the structural templates of multiple wooden and fibrous materials in materials technology, which emerged in the twentieth century in many variants.48 Here we find the development of both fibreboard and chipboard as a smooth transition from the plastic masses to modern wood-derived materials, and beyond that, to other hybrid material designs. Following the course of fibreboard, for example, leads even further back via the plastic masses to the development of papier-mâché, as we have seen, or to initial paper production. The development of industrially manufactured fibreboard (Fig. 3.6) can be followed most harmoniously via wood-flour or wood-pulp usage in the plastic masses to a modern wood-derived material. The production of fibreboard in gaseous media is not yet an option at this stage of its industrial development, because the necessary machinery and technical processing conditions are not yet available. The first patent on the production of fibreboard was filed at the Patent Office of the Deutsches Kaiserreich in 1893 and was granted a year later. The patent is still written in the style of plastic masses manufacture. It defines the wood fibre as a material-forming structural element and describes the manufacture of wood-fibre products made of wood fibre together with an otherwise unspecified artificial binding agent under the application of heat and pressure.49 While today fibreboards are divided into different types ranging from porous to extrahard, their production initially began at the turn of the century as simple porous or medium-hard fibreboard. This was due to aspects of process engineering having hardly been developed by then and the lack of compression technology for this material.50 The production of fibreboard at that time was carried out under simple conditions. The lignocellulose fibres obtained were first soaked in water and then formed in a sieve. It should be noted that the mechanically prepared wood fibres did not yet have the same degree of fineness as the wood fibres made available at the end of the 1920s with the introduction of the masonite process. This process, developed by the U.S. American William H. Mason (1877–1940) in 1926, made it possible to achieve a very fine degree of disintegration of wood chips into wood fibres in an autoclave by an explosive procedure. The inventor of this process, a close friend and long-time collaborator of the inventor and entrepreneur Thomas Alva Edison (1847–1931), after leaving Edison’s company developed his own type of fibreboard which he called masonite.51 Unlike conventional fibreboards, they had longer fibre filaments and were compressed without any binding agent. The lignin naturally present in the fibres and the felting of the fibres ensured the board’s cohesion. While masonite board production commenced in the USA about 1930, 48 Cf. König (2009), p. 54 f. and Berthold (1990), p. 211. 49 Alexander (1894). 50 Beuth-Verlag, ed. (2009). 51 Mason (1926).

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Fig. 3.6 View of the cross-section of a fibrous felt-like fibreboard of medium density, the fine fibres of which have been compressed under pressure and heat to form a tight fleece, and which here serve as the support material for the lighter-coloured furniture veneer on top. Photo A. Haka, 6 Sep. 2019

an alternative industrially exploitable fibre-production method was developed just one year later by the Swede Arne Johan Arthur Asplund (1903–1993). His defibrator process, which spread throughout Europe in the mid-1930s, was based on a grinding process in which wood splinters and chippings were processed into fibres under pressure and in hot steam.52 The resulting fibre pulp was then placed on a continuous metal-link belt press, which then discharged the fibreboard under heat and pressure in a multiplaten press. Finally, the fibreboard was finished in a separate drying process. From 1934 onwards, ˙ companies in Germany such as Kapag in Sorau (now Zary, Poland) or Henselmann in Gutenberg on the Upper Rhine produced fibreboard for industry and the crafts. The fibreboards were used almost exclusively as table tops, door filling material and insulation in the building industry. Nowadays, the production of fibreboard is usually carried out in two procedures—wet and dry. In the wet process,53 the fibres in a fibre suspension are shaped into a fleece and then pressed. In the dry process,54 dry fibres are compressed mechanically or by a gas medium into a non-woven fabric and pressed at high temperature.55

52 Asplund (1934). 53 Porous, medium-hard and hard fibreboards are produced in the wet process. 54 Medium-density and high-density fibreboards are produced in the dry process. 55 Cf. Niemz (1993), p. 14 f. and Berthold (1990), p. 756.

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The beginnings of the second wood-composite material studied, chipboard, which is widely used today, also date back to the end of the nineteenth century and, as with fibreboard, are closely linked to the production of the plastic masses. Different from fibreboard, however, the development of chipboard can be regarded as originating as a deliberate “construct”. So-called artificial wood (Kunstholz) stands at the outset of this development, which terminology alludes to the character of a constructed or specially created material. At the same time, the manufacturers implied value-adding design. The aim was, to suggest to potential customers the high quality of the new material, which could not fall under any of the conventional groups of materials. An unambiguous technical characterization of Kunstholz in terms of modern materials science is difficult, as there was no clear definition of this material at the time it was created. Moreover, the transitions from the plastic masses to artificial wood and later to the clearly defined chipboard were blurry. A characterization of “artificial wood” only took place insofar as a large part of the material was wood-based. One aspect of artificial wood that was difficult to pin down was the additives, which could not be clearly defined and varied from manufacturer to manufacturer. The admixture of mineral substances such as asbestos fibres can be found in various artificial wood materials, but without these ingredients being mentioned as in any way relevant to its material parameters. The lignin naturally present in wood chips was used as an early binder, as was natural glue, such as casein. The original intention to generate a material from wood shavings arose from the quest to utilize the sawdust produced in large quantities in industrial wood processing and was concomitant with the formation of the new set of plastic masses. The first verifiable ideas about chipboard production can be found in patents from the mid-1890s. For example, a German patent from 1893 described the manufacture of doors, stairs and furniture from pressed peat chips.56 The admixture of binding agents or additives was conceded in the patent description but was not defined in any detail. This material invention conceived the chipboard rather as an auxiliary or filler material. The first patent in which an early chipboard was registered as a construction element dates back to 1901. The artificialwood chipboard figured as a possible matrix material encasing a rigid supporting material made of solid wood or metal. As can be seen in Fig. 3.7 this material was patented for furniture manufacturing. The first tendencies to manufacture furniture industrially in large quantities was becoming apparent. This was practised just a few years later by Deutsche Werkstätten Hellerau with their “machined furniture”.57 Production of the first modern chipboards began in Germany in the mid-1930s. The urea-and-formaldehyde-based wood glue used, Kauritleim, contributed significantly to its success, as it was high-yielding and had very good material properties.58 56 Violin (1894). 57 Schenck (1901). 58 Cf. Stokes (2002), p. 255 and Dunky (2002), p. 252.

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Fig. 3.7 These patent drawings from 1901 illustrate the hybrid material structure of early chipboard

In the table leg shown in Figs. 1.2, 1.4 and 1.5, it encases an internal supporting material either of metal (Fig. 1.2) or of solid wood (Fig. 1.4). Source drawings from the patent J. Schenck from 1901 Kaurite glue was introduced onto the market by BASF in 1931 and was well received mainly in the wood industry and among craftsmen. The first modern chipboard corresponded broadly to the chipboard currently in use (Fig. 3.8), which is produced in accordance with the norms DIN EN 309 f. out of wood chips or other wood-like chip material and pressed into boards with one of a variety of binding agents.59 A convergence or transition from fibreboard to chipboard does exist, though. The early chipboard was patented in Switzerland in 1932. Today the invention of chipboard is almost exclusively associated with the German engineer Max Himmelheber (1904–2000), who hardly improved it but did diversify its processing. However, the Swiss chemist Alfred Schmid (1899–1968) was the first to initiate the patenting. Alfred Schmid was employed as 59 Beuth-Verlag ed. (2005).

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Fig. 3.8 Section through a chipboard according to DIN EN 309, in which the chips in the upper and lower layers were compacted more by the pressing process than in the core area of the board, which is essentially because of the differing chip sizes in the middle and surface layers. Photo A. Haka, 6 Sep. 2019

associate professor of physical chemistry at the University of Basle. He had hired Max Himmelheber as an assistant in his ongoing research project on the utilization of wood waste, which eventually resulted in the patent for the early chipboard, which Schmid and Himmelheber called Homogenholz.60 This university lecturer considered himself primarily a chemist and benevolently ceded to Himmelheber the rights to the commercial marketing and further development in 1932.61 Schmid still continued to monitor the marketing and advancement of homogeneous wood personally in an advisory capacity. According to the patent, homogeneous wood was a board-like material with a hardness and workability similar to wood, i.e. it was “homogenized wood”.62 This describes the early form of chipboard, which was still being produced by the wet process and involved a coarse-grained wood-fibre glueboard. The first early chipboard to be manufactured with artificially produced chips by the dry process, which largely corresponds to present-day chipboard, emerged after 1945. Max Himmelheber shared this development with Otto Herdey, Karl Steiner and Oswald Wyss. Industrial exploitation of this product started at the beginning of the 1950s and quickly spread world wide. It is astonishing that the Schmid-Himmelheber patent was still written in the technical terminology of the plastic masses, even though this way of speaking was no longer in use by the early 1920s. It can be assumed that Schmid as a chemist represented conventional 60 Homogenholz. Sauer (2016), p. 179 f. 61 Statement on the Invention of the Chipboard by Patent Attorney Dr. O. F. Wyss, 23 April 1948.

(MHS). 62 Kollmann (1966), p. 449 f.

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notions, and the engineering aspects perhaps introduced by Himmelheber received less notice. That is why the title of the first chipboard patent also reads: “wood-like mass and process for its manufacture”.63 The term Holzspanplatte for wooden chipboard does not appear in the Schmidt-Himmelheber patent. It was not until the standard DIN 4076 was issued in 1942 that this German term for chipboard was used for the first time.64 Himmelheber tried rather to establish the term homogeneous wood for chipboard but it did not catch on. This latter term is only drawn into account in the subsequent patent, in which Max Himmelheber, together with Alfred Schmid and the Swiss patent attorney Oswald F. Wyss, secured the technical processing side of chipboard production.65 The involvement of Max Himmelheber in the Basle research project, which began in 1929, was not without reason. Schmid and Himmelheber already knew each other from the organized youth movement Bündische Jugendbewegung and were both interested in philosophy and flying as a sport. Himmelheber had anyway already been technically initiated in working with wood, since his father owned the furniture and parquet factory Gebrüder Himmelheber Möbel- Parkettbodenfabrik AG in Karlsruhe and had set up a small workshop there for his son, where he experimented with wood materials and got the idea of homogeneous wood, as Himmelheber later recalled.66 Although Himmelheber graduated in electrical engineering in 1927 at the polytechnic in Karlsruhe67 under Johannes Thoma (1887–1973), who held the chair for high voltage technology and electrical systems and was the son-in-law of the well-known mechanical engineer in materials testing August Föppl (1854–1924),68 wood was ever present in Himmelheber’s life. Thus, with Schmid’s know-how as a chemist, Himmelheber was able to generate an emulsifier with which liquid phenol–formaldehyde resins could be emulsified in water to form a milk.69 This milky bakelite emulsion was mixed with wood pulp, and after extraction a raw board was produced which was wood-like in character. The chemotechnical groundwork for the development of chipboard had thus been laid in Basle.

63 Holzähnliche Masse und Verfahren zu deren Herstellung. Schmid and Himmelheber (1936). 64 Beuth-Verlag ed. (1942). 65 Wyss et al. (1943). 66 Unpublished manuscript by Max Himmelheber dated 10 May 1991 (Max Himmelheber Founda-

tion Archive [hereafter MHS]). 67 Urkunde zur Verleihung des akademischen Grades Diplom-Ingenieur der Technischen

Hochschule Karlsruhe an Max Himmelheber, 15 June 1927 (MHS). 68 August Föppl’s scientific work in applied mechanics and on Maxwell’s theory was widely

received. The integration of his remarks on electrodynamics is to be mentioned here above all, which had a quite considerable influence on Albert Einstein’s chain of argumentation on the special theory of relativity. See Haka (2014a), p. 107 f. 69 Unpublished manuscript by Max Himmelheber, 5 May 1991 (MHS).

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3.2.2.1 Standardization and Norms—The Holig Homogenholzwerke, from Aircraft Flooring to Prisoner Barracks The limited technical or mechanical resources available at the University of Basle tied Max Himmelheber’s hands. That was why Himmelheber returned to his home town of Karlsruhe and began to investigate the topic of homogeneous wood further in his father’s workshop. He founded the research group Studiengruppe Homogenholz for this purpose.70 This eventually created the spin-off Homogenholz Syndikat, an association of interested parties for the promotion of further development by Himmelheber and Schmid. Among them were the parquet manufacturer Alfred Brügmann from Dortmund, Bankhaus Kapff and Tekton-Gruppe, an alliance of wood processing companies.71 This syndicate eventually founded the Entwicklungsgemeinschaft Homogenholz GmbH in Görlitz in Upper Lusatia for the purpose of advancing the technological aspects of chipboard development. These interested parties wanting to help homogeneous wood to serial production were joined by the German Luftwaffe, which entered their circle in 1941, albeit without making it public. Ernst Udet (1896–1941) in his capacity as General Luftzeugmeister and representative of the reich minister of aviation and commander-in-chief of the Luftwaffe, put on record in June 1941 in a secret note that a Homogenholz-Gesellschaft was to be founded with participation of the Reich, which was to supply German aviation and especially the German air force with high-quality wood materials.72 To this end, he allocated a total volume of eight million reichsmarks for the construction of developmental and production facilities. The Swiss university lecturer Alfred Schmid and the patent attorney Oswald F. Wyss were designated as coordinators. On July 1, 1941, Holig Homogenholzwerke GmbH was founded in Görlitz, Saxony, with an administrative department, a development and testing laboratory and a production plant. Alfred Schmid, Oswald F. Wyss and Bank der deutschen Luftfahrt AG (Aerobank), an investment bank of the German reich, were appointed as shareholders.73 Upon founding this company, the reich minister of armament and ammunition decreed that all divisions of Holig Homogenholzwerke GmbH be classified as secret, and that the company be exempted from the provisions of commercial law due to its special importance to the defence economy.74 That was why Holig Holzwerke did not make any public appearances until 1945 and all armament products along with their financial transactions were handled by the specially founded cover company, Luftfahrtanlagen GmbH (LAG) with headquarters in Berlin.

70 Ibid. 71 BArch. R 8135 7521 Holig Homogenholz Werke (Bundesarchiv Berlin [hereafter BArch B]). 72 Note Aktenzeichen 66 p Nr. 1813/41 dated 19 July 1941. BArch R 8121/508, vol. 1/1 1941–1945,

Holig Homogenholzwerke. 73 Ibid. 74 Letter from Reichsminister für Bewaffnung und Munition to Reichsminister für Justiz dated August

6, 1941 (BArch. R 3001/24181/0340 Holig Homogenholz Werke).

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A second plant in Neustrelitz and licensed plants in Baiersbronn, in the Protectorate of Bohemia and Moravia, and in Hermagor in Carinthia, Austria, were planned at the same time. The plants in Neustrelitz and Baiersbronn were still being set up or under construction by 1945 but some production was already underway. Funding for the other plants ran out towards the end of the war and their plans were scrapped in 1944. The aviation ministry (RLM) planned the company’s product range both for the war economy and for the time thereafter as well, initially completely tailoring it to armamentsrelated items. This limitation was soon cancelled, however, in the same year in fact as the company’s founding, and civilian sectors could also be supplied. For example, the audit report of 1943 states that mainly wood-core plywood (i.e. laminated blockboard), a mouldable hard fibreboard as well as foam wood 75 were manufactured using the homogeneous-wood process at a production volume of around 90 tons per year. The anticipation was that the product line of Holig could compete with conventional wood-core plywood, fibreboards, presstoff materials, high-quality processed natural woods (especially balsa and oak), parquet products, linoleum, cork, iron-reinforced concrete with lead cladding, and ceramic bricks.76 The intended raw materials for the production were sawmill waste, high-quality wood pulp as well as straw and tropical grasses. The procurement of raw materials was secured by the RLM via the Reich Forestry Office, and their quality was monitored by independent experts and testing agencies.77 Holig was also supposed to enter into patent cooperations with other companies with whom it had close ties. The RLM likewise ensured that sufficient binding agents for the homogeneous wood product range be permanently available on a large scale, foremost kaurite glue, formaldehyde, and cresol. Furthermore, the plan was, to focus on woodderived substances and in this context to promote research projects in the field of woodbased binders in cooperation with wood research institutions in the university sector. In 1943 Max Himmelheber (Fig. 3.9) joined Holig Werke as technical director, as he had just returned to Germany from British captivity as part of a prisoner-of-war exchange programme. As a member of Akaflieg Karlsruhe and flight instructor, Himmelheber had become a reservist back in 1938. The responsibility for academic pilot groups after 1933 had been taken over by the RLM and Himmelheber’s call-up had then taken place promptly, with the RLM initially appointing him as head of the Research Centre on Homogeneous Wood in Varel near Oldenburg, a reich-owned enterprise.78 In 75 Schaumholzplatte = fibreboard made of ground-wood pulp in a wet process, which, when lami-

nated with thin plywood boards on either side, produced a sandwich composite. The density of this “foam wood” was approx. 0.2 g/cm3 and was developed as a substitute for balsa wood or cork. 76 Note on the organization and on the economic basis and development possibilities of Holig Homogenholzwerke vol. 1/2 (Barch R 8121/50). 77 Reichtsforstamt. This led to cooperations with Forstliche Hochschule Eberswalde, Technische Hochschule Dresden (its Institute of Botany) and the Materials Testing Office in Berlin. 78 Forschungsstelle Homogenholz. List of service in the Wehrmacht by Max Himmelheber, undated. (MHS).

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Fig. 3.9 Max Himmelheber (1904–2000), as a first lieutenant in the Luftwaffe in 1943. Source Himmelheber-Stiftung

this context, he received the title “Reich Commissioner on Homogeneous Wood”.79 With the onset of World War II, Himmelheber had been assigned to a fighter-pilot squadron (I. Jagdgeschwader Richthofen 2). The Swiss patent attorney Oswald Wyss had taken over the management of the company in Varel. Himmelheber flew numerous combat missions until September 1940 before he was shot down and, seriously injured,80 eventually ended up in British captivity.81 The fact that Max Himmelheber was easily able to take up his professional activities where he had left off before his enlistment has several reasons. Up to his call-up, he had been the driving force behind the development of homogeneous wood and as coowner of the chipboard patent of 1932 thus possessed very good qualifications in the field of wood materials technology. Moreover, he was considered politically loyal to the party and had connections to the RLM. Himmelheber had joined the nazi party (NSDAP) and the National Socialist Flying Corps (NSFK) in May 193382 —which facts happened to have slipped his mind after the war.83 His many years of involvement in the youth

79 Reichsbeauftragter für Homogenholz. See entry in the application for the issuance of a work book

dated 18 January 1944 and the information in the unpublished manuscript by Max Himmelheber dated 5 May 1991 (MHS). 80 Treatment and residence at the London-Woolwich Military Hospital from September 1940 to March 1941 (MHS). 81 Award Frontflüge I. Jagdgeschwader Richthofen 2, dated 28 Dec.1943 (MHS). 82 NSDAP-Zentralkartei 11,130,406, Himmelheber, Max, Party political questionnaire from 1939 Himmelheber, Max (BArch R 9361-VIII). 83 In the course of his denazification proceedings in 1946, Max Himmelheber could no longer recall his membership in the NSDAP and his status as reich commissioner, and stated in the questionnaires that he had never joined the NSDAP. On the basis of this information, Himmelheber was classified as “politically exonerated” (politisch unbelastet), on the grounds that: “The person concerned was not

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movement Bündische Jugend, which he also returned to after the war,84 evidently had not been documented or at least were not recorded in the nazi party’s statistical survey form from 1939. It had possibly been tolerated, though, since not few high-placed nazi functionaries, such as Heinrich Himmler (1900–1945) or Reinhard Heydrich (1904–1942), had been involved in that youth movement prior to 1933.85 For the RLM, Himmelheber was an ideal candidate for the position at Holig, since as a highly decorated86 fighter pilot as well as an aviation expert, he was very well acquainted with the technical aspects, especially as regards the materials used in aviation. Thus, several interests converged here: Himmelheber’s ambition to develop homogeneous wood, to which he and Alfred Schmid held a patent, and to generate industrial and standardized production; and the RLM’s desire to cover the large demand for wood materials for the German air force and for the German reich generally as well. In order to be able to meet the omnipresent demand for labour at this time, which grew steadily with the expansion of the company, workers from the Reich Labour Service (RAD) were primarily engaged, but foreign forced labourers were also deployed.87 The latter were housed in a separate barracks building88 on the Holig site in Görlitz, away from the other RAD workers. A similar solution was also planned in great detail for the plant in Neustrelitz. In total, the company had about 342 employees in the summer of 1943, of which 73 were forced labourers in production and 44 in the cleaning services.89 Himmelheber worked as technical manager in Görlitz, but he also coordinated the expansion into Neustrelitz and Baiersbronn. His main focus, however, was on developing the technical production of homogeneous wood products as well as making further advances in materials technology. The main customer was the RLM, which placed production and development orders with Holig Homogenholzwerke in Görlitz or the other branches. For the war effort, the Görlitz factory produced wood-core plywood, hard fibreboard and foam-wood composite panels. These latter were fine-grained fibreboards laminated with thin plywood panels. They were used in aircraft construction where they primarily served as cabin-flooring. They were also used in the fuselage of aeroplanes and as tail parts as well as in constructing experimental models in aviation development. a member of the NSDAP and did not support it.” See Max Himmelheber, Spruchkammerverfahren Freudenstadt, 28 Nov. 1946 (Landesarchiv Baden-Württemberg, Abt. Staatsarchiv Sigmaringen). 84 Sauer (2016), p. 51 f. 85 Ahrens (2015), p. 356 f. 86 Max Himmelheber was awarded the Iron Cross 1st Class, the Frontline Flying Clasp for Fighters in bronze and the Wounded Badge in silver (MHS). 87 Organisation und wirtschaftliche Grundlagen und Entwicklungsmöglichkeiten (Sept. 1943). (Barch R8121/510 Bl. 114–129 RS (229–260). 88 The report issued by the Holig Holzwerke on 20 Dec. 1943 just mentions a “prisoners’ accommodation”. Later, the term Gefangene was avoided, alluding merely to foreigners. On the blueprint drawings for the Holig factory in Neustrelitz, the accommodations for forced labourers is also labelled “Ausländer-Unterkunft”. (BArch R 8121/508 Anlage 5 zu Investitionsantrag Nr. 10.). 89 The nationality of these “prisoners” could not be determined.

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Fig. 3.10 Experimental aircraft trim tab for the model Me 109 made of foam wood (spruce) coated with a resin-impregnated sateen fabric. This composite material was manufactured by the homogeneous-wood process at “Holig”. Homogenholzwerke GmbH Görlitz 1944. Source Himmelheber-Stiftung, Photo: A. Haka, 10 June 2022

The target volume was 60 tons of foam wood per year, which after a transitional phase was to be produced entirely at the Holig plant in Neustrelitz. In concrete terms, foam wood and hard fibreboard panels from the Görlitz factory were used in various models of Messerschmitt aircraft: Standardized products were made for the models Me 108 (tail unit components), Me 109 (handwheel and adjusting wheels) and He 110 (the leading edge). The development of a prototype for Junkers models occurred in 1943, which later found application in the series. The production of a tail unit out of foam wood for the remote-control glide bomb by Blohm & Voss BV 246 (nicknamed “hailstone”) was also one of its prototype developments. Holig-Werke had already begun to work on another development contract in 1941 to design a lightweight fuselage for the Me 109 in cooperation with Messerschmitt.90 The fuselage was to be manufactured in a foam wood–textile sandwich construction, whereby the foam wood is enveloped in a sateen fabric impregnated with synthetic resin (Fig. 3.10). A final status on this development could not be established, however, just that a certain number of prototype fuselages had been completed. Other moulded-fibre parts used in the field of military aircraft construction included gun-mount covers or discharging hoods by Rheinmetall-Borsig made of foam wood. Between 1941 and 1945, Holig Holzwerke mostly produced components for the German air force, but at the time of its foundation it was already also using its capacities to satisfy the large demand for high-quality wood materials in various civilian sectors.91 For example, a foam wood–plywood composite was manufactured for the Siebel aircraft works in Halle-on-the-Saale applying this sandwich composite as cabin-floor panelling in

90 Organisation und wirtschaftliche Grundlagen und Entwicklungsmöglichkeiten (Sept. 1943).

(Barch R8121/510 Bl. 97–113 RS (195–228). 91 Organisation und wirtschaftliche Grundlagen und Entwicklungsmöglichkeiten (Sept. 1943).

(Barch R8121/510 Bl. 97–113 RS (195–228).

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their light transport aircraft Si 204. Foam wood without plywood planking was also utilized as an insulating material for the building and refrigeration industries, which would later be expanded once peace had been restored. Hard fibreboard and wood-core plywood were used in different variants in the furniture industry, interior decoration and wagon building. A civilian development project was started in 1943 with the company SiemensSchuckert to design and produce small wind turbine rotors built in a foam-wood sandwich construction. For the implementation of these production targets, cooperative agreements were concluded with numerous companies from the timber processing industry and group patents were filed by the RLM resp. its cover enterprise Luftfahrtanlagen GmbH in Berlin. In addition, there were extensive cooperations with various testing and research institutions, such as the Dresden polytechnic, the forestry college in Eberswalde, or the materials testing station in Berlin.92 The latter, for example, carried out outdoor weathering tests on various homogeneous wood materials on the Sylt peninsula and on the Zugspitze peak. Another civilian application was developed jointly with the company Christoph & Unmack in Niesky.93 In this project, homogeneous hardwood boards were planked with plywood panels and developed as a materials-saving sandwich composite for load-bearing wooden structures. The goal was to save on wood as a resource by substituting it with wood-derived materials. The focus here was on the construction of buildings and barracks, which was another in-house topic at Holig-Werke. The need for rapid but high-quality construction of administrative and manufacturing facilities had to be met, but also the expanding need for barracks as accommodations for RAD workers as well as for the forced labourers exploited in construction projects and principally in manufacturing. The Holig works also experimented with its own models for shed-like structures, but it has not yet been possible to determine the extent to which a completely unique barracks design was envisaged for serial production. With regard to the forced labourers deployed, the official correspondence only contains the neutral designations “foreigners” or “foreign workers”. In the internal communications with the construction planning office of the reich minister of aviation and air force commander-in-chief about the Neustrelitz branch,the term “prisoner accommodations” does appear, but not on the technical building blueprints for the investment application, where the term “foreigner accommodations” is used.94 These drawings (Fig. 3.11) were presumably intended to be passed on, which explains the reappearance of the vaguer designation “foreigners’ accommodations” (Ausländer Unterkunft). This was a self-evident cooperation for Holig, not only because of the short distance separating the two local companies, as Görlitz was just under 20 kms away from Niesky. 92 On these cooperations with Technische Hochschule Dresden, Forstliche Hochschule Eberswalde

and Materialprüfungsanstalt in Berlin, see Wyss (1942), p. 8. 93 Ibid, p. 7. 94 Organisation und wirtschaftliche Grundlagen und Entwicklungsmöglichkeiten (Sept. 1943).

(Barch R8121/508 Bl. 166.

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Fig. 3.11 Barracks blueprint by Holig-Werke using the designation “foreigners’ accommodations” for the forced-labourer barracks at the Holig Homogenholzwerke branch plant in Neustrelitz. It was part of the funding application submitted to the construction planning office of the Reichsminister der Luftfahrt und Oberbefehlshaber der Luftwaffe. Source Attachment 5 of the application, BArch R8121/508 Bl. 166

Christoph & Unmack was the leading wood processing company in Europe at that time. It had decided early on to extend its operations in steel, mechanical engineering and rail vehicle construction, among other things, to also include timber construction.95 The company was founded in 1882 and worked closely with important architects of the time, such as Konrad Wachsmann (1901–1980), who was a long-standing influence on the company’s building designs. For example, he designed the summer home of Albert Einstein (1879–1955) in Caputh, Brandenburg. It was built by Christoph & Unmack as a wooden house in 1929. The company’s heyday in the Weimar era, when it sought and found new methods of mechanical and serial timber construction also incorporating ideas of the Weimar Bauhaus, ended with the rise to power of the National socialists. Thus the 95 Wenzel (2013), p. 131f.

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longtime factory architect Konrad Wachsmann was forced to leave because of his Jewish ancestry, and the company quickly conformed to the new regime.96 In 1933, for example, the company sponsored the establishment of the Research and Design Association of the Reich Labour Service and the German Timber-Construction Convention (known as FOKORAD—its name was changed in 1943 from: Construction and Development Association of German Timber Construction, in Berlin), which was subordinate to the Reich Ministry of Economic Affairs and dealt with the typification of barracks for the purposes of the state. So far, little is known about this institution.97 A reappraisal of FOKORAD and its interlinkage with political structures of the nazi state, as well as its extensive cooperations in the timber industry and university research, is currently the subject of further analysis.98 The FOKORAD and Christoph & Unmack quickly found common ground and concentrated on the construction of temporary buildings, for which there was growing demand. This was not new terrain, as removable wooden barracks had already been in use early on, e.g. in military field medicine or as quarters for soldiers.99 The Danish officer Johann Christian Clemens Doecker (1828–1904), for instance, designed one suitable for a military hospital, which was prefabricated and could be quickly assembled on site.100 In World War I, the Doecker standard barracks were already being manufactured serially by Christoph & Unmack, which production was continued in World War II in cooperation with other companies in the German timber industry.101 The topic of industrial or standardized serial production of wood and wood-derived materials gained much momentum during this period. This was attended by further technical developments in pressing devices, which culminated for a while in the establishment of presstoff products.102 This is also where the line from the machined furniture103 by Deutsche Werkstätten Hellerau continues. As a logical consequence it had erected the first machined house in 1909 according 96 Wenzel (2014), p. 199. 97 The few published works to have focused on the Forschungs- und Konstruktionsgemeinschaft der

Reichsleitung des Reichsarbeitsdienstes und der Deutschen Holzbau-Konvention (FOKORAD) are primarily concerned with the institution from the perspective of architectural history or the social sciences, see Seuferling (2021), Wenzel (2014), id. (2013) or Doßmann et al. (2007). 98 Haka—“Die FOKORAD und sein staatlich-industrielles Netzwerk im Holzbau”. 99 Doßmann et al. (2007), p. 228 f., id. (2006), p. 133f. 100 Wurm (1969), p. 198 f. 101 See the drawing and design of the dismountable and relocatable commercial barracks (war barracks model 1916 “System Döcker” (Staatsarchiv Sachsen [hereafter SAS] Standort Leipzig, 20,036 Zuchthaus Waldheim, Archivsignatur 20,826 and 20,782 (1940)). On the cooperations with other companies, such as the Chemnitz company Holzhaus- und Hallenbau GmbH, see SAS, Standort Chemnitz, Bestand 31,111 VEB (B) Möbel-und Innenausbau Karl-Marx-Stadt und Vorgänger, Signatur 136 and SAS, Standort Leipzig, Bestand 21,006 Allgemeine Deutsche Kreditanstalt. Correspondence Christop and Unmack (1931–1944). 102 On the development of pressing technology in the context of presstoff production, see Sect. 4.1: “Between aesthetics and functionality”. 103 See the foregoing Sect. 3.2.1 on “Veneer wood versus plywood”.

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Fig. 3.12 Barracks by Christoph and Unmack, which was patented in 1933 and based on the Doecker standard barracks design by the Danish officer Johann Doecker. Source Patent Christoph and Unmack, Reichspatentamt, Patent No. 659 123, published 1938

to an individual design by the architect Mackay Hughes Baillie Scott (1865–1945), on the Heller fields near Dresden on Tännichtweg, as the first wooden house in that garden city.104 FOKORAD brought along with itself a small group of seven architects and engineers and a number of technical draftsmen to the small Saxon town of Niesky in the district of Görlitz in Upper Lusatia and began planning barracks accommodations for the Reich Labour Service (RAD), the highway construction units of the national railway (Reichsbahnautobau) and the air force.105 However, the demand for inexpensive and quickly erected barracks soared in other areas as well. This requirement profile generated type RL IV of a similar basic panel structure106 as the Doecker standard barracks. The experience that Christoph and Unmack had gained in producing the Doecker barracks during World War I was not the sole reason why its cooperation with FOKORAD intensified. One very important reason certainly was that Christoph & Unmack had registered a barracks design (Fig. 3.12) for patent protection in 1933. The similarities to the Doecker standard barracks are not surprising, but the Christoph and Unmack barracks design set its own accents, especially in the way they were dismantled and their joining technology, offering some improvement on the Doecker design.107 Building on this patent and inspired by the Doecker design, FOKORAD developed a series of barracks systems, which were approved by the plenipotentiary on timber construction by order of March 23, 1942 and were produced by Christoph & Unmack in cooperation with a large number of suppliers and licensees.108 Thus, the following barracks were specified for production within the scope of the issued type restrictions: 104 Gartenstadt Hellerau. Schlosser (2007), p. 20 f. 105 Wenzel (2014), p. 200. 106 Prefabricated house construction = wooden frame segments which are planked with selfsupporting panels. The enclosure space (building) is thus composed of separate panels. 107 Christoph and Unmack (1938). 108 Bevollmächtigter für Holzbau; Gabriel (1944), p. 201.

104

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• Several variants of the barracks design of the Reich Labour Service (type RL IV) • Several variants of barracks accommodations type 501/34 (barracks of the Reich Ministry of Aviation), further developed as BfH barracks type 20 601 • Horse stables, barracks type 260/9 (OKH) (of the Army High Command) • Vehicle and equipment shed, type 263/9 (of the Army High Command) • Field hospital, patient and disinfestation barracks. The SS eventually began to use the barracks from Niesky, too, and thus resorted to a serial product which had its starting point in an inconspicuous wooden barracks building, the headquarters of FOKORAD. This place still exists today (Fig. 3.13) and one would probably simply pass by it without knowing the role this site had played in the nazi system of extermination. Those U-shaped barracks now serve as storage space for the furniture factory Möbelwerken Niesky and is a historically protected building because it had been built by the company Christoph & Unmack.109 FOKORAD planned to build barracks with the type designation “260/9 (OKH)” just a few hundred metres away from the actual company premises (Fig. 3.14). They were supposed to serve as stabling for the horses of Army High Command. This barracks design was eventually used by the SS110 at Lublin, Buchenwald, (Dachau),111 Floßenbürg, Groß-Rosen, Breslau, Mauthausen, Neuengamme, Ravensbrück, (Natzweiler),112 Auschwitz and its satellite labour camps Heydreck and Blechhammer (at the chemical plantOberschlesische Hydrierwerke AG) or in the Gestapo labour camps (Arbeitserziehungslager) at Oberleutensdorf-Maltheuern (at the fuel processing plantSudetenländische Treibstoffwerke AG) as well as in other camp systems around Brüx113 to intern countless people under most crowded conditions.114 The barracks from Niesky thus became part of the extermination system of the nazi state, the scene of unspeakable suffering and countless crimes against many people from different nations. The question now is: Were the designers aware of this purpose of such barracks, or is it rather a matter of their drawings having been applied differently than originally intended? There is some support for the former, as the head of FOKORAD, the master carpenter 109 In the 1950s, the barracks were nationalized as VEB Schulmöbelfabrik Niesky, which was a manufacturer of kindergarten and school furniture in the GDR. The barracks also had office space and a small production workshop for apprentice trainees. 110 Correspondence Hauptamt Haushalt und Bauten dated 27 Nov. 1941. Hist. KZ Flossenbürg Nr. 409 (Arolsen Archiv, Bad Arolsen). 111 Barracks accommodations type 4/3. 112 Barracks accommodations type 4/3. 113 The German name for the town of Most in northern Bohemia in what is now the Czech Republic. 114 Customer list of the Sudetendeutsche Holzindustrie Christoph & Unmack Gmbh Tschernhausen dated 31 Oct. 1941. Here, IG Farben Auschwitz, IG Farben Heybreck, Oberschlesische Hydrierwerke Blechhammer, Sudetenländische Treibstoffwerke AG (part of Reichswerke Hermann Göring) as well as the Reich Labour Service camps Königsberg in East Prussia and Teplitz-Schönau are listed as customers. (SAS, Standort Dresden, Bestand: 13,131 Deutsche Bank, Dresden, Signatur 916).

3.2 Wood as a Fibre Composite and the Development of Industrially …

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Fig. 3.13 The barracks building at Neuhofer Strasse 4–6 in Niesky in 2021, which were the headquarters of FOKORAD until 1945. This inconspicuous building, currently a materials warehouse, was the place of origin of the barracks design used in the concentration camps of the nazi system, in which millions of people were forced to live under inhumane conditions and very often lost their lives. (Photo A. Haka, 11 Oct. 2021) The letterhead logo of FOKORAD is superimposed indicating the branch office in Niesky, where these barracks had been designed. (Compiled by A. Haka from documents at Barch RH 9/301 and Staatsarchiv Sachsen, Standort Chemnitz, Bestand 31,111, Signature 136)

Fig. 3.14 Blueprint of the horse stables of Army High Command of type 260/9 (OKH). This design was used by the SS at Auschwitz and elsewhere to accommodate prisoners

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Karl Gabriel, noted the following in his article on barracks construction for the reference work Holzbau-Taschenbuch: Besides having been used as a small workshop shed (type 265/9), these horse stables have also been utilized in various cases as barracks to house prisoners of war.115

Although there is no explicit mention here that such horse stables were used in concentration and extermination camps, this statement shows that it was at least known that people were in fact being interned in such special barracks. How closely FOKORAD or Christoph and Unmack really were involved in the nazi system of extermination, that is, with concentration and murder camps, becomes apparent elsewhere. Obergruppenführer Oswald Pohl (1892–1951) of the SS may have been the crucial link. Pohl joined the supervisory board of Christoph and Unmack in 1936.116 As head of the SS headquarters on economics, he was in charge of concentration-camp inspections.117 It can be assumed that Pohl was directly responsible for ensuring that the various barracks systems designed by Christoph and Unmack and the network of its cooperative partners in the German timber industry find their way into the many concentration and extermination camps besides other camps of the nazi state. Therefore, it can be said that FOKORAD as a planning entity, together with Christoph and Unmack as a manufacturing unit were a central building block in the nazi system of extermination and provided the periphery without which the camp systems could hardly have functioned in the known way. Holig Homogenholzwerke, in turn, served as a regional and supra-regional link, which supported this system with a large number of cooperative partners and suppliers. The development of homogeneous wood, which sought flexible and resource-saving production of woody materials, specifically catered to the wishes of the nazi state, and the company thus fell easily in line with the intentions of the high command of the German armed forces (OKW). During the war, the latter introduced a comprehensive classificatory system for materials, attaching a unique abbreviation to each material, thus providing clear identification for defence logistics.118 Timber and wood-derived materials were of enormous importance in military technology as well, because a wide variety of weapons systems of the Wehrmacht depended on them, e.g. military aircraft construction, small arms, packaging, housing, etc., even vehicle engineering. This granted the standard DIN 4076 for chipboard not negligible significance in defence technology.

115 Ibid, p. 216. 116 Christoph and Unmack, report on the business year 1936/37. This annual report documents the

membership of Oswald Pohl on the supervisory board of Christoph and Unmack. (SAS, Standort Dresden, Bestand: 13,131 Deutsche Bank, Dresden, Signatur 938). 117 Schulte (2011), Naasner (1998), p. 252f. 118 Kollmann (1942), p. 4 f.

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DIN 4076 also played an important role in the development and technical definition of hybrid-material designs, as it cast a bridge between wooden structure and its adaptability—by means of layering, for instance, or calculated fibre-load angles, binder and matrix choices, or an early form of the fibre composite. Systematization led to technical accessibility. The structure of early fibre-reinforced materials, such as presstoff materials, which will be discussed below in greater detail, could be uniformly correlated with DIN 4076 or its bionic structural model, natural wood. Although the DIN standard on wooden materials was not finally adopted and published until 1942, a draft had already been in circulation for discussion for several years beforehand in the technical committees on wood issues of the Association of German Engineers (VDI), at the German Forestry Association and the expert board on German industrial norms (DIN).119 This is particularly apparent in the standards DIN 7701 to 7703, which deal with the manufacture of presstoff materials, the first early forms of fibre-reinforced plastic.120 The first technical definition and structuring of this new class of materials—i.e. moulding compounds—began in 1936 with the fundamental standard DIN 7701, followed by DIN 7702 and 7703. One of the driving forces behind the establishment of DIN 7701 was the Dresden mechanical engineer Enno Heidebroek (1876–1955), who was engaged in the analysis of presstoff materials in the area of plain or slide bearings and whose personal network extended far into the VDI and its technical committees. The initial study of DIN 4076 for wood-derived materials in 1939 led to an adjustment of the mentioned pressed-materials standards. A revision of the technical and processing aspects took place. They had been removed from the materials group of the plastic masses with their mixed forms and incorporated into the fundamental standard DIN 7701 dating from 1936. However, subsequent progress already caused this to be considered obsolete by 1939. Technical differentiation and foremost the technical demarcation process for materials were a decisive turning point in the development of hybrid material systems. This had an impact not only on materials design, but also on design dimensioning121 and calculations for such materials. Defined materials testing was the outcome, which significantly increased the quality norms for these materials and thus enabled a large number of material hybrids to become established. Limited chipboard production began at the end of the 1930s. However, decisive steps in process engineering for chipboard production were lacking and first had to be developed, which initially put a damper on its market distribution. In addition, a timely introduction of this product onto the free market and its development, especially in Europe, was hindered by World War II. The first processing parameters for the production mainly of thin chipboards came from Dynamit AG in Troisdorf. Dynamit AG began to manufacture such boards in 1943 together with a practical partner using glue products produced inhouse and in-house multi-platen presses.122 After World War II a versatile production of 119 Beuth-Verlag ed. (1936), id. (1942). 120 Beuth-Verlag ed. (1939a), id. (1939b), id. (1939c). 121 Dimensioning of components, see here also Cuntze (2019), p. 13 f. 122 Kollmann (1966), p. 3.

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chipboard began in Germany, as well as in such countries as France, Great Britain and especially the USA. Wood, being a natural fibre-composite material, offers a multiple blueprint for the operating principles of a whole range of composite materials. This regards not only the principle of fibre reinforcement but also the static aspects affecting fibre-load angles in fibre-reinforced materials. The dissolution of natural wooden structures in the form of a processed wood-derived material can be seen as a prime example of a hybrid material whose properties can thus be applied in a double sense. These developments are primarily based on passed-on knowledge and research into wood as a basic material. The pioneering work here from the eighteenth century included the scientific inquiries of the French chemist, engineer and botanist Henri Louis Duhamel du Monceau (1700–1781), whose biological research on wood paved the way to more qualified utilization of wood.123 In this context, the scientific investigations on the properties of wood by Georges-Louis Leclerc, Comte de Buffon (1707–1788), should be mentioned. The Handbuch der mechanischen Technologie from 1837 by the teacher in the commercial arts and later director of the Polytechnische Schule in Hanover, Karl Karmasch (1803–1879), added further pointers about how best to deal with wood by describing the basics of industrial wood processing.124

3.3

Machine Elements—Early Designs with Hybrid Materials

3.3.1

Early Presstoff and Layered Materials From the 1880s to the Turn of the Century

There is evidence from as early as the close of the nineteenth century of the first hybrid materials in technical applications, which had been manufactured with the intent to reduce weight or heighten the load limits of the material. This was to be achieved by combining the most favourable parameters of different materials. However, the examples identified so far were always special applications or prototypes. No serial production with any claim to meeting the above criteria could be ascertained. One example is the patent application by the Berlin engineer Ulfers from 1882, who needed a low-maintenance stern-tube bearing for his shipbuilding models and had developed a plain bearing for this purpose whose bearing-shell design (Fig. 3.15) was comparable to the early forms of presstoff plain bearings. The structural material he used for this bearing was layered parchment paper.125 As can be gathered from two other patents by Ulfers, he was working on developing a reaction propeller, also known as a hydraulic propeller. This was an early form of water jet propulsion, which is currently 123 Cf. Egerton (2007), p. 147 f. and Niemz (1993), p. 14 f. 124 Karmasch (1851). 125 Ulfers (1883a).

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Fig. 3.15 Section through the bearing with shaft; the layered structure of pressed parchment paper, which rests against the shaft from above and below, is clearly visible. Source German patent specification, No. 23837, 1883

also known as a pump jet.126 Who the client or end user of Ulfer’s designs was could not be established in my research. It can be assumed that these elaborate designs and patents were motivated by commercial interest and therefore that it was commissioned work. This is supported by the fact that shipbuilders and engineers were already working intensely on the subject of reaction propellers at the end of the eighteenth century into the middle of the following century. In this sector, the developments on the experimental ship Hydromotor in Kiel in 1879 are the most famous, although they were not successful.127 It is well possible that they served as inspiration for Ulfers. The fact that this propulsion method did not become established until the second half of the twentieth century was mainly due to the low efficiency of the design at the time, but also to the high maintenance requirements of the overall system. Ulfers was not the only one to try to acquire the commercial rights and patent protection just then. The Frenchman Alfred Léon Segond is another, who managed to file a patent on a reaction propeller just a year later, because his engine design differed in many respects from the ones covered by the patent held by Ulfers.128 The Ulfers reaction propeller in the 1882 patent was described by its inventor as two turbine-like paddle-wheel rotors (“Schaufelradturbinen”) located inside a ship (Fig. 3.16) to push water through the length of the ship via piping to the stern, thus propelling the boat by recoil.129 Ulfers design was suitable for both inland waterways and marine use. His ocean variant was designed on the scale of a German navy ship. 126 Cf. Müller (1908), p. 221. 127 Ostersehlte (2002), p. 275 f. 128 Segond (1883). 129 Ulfers (1882).

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Fig. 3.16 Patent drawings of a reaction propeller, an early form of water-jet turbine. This design is of an inland vessel with two “paddle-wheel turbines” designed to force water through flow piping to propel the vessel in the water by recoil. Source German patent specification, No. 2370, 1882

One year later, another patent by Ulfers followed, which treated the same complex of topics but concentrated on the direct source of propulsion, a so-called Strahlstoßmotor. The basic operating principle of this jet-thrust “motor” was similar to a water turbine. Unlike a normal turbine, however, it combined elements of a steam engine with ones from a water turbine; its inventor wanted to exploit differing pressure states to drive the engine. Ulfers planned to fit both his reaction propeller and his jet-thrust motor with shaft bearings with bearing shells made of a robust material able to tolerate a wide thermal spectrum. Until then, the main materials for plain-bearings had been white metals. These were lead and zinc alloys, which required due maintenance. Ball bearings were not yet an option at this time, since the first ball grinding machine making the requisite quality of

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111

ball bearings feasible had just barely been developed by Friedrich Fischer (1849–1899) in 1883, precisely the same year as the Ulfers patent.130 The decision to use parchment paper as a bearing-shell material was innovative at this time, as parchment paper was not produced industrially in Germany until 1861 and was under British license.131 This shaft bearing was decades ahead of its time. Its design resembled the presstoff plain bearing in hard-paper or fabric layers developed at the beginning of the 1920s as an alternative technical material at lower operating cost to conventional plain bearings. This parchment design can therefore be regarded as an early form of such plain bearings. Apart from the basic oiling of the pressed parchment layers, these bearing shells only required a little water to maintain the lubricating film for the bearing shaft. Considering the maritime purpose of the reaction propeller or jet-thrust motor, one may regard this bearing as a very application-oriented development. Ulfer’s reaction propeller did not survive because the efficiency of the paddle wheels was far too low; just as with paddle-wheel steamers, the actual performance spectrum could not meet the propulsion and steering requirements. Thus, not only the development of the propeller and the engine fell into oblivion, but also the plain bearing developed within this context. The construction of a reaction propeller was more successful for the Dresden thermodynamicist and university lecturer Gustav Anton Zeuner (1828–1907), however. Nevertheless, the basic principle of his “Zeuner turbine” did not carry through in turbine design.132 In cooperation with the shipbuilding engineer Ewald Bellingrath (1838–1903), who headed the first German testing station for shipping in Dresden-Übigau, he developed a chain tug in 1891.133 This vessel pulled itself forward along a large chain laid in the river Elbe and also had two water-jet turbines for steering, which could be used for propulsion as well as to manoeuvre the ship on the spot. The cooperation between Dresden polytechnic and the experimental station ended in 1930 when the shipyard was shut down. From 1935, the workshop premises were occupied by the wharf and nautical engineering factory Übigau-AG Schiffswerft, Maschinen- und Kesselfabrik and the boiler factory Dampfkesselfabrik Übigau. In the latter, submarine segments were manufactured from 1940 onwards for the navy high command (OKM) in cooperation with the Dresden companies Kelle & Hildebrandt GmbH and Brückner, Kanis & Co. The testing of the submarine segments also took place in Dresden in the national high-pressure testing facility Reichseigne Hochdruckprüfanlage des OKM, which was located on the premises of Brückner, Kanis & Co.).134 130 Meer (1987), p. 237 f. 131 See the commentary in this study (Sect. 3.1.2) on the basics of vulcanized fibre and on the patent-

ing of parchment paper in 1957 by the British chemist W. E. Gaine; cf. White (1983), pp. 340, 348. 132 Busley (1895), p. 46 f. 133 Lehmann (1999), p. 36. 134 Haka (2014a), p. 264 f.

4

Composites in 20th-Century Polymer Chemistry

4.1

Between Aesthetics and Functionality—Bakelite, The First Years Until 1930

The development of plastics, which started at the beginning of the twentieth century, can be regarded as the groundwork to high-performance matrix materials for the composite materials we know today, particularly fibre-reinforced plastics. Yet this first developmental step was taken with what was thought to be a waste product toward the end of the nineteenth century: phenolic resin. The chemist and later Nobel laureate in chemistry Adolf von Baeyer (1835–1917) generated a whitish-to-pinkish resin in 1872 while experimenting with mixtures of phenol, formaldehyde and hydrochloric acid.1 The prevailing interest among researchers principally in crystallizable and distillable compounds at that time led him to dismiss this honey-like resin as a waste product. In the years that followed, his experiments were taken up and continued by a number of other chemists, but their efforts did not yield any substance that could become a commercial success.2 The Belgian-American chemist Leo Hendrik Baekeland (1863–1944) first managed to make profitable use of these initial researches in the field of phenolic chemistry (Fig. 4.1). Baekeland was very successful in other fields before the subject of phenolic resins attracted his attention. Through the invention of Velox photographic paper and his participation in inventing a process module in electrochemistry, he had amassed a great fortune between 1899 and 1907.3 When Baekeland started to work on the chemistry of phenolic resin, he was already aware of the dire shortage of insulating materials in electrical engineering from his experience in electrochemistry and his contacts with electrical 1 Hultzsch (1950), p. 3 f., Greth (1938), p. 719 f. 2 Nagendrappa (2014), p. 494 f., Reinhardt and Travis (2000), p. 179 f.. 3 Schwedt (2013), p. 65 f., Braun (2013), p. 194 f., Patterson (2012), p. 43 f., Billiter (1954), p. 232.

© The Author(s), under exclusive license to Springer Fachmedien Wiesbaden GmbH, part of Springer Nature 2023 A. T. Haka, Engineered Stability, https://doi.org/10.1007/978-3-658-41408-5_4

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Fig. 4.1 Leo Hendrik Baekeland, inventor and eponym of the plastic bakelite. Source Time Magazine, Vol. IV, No. 12, 1924

engineers and was on the look-out for alternatives. Although at that time many electric cables were already being coated with insulating materials made from natural resins (such as shellac or indene-coumarone resin from coal tar, the first industrially produced fully synthetic resins), they were insufficient in both quality and quantity. From about 1903 onwards Baekeland examined phenol–formaldehyde reactions together with his four assistants in his private laboratory, financed by his fortune, in search of an adequate insulating material. The outcome of these experiments was a condensation product obtained from formaldehyde and phenol in a pressure reactor subjected to high pressure and a temperature of 200 ºC. He named this colourless resin bakelite, a derivative of his surname.4 He applied for a patent for this invention in the USA in 1907.5 In the years that followed, a whole family of patents ensued, including the patent granted in Germany in 1911 for “a process for the production of condensation products from phenols and formaldehyde.” In technical circles, this was briefly referred to as the “heat-pressure patent”.6 The decisive feature of this patent was that it covered not only the production of the resin, but also the manufacture of products made of it. It also indicated the possible addition of filler material to the phenol–formaldehyde mixture or to the resulting reaction products.7 The addition of fillers turned bakelite into a composite material. The filler primarily used was wood flour or wood-flour mixtures. These compounds combined not only sawdust and wood shavings from various sawmills, but also mineral substances, such as 4 For various perspectives on bakelite, which is already well studied in the history of technology, see

among others: Strom and Rasmussen (2012), Kossmehl (2010), p. 10, Crespy et al. (2008), p. 3368 f., Glaser (2008b), p. 14 f., Braun and Collin (2001), p. 190 f. 5 Baekeland (1909a), p. 317 f., id. (1909b). 6 Baekeland (1911). 7 Baekeland (1911).

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Between Aesthetics and Functionality—Bakelite, The First Years Until 1930

115

asbestos, coal dust or crushed shells. The admixture of these fillers served to stabilize the resin mass and to economize on the material. The incorporation of fillers to specifically manipulate mechanical properties, as was later done with fibre-reinforced plastic within the framework of materials design in order to attain specific load horizons, did not yet exist in bakelite from this time. Such stabilizing fillers were supposed to increase the impact resistance of the cured resin mass and reduce the brittleness of this first thermoset plastic. From about 1903 onwards Baekeland examined phenol–formaldehyde reactions together with his four assistants in his private laboratory, financed by his fortune, in search of an adequate insulating material. The outcome of these experiments was a condensation product obtained from formaldehyde and phenol in a pressure reactor subjected to high pressure and a temperature of 200 ºC. He named this colourless resin bakelite, a derivative of his surname.8 He applied for a patent for this invention in the USA in 1907.9 In the years that followed, a whole family of patents ensued, including the patent granted in Germany in 1911 for “a process for the production of condensation products from phenols and formaldehyde.” In technical circles, this was briefly referred to as the “heat-pressure patent”.10 The decisive feature of this patent was that it covered not only the production of the resin, but also the manufacture of products made of it. It also indicated the possible addition of filler material to the phenol–formaldehyde mixture or to the resulting reaction products.11 The addition of fillers turned bakelite into a composite material. The filler primarily used was wood flour or wood-flour mixtures. These compounds combined not only sawdust and wood shavings from various sawmills, but also mineral substances, such as asbestos, coal dust or crushed shells. The admixture of these fillers served to stabilize the resin mass and to economize on the material. The incorporation of fillers to specifically manipulate mechanical properties, as was later done with fibre-reinforced plastic within the framework of materials design in order to attain specific load horizons, did not yet exist in bakelite from this time. Such stabilizing fillers were supposed to increase the impact resistance of the cured resin mass and reduce the brittleness of this first thermoset plastic. Influencing the colour was a subordinate issue. The admixture of fillers and the moulding process, which was performed under heat and pressure, did affect the transparent, slightly honey-coloured resin and gave the material a brownish hue. For purely practical reasons, a distinctive shade was retained for almost all technical products, such as technical cladding, plug sockets or insulation, in a darker shade produced by just small 8 For various perspectives on bakelite, which is already well studied in the history of technology, see

among others: Strom and Rasmussen (2012), Kossmehl (2010), p. 10, Crespy et al. (2008), p. 3368 f., Glaser (2008b), p. 14 f., Braun and Collin (2001), p. 190 f. 9 Baekeland (1909a), p. 317 f., id. (1909b). 10 Baekeland (1911). 11 Baekeland (1911).

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amounts of dye, mostly pulverized coal. For other everyday articles, various colour mixes were used covering every possible tint, even leading to the manufacture of imitation coral and pearl jewellery out of bakelite. Since bakelite resin was the only plastic resin available for a long time, bakelite became a generic term for phenolic resins until well into the 1950s. Even now, bakelite is synonymous with the dawn of the plastic age.12 The word Kunststoff , literally “artificial material”, was first used by the chemist Ernst Richard Escales (1863–1924) in the title of the journal he founded: Kunststoffe, with the subtitle “Journal for the production and use of refined or chemically manufactured materials”. It hence first arrived in the professional world four years after the introduction of bakelite.13 Nor did it get immediately adopted. The word Kunststoff and a definition of the term did not occur until the 1920s. Similar to the group of plastic masses or to “artificial wood” (Kunstholz), there were initial reservations about such “artificial substances” which did not occur naturally. It was only with the establishment of macromolecular chemistry by Hermann Staudinger (1881– 1965) that synthetic plastics came to be acknowledged as substances of high molecular weight in contrast to the low-molar substances of organic chemistry, which were already well known by then, and consist of large molecules.14 Bakelite became synonymous with early plastics because it was the world’s first massproduced mouldable synthetic mass. However, in technical terms, the material that came to be known under the brand name bakelite is simply a synthetic resin–wood-flour presstoff. Later such pressed materials, which carried various brand names in the 1920s, would be referred to by their constituents, such as their woven fabric or paper tapes, but not by any particular brand name. The German company Bakelite GmbH was founded in 1910 in Erkner near Berlin and embarked on the large-scale production of bakelite in Europe.15 Its founders were Baekeland and the chemical stock company Rütgers AG, which at that time was already working with phenol, a by-product of its tar production, and hence was already familiar with a number of processing sequences. In the same year, the General Bakelite Company in Perth Amboy in USA also started its production of bakelite. Bakelite Company, or resp. Bakelite GmbH in Germany, were able to maintain a monopoly position for almost 20 years until the end of January 1930 thanks to the patent family that Baekeland had secured. In the early years, bakelite was predominantly used as a cladding and insulating material because it was robust and resistant to a variety of aggressive media.16 The main 12 Cf. Braun (2013), p. 2 f., Koßmehl (2009), p. 1090 f., Kaiser (1991), p. 40 f. 13 Kunststoffe. Zeitschrift für die Erzeugung und Verwendung veredelter oder chemisch hergestellter

Stoffe. Escales (1911). 14 Cf. Weber and Deussing (2013), p. 81 f., Mühlhaupt (2004), p. 1072 f., Lechner et al. (2003),

Plumpe (1991), p. 319, Morawetz (1987), p. 95 f. 15 Cf. Kricheldorf (2014), p. 22, Bijker (2012), p. 172 f., Kaufmann (2011), p. 1 f., Patterson (2011),

p. 21 f., Bijker (1997), p. 101 f., Hagen (1997), p. 93. 16 Kausch (1931), p. 231 f.

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customers and early cooperative partners of Bakelite Gmbh in the first years were the electrical companies Siemens and Halske and Allgemeine Elektricitäts-Gesellschaft (AEG). Plastics were already ubiquitous by the mid-1920s (Table 4.1), and Bakelite GmbH was no longer the sole manufacturer in this industry.17 Even before the heat-pressure patent had expired, well over 100 large and medium-sized companies in Germany were engaged in the production of various plastics based on phenol and formaldehyde, metal salts, carbohydrates, cellulose, cellulose derivatives and proteins, especially casein. Products based on phenol formaldehyde, cellulose and casein can be considered as the most important plastics in materials technology. The exportation of plastic products was already relatively stable in the period 1926–1931, accounting for around ten milliard reichsmarks per annum in the German foreign trade budget.18 The monopoly position of Bakelite GmbH resp. Bakelite Company was compromised only by the plastics factory Hermann Römmler Preßstoffwerke in Spremberg, Lower Lusatia. The Römmler firm had developed the phenol–formaldehyde condensation process in parallel with the registered patent holder Bakelite Company. In order to avoid legal disputes, it was agreed in 1919 that the Römmler firm be permitted to produce synthetic resins as well without a license.19 In order to be able to handle the tasks ahead of them, the firm was converted into a joint-stock company to increase their capital investment. This enabled the resulting Römmler AG to expand its stock of machinery and to adjust its production processes. Pressing technology in particular required new solutions. The final transformation in the technical terminology of the associated manufacturing process of compression moulding began at the beginning of the 1920s. The term was essentially minted by Römmler AG, since it called its products Preßmassen, no longer Plastische Massen This concept of pressed masses can be regarded as established by the 1920s at the latest. The products made from this compound were referred to as Preßstoffe, i.e. compressed materials. This change in the terminology was closely associated with the manufacturing process and alterations in the technology of presses. This technical advancement in the early 1920s was conditioned by the state of materials science. The finding that some of the mechanical parameters, such as tensile and flexional strength, or the avoidance of resin pockets in the case of pressed materials, can be decisively altered by the technical parameters of the press during production led to leaps and bounds in press technology. Thus the ability to alter the duration and degree of pressure and temperature was improved, resulting in the entire compression regime becoming more finely tunable.20 Companies such as Siempelkamp (Krefeld), Werner & Pfleiderer (Bad Cannstatt near Stuttgart) and WUMAG (Görlitz) (Fig. 4.2) were able to launch new

17 Pöschl (1932), p. 193 f., Bahls (1932), p. 197 f. 18 K. I. (1932), p. 124 f. 19 Haka (2011), p. 74 f., Römmler (1938), p. 60 f. 20 Grodzinski (1933), p. 177 f.

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Table 4.1 A selective list of plastic products offered on the German market, broken down by sector, type of application and plastic (as of 1930). Compiled from the journal Kunststoffe covering the period 1925–1930 (no claim to completeness) Sector

Applications (a selection)

Plastic

Mechanical engineering

Gears, shafts, bearing systems, slot liners, housings, rail chairs

Phenol formaldehyde, phenol formaldehyde with fibre and textile insets

Aircraft industry

Aircraft propellers, speedometer housings, gearwheels, camshafts, brake bands, presstoff linings, cranks

Phenol formaldehyde, phenol formaldehyde with fibre and textile insets

Automotive industry

Gears, camshafts, headlight housings, windshield wipers, inside roof lining and trim, steering wheels, shift levers, plain bearings, body parts

Phenol formaldehyde, phenol formaldehyde with fibre and textile insets, cellulose derivatives

Building and furniture industries, interior design

Door and window handles, toilet seats and lids, wall panelling, table tops

Casein, phenol formaldehyde, cellulose derivatives

Clothing, textiles, attire accessories

Buckles, buttons, darning eggs, cap stiffeners, shirt collar reinforcements, tensioners for trousers, shoes and gloves, knitting needles

Casein, phenol formaldehyde, cellulose derivatives

Electrical engineering, high-voltage current

Insulators, insulating materials, sockets, switches, lighting fixtures, housing linings, antenna chains

Phenol formaldehyde, phenol–formaldehyde with fibre and textile insets

Instruments and apparatus

Carriages and carriage parts, photographic trays, slide-rules, cases, dials, turning knobs

Phenol formaldehyde, cellulose derivatives

Optical industry

Camera bodies, eyepiece rings, opera glasses, measuring instruments

Phenol formaldehyde

Toiletries

Toothpicks, toothbrushes, hairpins, soap boxes, washcloth holders, mirror cases, combs, brushes

Phenol formaldehyde, cellulose derivatives

Nursing utensils

Spectacle frames, medical devices, ear Casein, phenol formaldehyde, cellulose spoons, safety and sunglasses, bedpans derivatives

Toys

Inflatable creatures, balls, dolls, dice, dominoes, chess pieces

Stationery

Pens and fountain pens, stencils, rulers, Casein, phenol formaldehyde, cellulose folder covers, boxes derivatives

Musical instruments

Piano keys, wind-instrument mouthpieces, guitar and mandolin plectra

Casein, phenol formaldehyde, cellulose derivatives

Casein, cellulose derivatives

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Fig. 4.2 A new 2500-ton ten-platen press of the company WUMAG Görlitz in the production hall of Römmler AG in 1926. Each level accommodated a material plate for individual pressing. Source Weigel (1942), p. 19

presses on the market at this time.21 They offered fine adjustability and partially automated sealing processes. This revamping in the press technology was accompanied by a reorganization of production logistics. The development of heatable multiplaten presses made it feasible to produce a high-quality presstoff material in series, which reduced to a minimum the expensive quality controls during production, and at a number of plants even completely eliminated them. A parallel development was a rise in professional qualification within the context of production. The position of the foreman, in particular, was elevated to that of a technically experienced middleman. Whereas up to that point the foreman had been regarded primarily as a technical authority on the shop floor, he henceforth became an active link between production and plant logistics or the preliminaries to production taking economic aspects into account and the need for more efficient use of the resources besides a more refined assurance of quality. The novel press technology and growing demands on quality for presstoff products particularly during the 1920s led to an influx of a number of aesthetic aspects for additional incorporation into product design. This was supported by better phenolic resins, which allowed shorter press sealing times and higher product output. The term rapidpress resins (Schnellpreßharzen) emerged.22 The focus had hitherto been on stability and 21 Cf. Thum and Jacobi (1939), p. 1045 f., Küch (1940), p. 1 f., van Hüllen (1939), p. 602 f.,

Grodzinski (1933), p. 177 f. 22 Brandenburger (1938), p. 38 f., id. (1937), p. 11 f.

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Fig. 4.3 Desk lamp from 1930 made of bakelite, manufactured by Römmler AG in Spremberg after a design by Christian Dell. Photo A. Haka, 3 May 2019

functionality. This new mastery of the manufacturing process and rising output totals soon set new standards in moulding and aspects of surface design. New urea resins, such as urea–formaldehyde and carbamide resins, permitted the production of various surface effects with different colour tints. The age of plastics design was ushered in by the command over these processes and by new multifaceted resin systems. Römmler AG counts as one of the pioneers in the field of everyday objects made of plastic. Upon hiring the former master craftsman at the Weimar Bauhaus, the silversmith Christian Dell (1893–1974), at the end of the 1920s, this firm was able to apply its synthetic material to popular everyday products. In addition to designing plastic tableware and trays, Dell also designed a desk lamp in 1929 (Fig. 4.3).23 Dell’s design of the phenolic-resin adjustible lamp set standards and made successful use of the new material, plastic, in an aesthetically pleasing form. With this one product Römmler AG succeeded in winning over both the cultivated living-room and the business office. The material used for this lamp was the moulded presstoff and composite called hares, an early prestigious trademark product of that company. The specific material designation was hares S type S, a phenolic resin with wood flour as the filler.24

23 Lattermann (2013), p. 1, id. (2003), p. 111 f. 24 Römmler (1938), p. 75 f.

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Bakelite “A-Wing”

Ideas about the creation of complex technical structures banking on phenolic formaldehyde condensation products, and in particular bakelite, as the supporting matrix and aimed specifically at the application horizon of lightweight construction, can already be found in the first half of the twentieth century.25 At first glance, the sources reviewed in this regard give the impression that this must be the decisive technical advance towards modern fibre-reinforced plastics. However, closer examination shows that this can at best be regarded as an isolated paving stone along that path. The central aspect in the materials design of an FRP, its typical load orientation, was not yet a matter of consideration at this early stage. The character of modern lightweight construction is broached in these early hybrid-material designs, however. Far greater quantities of stabilizing materials are almost recklessly incorporated into the bedding matrix in an attempt to improve stability. Furthermore, much attention is devoted to the optical impact of a material design. Later this aspect gives way almost completely to functionality. One such function-oriented material design from 1916 will be described here within the context of two patent specifications26 registered by employees of the Westinghouse Electric Company: Robert Kemp and Frederick Johnson. The aim was, to generate a new material for aircraft construction and to qualify it, i.e. to certify the material’s suitability for aviation. For lack of source material, nothing else is known about the true technical intentions of these two patent applicants, nor about them personally. Their immediate circumstances allow one to make various assumptions about their developmental work, though. At the time of the patent application, Kemp and Johnson were employees at the research laboratories of Westinghouse Electric Company. This enterprise had been founded in 1886 by George Westinghouse (1846–1914) and was initially engaged in the manufacture of electric lighting and long-distance and high-voltage transmission in the USA and it did pioneering work in this area. Westinghouse Electric Company was one of the first major industrial companies in the United States to establish a scientific research laboratory.27 This independently operating research laboratory had flexible research structures, in terms of both staffing and its laboratory equipment. The policy of employing researchers on temporary contracts was due to the wide range of topics covered. In addition, parts of the laboratory were used by other companies for their research and experiments. This was possible because the laboratory had movable partition walls and multiple sockets for access to electricity, gas, water and vacuum, and was thus able to provide space for different research topics and teams at the same time. 25 Haka (2017). 26 Kemp (1916), Kemp and Johanson (1916). 27 Coltman and Furfari (2004), p. 9 f.

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Fig. 4.4 Details of a patent filed by Robert Kemp in 1916. Figure 1.2 provides the key to the aircraft components that can be made of early fibre-composite material. Figure 1.6 shows the material types. No. 39 represents plate material showing layerings of paper impregnated with phenol and formaldehyde. No. 40 indicates plate material containing fabric tapes as a reinforcing agent. No. 41 shows material with wood-fibre reinforcement and number 42 shows impregnated wood. Source Patent—Kemp, 1916, US Patent No. 1,435,244

The first patent, filed in May 1916 by Robert Kemp on his own, discussed a new material which was supposed to be used as a plate-shaped material for components of a propeller aeroplane. This material was presented in four variants, the supporting matrix of which consisted of condensation products of phenol and formaldehyde, and which could be reinforced either with paper, fabric, wood fibre or wood for reinforcement (Fig. 4.4). The patent filed just a month later by Kemp and Johnson barely mentioned the material anymore, devoting itself instead to details of aircraft construction and emphasizing the innovative character of various design details (Fig. 4.5). From this patent onwards at the latest, it becomes apparent that the primary point was to build up a family of patents to commercialize a building-block system in aircraft construction. The material to be used had, by virtue of its properties, become a flexible construction element which could be affixed to the aircraft components commonly in use at that time. However, the various joining techniques described in the patent, such as bonding or bolts to attach these early fibre-composite materials to metallic components, can only be considered hypothetical. This material had not yet been applied in aviation by then, so there was no knowledge about suitable joining techniques, which today can still be viewed as key technologies in multimaterial design. Kemp’s patents and the one he held jointly with Johnson followed the technical vagaries of the day: New impulses in materials technology for aviation were presented. This was perhaps the first exposition of the principle of modern fibre-reinforced plastics, nevertheless it is purely statistical in nature. From an objective point of view, Kemp merely borrowed Baekeland’s heat-pressure process, which was just a few years old at

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Fig. 4.5 Excerpt from the patent by Kemp and Johnson, in which they describe a new composite material for use in aeroplane construction. Source Patent—Kemp and Johnson, 1916, US Patent No. 1,414,419

the time. Unlike Baekeland with his bakelite products, which relied on powdery fillers or occasionally also mineral or lignocellulose short fibres for stability, these patent applicants this time indicated a selection of possible ingredients. Primarily paper, woven fabric or fibrous materials were named as flat stabilizers, embedded in a phenol–formaldehyde matrix. This application of flat stabilizing materials in the supporting matrix, envisaging the usage horizon of creating an alternative in materials technology for aircraft construction, were the forte of the mentioned patents. However, neither in this patent nor in any of the subsequent patents up to 1923, for which Kemp alone was responsible, was the topic of the load distribution addressed as would later be the case in designs for future composite materials. The primary goal of the Westinghouse research facility was to develop existing products among its own assortment and to open up new fields of study. The developments by Kemp and Johnson thus fitted very well into this research environment. Kemp’s work for Westinghouse Electric is particularly traceable. There was good reason to focus on profitable marketing of Kemp’s patent family in aircraft design. No other industry experimented as much with new shapes, materials and design solutions. Aircraft construction was booming at the time and enjoyed the necessary prestige to implement technical innovations promptly and attract the support of wealthy investors with its high public profile. This focus by Kemp on material can be attributed to the close ties that Westinghouse Electric entertained with Baekeland and Eastman Kodak Company.28 The background to 28 Bijker (1997), p. 134 f., Meikle (1995), p. 56 f.

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Fig. 4.6 Advertising leaflet on the camera Autographic Kodak Special No. 1A from 1917. Its housing is made of the composite material micarta. Source Packaging insert for the model Autographic Kodak Special No. 1A from 1917 by Eastman Kodak Co., Rochester, N.Y

this was that in 1910 Eastman Kodak began to use a material developed by Westinghouse, its micarta brand, for the housing of its camera model Autographic Kodak Special No. 1A (Fig. 4.6).29 This application of micarta had another effect as well, which can be viewed as a bridge between the afore-mentioned players and dates back to 1899. In that year, Baekeland sold the first company he had founded, Nepera Chemical Co., to the photographic market leader Eastman Kodak Company.30 With the sale of this enterprise, Baekeland’s first major invention, the rapid-copy photographic paper Velox, also changed hands, replacing the conventional photographic paper which reacted more slowly when technically processed. Baekeland, an industrial global player, inventor and manager, was also known for continuing to promote widely and advance many of his products even after they had been sold or licensed. Further development of bakelite by adaptation to applicable products was entirely in line with Baekeland’s intentions. The cooperation with Westinghouse Electric Company was thus probably a logical step for him. Consequently, micarta was a further developed form of bakelite. Thin layers of paper were bound into the compound instead of the usual stabilizing ingredients. Here we can see the door to the modern FRP standing ajar, without the crucial step across the threshold being taken. Optical enhancement was the basic idea behind the material design of micarta, or merely the intention to provide the mentioned camera with a colour-intensive and high-quality material surface, which the embedding of paper layers made possible. The added stability imparted by the integration of paper sheets was perceived here as a beneficial side effect for an object of utility. It can therefore be assumed that Kemp profited highly from the afore-mentioned patent network. His later developments in materials and process technology manifest the same degree of innovation as his original patented idea. Robert Kemp filed a new 29 Kausch (1932), p. 222 f. 30 Brayer (1996), p. 200 f.

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Fig. 4.7 Excerpt from Robert Kemp’s patent from 1918. Figures 1.1 and 1.2 show two interlocked pipes encased in fibre-reinforced plastic (5 and 7). Source Patent—Robert Kemp, 1923, US Patent No. 1,447,361

independent patent almost every year until 1923 and apparently tried to secure the rights for Westinghouse to the complete production chain for an aircraft built of composite materials.31 Kemp’s patents even anticipated a number of later developments in the field of fibrereinforced plastics. For example, his patent Composite Structure (Fig. 4.7), submitted in 1918, deals with the encasement of a metal tube within a fibre-composite structure. Kemp patented several aspects of this, such as lightweight stiffening of a raw structure in aircraft construction by fibre-reinforced plastic cladding; the joining of a fibre-composite structure to metallic elements; and bullet-proofing a metallic structure by means of fibrecomposite shielding. This patent specifically mentions that components clad in this way should be considered for military aircraft construction and would serve as a persuasive sales argument. The 1918 patent was the first to demonstrate the embedding of a metallic structure in a fibre-reinforced plastic, a so-called metal inlay. Modern fibre-composite structures of the like were not developed until the 1970s, which also serve as solid joining points for good transmission of load.32 The subject of joining technology, which today represents a central component of lightweight construction in the field of hybrid-material designs—namely, the connection of lightweight fibre-composite structures to classical metallic structures—was addressed by Kemp in his patent submitted in 1919.33 He discussed there a number of aspects of lightweight construction that are still valid today, such as grid-structure designs for 31 Cf. Kemp (1922), id. (1922a), id. (1919), id. (1921), id. (1923). 32 Kemp (1923a). 33 Kemp (1923).

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Fig. 4.8 Excerpt from Robert Kemp’s patent from 1919, which deals primarily with technical joining aspects for connecting fibre-composite structures to metallic structures. Source Patent—Robert Kemp, 1923, US Patent No. 1,469,220

weight reduction combined with modern joining concepts such as affixing fibre-composite structures by bolting, riveting or bonding (Fig. 4.8).34 Kemp’s last patent, which he submitted in 1921 and was approved in 1926, dealt with the manufacture of fibre-composite structures (Fig. 4.9).35 Parallels to the injection process now in use known as resin transfer moulding or RTM are obvious and show that the novel material for the time had been subjected to thorough study.36 The comprehensive patent family that Robert Kemp assembled for Westinghouse documents that this enterprise tried to set up the new fibre-composite material as a licensed product at low cost. The Kemp patents cover two large product areas: aircraft and boat construction, which held the prospect of lucrative commercial sales. There is no evidence that these patents were actually implemented in the form of related aeroplane or boat models. This was probably due to the load horizons of both the reinforcement and supporting 34 AVK (2013), p. 536, 518 f., Haka (2009), p. 2 f. 35 Kemp (1926). 36 Gay et al. (2003), p. 27 f., Flemming et al. (1999), p. 200 f.

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Fig. 4.9 A cross-section detail of a closed two-part mould (3 and 4). Via an inflow tube (8 and 9) which is integrated into the mould, a hot liquid enters and increasingly presses movable small nonmeltable spherical bodies (11) against the fibre sheets (2) lining the inside of the mould, thus forming two fibre-composite shells. Kemp asserts that fibre-composite structures for an aeroplane or boat could be fashioned in this way. Source Patent—Robert Kemp, 1926, US Patent No. 1,572,936

matrix materials, which did not yet have the requisite material characteristics. Micarta, that Westinghouse trademark product, was manufactured until the mid-1920s with paper sheets as the reinforcement material. It was not until later that the company began to incorporate woven fabrics. The supporting matrix did not yet have sufficient strength to permit mass production of the intended components or at least in adequate quantities. It was only with the establishment of polymer chemistry by Hermann Staudinger at the beginning of the 1920s that appropriate matrix materials emerged. It is presumable that Robert Kemp’s work was mainly on the scale of prototype production.

4.1.2

“Old” Materials in Early Lightweight Designs the Productive 1920s

4.1.2.1 John Dudley North In 1917, almost at the same time that Kemp formulated his theoretical proposition that fibre-reinforced plastic was a lightweight material suitable for aeroplane construction, the ambitious aeronautical engineer John Dudley North (1893–1968) (Fig. 4.10) began to set up an aircraft development department for the British manufacturer Boulton and Paul Aircraft in Norwich.37

37 Crocombe (1970), p. 787 f., Anon (1968), p. 75.

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Fig. 4.10 John Dudley North (1893–1968), the first aeronautical designer and later director of the British manufacturer Boulton & Paul Aircraft, in 1919. Source Flight. The Aircraft Engineer and Airships, 1919, No. 49, Vol. XI, p. 547

North, who had initially studied shipbuilding in the family tradition, soon took up aircraft construction after first becoming an aviator himself. When he also won a model aeroplane competition of the magazine Aeroplane, he began to work more intensely on aircraft construction, initially building gliders. A short time later he was employed as chief engineer at Grahame-White Aviation Company which had just been founded by the aviation enthusiast Claude Grahame-White (1879–1959) in Hendon, Middlesex in Great Britain.38 It was here that North designed his first serial-production aircraft, the GrahameWhite Type X Charabanc passenger biplane. This aircraft could carry nine passengers and stay in the air for twenty minutes, which in 1913 set the world record. Two years later, John North moved to the Royal Aircraft Factory for a short time to oversee a light reconnaissance biplane model, Royal Aircraft Factory R.E.7, built for the Royal Flying Corps. This is where North first became acquainted with the subject of lightweight construction and took an interest in the principle of all-metal aircraft.39 The inadequate armament on board the R.E.7 brought payload transport to the fore as an alternative application. The consequence of this was the rededication of this aeroplane into a lightweight bomber. The design of aircraft components for agile aeroplanes, taking the corresponding payload horizons into account, was a new field of activity for North. John North’s decision to transfer to Boulton and Paul Aircraft in 1917, where he was offered the opportunity to set up a development department for new aeroplane models, was a logical step for him to take. North’s design of the Boulton and Paul P.3 Bobolink, a single-engined fighter, was a continuation of his previous work at the Royal Aircraft Factory. It also marked the final transition for Boulton and Paul into aircraft manufacturing. (It had hitherto been making wooden houses.) That aeroplane was unable to compete with a rival model, however, and did not progress beyond prototype status. 38 Lewis (1962), p. 284 f. 39 Crocombe (1970), p. 787 f.

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Fig. 4.11 The Boulton and Paul P.10 at the Parisian Salon de l’Aéronautique 1919. The tail, wings and part of the fuselage had not been planked in order to reveal the structure. The P.10 was the first British all-metal aircraft and probably the first practical application of fibre-reinforced plastic in aircraft design. Source Flight. The Aircraft Engineer & Airships, 1919, No. 1, Vol. XII, p. 12

Nevertheless, North was able to develop the Boulton & Paul P.10, putting into practice the topics of lightweight construction and stability.40 Unlike the previous model, the airframe of this aircraft was not made of wood but of rolled steel elements, and the rear fuselage consisted of a monocoque, i.e. a fuselage in a stressed-skin construction. This shell construction, which had rarely been used before, was not the only innovation. North also created the first multi-material design with metals and an early fibre-reinforced plastic. The fuselage envelope was made of load-bearing dilecto panels, a licensed bakelite product.41 Boulton and Paul exhibited the P.10 at the Parisian Salon de l’Aéronautique in 1919 (Fig. 4.11). Because of its supporting dilecto panels and profiles out of steel piping and rolled steel, the biplane was hailed as the aircraft of the future. The dilecto plates, which Boulton and Paul had supposedly developed themselves, were presumably rather imported goods from the USA, manufactured by Continental-Diamond Fibre Co.42 It is unlikely that the panels were an in-house development of Boulton and Paul and this is presumably a journalist’s interpretational error.43 What had probably been meant was that North had adapted the dilecto panels to the aircraft structure, and had conceived the technical joining aspects of the fibre-reinforced composite to the metal:

40 Brew (1993), p. 170 f. 41 Spooner (1920), p. 11 f., id. (1919), S. 1612. 42 Meikle (1995), p. 57. 43 Brew (1993), p. 28 f.

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rivets. By using this novel load-bearing plate material, North had entered new terrain in aircraft design in both technical respects. The material of these plates was a phenol–formaldehyde product, i.e. a bakelite resin with embedded layers of paper. This bakelite product from Continental-Diamond Fibre Co. was marketed under the licensed brand name dilecto, primarily for attractive tabletop surfaces and door panelling as well as for insulating elements in the electrical industry. John North designed the P.10 primarily as a prototype aeroplane for the military. He wanted to demonstrate his skills and innovative spirit as well as recommend Boulton and Paul as a supplier. The biplane constituted a novelty in British aviation, because it was the first aeroplane with an all-steel structure. However, it was not the first British all-metal aircraft. That had already been drafted in 1910 by the British naval lieutenant John W. Seddon (1886–1969) jointly with Alfred George Hackett (1880–1974) and bore the name Seddon Mayfly.44 The steel structure found favour as a true innovation and underwent further development in the years to come. But the utilization of fibre-reinforced composite skin in a segmental construction remained exclusive to this aircraft for a long time. The decisive aspect is that this composite material was thus initiated into practical aircraft design. Furthermore, and of relevance to this account is, on one hand, the innovative aspect of lightweight construction and, on the other hand, the comprehensive solution found in engineered materials, which North purposefully introduced into aircraft design. He argued that the utilization of dilecto panels could also be regarded as an extensive solution to other technical problems involving materials in aircraft design.45 In contrast to wood, the hitherto conventional aeronautical material, its panels were neither hygroscopic nor susceptible to insect infestation and also had high fire resistance. Moreover, his decision to use this material was a lasting response to the mechanical and medial stresses on metals in aviation operations, which usually ended up as corrosion. Although North worked with traditional techniques and used rivets and bolts to join individual material segments as was typical in the aviation industry, he introduced a previously undefined group of materials into aircraft construction which combined the properties of metallic and non-metallic materials and was even superior to these groups in many areas.

4.1.2.2 Albin Kasper Longren Much more extensive use of early fibre-reinforced composites can be ascertained in the technical developments by Albin Kasper Longren (1882–1950), the son of Swedish immigrants in the USA and a technical autodidact. His first major technical achievement came at the age of 23 when he designed and built an automobile and drove it around his hometown, which attracted regional attention.46 His technical talent got him hired as an inspector of gasoline engines, among others for the 44 Spooner (1910), p. 733 f. 45 Brew (1993), p. 172. 46 Lambertson (2015), p. 64 f.

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Santa Fe Railway. At first, he did not let on that he had since turned his attention to aircraft construction. It was not until he had completed his aircraft design, Topeka I, which he presented to the public in 1911, that he drew notice nation-wide. With the money he earned from demonstrations of his aeroplane, he built up a business in Topeka, Kansas.47 The quality of his biplane was so convincing that he was able to build and sell a whole series of this model. The company collapsed when one of his planes crashed and his investors withdrew. During World War I, he accepted a job as aircraft inspector at McCook Field in Dayton, Ohio.48 There Longren made the acquaintance of numerous pilots, engineers, and aeroplane manufacturers and could profit by their expertise in aeronautical research. Longren returned to Topeka after the war, taking the knowledge he had gained in Dayton with him, and began to design a new aircraft and establish a new aeroplane manufacturing company. His idea was to bring to market an aircraft that was both simple and easy to build. He described the target customer of his aeroplane as being “the doctor, the rancher, the traveling man, and the farmer.“49 It was to become a “Ford” of the skies. He completed his new model: The New Longren Airplane, in 1921. It was a two-seater biplane (Fig. 4.12) constructed in the building-block style.50 With this aircraft Longren set standards for aviation with two decisive innovations. He designed the fuselage as two complete semimonocoques. A few earlier aircraft models already had a monocoque fuselage, but they had always been made of wood and as a segmental construction.51 Longren designed his fuselage monocoques as two complete shells, however, and similar to John North, used a composite material that already existed. Longren thus probably developed the first fibre-reinforced composite fuselage monocoques ever for an aircraft, by modifying for his application vulcanized fibre—that laminate composite material patented in 1859 by the Briton Thomas Taylor—which is the second central innovation. To achieve this, Longren developed a mould for the fuselage monocoques which he lined with vulcanized cellulose-fibre sheets in three layers, planked them on both sides with rotary-cut veneers and compressed them (Fig. 4.13). With two patents in 1922, Longren secured both his idea of a building-block aircraft and the production of the fibre-reinforced composite fuselage monocoques.52 These fuselage monocoques represented a significant innovation and improvement in terms of stability and made a decisive contribution toward simplifying production and assembly. Longren had thus met his own claim to build an aircraft for everyone. Because the Longren AK, as the aeroplane was also called, had retractable wings, the plane could be efficiently stored away in a barn.

47 Bush (2011), p. 1 f. 48 Lambertson (2015), p. 64 f. 49 Anon. (1921), p. 47. 50 Spooner (1922), p. 331 f. 51 On the development of monocoque construction, see also Hassinger (2013), p. 45 f. 52 Longren (1923a), thes. (1923b).

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Fig. 4.12 Excerpt from the patent by Albin Longren from 1922, which shows in Fig. 1.1 the basic structure of the Longren AK. In Fig. 1.2 Longren describes, on one hand, the stressed-skin structure of the fuselage and, on the other hand, that the semimonocoques should be made of vulcanized fibre in a single piece. Source Patent specification Albin Longren, 1922, US Patent No. 1,541,976

The technical quality of the material and the stability of the fuselage, and even the technical properties of the Longren AK during flight in practical tests were persuasive. In 1921 the aircraft won the looping flight category both at the Legion Flying Meeting in Kansas City as well as at the Omaha Meeting.53 The military was interested in the aircraft as an inexpensive make and also in the materials used. Not only was the monocoque fuselage very convincingly stable and robust, but it was also excellently bullet-resistant. The elastic layered structure of the hybrid-material composite braked projectiles in stages, removing so much energy as they penetrated the last two layers that they got lodged in the side of the aircraft. Longren considered the military a good partner in a cooperative arrangement. Evidence for this is that he already contacted the military at the founding of his new aviation company and by 1921 was already listed as an official aircraft engineering service provider

53 Spooner (1922), p. 331.

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Fig. 4.13 Excerpt from Albin Longren’s second patent from 1922, in which he describes the manufacture of fuselage semimonocoques by means of a preformed shell mould. Regarding Fig. 1.2, he indicates that a thin rotary-cut veneer is first placed inside the mould, three layers of vulcanized fibre mats are placed on top of it, and these are then covered with a face veneer. Under pressure and heat, this hybrid material construction is then compressed into stable fuselage semimonocoques for the aeroplane, as shown in Fig. 1.3. Source Albin Longren patent specification, 1922, US Patent No. 1,471,906

for the US Army.54 The US Navy ordered three prototypes of the Longren AK in 1924 and held out the prospect of further funding.55 The materials utilized in these aircraft (i.e. fibre-composite systems) were supposed to undergo thorough bullet-proof testing for future military aircraft. Reservations by the decision-makers in the military ultimately prevented the introduction of modified vulcanized fibre as a load-bearing material in aeronautics. The preference was rather to take recourse in conventional metallic materials. However, the moulding technology that Longren had developed for aircraft models of his own design as well as for others and his metal-processing methods were readily taken up by military and civil aircraft engineers. Since he had neglected to secure these things under patent law, he was unable to enter into any partnership with them. Longren’s aircraft manufacturing venture failed again because he placed his design aspirations above commercial manufacturing.56 As a result, he initially found employment as a technical advisor in aircraft and mechanical engineering. The company he founded a short time later concentrated on the moulding and supply of metallic components and aggregates in aircraft design. His customers in the aircraft manufacturing sector included Douglas Aircraft in Santa Monica, Lockheed in Burbank, Boeing in Seattle, and the then 54 Spooner (1921), p. 238. 55 Spooner (1924), p. 558. 56 Lambertson (2015), p. 64 f.

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still fledgling company Northrop in Burbank. In old age, he decided to sell his company in 1945 and retire to his ranch. John North and Albin Longren can both be seen as pioneers belonging to an early generation of fibre-composite users. Whereas it had hitherto been assumed that early bakelite resin-based composites were not suitable for load-bearing structures in technical systems, mainly because of their brittleness, these early examples prove the opposite. By choosing to use dilecto panels, John North opened up new horizons for materials technology in the field of aeronautics. He was the first to demonstrate the potential that risk-taking in materials design and constructive adaptability afforded. The extent to which Albin Longren was informed about North’s work is unknown, although it is not unlikely that the parameters of the P.10 became known since the Parisian Salon de l’Aéronautique of 1919 among the then still very limited community of specialists. Longren probably had no reservations about considering a plastic for supporting structures. However, his quest for a simple design and production method was pursued far more radically. He modified a familiar “old” material, as North had once done with his dilecto panels. He adapted vulcanized fibre, another extant laminate composite material, by lining a compression mould with sheets of cellulose fibre. This process is almost identical to the draping of modern fibre-composite structures on an appropriate manufacturing mould.57 North and Longren struck out on new paths in materials technology and design, thanks to the rapidly growing and promising aeronautical industry of the time and the enterprising spirit of its investors.

4.2

A High-Performance Material Matrix From Polymer Chemistry in the Early 1920s

Substances of high molecular weight, above all natural rubber, sparked the interest of chemists s early as the nineteenth century, even though many of these substances—initially dismissingly referred to as “grease” or “resins”—seemed not to offer any scientific or practical added value.58 From 1850 onwards, substances such as cellulose and its esterification, nitrocellulose, as well as proteins such as serum or casein, were taken up and new technical fields of application emerged, for example, insulation materials required in the electrical industry. For lack of the related analytics, the chemical structure of these substances was hardly known. The scientific and practical leap into the age of plastics is primarily and inseparably associated with the chemist and Nobel laureate Hermann Staudinger (1881–1965), although some of his postulates on polymer chemistry were already known, discussed

57 Flemming (1999), p. 24, 58 f. 58 Heim (2013), p. 56 f., Braun (2012), p. 310.

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and published before then.59 Staudinger deserves credit for having recognized the large molecular structure of these substances. His papers on the subject, published between 1919 and 1922, set in motion a broad-ranging scientific dispute, which he was able to decide in his favour just under a decade later.60 Staudinger presumed that the substances in question were not made up of small molecules, as was being assumed, nor locatable within colloidal chemistry, but rather were composed of large molecules, which he called “macromolecules”.61 Staudinger predicted that “his” macromolecules were not only scientifically valuable, but also had potential for practical application. He thus not only laid the foundation for macromolecular chemistry, but also set in motion extensive national and international research and development in this field. An extensive plastics industry was forming at this time and materials science was expanding broadly.62 Staudinger’s research activities were not inconsiderably influenced by the endeavours of the dye trust I.G. Farbenindustrie AG, which lent him support as what was to become the dominant German company in this sector.63 Polymer chemistry also laid the foundations for a highperformance supporting matrix for fibre-reinforced plastics by enabling the shift away from practical optimization of the plastic masses, that is, early resin systems, towards technically adjustable materials design at the molecular level.

4.2.1

“Engineered Stability”—Layered Presstoff, a Modern Fibre Composite

The change away from the foregoing bakelite resin products, whose stability and physical appearance depended largely on the fillers used, towards defined composite materials of calculated strength occurred at the beginning of the 1920s. The emergence of macromolecular chemistry granted greater freedom in designing the bearing matrix and its material properties; but the embedded materials also experienced change. Carefully devised reinforcing materials now replaced the former simple fillers, such as wood flour, crushed shells or coal dust, whose proportions had determined the stability of the resin products. New product specifications thus replaced the rough list of filler ingredients with exactly defined fibre tapes. A pioneering role in this area was played by the compression-moulding factory (Preßstoffwerke) of Heinrich Römmler AG in Spremberg, Lower Lusatia. The phenolic formaldehyde condensation process that Römmler AG had developed in parallel with the 59 See, among others, Weber and Deussing (2013), p. 81 f., Braun (2012), p. 311 f., Mühlhaupt

(2004), p. 1072 f., Deichmann (2001), p. 249, Priesner (1980), p. 350 f. 60 Staudinger (1919), p. 1 f., 28 f., 60 f., id. (1920), p. 1073 f., Staudinger and Fritschi (1922), p. 785

f. 61 Mülhaupt (2010), p. 121, Ringsdorf (2004), p. 1064 f., Priesner (1987), p. 151 f. 62 Lechner et al. (2003), Haka (2011), p. 72, Kaiser (1991), p. 44 f. 63 Plumpe (1990), p. 319.

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Bakelite Company gave it a considerable technical lead over other companies in the area of synthetic resin production. The company started to expand its product line already early in 1920 in the course of revamping its equipment, especially its compression technology.64 This was carried out with an eye not only to the resin systems but also to the stabilizing materials. Consequently, an early extension of the Römmler AG product range was fibrous materials arranged in layers. This numerically defined material design was thus probably the first truly modern fibre-reinforced plastic of the twentieth century. The transition from the pressed-mass moulding compound (Preßmasse) to laminated presstoff (Schichtpreßstoff ) marks the birth of modern fibre-reinforced polymers. Pre-impregnated paper and fabric tapes were used as the reinforcing materials with a defined load-bearing pattern to yield specific material parameters (such as strength) gauged by those parameters of metallic materials. Contrary to the conventional manufacture of bakelite products, compression moulds were not used in the production process. Instead, continuous material tapes were pre-impregnated by machine with a slow-curing resin, such as cresol resin.65 These fibre tapes then passed through a production line that heated them up to 120 ºC, during which both the alcohol and water content in the resin evaporated away. This effectuated an initial hardening process of the fibre tapes without them losing their binding ability. The subsequent cutting into plates enabled a defined stacking of the individual fibre pieces and final pressing into panels. The automated impregnation process just described was borrowed from the enamelling industry as early as the beginning of the 1920s and adapted for impregnation of the mentioned fibre tapes. It still corresponds, with a few minor technical modifications, to current-day wet lamination of woven fabrics, mats or rovings.66 This was a technical standard that has experienced a revival or been drawn into focus by manufacturers in production today as a purported “new invention”. The parameters such as pressure, temperature and pressing times, which were more controllable as a result of the mentioned advances, determined the panel quality, then just as they do now. The associated quality management likewise changed. Whereas quality control used to be carried out at the end of the production process, it henceforth began with the inspection of the fibre tapes prior to processing. For example, the paper used as a reinforcing material had to have good absorbency and a certain degree of evenness to ensure its ability to run smoothly through the machinery. For this reason, soda pulp paper was usually used for this material. Similar requirements were also placed on fabrics used as reinforcement. Primarily highly absorbent cotton fabric was utilized or else a fabric blend of cotton and cellulose. The original processing of rags of different quality grades for cost reasons was soon replaced by specially defined material textiles in various weaves, in order to be able to guarantee a uniform quality standard. 64 Römmler (1938), p. 34, 61, Bürgel (1934), p. 519 f., Wiesenthal (1934), p. 110 f., Brandenburger

(1933), p. 253 f., id. (1932), p. 73 f. 65 Mehdorn (1939), p. 211 f. 66 Flemming et al. (1999), p. 29 f.

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Later, asbestos fabric and mixed fabrics were added as reinforcement materials. After a year of trials, serial production finally started in 1925 with phenolic, cresol and urea resins as the supporting matrices. Materials in plate and tube form were manufactured in various quality grades. In the technical jargon of the day, these materials were referred to as layered moulded materials (geschichtete Preßstoffe) and set standards both in terms of their material stability and their associated design applications.67 Römmler AG designed these panels for the furniture industry, e.g. for use as tabletops or door panels, on the one hand, and for carriage, ship and vehicle building industries, on the other. One example with broad technical impact was the laminated presstoff used in the rigid airship LZ 127 Graf Zeppelin, which was put into service in 1928. In this airship, such panelling with hard-paper laminate was used as load-bearing wall segments in the passenger lounge and dining room (Fig. 4.14). To reduce the fire hazard, the walls were also given a 0.2 mm-thick aluminium foil backing, which added additional stability to the walls.68 The wall construction made of pressed materials for the cabin area was convincing, if only because of its lower weight compared to conventional wooden structures. In addition, unlike wood, presstoff did not absorb moisture and could not corrode like metallic materials. The textile department of the Institute of Materials Research at the German Aviation Research Institute (DVL) in Berlin-Adlershof, which was involved in the development of this material, considered this layered moulded material as a promising option for various research projects. Nevertheless, presstoff was not able to establish itself as a construction material in aviation. The layered presstoff used in such a famous object as the Zeppelin airship was good publicity and significantly raised interest in such panelling materials by Römmler AG, especially among interior decorators. One of the most sought-after and best-known brand names in this segment was RESOPAL.69 Due to their low specific weight, these panels were primarily used as cladding material for walls or to cover fittings. The material was a resounding success. After World War II and the forced expropriation and dismantling of the factory, Römmler-Werke was rebuilt in the GDR under the name VEB Sprela-Werke Spremberg. RESOPAL panels were marketed there under the brand name Sprelacart and were primarily used as supporting panels in kitchens.

67 Weigel (1942), p. 18 f. 68 Kraemer (1933), p. 388. 69 Brandenburgisches Landeshauptarchiv, Rep. 75 Chem. Werke Römmler 18 [hereafter BLHA]: see

the account about RESOPAL and aminoplast processing by Römmler AG, which began in 1927, and Brachert (2002), p. 38 f.

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Fig. 4.14 View into the dining room of the rigid airship LZ 127 Graf Zeppelin, the interior walls of which were made of layered presstoff. These pressed panels were wallpapered for decorative reasons. Source Postcard 1929, Graphic Department of Luftschiffbau Zeppelin GmbH

4.2.2

Machine Elements as “Fibre-Composite Pioneers”—the Development Between 1925 and 1945

In addition to producing the already mentioned product family of laminate plastics, Römmler AG also continued to manufacture simple filler-based synthetic-resin products used, among others things, as light switches, fittings, insulating housings or containers for the chemical industry.70 These so-called compression moulded parts (Formpressteile) represented the company’s largest product range by virtue of the sheer number of variants. The so-called presstoff plain bearings (Fig. 4.15) were its most challenging product, however. With the start of production of machine elements, engineered design, the machining and finishing of the material as well as quality control of the final product became the focus of its attention. This segment was new territory for Römmler AG. Between 1928 and 1945, it was the sole company in Germany to cover the entire production spectrum from the raw plastic material to the end product. It is remarkable that it was able to develop and manufacture such a broad product portfolio (Table 4.2). In anticipation of the expiration of the heat-pressure patent in 1931 and the resulting release of synthetic-resin production onto the free market, Römmler AG expanded its development and production of presstoff plain bearings. Its manufacture of this machine 70 See the in-house description of all Römmler semi-finished products (BLHA, Rep. 75. Chem.

Werke Römmler 32) and Römmler (1938), p. 59.

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Fig. 4.15 Bearing bushings and shells made of presstoff (i.e. phenoplast, with wound fibrous tape as filler, brand name Gerohlex GR) by Römmler AG for use in mechanical engineering. Source Handbuch der Römmler Presstoffe, Römmler AG 1938, p. 142

Table 4.2 Römmler AG product range at the beginning of the 1930s in the field of synthetic-resin plain bearings. Author’s compilation (on the basis of Römmler AG 1938, p. 138 f.) Material/trademark

Composition

Processing type

Gerohlit

Phenoplast with organic yarn (asbestos) as filler

Pressed into thermoset dies; compression moulding

Gerohlit ST Deurolith N Deurolith S

Phenoplast with cellulose chips as filler

Deurolith NG Deurolith SG Gerohlex G Gerohlex F Gerohlex GR Gerohlex FR

Phenoplast with fibre tapes as filler Pressed into plates in progressive presses Phenoplast with wound fibre tape as filler

Wound on mandrils and then pressed into shape

element constituted its commercial entry into this branch of mechanical engineering with all its versatile applications. The unique selling point of being able to offer a machine element made of synthetic resin won Römmler AG a monopoly position and it could exert considerable influence on the price regimes of suppliers in this segment of mechanical engineering.

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The properties of the new group of synthetic-resin hybrids had hitherto been exclusively reserved to metallic materials, and by producing machine elements from just these materials, this firm heralded in a new design culture in mechanical engineering. Machine elements including the afore-mentioned plain bearings were fundamental to machine design, since they were used in the same or similar form and function in other machinery as well.71 With the advent of turbomachinery, electrical generators and the associated significantly higher shaft speeds, a whole series of aspects in mechanical engineering took on new significance in the design, manufacture and operation of machines: for instance, the inherent rigidity of a shaft, the vibration stress of component parts and aggregates, the heat transfer and the lubrication of the bearings.72 Up to that point, machines had mainly been conservative in design, i.e. the emphasis having been placed on mass and stability. At the beginning of the twentieth century, the search began for new approaches in their design. New scientific findings, especially in physics, the developing field of technical thermodynamics, and fluid mechanics, were taken as guide-lines—all this in pursuit of the best possible efficiency, which had become numerically determinable. The majority of this knowledge arose from scientific developments in the second half of the nineteenth century. A large number of machine elements underwent extensive technical development, sometimes reaching the stress limits of the materials used. The quest for new design approaches was therefore also a quest for new materials or combinations of materials in order to be able to meet the changed requirement profiles. The bearing played a special role here, since there was and still is hardly any other machine element that has such a decisive influence on the performance of a machine. The metallic materials preferred until then for bearings, such as bronze, were put to the test one after another and had to hold their own against synthetic-resin hybrid materials. Central properties, such as vibration resistance, tribology, running performance and above all lubrication, had to be re-evaluated and taken duly into account in the design. The quantities and tools used in the manufacturing process also underwent revision. The efficiency and low cost of synthetic-resin products, in general, eventually paved the way for the synthetic-resin bearing as well. The first manufacturing specializations soon followed within synthetic-resin production. Whereas the production of syntheticresin panels, e.g. for table tops or doors, was relatively crude, the production of presstoff plain bearings had to be much more precise. Soon accuracy was no longer measured in millimetres but in micrometres. Further refinement of the control system in press technology was unavoidable. In particular, the heating and cooling times, the permanent control and qualitative maintenance of the resin systems and the pressing regime became control variables and qualitative prerequisites for the presstoff plain bearing as a product. The entire chain in the production process thus became much more important than before. 71 Haka (2014a), p. 192 f., Haberhauer and Bodenstein (2011). 72 Cf. Haberhauer and Bodenstein (2011), Affenzeller and Gläser (1996), Heidebroek (1939).

4.2

A High-Performance Material Matrix From Polymer Chemistry …

4.2.3

141

First German Presstoff Plain-Bearings Research in Darmstadt and Dresden

In the course of the afore-mentioned development of these hitherto preferentially massive machine designs, during the first two decades of the twentieth century mechanical engineers inevitably began to concentrate their focus on the bearing. Its layout and design and the related compatibility as well as the manufacturing and technical load horizon of the material were considered as an overall complex, in other words, it was viewed holistically. But due attention was also paid to the functionality of the bearing in terms of shaft design, operating characteristics and lubrication. The latter was attended by a re-evaluation of the use of natural crude oil in favour of synthetic lubricants; and the search commenced for the best suitable bearing material or alternatives in materials technology. However, many of the problems encountered in practice with machine elements, and especially with bearings, were initially tackled purely theoretically. Researchers in German mechanical engineering did not address this discrepancy between theory and practice until very late. It was not until the early 1920s that many detailed questions could be resolved in greater depth. One of the first and most important figures in German mechanical engineering to grapple with high-speed machines at a very early stage, was the mechanical engineer Enno Heidebroek (1876–1955) (Fig. 4.16).73 His pioneering work on plain-bearing systems, in particular, and the associated issues concerning tribology, brought him unrivalled recognition (which outlasted diverse political systems) at the polytechnics in Darmstadt and later Dresden. Heidebroek’s research is extraordinary in multiple respects and spans four decades. The broad scope of his research and development ranges from basic research, venturing far beyond the bounds of the specialist discipline of mechanical engineering, to design and manufacturing aspects, to the chemical development of lubricants. His investigations in the field of constructive design in mechanical engineering—classical plain-bearing development—ranges from the conceptual design to the final choice of metallic material and has already been treated in an earlier publication of mine.74 An account of his developmental work on natural and synthetic lubricants is reserved for a more extensive study. Heidebroek chose a theoretical approach for his bearing research, the study of hydrodynamic theory, which already existed at that time. In particular, his research work on hydrodynamic bearing friction, begun in Darmstadt and continued in Dresden, should be mentioned.75 Considering his experiences in industry (from 1902 until his appointment to the Darmstadt chair in 1911, he had been employed as a technical manager and developer 73 Enno Heidebroek’s chair at the TH in Dresden was called: Lehrstuhl für Grundlagen der Maschinenkunde und Fördertechnik. For a detailed account of his research or more about his academic network, see: Haka (2014a), p. 192 f., and on his “hydrodynamic theory”, esp. p. 228 f. 74 For more information on the development of plain-bearing research, see Haka (2014a), p. 202 f. 75 During this period Heidebroek studied publications by Sommerfeld (1904) and on the subject of hydrodynamic theory, the publications Petrow (1927), Gümbel (1917) and Stribeck (1902); cf. Heidebroek (1939), Heidebroek, E. Meine technische Lebensarbeit p. 4 (Archiv des Vereins zur Förderung von Studierenden der TU Dresden [hereafter AFTUD]: Enno Heidebroek papers). For

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Fig. 4.16 Enno Heidebroek, mechanical engineer and holder of the chair for fundamental mechanical engineering and transport technology at the polytechnic in Dresden (photograph: Heeresversuchsanstalt Peenemünde 1940). Heidebroek established the Laboratory for Bearings and Lubrication Research, which was later transformed into the Institute of Lubrication and Bearings Research. Source Enno Heidebroek papers, AFTUD

of pumps in mechanical engineering companies in Berlin and Halle an der Saale), it is not surprising that his research should treat topics of such immediate interest to industry.76 Although Heidebroek was initially attracted to engine design in Darmstadt, he soon began to concentrate on the bearing as a central machine element. Heidebroek presented his first documented results on bearings research as early as 1914 before the VDI, the most important association of engineers in Germany at the time. He was to return there to use it increasingly as a discussion platform for his research results.77 His ambition to verify practically the model of hydrodynamic theory led Heidebroek into new territory and he can be regarded as a pioneer in this field within his discipline. His research in Darmstadt was able to show for the first time in the years that followed that the actual processes in a plain bearing can be represented only to a limited extent by the classical hydrodynamic theory and that new approaches were needed to obtain

more in-depth information on Heidebroek’s theoretical and practical approaches to hydrodynamic theory, see Haka (2014a), p. 227 f. 76 Employment opinion on Enno Heidebroek as head of the technical office (period from 1902 to 1903) at Maschinenfabrik Gans & Co. Berlin dated 12 Sep. 1903, notice of employment for Enno Heidebroek as head of the newly founded “Department for Centrifugal Pumps” at the firm Weise & Monski in Halle an der Saale, as well as correspondence between Enno Heidebroek and the board of Weise & Monski between 1903 and 1911 (AFTUD, Heidebroek papers). 77 Heidebroek (1914), p. 1018 f.

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applicable results.78 Heidebroek’s intense examination of questions concerning the surface roughness of shafts and bearing bushings as well as their wear were almost exclusively material-induced and identify him and his early work as a German pioneer in the then nascent field of tribology.79 While studying bearing systems, a new world in materials technology opened up for him by virtue of his proximity to industry. A position he held in addition to his academic post on the supervisory board of his father-in-law’s brown-coal company, Gustav Hasse Braunkohlengesellschaft near Merseburg, brought him repeatedly into direct contact with the steel industry.80 There he observed the replacement in rolling mill technology of bronze bearings by presstoff bearing shells.81 The supplier of these bearings was Römmler AG in Spremberg. This company had already been producing plain bearing systems out of various pressed materials since 1928.82 It had begun with an extensive in-house trial in which bronze bearing shells of a transmission ring bearing were replaced by prototype presstoff shells in a dust-contaminated room. The test run of this bearing covered 4000 h without any sign of wear or cracks on the bearing shell. This result was the trigger for the company to dedicate itself to the design and manufacture of presstoff plain bearings. Initially, the focus was limited to two types of presstoff plain bearings.83 The first was the so-called full bushing, in which a wound textile fibre tape was coated with phenolic or cresol formaldehyde resin and then hot-pressed by machine, and secondly, the hybrid bushing, in which thin layers of hard paper were pressed or glued onto a compression moulding shell. Later, mineral materials such as asbestos were added as shell materials, or else paper and textile shreds for less stressed bearing systems. Römmler AG eventually turned to the renowned mechanical engineer Enno Heidebroek in order to have the mechanical suitability of its presstoff plain bearings verified by a neutral authority.84 The research project initiated at the beginning of 1936 between Römmler AG and 78 Heidebroek, E., Meine technische Lebensarbeit, Dresden, 1950 (unpublished memoirs) (AFTUD,

Heidebroek papers). 79 Tribology deals with the scientific description of friction, wear and lubrication. The technical term

“tribology” was not introduced until 1965. Hence, Enno Heidebroek was not familiar with this term. See Haka (2014a), p. 234 f. for more details. 80 For detailed information on Enno Heidebroek’s family circumstances, see Haka (2014a), p. 192 f., especially on kinship relations, see p. 198 f., 201 f. 81 Renate Heidebroek, née Hasse, Ein Gedenken an ihre Jugend, recorded by Friedrich Hasse (unpublished manuscript) (AFTUD, Enno Heidebroek papers), see also Ministerium für Raumordnung, Landwirtschaft und Umwelt des Landes Sachsen-Anhalt, ed. (2000) as well as Heidebroek (1939), p. 48, Gümbel (1917), p. 236 f. 82 Report to Russian officers of 18 Sep. 1945 on Römmler AG products (BLHA: Rep. 75 Chem. Werke Römmler 23). 83 Report to Russian officers of 18 Sep. 1945 on Römmler AG products (BLHA: Rep. 75 Chem. Werke Römmler 23), as well as Heidebroek’s notes about his investigations for Römmler AG and Dynamit AG Troisdorf from the years 1935–1939, 1941–1944 (AFTUD, Enno Heidebroek papers), and Heidebroek (1950), p. 11 f. 84 For a summary of the results of the Römmler trials, see Heidebroek (1950), id. (1937a, b).

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Heidebroek comprised both a technical materials analysis and a technical examination of how the entire product range of presstoff plain bearings functioned. Heidebroek’s confirmation that the quality of Römmler’s presstoff bearings was remarkable and his assessment of a wide range of possible applications for the bearings in mechanical engineering contributed significantly to the company’s decision to continue to expand in this area and develop presstoff bearing systems further. In 1938, the findings of the renowned mechanical engineer Heidebroek were passed on to its customers, industrial partners and offices of the Wehrmacht in the form of excerpts in the so-called Römmler-Handbuch.85 Heidebroek immediately recognized that presstoff plain bearings as high-performance bearing systems could pose an alternative in mechanical engineering design or, depending on the application, at least serve as a supplement. In addition, the presstoff plain bearings opened up an elegant opportunity for him to present his academic research on hydrodynamic bearing friction in a targeted manner.86 The material and design properties of a presstoff plain bearing enabled him not only to consider the bearing in its individual components (bearing material, shaft and lubricant), but also to study their affinity to each other. Abandoning high-quality oil lubrication in favour of water with the addition of a small quantity of grease opened up new maintenance prospects in practical usage and promised remarkable service lives for material and machine alike. The presstoff plain bearing, which functioned with a particularly thin film between the shaft and the shell (in contrast to classical bearings with an oil film as lubricant), was ideally suited for him to investigate so-called boundary friction. This is a central aspect of the operational reliability of a bearing. The description of the molecular forces between shaft and shell and the associated description of absorption effects and polarities of oil molecules led Heidebroek far into the fields of chemistry and physics. The Laboratory for Bearings and Lubrication Research, which he established after moving to Dresden to take up his chair at the polytechnic, acquired the status of an institute in its own right after 1945. Heidebroek’s professorship and, above all, his laboratory can be seen as the central hub of German bearings research and particularly presstoff plain-bearings in the 1930 and 1940s.87 The work on presstoff plain bearings soon called for the development of an appropriately specialized testing machine. A custom-made machine (Fig. 4.17) was built in 1934 in Dresden by Hille Motoren AG as a unique model. This company in the field of engine and vehicle construction also built tools and specialized machinery, including a number of other testing machines for Heidebroek’s laboratory, such as the ones produced in 1939 and 1942.

85 Römmler (1938), p. 144 f. 86 Heidebroek (1941), id. (1936). 87 See Heidebroek “Meine technische Lebensarbeit” (unpublished manuscript); see also “Chronik.

Gewidmet unserem hochverehrten Institutsdirektor Herrn Prof. Dr.-Ing. Dr.-Ing. e.h. Heidebroek anlässlich seines 75. Geburtstags von den Mitarbeitern des Instituts für Allgemeine Maschinenkunde und Maschinenelemente” including the staff of the affiliated Laboratorium für Lager- und

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Fig. 4.17 The first of three presstoff plain bearings testing machines developed by Enno Heidebroek in 1934 in the Laboratory for Bearings and Lubrication Research at the Dresden polytechnic. It was used to investigate the stress limits of presstoff plain bearings. All three of these models by Enno Heidebroek were dismantled by the Red Army shortly after its arrival in Dresden in 1945, as reparations. Source Enno Heidebroek papers, AFTUD

Heidebroek also organized a local network of mechanical engineering companies, which initially installed presstoff plain bearings in their machines on a trial basis and later incorporated them serially. In addition to Hille Motoren AG, they included, for example, the Dresden firms Universelle-Werke J. C. Müller & Co. and Brückner, Kanis & Co.88 The testing technology developed by Heidebroek and his laboratory became particularly important during World War II when a large number of armaments contracts were entrusted to him.89 In this situation, Heidebroek was able to append a chemical laboratory to his institute (Fig. 4.18) specialized in the testing of synthetic-resin products and specifically of presstoff materials. A quite inconsiderable number of qualifying academic theses and research topics were assigned in connection with Heidebroek’s professorship

Schmierungsforschung, dated 15 Nov.1951. (AFTUD, Enno Heidebroek papers); for further details about Heidebroek’s researches at TH Dresden in general, see also Haka (2014a), p. 219 f. 88 Reports I–IV by Enno Heidebroek between 1942 and 1945 on his experiments for the company Hille Motorenwerke in Dresden on bearing materials and bearing systems (Universitätsarchiv der TU Dresden [hereafter UA TUD]: 64, Fak. MW/Abt.). On the Dresden armaments research network, see Haka (2014a), p. 264 f. 89 See the correspondence between Heidebroek and the factory director Lucas of AEG, Henningsdorf plant, dated 25 May and 1 June 1943 (UA TUD: 93, Fak. MW, Wissenschaftlicher Schriftwechsel), as well as the memorandum from the desk of OKH Wa Chef Ing 1 dated 31 May 1943 (ibid.).

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Fig. 4.18 The assistant to Prof. Heidebroek, Dipl.-Ing. Rudolf Scheiner, examining materials for presstoff bearings in 1943 in the chemical laboratory affiliated with the Dresden chair. Source Enno Heidebroek papers, AFTUD

and were published as well, provided they did not fall under the secrecy provisions for technical matters of military relevance.90

4.3

Römmler AG Versus Dynamit Nobel AG

After the expiration of the heat-pressure patent for bakelite in 1931, development of presstoff materials accelerated, especially laminate presstoff and presstoff plain bearings.91 The way was now open for other companies to use the phenolic formaldehyde condensation process for the production of synthetic resins. Thus, presstoff started to attract wider public attention. Technical associations such as the VDI and state testing authorities in particular began to study such materials more comprehensively.92 This was becoming essential, because a large number of companies of various sizes promptly started to offer synthetic-resin products of diverse quality on the free market.

90 Cf. inter alia Döring (1940), id. (1939); qualifying theses are listed in Haka (2014a), p. 229, Table

4.11. 91 Gebhardt (1929), p. 181. 92 Cf. Maier (2010), p. 156 f.

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147

Fig. 4.19 Presstoff inspection seal for Römmler AG. The stylized letters M and D in the seal logo stand for Materialprüfungsamt Berlin-Dahlem. The number 32 is the manufacturer’s identification number, in this case Römmler AG. The letter S stands for the simplest type of such compressed thermoplastics: phenolic resin with a wood-flour filler. Source Prüfprotokolle, Rep. 75 Chem. Werke Römmler; BLHA

The first comprehensive technical regulation of this market in Germany occurred in 1936 with the issuance of the already mentioned standard DIN 7701, defining such compressed synthetic-resin thermoplastic compounds.93 Efforts to regulate the technical and commercial aspects of presstoff materials date back to the early 1920s. By categorizing these materials into a classificatory system, synthetic-resin products were systematized for the first time on a broader scale and technically quantified by defined mechanical and thermal characteristic values.94 The use of presstoff materials in the electrical industry and in the area of insulation led in 1928 to the first extension to the previous characteristic values, adding electrical conductivity and thermal conductivity. Henceforth presstoff was divided into different types of materials, each with its own production-related technical parameters. Four years later, the national Materials Testing Office in Berlin-Dahlem (MPBD) took over the task of testing presstoff materials according to the previously established quality characteristics as a neutral authority and, in this context, issued its presstoff certification seal (Fig. 4.19). This certification seal, attached to the respective product, allowed the manufacturer to guarantee its quality. It also revealed the specific type of compression moulded material used in the given piece. This inspection seal was not compulsory for manufacturers but merely a recognized mark of quality. In 1937, the MPBD refined its testing canon for these presstoff materials by adding the “notched toughness”95 value.96

93 DIN-Normblatt 7701 Kunstharz-Preßstoffe, warmgepreßt. Haka (2011), p. 81, Beuth-Verlag

(1937). 94 Fachgruppe “Kunststoffe” der Wirtschaftsgruppe Chemische Industrie (1935), p. 217 f. 95 Kerbzähigkeit, meaning: bending strength in a notched bar test. 96 Cf. Nitsche (1943), Krassowsky (1943), p. 78, Mienes (1939), p. 5, Leysieffer (1938), p. 555.

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The DIN standard was extended in 1943 to accommodate further developments in these compressed thermoplastics. In that year, synthetic resins were also subdivided into patent classes in order to limit the increasingly dubious mixtures of presstoff materials appearing on the market under ever changing fantastical names.97 These developments are easily traceable in the Reich Patent Register. Class 39 contains all the innovations of most importance in the plastics industry at that time. The expanding German plastics market led to a subdivisioning of class 39 at the beginning of the 1930s. This indicates that presstoff materials had been undergoing development on a considerable scale for some time already. Class 39a (Group 19.06) drew into account the processing of fibres and woven fabrics impregnated with a plastic.98 This meant that early fibre-reinforced plastics had become established as a material in Germany. It can therefore be asserted that by the early 1930s, wet-laminated fibre-reinforced plastic as we know it today in materials science was already available to technical users at a noteworthy level. Although increasing numbers of companies began to offer synthetic-resin products since the expiration of the patent, two companies had already divided up the market between themselves and had the lucrative sales firmly in hand through patenting or licensing. One of these was the former leader in the German market, Heinrich Römmler AG Preßstoffe in Spremberg, Lower Lusatia, and the other was Dynamit Nobel AG in Troisdorf. Römmler’s products dominated the German market for a relatively long time. Although well over a hundred companies were manufacturing compressed thermoplastic items in Germany after the patent was revoked and Römmler’s product range of high-quality presstoff materials was considerable, Dynamit AG, which was superior in terms of capital and resources, dominated this market segment from 1933 at the latest. Dynamit-ActienGesellschaft (DAG)—formerly Alfred Nobel & Co.—as the company was called from 1932 onwards, was a corporate empire born of the company of the dynamite inventor and Nobel Prize donor Alfred Nobel (1833–1896).99 At the time of the merger with RheinischWestfälische Sprengstoff AG (RWS) and other smaller explosives firms in 1931, DAG had a total share capital of 47 million reichsmarks and was the largest explosives and ammunition manufacturer in Germany. The contractual ties between DAG and the chemical concern I.G. Farben, which Hermann Schmitz (1881–1960) and Fritz Gajewski (1885–1965) established as members of the boards of both companies in the 1930 and 1940s, gave the Troisdorf site had almost unlimited resources for the development and production of presstoff materials. 97 In 1943, the VDI (Association of German Engineers) and the VDE (Association of German

Electrical Engineers) decided that “compression moulding materials” (Formpreßstoff ) are materials which are produced in a pressing tool in which there are randomly distributed, non-continuously layered fillers (with the exception of types T3 and Z3, which are layered presstoff materials and were renamed types 57 and 77 in 1943); “laminated compression moulding materials” (Schichtpreßstoff ) are pressed materials with continuously layered fillers, such as woven fabric tapes. In addition, DIN 7701 is divided into four new DIN standards—DIN 7704 to DIN 7707. 98 Vieweg (1939), p. 1053 f., Beuth-Verlag (1937), Anon. (1933), p. 134. 99 Haka (2012), p. 7 f., id. (2011), p. 74 f., Dederichs (2008), p. 25 f., Heine (1990), p. 131, 161.

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149

From 1925 onwards, under the direction of the plant director, the chemist Gustav Leysieffer (1889–1939), preparations were made in DAG’s own plastics factory for an all-round entry into production and analysis of compressed thermoplastic, both for processing as structural materials and for applications in mechanical engineering—especially presstoff bearings. For this purpose, presstoff materials available on the market were comprehensively examined, developed further and subsequently new products of their own designed, reusing left-over stocks of synthetic resins from RWS. The technical processing know-how gathered by Römmler AG over the years could not be copied so easily or recouped by Dynamit AG. Therefore, in view of the imminent revocation of the heat-pressure patent, DAG went on the offensive in early 1930. After various negotiations, a contractual agreement was reached behind closed doors in 1933 which gave both companies far-reaching manoeuvring room.100 Römmler AG granted Dynamit AG access to its clientele in Germany and also made its complete technical know-how and ongoing developments available to it royalty-free. At the same time, Römmler AG terminated all patent and licensing disputes with I.G. Farben, which had close contractual ties with Dynamit AG, and from then on the two companies regarded themselves as a consortium sharing common interests and production aims. Römmler AG also committed itself to purchasing all its raw materials for synthetic-resin production exclusively from Dynamit AG. In return, Römmler AG received an annual payment of 60,000 reichsmarks from DAG. At the same time, Römmler AG received the right to act as the sole supplier of laminate presstoff materials and to continue to concentrate on expanding its production of presstoff plain bearings as well as other machine elements, such as gear wheels. In exchange, Dynamit AG took over the production of the major synthetic-resin product groups “housing” and “insulation materials”. This division also affected existing trademark products. This confidential agreement was not visible on the market, as Dynamit AG’s in-house retailer, Venditor Kunststoff-Verkaufsgesellschaft in Troisdorf, distributed the products of both companies with immediate effect.101 Römmler AG benefited from this agreement to a quite considerable degree. For example, it began right away to produce the branded laminate TROLITAX, a trademark of Dynamit AG in improved quality. However, this product continued to be identified as a Dynamit AG product, which was possible because the resin system was supplied by DAG and the final inspection step was also carried out in Troisdorf. The production and further expansion of plain-bearing systems in the high-priced mechanical engineering sector was a profitable line of business for Römmler AG. The development and production of gear wheels, sealing rings and washers made of presstoff promised high profits in a hardly surveyable market at that time.

100 Contract between Römmler AG and Dynamit Nobel AG dated 1 July 1933 (BLHA: Rep. 75 Chem. Werke Römmler 18). 101 Letter dated 18 Nov. 1934 between the DAG and Venditor. (Rep. 75 Chem. Werke Römmler 11).

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Presstoff, an Emancipated “Substitute Material”?

Latest by the mid-1930s, the development of laminate presstoff had progressed so far as a material utilized in mechanical engineering in Germany, for instance for engine bearings, that in various cases the quality was even rated above that of metallic bearings and it was used instead.102 Both Römmler AG and later Dynamit AG offered a wide range of products in this field and had them comprehensively tested by Enno Heidebroek at the Dresden polytechnic.103 The stamp of excellence of the bearings issued in Dresden, as well as at the MPBD, certified both companies as the leading manufacturers of compressed thermoplastic and presstoff plain bearings. When the National socialists rose to power and not long afterwards promulgated their Four-Year Plan in 1936 with the consequential intensification of nazi autarky efforts, both companies came to regard the military as a lucrative partner.104 The impression has arisen that synthetic-resin products were used merely as substitutes in everyday applications and as specific substitutes for metallic materials, such as for bearings. My investigations show a completely different picture, however. At the time of the German self-sufficiency drive, presstoff materials had reached such a high technical level of development as a manufacturing material that they often posed as a real alternative to metallic materials by virtue of their characteristic values and modest production cost. The German rearmament with its associated restrictions on materials strongly promoted the utilization and rapid assimilation of synthetic-resin products in the otherwise conservatively minded mechanical engineering sector. The afore-mentioned research and testing results by the plain-bearing expert Enno Heidebroek and the MPBD demonstrate the high level of development that a large number of presstoff products had attained and their technical progress during this period, which was entirely independent of the economic self-sufficiency efforts. Given this background, it was a logical step for DAG as a manufacturer of explosives and ammunition to intensify its long-standing contacts with the military resp. the Wehrmacht with regard to its product range, as a commercially active company in tandem with its partner Römmler AG.

102 Enno Heidebroek. Technischer Forschungsbericht. Zwischenbericht Nr. 21. Laufversuche eines

Automobilmotors mit Preßstofflagern auf der Kurbelwelle (AFTUD: Enno Heidebroek papers). 103 Heidebroek’s research reports of 6 June and 27 July 1942, and 16 Sep. 1944, for DynamitActien-Gesellschaft Troisdorf at the TH Dresden (UA TUD: A/872, Berichte und Diagramme über Verschleißversuche an Kunstharz-Pressstoffen im Auftrag der Dynamit AG bzw. A/887, Lageruntersuchungen, Versuchreihe GW-01). For more information on Heidebroek’s research and testing of bearings at his Dresden institute, see Haka (2014a), p. 244 f. 104 On the subject of NS autarkic manufacturing materials (Werkstoffe) see, among others, Maier (2010), p. 146 f., id. (2007), p. 66, Luxbacher (2011), p. 46 f., id. (2004), p. 7 f., Löser (1991), p. 73 f.

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151

The general director of Dynamit Nobel AG, Paul Müller (1876–1945, and his brotherin-law, the chairman of the supervisory board and Wehrwirtschaftsführer Hermann Schmitz (1881–1960), had already worked for the military authorities during World War I and therefore regarded the military as a regular and reliable partner, and a good network was already in place.105 It is therefore not surprising that the military was already being counted on as a client for Troisdorf’s synthetic-resin products as early as the beginning of 1930. In particular, the Troisdorf firm and Römmler AG perceived the application areas for their plastics to be in mechanical engineering and the automotive industry. The first major defence order for Dynamit AG came at the end of 1935, to develop and produce vehicular bodies in parts or one piece for the model DKW F-8 (Fig. 4.20), which was manufactured by Auto Union AG. The material used carried the brand name DYNAL. The cooperation with Römmler AG and its far-ranging technical competence in the field of laminate presstoff led to the production of a series of body parts being carried out in Spremberg. DYNAL was a layered compressed moulding material with a cellulosebased hard-paper insert. DYNAL was designed as a semi-finished product, i.e. cellulose tapes pre-impregnated with a resin system were laminated onto an appropriate surface mould106 (Fig. 4.21). This process is almost identical to the draping of modern fibrecomposite structures on suitable production moulds.107 This is illustrated by the process registered by Auto Union AG in Chemnitz for preshaping hollow bodies with layers of fibrous material impregnated with synthetic resin.108 The prototype model achieved roadworthiness status and went into military field testing as a small-scale series. In the first year after the opening of the market in 1931, about a hundred companies started manufacturing synthetic resin products in Germany. By 1940, the number of manufacturers had already increased fivefold.109 Whereas synthetic-resin products were generally advertised primarily as a new everyday material, Dynamit AG and Römmler AG began to devise military applications for their synthetic-resin products.110 The afore-mentioned aspects thus answer the first guiding question posed at the beginning: on the one hand, when were composites first considered as lightweight materials and, in particular, as structural materials for the purpose of industrial utilization? and on the other hand, in which product group can they be found? The work of Römmler AG with regard to the industrial use of presstoff in mechanical engineering in bearing systems had already been established, whereby press materials were used here primarily as ancillary or supporting materials. However, it was not until the strategic alliance was agreed 105 On the interlinked corporate relationships at Dynamit AG, see also Haka (2011), p. 74 f. 106 A semi-finished product is preshaped by application onto a moulding surface. 107 Lamination process by hand/wet lamination process, see Flemming et al. (1999), p. 23 f. 108 Auto-Union A. G. (1940). 109 Staatliches Materialprüfungsamt Berlin-Dahlem (1942), p. 277 f. 110 See the Römmler AG and Dynamit AG product catalogues for tableware and interiors from 1934

to 1945. In this context, see also the training documents for sales, especially for the distributor Venditor Kunststoffvertriebsgesellschaft (BLHA: Rep. 75. Chem. Werke Römmler 11).

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Fig. 4.20 Prototype of a car door made of the laminate presstoff DYNAL for the model DKW F-8, a vehicle for the German army manufactured by Dynamit AG in 1938. Source Mehdorn 1939, p. 191

Fig. 4.21 Cross-section of a production mould (no. 1 in the patent drawing) onto which the prepreg cellulose tape (no. 11) is laminated with a hand roller (no. 12). The manufacturer Auto-Union in Chemnitz applied for the patent in 1936, which was granted in 1940. Source Patent—Auto-Union Chemnitz, Patent No. 684981, 1940

between Römmler AG and Dynamit AG that the first plans were made for the industrial use of presstoff materials in product segments of lightweight construction and structural materials. The above-mentioned planned serial production of a presstoff-based car body was one product which my investigation was able to identify and one enterprise it was able to localize.

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Römmler AG Versus Dynamit Nobel AG

4.3.2

153

Top-Secret Order on “Presstoff”—Compressed Thermoplastic in Armaments Research and Production in the 1930s and 1940s

Presumably with the issuance of the presstoff inspection seal by the MPBD from 1932 onwards, but certainly at the latest with the founding of the Technical Committee on Plastics and Presstoff in the VDI just three years later (and the concomitant standard DIN 7701), compressed thermoplastic had become established as a hybrid material for technical products in Germany.111 At that time, the general public still perceived presstoff as a new material primarily intended for everyday items, which first had to prove its merit against classical metals and other materials. As early as the end of 1934, military authorities in the Reich Ministry of Armament and Ammunition were planning to use presstoff on a large scale in military equipment.112 With the outbreak of war in 1939, the first step was, to found the Independent Special Ring for Plastics and Presstoff at the Reich Ministry of Armament and Ammunition, which expert panel was later renamed “Hauptring Kunst- und Preßstoffe”.113 The allocation of chemical resources, such as various resins and chemical resin additives, was done in coordination with the Reich Office for Economic Expansion (which was headed by Carl Krauch (1887–1968), general plenipotentiary for special questions of chemical production and simultaneously a board member at IG Farben) as well as with the Department for the Distribution of Synthetic Resins and Pressed Masses at the Reichsstelle Chemie, under Claus Ungewitter (1890–1946).114 Several subordinate Arbeitsringe or expert working committees operated under the Hauptring (Fig. 4.22). These mediated between the state authorities with their defence technology requirements and the leading manufacturers of compressed thermoplastics, such as Römmler AG, Dynamit Nobel AG, Bisterfeld and Stolting Radevormwalde or Allgemeine ElektricitätsGesellschaft (AEG) in Hennigsdorf near Berlin, as well as various weapons contractors in Germany and the Protectorate of Bohemia and Moravia. Initially, the chairman of the above “Main Ring on Plastics and Presstoff”, Gerhard Lucas (1886–1970), was in charge. He was head of sales for insulating and presstoff materials at AEG in Hennigsdorf and also chaired the Technical Committee on Plastics and Presstoff of the VDI.115 Quite a few of the contracted companies in the Protectorate had their own proving grounds to test their weaponry for the 111 Mehdorn (1934). 112 For popular reporting about presstoff, see: Wiesenthal (1933), p. 84 f., id. (1932), p. 111 f. 113 Selbständiger Sonderring Kunst- und Preßstoffe beim Reichsministerium für Bewaffnung und

Munition. Maier (2015), p. 298. 114 On the Reichsamt für Wirtschaftsausbau or national socialist research funding and Carl Krauch, see Maier (2016), p. 283 f., Flachowsky (2015), p. 198 f., Maier (2016), p. 283. 115 Reports and correspondence from the companies Dynamit Nobel, Römmler AG, Bisterfeld & Stolting, AEG and Hauptring für Kunst- und Preßstoffe, the Reichstelle Chemie and Reichsamt für Wirtschaftsausbau in the period from 1940 to 1945 (BLHA: Rep. 75 Chem. Werke Römmler 4, 9, 10); minutes of the meeting of the VDI Fachausschuss Kunst- und Preßstoffe, Arbeitsgruppe Prüfung von Preßstofflagern under the direction of Enno Heidebroek on 25 May 1943 (UA TUD: 94, Fak. MW, scientific correspondence of Heidebroek from N to Z, 1942–1947).

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Army High Command OKH

Reich Ministery of Armament and Ammunition

chief of Army armaments & commander of army reserve

Weaponry Committee Special Commission “ArtilleryI”

General Army Office AHA Special Staff A Major-General Hans von Hanstein

commissioner on plain-bearing issues in the Main Committee on Weaponry

head: Factory Director Gerhard Lucas (AEG)

head: Wilhelm Wolfstieg (Rheinmetall-Borsig)

(also chairman of the Technical Committee on Plastics & Presstoff of the Engineers Association VDI)

Army Ordnance Office WA Prüf 1 Sr.Government Councillor Dr. Kutterer

Commissioner of the Four-Year Plan Plenipotentiary on Special Issues in Chemical Production

Wa J Rü Mun 2 Major Abendroth Wa Chef Ing 1 Ministerialrat Steinmüller WA Chef Ing 3/Hz Dipl.-Ing. Rust Wa Prüf 4,5, 6 and 7 Lt. Colonel Schmidt

Vulnerability Assessment Centre (S.A.Z.) (Düsseldorf) head: Sr.Planning Officer Sallandt Army Inspections Division at Th. Bergmann & Co KG Velten shooting and trial range of the Army for presstoff materials Dynamit Nobel AG (Troisdorf) Prof. Paul Müller manufacture of presstoff moulded parts for all the Armed Forces Venditor KunststoffVerkaufsgesellschaft GmbH retail head: Dr. Elbel (Troisdorf) Römmler AG (Spremberg) Director Eberhard Römmler Techn. Director Dr. Albert Kuntze manufacture of presstoff plain bearings and bushings for all the Armed Forces

Main Ring on Plastics and Presstoff

State Materials Testing Office Berlin MPBD

Carl Krauch (IG Farben)

Prof. Nitzsche Prof. Bußmann

Reich Office on Economic Expansion Department Chem. IV

testing of presstoff products

Dipl.-Ing. Tschacher

Working Committee on Pressed Moulded Parts

Reich Office for Chemistry Dr. Claus Ungewitter

head: Director Dr. Holm, (Scherb & Schwer firm, Berlin)

distribution dept. for synthetic resins & pressed masses Dr. Blankenfeld

Head of the Working Committee on Lignine Pressed Masses (fabric-based laminate) Dr. Pfahler (Dynamit Nobel AG, Troisdorf) Working Committee on Hard Paper Dr. von Hartmann Römmler AG, Spremberg

Bakelit Gesellschaft GmbH Erkner/Berlin Director Rieß production of twist caps for longdistance grenade launchers Commercial Group Chemistry Tech. Group “Plastics” overseer of Department III synthetic-resin pressed compounds

Working Committee on Fabric-based Laminates head: Director Flötgen (AEG, Hennigsdorf)

AEG (Henningsdorf, Osthavelland) head: Director Flötgen presstoff plain-bearings for the tanks programme

Fig. 4.22 Network of the most important German compressed thermoplastics manufacturers, their expert bodies, testing and trials facilities, in the context of German armaments production in the year 1940/1941. The products were: Presstoff plain bearings, presstoff bushings and laminate presstoff panels. Reinforcement materials: hard woven fabric and hard paper (bearings, bushings and plates), glass-fibre fabric (plates), resin matrix: cresol-resol, phenol-resol, aniline-formaldehyde and from 1944 on also lignite phenol as a substitute resin. (Thick connecting lines = production supply, thin lines = information flow). This network diagram (excerpted) was compiled on the basis of correspondence from and to Römmler AG (Brandenburgisches Landeshauptarchiv) and from E. Heidebroek found at the Bundesarchiv, the Archives of TU Dresden, Sächsisches Hauptstaatsarchiv and AFTUD. Diagram by the author. See the List of Abbreviations for the designations of the Army Ordnance Office (Heereswaffenamt) resp. the Heeresamt (AHA)

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Römmler AG Versus Dynamit Nobel AG

Aachen polytechnic Prof. Herwart Opitz, chair for tooling machines & operations theory Head of Main Committee on Tanks and Tractors for the reichminister on armaments and war production

155

Berlin polytechnic

Darmstadt polytechnic Prof. August Thum chair for materials science

Prof. Wilhelm Röhrs Institute of Research on Plastics and Coatings

Materials testing office, Darmstadt polytechnic, characteristic values of presstoff plain bearings

Trials and evaluation of presstoff materials

Prof. Richard Vieweg Institute of Technical Physics

testing of presstoff plain bearings

plenipotentiary on synthetic materials heat-transmission testing of plain bearings

Dresden polytechnic Prof. Enno Heidebroek, chair for fundamental mechanical engineering and transport technology

Maschinenfabrik und Eisengießerei Ing. J. Vlatavský in Rakonitz (now Okres Rakovník) Protectorate of Bohemia and Moravia

head of the Laboratory for Research on Bearings and Lubricants at the Dresden polytechnic testing station for sliding elements of OKH (1939–1940) operating and organization manager of Army Testing Station in Peenemünde

Eng. Valdimír Vlatavský, Eng. Milen Vlatavský, Jirí Vlatavský businessman trials and production of fabric-based presstoff bushings for tanks and tractors (Daimler-Benz 10)

head of the Working Group on Testing Presstoff Plain Bearings at VDI Pressing and Turnery Factory “Spilba”– Kaiser & Pirkl in Libáň Protectorate of Bohemia & Moravia

(from 1943) commissioner on the conversion of rolling bearings to plain bearings for all the Armed Forces

Engineer Valec twist cap manufacturing and testing for long-distance grenade launchers

Focke-Wulf Flugzeugbau GmbH Bremen Senior Engineer Schmiedle

Škoda-Werke Pilsen (Plzeň) Protectorate of Bohemia & Moravia

presstoff plain bearings testing at Focke-Wulf Fw 190

driving trials of tanks with presstoff and composite plain bearings

Engineer Kohl

prototype manufacture and testing of pure-presstoff aircraft segments (fabric-based laminates and glassfibre woven fabrics)

Servotechna AG Prague Protectorate of Bohemia & Moravia presstoff twist-cap manufacturing and trials

Lumophon-Werke Nürnberg Dipl.-Ing. Jantsch Ernst Heinkel Flugzeugwerke AG (Rostock)

testing of throat microphones of layered presstoff (fabric laminate and hard paper) for tank speaker apparatus, for OKH

Dipl.-Ing. Roggelin testing of presstoff plain bearings and Harex presstoff plates (aviation)

testing of aniline formaldehyde as a supporting matrix German Aviation Research Institute (DVL) Berlin-Adlershof Institute of Manufacturing Materials Research Dr. Paul Brenner Dipl.-Ing. Hans Perkuhn Dipl.-Ing. Wilhelm Küch presstoff prototype construction and materials analysis for various aeroplane types

Fig. 4.22 (continued)

IG Farben AG (Frankfurt am Main) Arado Flugzeugwerke Brandenburg/Havel Dipl.-Ing. Feld testing of presstoff plain bearings and lubricants (aviation)

Dr. Jakob production and analysis of synthetic lubricants for presstoff plain bearings

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Germans. This was carried out in cooperation with various Wehrmacht units, the Waffen-SS and the Heereswaffenamt as well as the Materials Testing Station in Berlin-Dahlem, and their tested products were also adapted there if necessary or developed further.116 These testing and production facilities paid off when from 1942 onwards the Allies increasingly began to bomb production facilities in Germany. Many companies committed to the armaments industry especially in the Protectorate of Bohemia and Moravia were able to supply the Wehrmacht with war equipment and machine elements until shortly before the war ended.

4.3.2.1 Competency Disputes About Where to Apply the Materials Technology The mostly theoretical flanking and validation of presstoff products for implementation by the armed forces was in the hands of a number of universities and academic teachers. For example, the technical physicist employed at the Darmstadt polytechnic, Richard Vieweg (1896–1972), kept abreast of the developments in synthetic resins in particular and analysed compressed thermoplastic products generally as the plenipotentiary on plastics. Another such influential figure was the mechanical engineer Herwart Opitz (1905–1978) from the Aachen polytechnic, who studied the design of plain bearings made of presstoff materials and the related functional issues. As head of the main committee on tanks and tractors at the Reichsministerium für Rüstung und Kriegsproduktion, Opitz concentrated primarily on technical equipment for deployment in the army. This is in stark contrast to the afore-mentioned mechanical engineer and leading expert on plain bearings in Germany at the time, Enno Heidebroek, who had begun to investigate and develop presstoff plain bearings systems early on, in the 1920s, and cooperated with all the branches of the Wehrmacht in the area of armaments research. This is explained by the fact that Heidebroek held a whole range of offices and functions on expert boards and thus maintained an impressive network (Fig. 4.22) with contacts in research, industry and politics.117 As early as 1914, Heidebroek was the first mechanical engineer in Germany to sensitize the VDI to the topic of bearings research and used this association of German engineers as his primary discussion platform for his own research findings.118 As a member of the main board of the VDI in Berlin (term of office 1923–1926), he promoted research into machine elements and continued to do so in his capacity as head of the Technical Committee on Machine Elements and as head of the Working Group on Testing Presstoff Plain Bearings in the VDI.119

116 Haka (2014a), p. 260 f. 117 On Heidebroek’s expert committees and offices, see in depth Haka (2014a), p. 310 f., 319. 118 Heidebroek (1914), p. 1018 f. 119 Cf. Heidebroek (1937a), id. (1937b).

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157

Heidebroek’s proposals regarding the use of presstoff plain bearings in army vehicles caused some annoyance already at the beginning of 1942 for Gerhard Lucas, the chairman of the Main Ring on Plastics and Presstoff.120 Lucas had his own opinion about the design, production and application of presstoff plain bearings. A number of unresolved technical issues still existed, such as the thermal stability under continuous stress or the mechanical medial load capacity, which up to that point had only been investigated on the basis of prototypes. No sufficiently validated results were available yet. Due to these deficits, Lucas wanted to create a solid technical basis and have the remaining open questions resolved within the framework of a conclusive research project at the State Materials Testing Office in Berlin. As he saw it, the presstoff plain bearings produced by his company (AEG) ought to be used for this purpose and, where necessary, improved. This project should also develop an initial quality control for presstoff plain bearings produced by other suppliers to the Wehrmacht. To this end, Lucas attempted to standardize a short testing procedure normally used at AEG. In his function as head of the Main Ring, Lucas had even single-handedly initiated a corresponding order for this at the Materials Testing Office. Lucas presumably wanted to have his own company’s presstoff plain bearings awarded the quality seal issued by the Materialprüfungsanstalt in order to reserve for it the ability to sell large quantities of thus certified bearings to the armed forces in Germany. Heidebroek held his ground against Lucas here and argued that introducing machine elements without the cooperation of the Army Ordnance Office (Heereswaffenamt), which Lucas vehemently opposed, would not make sense. Heidebroek had already prepared and delivered technical equipment for deployment in World War I as head of an automotive branch factory of Fahrzeugtechnik Eisenach and regarded cooperation with Army Ordnance as a mandatory prerequisite to successful operations.121 Heidebroek explained in this dialogue that under combat conditions technical equipment was often subjected to exceptional stresses and that a practice-oriented testing regime for the plain-bearing systems was therefore required. The dispute between Lucas and Heidebroek escalated and led to Gerhard Lucas being removed from office after Major-General Hans von Hanstein (1883–1975) appointed the Laboratory for Research on Bearings and Lubricants led by Enno Heidebroek at his chair in the Dresden polytechnic as the central testing laboratory for sliding elements for the German Army High Command (OKH).122 Hans von Hanstein was head of Special Staff A (the staff for furnishing army equipment, technical personnel and maintenance) as well as head of the General Office of the Army (Allgemeines Heeresamt AHA). Although Lucas continued to chair the Main Ring, he confined himself to administrative matters from then on. 120 Cf. the exchanges between Gerhard Lucas and Enno Heidebroek of 25 May and 1 June 1943 (UA

TUD: 93, Fak. Masch. Schriftwechsel). 121 Haka (2014a), p. 206 f. 122 See the memo from the OKH chief designer (Wa Chef Ing 1) dated 31 May 1943 (UA TUD: 93, Fak. MW, Wissenschaftlicher Schriftwechsel).

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The testing regime for plain bearings developed by Heidebroek especially for suppliers of compressed thermoplastics ultimately prevailed and represented realistic moments of load for army vehicles on the ground. Heidebroek summarized this testing regime and the associated framing conditions in the “technical terms of delivery for bearings, sliding blocks and other parts made of presstoff”.123 The regime included, in addition to a pragmatic machine load test, trial runs of these machine elements in test vehicles driven in the heath just thirty minutes away from the polytechnic in Dresden. In this context, Heidebroek was also able to refer to earlier tests he had conducted with his local collaborator, Georg Beck (1901–1943), the former head of the Institute of Automotive Engineering at the Dresden polytechnic, who had relocated to Dresden from his position in Berlin as head of the Automotive Testing Station of the Army Ordnance Office. In a joint research project, Heidebroek and Beck had already tested the application potentials of crankshafts wrapped in hard-fabric presstoff for engines in military vehicles at the beginning of 1939 and therefore were very well informed about the problem areas of then-current technical equipment under wartime conditions.124 Lucas ultimately had to give way to Heidebroek and his testing regime when the AEG plain bearings fell behind those by Römmler AG in terms of material quality and manufacturing costs.125 After due inspection, the licensed production of presstoff plain bearings by the AEG process was immediately stopped by the Technical Office and the Armaments Supply Office under the reich minister of armaments and war production. Heidebroek’s recommendation favouring the technically further advanced and materially better conceived principle of the Römmler presstoff plain bearing was finally taken as a production template for Wehrmacht suppliers from 1944 onwards.126 Heidebroek became involved in almost all aspects of rolling and plain-bearing applications within the German armaments industry, whether on questions of design, material selection, manufacture or testing, when he was appointed in 1943 commissioner on the conversion of rolling bearings to plain bearings, as part of the rapid-action project Schnellaktion Schweinfurt.127 As commissioner Heidebroek also promoted the selection of presstoff plain bearings wherever the technical conditions permitted. At the same time, he concentrated on the special lubrication of these bearings with new synthetic lubricants, which showed less signs of deterioration over time and were less prone to attract bacteria. 123 Technische Lieferbedingungen für Lager, Gleitschuhe und andere Teile aus Preßstoffen. See

the correspondence between Enno Heidebroek and the OKH on 23 Mar. 1944 (UA TUD: A/878, Fakultät für Maschinenwesen, Zusammenarbeit mit dem Oberkommando des Heeres bei der Prüfung von Preßstoffbuchsen, Laboratorium für Schmierungs- und Lagerforschung, 1943–1945). 124 Döring (1940), p. 1. 125 See the memo on the meeting between OKH and Römmler AG of 23 Feb. 1944 (BLHA: Rep. 75. Chem. Werke Römmler 11). 126 See the letter from Römmler AG dated 21 Feb. 1944 to the OKH semi-finished products division, Wa Chef Ing 3 Hz (ibid.). 127 On this rapid-action project or Heidebroek’s involvement in it, see for details Haka (2014a), p. 214 f.

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Heidebroek was formally required to report to Erich Rosenthal, the managing director of the manufacturing division in the technical office (Amtsgruppe Fertigung im Technischen Amt) of the Reich Ministry of Armaments and War Production, regarding the progress made in the conversion from roller bearings to plain bearings. But Heidebroek was de facto the final academic authority on the conversion operation directly under Albert Speer as reich minister of armament and war production. His appointment as commissioner turned him into a contact point for representatives of all the branches of the armed forces, suppliers and members on technical boards such as at the VDI.128 The use of compressed thermoplastic plain bearing systems mainly covered technical equipment for the army and air force, in particular tanks and tractors, passenger cars, anti-aircraft guns and aeroplane engines using newly developed synthetic lubricants. Approximately 60% of the installed presstoff plain bearings in armaments production were manufactured by Römmler AG.129 From 1939 onwards, the main producers of presstoff plain bearings for military applications to come forward besides Römmler AG, apart from the main suppliers of lubricating oil for military applications under separate cooperation agreements with Dynamit AG in Troisdorf and the chemical concern IG Farben, were Schäfer-Preßstoff GmbH in Berlin (primarily for aircraft engines), Bisterfeld and Stolting Radevormwalde, the iron foundry Eisenhüttenwerke Thale in the Harz Mountains, and Allgemeine Elektricitäts-Gesellschaft (AEG) in Berlin. The network described above permits the naming of a number of central actors in the sense of the second key question posed at the beginning: To what extent can central actors be identified who have promoted the development of composite materials? For identification purposes, a simple network analysis on centrality and prestige has been carried out here.130 In the present case, the centrality measure used was degree centrality, which divides the total number of direct neighbours of a node (actor) by the total number of edges (relationships) connecting the actor to other nodes.131 The correspondence which I have found and evaluated132 on central aspects of the development of composite materials has served as a basis, such as, on research in general, on developers, actors within the context of component design and testing, on manufacturing and processing, as well as on applications. In the selection process briefly described above, the following key actors could be identified for the period from 1920 to 128 See the correspondence between E. Heidebroek and M. Koehler dated 15 and 20 May and 6 June

1944 (UA TUD: 64, Fak. MW/Abt. Maschinenbau). 129 Cf. the report to Russian officers of 18 Sep. 1945 on Römmler AG products (BLHA: Rep. 75. Chem.Werke Römmler 23). 130 For basics and terminology see Jansen (2003), p. 53 f. 131 On the identification of dominant network actors and the related procedures of network analysis, see in depth Haka (2014a), p. 22 f. 132 For this purpose, the sources evaluated were: correspondence by the Römmler AG (Brandenburgisches Landeshauptarchiv), the Enno Heidebroek papers, documents from Bundesarchiv, the University Archives of the TU Dresden, AFTUD, the archives of the Horten family and the private holdings of Dr. Kärcher and Dipl.-Ing. P. Selinger.

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1945: Leo Hendrik Baekeland (entrepreneur, Bakelite Gesellschaft), Eberhard Römmler (entrepreneur, Römmler AG), Albert Kuntze (Römmler AG), Gustav Leysieffer (Dynamit AG), Paul Müller (Dynamit AG), Enno Heidebroek (TH Dresden), Paul-August Koch (TH Dresden), Friedrich Tobler (TH Dresden), August Thum (TH Darmstadt), Richard Vieweg (TH Darmstadt), Gerhard Lucas (AEG), Paul Brenner (DVL), Wilhelm Küch (DVL), and Kurt Riechers (DVL).

4.3.2.2 Specialized Navy and Army Orders for Römmler AG The Römmler joint-stock company supplied project-related presstoff plain-bearing systems to the navy but on a far smaller scale than for the army and air force. In one of these projects, the company was involved in the development of presstoff plain bearings required to satisfy maritime conditions. The plain-bearings expert Enno Heidebroek from the Dresden polytechnic was also involved as a cooperation partner, because this project involved the development of a complete system. Starting with the design of a new plain bearing and specific choice of compressed thermoplastic material and appropriate lubrication, the project followed right through to the integration of the bearing in different engine models. Römmler varied the composition of different fabric-based laminates with regard to weave density and type (for improved and more durable properties during operation) as well as with regard to the plastic supporting matrix (susceptibility to deterioration by a saline solution).133 The navy even wanted a “technical camouflage cover” for these bearings, which on the design side required special salt resistance for the seal between that machine element and sea water, in order to avoid lubricant leakage into the water. To this design challenge was added the development of a lubricant not detectible in water. This requirement was one aspect of the enemy-detection strategy to suppress any chemically identifiable signature of machine aggregates in water. Coupled with this was another project—namely, reorientating the issues involving bearings and lubrication to the torpedo engine. The presstoff bearings required for comparative purposes were supplied by Internationale Galalith-Gesellschaft in the Harburg suburb of Hamburg, and the lubricants were provided by IG Farben in the form of a series of experimental oils.134 The navy participated in addition with its Chemisch-Physikalische Versuchsanstalt der Marine in Eckernförde. The presstoff plain bearings developed in this way by this group of developers for the

133 Memorandum on the start of the project in November 1942 and the progress report of the project,

undated (UA TUD, A/885, Verzeichnis der Forschungsarbeiten und Inventar der Prüfgeräte am Lehrstuhl Prof. Heidebroek 1943–1944). 134 Letters from Enno Heidebroek to I. G. Farben dated 17 Nov., 3 and 10 Dec. 1942, regarding lubrication trials in Kiel and Eckernförde, as well as the letter dated 16 Dec. 1942 from Heidebroek to Römmler AG and Internationale Galalith-Gesellschaft Hamburg-Harburg regarding the testing of synthetic presstoff bushings for the Kriegsmarine High Command (UA TUD: A/881, Fakultät für Maschinenwesen, Laboratorium für Schmierungs-und Lagerforschung. Lager-und Schmierungsversuche für MAN und Kriegsmarine, 1942–1943).

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propulsion engines of submarines and torpedoes were ready for operation at the beginning of 1944. A special order placed by the army with Römmler AG was to develop “special pressed mass no. 3721”. The first negotiations with the OKH about it occurred at the end of 1939. The “recipe” for this special pressed compound was classified as secret (Geheime Kommandosache) and was the material used to make the twist cap (Drallkappe) of shells for the “long-distance” rifle grenade launcher (“Weitschuss” Gewehrsprenggranate) and later also for other models. The twist cap formed the upper part of this grenade. The cap could be easily twisted off the shell to then be thrown as a hand grenade. Presstoff was used here as a stable lightweight material, which did not affect the ballistics of the grenade when it was fired, but shattered when the grenade hit the ground and triggered its head fuze. The twist cap was made of a special compressed thermoplastic with a supporting matrix consisting of various resin components, such as phenolic and cresylic resins, as well as magnesium oxide. Initially, veneer wood chips were used as reinforcement material, but later, due to the negative hygroscopic properties of wood, this was replaced by hard-paper cuttings.135 This shell could be fired with a rifle grenade launcher at a range of about 200 m and was preferably used to engage targets in trenches, bunkers or fortified buildings.136 The Römmler twist caps were tested at the Army Inspections Division in Velten near Berlin and were manufactured in the then Protectorate of Bohemia and Moravia by the company Servotechna AG in Prague, which was under German management.137 Further cooperation partners in the development of the twist caps included the companies Heinrich Diehl GmbH in Nuremberg, Blumberg & Co in Lintrof and Gebrüder Spindler Brothers in Köppelsdorf. The twist cap was produced up to the end of the war. Within the context of this twist-cap development, an evaluation was made of the mass distribution of the MP 43 assault rifle, which had been in use since 1943. Loaded with standard ammunition, the weapon was already considered very heavy. Combined with the grenade attachment plus the additional option of an aiming telescope, the Infantry Division of the Army Ordnance Office (Wa Prüf 2) ranked it negatively as overly restricting the mobility of a soldier in action.138 A reduction in weight while maintaining the stability of the weapon was seen as a possible solution. That was why Römmler AG developed a butt made of presstoff for the developer of this rifle, C. G. Haenel located in Suhl Thuringia and known for its traditional hunting weapons. The rifle butt for the successor model, 135 Memorandum on the composition of Sonderpreßmasse 3721 dated 31 Jul. 1944 (BLHA: Rep. 75 Chem. Werke Römmler 9). 136 See “Abnahmeanweisung für die Sonderpreßmasse 3721” of May 1943 as well as the correspondence between Römmler AG, the OKH division Wa Prüf (BuM) 1 Inf., and the company Servotechna Prague (ibid.). 137 Memorandum by Eberhard Römmler on the production conditions at the Servotechna firm in Prague, dated 11 Jan.1945 (ibid.). 138 Reports on the development of Sturmgewehr MP 43 (Landeshauptarchiv Thüringen, Staatsarchiv Meinigen: Bestandssignatur: 4-94-1203 (Fa. C. G. Haenel), Archivaliensignatur: 190).

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the MP 44 assault rifle, was primarily designed with low weight in mind. Römmler AG chose for this purpose hard paper as the reinforcement material enveloped in a supporting matrix mix of phenolic or cresylic resin.139 The weapon did not get a solid presstoff butt but merely a casing of two semi-monocoques bolted onto a single metal supporting frame in the required butt shape. This special model for the MP 44 assault rifle with a presstoff butt was completed shortly before the war ended, so only a few weapons were sent to the front line. There is no evidence of this weapon model having been deployed. Probably the most extensive production order in the area of compressed thermoplastic materials was also placed with Römmler AG, in April 1942, within the framework of the tank programme of Army High Command. It involved the production of load-bearing cylindrical presstoff bushings for a plain-bearing system,140 which supported the shaft on a very thin lubricating film. Depending on the application, the bushing could be replaced as a wearing part without having to replace the entire bearing system. Initially, the OKH assumed a daily production of 20,000 fabric-based laminate presstoff bushings for various applications in tanks and tractors of different models, e.g. in the “special purpose” halftrack vehicle Sonder-Kraftfahrzeug 9.141 At the beginning of 1944, Römmler AG eventually produced 40,000 of the aforementioned presstoff bushings per day in 110 different types.142 A company in the Protectorate of Bohemia and Moravia under German management was also contracted to manufacture the Römmler laminate presstoff bushings. This was the once owner-operated machine factory and iron foundry Maschinenfabrik und Eisengießerei Ing. J. Vlatavský in Rakonitz, Bohemia (Okres Rakovník, Czech Republic), which was formally directed by three members of the founder’s family.143 At the end of 1944, Römmler AG still issued production licenses for the above presstoff bushings to about ten small companies in southern Germany not yet subject to any war-related hindrances. The importance assigned to presstoff bushings becomes apparent at a meeting held in 1944 at the Army Ordnance Office led by Major-General Hans von Hanstein from Special Staff A of the General Army Office (AHA).144 In the case of presstoff bushings or bearing bush systems, the Special Staff received an increasing number of failure reports. At this meeting in the Heereswaffenamt in which representatives from the military, the 139 See the report on the holdings of Firma C. G. Haenel in 1945 (ibid., arch. sig.: 161). 140 Plain bearing systems (usually as axial bearings or radial bearings) = as a rule, consisting of

the bearing housing (one or two-piece) with lubrication device, the bushing (split or unsplit) and the running shaft in it. 141 Letter from OKH to Römmler AG dated April 1942 (ibid. Rep. 75 Chem. Werke Römmler 4). 142 Report by Römmler AG dated 14 Feb. 1944 (BLHA: Rep. 75 Chem. Werke Römmler 23) as well as letters between the Sonderring, or later: Hauptring für Kunst-und Preßstoffe and Römmler AG (ibid. Chem. Werke Römmler 4). 143 Letters dated 23 Aug. 1943 resp. 1944 between the Vlatavský company and Römmler AG (ibid. Chem. Werke Römmler 4). 144 Minutes of the meeting at Heereswaffenamt on 15 May1944 (UA TUD 66, Fak. MW/Abt. für Maschinenbau).

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manufacturers and the expert committees took part, the failure cases concerning presstoff products were discussed. Various armourers and their assistants had previously reported this to the Vulnerability Assessment Centre (S. A. Z.) of the Army Ordnance Office, which had been set up in Düsseldorf specifically to collect, analyse and evaluate such problems with technical equipment in combat operations. In many cases, the failures were in the area of automotive technology, tanks and mobile artillery requiring increased amounts of lubrication. The very long drives in Russia and Africa were the cause as well as increased contact of the presstoff plain bearings with sand, mud and permanent dampness or subzero temperatures. However, properly maintained presstoff bushings and bearings proved to have a longer service life than metal plain bearings or roller bearings subject to higher levels of stress. These findings mainly affected the tank models V “Panther”, VI “Tiger” and Panzer III. The presstoff materials mainly had type T 2 (shredded fabric laminate) and type T 3 (fabric-tape laminate) reinforcements in a phenolic or cresylic resin matrix.145 The report evaluations revealed that neither the design nor the material quality of the presstoff were the cause, but rather improper maintenance. Poorly trained personnel on site damaged or rendered unusable a large number of defence equipment such as tanks and tractors by making grave maintenance errors shortly after or during combat operations. The analysis showed furthermore that technical personnel had little or no experience with handling presstoff and treated it like a metallic machine element during maintenance or repairs, which posed a major problem especially regarding lubrication. The fear that presstoff plain bearings could swell up from lubricating oils led to erroneous washing or lubrication with water. One participant at that meeting, Hans von Hanstein (1883–1975) was, among other things, editor of a technical information sheet called: “From the front line to the front line—Pointers and reports for technical aids”146 since its inception at the beginning of 1944. From this meeting he concluded that the maintenance and handling of presstoff by the technical personnel in combat operations was a fundamental problem.147 A memorable form was found to solve it—namely, an instructive comic appearing in that information sheet. Its message is conveyed by two very different soldiers in rhyme. These comical figures were the ignorant serviceman Murcks, whose name translates as “botch”, i.e. a 145 “Bericht 1” of Sonderführer Dipl.-Ing. Frank of the Hauptring für Kunst-und Preßstoffe1944. (UA TUD 66, Fak. MW/Abt. für Maschinenbau). 146 Von der Front für die Front. Vorschläge und Berichte für technische Behelfe, a technical information sheet for the Wehrmacht and SS, first appeared on 1 Jan. 1944. It was designed for technical maintenance personnel in combat operations and was published in 18 issues until 25 Nov. 1944. It discussed technical problems concisely and offered simple solutions, with simple sketches to illustrate the problems that arise with weapons and accessories as a result of wear and tear or the effects of combat, or that have to be adapted to the daily routine of combat operations. Soldiers were also encouraged to submit their own improvement tips, which were then printed in the information sheet in an informal way. 147 Minutes of the meeting at Heereswaffenamt on 15 May 1944 (UA TUD 66, Fak. MW/Abt. für Maschinenbau).

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Fig. 4.23 The information sheet Von der Front für die Front with the rhyming dialogue about the proper maintenance of presstoff bushings. Source Zentrum für Militärgeschichte und Sozialwissenschaften der Bundeswehr

botcher (Fig. 4.23). Luchs is the knowledgeable serviceman who admonishes Serviceman Murcks not to slavishly scrub presstoff bushings clean but rather to lubricate them liberally. His name, meaning “lynx” and bearing the positive connotations of that animal, such as acute eyesight and hearing and skill as a cunning hunter, is popularly associated with smartness, as the counterpart to clumsy dolt Serviceman Murcks.

4.4

4.4

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Between Professional and Political Ambivalence—Fibre Research from 1920 to 1945

The performance of composite materials depends on the supporting matrix and even more so on the quality of appropriately laid load-bearing fibres. This latter is especially important in the multifarious fibre-composite applications. Due to their higher rigidity compared to the supporting matrix, fibres—whether they be filaments,148 a roving,149 fibrous woven fabric150 or a fibre mat—conduct the exerted forces onto the respective component.151 That is why fibres became the focus of research and development early on. At the beginning of the 1920s, Hermann Staudinger, the founder of polymer chemistry, brought new matrix materials for composites within reach, in particular for the early fibre-reinforced plastics. Almost at the same time, university and non-academic research began to explore various fibres and focus on potential applications, mainly with an eye to their use in textile applications. Interest in fibrous materials, or their quality and availability, had already been growing amongst specialist circles since the shortages of World War I with a view to securing raw materials for the German textile industry.152 The head of the Economics Department of the Reich Clothing Office, Paul Arndt (1870–1942), presented a sobering survey highlighting in particular a heavy reliance on imports for high-quality fibres. The total mass of imported fibrous materials, especially of cotton, wool, jute, flax, hemp and silk, came to about 930,000 t in 1913. This was juxtaposed against a domestic production of 15,300 t, which was limited to wool, flax and hemp.153 There were an additional 22,500 t of cotton, wool and hemp, which could be imported from the colonies or from German spheres of influence, especially Togo, Cameroon and East Africa. However, in the context of military conflicts or a possible naval blockade their availablility had to be regarded as critical. With the outbreak of World War I, a quota-based allocation of fibrous materials was laid down, which was primarily aimed at ensuring the availability of cloth for the German army and was controlled by the War Raw Materials Department of the Ministry of War. The Reich Clothing Office was founded in 1916 at a time of material shortages in the textile sector and was in charge of the supply of textiles for the civilian population.154 The intention of both these agencies was to activate domestic fibre resources, which set in motion a kind of fibre substitute industry. Pulp from coniferous wood was the most 148 Filament = a single fibre. 149 Roving = a bundle of untwisted fibres. 150 Fibrous woven fabric (Fasergewebe) = flat fabric with its two strands (warp and weft yarns) or

fibre bundles oriented at right angles to each other. 151 Fibre mat = flat fabric with randomly arranged fibres; they are joined together to form a mat either by an adhesive or by needling the fibrous material. 152 Löser (1991), p. 276 f. 153 Volkswirtschaftliche Abteilung der Reichsbekleidungsstelle. Arndt (1918), p. 8 f., Tobler (1917). 154 Kriegsrohstoff-Abteilung des Kriegsministeriums. Boldorf and House (2016), p. 339.

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important fibre. It was used as a pulp-yarn substitute for cotton, wool and jute, and found its way into the domestic textile industry under the designation “paper yarn”.155 The first customers for the textile fabrics produced in this way were the army administration for soldier attire. Later there was a limited release of this textile fabric among the civilian population as well. Upon closer examination it can be asserted that in reality there were no introductions of truly new substitute fibre materials. In most cases it was rather a revival of already known indigenous plant fibres and traditional old craft techniques for processing fibrous materials with a horizon for textile applications. A consultation of the two-volume work on the “technical history of plants which are already being used in the crafts, arts and manufactories or can still be useful” from 1794 (Fig. 4.24) shows this clearly. Its author, the medical doctor and professor of botany at the University of Wittenberg, Georg Rudolph Böhmer (1723–1803) (Fig. 4.25),156 describes especially in the fourth chapter on materials for spun, woven and braided wares, how a large proportion of native fibre plants can be utilized, or forgotten plants made useful again.157 This suggests that indigenous fibre plants were already being used extensively for textile applications. Nettles are one example and the nettle cloth made from it. There is evidence that a nettle manufactory existed in Leipzig as early as 1723.158 This work thus can prove that nettles were in fact rediscovered or put to new use for the production of textile fabric. However, the low and inhomogeneous plant quality and quantities cultivated led to nettles being discarded as a “substitute fibre” (Ersatzfaser). The mobilization of domestic fibre plants for the textile industry experienced a flourishing renaissance during World War I and II. In this context, during both these periods of conflict the botanist and fibre researcher Friedrich Tobler (1879–1957) called for a reappraisal of Böhmer’s work, but in vain.159 Therefore, it is necessary to change the perspective especially with regard to the substitute debate in the field of pulp utilization during the two world wars, and rather speak of a new use or rediscovery of traditional plant pulps implemented by means of maschine technology.160 The need for action identified during World War I sought in particular the exploration, processing and technological utilization of indigenous fibrous materials and their further 155 Papiergarn. Arndt (1918), p. 13 f. 156 Technische Geschichte der Pflanzen, welche bey Handwerken, Künsten, Manufakturen bere-

its im Gebrauche sind oder noch gebraucht werden können, Böhmer (1794); (University Archives Martin Luther University Halle-Wittenberg [hereafter UAHW] Rep. 1, No. 4221), for biographical information on Georg Rudolf Böhmer, an account of part of his work from 1754 to 1773, and lectures by Georg Rudolf Böhmer as rector of the University of Wittenberg, among other things, on the “Technical History of Plants”. 157 Ibid, p. 490 f. 158 Reimers (1919), p. 3 f. 159 Tobler (1917), Luxbacher (2004). 160 In the context of the Ersatzstoff debate, see, among others, Luxbacher (2011), id. (2004), Flachowsky (2008), Maier (2007a), Heim (2003), Wengenroth (2002), Marsch (2000).

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Fig. 4.24 Title page of the book by Georg Rudolf Böhmer on the “Technical History of Plants” from 1794. Source Sächsische Landesbibliothek—Staats-und Universitätsbibliothek (SULB), Dresden, Technol. A.311–1

development with a view to prospective uses. The result was the establishment of various specialist institutions. State authorities, especially the military, but also the paper and textile industries as well as companies from the agricultural sector, contributed in different ways to the emergence of a multifaceted research landscape in this field.161 The first results of these efforts came to fruition before the end of World War I in the form of

161 On the KWI institutes, see, among others, Luxbacher (2004), Heim (2003), von Brocke & Laitko (1996), Löser (1992), id. (1991).

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Fig. 4.25 Silhouette portrait of Georg Rudolf Böhmer from around 1771/1800, brush, woodcut, unknown artist. Source LWL Museum für Kunst und Kultur, Westfälisches Landesmuseum, Münster, Diepenbroick Portrait Archive

research institute establishments, each tackling different focal points of fibre research and their neighbouring areas. These institutes were the following: • In 1916 the founding of the German Institute of Textile Materials in Karlsruhe, which investigated topics concerning textiles and fibrous materials.162 • In 1917 the founding of the Sorau Research Institute of the Association of German Linen Industrialists in Lower Lusatia by Alois Herzog (1872–1956).163 His successor was the botanist Friedrich Tobler who turned the institute into an efficient research and testing centre in the field of bast and hard fibres. After Tobler’s departure, the botanist Friedrich Wilhelm Ludwig Kränzlin (1847–1934) took over the direction of the institute from 1924 to 1930. The transformation of the institute into the Kaiser Wilhelm Institute of Bast Fibre Research occurred in 1938 under his successor, the Tobler pupil Ernst Carl Magnus Schilling (1889–1963).164 The reorganization into a KWI institute, brought with it massive expansion, with bast-fibre remaining the dominant object of research. • In 1918 the foundation of the German Research Institute of the Textile Industry in Dresden, in affiliation with the Dresden polytechnic. The founding director Ernst Müller (1856–1929) was at the same time professor of fibre technology and director of the Mechanical and Technological Institute at the Dresden polytechnic.165 The special

162 Deutsches Institut für Textilstoffe. Heermann (1930), p. 774, Goebel (1921), p. 68. 163 Forschungsinstitut Sorau des Verbandes Deutscher Leinen-Industrieller, Niederlausitz. See the

report on the development of the Institut für Textiltechnik at the TH Dresden by Alois Herzog from 1954 (UA TUD: Personalakte Prof. Müller, Ernst). 164 Cf. Henning and Kazemi (2016a), Luxbacher (2004), p. 23 f., Böhm (1997), p. 354. 165 Curriculum vitae in Ernst Müller’s staff file (UA TUD: Personalakte Prof. Müller, Ernst).

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research focus of the institute was on the mechanical and chemical technology of fibres. In the same year, a second German Research Institute of the Textile Industry in Mönchengladbach was also founded, in close cooperation with the local textile college, Höhere Textilfachschule. Under Julius Rudolf Obermiller (1873–1930), who headed the institute from 1920 to 1924, the institute specialized in research methods for fibrous materials. A third German Research Institute of the Textile Industry was also founded in Reutlingen in 1918 and is associated with the Stuttgart polytechnic and the textile college Höhere Textilfachschule in Reutlingen. Its research focus was on the mechanical and chemical technology of fibres, with cotton and other staple fibres investigated in particular.166 The German Institute of Textile and Fibre Research in Denkendorf emerged out of the local German Research Institute of the Textile Industry. This institute is one of the world’s leading centres for the research and production of carbon fibres today. In 1920 the colour analysis station Deutsche Werkstelle für Farbkunde was founded by the chemist and Nobel laureate Wilhelm Ostwald (1853–1932) in Dresden, with branches in Meissen and Chemnitz. This research centre worked primarily on measuring colour brilliance according to Ostwald’s standardized colour scheme. The head of the research institute, Franz August Otto Krüger (1868–1938), investigated the effect of colours on fibrous materials and leather on a large scale for industry. The institute was incorporated into Prof. Müller’s German Research Institute of the Textile Industry in Dresden as early as 1925.167 The Textile Research Establishment in Krefeld was founded in 1920. The research focus was initially the investigation of cotton, natural and artificial silk. Fibre research was part of its research range.168 Fibre and yarn research was expanded there after the appointment of Wilhelm Weltzien (1890–1962), who came to Krefeld from the Kaiser Wilhelm Institute of Chemistry in Berlin. He integrated the institute, originally founded in 1842 as the Oeffentliche Seiden-Trocknungs-Anstalt zu Crefeld, into his institute as a materials testing station for textile businesses (Öffentliche Prüfstelle für die Spinnstoffwirtschaft). In 1933 Weltzien became honorary professor of the chemistry and physics of fibrous materials. From 1943 onwards, he was deputy chairman of the working group on fibre processing in the Reich Research Council (Reichsforschungsrat) and promoted military contracts in this field.169 A special focus of this research institute’s work was natural and artificial silk. In the same year, the Kaiser Wilhelm Institute of Fibre Chemistry was founded in BerlinDahlem with Reginald Oliver Herzog (1878–1934) as director. It had emerged from the textile department of Fritz Haber’s (1868–1934) Kaiser Wilhelm Institute of Chemistry.

166 Staple fibres = all natural and synthetic textile fibres. 167 Gesellschaft Deutscher Chemiker (2005), p. 10. 168 Textilforschungsanstalt Krefeld. Tobler, Friedrich (UA TUD: Personalakte S.II/F.3 Nr. 1029). 169 Brandt (1954).

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The institute’s research, conducted in various departments, focused primarily on the study of the elementary science of fibres, the clarification of technical procedural issues in the processing of natural fibres, such as cotton, wool, cellulose and flax, and the production of synthetic fibres.170 The head of the organic chemistry department of this institute was Max Bergmann (1886–1944), who soon moved away again in 1921, however, to take up a post as founding director of the Kaiser Wilhelm Institute of Leather Research in Dresden. After Herzog’s emigration,171 the institute was shut down in 1934 due to a lack of funds. • The Kaiser Wilhelm Institute of Leather Research was founded in Dresden in 1921.172 In addition to treating questions on leather, this institute under its director Wolfgang Grassmann (1898–1978), who had assumed Director Max Bergmann’s post after his emigration in 1934, also began to work more on fibrous materials from 1939 onwards.173 • With the appointment of Friedrich Tobler174 to his professorship in botany at the Dresden polytechnic, luring him away from his position as head of the Sorau Research Institute of the Association of German Linen Industrialists, intensive fibre research commenced in Dresden. Tobler’s main research focus was on natural fibres, especially pulp production. At the same time, his institute operated as a testing station for fibrous material within the framework of the Four-Year Plan.175 • The Materials Research Institute of the German Aviation Research Institute (DVL) which operated under the name Stoffabteilung der DVL until 31 January 1936, began to deal with classical aeronautical materials after the appointment of Paul Albert Brenner (1897–1973)176 as its director in 1926. It also researched fibres for parachute 170 Cf. Haka (2014a), Henning and Kazemi (2009), p. 71 f., Löser (1996), p. 287 f. 171 The issuance of the Law for the Restoration of the Professional Civil Service led to Reginald

Oliver Herzog’s emigration, see Henning and Kazemi (2009), p. 75. 172 Henning and Kazemi (2016b), p. 890 f., Sudrow (2002), p. 214 f. 173 Max Bergmann’s Jewish background was the reason for his emigration as a consequence of the Law for the Restoration of the Professional Civil Service, see Schmaltz (2005), p. 295. 174 Tobler, Friedrich (UA TUD: Personalakte S.II/F.3 Nr. 1029), Czaja (1957), p. 269 f. 175 On the Four-Year Plan see, among others, Petzina (1968). 176 Paul Albert Brenner (20 Mar. 1897–30 Mar. 1973), studied mechanical engineering at TH Stuttgart 1918, interrupted his studies to join the paramilitary unit Freikorps Hasse, participated in the fights in support of the Weimar Räterepublik, graduated as a certified engineer (Dipl.-Ing.) in 1922, joined the DVL in 1923 as assistant to Prof. Dr. Wilhelm Hoff, was appointed director of the materials department of the later Institut für Werkstoffkunde in 1926, took his doctorate as Dr.-Ing. at TH Berlin in 1927, became director of the research institute of Vereinigte Leichtmetall Werke GmbH in Hanover in 1936, accepted a lectureship on light metals at TH Hannover in 1941; from 1946–1948 he worked in the materials research institute of the Royal Aircraft Establishment in Farnborough in Great Britain, was then again director of the research institute in Hanover as well as of Vereinigte Aluminium-Werke in Bonn; in 1952 he was appointed honorary professor at TH Hannover. (UA Hannover [hereafter UAH]: Sign./Akz. Best. 5, Nr. 3292, PA Paul Albert Brenner), and Brenner (1937).

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and covering materials and, from 1931, presstoff laminates. When Brenner took over the management of the research institute of the United Lightweight Metal Works in Hanover in 1936, the afore-mentioned fabrics department of the DVL was expanded. It moved into a new building which was completed in 1935 and the materials department was renamed Institute of Materials Research (Institut für Werkstofforschung) of the DVL in Berlin. The engineer Franz Bollenrath (1898–1981) was appointed director.177 Bollenrath expanded the research both on fibres as well as on presstoff laminate materials. Under his directorship, the utilization of glass-fibre-reinforced plastics (GFRP) as a structural material was investigated at this early stage on a larger scale.178 • The aviation research institute Luftfahrtforschungsanstalt in Stuttgart, founded in 1936 out of the Flugtechnisches Institut at the Stuttgart polytechnic, was directed by Georg Madelung (1889–1972) from 1936 to 1945 and officially acquired the name Forschungsanstalt Graf Zeppelin (FGZ) in 1943.179 Their department on parachute and brake-chute development, under the engineer Theodor Knacke (1910–2001), carried out extensive research on alternative spinnable fabrics and fibres as part of their parachute investigations, because from 1943 onwards conventional textile materials were in short supply. • The Institute of Chemical Technology of Synthetic Fibres at the Breslau polytechnic began operations on December 1st, 1943 under Karl Lauer. Apart from conducting general synthetic fibre research, the focal topics at this institute concerned artificial cellulose fibres.180 The research primarily pursued at these institutes initially had a textile application horizon in view, and the German efforts to attain autarky from 1936 onwards expanded it further.181 With an eye to the domestic market, the research focused on natural fibres. Particular attention was paid to animal and vegetable natural fibres as well as semi-synthetic cellulose-based fibres, and later on fully synthetic fibres.182 Internal documentation from the Reich Aviation Ministry underscore the relevance of the subject of fibres per se, even beyond the textile industry in the mid-1930s.183 The Army Clothing Office was particularly interested in spinnable, robust materials and flat textile fabrics for army attire. The Luftwaffe also took a greater interest in fibres, yarns and woven fabrics, however. Among the above-listed research institutions, the ones identifiably interested in military applications 177 PDM – Haka (2014b); Franz Bollenrath was full professor of materials science at the polytechnic RWTH Aachen from 1948–1966. 178 DVL report of 15 May1942 by Perkuhn and Küch (AFTUD: Heidebroek papers. Publication collection). 179 Elsässer (2016), p. 1 f., id. (2021), p. 97 f. 180 Crane (2018), p. 190 f., Lauer (1942), p. 982. 181 Maier (2007a). 182 Heim (2003). 183 Riechers (1938a).

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Fig. 4.26 Friedrich Tobler as an “Alter Herr”, an alumnus member of the student fraternity Sängerschaft Erato at the Dresden polytechnic in 1934. He is wearing his fraternity’s ribbon colours on his lapel. Source Enno Heidebroek papers, AFTUD

are: The KWI of Fibre Chemistry, the Institute of Materials Research of the German Aviation Research Institute in Berlin, the Graf Zeppelin Research Institute (FGZ) in Stuttgart and the Institute of Botany at the Dresden polytechnic.

4.4.1

Friedrich Tobler—Botanist, Fibre Researcher, Raw Materials Expert

The investigations by the national conservative natural scientist Friedrich Tobler (1879– 1957) during the two world wars (Fig. 4.26) in the area of German research on fibrous materials had a particularly strong impact on the technical aspects of textile products.184 Among these can be counted presstoff products with reinforcing fabric-based laminates. Alternative engineered materials needed to be found for such woven fabrics, especially during World War II. The woven fabrics used in presstoff products in the past, which are also referred to as technical textiles, were generally made of cotton, flax or jute fibres. Due to the wartime limitations, alternative fibres or fabrics had to be found and verified. Tobler’s researches in the field of technical applications of indigenous, tropical and subtropical fibre plants thus made him one of the most important German researchers and raw-material experts in this field in the first half of the twentieth century.185

184 Tobler, Friedrich (UA TUD: Personalakte S.II/F.3 Nr. 1029), Czaja (1957), p. 269 f. 185 Tobler (1938).

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After completing his scientific studies at Heidelberg, Berlin and Leipzig followed by various scientific stays,186 Friedrich Tobler succeeded the founding director of the Sorau Research Institute of the Association of German Linen Industrialists, Alois Herzog (1872– 1956), in 1920. In that same year, Herzog moved to the German Research Institute of the Textile Industry in Dresden, where he accepted a professorship on paper and textile technology at the Dresden polytechnic in 1925.187 Tobler continued to follow his predecessor’s course at the Sorau Institute in Lower Lusatia, focusing in particular on hard-fibre plants. He founded the journal Faserforschung, Zeitschrift für Wissenschaft und Technik der Faserpflanzen und der Bastfaserindustrie in 1921, which initially appeared in the name of the Sorau Research Institute under his editorship, thereby bringing together the most renowned fibre researchers in the years that followed and establishing a global network of scientists and research institutes.188 After his appointment in 1924 as full professor of botany and head of the Botanical Garden at the Dresden polytechnic, Tobler was able to expand this network and devote himself increasingly to the exploration of new natural-fibre varieties. With the rise to power of the national socialists in 1933, however, Tobler found himself increasingly exposed to the hostility of the reich governor of Saxony, Martin Mutschmann (1879–1947).189 The reason for this hostility was that Tobler’s wife, Dr. Gertrud Wolff (1877–1948), was Jewish. Like her husband she, too, was a researcher in the field of fibrous plants and had also participated in his research expedition to East and South Africa. She submitted papers on independent specialist topics in the journal for fibre research founded by Tobler and thus also figured in the public eye. That was one reason for the harassment that occurred after the nazis took over government.190 Although Tobler moved among nationalist conservative circles, his attitude towards national socialism remained ambiguous.191 His life changed with the enactment of the Nuremberg Laws when his wife was no longer free to appear in public and he himself also

186 Friedrich Tobler (born 1 Oct.1879 in Berlin–died 11 May 1957 in Trogen, Switzerland), studied the natural sciences at Heidelberg, Berlin and Leipzig. In 1901 he defended his doctorate at the University of Berlin and joined the scientific staff at the Zoological Institute in Naples (Italy) in 1902. In 1903 he was employed at the station for marine biology in Bergen (Norway) and from 1905 taught as private lecturer at the University of Münster until he was appointed budgetary senior lecturer (etatmäßiger außerordentlicher Professor) of general physiology and botany there in 1911. He served in the war 1914–18. In 1920 he took over the direction of the Forschungsinstitut Sorau des Verbandes Deutscher Leinen-Industrieller in Niederlausitz. See Czaja (1957), p. 269 f. 187 On Alois Herzog, see PDM—Haka (2014b). 188 See the 1st issue of Faserforschung published by the Sorau Research Institute in 1921. 189 See, inter alia, the letter from the rector of the TH Dresden, Enno Heidebroek on the Tobler case, 11 Sep. 1946 (UA TUD: Personalakte S.II/F.3 Nr. 1029); on Reichsstatthalter Martin Mutschmann, see Schmeitzner (2012), p. 22 f. 190 See, among others, Tobler, G. (1935). 191 Tobler’s report of 6 Oct. 1946 (UA TUD: Personalakte S.II/F.3 Nr. 1029).

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suffered increasing restrictions.192 Public appearances, which had previously been almost exclusively of a professional nature or portrayed economic aspects within the context of raw materials around the world, were increasingly hampered. There was no outright attack on Tobler, however, because he enjoyed an international reputation and as Germany’s leading fibre researcher was rated as indispensable (unabkömmlich) for research important to the war effort.193 Besides, his dual Swiss citizenship also gave him some protection. He received a great deal of support among the professors at the Dresden polytechnic as well. It was not until 8 March 1945 that the reich governor of Saxony ordered Tobler’s removal from office.194 Tobler encountered very similar problems at the Dresden polytechnic after the war. He was accused of having strongly promoted the nazi ideology with his research of importance to the war effort. He tried to refute this suspicion several times in various statements.195 This is where an effective network acted on his behalf at various levels. The mechanical engineer Enno Heidebroek exercised the strongest influence in his capacity as post-war rector of the Dresden polytechnic. He mediated between Tobler and the Saxon state administration, which was arguing along the lines of the Red Army.196 Heidebroek was a personal friend of Tobler’s and also consulted him professionally about various hard-fibre fabrics for presstoff plain bearings and other business as head of the mechanical engineering department of the experimental and materials testing office of the Dresden polytechnic.197 Both also knew each other from their student fraternity days or as fellow alumni. Friedrich Tobler was a member of the student fraternity Sängerschaft Erato Dresden and Heidebroek of Corps Altsachsen Dresden.198 Friedrich Tobler’s private assistant, Annemarie Lauche, was also married to one of Tobler’s doctoral students since 1937: the later head of the Department of Bast Fibre Research at the Institute of Fibre Technology at the Dresden polytechnic, Klaus Menzel (1907–1995) (Fig. 4.27). Like Heidebroek, Menzel too was a fraternity member of Corps Altsachsen Dresden.199 Heidebroek arranged that Tobler be reappointed as director of the Botanical Garden of 192 Essner (2002). 193 See the memorandum of 26 Sep. 1936 by Mr. von Seydwitz, Dienststelle des Reichsstatthalter

von Sachsen, Landesregierung, Ministerium für Volksbildung (UA TUD: Personalakte S.II/F.3 Nr. 1029). 194 Letter from Reichsstatthalter Martin Mutschmann dated 8 Mar. 1945 (UA TUD: Personalakte S.II/F.3 Nr. 1029). 195 See, inter alia, the letter dated 5 Oct. 1946 from Friedrich Tobler (ibid.). 196 Letter from Enno Heidebroek dated 11 Sep. 1946 to Erster Vizepräsident der Landesverwaltung Sachsen (ibid.). 197 Haka (2014a), p. 246. 198 See the membership directory, Mitgliederverzeichnis Alte-Herren der Kameradschaft Annaberg from 1943. (AFTUD Nachlass Heidebroek); on the networks of student fraternities at TH Dresden for Enno Heidebroek see also Haka (2014a), p. 195 f., 279 f. 199 Dr. rer. techn. Hellmuth Schierig (1908–2001), doctoral student of Prof. Friedrich Tobler, obituary of Dr. rer. techn. Menzel, manuscript (AFTUD Nachlass Schierig).

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Fig. 4.27 Klaus Menzel (1907–1995), doctoral student of Friedrich Tobler and later head of the bast fibre research department at the Institute of Fibre Technology at the Dresden polytechnic. Here as an alumnus wearing the tricolour sash of his student fraternity and a “Biertönnchen” cap, 1993. Photo Helmuth Schierig, Schierig papers AFTUD

Fig. 4.28 Paul-August Koch (1905–1998), from 1939 the joint holder of the chair for fibrous materials science and the extraordinary professorship on textile and paper technology at the Dresden polytechnic. (Photo undated, probably taken as professor of fibrous materials science). Source Courtesy of the University Archive of TU Dresden

Dresden. However, Tobler, who again faced hostility from the state, moved away from Dresden a year later to his native country of Switzerland, where he took up a position at the Materials Testing Office in St. Gallen.200 Like many scientists after 1945, Tobler regarded his professional commitment under national socialism primarily in terms of his field of expertise, without assessing the full consequences of his actions.201 Few saw that their research often was what made the war economy possible, kept it running or even decisively furthered it.

200 Materialprüfungsamt St. Gallen. Czaja (1957), p. 271. 201 Haka (2014a), p. 190 f., 314, König (2010), p. 75 f., in this context in particular also “I served

only technology” (“Ich diente nur der Technik”, Museum für Verkehr und Technik, ed. 1995).

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Table 4.3 Commissioned fibre-research projects at the Dresden polytechnic, conducted at the Institute of Botany there between 1937 and 1945 by and under Friedrich Tobler204 Client

Topic

Researcher

Reich Research Council

Studies on jute substitutes

Frederick Tobler

Reich Office of Economic Expansion

Research on reed utilization

Frederick Tobler

Reich Office of Economic Expansion

Plant-fibre research

Frederick Tobler

Reich Research Council

Influencing cultivar germination

Frederick Tobler

Reich Research Council

Medicinal plant research

Frederick Tobler

Pflanzenkautschuk-Forschungs-und Anbaugesellschaft m.b.H

Rubber

Frederick Tobler

Reich Office of Economic Expansion

Raw Materials Index

Frederick Tobler

Tobler played a central role in the field of natural fibre research, helping the nation’s efforts to achieve autarky during World War II. He also advanced useful economic descriptions or interpretations of the raw-material resources around the world for the associated textile industry as a decisive basic supplier of the military and the population. All of Tobler’s projects listed in Table 4.3, which he conducted on commission of the Reich Research Council (Reichsforschungsrat, RFR), the Reich Office of Economic Expansion (Reichsamt für Wirtschaftsausbau) and a German rubber-plant research and cultivation company, Pflanzenkautschuk-Forschungs-und Anbaugesellschaft m.b.H., between 1937 and 1945, treat central war-related topics on the economy and provision of materials for the nazi system. The fibre research archive, which Tobler established back in 1920 and which was also introduced as a rubric in his journal Faserforschung in 1940, provides insight into central topics of plant fibres and global raw-material resources in his day.202 The raw materials card catalogue Rohstoffkartei compiled for the Reich Office of Economic Expansion (Table 4.3) relied largely on this collection and provided information on fibre plants, raw-material resources and the various related industrial branches. Tobler also presented excerpts in his article on an “overview of plant-fibre raw materials with a view to their mutual substitutability” in his journal.203

202 Archiv der Faserforschung. Tobler (1940), p. 179 f. 203 Übersicht von pflanzlichen Faserrohstoffen im Hinblick auf ihre gegenseitige Ersatzmöglichkeit,

ibid. p. 230 f. 204 List by the rector about the research projects carried out at TH Dresden during World War II (UA

TUD: 833, Rektorat 1945–1968, Tätigkeit des Dolmetscher Büros, 1946).

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His research for the rubber company dealt with a complex of issues of central importance to a nation at war, since rubber was an essential basic tyre material for military vehicles. Susanne Heim has comprehensively described nazi rubber research and the political framing conditions.205 Tobler’s investigations into jute substitutes for the Reich Research Council or parallel investigations in the Institute of Botany at the Dresden polytechnic on paper yarn and New Zealand flax, as well as on fibre diagnostics and testing, brought him into contact with Enno Heidebroek and Römmler AG.206 This company contacted Friedrich Tobler about ways to convert cotton quality from fine to coarse woven fabrics for application in hard fabric-based tape in presstoff, and also about experimental conversions to jute and paper-yarn fabrics.207 It is not ascertainable whether Enno Heidebroek acted as an intermediary.

4.4.1.1 Glass-Fibre-Reinforced Plastic—A Secret Serial Product for the Luftwaffe from the 1940s It has hitherto been assumed that glass-fibre-reinforced plastic (GFRP) was first tested in the USA in the early 1940s for military applications as a substitute for aluminium alloys, which were very limited at that time.208 The developments there, which were primarily initiated by the U.S. Air Force, were usually custom-made products and prototypes. The quality of the GFRP varied greatly, and the use of special polyester resins caused major problems in the area of fibre-matrix bonding. For this reason, serial production could not be realized in the USA until the end of World War II.209 It was only once epoxy resins were applied that the bonding problem between matrix and fibre could be solved. The basis for this was the patent granted to Gebrüder de Trey AG in Switzerland in 1940 for the production of a curable synthetic resin.210 The associated validation and subsequent entry into serial production of the new matrix material in combination with glass-fibre fabrics did not take place until after 1945.

205 Heim (2013), p. 59., id. (2003), p. 125 f. 206 Cf. Tobler (1940), p. 232, id. (1939), p. 184, id. (1936), p. 115 f., id. (1935), p. 8, Steite (1939),

p. 89 f., 97 f. On questions of fibre testing, see, among others, Tobler and Ulbricht (1940), p. 178 f. 207 See Römmler semi-finished products (Halbfabrikate) (BLHA: Rep. 75. Chem. Werke Römmler 32); Heidebroek (1950). 208 Schürmann (2007), p. 4, Ehrenstein (2006), p. 15, Flemming et al. (1995), p. 51, Rosato (1982), p. 6 f. 209 Spurr (2004), p. 12 f., Hagen (1956), p. III. 210 Gebrüder de Trey AG (1940).

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Whereas the supporting matrix for GFRP is an invention of the twentieth century, the early glass fibre, which forms the reinforcing fibre in this composite material as a roving or woven fabric, originates from Han Dynasty China (ca. 200–220 AD).211 In Europe the first production of glass filaments began in Venice at the end of the eighteenth century.212 The first documentable industrial production of glass filaments dates to the nineteenth century. As early as 1850 Carl Hartmann reported in his book about “all aspects of glass making”, that the industrialist Ignace Dubus-Bonnel from Lille in France had found and patented a method permitting him to produce glass threads.213 Dubus-Bonnel’s glass threads were probably not glass fibres of textile quality. A new glass-fibre quality was developed by Julius de Brunfaut, an industrialist based in Breslau (Wrocław).214 These fibres, produced by a thread-drawing process, had a diameter of about 6–12 µm. Although their quality can be described as resembling that of textile, the brittleness of the glass fibre of the time prohibited it from being actually processed as a textile. The glass threads consisted of alkali-lime glass and were more susceptible than average to glass corrosion.215 In 1898, Elisabeth Teinský registered the first patent in Austria for the production of weavable glass wool. This fibre was composed of lead glass and alkali glass at a ratio of 1:2 ratio.216 Industrial production of glass filaments yielded a definition or classification of such fibres, modelled on natural and animal fibres.217 Since then, a distinction has been made between glass wool, spun glass, glass silk and glass wadding. Textile glass-fibre processing, i.e. for the manufacture of woven glass fabrics used as fibre reinforcement in GFRP, preferably employs ready-to-weave yarn made of glass silk or short-fibre glass wool in spunbonded form.218 The company Thüringische Glaswollindustrie, formerly called Koch GmbH, produced glass fabrics of low quality for insulating purposes and for various technical applications.219 The patent was registered by its development engineer Carl Alfeis (1891–?) in 1931 for an insulating material that is moisture-repellent, waterproof, unrottable and non-swelling. Among other things, it describes a variant process for glass-fabric applications. The glass fabric described by Alfeis is not compatible with the later textile standard for glass-fibre fabrics.

211 Walker (2014), p. 111 f., Flemming et al. (1995), p. 51. 212 Koch and Satlow (1940a), p. 211. 213 Die Glasfabrikation in ihrem ganzen Umfange, Hartmann (1850), p. 206. 214 Tscheuschner (1855), p. 477 f. 215 Glass corrosion = structural change of the glass surface upon the degradation of various components of the glass; clouding of the glass caused by light and moisture penetration. 216 Teinský (1902). 217 Koch (1940), p. 21 f. 218 Spunbond = a roving which is twisted into glass-wool yarn and can be used to make woven fabric. 219 See the patents by Carl Alfeis; among others Alfeis (1931).

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179

The question of glass quality was also important to Allgemeine ElektricitätsGesellschaft (AEG) in Berlin. This company experimented with glass fibres for glass wool to incorporate into a synthetic-resin moulding compound. Twisted high-quality fibres, in this case very fine glass filaments with a thickness of 0.02 mm, were needed to develop a composite material that had good mechanical properties for insulation purposes. The resulting glass-wool presstoff sheets were probably the first true glass-fibre-reinforced plastics in the world. The patent was filed in 1935 and granted in 1942.220 Their utilization was as cladding for switch cabinets not expected to bear any significant static load. The decisive investigations into the definition and utilization of glass fibres in textiles were carried out by Alois Herzog’s student, Paul-August Koch (1905–1998)221 (Fig. 4.29). From 1939 he occupied the chair for fibrous materials science at the Dresden polytechnic as well as filling the post of associate professor on textile and paper technology at the same institution.222 Together with his assistant Günter Satlow (1914–1979) (Fig. 4.29), the later director of the German Wool Research Institute at the Aachen polytechnic, he carried out fundamental investigations on the characterization of glass silk and glass-fibre yarn. Their researches defined and influenced the usage of glass fibres or glass-fibre fabrics in textiles world wide.223 Immediately upon his appointment to Dresden, Koch and the staff subordinate to his chair began to work on research topics related to conventional fibrous materials as well as, with particular intensity, on glass fibres and glass-fibre fabrics. The afore-mentioned basic investigations into the technological properties of glass silk and glass wool, which Koch and Satlow published in 1940, produced the first results in this field. In order to be able to verify the material characteristics of glass fibres and glass-fibre fabrics, Koch’s team 220 See the patent filed by AEG from 1935. Inventor: Hans Schuhman; patent application: Körper

aus Preßharzmasse; patent number: 728757; applicant: AEG; filed: 18 Oct. 1935; patent granted: 5 Nov. 1942 by the Reichspatentamt. 221 Paul-August Koch (born 6 Apr. 1905 in Radebeul near Dresden—died 28 Jun. 1998 in Aachen) studied mechanical engineering, specializing in textile technology at TH Graz and TH Dresden. 1931 diploma at TH Dresden, 1929 plant engineer at Deutsche Werkstätten Hellerau, 1930 assistant on textile and paper technology at TH Dresden under Prof. Alois Herzog, 1935 appointment as lecturer at Höhere Fachschule für Textilindustrie in Wuppertal-Barmen, 1937 doctorate under Prof. Alois Herzog at TH Dresden, 1939 dual appointment to the chair for fibrous materials and the extraordinary professorship on textile and paper technology at TH Dresden, 1948 head of a scientific department of the Stoffel company, 1956 lectureship at Ingenieurschule für Textilwesen in Krefeld, in 1964 lectureship in textile technology at RWTH Aachen, in 1970 honorary professor at that same polytechnic. Personalakte Koch, Paul-August (UA TUD: II/486) and PDM—Haka (2014b). 222 List by the rector about the research projects carried out at TH Dresden during World War II (UA TUD: 833, Rektorat 1945–1968, Tätigkeit des Dolmetscherbüros, 1946). 223 See also the notes about Paul-August Koch in the report on Entwicklung des Instituts für Textiltechnik an der TH Dresden by Alois Herzog from 1954. (UA TUD: Personalakte Prof. Müller, Ernst), and see also the most important works on this by Paul-August Koch and Günther Satlow: Koch and Satlow (1943), p. 85 f., id. (1940a), p. 211 f., id. (1940b), p. 542 f.

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Fig. 4.29 Günther Satlow (1914–1979), assistant to the chair for fibrous science at the Dresden polytechnic, from 1954 deputy director of the German Wool Research Institute at the Aachen polytechnic. The picture shows him as an alumnus of the student fraternity Corps Altsachsen, donning the fraternity cap. Source Schierig papers, AFTUD

developed two testing instruments, one by commission of the Reich Office for Economic Expansion and one for the Reich Ministry of Aviation (Table 4.4). Two testing instruments were commissioned because separate tests were needed for the glass fibre and the fabric. The glass-fibre research commissioned by the Reichsluftfahrtministerium had the goal of developing special glass fibre or glass-fibre fabric for technical textiles in GFRP. The glass filament became a focal interest of the fibre researchers around Paul-August Koch, as glass wool was already being used as a chemical and thermal insulation material in the building industry and was regarded as the closest “neighbouring fibre” to asbestos. The fact that the latter was already being laid unidirectionally in presstoff fabrics suggested that glass fibres could be applied likewise and even used like textile fibres in woven fabrics. Another reason for researching glass fibre was that a substitute for asbestos was being sought, as the harmful effects of asbestos fibres on health were already under discussion at that time.224 With a view to saving on glass fibre, which was relatively expensive then, Koch and Satlow experimented with various forms of mixed fabrics. Koch preferred the jute–glass-fibre combination because of its good material characteristics. In addition, jute fibre was comparable to glass fibre in terms of its resistance to tearing, which meant that the two kinds of fibre suited each other well. Koch and Satlow procured the materials for their first investigations (glass silk and glass yarn) from Thüringische Glaswollindustrie, the former Koch GmbH in Hamburg, and from Actien Gesellschaft der Gerresheimer Glashütte, formerly named Ferdinand Heye, in Gerresheim near Düsseldorf.225 Both of these companies continued to be major suppliers of glass-fibre products after the end of World War II, one in the FRG, and the other in the GDR under the name VEB Werk für Technisches Glas in Ilmenau. 224 For more details see the remarks in Sect. 3.1.1 above on characteristic values and technical design of the plastic masses. 225 Koch and Satlow (1940a), p. 211.

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181

Table 4.4 Commissioned research at the chair for fibrous materials science of the Dresden polytechnic between 1939 and 1945226 Client

Topic

Researchers

Reich Ministry of Aviation

Glass fabric research

Paul-August Koch Günter Satlow Wolfgang Bobeth

Reich Ministry of Aviation

Glass filament research

Paul-August Koch Günter Satlow Wolfgang Bobeth

Reich Ministry of Aviation

Tensile impact testing machine

Paul-August Koch Günter Satlow

Reich Office of Economic Expansion

Evaluation of textile-fabric testing Paul-August Koch Günter machine Satlow

Reich Office of Economic Expansion

Glass research

Paul-August Koch Günter Satlow

Reichsgruppe Industrie (Economic Group on the Textile Industry)

Investigations on the moisture absorption of glass silk and glass yarn

Paul-August Koch Günter Satlow

Reich Office of Economic Expansion

Assessment

Paul-August Koch Günter Satlow

Reichsgruppe Industrie (Economic Group on the Glass Industry)

Glass research

Paul-August Koch

German Technical Glass Society Frankfurt am Main

Glass filament research

Paul-August Koch Günter Satlow

The investigations on glass-fibre fabric, in particular its materials testing, were performed by Paul-August Koch’s assistant, Wolfgang Bobeth (1918–1996), the later holder of the chair for textile raw materials and textile testing at the Dresden polytechnic; and various tests were carried out in cooperation with the Materials Testing Office of the Dresden polytechnic.227 As early as 1942, Koch and Bobeth published their opinion that 226 List by the rector about the research projects carried out at TH Dresden during World War II (UA

TUD: 833, Rektorat 1945–1968, Tätigkeit des Dolmetscher Büros, 1946). 227 Bobeth (1943), appendix. Wolfgang Bobeth (born 15 Feb. 1918 in Löbau—died 2 Apr. 1996 in Dresden), took his Diplom degree in mechanical engineering in 1941 at TH Breslau, he was assistant to the chair for fibrous materials science at TH Dresden 1941–45, earning his doctorate there in 1943. Having joined the NSDAP in 1941, he was expelled from university employment in 1945 because of this party membership. 1945–48 he worked as an assistant at the dye and weaving factory Löbauer Stückfärberei und Weberei in Löbau, 1949–50 as laboratory manager at VVB Weberei in Löbau, 1950 was on the scientific staff and department head on an individual contract at the Institute of Fibre Technology in Pirna-Copitz for the German Academy of Sciences in Berlin. In 1952 he accepted a lectureship (fibre microscopy) at TH Dresden, 1955 was on the scientific staff at the Ministry of Lightweight Industry of the GDR, and in 1956 he completed his habilitation degree at TH Dresden. In 1957 he received a teaching assignment as professor and in 1960 assumed the chair for

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glass-fibre fabrics could conceivably enter serial production, but that a quality standard and appropriate materials testing were prerequisites. Both not only envisioned glass-fibre woven fabrics as insulation or as a classical textile but also recognized its potential for applications in other areas.228 There is no mention in their publication that Koch and Bobeth had already tested glass fibre or glass fabric as a technical textile for glass-fibrereinforced plastic. However, some of those results can be found in Bobeth’s dissertation, which he published in 1943. The main part of that thesis deals with fibre strength, which was explored as part of the research for the Luftwaffe and was later classified as secret.229 The evaluation, further technological parameters of the investigations as well as the developed testing instrument and testing regime found room in its appendix. As the still available library copy of the thesis shows, this appendix was only included in the original submission copy at the institute. However, that original copy has been lost since 1945. The investigations into glass-fibre materials conducted for the Luftwaffe between 1940 and 1945 at Paul-August Koch’s institute are partly establishable in Bobeth’s habilitation thesis from 1956 on improving textile glass-fibre products.230 Bobeth indicated that the tests performed at that time with a universal testing instrument developed according to the Dr. Frenzel-Hahn principle,231 permitted rapid testing of the strength properties of material samples. This rapid testing procedure developed in this context had presumably been an air force requirement at the time, which wanted to test large quantities of material as soon as possible. There was a comprehensive comparative test in addition. The material parameters of linen, which was used as a fabric laminate in presstoff , was thus compared against the characteristic values obtained for glass fabric. The test parameters lead one to conclude that the Luftwaffe was planning to use GFRP as a structural material. The material properties of the GFRP tested at that time are comparable to those obtained in the 1950 and 1960s. textile raw materials and textile testing. 1959–81 Bobeth was the part-time director of the Institute of Fibre Technology at Dresden for the German Academy of Sciences in Berlin, in 1968 he became the director of the Institute of Textile Technology at TU Dresden, and in 1969 full professor there (UA TUD: Personalakte II/7677, Bobeth, W., Prof.). 228 Koch and Bobeth (1942), p. 675 f. 229 Bobeth (1943). 230 Beitrag zur Verbesserung der Textilglasfaser-Produkte, Bobeth (1956), p. 396 f. 231 A testing instrument developed by Prof. Walter Frenzel (1884–1970). From 1921–25 Frenzel headed the Imperial Fibre Research Institute in Delft, the Netherlands, 1925 became director of the spinning and weaving mill in Goirle, Netherlands, 1932–1942 headed two technical textile colleges in Chemnitz, 1942 headed the textile engineering school and the testing office in Sorau, 1945–1949 took up employment in the state administration of Saxony and headed the research and development department of the Province of Saxony, 1947–1957 was full professor of textile technology and head of the Institute of Textile Technology at TH Dresden; at the same time from 1949–1957 he directed the Dresden Institute of Fibre Technology of the German Academy of Sciences in Berlin. PDM—(Haka (2014b).

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Römmler AG in Spremberg took over the conversion of the glass fibre or fabric into a composite and their corresponding preliminary testing as a structural material. As early as the beginning of 1942, Römmler AG was able to provide the Luftwaffe with glass-fibrereinforced plastic based on the developmental research conducted at Paul-August Koch’s institute. A glass-fabric panel under the brand name Harex entered secret serial production for the Luftwaffe.232 An internal report by the Römmler AG states that the manufactured synthetic-resin presstoff panel reinforced with glass-fibre fabric was a product specially developed for the Wehrmacht and that its quality satisfied the technical requirements. The production costs were higher than those of an asbestos panel, however. Consequently, Römmler AG viewed continued production of GFRP in peace-time with scepticism. The Dresden fibre researchers and clients can therefore be considered pioneers in the basic research as well as the applied research on GFRP. The extent to which PaulAugust Koch, Enno Heidebroek and Friedrich Tobler actually exchanged ideas about fibre-reinforced plastics can only be surmised. If one considers that Paul-August Koch’s assistant, Günter Satlow, was also a member of the student fraternity Corps Altsachsen in Dresden, of which Friedrich Tobler’s assistant, Klaus Menzel, and Enno Heidebroek were also members, it is likely that there was some exchange between them about fibrous materials and specifically about GFRP beyond the bounds of professional duty.233

4.4.2

Institute of Materials Research at the DVL—New Materials and Conventional Knowledge—Researches Between 1930 and 1945

The fields of application of the compressed thermoplastics developed thus far were often left open and addressed a wide range of users in mechanical engineering or the textile industry. The textile department of the German Aviation Research Institute (Stoffabteilung der DVL) and its reestablishment in 1935 as the Institute of Materials Research (Institut für Werkstoffforschung), on the other hand, focused on a surveyable field in mechanical engineering—namely, aircraft construction. The director of the institute until the beginning of 1936, the engineer Paul Brenner, defined the tasks of his institute in this context as follows: 232 See the description of the development and usage of Glasgewebeplatten in the report “Fertigungs-, Kalkulationspreise-, Preis-und Verkaufsgrundlagen für geschichtete Kunstharzpreßstoffe der Römmler AG” from 1945, p. 11 f., 18 f. (BLHA: Rep. 75 Chem. Werke Römmler 32). 233 Membership list of the Alte Herren Verein des Corps Altsachsen Dresden from 1943 (AFTUD Nachlass Schierig).

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The investigation of all materials considered for aeroplane and aircraft engine construction and the establishment of bases for the greatest possible exploitation of materials through appropriate structural design, processing and utilization. Added to this is the investigation of material deficiencies from practice and the development of testing methods and equipment.234

The expansion of aviation research under national socialism was extensive, and the DVL and its institutes were an integral part of it. No other branch of the armed forces experienced such a large-scale expansion of R & D as the air force, which had been heavily regulated up till then and had been scaled back by stipulation of the Treaty of Versailles.235 During the years of expansion in the DVL, metals dominated materials research as the object of study, and the focus was placed on questions of efficient production. One reason for this was conventional notions of material stability, which had been associated with metallic materials for generations and thus left little room for manoeuvre within the engineering tradition. Another reason was the commitment to all-metal planes.236 Another complicating factor was that one of the most important aircraft builders and entrepreneurs of his day and a prominent expert, Hugo Junkers (1859–1935), spoke out in no uncertain terms in favour of all-metal planes and received strong backing by the dominant lobby of the metal-processing sector.237 This lobby propagated the general argument comparing or equating presstoff materials with wood and underscoring the latter’s disadvantages, such as its susceptibility to moisture absorption and rotting. The most powerful argument, however, was comparing high-performance metallic materials with the strength characteristics of wood-derived materials, albeit without actually differentiating between the various technical materials. Further arguments were the lack of long-term experience or successful exemplary applications. Many users, decision-makers and other branches of industry adopted these arguments and considerable effort was needed to refute them. Junker’s ideas and his company initiated a trend reversal in materials technology that went far beyond the material itself. His ideas about metallic products even extended to the Bauhaus in Dessau and metallic everyday creations, such as metallic furniture.238 When Junkers died, only 20 years had elapsed since he had presented the first all-metal aeroplane and arranged for its serial production. It was therefore the more regrettable that his “legacy” came into the line of sight of the young nazi state and its rearmament plans during his lifetime. It avidly helped itself to Junker’s copious patents and his company’s wealth of technical experience in production while it proceeded to oust the 234 Brenner (1937), pt. I, p. 580. 235 Trischler (1992), p. 174 f., 203 f. 236 For more on all-metal aircraft or the use of metallic materials in civil and military aircraft

construction in Germany, and the companies involved, see Budraß (2007), p. 157 f. 237 Haka (2017), p. 83, Hassinger (2013), p. 209 f., Brenner (1933), p. 497 f., Riechers (1937), p. 236 f. 238 White (2010), p. 18 f., 63 f.

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company’s owner.239 The nazi state was convinced of the stability afforded by the new technical materials, however, because of the decisive advantages they offered especially in military aircraft design, such as good serial production properties and assembly, higher flight speeds due to the new load horizons or better armouring against projectiles. In addition, a great deal of basic knowledge about metallic materials was already available. Governmental and industry-related research and development in this area promised to promptly deliver useful results that could be incorporated directly into the development of armaments.240 The developments in aeroplane design and prototype testing of materials that were fundamentally new at that time, including layered presstoff materials in particular, fell on fertile ground, especially in a field such as aeronautical research, so used to breaking records. In no other area of mechanical engineering were developers and testers so open to innovations, since the military sector in particular was constantly facing new extremes. Unnoticed by the professional experts, shortly after the revocation of the heat-pressure patent on bakelite in 1931, in-depth investigations began in the fabrics department of the DVL. Presstoff materials were initially qualified as prototypes for load-bearing structures in military aircraft construction. In this connection, the presstoff was prepared as a classical U-shaped structural beam (Fig. 4.30). Another step was made towards a better understanding of construction with presstoff by the DVL’s textile department, Stoffabteilung, while it was devising prototype components for a Heinkel aeroplane—the light combat aircraft He 45. Rather than employing aluminium to produce the rudder unit, the DVL decided on presstoff (Fig. 4.31).241 The results of these trials were initially disappointing until it was realized that the underlying structural principles hitherto so successful in aircraft design only applied to classical wood and metal constructions. Whereas they failed here. Added to that, none of the engineers involved in the project planning had any significant experience with presstoff as a structural material, so the necessary know-how had to mature slowly. A pertinent study by the DVL’s Institute of Materials Research revealed the prospective benefits of employing presstoff structures and also considerable monetary benefits at the stage of serial production. The study showed that such verticle stabilizers out of presstoff were many times cheaper than fins out of aluminium. Extrapolating on the basis of the prototype tail-plane shell, one arrived at a cost savings of 710 reichsmarks per piece for 500 tail-plane shells made of layered presstoff compared to the metallic equivalent.242 From the technical point of view of production, this sum was substantial, especially when one considered that the much more costly pressing moulds for the composite structures were already included in the calculation. 239 Cf. Maier (2007a), p. 409 f., Hachtmann (2007), p. 295 f., Budraß (2002), p. 142 f., 157 f., Trischler (1992), p. 208 f., 242 f., RLM-GL/Fertg. (1942). 240 Oeckl (1937), p. 25 f. 241 Küch (1937). 242 Küch and Riechers (1941), p. 16 f.

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Fig. 4.30 Structure and dimensions of a synthetic-resin spar. A prototype flange spar for structural application in aircraft construction, diagramme from the DVL’s textile department 1937. Basically, two presstoff U-profiles made of cellulose (paper) tapes with phenol–formaldehyde resin as the supporting matrix and a birch veneer (cross pieces: fivefold plywood with fabric outer layers, pressed together with synthetic-resin glue and screws). Source DVL research report 1937, Riechers (1937), p. 58, Fig. 3.6 Fig. 4.31 View of a rudder-unit shell made of laminate presstoff by the DVL, with cellulose tape as reinforcement material for the lightweight bomber plane Heinkel He 45 from 1934. Source Küch, Riechers 1941, p. 16

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The testing engineer Kurt Riechers, a staff member at the DVL’s Institute of Materials Research, explained in a report that neither was there any understanding of such moulding compounds (synthetic-resin pressed mass) nor of their fillers (reinforcing fibres). That was the reason for their failure to design appropriate aeroplane structures suited to the materials used.243 Here, conveyed academic knowledge about isotropic materials clashed with the as-yet-untaught anisotropic behaviour of presstoff materials.

4.4.2.1 Uncharted Academic Territory Far Removed From University Research The experiments with presstoff materials showed that a complete rethinking was needed for the design, production and especially the joining techniques involved. From 1934 onwards, a start was made to build up the necessary knowledge in order to be able to make further progress. Two years later, the essential basics about layered compressed thermoplastic as a structural material were already at hand. Enquiries made to university researchers had been futile, though, because traditional mechanical engineering—especially lightweight design, which concentrated primarily on aluminum—did not regard the implementation of such a material as within its purview. Therefore, cooperative partners had to be sought elsewhere, among manufacturers and users of presstoff. According to the available evidence, the central actors who were concentrating on numerical designing of presstoff as a structural material in industry were: Römmler AG in Spremberg, Dynamit Gesellschaft in Troisdorf and Bisterfeld & Stolting in Radevormwalde.244 Beyond this group of actors, only a small group of autodidacts could be identified, who were operating on the same level as the researches conducted at the DVL and were juggling with the interplay between practical experiment and numerical design of presstoff materials. These included the brothers Walter and Reimar Horten and their immediate collaborators. What this work looked like is described in the case study in Sect. 4.6. Amongst the known types of moulding materials already defined by DIN 7701 in 1936, the DVL regarded layered presstoff as a promising structural material. The DVL institute had already investigated the chemical compositions of synthetic resins and possible fillers in extensive tests. The production of laminate presstoff thus far and the handling of the layered stacks of fabric and hard-paper tapes in the supporting matrix revealed the strengths that could potentially be achieved by an appropriate alignment of the fibre structures in the pulp layers and warp and weft thread arrangements.245 Although this conventional production 243 Ibid (1941). 244 UA TUD: test reports of Dynamit AG and Vertriebsgesellschaft Venditor from 1942–1944,

respectively, as well as the minutes of the meeting of the VDI Arbeitsgruppe Prüfung von Preßstofflagern dated 25 May 1943 (ibid., A/887, Lageruntersuchungen, and A/872, Berichte und Diagramme, resp.) as well as Küch & Riechers (1941), p. 3 f., Thum and Jacobi (1939), p. 1044, Leysieffer (1939), p. 662 f., Brenner (1933), p. 497 f. 245 Küch (1938), p. I 561 f.

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of such panels was technically cost-effective and the material values quite impressive compared to metallic materials, they could only partly satisfy the design requirements and individual structures needed to produce high-quality aircraft. This capacity limit once reached in the mid-1930s was when the engineered designing craft of modern fibre-reinforced plastics of the twentieth century finally began. Under the leadership of Paul Brenner, the engineers Kurt Riechers and Wilhelm Küch defined the insertion of individual fibre rovings in a resin system suited to a given load and rejected the production of layered presstoff hitherto employed in favour of a load-oriented fibrecomposite design.246 The resulting compressed thermoplastic material was referred to as armed presstoff (bewehrter Preßstoff ). This application of fibres and their incorporation into presstoff materials to support the desired load had already attained an impressive level by this time and were certainly on a par with current design concepts of fibre-reinforced polymers. The DVL soon began to develop alternative fibres to the classical fillers including fabric and hard paper, which had usually consisted of cotton or cellulose fibres, and to insert them unidirectionally into presstoff. The Riechers report explains: [...] the inlaying of suitable raw fibres provides the means to achieve very considerable increases in strength. Tests carried out by the DVL with agave fibres, with sisal and aloe fibres, have produced a synthetic, the strength properties of which are shown in the figure [cf. here Fig. 4.32]. It is noteworthy that the quality characteristics are already of the same order of magnitude as for metals of the highest quality, and some even variously exceed them.247

These experiments showed, Reichers continued, that the thus engineered stability for presstoff is equivalent to conventional metallic structural materials: In addition, the elasticity modulus reaches a value that is about 3 to 4 times greater than the elasticity moduli of normal commercial plastics. With a specific weight only half that for light metal and also an elasticity modulus already 1/3 to almost ½ of it, a material has been created that is competitive with previous materials.248

A further development of armed and laminate presstoff materials with fibre or fabric insets as engineered materials for aeronautical applications can be traced back to 1941.249 A comprehensive report in Ringbuch der Luftfahrttechnik, the confidential publication medium introduced by the RLM to communicate the latest methods, materials and processes from research to select industrial enterprises, announced success in the production 246 No further personal data on Kurt Riecher and Wilhelm Küch are available, as the complete personnel files were confiscated by the Red Army after 1945 and have since been considered lost. (Information provided by Dr. Wichner, German Aerospace Centre (DLR), Central Archive). 247 Excerpt from the DVL report by Kurt Riechers: Riechers (1937), p. 50 f., citing original Fig. 2.4. 248 Ibid. 249 Küch and Riechers (1941).

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Fig. 4.32 Characteristic values of prototypical armed presstoff containing raw-fibre inlays with orientated strengths determined at the DVL’s textiles department in 1935. It indicates the yarns in normal, twisted and stretched states for their tensile, compressive, flexural and impact strengths, along with their elasticity moduli and specific weights. Source excerpt from the DVL report by Kurt Riechers, 1937, p. 50, original Fig. 2.4

of hollow profiles, fins and structural components made of presstoff materials for aeronautical applications as well as in their testing. Trials were performed on common materials used in aviation such as hardwood and duralumin for comparison against armed and laminate presstoff materials. The conventional strength examinations, such as tensile, compressive and flexural tests, were supplemented by other materials testing particularly suited to representing the dynamic load horizons in aircraft construction. They included, for example, the plotting of stress-number curves. These foregoing accounts show that a turn-about in the field of aeronautical materials could perhaps have occurred by about the mid-1930s or could at least have led to an addition to the portfolio of aviatic or lightweight construction materials with layered or armed presstoff materials. The research by the company Focke-Wulf-Flugzeugbau in Bremen, for example, shows that aeronautical research was ready to venture down new paths. When in 1939 Focke-Wulf presented one of the most capable fighter planes of World War II, which had been designed as an all-metal aeroplane, a patent was immediately filed by the company at the Reich Patent Office.250 This patent, if it had been applied, would have

250 Haka (2011), p. 83 f.

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recognized the possibility of producing large workpieces in aeroplane construction, i.e. entire aircraft structures made of synthetic resins or similar plastics.251 The load limits of presstoff materials, especially of armed presstoff, seemed at that time to have been reached. The conservative vagaries of traditional mechanical engineering and the orientation of German design caused this alternative to duralumin to stagnate.252 The clear affinity in materials science for metallic materials, which found its way into practice in research and industry through the education of engineers over the decades, can be retraced in the course curricula of many polytechnics in Germany from the 1920s onwards. Materials science was granted little attention in these lectures. The focus was on the basic disciplines (technical mechanics, technical thermodynamics and fluid mechanics) and on component and engine design.253 This affinity unduly hindered the establishment of presstoff products as a material for load-bearing structures, and rather reduced them to insulation and accessories in engineering applications. Experts in the presstoff industry, who had joined forces in the Association of German Engineers (VDI), attempted to counter this trend.254 The outcome was a training course on “Plastics and presstoff as construction tools” lasting several days in 1937 at the VDI’s Working Group of German Design Engineers of the National Socialist League of German Technicians (NSBDT). This course was primarily intended to sensitize design engineers to these materials.255 But no subsequent training courses in this area were offered. Such endeavours in the leading journal for engineers, Zeitschrift des Vereins Deutscher Ingenieure, also waned. Only a small circle of materials specialists dealt with a modest number of topics on design issues related to presstoff. It is therefore all the more astonishing that the members of this specialist community were able to make considerable gains. In the early 1940s, numerical evaluation or design of presstoff materials attained an astonishing level for its time. One good example of this is the research by Richard Vieweg (1896–1972), the plenipotentiary on plastics on the teaching staff of the Darmstadt polytechnic in the field of technical physics. His paper on “Directionally dependent thermal expansion of layered plastics” analysed several samples of presstoff and hard paper. An illustration there depicts the thermally induced expansion of individual layers of the presstoff material.256 Vieweg dealt further in this context with the anisotropic material properties of 251 Focke-Wulf Flugzeugbau GmbH Bremen (1943). 252 Haka (2014a), p. 328 f. 253 See the selective course lists of the Technische Hochschulen in Berlin, Munich and Dresden

covering the period 1925–44; a sector-specific and staff-related account on research conducted in German mechanical engineering 1920–70 is available in Haka (2014a), p. 326 f. 254 Vieweg (1939), p. 1053. 255 “Die Kunst-und Preßstoffe als Konstruktionsmittel”. See the conference programme of the Arbeitsgemeinschaft Deutscher Konstruktionsingenieure des VDI im Nationalsozialistischen Bund Deutscher Technik in December 1937; employees of Römmler AG were among the participants. 256 According to the modern definition, layered presstoff is a multilayered composite.

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such layered composites.257 His analysis points in the direction of modern-day numerical evaluations of individual layers (= plates) in the classical laminate theory.258 This theory was developed in the 1960s and is based on the classical elastic plate theory by Gustav Robert Kirchhoff (1824–1887).259 Vieweg’s research here was theoretical and related to a special case of moist presstoff materials. The research of Wilhelm Thielemann (1908–1985), however, the later holder of the Braunschweig chair of aircraft and lightweight construction, can be taken as the practical state of knowledge in the mid-1930 and 1940s, even though it cannot be assumed to apply to aircraft construction as a whole of that time. Thielemann worked from 1937 as head of the department on statics and strength at the Siebel Flugzeugwerken in Halle (Saale). His task was to verify the strength of new aircraft designs and completed aircraft models by means of numerical methods and by testing.260 Thielemann’s research results, which were later confiscated by the Russian Allies, can be traced well in his dissertation submitted to the Berlin polytechnic in 1944. (Thielemann himself was conscripted and sent to Podberezye near Moscow in 1946.)261 Although Thielemann did not study layered presstoff materials, his numerical calculation of plywood layers is already very close to the classical laminate theory262 for composite materials known today.263 The problem of the stability of orthotropic or isotropic panels had already been investigated in 257 Vieweg and Schneider (1942), p. 295 f. 258 Classical laminate theory = method for calculating the stiffness and stresses of a planar and

usually anisotropic multilayer composite, see also Cuntze (2019), p. 35. 259 Mittelstedt and Becker (2016), p. 144 f., Altenbach and Becker (2003), p. 4 f., Kirchhoff (1850). 260 Wilhelm Thielemann (1908–1985) studied aeronautical engineering at TH Berlin under Prof. Herbert Wagner 1928–34, becoming his first assistant 1935–1936; 1960–1976 he was appointed full professor of aeronautical and lightweight engineering at TU Braunschweig, from 1937–1945 headed a department at Siebel-Flugzeugwerken in Halle-on-Saale, took his doctorate in engineering 1946 but was then conscripted to Podberezye (near Moscow, USSR) as department head on aeroplane dynamics, where he worked on supersonic aircraft. In 1953 he returned to East Germany, where he worked for a short time at the Institute of Applied Mathematics at the Academy of Sciences in Berlin. He declined a professorship in mechanics at TH Dresden and the College of Transportation in Dresden; in 1954 he moved to the Institute on Stability at the Aachen polytechnic, from 1960–1976 he was full professor of aircraft and lightweight construction at TU Braunschweig, becoming emeritus there in 1976. University archive of TU Braunschweig [hereafter UAB]: B7: 487, curriculum vitae of Prof. Dr. Wilhelm Thielemann. 261 Thielemann submitted his dissertation in 1944, which was based on his work at the Siebel aircraft factory in Halle (Saale). Due to the war, however, the defence did not take place until 1946 under Prof. Georg Schnadel and Prof. Alfred Teichmann, “On the buckling of an obliquely cut orthogonalanisotropic plate strip, in particular an obliquely cut plywood strip”. Thielemann was only able to publish his dissertation after his return from the USSR in 1956, see here Thielemann (1946). 262 For comparison see Navier’s solutions within the framework of the classical laminate theory, in particular on the buckling behaviour; Mittelstedt & Becker (2016), p. 332 f. 263 I would like to thank Prof. Dr. Stephen Tsai (Stanford University, California, USA), who conveyed to me information on the development of composite materials and the early work of Wilhelm Thielemann in several conversations.

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a few papers in the mid-1920s.264 The papers were all concerned with the investigation of orthotropic plates with a main stiffness orientation running parallel to the edges of a rectangular plate. Starting from this, Thielemann’s work investigated orthotropic plates with a main stiffness orientation not parallel to the edges. Thus, for example, he took differently positioned plywood layers into account, such as a barrier ply positioned at 45º. As can be gathered from his dissertation, he was guided primarily by the work of two experts in materials statics, one being the versatile German aeronautical engineer and physicist Hans Jakob Reißner (1874–1967),265 and the other being the Polish civil engineer and mathematician Maksymilian Tytus Huber (1872–1950).266 Thielemann’s report “On the buckling of anisotropic plate strips”, published in 1956 at the German Aviation Research Institute (DVL), clearly points out the way to the classical laminate theory.267 So Thielemann can also be considered its intellectual father. The importance of Thielemann’s fundamental work during World War II is reflected in his academic aura after 1945. The now professor emeritus of aeronautics and astronautics at Stanford University, Stephen W. Tsai (born 1929)268 Fig. 4.33, while reminiscing about his professional beginnings 264 Southwell and Skan (1924), Reißner (1926), Huber (1929), Bergmann and Reißner (1932),

Schmieden (1935), Timoshenko (1936). 265 Hans Reißner can be seen as one of the most influential engineers and physicists of his generation. His paper on “Inherent gravity of the electric field according to Einstein’s theory”, published in 1916, was later developed into the “Reißner-Nordstrom Theory” of black holes. His investigations on the statics of metallic aircraft components and his introduction of the wind tunnel into research on aerodynamics showed the way in aviation around the world. Reißner had to emigrate to the USA in 1945, see Reißner (1928), id. (1916). 266 The Polish civil engineer, mathematician and astronomer Maksymilian Tytus Huber, who was professor of mechanics at the polytechnic in Lemberg (Lviv) from 1908 and was elected rector there in 1921/22, worked primarily in the field of theoretical mechanics. His hypothesis on the mechanics of solid bodies was a decisive contribution to modern mechanics. Today, this hypothesis is part of the maximum distortion criterion (Huber, von Mises, Hencky), see Ditchen (2015), p. 149 f. 267 Über die Beulung anisotroper Plattenstreifen, Thielemann (1956b). See in particular the sketch of the transformation equations and the matrix inversion, both of which form the “backbone” of the classical laminate theory. 268 Stephen W. Tsai (*1929), 1952–58 engineer at Foster Wheeler Corporation, 1961–1966 fibre composite engineer at Ford Aeronutronic, 1966–68 professor at Washington University, 1968–1972 chief Scientist at Air Force Materials Laboratory, 1969 Battelle visiting professor at Ohio State University, 1972–1990 director of mechanics of composites at Air Force Materials Laboratory, 1982 adjunct professor at the Naval Postgraduate School, 1992–2001 research professor in aeronautics and astronautics, Stanford University, 1991–now: chief engineer, think composites, 2001–now: research professor emeritus, aeronautics and astronautics, Stanford University. Stephen W. Tsai’s research led to several formulas and failure criteria for composites which now bear his name, such as TsaiWu, Tsai-Hill. They have become common practice in composite design and have been implemented multiply in commercial software. These criteria are standard textbook material and have been used in most research articles on composite structure design and analysis. In 2020, his colleagues decided to name his discovery of a master layer in CFRP composites as a Tsai module. His most recent efforts in CFRP have instructed industry to change many fundamental practices that prevented more optimal use of composites until then. Examples include asymmetry, homogenization which has

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Fig. 4.33 Stephen W. Tsai in 2020, research professor emeritus, aeronautics and astronautics, Stanford University. Photo Courtesy of Stephen W. Tsai, 1 July 2020

at Ford Aeronutronic, specifically remarked about Wilhelm Thielemann’s research work during World War II: It laid out the basics of what we now refer to as the classical laminated plate theory. That was in 1961 when I started working for Ford Aeronutronic, a division that was doing space-related work. [...] I started with glass/epoxy composites which were used for solid rocket casing, like the Polaris missile for the US Navy. From Prof. Thielemann’s report I learned that there were 4 elastic constants for plane stress: Ex, Ey, Es and nu/x. The pressure vessel design at the time used only one constant, the stiffness of glass fiber. So I proposed to NASA to measure those 4 elastic constants for glass/epoxy and impressed upon them the importance of having them so the vessel can be designed as a laminated structure. [...] Later I extended the stiffness study to strength and I used Hill’s plasticity criterion which was referred to as Tsai-Hill.269

Tsai’s remarks show that particularly the theoretical insights into designing fibrereinforced composites and especially glass-fibre reinforced plastics had still not become firmly established in the USA long after the end of World War II. The researches by Vieweg, Thielemann, the DVL as well as the presstoff manufacturers Dynamit Nobel AG and Römmler AG show that numerical design of reinforced and layered composites and their application as structural materials in a complex structure such as an aircraft was already feasible from an engineering point of view in the mid1930s and certainly latest by the end of that decade.270

made shape optimization possible, multi-angle weave to increase productivity, and an entirely new method of generating a design that can accelerate the certification of new materials and processes for applications. (Interview with Stephen W. Tsai, 28 Dec. 2020.). 269 Interview with Stephen W. Tsai, 28 Dec. 2020. 270 See here, e.g. Jacobi (1942), p. 8 f., Thum and Jacobi (1939), p. 1044 f., Küch (1940), p. 1 f.

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Before the collapse of the national socialist regime in 1945 and the temporary standstill in German aeronautical research brought on by Allied Control Council Directive No. 25,271 an imposing advance was achieved in the development of hybrid materials. The results of the basic research on glass fibres and glass-fibre fabrics conducted at Dresden afforded to the German air force another fibre material to add to its investment portfolio of interesting topics of investigation. The DVL helped itself to the basic research findings on textile fabrics and fabric design from Dresden in 1941 and developed the first synthetic-resin laminate with glass-fibre fabric inserts.272 The structural materials developed from this showed that their material characteristic values, especially tensile strength, were clearly superior to those of duralumin. Thus, by the early 1940s, German aviation, and in particular the German air force, already had a hybrid high-performance material at its disposal. However, apart from the production of prototype aircraft structures and individual supporting elements, there was no concrete aeronautical implementation in an aircraft model using GFRP. This was despite the fact that in 1944 the Reich Aviation Ministry had issued an order for the development of high-strength plastics with layered inserts of glass-filament fabric and the development of mouldings, which meant its qualification for serial production of aircraft components in GFRP. The research leadership under the reichsminister of aviation and commander-in-chief of the Luftwaffe introduced the topic into the priority programme of the aviation research institutes just a few months later.273 The accelerating dynamics of the war and the limited availability of staff and material stood in the way.274

4.4.3

Fibre Research—The Institute of Materials Research at the DVL and the Graf Zeppelin Research Institute

The investigation, analysis and rapid implementation of fibrous materials as reinforcement in composite materials as well as applications of the Dresden research results in the field of glass-fibre fabrics were based on well-founded knowledge and active fibre and textile research in the Textile Department (Stoffabteilung), the subsequently renamed Institute of Materials Research of the DVL.

271 Heinemann (2001), p. 167 f. 272 DVL report of 15 May 1942 by Perkuhn and Küch (AFTUD: Heidebroek papers. Publication

collection). 273 Development order by Reichsluftfahrtministerium to Institut für Werkstoffforschung der DVL dated 1 Apr. 1944. The use of GFRP mouldings was later included in the “Schwerpunktprogramm der Luftfahrt-Forschungsanstalten”. See the related list dated 15 July 1944, issued by the Forschungsführung des Reichsministers der Luftfahrt und Oberbefehlshaber der Luftwaffe (Historisches Archiv der TU Munich. Ernst Schmidt papers, no. 3600. Institut für Motorenforschung. Aufträge Luftfahrtforschungsanstalt Herman Göring). 274 Tooze (2008), p. 561 f.

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Between Professional and Political Ambivalence—Fibre Research …

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Three dominant topics are identifiable which occupied an important place, foremost all the broad-ranging subject of cloth coverings. This involved analyses of linen, flax and cotton fabrics and their utilization as a covering stretched over an aerofoil as the outer skin of a wing, for instance, as well as for winding and adhesive tapes.275 In this context, waterproof sealing of fabric by means of various varnish systems was explored, as well as waterproof processing of felled and quilted seams under load. Balloon fabrics for free and tethered balloons is another area. Here, too, water absorption and the load horizons of the fabrics were looked at more closely. In connection with these issues of moisture absorption, the gumming of linen, cotton and silk fabrics, their load absorption and aging under atmospheric influences were another broad research focus. The last major field of research dealt with parachute fabrics and parachute accessories. This subsumed the wide field of natural silk applications. In particular, mainly the processing of silk from the mulberry silk moth and alternatively the tussah silkworm, for parachute canopies. There was extensive development of hitherto unavailable testing technology, in particular the bursting test, and of adequate testing regimes. This was new territory in this field world wide, both in terms of materials technology and process engineering. The testing device illustrated in Fig. 4.34 permitted, among other things, macroscopic materials diagnostics to be conducted on the burst specimen while the test was underway and one could proceed down to the microscopic level.276 The thus determined parameters were examined in a completely new test scenario and for the first time addressed analytically fibre-relevant quantities within the context of materials engineering, such as the type of textile weave, air permeability, fatigue strength of the fabric under reversed bending stress, fibre breakage and climate resistance. In addition, long-term investigations were carried out with regard to mechanical medial failure and shelf life under different storage conditions. The topic of parachute development and within this context also fibre, fabric and textiles were also treated in specialized research at the Graf Zeppelin Research Institute (FGZ) in its Parachute and Brake-chute Development Department under Theodor Knacke (1910–2000).277 A fundamental reorientation took place with regard to the use of fibre and fibrous materials due to shortages in high-quality textiles latest by 1943. Ancient Japanese papermaking techniques were consulted by Theodor Knacke’s team to develop parachutes made of modified cellulose-based paper-yarn fabric. Bitumization and crimping further strengthened the parachutes. Material shortages also led to completely new fibres being used, for example, the first fully synthetic fibre in the world, developed in 1931 by Emil Hubert (1887–1945), PeCe fibre.278 Another was polyamide fibre developed in 1938 by Paul Schlack (1897–1987), which later became known by the brand name perlon. Under 275 Tooze (2008), p. 5 f. 276 Riechers (1938), p. 6 f. 277 Abteilung Fall-und Bremsschirmentwicklung der Forschungsanstalt Graf Zeppelin, Heinrich

(1943), id. (1941), Beck (1942), Elsässer (2022), p. 164 f. 278 Polyvinyl chloride fibre, PVC for short, is a thermoplastic polymer.

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Fig. 4.34 Cross-section diagram of the instrument for parachute-fabric burst testing developed by the DVL in Berlin in 1938. A fabric sample is clamped firmly and air-tight between two rings. Pressurized air is fed underneath the rubber membrane from below, causing it to bulge upwards. The bursting process of the fabric above it is observable under the pressure hood through a viewing window. A sensor (from above) with a gauge record the time and load exerted on the sample. Source Riechers (1938a)

the direction of Theodor Knacke, perlon fibre was used, for instance, by the FGZ to develop a tail-surface braking chute with a diameter of 8.7 m (weight: 200 kg) for the army testing station in Peenemünde.279 This parachute could be forced open at an altitude of 50 to 60 km by means of built-in air hoses. At the tip of Aggregate 4 (a V-2 rocket),280 a measuring-instrument barrel called the “Gertrude device” (also known as a “Regener barrel”)281 was installed for ejection at high altitude. The barrel’s subsequent descent was significantly slowed by the braking chute tied to its tail surface, allowing the Gertrude device to record measurements of the atmosphere. In 1945 there was still enough time to test the functionality of this parachute with success at the army research stations in Peenemünde and Bad Saarow. But no tests of the instrument barrel were done. The Gertrude device did eventually get deployed in a V-2 rocket, but only later, in 1948 in the USA, making feasible the first photographs of Earth taken from space. The Getrude device and its tail-surface braking chute were a joint development of the Forschungsanstalt Graf Zeppelin in Stuttgart, the Heeresversuchsanstalt Peenemünde, the research centre for physics of the stratosphere of the Kaiser Wilhelm Society (in Friedrichshafen on Lake Constance) 279 Heeresversuchsanstalt Peenemünde. See the itemization of the research on the “Gerät Gertrud” measurement barrel from 1945—“Auftrag zur Entwicklung eines Fallschirmes für große Höhen der mit Preßluft (Stickstoff) künstlich geöffnet wird” (T. Knacke papers, Ostfildern City Archives). 280 Type designation: Aggregat 4 (A-4), with the propaganda name Vergeltungswaffe 2—“retaliation weapon 2”, V-2 for short. 281 Gerät Gertrud was later known as the Regener-Tonne, named after the developer of this barrel of recording instrumentation, the physicist Erich Regener (1881–1955), one of the project participants who headed the Forschungsstelle für Physik der Stratosphäre, see Globig (2006), p. 56 f.

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and the Luftfahrtforschungsanstalt Ainring (the former glider research station Deutsche Forschungsanstalt für Segelflug, DFS). The just-described developmental project of the Graf Zeppelin Research Institute until 1945 had extraordinarily long-lasting repercussions. But it was not the only after-effect. The agencies of the Wehrmacht itself gained little profit by it, since its influence dissipated with the end of World War II.282 The harvest of these researches was mainly wreaped by the United States after the war. The developmental work performed by the Graf Zeppelin Research Institute in military, aeronautical and later even space research bore fruit in particular. Likewise, the results especially in parachute development were implemented in many areas of civilian aviation—for example, in passenger aircraft and/or hobby parachuting. This technology transfer from Germany to the USA was not just a continuation of old research projects initiated during the nazi era along with new topics emerging from them. In many cases it was also a transfer of scientific staff to American weapons research and industry. Moreover, these personnel also found direct access to American academia in the form of lectureships or professorships and thus had a formative effect on rising generations of scientists and engineers. Just one example is the afore-mentioned engineer Theodor Knacke and a number of his colleagues from the Graf Zeppelin Research Institute, who developed a whole series of brake and landing parachutes (ribbon parachutes) in Stuttgart until 1945 which were later used in the Mercury, Gemini and Apollo missions, contributing decisively towards their success.

4.5

Aviation Case Study I: Fibre-Aligned Wood Construction. Developing an Aircraft that Never Flew—The Hütter Hü 211

In November 1943, in the midst of the war economy and material shortages, the then still unknown aircraft designer Wolfgang Hütter (1909–1990)283 (Fig. 4.35) defined, at the behest of the Reich Aviation Ministry (RLM), the essential key points for a long-range reconnaissance aircraft made entirely of wood, Hütter model Hü 211. Unlike his younger brother Ulrich Hütter (1910–1990),284 who was able to establish himself as a university lecturer and pioneer of German wind-turbine technology particularly after World War II, Wolfgang Hütter still is mainly associated with glider construction. An evaluation of the available source materials reveals that this categorization leaves much out.

282 Elsässer (2022), p. 1 f. 283 Born in Vienna, he studied mechanical engineering in Stuttgart, graduating there as a certified

engineer in the field of aviation. He joined the NSDAP on 1 July 1932 in Vienna, Austria (NSDAP membership number: 1205379) (BArch, NSDAP-Zentralkartei). 284 On Ulrich Hütter, see Sect. 5.2.1 on student involvement leading to a CFRP series product.

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Fig. 4.35 Wolfgang Hütter (1909–1990), photograph taken in 1942. Source Frits Ruth papers via Peter F. Selinger

Prior to the project on the Hü 211, Hütter was employed by the company Wolf Hirth GmbH in Nabern. One of his tasks there was to build a wooden wing for the Messerschmitt Me 109 K. Although this wing was ultimately rejected in favour of a metal model, Wolfgang Hütter’s design for the Me 109 K was well received at the RLM. This led to him eventually being assigned the task of designing the long-range reconnaissance aircraft designated as Hü 211 made entirely out of wood.285 To complete this task Hütter left his job at Hirth, founded Hütter GmbH and leased the premises of Schempp-Hirth OHG in Kirchheim. The core of the company was a barracks building big enough for the production facility of the 24-m-long wing (Fig. 4.36). Its location was the so-called “gravel pit” between Dettingen unter Teck and the motorway.

4.5.1

Preamble to the Reconnaissance Aeroplane Hütter Hü 211

Wolfgang Hütter wrote a kind of preamble in 1943 within the context of the task assigned to him by the RLM to design a long-range reconnaissance aircraft and produce prototypes. On one hand, he referred to the critical situation of availability of aeronautical materials and, on the other hand, to the consequential task of conceiving an aircraft design not only able to parry the materials problem, but also to outdo the enemy.286 He arrived at the following construction approach:

285 Selinger (1986), p. 99. 286 Preface to the account by Wolfgang Hütter on the technical framing conditions of the Hütter Hü

211 dated 8 Nov. 1943 (Archive of Peter F. Selinger [hereafter APS]).

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Fig. 4.36 Construction of the pressing facility in the summer of 1943 for the manufacture of the shell wing of Hütter model Hü 211. Source APS A building approach must now be sought which allows the wing weight to stay within acceptable limits despite the given requirements. A pure shell construction constitutes such an approach, in which the single shell fulfils all the tasks of spar flanges, spar frames, ribbing and planking. Present-day methods only permit a shell construction carried out in wood.287

This construction approach gave Hütter a whole range of advantages. They included a very high degree of slenderness with simultaneous high load-bearing capacity, a bucklingresistant wooden shell, economical use of materials and shorter production times. The production of a metallic wing would have taken about 2–3 h longer, which was quite an important factor, considering the precarious economic and military situation in the mid-1940s. Wolfgang Hütter introduced his idea of a shell construction in the complete aeroplane blueprint from the very beginning. His original design—with contra-rotating propellers in the fuselage—was rejected by the RLM as too “audacious”.288 For lack of time and funding, an already existing aeroplane model was used for drafting purposes, and Hütter’s design as a whole did not come to fruition. Essentially, the fuselage, the tail unit and the landing gear of a Heinkel He 219 were to be used. Just the mid-section of the fuselage was supposed to be redesigned.289 Two Junkers Jumo 222 AB-3 engines were planned. 287 Excerpt from the introduction to the account by Wolfgang Hütter on Hü 211, 8 Nov. 1943 (APS). 288 See the letter from Frits Ruth to Peter F. Selinger, 12 Apr. 1991, where he reports about his

experiences as a foreign worker at Hütter GmbH from 1943–1945 (APS). 289 Ibid.

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Fig. 4.37 Model of the Hü 211, which had probably been made in Nabern or Kirchheim unter Teck. The photographer was probably Gisela Ruth (née Remy), the wife of Frits Ruth, who worked for Wolfgang Hütter as a foreign worker in the 1940s. Source APS

Although jet engines were also being considered, this topic was not pursued further on the drawing board. In addition, the on-board arms were set to a total of four Mauser type 151 machine guns, arranged in pairs, two pointing forwards and two backwards. In the end, Wolfgang Hütter had defined the wing-span of 24.5 m, with a wing surface area of 40 m2 and an aspect ratio of 1:15, for the Hü 211.290 A photograph of a model is all that is left of the original aeroplane design (Fig. 4.37),291 which gives an impression of what the Hü 211 probably would have looked like, had a prototype been built according to the RLM’s original order. Once the surrounding conditions had been settled, however, little remained of the innovative aircraft in wooden shell construction. Nevertheless, the degree of innovation of the planned aeroplane is apparent in the way it solved numerous technical aspects of the material employed for its wing design, in particular, the load-specific fibre alignment of the wood or custom-made wood composite. Hütter and the cooperation partners involved in the project used the limited time available to perform a large number of technical analyses of the materials for the wooden wing. Great importance was also attached to the manufacturing process which, in view of the dimensions of the wing shell, was also a given and demonstrates the quality standard of the project. The present examination of the Hü 211 will therefore be primarily focused on the technical material aspects of the wing design and will view the technical production conditions then available in the “gravel pit”.

290 Ibid. 291 Wolfgang Hütter had brought the model along to a meeting at the Reichsluftfahrtministerium in

1944, but it was never returned to him and has since been considered lost.

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Fig. 4.38 Cross-section drawing by Wolfgang Hütter of the structure of the Hü 211 aerofoil. Source APS

4.5.2

Fibre-Aligned Lightweight Wood Construction and Conventional Moulded-Wood Production

Hütter designed the wing shell in three parts: nose or leading-edge area, shell body and terminal section to the trailing edge (Fig. 4.38). All three segments supported specific functions. The nose section, for example, consisted of a glued plywood panel moulded into shape, the thickness of which diminished from 8 to 4 mm from the interior outwards. It was composed of several electrical de-icing mats, which the Allgemeine Elektricitäts-Gesellschaft (AEG) had supplied, laid on a plywood plate of 1 mm thickness and pressed together with other veneers to form a smooth panel composite. The technical precision required to produce this nose section thus lent this part particular importance. The terminal section contained among other things the landing flaps and gear, headlights and electric cabling. The shell body as such served as the main bearing composite and was supposed to accommodate some of the fuel tanks. The shell body was composed of six elements: upper and lower shells, ribs, central and outer webs, the installed overflow pipes and the connection fittings. The upper and lower shells were the core piece. Employing only beech veneers of quality grades I and II, the fibre-aligned processing was decisive. Their structure was orientated to handle the exerted longitudinal and shear forces. This wood composite for the shells consisted of eight veneers of 0.5 mm thickness with their fibres oriented either diagonally or longitudinally, depending on the local stress profile (Fig. 4.39). It can be seen as an interesting form of a modern, albeit segmented, fibre-reinforced composite. In some respects, parallels can be drawn with the duramold 292 composite-material processes which became known in the USA at this time, but Hütter’s processes are far more innovative and finely worked out. In particular, the use of additional blocking angles of the veneer layers, as well as their grade quality, the targeted and alternating fibre cuts and also the moulded wood manufacture exceed the duramold process by far. The numerical approach to the shell-construction method is likewise more comprehensive. The computational verification for model Hü 211, which can be gathered from the theoretical elements

292 For more details on “duramold”, see Sect. 4.6.5 on composites and their applications in engineering abroad.

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of the design with characteristic value determinations and materials testing, is very similar to the classical laminate theory293 used today to calculate stiffnesses and stresses in multilayer composites.294 Thus, the actually realized part of the Hü 211, the fully drafted wing, represents an interesting intermediate advance in materials engineering within the overall development of composite materials. Starting from classical timber construction, this composite differentiates itself by its filigree form of construction with wooden material, borrowing from moulded-wood construction,295 into a completely unique and new lightweight composite. Indeed, a combination or even outright substitution by “synthetic panels” (Kunststoffplatten) was even considered, that is, by early fibre-reinforced composite presstoff material. Hütter filed a patent about this in which he states: The demand for ever faster flying aeroplanes cannot be met solely by improving the propulsion, but by also suitably adapting the airframe [...] The subject of this invention is a main supporting shell-body wing made of glued wood veneer or synthetic panels, which are specifically intended for aircraft and which permit the construction of wings with a large aspect ratio with sufficient strength and at most the same total weight as conventionally constructed wings with a low aspect ratio ...296

By referring to presstoff within the context of shell construction with a high aspect ratio and a focus on higher flight speeds, Hütter was probably insinuating the Messerschmitt Me 109, which consisted of a semi-monocoque construction as of the cockpit section. The load-bearing fibre orientations (Fig. 4.39) for the plywood veneers is emphasized in detail in the patent within the context of moulded-wood production of the upper and lower shells and is defined as the key to the wing statics.297 The reference to presstoff indicates the innovative potential of future possibilities. The extent to which Hütter actually envisaged a combination with presstoff materials, or how realistic a future complete shell out of presstoff was to him, is a matter of speculation.298 However, it is also possible that the intention was merely to increase the patent scope by incorporating that relatively new fibre-aligned compressed thermoset plastic. It can be assumed that Hütter had access to presstoff or, respectively, was aware of its early applications as a structural material. 293 For more details on the classical laminate theory, see Sect. 4.4.2 on the Institute of Materials

Research at the DVL. 294 On the theoretical principles of that wing design, see “Theoretische Grundlagen für den Flügelentwurf” and about the trials on its wooden-shell construction, see “Versuche zur Holzschalenbauweise des Flugzeugtragflügels Hü 211” (both APS). 295 Formholz, moulded wood = wood deformed under heat and pressure. 296 See the wording in Patent A 20,029 prepared by the Stuttgart patent attorneys “Dr. Göller & Dipl. Ing. Boshart” for Wolfgang Hütter: “Haupttragende Flügelschalenkörper insbesondere für Flugzeuge aus verleimten Holzfurnieren oder Kunststoffplatten “ (APS). 297 Ibid. 298 See the work by John Dudley North and Albin Kasper Longren in Sect. 4.1.2 on “old” materials in early lightweight construction during the productive 1920s.

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Fig. 4.39 Specification of the fibre-alignments of the shell veneers for the Hü 211 wing. Taken from the production instructions by Hütter GmbH from 1945. It lists the veneer compositions by the enumerated shell bodies (|| for longitudinally, // for diagonally aligned veneer fibres, the dot indicates “Polystahl” or P600 adhesive layers; the columns on the right indicate their thicknesses, number of veneers in total, followed by longitudinal and diagonal ones, and their proportional %). Source APS

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Fig. 4.40 Shell-body veneers of a wing design illustrating the defined fibre orientations of the plywood layers for the upper and lower shells of Hü 211. Excerpt from patent specification A 20,029 “Haupttragende Flügelschalenkörper insbesondere für Flugzeuge aus verleimten Holzfurnieren oder Kunststoffplatten”. This fiber architecture is comparable to a modern multi-axial non-crimp fabric. Source APS

The patent prepared by the Stuttgart patent attorneys Göller & Boshart, including its drawings (Fig. 4.40), can no longer be verified at the German patent office.299 Judging from the existing patent design and the appended drawings, it would appear that this must have been a copy of a secret patent. Hütter’s work on the model Hü 211 had entered uncharted territory in terms of materials science and technical design. Its military relevance is a possible explanation for why no record of the patent can be found at the patent office. Glue and conservation products were a quite significant bridging element for this lightweight wooden construction. Given his experience with the wooden tail plane of the models Me 321 and Me 323 (Gigant or “giant”), Hütter must have recognized similar problems working with the Hü 211. Besides the familiar problems that plagued timber construction, such as insect infestation, there was also the issue of fuel containment, as most of the wing housed the naked fuel tanks. Leakage prevention was hence of central importance.300 Pertunol from the Mannheim company Gross & Pertun was the planned petrol-proof varnishing system. This trade name is still in use today for a product series of that company.301 But the product line by Dynamit Nobel AG in Troisdorf was much more important, which had been developed especially for aircraft construction from the mid-1930s onwards. Given the close ties to the military of Dynamit Nobel AG as a manufacturer of explosives, it is no surprise that it was closely linked to such military projects as the Hü 211. This connection to aviation was also fostered by its operations director at 299 The mentioned patent by Wolfgang Hütter could not be located in the inventory “Patente

von 1877–1968, Geheimepatente, Gebrauchsmuster und Warenzeichen” at Deutsches Patentamt, research dated 17 Juli 2022. 300 See Wolfgang Hütter’s instructions for joining and coating the plywood structure from 1943, Ausführungsbeschreibung zum Fügen und Beschichten der Sperrholzstruktur (APS). 301 According to information provided by the sales manager of Gross and Pertun on 18 Aug. 2022.

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Dynamit Nobel, Gustav Leysieffer (1889–1939), who was an enthusiastic glider pilot.302 The phenolic resin-based glue bearing the product name P-600 was used as the bonding agent for the plywood layers of the aerofoil; and alternatively, the phenol–formaldehyderesin glue called polystahl was used for trials.303 This was a development of Dynamit Nobel AG under the direction of the chemist Peter Pinten, who developed various adhesive systems, in particular also for presstoff materials and insulation.304 Both these glues could be applied to the above-mentioned pertunol varnishing system and supplied the required stiffness.305 In addition, various veneer packages were glued with tego-film, an alkaline hardening phenol–formaldehyde resin product of Goldmann AG from Wuppertal. However, the “glue patterns” were not always optimal. In some areas, for example, dark “runny noses” were produced by the polystahl glue during pressing or else by the blackish-brown tego film, especially when the pressing temperature was not optimally set. There was also unsightly discolouration when parting agents were used, which caused dark lichen-like residual stains on the veneers. These two glues were not only used for the upper and lower shells but also to affix the ribs and webs inside the shell. It is notable that the ribs ran inside the shell area of the wing, whereas in the outer wing section the ribs extended through the full chord. Unlike the usual constructions, in which the webs and spar flanges go through together, the webs were interrupted by the ribs.306 The underlying reason for this decision was presumably that the few ribs were significantly stronger than the webs. The introduction of large torsion moments subjected the ribs to very large bending stresses. These heavily loaded ribs were composed of three-to-four webs made of 8-to-12-mm-thick diagonal plywood of beech veneers and flanges made of pine wood, which essentially formed the shear link between the shell and the rib web.

4.5.3

Testing of Construction Methods and Materials to Underpin Design Specifications

The aligned-fibre shell construction for Wolfgang Hütter’s aircraft wings broke new ground at this time in materials technology and thus also in design. The shell design 302 Gustav Leysieffer also appears in the context of the development of “the Horten Va” in the following case study in Sect. 4.6 on new load horizons for flying equipment—the fibre composite flying wing of the Horten brothers from 1935. 303 Ibid., preferably used as a moisture-resistant glue. Its development in connection with presstoff materials for the Horten Va is discussed in Sect. 4.6. 304 Dr.-Ing. Peter Pinten produced a series of patents for Dynamit AG as an important developer of that company; he was closely involved with issues concerning presstoff materials and their bonding. 305 See Wolfgang Hütter’s instructions for joining and coating the plywood structure from 1943 (APS). 306 Ibid.

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Fig. 4.41 Experimental mould for shaping the layered veneer shell at Wolf-Hirth, the manufacturer of Wolfgang Hütter’s shell bodies for testing purposes. The stepped stack of veneer layers constituting the shell body are clearly visible on the left-hand side. Photo undated, probably 1943. Source APS

with the statics determined by fibre orientation can be regarded as the core of his developmental achievement. The conventional structure of a plywood panel had the fibres of each veneer arranged at a 90º angle to its adjacent layers. More angles were used in arranging the plywood composite of a shell body. Hütter varied the statics with angle settings of 0, 20, 45 and 90º and also experimented with grade quality for different wood types, with symmetrical and asymmetrical shell geometries. Hardwood beech veneer was exclusively used for the upper and lower shells of quality grade I, but with quality grade II also incorporated into the middle layer. Fibre-alignment was also used for the ribs and web cross pieces, but in a softwood such as lime and pine to reduce the weight. The aerodynamic contours of the shell were created by bending the veneer layers, which was referred to as Formholz, “moulded wood” (Fig. 4.41). Hütter cooperated very closely with the leading moulded-wood company of the time, Erwin Behr Wendlingen am Neckar. A comprehensive analysis of the shell behaviour was needed with regard to strength, extension, deformation and shaping in order to meet the specifications with a fibre-aligned shell structure in the required proportions and construction for a shell wing. Closer examination has revealed that despite a shortage of manpower and material resources, Wolfgang Hütter could rely on a well-functioning network. The Materials Testing Institute in Stuttgart (MPA), under the direction of Otto Graf (1881–1956), assumed an important amount of the basic examinations there and also functioned as a service partner for the calibration of the testing and production technology, both at Hütter GmbH as well as at the Wolf-Hirth company.307 Certainly one reason for this was that Wolfgang and his brother Ulrich were both graduate students of Georg Madelung (1889–1972) in 307 Materialprüfungsanstalt für Bauwesen in Stuttgart-Cannstatt “Schalenflügelversuch I” on 20 Mar. 1943, “Biege-Bruch-Versuche, Schalenflügel” on 17 June 1943, “Schalenflügelversuch II” on 22 June 1943, “Prüfberichte über Schalenfügelversuche” on 2 Nov. 1943, “Lochleibungsversuche im Buchenfurnier, Schalenflügel” on 14 Nov. and 22 June 1943 and on 20 Mar. 1944 (APS). On the Stuttgart MPA and Otto Graf, see Ditchen (2009), p. 52 f.

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Fig. 4.42 Construction method tests on rib and shell curvature and web dimensioning of the shell for Hü 211 from 1943 at Hütter GmbH. Source APS

the field of aeronautics at the Stuttgart polytechnic and good ties therefore already existed to the polytechnic and its materials testing institute. Almost right at the time of Wolfgang Hütter’s project, Madelung engaged his brother Ulrich at the Graf Zepplin Research Institute in Stuttgart (FGZ), appointing him in 1943 as instructor to train his staff.308 Ulrich Hütter was involved in the development and testing of military flight equipment and later also worked there as an autonomous aircraft designer. The contacts in military aircraft construction were thus excellent. With a staff of 200 employees in 1943, the MPA was also in a good position to handle larger orders for testing.309 The majority of orders that Otto Graf was able to attract came from the armed forces, which in 1944 led to a secret agreement between the Stuttgart MPA and the German reich, the latter represented by the High Command of the Army (OKH). Wolfgang Hütter and his company in Kirchheim unter Teck designed the prototype shells for the test series and mainly performed the tests on how to construct them (Fig. 4.42). These trials were multifaceted and involved a whole range of models focusing on various shell thicknesses, shell curvatures as well as rib and web tests. In the latter, investigations were also carried out with different dimensionings as to material thickness, radius and stable gluings. For this purpose, some of the experimental equipment and prototype shell bodies were built by the company Schempp-Hirth in Kirchheim unter Teck and some were manufactured by the company Wolf-Hirth in Nabern unter Teck. This also shows how close the cooperation was with these companies in particular. The bending of the veneers to the

308 On the work at the Forschungsanstalt Graf Zeppelin and Ulrich Hütter’s employment there, see

Elsässer (2022), p. 159 f.; see also Sect. 4.4 on fibre research between professional and political ambivalence–1920–1945 and Sect. 5.2 on new load horizons from “black gold”—early 1970. 309 On the acquisition of Wehrmacht orders for the Stuttgart MPA by Graf, see Ditchen (2013), p. 92 f.

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intended curvature for the shell was done on a provisional cold press with moulds provided by the company Brömel & Söhne from Leipzig in Saxony. In addition, prefabricated webs made of pine and limewood were built by the company Erwin Behr Wendlingen am Neckar.310 The subsequent tests on tension, pressure, bending, torsion, hole pressure and special tests on the tear-out behaviour of the inserts and screw anchors were carried out in 1943 and 1944 under the direction of Otto Graf at the MPA in Stuttgart and selected tensile and perforation tests at Wolf-Hirth. The final tests on shell behaviour under static loading were conducted in 1945 at Luftschiffbau Zeppelin GmbH in Friedrichshafen on Lake Constance.311 The extensive materials testing, which was performed in preparing the wing dimensions, can only be presented exemplarily due to its scope. As an example, three tests were conducted at the Materialprüfungsanstalt in Stuttgart, carried out in a staggered manner and ultimately focused on the fibre-alignment construction method. Bending tests were the starting point, one component in determining the shell design. Within the framework of this investigation, 360 shell specimens were tested, which were dimensioned to a length of about five metres. These specimens were tested on a test frame (Fig. 4.43) for bending up to the breaking point (Fig. 4.44). In addition to the determination of the edge stress and the modulus of elasticity under bending load, the main focus was on the behaviour of the fibre-aligned material. The parameters set for the investigation as variables were the veneer thickness, the diagonal veneer proportion, the diagonal veneer angle, the beech veneer type, and the shell thickness. The dependence of the strength on the moisture content was not investigated. These tests showed that the veneer thickness had a significant influence on the operational strength of the shell and that the selected veneer thickness of 5 mm represented the most stable form. Furthermore, the mixed veneer composition with beech veneer of quality grade I in the outer layers and two grade II veneer layers in the middle layers yielded the best results with a stacking of the fibre-aligned veneer layers at 0, 45 and 90º angles.312 Angles set between 20 and 45º did not make any significant difference, so the 20º setting was not pursued further. As the proportion of diagonally aligned veneers rose, good results were obtained especially in the torsion and tensile tests, where the angle settings varied in accordance with different load scenarios. The decisive factor in these tests was ultimately the enormous harvest of parameters for these materials and the thorough analysis of the effect that fibre-aligned plywood had in construction within the context of moulded wood manufacture. The orientation of the fibres became the adjustment screw for the statics of the wing shell, which could be 310 See the minutes, “Versuche zur Holzschalenbauweise der Hü 211”, 3 Jan. 1945 (APS). 311 Luftschiffbau Zeppelin GmbH “Versuche zur Holzschalenbauweise des Flugzeugtragflügels

211”, 3 Jan. 1945 (APS). 312 See “Versuche zur Schalenauweise des Flugzeugtragflügels der Hü 211. III. Versuchsergebnisse. Schalen-Eigenschaften, Schalenbeanspruchung bei reiner Biegung” 23/25 Nov. 1943 (APS).

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Fig. 4.43 Bending test with and without load as part of the shell tests for the Hü 211. A sample shell of about 5 m length (above) was loaded to failure (below). The test took place on 20 March 1943 at the MPA in Stuttgart under the direction of Otto Graf. Collection of photos on materials testing as part of the preliminary investigations into the dimensions of the wing of the Hü 211. Source APS

differentiated even further in a series of special trials. Wolfgang Hütter and his colleagues studied in particular questions related to joining technique, such as, e.g. the strength of a perforated sample at specific fibre-alignment angles and in defined proportions of the veneer material. Other examined problems related to chemical joining techniques as well as classical joining elements like wood screws.

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Fig. 4.44 Analysis on shell construction with fibre alignment. The stability fracture of a shell specimen of 10 mm thickness with a veneer proportion of 18% in diagonal orientation, made of quality grade I beech and a fibre-alignment positioned at 45º. Dated 22 June 1943 as part of the preliminary investigations for the Hü 211 wing dimensions at the Materials Testing Institute in Stuttgart. Source APS

4.5.4

Moulded Wood Versus Shell Fabrication

It is not surprising that Wolfgang Hütter chose to adapt moulded wood to produce the Hü 211 plane, since he had already worked with it for Messerschmitt on the Me 109 Kmodel. The company Erwin Behr mentioned above was the central supplier of interior components made of moulded wood for a whole series of Messerschmitt aircraft, including the Me 109 (Fig. 4.45). Moulded wood is permanently reshaped wood as a result of the application of heat and pressure. A distinction is made between “layered moulded wood” (Formschichtholz, veneer layers with the same direction of grain) and “moulded plywood” (Formsperrholz, composed of at least three veneer plies, rotated by 90º in relation to each other). This process is based on the early experiments conducted by the Austro-German master cabinet-maker Michael Thonet (1796–1871), founder of the bentwood furniture factory Gebrüder Thonet Bugholzmöbelfabrik in Vienna. As early as 1830 Thonet experimented with gluing together veneer layers and deforming them in steam. He became famous for his bentwood process, which he primarily used to reshape rods out of solid wood into supporting furniture structures.313 Moulded plywood was used for the Hü 211 wing and, as described in the foregoing section, other blocking angles were used besides the classic 90º angle, in order to increase the operational strength or to adapt it precisely to specific requirements. The design of the pressing device to bond the wooden shells of the Hü 211 wings was begun in parallel with the materials testing. The designer of the press was Gerhard Sauerbier, who was sent to battle in 1944, however, and was killed in action. The final 313 Cf. Ottilinger (2003), Kähne (1999), Bangert (1997).

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Fig. 4.45 Showroom of the Erwin Behr firm in Wendlingen am Neckar displaying aircraft parts made of moulded wood for the aeroplane type Me 109 built by Messerschmitt AG. Moulded wood components from Erwin Behr were also used in the models Me 110, Me 210 and Me 309. The sign defines Formholz as “chipless reshaped pressed layered wood”. Source APS

design of the press was completed by the Dutch designer, Dirk Ruth (1919–2014), who like his brother Frits Ruth (1918–2014), was under Wolfgang Hütter’s employ. Their employment there along with other foreign and forced labourers will be discussed in greater detail below.314 Time pressure left no leeway to contract a company to produce a press, which was estimated to cost two million reichsmarks.315 For this reason, it was decided to improvise and build a press themselves, which was finally set up and ready for operation five months later at a cost of 300,000 reichsmarks. This press (Fig. 4.46) measured 25 m in length, had a total width of 4.80 m, a clear width of 1.80 m each (for the two pressing surfaces), a stroke of 200 mm and a pressing pressure of 6300 t. The press was designed for a bonding temperature of 80 ºC.

314 Exchange of letters between Frits Ruth and Peter F. Selinger, 15 Mar. 1991 (APS). 315 Notes by Wolfgang Hütter on the design of the wing-shell press “Konzept 6000 to Pressdruck”,

16 Nov. 1943 (APS).

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Fig. 4.46 Press for the upper and lower shells of the wings for the aeroplane model Hü 211 shortly before completion in 1944. Source APS

It was built symmetrically with two pressing surfaces, presumably in order to be available for serial production of the shells and in order to avoid having to exchange the moulds for the upper and lower shells. There would otherwise have been considerable loss of time during production. A 60 cm corridor was left between the two press parts to allow access to those parts. The hydraulic pump, the raw cabling and the air vessel were mounted on the press in order to leave space around the press for the operations. The loading of the press was done on the broad side, for which purpose a series of bolts had to be loosened, which secured the tension brace. The press was set on a concrete foundation. The base consisted of two-by-five concrete blocks, which were heavily reinforced to relay the action.316 Subdivisioning into individual blocks thus served to prevent cracks from forming along the length of about 25 m. Another reason was probably the transportability of the press, so that it could be relocated in an emergency. This conjecture is corroborated by the fact that the nearest railway track was only 150 m away from the press. A high-frequency heating system and glass tubes with heater wires were installed in the concrete blocks to supply the bonding temperature (Fig. 4.47). The pressure rams consisted of five reinforced concrete blocks.

316 Ibid.

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Fig. 4.47 Hütter GmbH employees inserting glass tubes with heater wires into one of the concrete blocks of the press for the Hü 211 in 1944. Source APS

The hydraulic pressing cylinders were initially supposed to be provided by the Krefeld company Becker van Hüllen.317 However, due to war-time delivery problems and the company’s deadline orders, it was necessary to improvise here as well and to look for an alternative. In the end, it was possible to produce suitable hydraulic pressing cylinders out of steel blanks for aircraft engine cylinders, light-metal blanks for aircraft engine pistons and wing connections for the spherical plain bearings of a Me 110. The fuselage construction had been assumed by the airship builder ZeppelinLuftschiffbau in March 1944.318 Schempp-Hirth worked until the end of the war on prototypes of a wing dummy piece (Fig. 4.48), the mountings and fairing for the Jumo 222 engine, and the main landing gear for the Hü 211. At the same time, the fuselage cross-section and the wing were tested in the wind tunnel of the Dornier firm.319 Shortly before war’s end, Hütter GmbH was relocated to Rheinau-Höchst on Lake Constance near the Swiss border, but before the company could resume operations there, the advancing

317 Notes by Wolfgang Hütter on the design of the wing-shell press “Konzept 6000 to Pressdruck”, 16 Nov. 1943 (APS). 318 Letter from Reichsluftfahrtministerium dated 10 Mar. 1944. In: Huetter 8–211 Long-Range Reconnaissance Aircraft. Huetter G.m.b.H., Kirchheim. Report 28 Oct. 1944 (APS). 319 Letter from Frits Ruth to Peter F. Selinger, 12 Apr. 1991 (APS).

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Fig. 4.48 Wing dummy with engine and landing gear segment for developing a prototype of model Hü 211 at Schempp-Hirth, 1944. Source APS

French army confiscated a large number of the company’s files. Work on the Hü 211 came to a standstill. Neither a fuselage nor a wing shell could ever be produced. This processing of wood-derived materials, taking fibre alignment into account to support the material statics, can be seen as a brief intermediary stage on the way towards load-oriented fibre-reinforced composite materials. The moulded wood—or more precisely put, the moulded plywood—specifically chosen by Wolfgang Hütter as the material for the wing shell and for his design of the entire aeroplane has its origins in Thonet’s research. Hütter’s innovation is his fine-grained exploration of the effect of fibre alignment on plywood stability, examining other orientational blocking angles beyond the regular 90º, analysing 20 and 45º angles as well towards improving the material statics. As mentioned in his patent, he also added technical mouldability of these compressed materials for three-dimensional shaping. Thus, the concept behind this material used by Hütter for the long-range reconnaissance aircraft Hü 211 becomes a forking branch in the development of composite materials. This concept begins with classical wood construction and, as a plywood composite, develops into a wood-derived material which by virtue of its fibre alignment and moulding is ultimately already situated among the modern fibre-reinforced composite materials. This composite could thus be described as a fibre-aligned lightweight wood-derived composite material.

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4.5.5

215

Foreign and Forced Labour for the Hü 211

Since the appearance of the first study on foreign labourers by Ulrich Herbert in 1985,320 numerous analyses on this topic have been completed, attended by the public controversy about the associated issues of compensatory payments.321 By now it is presumable that in national socialist Germany, private-sector companies were the main exploiters of foreign and forced labourers, including concentration-camp prisoners. It occurred in almost all areas, most especially in the armaments industry. One of the main reasons behind it was the attempt to remain competitive despite a dwindling work-force, which had been depleted by the war. Today it is assumed that economic aspects were usually in the foreground, however, and ideological ones were much less obvious, although not rarely violent exploitation of people was the outcome.322 The employment of foreign and forced labourers is also known to have occurred in the case of the Schempp-Hirth and Hütter aircraft companies, although the source situation here is difficult. Most of the administrative documents from the period before 1945 into the early post-war years were ignorantly destroyed in the 1970s when the company moved into its present premises.323 What has survived, however, is a whole series of portrait photographs which had been taken to make company identity cards. Only in individual cases do they allow a distinction to be made between local staff and foreign and forced labourers. It can be assumed, however, that the company management left no doubt about the fact that the company was producing in the interests of the nazi state. Photographs of company assemblies from this period display this.324 But there, too, a purely visual distinction between the actual work-force and foreign and forced labourers is not possible (Fig. 4.49). For example, forced labourers from eastern countries, such as Poland or Russia, wore neutral company uniforms at work without the distinctive labels “OST” (for “east”) sewn on them. However, a few accounts by former forced and foreign labourers exist, such as the one by the Dutch woman Corry Huyton, who was deported from her native country and forced to work in Germany. Another case is the already mentioned Dutch foreign worker Frits Ruth, who was interested in working in aircraft construction, responded to an advertisement and was entirely legally hired. That is how he came to Germany and remained there up to his death in 2014.325 These two different fates will be briefly presented here to provide some insight into the associated circumstances in which the development and testing of the Hü 211 plane was embedded. 320 Herbert (1985). 321 See, among others, Hachtmann (2012), Heusler et al. (2010), Lindner (2005), Hayes (2004),

Abelshauser (2002), Spoerer (2001), Gall (2000). 322 Heusler et al. (2010), p. 3 f. 323 Interview with Peter F. Selinger, 11 Aug. 2022. 324 Picture collection Hirth and Hütter (APS). 325 See the related correspondence from 1991 and 2016 (APS).

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Fig. 4.49 Staff assembly in the factory hall at Schempp-Hirth, presumably in 1943 or 1944. The speakers and participants at this meeting could not be identified. Photo by Gisela Ruth. Source APS

Corry Huyton recalled that the SS came to pick up her then boy-friend and future husband Peter at his home in Holland because he had not complied with the call to register himself as a volunteer worker in Germany. Having justified himself with the argument that he did not want to leave his girl-friend alone, they were both deported to Germany as foreign labourers. Their experiences with the German occupying forces in Holland and the looting by the SS made them very fearful of what to expect in Germany and plagued the first days after their arrival in Oberlenningen and later Kirchheim. They were amazed by the friendly welcome they received locally in Germany. Corry Huyton recalled in her reminiscences about this326 : I and Peter were finished at noon327 and then French prisoners of war came; they were accompanied by a German with a rifle, but that was a nice man who immediately befriended the Frenchmen, they were officers... [Peter continued,] When Corry was expecting, we used to go to the Störer bakery to get bread at the counter. One day a German air force officer was also standing there; we said “Grüß Gott” as always and went home. The next day we went to the bakery again and the lady there said that Herr Offizier had left bread-coupons for her. We were very grateful to that man; he did this many 326 Letter from Peter Huyton, 12 Apr. 2006 (APS). 327 Their registration upon arrival by train in Germany is meant. Letter from Corry Huyton, 12 Apr.

2006 (APS).

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more times, but we never saw him again ourselves. What a pity; we would have liked to say thank you to him. We encountered very much kindness (to us) by people that way.

Peter Huyton described that his later wife initially had to work for a baker, where she was very well treated and she could always eat her fill. He was already working for SchemppHirth in the welding shop and managed to get her transferred to that company as well. At first, she worked in the fabric-stretching department, later in quality control. Having learnt German at school, she was able to move about in the company almost without any problem. They both got home leave for their wedding and could return to Holland for two weeks. Their child was born in Kirchheim. Both described a great willingness on the part of the company to help particularly in connection with the birth, and likewise on the part of a number of German acquaintances in the town. Some of these acquaintances became life-long friends. Whereas Schempp-Hirth took care of its workers and provided food and accommodations, conditions in the town itself were very different. Peter Huyton reported that forced labourers from the Low Countries and Belgium were preferentially employed in more elevated jobs. Women from these countries were allowed to work in a hospital, for example, as opposed to women from the Czech Republic and Russia, for instance.328 The latter were furthermore stigmatized by having to wear yellow clothing with the sewn-on “OST“ sign. Foreign and forced labourers were occasionally even pelted with horse manure by locals, which also happened to Corry and Peter Huyton. Foreign and forced laborers presumably had to endure much more and probably even worse treatment, at least Peter Huyton’s remarks hint at this without, however, giving concrete examples. The experiences by the Dutch foreign worker Frits Ruth were also positive. At the outbreak of the war, Frits Ruth had been a student pilot in the commercial flying school at Schiphol airport. When operations there had ceased because of the war, he responded to a newspaper advertisement in which Wolf Hirth (1900–1959) was looking for aviation enthusiasts for his company in Nabern. Ruth thus joined the design office there.329 He also paved the way for his brother Dirk to join the company, who, as already mentioned, was later to figure as the designer of the ultimately planned large wing press. In Frits Ruth’s memoirs, technical issues primarily dominate within the context of the Hü 211 development, which also demonstrates the brothers’ proximity to the designing process. From Frits Ruth’s point of view, the corporate climate at Schempp-Hirth and Hütter was international. Aside from him and his brother, there were other foreign workers in the company from Norway330 and Denmark. At the same time, he also mentions that the forced labourers in the production of instrument boards for the Me 109 G-6 in Nabern mainly came from Poland. Russian peasant women were also employed at Schempp-Hirth 328 Ibid. 329 Interview with Peter F. Selinger, 11 Aug. 2022. 330 The name Bjärne Reier from Norway is mentioned here. Exchange of letters between Frits Ruth

and Peter F. Selinger dated 15 Mar. 1991 (APS).

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at first, but according to Ruth, they could not be entrusted with constructing the filigree ribbing. Another report confirms this impression that under these circumstances the corporate climate in both companies was still relatively moderate. It was written by Gunilde Horten,331 the sister of the flying wing designers Reimar and Walter Horten. She reported that during her physics studies at Tübingen she was allowed to complete the compulsory training semester in industry at Schempp-Hirth in Nabern. In this context she mentioned an unwritten rule for German employees to support the foreign workers put up in the camp, e.g. by bringing along an extra slice of bread for the break.332 This also includes Wolfgang Hütter’s enquiry into how much one might be able to economize on covering material in the production of parts for the Messerschmitt Gigant model, in order to be able to use the savings as bed linen for the foreign workers in the camp. A final evaluation of the working conditions in the companies involved in the development and production of the Hü 211 plane cannot be conclusive due to the poor availability of sources. Only isolated instances can be highlighted. All that one can establish is that foreign and forced labourers were employed for long periods of time in these companies— as in almost all areas of German armaments production. The perceptions of the actual conditions diverge widely, as the above reminiscences indicate, and they can only give a rudimentary impression of what it meant to live and work under war-time conditions in a dictatorship.

4.6

Aviation Case Study II: New Load Horizons for Aircraft—the Horton Brothers’ Fibre-Composite Flying Wing from 1935

4.6.1

Introduction

The developments of compressed manufacturing materials presented thus far, in particular reinforced and layered presstoff , concerned basic materials and design details, technical manufacturing conditions and the multifaceted manifestations of these hybrid materials. The expiry of the heat-pressure patent of 1931 considerably promoted this development. In mechanical engineering this initially took place within the framework of the development of plain bearings, which was enduringly influenced by the presstoff manufacturer Römmler AG and later also by Dynamit AG and AEG. The use of presstoff materials as a structural material for complex technical products seems to have appeared late. However, my investigations show that just four years after the opening of the presstoff market with the expiry of the mentioned patent, a technical product was developed early on which 331 For a detailed account about Gunilde, Reimar and Walter Horten, see Sect. 4.6 on new load

horizons for aircraft. 332 Interview with Peter F. Selinger, 11 Aug. 2022.

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demonstrated how suitable presstoff material was as a structural material, having unexpectedly passed developmental muster in such a short time. This was the flying wing aircraft Horten V-a from the years 1935/36 developed by the brothers Walter-Max Horten (1913–1998) and Reimar Horten (1915–1994) from Bonn. A later development by the Horten brothers was the model Horten IX,333 which was completed and flight tested as a prototype in version 2 (V2) shortly before the end of World War II. This model also had a hybrid-material structure and a jet engine. Both models represented new territory in view of materials design or in their combination of technical specifications and were about 30 years ahead of the aviation standards of the day. My investigation of the technical materials developed for both aircraft models was carried out largely on the basis of new source material, since an evaluation of the existing secondary literature proved problematic.334 The existing image of the Horten brothers and their flying-wing development was essentially shaped by the publication by Reimar Horten himself and his co-author Peter F. Selinger (*1940).335 In my conversations with this coauthor, Selinger admitted that his collaboration with Reimar Horten had been difficult. Shortly after the book appeared, Selinger was already critical of the joint publication because facts he had pieced together himself clashed with statements made by Reimar Horten.336 A number of publications on the Horten brothers were also written by the U.S. historian David Myhra (*1939), whose accounts are based primarily on interviews and pictorial material by Reimar and Walter Horten, which has shaped the image of the Horten brothers, especially in the English-speaking world.337 However, there are considerable contradictions in Myhra’s accounts about people and the aeronautical facts he presents. Many details, whether with regard to biographical information on persons338 or with regard to technical aeronautical facts, often do not stand up to scrutiny or cannot be verified for want of sources.339 An example of this is the one-sided description of the crash of the jet-powered model Horten IX V2.340 The alternative sources that have been 333 This model is also called (Gotha) Go 229 in some places, after the planned production company,

Flugzeug-und Straßenbahnbau Gotha. 334 See, inter alia, Meier (2006), Storck (2003), Myhra (2016), id. (2002), id. (1998), id. (1990), Lee (2011), Dabrowski (1995), Nickel and Wohlfahrt (1990), Colemann and Wenkmann (1988), Horten and Selinger (1983). 335 Horten and Selinger (1983). 336 Interview with Peter F. Selinger on 31 July 2017 and 8 Feb. 2018. 337 Myhra (2016), id. (2002), id. (1998), id. (1990). 338 David Myhra states in his most famous book: The Horten Brothers and Their All-Wing Aircraft, (1998) for example on p. 25, that Reimar Horten died in 1994 at the age of 80, but in fact Reimar Horten died on 14 Aug. 1993 at the age of 78. 339 Myhra (2016), id. (1998). 340 Myhra (1998), p. 191; the Horten employee Heinz Scheidhauer is indirectly blamed for the crash, who demonstrably had not been there at all. See the written statements by Karl Nickel about the false statements in this publication (See on this Karl Nickel’s letter to Andy Kecskes of 26 June 1998 (Archive Peter F. Selinger [hereafter APS]).

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found here paint a different picture of the events of that time than the representations and conclusions drawn by Reimar Horten, who did not personally experience the crash.341 The existing eyewitness account of the accident presents the crash as the result of engine failure and a chain of unfortunate technical circumstances. The allegation that another test pilot, Heinz Scheidhauer (1912–2006), had been on site but had gone away for a meal without permission during the test flight of the Horten IX V2, leaving the radio unmanned and preventing possible assistance to the pilot by radio, does not agree with the facts.342 There is evidence that the test pilot in question had not been there at all but was elsewhere on that day.343 In addition, an evaluation of more than two hundred technical drawings of the Horten all-wing model H IX, of material samples and private correspondence from the 1940s has shown that many statements by Reimar Horten in particular had obviously been misinterpreted, if not indeed misrepresented out of self-interest.344 The sober and sometimes naïve private records by his brother Walter,345 as well as the very precise written documents by his brother-in-law Karl Nickel,346 often paint a different, more detailed picture of various developments and events. The written documents and images evaluated for this study draw a portrait of the two brothers as self-taught engineers who designed many innovative flying wing aircraft. Reimar Horten is primarily responsible for their design achievements. His brother Walter was, in the estimation of his military superiors, a gifted military pilot. Notwithstanding these qualifications, it is noteworthy that Walter Horten flew hardly any of the aircraft designed by his brother. Walter Horten’s contribution to the success of these allwing projects, putting aside his qualities as a military pilot, was largely organizational, serving as a mediator within the military agencies. Various letters between Walter and Reimar Horten from 1941 document both of them as rigorous in their choice of means to achieve their goals.347 The targeted exploitation of military resources for their own benefit, exaggerated representations of their own achievements, and sometimes also even ruthless behaviour towards third parties, were not uncommon. 341 Eyewitness report, a sketch of the crash and take-off data of Horten IX by its flight attendant,

Walter Rösler, dated 8 Aug. 1984—see Memorandum: Die Horten-Nurflügel-Flugzeuge. Erinnerungen von Karl Nickel, unpublished memoirs of Karl Nickel [hereafter MKN] (APS). 342 Cf. Myhra (1998), p. 191. 343 Unpublished memoirs of Karl Nickel (MKN), see Chap. 13. 344 Myhra (2016), id. (1998), Horten & Selinger (1983). 345 See Die Gebrüder Horten,—ihre Nurflügelflugzeuge und was sie während des WWII so alles erlebten. Unveröffentlichter Erinnerungsbericht von Walter Horten von 1982 [hereafter LEWH] (APS). 346 See here MKN (APS). 347 See the letters from Reimar Horten to his brother Walter dated 2 Apr., 12 Apr., and 10 May 1941, as well as Reimar Horten’s letter to his co-author Peter F. Selinger dated 7 Aug. 1982, in which he forbids him from contacting contemporary witnesses or evaluating or using documents unfavourable to him (see also the notes in MKN) (APS).

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One particularly graphic example of exaggerated posturing by Reimar Horten, within the context of materials technology, is the assertion that he had introduced his own specially designed charcoal glue layer to bind the plywood layers of the H IX model as radar camouflage.348 The considerable deficiencies found in the secondary literature and especially in the existing accounts by Reimar Horten made it inevitable to look for and appraise new sources. However, it is not the aim of my investigation to present a counterargument to existing publications or to list the deficiencies found there nor even to describe the development of tailless and all-wing technology and rewrite the history of its developers Walter and Reimar Horten. Materials design of these two Horten models is the focus of the present study as well as the working environment of their developers at the time.

4.6.2

The Horten Brothers

The Horten brothers, oft-cited in connection with all-wing technology, were Walter-Max and Reimar Horten, both born in Bonn as the children of Max Horten (1874–1945), außerordentlicher Professor of oriental studies at the University of Bonn349 and his wife Elisabeth Antoinette Horten, née aus dem Kahmen (1879–1970).350 Max Horten was also the uncle of the department store entrepreneur Helmut Horten (1908–1987) (Fig. 4.50). The latter supported Walter Horten when he was in poor health after World War II and Walter had also completed a commercial traineeship with him as a youth.351 The elder brother of Walter and Reimar, Wolfram Horten (*1912, missing since 21 May 1940), is rarely mentioned in the descriptions of flying-wing technology, although Wolfram Horten had often funded the aircraft projects of his two younger brothers. As a professional soldier and naval aviator, he had obtained financial independence much earlier. He also occasionally helped them construct their model aeroplanes and accompanied them to flying events and competitions. Wolfram Horten (Fig. 4.51) had married Ursula Horten, née Hoffmann (1912–2011), on May 19, 1938.352 During this time his wife was working as a laboratory assistant on a mercury poisoning project in the private laboratory

348 Horten and Selinger (1983), p. 136, Horten (1950), p. 245. 349 Max Horten held a librarian position at the University of Breslau 1932–1939 and he and his wife

therefore preferred to live in Breslau during this time. Both parents were thus rarely in Bonn, where their children lived. As adolescents or young adults Walter, Reimar and their sister Gunilde mainly lived alone at home without their parents as a result (Interview with Klaus W. Horten on 20/21 Aug. 2018.). 350 Family tree of the Hortens (APS). 351 Recollections in LEWH, p. 3 f. (APS). 352 Pers 6/148807 Personalakte Wolfram Horten (Bundesarchiv Freiburg [hereafter BArch F]).

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Fig. 4.50 Helmut Horten (1908–1987), the department-store entrepreneur who supported Walter Horten after World War II. Source Reproduced by courtesy of Gräfin Goëss-Horten

of the chemist Alfred Stock (1876–1946), who held a position at the Kaiser Wilhelm Institute of Chemistry in Berlin.353 This is where she also met Otto Hahn (1879–1868), the later Nobel laureate in chemistry, and his close collaborator, the Austrian nuclear physicist Lise Meitner (1878–1968). Ursula Horten left the KWI at the end of March 1939, as she was expecting her son Dirk Horten, who was born on December 14, 1939.354 (Dirk joined the navy as a professional soldier after World War II, as his father had once done, retiring in 2000 as vice admiral and commander-in-chief of the Fleet Command of the Federal Republic of Germany.) In December 1938 Otto Hahn and Fritz Straßmann (1902–1980) at the KWI of Chemistry discovered nuclear fission, which Lise Meitner and her nephew Otto Robert Frisch (1904–1979) had interpreted as such in Sweden. Wolfram Horten as a first lieutenant in 1940 had a fatal accident while flying his aeroplane near Boulognesur-Mer (France), caused by the premature activation of a sea mine due to an error by the ammunition warden.355 The fourth child of Max and Elisabeth Horten was their daughter Gunilde Horten (1921–2016).356 Although she did not participate in her brothers’ constructions, she was nevertheless present at many of Walter’s and Reimar’s flight tests and competitions and 353 Kaiser-Wilhelm-Institut für Chemie. Interview with Dirk Horten, son of Wolfram and Ursula

Horten, on 31 Aug. 2018. 354 Dirk Horten entered into the German Navyin 1958, 1977–1980 was officer in the Federal Ministry of Defence, 1980 captain at sea—head of department on the staff of the German military delegation on the NATO Military Committee in Brussels, 1986 commander of the submarine flotilla, 1988 fleet admiral, 1993 rear admiral, and 1995–2000 vice-admiral commander of the Fleet Command—see the interview with Dirk Horten on 31 Aug. 2018, as well as Pfeiffer (2012), p. 73 f., Rahn (2005), p. 2 f. 355 Staff file on Wolfram Horten (BArch F), as well as information in LEWH (APS). 356 On Gunilde Horten’s internship at Schempp-Hirth as physics student in Tübingen, see Sect. 4.5.5, the first aviation case study on fibre-aligned wood construction.

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Fig. 4.51 Ursula and Wolfram Horten in the year of their wedding. Source Archiv D. Horten

was well acquainted with their circle of friends. In the summer of 1941, she met her future husband Karl Nickel (1924–2009) at a “pilots’ camp” on Klippeneck hill, who later became the director of the Institute of Applied Mathematics at Albert Ludwig University in Freiburg.357 When Reimar Horten was looking for staff for Sonderkommando IX, the special project headed by Walter Horten in Göttingen, Gunilde Horten recommended to him her friend Karl Nickel and a friend of his, Hermann Strebel.358 Karl Nickel, who in the meantime had become a soldier, thus joined Sonderkommando IX. During this period, Nickel got to know the two brothers Walter and Reimar well, both privately and professionally, and as a student of mathematics he was substantially involved in the computations of some Horten flying-wing models. In particular, he carried out calculations on lift distribution, basic calculations on longitudinal stability and on the stalling behaviour of various Horten models.359 Walter-Max Horten (Fig. 4.52) and Reimar Horten (Fig. 4.53) grew up in Bonn in relative freedom. Although their parents originally envisaged their leisure being spent in 357 Karl Nickel (9 Apr. 1924–1 Jan. 2009), studied physics and mathematics at Göttingen and Tübingen, in 1948 obtained his Diplom and 1949 his doctorate in mathematics at Tübingen, 1950/51 he was a teaching assistant at TH Stuttgart, 1951–1955 he worked on aircraft development in Córdoba in Argentina, 1958 acquired his habilitation degree and 1961 accepted an appointment as außerordentlicher Professor, in 1962 obtaining full tenureship in numerical mathematics and large computer systems and the directorship of the Institut für angewandte Mathematik at the Karlsruhe polytechnic, in 1968 he was the founding director of the Institute of Computer Science there; in 1976 he became director of the Institute of Applied Mathematics at the Albert Ludwigs University of Freiburg, becoming emeritus in 1989. 358 See the recollections in MKN (APS). 359 Karl Nickel later elaborated on a variety of mathematical aspects in the design of tailless and all-wing aircraft in his book Nickel and Wohlfahrt (1990).

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Fig. 4.52 Walter-Max Horten as a flying officer (Oberleutnant) in the Luftwaffe in 1939. Source Horten family archive; Klaus W. Horten

Fig. 4.53 Reimar Horten as a non-commissioned officer (Unteroffizier) in the Luftwaffe in 1936. Source APS

playing music, both were more interested in aircraft construction, whereas their elder brother Wolfram was actively engaged in sailing at the Bonn Yacht Club, which later influenced his decision to join the navy.360 A neighbour having initially sparked their interest in kite building, in 1925 Walter and Reimar Horten joined a club for airship enthusiasts, Niederrheinischer Verein für Luftschifffahrt in Hangelar heath near Bonn, where they received their first theoretical instruction in amateur aviation and aircraft construction. Their first teacher in aircraft design was Hermann Landmann (1898–1977), who was later appointed professor at the

360 See the recollections in LEWH, p. 15 (APS).

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Dresden polytechnic.361 This also included building glider models where both brothers were able to assemble prefabricated parts and even develop and build their own creations. Two years later they completed a junior pilot course in which they learned the basics in aeronautics. A while later they also acquired their licenses in glider flying. The switch to the Academic Flying Group at the University of Bonn in the same year granted both of them access to higher-quality aircraft and design issues.362 Membership in this group of aviators was opened to them by their father, who was on the staff of that university. According to Walter Horten, he and his brother became so heavily involved in that flying group that their achievements at school deteriorated rapidly during this time and Walter Horten eventually failed to keep up with his class. Walter Horten nevertheless finished school and earned his school-leaving certificate at a non-classical secondary school, the Oberrealschule in Bonn in 1934; his younger brother Reimar Horten followed suit a year later.363 One year prior to that, Walter Horten had joined the NSDAP, three days after Hitler’s seizure of power in 1933, as did his brother Reimar two months later, both on the strength of their nationalist convictions.364 Their first jointly built aircraft was also completed in that year, a replica of a simple glider, the model called Hol’s der Teufel—“Let the devil take it!” Due to a lack of storage space for their model aeroplanes, they came up with the idea of developing a more space-efficient design. They started working on tailless aeroplanes. Both had already seen this form of aircraft in the Rhön mountains, a model by the aircraft designer Alexander Lippisch (1894–1976). Different influences came together in the design of their own first flying wing in 1933, the Horten I. According to Walter Horten, both of them had been inspired by the allwing patent filed in 1915 by Hugo Junkers,365 and by the tail-less aeroplane designed by Alexander Lippisch, which the brothers had observed in flight and which resembled the winged Zanonia seed (lat. Alsomitra macrocarpa) (Fig. 4.54) in shape.366 The doubletrapezoid swept-back wings typical of almost all the Horten flying wings thus appear to have emulated the wing shape of the Zanonia seed.367

361 On Hermann Landmann and his research at the TH Dresden, see Sect. 5.3.3 comparing composite-materials development in the two Germanies. 362 Jungfliegerkurs; Akademische Fliegergruppe. See the recollections in LEWH, p. 18 f. (APS). 363 See the curricula vitae in the military staff files of Walter and Reimar Horten (Pers 6/171683 Personalakte Walter-Max Horten; Pers 6/107336 Personalakte Reimar Horten (BArch F). 364 See on this: R 9361-VIII, NSDAP-Zentralkartei, Kartei 12,510,806, Mitgliedsnummer:1,473,252 Horten, Walter; R 9361-VIII, NSDAP-Zentralkartei, Kartei 12,510,805, Mitgliedsnummer: 1,634,034 Horten, Reimar (Bundesarchiv Berlin [hereafter BArch B]). 365 Junkers (1915). The patent was submitted in 1911 and granted by the Patentamt in 1915, although Junkers was not the first to design a flying wing, but the Austrian aircraft designers Ignaz Etrich and Franz Wels with a patent from 1906—cf. Etrich and Wels (1906). 366 Recollections in LEWH, p. 26 (APS). 367 Ahlborn (1897), p. 1 f.

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Fig. 4.54 Illustration of the Zanonia seed leaf (lat. Alsomitra macrocarpa), a tropical gourd-bearing plant. There are transparent wing-like areas to the right and left of the seed—shown here in yellow. The Zanonia is native to Malaysia, Indonesia, Thailand and New Guinea. The German zoologist and physicist Friedrich Ahlborn (1858–1937) first described the flight characteristics of this seed in detail in 1897 in a paper “On the stability of flying apparatus” (Über die Stabilität der Flugapparate), which was later used by the aircraft designer Ignaz “Igo” Etrich (1879–1967) as a model for the first flying wing built. Source Ahlborn (1897) p. 1 f., Samenflug im Pflanzen Reich from 1934, LiebigSammelbilder series no. 1091

Immediately after finishing school, Walter Horten joined III Jägerbataillon Infanterieregiment 17 in Goslar as a professional soldier. Its commander was Major Erwin Rommel (1891–1944), the later Generalfeldmarschall.368 His brother Reimar began to study mathematics at the University of Bonn but dropped out after two semesters to likewise pursue a military career. In 1938, Reimar attended two more semesters of lectures in aircraft construction at the Berlin polytechnic. However, it was not until after World War II that he completed his studies in Göttingen with a Diplom in mathematics and also began to write his dissertation there, which, however, almost failed due to the low technical level of the thesis.369 The Horten brothers were able to achieve their first respectable success at a gliding competition in 1934, when they received a prize for the design of their Horten I model. This was where they met Ernst Udet (1896–1941), a successful military ace from World War I, who was benefiting at that time from his friendship with Hermann Göring (1893– 1946), the commander-in-chief of the German air force, which enabled him to rise to the rank of Generaloberst by the time of his suicide. Hermann Göring initially appointed Udet 368 Staff file Walter-Max Horten (BArch F). 369 Horten (1946); Reimar Horten’s dissertation was not accessible in the library due to the poor

condition of the extant copy. On the quality of its content and the near withdrawal of Reimar Horten’s doctoral title by the faculty, see the recollections in MKN, p. 6.

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chief of the Technical Office in 1936. In this capacity, he was responsible for coordinating the technical development and industrial production for the German Luftwaffe. This was followed in 1939 by his appointment as General Luftzeugmeister. His main task was to organize the development, testing and procurement of all the matériel for the German air force.370 Although Udet had a prominent status as a successful pilot, he was also a popular figure. He immediately started to support young aviators and aircraft designers from the early 1930s onwards. This was when he also took under his wing the Horten brothers and the pilot Hanna Reitsch (1912–1979), who was almost their age. The Horten brothers made the acquaintance of Reitsch upon meeting Udet.371 Hanna Reitsch, who has escaped the scrutiny of historians of science and technology until now, can be regarded as a central and mediating player in the network of the Horten brothers.372 She also joined the Horten brothers’ closer circle of friends. From 1934 Reitsch worked as a test pilot at the German Research Institute of Glider Flight and from 1937 at the Rechlin testing station, the Central Testing Facility for Aircraft in the German reich, and she repeatedly made public appearances at national socialist flight shows and events.373 Their close contact with Ernst Udet enabled the Horten brothers to gain access to various aviation companies and research institutions, such as the Kaiser Wilhelm Institute of Fluid Dynamics Research,374 the Aerodynamic Testing Station (AVA) in Göttingen, the DVL375 in Berlin and the army testing station in Peenemünde.376 For example, Walter

370 Technisches Amt der Luftwaffe. Hümmelchen (1998), p. 258 f. 371 Recollections in LEWH (APS); about the course of the 15th Rhön Gliding Competition 1934 see

also Ursinus, ed. (1934), p. 347. 372 The previous accounts about Hanna Reitsch are invariably clumsy, as they insufficiently take due consideration of the political ambivalence and the technical contexts in which her work was closely connected, to illuminate them within the context of the time. See, among others, Jackson (2014); Sigmund (2002); Lomax (1990). The conversations I had in August and September 2018 with Dr. Evelyn Crellin of the National Air and Space Museum—Smithsonian Institution, Aeronautics Department (Washington, D. C.), who has been actively researching Hanna Reitsch and her environment for several years and has been able to access and evaluate numerous original sources, rather lend support to this assessment. 373 Deutsche Forschungsanstalt für Segelflug and Erprobungsstelle Rechlin, Lomax (1990). 374 Here in particular on Ludwig Prandtl (1875–1953), the director of the KWI der Strömungsforschung, who was interested in the aerodynamics of all-wing aircraft and advocated their construction. For recollections in LEWH, see, among others, p. 5 f. (APS). 375 In particular, the support by Günther Bock (1898–1970), air-frame director at the Deutsche Versuchsanstalt für Luftfahrt 1936–1945, in the context of the “Bombervergleichssitzung” (ibid.). 376 See the comments by Walter Horten about the false start of a V-2 in 1942, who witnessed this launch as a guest observer. For recollections in LEWH, see, among others, p. 8 (APS). The Heeresversuchsanstalt Peenemünde and its actors have been the subject of a great deal of research, see, among others, Aumann (2015), Haka (2014a), p. 236 f., Pulla (2010), id. (2006), Ciesla (2007), p. 177 f., Neufeld (2007), id. (1999), id. (1996), id. (1994), Pommerin (2003).

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Horten was present during the false start of the V-2 rocket377 in Peenemünde on June 13, 1942 as a guest observer. The remarkable network of the Horten brothers, not least supported by their early membership in the NSDAP and their associated political stance, which is multiply documented in their staff files, paved the way for the two brothers.378 It is due to their prominent backing that they gained a certain degree of flexibility with regard to their military duties from 1935 at the latest. It supplied the permission to use material from army stocks as well as to use research equipment and, in some cases, to acquire personnel for the implementation of their own flying-wing projects. They often operated at the very limit of legality or occasionally even crossed it. Ernst Udet presumably informed his friend Hermann Göring about the competence of the Horten brothers. Private notes by Walter Horten do not confirm accounts379 which attribute to Reimar Horten employment in Göring’s residence, Carinhall, and which allege that discussions had taken place between the Horten brothers and the commander-inchief of the Luftwaffe about the construction of a long-range bomber. Walter Horten only describes a single short encounter with Hermann Göring in Carinhall in February 1945, which had a rather sobering outcome. This memoir also shows how little the Horten brothers reflected on the devastating side effects of the nazi system, indeed, seemed to simply accept them—for instance, the exploitation of concentration camp prisoners, who were forced to work in weapons production, especially during the final phase of the nazi regime. From the point of view of the Horten brothers, the only thing that counted was the implementation of their flying-wing project. Walter Horten’s account reads as follows: Well, we were sitting in the entrance hall at a round table; one of the adjutants had received us and led us there, – until later, after 15 to 20 minutes of waiting, – Hermann Göring, at that time “Reichsmarschall of the Third Reich” came down the stairs with his personal adjutant. Halfway down the stairs he paused a little, – saying softly to him: “– is that them down there!?” – we overheard this dialogue with perked ears, and then he stood in front of us, – we reported to him, – also confirming to him that it was us, all right, – the Horten Bros. with their flying wing, – which could fly to America and back, – without refueling. He greeted us jovially and friendlily, and then spoke a few short words to us: “– So, you’ve completed this project!? – Do you know that you have done the greatest pioneering work by this? – The entire German aviation industry was compelled to give up on it! – I’m delighted with your work! – You shall collaborate with the Junkers firm to build this aeroplane as quickly as possible!” Those were his words; – and after continuing to converse a little, he withdrew and the Horten Bros. were dismissed. We’re supposed to be cooperating with JUNKERS now! – Well, that will be some task! – We knew too well that a lot had been destroyed in Dessau and that the company was intending to move into the Harz mines! – We drove back to Göttingen in

377 Retaliatory Weapon 2 (Vergeltungswaffe 2, V-2) = Aggregate 4 (A-4), surface-to-surface ballistic missile with liquid propellant. 378 See the staff files of Walter and Reimar Horten (BArch F). 379 Here in particular the presentation by Myhra (1998), p. 5 f.

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disbelief and made a detour through the Harz region. – I think it was Elbingrode near Blankenburg,380 – where the entrance to the much-too-narrow tunnels was supposed to be. What we saw there was more than pathetic! Emaciated people –guarded by SS soldiers, –incapable of decent work, in short: chaos, – which was pretty much a lost case! So, we were glad to be back in Göttingen – but we never heard a thing from the JUNKERS company either. (Source: From the private notes of Walter Horten, 1988. By courtesy of Klaus W. Horten).381

This contact with Ernst Udet resulted in another connection of even further-ranging significance, especially for Walter Horten—namely, Udet’s chief secretary, Sabine von der Groeben (1910–1995) (Fig. 4.55), whom he later married on March 26, 1943.382 After the suicide of Ernst Udet in 1941 she became the secretary of his successor, Erhard Milch (1892–1972), where she worked until 1943 and then followed her husband to Sonderkommando IX headed by her husband. During her time in service, Sabine Horten was both an information hub and a quite important mediator, because her job gave her extensive contacts and insights into administrative issues of the Luftwaffe. This is also apparent in the correspondence with Hanna Reitsch, which has been preserved by the Horten family, who were close friends of hers.383 These contacts outlasted the collapse of the national socialist regime and were sometimes marked by naïve views about her own work in the agencies of the Wehrmacht or in the political system. The Hortens themselves interpreted their employment matter-of-factually and apolitically.384 The attempted denazification process after 1945 was often perceived as a betrayal of one’s own country. In this context, Hanna Reitsch wrote to her friend Sabine Horten in 1947: Dearest Sabine, After being away for 4 months, I have just returned to Oberursel, my small, new home, and found your dear, sweet letter amongst mountains of post. I can hardly express to you in words how immensely happy I was about it. We were often together in thought, that I knew exactly, and I also knew from my enquiries about you that you are alive.

380 This probably refers to the Blankenburg-Oesig subcamp, which was initially assigned to the

Buchenwald concentration camp and from 1944 to the Mittelbau-Dora concentration camp. Officially, it was run under the code name “Klosterwerke GmbH”, see Wagner (2007), p. 183 f. 381 Recollections in LEWH, p. 9 (APS). 382 Interview with Klaus W. Horten on 20/21 Aug. 2018. 383 See the correspondence between Hanna Reitsch and Sabine von der Groeben (Horten) from 1941 and 1953. 384 On the apolitical argumentation of actors in the nazi system, who interpreted or understood their conduct as solely of a technical nature (“I served only technology”), see Museum für Verkehr und Technik (1995). The book by Karl-Heinz Ludwig (1974) on technology and engineers in the Third Reich is also fundamental in this regard. See also various contributions to the volume edited by Herbert Mehrtens and Steffen Richter (1980) on science, technology and nazi ideology, as well as Lorenz and Meyer (2004), Renneberg and Walker (1994), Mehrtens (1994).

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Fig. 4.55 Sabine von der Groeben next to her superior Ernst Udet on a private excursion in June 1937. At this time Ernst Udet held the rank of major general. The position of Generalflugzeugmeister was assigned to him by Hermann Göring in 1939. Source By courtesy of Klaus W. Horten I have become a silent wanderer between two worlds, – with my heart in the beyond, with my duty here. Since Herr v. Greim385 took me to Berlin for these last missions away from my family in Salzburg whither they had fled, everything has collapsed which had lent my life this deep, deep richness, as I was so graced to experience throughout my life. After this hell in Berlin, I was taken prisoner in the south and learned as a prisoner that my dearly beloved family was no longer alive. As a prisoner I was then led before the 8 graves of my most beloved persons. Mutti, Vati, my dear sister Heidi and her children Hans-Jürgen, Ellen, Jörn and my faithful Anni and Herr v. Greim. I was then sent to the prison cell in Salzburg because I was supposed to have hidden Hitler in Argentina. The so-called “eye-witness reports” which have appeared under my name are all fabricated as sensational “stories”, – with one thread of truth, namely the fact that I flew into Berlin, was in the bunker until Apr. 29th and came out again with Herr v. Greim. After 15 months of imprisonment (Salzburg, Freising, Oberursel), during which I remained alive only in the hope of being allowed to stand before Germany in Nuremberg and before Germany’s idealists. 385 Robert Ritter von Greim (1892–1945) was appointed Generalfeldmarschall by Adolf Hitler in

1945 to succeed Hermann Göring as commander-in-chief of the German air force after the latter’s removal from office. See also the ambivalent account by Kurt Braatz in his biography of Robert von Greim. Braatz’s book, which contains many quotations, shows, among other things, the close relationship between Robert von Greim and Hanna Reitsch; on this see Braatz (2018), p. 82 f. He likewise illuminates the relationship between von Greim and Ernst Udet. However, Braatz’s biography makes it considerably difficult to gain deeper insight into the descriptions and individual facts, partly due to sparse cross-referencing, missing context and lacking sources in the references, as well as for images. On Robert von Greim and Hanna Reitsch, especially their political stance, see Liebrandt (2017), p. 174 f., Mitcham (1998), p. 153 f.

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(Source: Excerpt from Hanna Reitsch’s letter to Sabine Horten, Dec. 11, 1947, Horten Family Archives; Klaus W. Horten).386

During the war, the Horten brothers often worked in various agencies of the Luftwaffe or aeronautical research establishments. Exceptions to this were the work on the Horten model H V-a and from 1941 on their joint employment in Göttingen in the Sonderkommando IX headed by Walter Horten.387 The central players in Göttingen were Reimar Horten in the area of design and Karl Nickel for the calculations. Walter Horten was only temporarily on site, as he commuted between Berlin and Göttingen. After the end of World War II, Walter Horten first worked as a driver for the British military and was then in the employ of the US military through the matchbox program.388 It did not result in a more intense collaboration between Walter Horten and the US military, however. This was followed by his recruitment as a lieutenant colonel in the new federal German army, where he remained inconspicuous until his retirement. Reimar Horten emigrated to Argentina in 1948, where he was able to carry out various flying-wing projects with government funding in the aviation company he founded there.389

4.6.3

The Horten Flying Wing Model H V-a Made of Layered Presstoff

Through the mediation of an acquaintance and glider pilot from the Eifel region, who was an employee of Dynamit-Actien-Gesellschaft (the former Alfred Nobel & Co.), Reimar Horten had occasion to contact the company’s director of operations, Gustav Leysieffer (1889–1939), and to exchange ideas with him on the subject of lightweight design.390 At this time, Reimar Horten was an ensign undergoing officer training at an aviation warfare college in Potsdam.391 Leysieffer, who was also interested in aviation and was looking for new fields of application for DAG products, viewed Reimar Horten and his flying wing models as an opportunity to open up new commercial prospects. These conversations between Reimar Horten and Gustav Leysieffer led to the latter offering to provide a very stable layered presstoff material free of charge for the construction of a flying wing. This offer included access to a workshop on the DAG premises in Troisdorf as well as its materials laboratory. Reimar Horten immediately seized this

386 Family archive of Klaus Horten, the son of Sabine and Walter Horten [hereafter FKH]. 387 See the staff file of Reimar Horten in the war assessment of 1 Oct. 1944 (BArch F). 388 Matchbox program = US programme of the Psychological Warfare Division-SHAEF and the Office of Strategic Services in Washington for the acquisition of military specialists from the nazi military, see Heideking (1993), p. 261. 389 Interview with Klaus W. Horten on 20/21 Aug. 2018. 390 See the recollections on the H V-a Horten model in LEWH (APS). 391 Luftkriegsschule 3 Wildpark/Werder. Staff file Reimar Horten (BArch F).

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opportunity and began to test the material samples provided with regard to their technical characteristic values. The results were promising, but both brothers were tied up in their respective employments at the time.392 The way to Troisdorf was finally cleared by Ernst Udet who ensured that first Walter and later also Reimar Horten be transferred to Troisdorf. In the summer of 1936, Walter Horten was finally transferred to the 134th fighter squadron and was assigned “to build new types of aircraft at Troisdorf (Dynamit AG)”.393 The transfer of Reimar Horten from the warfare college to the 232nd fighter squadron in Bernburg followed a few months later. He got transferred to Troisdorf on December 1, 1936 “for the modification of the tail-less aeroplane of his own design made of presstoff”.394 Both Dynamit AG and the Luftwaffe were interested in the brothers’ work and also involved the DVL in this project. The latter had the task of technically verifying the materials of any components and ensuring the necessary aviation certification. The military interest motivated Reimar Horten to design the model H V-a also as a fighter aircraft. In order to demonstrate the military suitability of the flying wing to the Reich Aviation Ministry, he accommodated two small but powerful engines from Hirth Motoren GmbH which left enough space for on-board arms. The propellers were custom-made of laminated wood, and one of the two engines had been reversed, making the two pressure-type air screws counter-rotate. The pressing tools for presstoff materials were expensive so Dynamit AG initially demanded an adequate prototype for testing purposes. The model used for this purpose was the Hol’s der Teufel glider wing (Fig. 4.56), which Reimar and Walter Horten had already built as a model set and knew well. Not least for lack of experience and presumably in order to become acquainted with the material, they made the wing as a classical wooden structure. For the performance specifications, the brothers and their small team produced two wings, one for flight testing and the other for materials testing.395 In addition to tensile, compression, shear, bending, impact, and notch tests, a standardized outdoor weathering test was also carried out according to DIN standard 4850, which was rather unusual and remarkable for the time, as this standard had only been in existence for three years.396 It is notable that already at this time an early form of a mechanical medial test to determine the characteristic values was used, although vibration resistance tests, which are part of the testing regime today, were not part of the examination at that time. Apart from the technical data of direct relevance to the material, which were collected during the course of outdoor weathering tests in order to determine the material’s resistance to the elements, the standardized outdoor weathering test also suggests further intentions. 392 See the recollections on the H V-a Horten model in LEWH (APS). 393 Jagdgeschwader 134. Staff file Walter Horten (BArch F). 394 Jagdgeschwader 232. Staff file Reimar Horten (BArch F). 395 Horten and Horten (1943), p. 249 f. 396 Haka (2020a), p. 2.

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Quite evidently, the material characteristics were also supposed to supplement the military materials portfolio of the Luftwaffe. Comparability with other materials granted the means to remain flexible with technical materials for a given military product so that in an emergency material bottlenecks could be easily alleviated by alternatives. Here, it was not a matter of finding substitute materials but of conceiving scenarios for variable and stable production under military-related aspects or war conditions. The lightweight material that Leysieffer placed at their disposal was a layered presstoff developed by DAG under the brand name TROLITAX397 (Fig. 4.57). This was a duroplastic synthetic consisting of a phenolic formaldehyde resin matrix with several layers of hard paper tape as the reinforcing material. This trade mark was registered at the patent office in 1928.398 From this it is clear that this material is one of the preliminary developments of DAG. As early as 1925, the company had begun to process old stocks of Rheinisch-Westfälische Sprengstoff AG (RWS) and to create its own new products.399 They were supposed to facilitate their entrance into the market upon the expiry of the heat-pressure patent of 1931 in the field of presstoff production. The material TROLITAX was a developed system to cover a wide range of users. That was why there were three quality grades for the application fields: construction (grade I), pressable plates (grade II), telephone design (grade III) and tropical applications (also grade III). It cannot be established with complete certainty anymore which material quality was finally used for the construction of the prototype wing or later for the H V-a. However, it can be assumed that two different material qualities were taken, not only the version for structural applications, which was listed under the trade name TROLITAX SUPRA but also the quality grade II pressable plates with the trade name TROLITAX.400 The data sheet indicates that both these material variants had a directed load-bearing laminate structure of several layers of hard paper with two different fibre orientations inlayed in the phenolic resin matrix. Thus TROLITAX can be regarded as a biaxial laid web according to the present-day understanding of fibre composites.401 At that time, the layers were joined almost exclusively by means of fabric bonding, as the layers underwent resin impregnation before being laid. This is why it is also referred to as a semi-finished fibre-composite product.402 The difference between the two material qualities was mainly defined by a chemical additive, giving TROLITAX SUPRA a 397 The brand name “Trolitax” insinuates the location of the DAG premises in “Tro-isdorf”. 398 The trade mark was registered at the German patent office on 13 Feb. 1928, registration number

385104 (Deutsches Patentamt). 399 Haka (2011), p. 75. 400 TROLITAX advertising leaflet from January 1937. My thanks here to the Verein KunststoffMuseum Troisdorf (Museumsverein) e. V. for their kind support and making this advertising leaflet available to me. 401 As a rule, a biaxial fabric has a fibre ply orientation of +45º and –45º. Today, modern laid webs in the field of technical textiles are mostly so-called multiaxial laid webs, where the orientation of the layers is 0, +45, –45º and +90º, see Hausding and Märtin (2011), p. 294. 402 Semi-finished fibre-composite product = fibres or fibrous fabrics impregnated with a resin before being laid. A prepreg is currently the best known semi-finished fibre product.

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Fig. 4.56 Prototype wing of the glider Hol’s der Teufel, which was built by Reimar and Walter Horten and their staff at Dynamit Nobel A. G. The complete strut mechanism is built according to classical wooden construction, but layered presstoff was applied here. The smooth and shiny polymer surface of this material can be seen on the right-hand side along the leading edge of the airfoil, which has already been planked. The rest of the wing was later covered in fabric. Source Willy Radinger. Reproduced by courtesy of Peter F. Selinger

better surface quality and lower moisture absorption. Thus, from 1928 onwards, a mature hybrid high-performance material was available, which was certified after seven years of prototype testing and applications for the H V-a as an aeronautical material. The TROLITAX material used by the Horten brothers had most probably been produced by Römmler AG, if one draws into account the company agreement between Römmler AG and Dynamit AG.403 As already mentioned, the companies shared different product areas between them from 1933 onwards. DAG mainly concentrated on the production areas for “housing” and “insulating materials” and Römmler AG focused on layered presstoff, in particular plate material and machine elements made of presstoff. However, TROLITAX was still identified as a product of Dynamit AG, which was possible because Dynamit AG provided the resin system, and the final inspection step also took place in Troisdorf. The inspection was carried out once again by Venditor KunststoffVerkaufsgesellschaft during packaging and shipping which ensured a typical externally sourced appearance for the brand. This sharing arrangement on the product assortment

403 Contract between Römmler AG and Dynamit Nobel AG dated 1 July 1933 (BLHA: Rep. 75 Chem. Werke Römmler 18).

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Fig. 4.57 Advertisement for the TROLITAX brand of laminated presstoff produced by Dynamit Nobel A. G. in 1937 but manufactured by Römmler AG in Spremberg and distributed by Venditor KunststoffVerkaufsgesellschaft m.b.H. Source Courtesy of Verein Kunststoff-Museum Troisdorf (Museumsverein) e.V

was thus not visible to the consumer. Successful testing of the wing led to the implementation of the Horten V flying wing, or its adapted model V-a, by Reimar Horten, with the assistance of his brother Walter. The basic structure of the flying wing was a tubular steel frame (Fig. 4.58). Apart from the basic frame, only the engines and the landing gear with the suspension were made of metallic materials in the flying wing. The struts and the outer planking were, with two exceptions, exclusively made of the material TROLITAX. The two exceptions were located in the visual range of the cockpit: The windows were made of ASTRALON panes,404 which are comparable to modern plexiglass; the transition between the window and the TROLITAX structure was made of DYNOS, a vulcanized fibre material. The present investigations on the H V-a model could find no evidence of the materials DYNAL and TRONAL mentioned in David Myhra’s publication and the associated manufacturing processes, in which Reimar Horten considered himself to have had a share in their development.405 Reimar Horten had evidently learned of their development later, since both Horten brothers remained in contact with DAG even subsequent to the production of their model and they continued to use their adhesives from time to time.406 Neither could any evidence be found of Reimar Horten’s purported patents filed by DAG or by Gustav Leysieffer personally, in which Reimar Horten received no share in the royalties. Neither the patents filed by the DAG nor those filed by Gustav Leysieffer during 404 ASTRALON = thermoplastic (mainly hard and soft polyvinyl chloride) with a very smooth sur-

face. ASTRALON was used especially for window panes under the brand name ASTRAGLAS. The manufacturing process for this is a development from the year 1933. 405 Myhra (1998), p. 74 f. 406 See the recollections in LEWH, p. 64 f. (APS).

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Fig. 4.58 The Horten V-a under construction in the DAG workshop in Troisdorf, 1936. The visible skeletal structure consisted of steel tubes. The shiny plane areas on the right and left are clearly discernable; they are already planked with the layered presstoff TROLITAX SUPRA with inlaid hard paper. Source Reimar Horten, courtesy of Peter F. Selinger

this period were relevant to layered presstoff or resin systems. The patenting of layered presstoff by the company or by Leysieffer personally either predates 1930 or else were made on the basis of the preliminary investigations into the TRONAL material in 1942. These investigations were carried out on behalf of the Reich Aviation Ministry. The aim of the preliminary investigations was to find out whether special DAG products, including TRONAL, could be used for load-bearing structures in aircraft construction.407 The Horten brothers demonstrably had no part in this work, however. It is rather improbable that Reimar Horten would have been actually involved in the chemical processes in developing synthetic resins or fibre technology while building their H V-a model. Neither the Horten brothers nor the use of this material in a flying wing model are mentioned in the surviving report on the TRONAL tests by the DAG.408 Thus it can be assumed that, as in other cases, in his interviews with David Myhra in the 1990s or, as in the case of the afore-mentioned example of the camouflage capability of one of Reimar Horten’s flying wing models, he reinterpreted later knowledge to his advantage. The documented preliminary investigations on TRONAL demonstrate that consistent further development of hybrid lightweight materials was underway at DAG during the 1940s. Therefore TRONAL can also be regarded as a consistent step forwards from 407 Extract from the Dynamit AG report dated 4 June 1942, sheets 48a–80a. “Kunststoffe in tragen-

den Bauteilen des Flugzeuges.” Commissioned by the RLM—GL/CE 2 (AFTUD, Prof. Dr. Enno Heidebroek papers). 408 Extract from the Dynamit AG report dated 4 June 1942.

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TROLITAX into a modern hybrid laminate, which was designed as a lightweight material for load-bearing structures specifically for aeronautical applications. The material was referred to as a lightweight fibre material (Faserleichtstoff ). This was a mechanical wood pulp409 embedded in a phenolic formaldehyde resin supporting matrix.410 For further stiffening, the material as a core was appropriately covered in either hard paper, vulcanized fibre, plywood, aluminium or duralumin. Considerable strengths were achieved in this way of comparable quality to modern lightweight construction materials in this area. The matrix of this hybrid laminate composite was a phenolic formaldehyde resin compound. Since this was a materials development for the German air force and no conventional presstoff application, the contractual agreement between Römmler AG and DAG, which allocated layered materials to the product portfolio of Römmler AG, evidently did not hold. That is why TRONAL counts as a DAG product. It would have been conceivable for the likewise named material DYNAL to have been used in the H V-a model, although here too it is more likely that it was merely a familiar material to Reimar Horten that had actually not been chosen for technical reasons. DYNAL was a TROLITAX equivalent,411 and it also consisted of a phenolic formaldehyde resin matrix with cellulose reinforcement material. As already described within the context of the Auto Union patent, unlike TROLITAX, DYNAL was designed as a semifinished material412 and not as a finished laminate. Considering the time constraints on the development of the H V-a model, it would presumably have been far more labourintensive to use DYNAL and more technically demanding. Just using TROLITAX on the H V-a flying wing would therefore have been most likely. Walter Horten also alluded to its use.413 The work on the H V-a model initially proved difficult. Reliable technical parameters for manufacture with TROLITAX were available for basic usage of the material. However, not so for the joining technology and certainly not for its use in supporting structures414 — and most particularly as regards the mixed construction they employed, what is referred to today as multimaterial design415 : the joining together of different types of materials. Whereas nowadays various joining concepts are available, especially in the aeronautical 409 Mechanical wood pulp (Holzstoff ) = is produced by the mechanical defibration of wood. Two

processes are used, the refiner process or wood-chip and ground-wood pulping. Ground-wood pulp was used for TRONAL, where wood is crushed against a stone moistened with water and shredded. The resulting pulp was then impregnated with phenol–formaldehyde resin and pressed into a board. On mechanical wood pulp or its processing, see Berthold et al. (1990), p. 365 f. 410 Laubenberger (1983), p. 13. 411 Ibid, p. 3. 412 Semi-finished material (Halbzeug) = prefabricated raw materials and semi-finished products. 413 See the recollections in LEWH, p. 63 f. (APS). 414 See the specifications of TROLITAX which mention various parameters for processing. 415 Multimaterial design = definition of joining processes in lightweight construction in which different lightweight materials, such as aluminium and fibre-reinforced plastics, are joined.

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Fig. 4.59 Sandbags were used to weigh down the glued surfaces of the H V-a wing panelling, which is made of laminated presstoff, in order to avoid possible de-gluing. Source Walter Horten, courtesy of Peter F. Selinger

and automotive industries, when the H V-a was being built this was completely uncharted territory. Gluing the numerous nodes and cross-struts proved to be complicated.416 How to glue complex load-bearing structures made of presstoff first had to be tested, and it was found that the existing glues from DAG were only partly useful. Preliminary tests already showed this. Varying temperatures by day and night and fluctuating air humidity in the workshop initially caused severe warping of the presstoff material or de-gluing of many seams. In this context, the available glues from DAG had to be chemically modified with regard to their consistency and curing times. The Horten brothers and their team used sandbags and metal weights (Fig. 4.59) to keep the glued joints in place during hardening. Similar to today, a surface activation of the resin system was also necessary to allow a suitably strong adhesive bond to form. In the case of the H V-a, a surface treatment was carried out by means of stationary blasting.417 Another problem area was the mechanical joining technology, as not all parts could be joined by gluing, especially the outer panelling. The classical bolt connection was used only in the steel-tube frame. The TROLITAX panels were heated after being cut to shape, then fixed and riveted. Due to the material’s notch sensitivity, the riveted joints initially ripped, making those TROLITAX panels unusable. Special press moulding later made it possible to preshape the plates three-dimensionally as needed, after which they were riveted to the steel structure. Classical rivet formations were distributed over the surface. 416 See the recollections in LEWH, p. 9. (APS). Horten and Selinger (1983), p. 46 f., Horten and Horten (1943), p. 250. 417 AVK (2013), p. 526.

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Fig. 4.60 The completed Horten V-a in the DAG workshop in Troisdorf, as it was presumably presented to the participants of the Lilienthal Society meeting in January 1937. The shiny fuselage planking of layered presstoff, TROLITAX, is clearly visible. The panels have been butt-jointed to the supporting frame by means of a double row of rivets. The steel-tube framework is also visible through the transparent ASTRALON panes into the cockpit as well as the two Hirth engines with hardwood propellers at the tail end. Source Walter Horten, courtesy of Peter F. Selinger

The extent to which these “rivet formations” had been numerically predefined could not be clarified, but given the prototypical character of the flying wing, this is unlikely. The evaluation of the completed Horten H V-a (Fig. 86) was carried out in January 1937 within the framework of a secret conference held by the Lilienthal Society for Aeronautical Research on the subject of flying wing aircraft.418 Here the representatives of the leading German aviation companies,419 such as Heinkel, Focke-Wulf , Junkers, Dornier, and Henschel, as well as representatives of the Reich Aviation Ministry or from research institutes like the DVL, could view the model and the materials (for a list of the participants, see the Appendix). In the conference report, the model H V-a is assessed as follows:

418 Report of the Lilienthal-Gesellschaft für die Luftfahrtforschung, Fachgruppe für Aerodynamik of 18/19 Jan. 1937 (AFTUD, Prof. Dr. Enno Heidebroek papers). 419 See the Appendix for a complete list of the participants at the conference on 18/19 Jan. 1937.

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This forward-looking building material can already compete with light metals, even when finished by craftsmen, and is superior to wood in every respect. It is impossible to estimate what advantages the use of Troisdorf plastics bodes for the future with further progress in the pressing technology. In any case, the possibility of producing a plane in a few pressed parts opens up perspectives that still seem incredible today in aircraft design. (Source: Excerpt from the conference report of the Lilienthal Gesellschaft für die Luftfahrtforschung on the subject of all-wing aircraft in January 1937).

The positive reactions to the conference on flying-wing aircraft reveals that almost all of the participating aviation companies were working on developments for tailless or allwing aeroplanes as well as on the subject of swept-back wings. The focal points of their research ranged from design issues to aerodynamics, mass analysis, stability in flight, and materials technology within the context of performance enhancement. This conference also shows that already by the mid-1930s, German aeronautical companies had reached such an advanced stage that a major turning point in aircraft construction would have been feasible, both in design as well as in materials science. In particular, the stamp of approval of layered presstoff materials by aviation experts as well as the promising characteristic values and practical suitability manifested in the H V-a, would have been a solid basis upon which others could have proceeded. Effective further developments in materials technology would have soon made it possible to introduce a new high-performance material into the portfolio of aeronautical designers. The H V-a prototype was not an isolated case with regard to the use of presstoff for supporting structural components. Although the H V-a ultimately only lifted off the ground for a short distance before crash-landing again due to a number of defects, the Horten brothers, the DAG, the DVL and the RLM regarded laminated presstoff as an aeronautical material of the future. This must also have been the impression of the participating companies at the Lilienthal conference. It is presumably also why the aircraft manufacturer Focke-Wulf Flugzeugbau AG filed a patent in 1939 for the production of a complete aeroplane structure composed of two semimonocoques out of laminated presstoff, along with the required pressing tools.420 The H V-a had sparked interest among the technical experts at the Reich Aviation Ministry. Further certification of such layered moulded materials and hybrid laminate composites was therefore pushed forward by Dynamit Nobel AG as well as by the DVL.421 The outbreak of World War II drew other topics increasingly into focus for developers and designers. The promising approaches up to that point were therefore left waiting at the prototype level.422 420 See patent application by Focke-Wulf Flugzeugbau GmbH Bremen. Verfahren zur Herstellung von Bauteilen aus Kunststoff. Submitted in 1939. 421 Cf. research project LG 078/007: Kunststoffe im Flugzeugbau, DVL, 1937; and DAG on behalf of the RLM—GL/CE 2: Kunststoffe in tragenden Bauteilen des Flugzeuges (AFTUD, Prof. Dr. Enno Heidebroek papers). 422 Küch and Riechers (1941), p. 9 f., 21.

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Fig. 4.61 Beginning to mount a Jumo 004 engine into the structural frame of the Horten IX V2 in the maintenance workshop of the Göttingen Autobahn. Some elements of what would be the wooden engine housing are also visible in the tubular skeleton. Source Reimar Horten, courtesy of Peter F. Selinger

4.6.4

The “Composite” Flying Wing IX V2/V3 by the Horten Brothers

Hardly any other flying wing model has been discussed as often as model IX423 by the Horten brothers.424 In its overall concept, this model was special in many respects and, like the H V-a model, set standards. The Horten brothers designed their model as a wooden structure. Plywood veneers were glued together in stacks and moulded over a metallic skeleton. For the propulsion they used the jet engine Junkers Jumo 004 which had just been developed (Fig. 4.61). The physicist Hans Joachim Pabst von Ohain (1911–1998) had developed this propulsion technology in the mid-1930s at the Heinkel firm. On the basis of Ohain’s work, a team led by Anselm Franz (1900–1994) at Junkers Flugzeug-und Motorenwerke AG in Dessau developed the world’s first serially produced jet engine. The first engines were delivered in 1944, and the Horten brothers received engines from this batch for their prototype flying wing.425

423 This model is also called Gotha Go 229. This designation was derived from the company that

was supposed to take over the production of the flying wing, Gothaer Waggonfabrik. 424 Cf. inter alia: Meier (2006), Storck (2003), Myhra (2016), id. (2002), id. (1998), id. (1990), Lee (2011), Dabrowski (1995), Nickel and Wohlfahrt (1990), Colemann and Wenkmann (1988), Horten and Selinger (1983). 425 Von Gersdorf et al. (1981), p. 209.

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As had been the case with model H V-a, the design and construction of model IX was carried out under considerable time pressure. The material bottlenecks caused by the war left little alternative to working with already available materials. The choice of materials in both cases therefore cannot to be seen as a voluntarily creative element of the design. The two self-taught aircraft builders Reimar and Walter Horten worked in either case with whatever materials were at their disposal at the time. The choice of DAG presstoff for model H V-a had been reached because Dynamit AG supplied the material free of charge. Likewise, for model IX: The originally intended material, duralumin, could not be obtained in sufficient quantities for model IX V2.426 Consequently, the Horten brothers reverted to wood, the conventional aviation material, in constructing this flying wing. When looking at the development of the Horten models IX V2 and V3, the prior models should be mentioned, which were intended to solve particular theoretical questions with regard to propulsion and flight behaviour of flying wings.427 They were, on one hand, the Horten H II model and, on the other hand, the Horten H IX V1. The latter was designed as a glider for cost reasons and to save time. The generally poor supply of materials also played a part. Its first real flight took place at the beginning of March 1944 in the snow. The landing was bumpy, though, as the brake chute released too late and the glider could only be stopped from running into an adjacent road by pulling in the nose wheel (Fig. 4.62). The fact that the Horten brothers were able to rely on a solid network among the military authorities and in armaments-related research in connection with the development of their H IX was already evident while the first version, the H IX V1, was under development. In the photo taken after its first flight (Fig. 4.62) one can clearly see the brake chute lying in the snow behind the glider. This parachute was unusual enough for Walter Horten to consider it important to photograph it again separately (Fig. 4.63). This brake chute was a ribbon parachute designed by Theodor Knacke (1910–2001), head of the department on parachute and braking-chute development at the Graf Zeppelin Research Institute (FGZ) in Stuttgart. As already mentioned,428 Knacke took this development with him when he emigrated to the USA after 1945, where the ribbon parachute decisively contributed to the successes of the Mercury, Gemini and Apollo missions. The parachute could not demonstrate its full potential here because it had been designed and manufactured for an aircraft carrying a jet engine. The H IX V1 glider lift-off served as a test run for the H IX V2. Therefore, the technical parameters of the chute had probably not matched. Because technical textiles were a limited resource, it is unlikely that the FGZ would have produced a separate brake chute for the H IX V1 glider.

426 The first version, Horten model IX V1, was planned and manufactured as an unpowered glider. 427 LEWH, p. 48 f. (APS). 428 Knacke headed the Abteilung Fall-und Bremsschirmentwicklung at the FGZ. See Sect. 4.4.3 on

fibre research at the DVL Institute of Materials Research and the Graf Zeppelin Research Institute, as well as Elsässer (2022), p. 103 f.

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Fig. 4.62 The landing of the Horten IX V1 after landing with a brake chute (a ribbon parachute) in the snow in March 1944. Photo H. Zübert, APS

Fig. 4.63 The braking chute of the Horten IX V1. This ribbon parachute was developed at the Graf Zeppelin Research Institute in Stuttgart under Theodor Knacke. Photo Walter Horten, APS

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The blueprint for the IX V2 model was primarily based on Reimar Horten’s design, who was in Göttingen at the time. The calculations for this second version were provided almost exclusively by the mathematics student Karl Nickel, who had just turned twenty and was destined to become the brother-in-law of Reimar and Walter Horten.429 The developmental work and construction was conducted under a special working relationship borne by another unusual network that certainly occupied a special position in the German armed forces at that time. This network enabled the Horten brothers to pursue the design and construction of their flying wing models almost autonomously. Generalflugzeugmeister Erhard Milch (1892–1972) initially planned to have both brothers transferred to Augsburg to work for the prominent aircraft designer Alexander Lippisch (1894–1976) at Messerschmitt AG. However, the brothers ultimately managed to assert their wish to work independently on their models in Göttingen.430 The brothers probably owed their transfer to the intercession of Ludwig Prandtl (1875–1953) (Fig. 4.64), the director of the Kaiser Wilhelm Institute of Fluid Dynamics Research, who sponsored all-wing technology and supported the Horten brothers.431

429 See the recollections in MKN (APS). 430 See the letter from Luftwaffepersonalamt dated 18 May 1942 (Personalakte Reimar Horten

(BArch F). 431 Kaiser-Wilhelm-Institut für Strömungsforschung at Göttingen. The flying-wing technology of the Horten brothers was also of interest to the Waffen-SS. The general of the Waffen-SS, Hans Kammler (1901–1945), tried several times to win over the Horten brothers to his department. In a conversation between Hans Kammler and Walter Horten, the latter declined shortly before receiving his order to Göttingen, because both brothers wanted to work autonomously, referring in this context to Ludwig Prandtl’s interest in the subject. (Interview with K. W. Horten.).

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Fig. 4.64 Visit by Ludwig Prandtl (director of the Kaiser Wilhelm Institute of Fluid Dynamics Research in Göttingen) on the Göttingen airfield in 1943. From the left: Robert Wichard Pohl (1884–1976) (director of the 1st Physics Institute at the University of Göttingen and doctoral advisor of the physicist and inventor of the jet engine Hans Joachim Pabst von Ohain), Walter Horten, Ludwig Prandtl, Eduard Hildenbrand and Reimar Horten. Source Courtesy of the DLR Archive, Göttingen432

A note by Ludwig Prandtl in the secret file documents that further research on the flying wing was to be carried out within the framework of academic inquiries.433 A small gathering was arranged in the study of Albert Betz (1885–1968),434 the director of the Aerodynamic Testing Station (AVA) in Göttingen, was arranged, also attended by Ludwig Prandtl, Josef Stüper435 and Walter Horten, to determine the official organization of Special Commando IX, Sonderkommando IX (Horten), which Albert Betz or Ludwig Prandtl presumably authorized following that meeting. Prandtl was the scientific head of German aeronautical research and a member of the research leadership under the reichminister

432 I would like to thank Dr. Jessika Wichner, head of the DLR Central Archive in Göttingen, for

her kind support of my research. 433 See Ludwig Prandtl’s note of 26 Mar. 1943 (DLR Archiv Göttingen [hereafter DLRG] 43 AVA-

GOAR_1002). 434 On Albert Betz or the Aerodynamische Versuchsanstalt, see, among others, Eckert (2017), p. 96 f., id. (2007), Schmaltz (2016), p. 326 f., Haka (2014a), p. 91 f., Budraß (2016), p. 296 f., 300, id. (1996), p. 28, Trischler (1992), p. 203 f. 435 Prof. Dr. Josef Stüper, director of the institute of research flight operations and aviation at the Aerodynamische Versuchsanstalt in Göttingen, see here also Henning, Kazemi (2016c), p. 33, 36.

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of aviation and commander-in-chief of the Luftwaffe during World War II.436 This small circle laid down the following points: • The Aerodynamic Testing Station (AVA) shall assume the scientific supervision of the sphere of tasks by Special Commando IX (Horten). • The economic support concerning accommodations, wages and provisions as well as the replenishment of materials shall be carried out by the air base commandant’s office in Göttingen. • Order: Preliminary research for the creation of a high-speed fighter aeroplane; to this end, an aeroplane shall be delivered to the Horten Bros. for research purposes by the company Peschke Flugzeugbau GmbH in Minden. This arrangement granted the Horten brothers a carte blanche to work autonomously and in fact not be assigned or subordinated to any military agency. The disused roadmaintenance depot of the Göttingen Autobahn was allocated to the “Aeroplane Designing Special Commando of the Air Force x Special Commando IX (Horten)”,437 as it was officially called. This also became the official place of residence of Reimar and Walter Horten as well as Walter’s wife Sabine. In addition, the restaurant Springmühle near Grone was requisitioned and converted into a sheet-metal workshop.438 The staff of Special Commando IX, which at times numbered up to thirty members, had separate quarters outside the premises. Aircraft produced at the road-maintenance depot, besides other Horten allwing models, included the jet-powered model H IX V2. The Horten brothers had designed the load-bearing centre section as a stainless-steel tubular structure, which was joined by means of welded-on connecting plates, or in some sections also bolted together. The outer skin of the H IX V2 was made of plywood planking with ribbing as reinforcement. The jet engines received a sheet-metal housing attached to the wood.439 Thus just a few millimetres separated the pilot from the jet engines. The wing segments were wooden constructions reinforced with metal fittings, with a supporting wooden spar, rigidly connected to a thick leading-edge or nose shell (Fig. 4.65) which was stiffened by ribbing constituting the torsional rigidity and force-absorbing composite. Steel tanks were set inside the aerofoil. The rear wing section was a wooden ribbed composite with an auxiliary spar and a wooden shell. Conventional carpenter’s wooden joints were occasionally employed

436 Forschungsführung des Reichsluftfahrtministers und Oberbefehlshabers der Luftwaffe. On Lud-

wig Prandtl and his work in nazi aviation research, see, among others, Haka (2014a), p. 79 f., 129, Eckert (2017), id. (2007), p. 51 f., Maier (2007b), p. 106 f. 437 Flugzeugkonstruktions-Sonderkommando Lw. x Sonderkommando IX (Horten). See the entry in the staff file, Personalakte Reimar Horten (BArch F). 438 Sabine Horten’s letter to Oberbürgermeister der Stadt Göttingen, 19 Apr. 1945 (FKH). 439 See the recollections in MKN, p. 211 f. (APS), Stadler (1989); I thank Mr. Reinhard Stadler for pertinent pointers on the aircraft statics of the H IX.

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Fig. 4.65 Detail drawing 9 of the massive wing nose (section G–H in the drawing) made of plywood for Horten model IX V2. In order to be able to lay the inner layers with the appropriate radius curvature, the two inner converging plywood layers were scarf jointed (red arrow) in the common fashion employed by carpenters. Source Detail drawing 9; constructional drawing of the Horten IX V2; APS

for the wooden structures and for the wing’s thickened leading edge as had subsequently been determined by the torsion. As had been the case with the Horten H V-a, the development of the Horten IX V2 suffered initially from a shortage of skilled workers. The soldiers and technicians assigned to the site first had to familiarize themselves with woodworking. Most of the work was done on metalworking equipment, since appropriate woodworking tools could not be procured until later. As can be gathered from the construction drawings of the Horten IX V2, the design was completely oblivious of the associated hazards. It is also possible, though, that knowledge was simply lacking about how to accommodate engines.440 Karl Nickel, the aircraft structural engineer and mathematics student at the time who carried out the performance, structural-strength and torsion calculations for the IX V2, determined that unlike the unpowered model V1, it was absolutely necessary for the second version to have thickened plywood planking to handle flight manoeuvres approaching the speed of sound. The plywood thickness in this context increased from 8 to 17 mm in the Horten IX V3, with its required inner radius achieved by means of scarf jointing.441 The production 440 217 detailed drawings on the Horten IX V2 were examined for this purpose (APS). 441 The aircraft statics of the Horten IX V2, filling 195 pages, by Karl Nickel were perused, esp. the

calculation of the torsional moments on p. 152 f. (APS).

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of this third version was not carried out by the Horten brothers but by Gothaer Waggonfabrik. This company made various design alterations, such as the engine cowling, which made the central section appear more massive. However, the H IX V2 and V3 models were prototypes unsuitable for serial production. The collapse of the nazi regime stopped further pursuit of this line of research. The carbon-glue layering described by Reimar Horten, which had purportedly been inserted into the plywood layers in order to make the H IX V2 flying-wing model radar-proof, could not be established.442 The materials examination443 performed by the American Institute for Conservation of Historic and Artistic Works (AIC) in Washington, which analysed the material of the only surviving corpus of the Horten IX V3 model, and which is stored in the National Air and Space Museum—Smithsonian Institution, Aeronautics Department, shows that the plywood planking was carried out exactly as indicated on the H IX blueprints. The adhesive layers (Fig. 4.66), now amber in colour, do not contain any additives, and a separate carbon layer could not be detected either. It is conceivable that the dark residues described earlier were meant. Those “runny noses” in the context of the work on the Hü 211 model were the result of suboptimal settings of the press or were brownish-black staining from the tego film parting agent on the press.444 One must rather assume that Reimar Horten was attempting to embellish his model or his professional competence with technical knowledge that actually stemmed from the post-war period. This is also supported by the fact that no source from the time of the creation of the H IX refers to this rather important point. An equally negative finding is to be made about the plywood panelling surface of the flying wing. No additional coating of relevance to radar detectibility could be found either. Since it was a prototype, and for lack of time and material resources, no surface treatment of the plywood planking was done at all in 1944 and 1945, especially not paint and varnish systems for the exterior.445 The known superficial motif on the last extant Horten model IX V3 in the National Air and Space Museum with a swastika and an identification number on a grey background (Fig. 4.67) had been painted after its shipping to the U.S. by the American allies, in order to distinguish it graphically as nazi technology. My investigation shows that the two flying-wing aeroplanes designed primarily by Reimar Horten can be assessed as innovative and sophisticated developments as regards their material properties. However, no purposefully constructive radar shielding was attempted with these models.446 442 Horten and Selinger (1983), p. 136, 141, Horten (1950), p. 245. 443 Horelick et al. (2014). 444 See Sect. 4.5.2 on fibre-aligned lightweight wood construction and conventional moulded wood production. 445 See the recollections in MKN (APS). 446 The replication of the Horten model Ho 229 V3 by the Northrop Grumman Corporation in the USA in consultation with the historian David Myhra, must be questioned in this context. The documentary film about the replica (2009) presents clear deviations in design and materials from the original all-wing aircraft. The radar measurements taken by Northrop in this context are therefore also compromised. Likewise, a number of biographical details in Myhra’s documentary about the

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Fig. 4.66 Cross-section of the plywood panelling of the Horten model IX V3 from the material analysis at the American Institute for Conservation of Historic and Artistic Works. Numbers 1–5 on the image show the fivefold layering of laminate panels, which are glued together with an ambercoloured adhesive. Each panel layer consists of approximately 20 layers of veneer. The white arrow points to one of the layers of adhesive bonding together the 5-ply plywood packages. No carbon film applied as radar shielding could be detected here. Nor could the particle analysis detect any carbon residues, only dirt particles presumably from the parting agent used in the press at that time.447 Source Courtesy of Lauren Horelick via E. Crellin

These built models were about 30 years ahead of the aviation standard of the time. Of particular note is their use of hybrid material systems, especially in the model H V-a, with its use of layered presstoff TROLITAX, ASTRALON panes and DYNOS vulcanized fibre material. The theoretical and practical knowledge about hybrid material structures gained from the fabrication of this model, such as notch sensitivity of laminated presstoff and the novel and sophisticated joining techniques developed as a consequence, count today as basic knowledge in dealing with hybrid material systems, especially fibre-composite structures. Likewise, a large number of manufacturing aspects can be subsumed, such as the numerically determined load-aligned embedding of reinforcing material within a supporting matrix, the product-specific production of suitably moulded semi-finished products, or chip treatment of presstoff.

Horten brothers diverge considerably from ones found in archival sources, such as details about Wolfram Horten or the meeting between the Horten brothers and Herrmann Göring. See https://www.nat geotv.com/ca/hitler-s-stealth-fighter. 447 Horelick (2014).

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Fig. 4.67 Fuselage section of the Horten IX V3 in the workshop of the National Air and Space Museum—Smithsonian Institution in 2017. The swastika and identification number had been painted on after its arrival in the U.S. in 1945 to distinguish it as nazi technology. Source Courtesy of Peter F. Selinger

Similar insights can also be gained in connection with the H IX model. It can be considered as unprecedented that bonded plywood panelling be chosen for such a highperformance aircraft with an application horizon approaching the supersonic range. This also applies to its structural design based on glider construction. The load-specific shaping of the hybrid laminate composite is equally remarkable, as is the use of joining techniques from conventional carpentry, which thus impressively marries craftsmanship with highperformance materials and technologies. These analyses have also shown that the choice of materials mentioned had not come from the Horten brothers’ intended designs. On the contrary, it is often attributable to special circumstances, such as the brothers’ permanent lack of funding or the wartime economy of scarcity. The Horten brothers’ integration in the military apparatus of the nazi system, as well as their own networking incorporating the associated patronage, made much of their developmental research possible in the first place. Their clear avowal of national socialism opened many additional avenues for them, even though they, like many technical actors of the period, regarded themselves as apolitical and focused on professional questions.448 In order to realize their ideas, they exploited the available resources under wartime conditions to their own advantage to some extent without duly considering third parties. The endeavours of friends, colleagues and superiors were at times not only 448 Haka (2014a), p. 187 f., 314 f.

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slowed or manipulated as they saw fit, but pressure was applied verging on ruthlessness. The ambition to achieve goals in technical design or to posture themselves personally led not infrequently to the brothers even fighting between themselves.449 According to the classificatory scheme for engineers under national socialism proposed by Wolfgang König, the Horten brothers must be ranked among the class of opportunists.450

4.6.5

Composite Materials and Their Applications in Foreign Design

Whereas in Germany further development of presstoff in many areas is ascertainable in materials science of the 1930 and 1940s, both as regards various reinforcing materials and the supporting matrix, companies in the industrialized nations, primarily the USA but also Great Britain, concentrated mainly on developing wooden and wood-derived materials and their further modification and refinement. Very similar to in Germany, in these countries the search for lightweight construction concepts under the premise of new technical performance limits for materials was evident, especially for aviation applications. The outbreak of World War II brought military ideas in combination with material requirements for long-range aeroplanes to the forefront of development. Indeed, the dwindling supply of metallic materials had to be effectively countered. One example of such developments in Britain is the research conducted by the De Havilland Aircraft Company. Creating a laminate composite from which to make fuselage shells formed the basis of this work. This composite consisted of two layers of plywood impregnated with phenolic resin and a 25-mm-thick layer of balsa wood as the core material. The wings were simple wooden structures. This hybrid structure was ultimately used in the model DH 91 Albatross.451 This model by De Havilland Aircraft Company also marks the pinnacle of modern wooden aircraft construction.452 The material applications implemented here formed the basis of the multipurpose aircraft DH 98 Mosquito which was primarily deployed as a fighter-bomber during World War II. The fuselage was manufactured in a shell construction, which was rendered as a multi-layered laminate composite. Thereby an advantageous combination of different types of wood yielded high-performance lightweight materials. In the USA, various companies pursued approaches similar to those of De Havilland Aircraft Company. They developed a range of wood-derived laminate composites with binders and surface films based on phenolic resins. One of the best-known composite processes was the duramold process.453 The resulting duramold material was intended to help redress the wartime shortages of metallic materials impairing the aeronautical industry. 449 See the recollections in MKN (APS). 450 König (2010), p. 75 f. 451 Richter (1942), p. 294. 452 Jackson (1978), p. 158 f., 381, 405. 453 Schatzberg (2000), p. 183 f.

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The engineering officer Virginius Evans Clark (1886–1948) had developed this process with the assistance of Bakelite Corporation and Haskelite Manufacturing Corporation in Grand Rapids, Michigan.454 The process was also used to make aircraft fuselage shells. They were draped onto a final mould in the form of several thin plies of wood veneer, with phenolic resin acting as a binder and coating. The shells were then compressed and cured under pressure at about 90º Celsius in an autoclave.455 One of the most famous aircraft produced by this process is the Hughes H-4 Hercules by the American industrialist Howard Hughes (1905–1976). Employing an autoclave was no innovation. This versatile pressure unit is based on the development by the French biologist Charles Chamberland (1851–1908) and the early form on the work of his compatriot, the physicist Denis Papin (1647–1713).456 Originally, the autoclave was used to sterilize medical equipment. It was not used in materials production until the early 1920s in the wood industry. A very similar process called aeromold 457 was developed by the Timm Aircraft Company in Los Angeles, California. A modified phenolic resin was used in this process. Unlike the duramold process, the resin in the aeromold process was cured at well below 90º Celsius. Another process, named vidal after its inventor Eugene Luther Vidal (1895– 1969), was developed at the Aircraft Research Corporation in New York. The vidal process operated primarily with new resin systems.458 Contrary to the previous processes, a thermoplastic resin was used instead of a thermosetting resin. It could be processed at lower temperatures and at lower pressure. Because the resin system unglued again if the components were reheated, the segmental construction method had to be employed. Although a large number of reports appeared in the 1930 and 1940s, particularly in the USA and the German and European trade press on aircraft made of plastics, only a few reports can be found which go beyond a mere announcement and reflect on the subject from a technical point of view.459 The catchword plastic was often given more importance in these reports than any comprehensive discussion of the facts. In the publications mentioned above, the focus of discussion is primarily on the various methods of wood modification and refinement, whereas there is hardly anything to be found on the subject of presstoff materials, which correspond most closely to modern fibre-reinforced composites. Only one brief press report in the journal Zeitschrift des Vereins Deutscher Ingenieure (VDI) indicates that British researchers and developers were working in the field of such laminate compressed moulding materials. The half-page report briefly describes some details about a pilot seat from a captured British fighter

454 Anon. (1939), p. 244. 455 Richter (1942), p. 293. 456 Pommerville (2010), p. 189. 457 Anon. (1942), p. 17 f. 458 Elder and Thom (2005), p. 120, Riechers (1942), p. 85 f. 459 Richter (1942), Anon. (1942), Anon. (1940), p. 15 f.

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plane, a Spitfire, and points out that the seat was made of layered presstoff.460 According to this report, it fell within the range of type Z3 of the German standard DIN 7701.461 It was therefore a compressed thermoset material composed of a phenolic resin reinforced with cellulose tape layers. Furthermore, it reported that the quality of the seats from the captured plane varied greatly, but such a “large-scale production” permitted conclusions to be drawn about the “front-line maturity” of the product. It is difficult to determine the actual state of development of laminate presstoff in Great Britain. The period of time during which the seats were built can only be narrowed down on the basis of an analytical report from the DVL in Berlin-Adlershof from the year 1941. The report about captured Spitfire II-type planes, which were mainly deployed at the end of 1940, contains detailed material analyses. It documents that at the time of its publication the pilot seats made of laminate presstoff did not yet belong to the model in question. It can therefore be assumed that the pilot seat found in the captured British fighter plane was probably a revamping of the Spitfire model series and that this seat was not part of the original design. One possible explanation would be that the limited availability of aluminium alloys in Great Britain motivated the installation of such a seat, and another would be its time-saving manufacture, that great advantage of presstoff materials.462 It is reasonable to assume that laminate materials were being developed in the UK, but the product quality was not sufficient for larger scale serial application. In hybrid-materials development in the USA there was one exception at the beginning of the 1940s: glass-fibre reinforced plastic (GFRP). A one-liner news item in an aviation magazine is the only reflection on this development for the German public.463 At that time few people were aware that GFRP structures had already been certified in German aviation. These developments were probably not noticed outside Germany due to the largely separate research and development on fibre fabrics or possible matrices. The central player in the USA in this field was Owens-Corning Fiberglas in Wilmington, Delaware. Much like the German company Thüringische Glaswollindustrie, this American company began to produce insulating materials out of glass wool and spun glass for the construction and electrical industries in the 1930 and 1940s.464 It had only just then found solutions to large-scale production of glass fibre in a technically reliable process, as a series of patents filed at the end of the 1930s reveal.465 Many of the developments by OwensCorning Fiberglas were market-driven, not spearheaded by research. This also applied to manufacturing aspects, as can be gathered from its patents on glass-fibre production during this period. New technical specifications with regard to machine technology and manufacturing processes appeared in stages, as there was no guiding conceptual outline. 460 Schmidle (1942), p. 398. 461 Haka (2012), p. 11 f., id. (2011), p. 82. 462 Känzle (1942). 463 Anon. (1944), p. 68. 464 Slayter (1939). 465 See here, among others, Ceretti (1939).

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Fig. 4.68 Detail from the patent by Henry Ford and Eugene Gregorie. The detail shows part of the basic structure of the vehicle. The patent does not contain any information about the materials used, neither that it was a hybrid material, nor that a special supporting matrix was planned, only the indication that the overall structure of the car was considerably lighter than previous vehicular structures. Source Patent H. Ford, E. Gregorie, 1942

There was no systematic investigation of fibrous materials or possible matrix materials in the US. It was not until the US Air Force was militarily reorganized in 1941 that its newly appointed commander-in-chief, Henry Harley Arnold (1886–1950) issued an order to Wright-Patterson Air Force Base in Dayton, Ohio, to engage in the research and development of plastics in aviation.466 The Scientific Advisory Group, headed by the emigré Hungarian physicist Theodore von Kármán (1881–1963), was founded in this context, which also recommended that new materials be developed for the Air Force.467 This recommendation also included fibreglass, which led to various prototypes in military aircraft and boat construction. Serial production of GFRP only began after World War II had ended. My investigations could not confirm the hitherto prevalent assumption that the USA had been the earlier and dominant developer of glass-fibre-reinforced plastics. R & D efforts in Germany were mostly not publicly available and especially in the area of fibre research began much earlier and more comprehensively than in the US. This is also notable of the manufacturing nuances of matrix resins in Germany, which were already 466 Barber and Damms (2012), p. 27. 467 Gainor (2018), p. 45 f.

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available for a hybrid material structure in the early 1940s. This know-how was eventually conveyed along lines of intelligence to the USA and adapted.468 Although differences in the individual developmental stages and characteristics are identifiable with regard to the certification of GFRP in the States, its development in the 1940s ran parallel to German work. The production capacities and material output were more extensive in the US than in Germany, of course, due to far a greater demand for such products and the almost intact state of industry despite the drain by the war. Otherwise, American GFRP was mainly used in construction and the electrical industry. Lightweight materials with a hybrid structure were developed beyond the field of aeronautical applications as well. A fibre-composite material was developed in the American automotive industry, which is comparable to the composite material developed by Auto Union in Germany in the mid-1930s. This was a development by the US car maker Ford in 1940. It has previously been assumed that Ford had developed a sheet material based on phenolic resin-impregnated plant fibre, which was comparable to presstoff and served as a bearing structure for a motor vehicle. The composition of this material was frequently discussed in publications. The reinforcing material was described as soybean fibre. That is why the vehicle became known as the soybean car. However, the true ingredients of the material are still unknown today. Since it was a prototype car, no permanent documentation on it was kept by the company.469 The pertinent patent specification470 by its developer Henry Ford (1863–1947) and its designer Eugene Gregorie (1908–2002) only discussed the car body (Fig. 4.68). The envisaged lightweight material was not mentioned.

468 Spurr (2004), p. 12 f. 469 Skrabec (2013), p. 149 f., Anon. (1941), p. 38 f. 470 Ford and Gregorie (1942).

5

Development of Hybrid Material Systems in the Second Half of the Twentieth Century

5.1

The Bridge to the Future—Glass-Fibre-Reinforced Plastic and the Akafliegs

Allied Control Council Directive No. 25 of April 29, 1946 on the regulation and monitoring of scientific research, initially prevented open pursuit of topics in aviation, the field in which hybrid material systems had been most intensely promoted or needed until then.1 Not only aircraft construction, but also the majority of the other mechanical engineering disciplines and some of the applied natural sciences were also affected. However, ways and means were found to tie in with research topics from before 1945. The materials research category was the easiest way to circumvent these restrictions, by assigning neutral titles to the work or placing materials in a new application context. This was the case with layered presstoff and materials with direction-specific strength. A good example of this tactic is the research by Franz Bollenrath (1898–1981) at the RWTH Aachen, which also manifests staff continuity in the field of aeronautical research after World War II in Germany.2 Bollenrath, a former Professor im Reichsdienst,3 was editor of the aeronautical reference work Ringbuch der Luftfahrttechnik in the late 1940s and was responsible for all confidential research reports from section “C” on materials (Werkstoffe).4 He thus had full access to all the documented findings of the most important 1 Haka (2011), p. 84., Heinemann (2001). 2 Haka (2014a), p. 337, Stegmann (2009). 3 Academic promotion in the form of an appointment as Professor im Reichsdienst was part of a

catalogue of measures by Adolf Baeumker (member of the Luftwaffe’s research leadership) at the end of 1936 to recruit good specialists for aeronautical research or to prevent a thinning out of the work-force through migration to the financially more lucrative positions in industry. For details see Haka (2014a), p. 89 f. 4 ZWB (1937).

© The Author(s), under exclusive license to Springer Fachmedien Wiesbaden GmbH, part of Springer Nature 2023 A. T. Haka, Engineered Stability, https://doi.org/10.1007/978-3-658-41408-5_5

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aeronautical research institutions of the Third Reich. Presumably some of the research topics he initiated at Aachen, which were almost exclusively intended for the aerospace industry of the young Federal Republic of Germany (FRG), were based on final results from the years 1944/1945. One of his first publications in 1946 dealt with synthetic resin laminates with glass fibres.5 The footnotes in the publication all date from the 1930 and 1940s and mainly refer to research reports by the DVL as well as the central Dresden researches on glass-fibre fabrics and their textile properties conducted by Paul-August Koch. This publication can thus also be viewed as a kind of commentary on the then state of the art with regard to GFRP at the DVL. The paper also shows the considerable level already attained by this work in materials technology. GFRP quickly established itself in glider construction in the young Federal Republic. Its application in larger aircraft, whether civil or military, in the near future could only be considered, if at all, after Allied Control Council Directive No. 25 had been repealed in 1955. Pioneering work in Germany on the first GFRP structures in aircraft construction is attributable to the aviation Akaflieg groups at technically oriented academic institutions, most of whose members were students who spent their spare time building, developing and exploring aeronautical questions principally for gliders. The origin of the Akafliegs dates back to the time of the Treaty of Versailles, which forbade Germany from pursuing motorized sport aviation after World War I. Thereupon gliding became the alternative of choice in order to be able to pursue aeronautical topics further. After 1945 a similar situation arose again in Germany, pre-conditioned by the Control Council Directive.6 One of the most important achievements on GFRP structures during this period came from the designers Hermann Nägele (1925–1996) and Richard Eppler (*1924) of the Akaflieg in Stuttgart.7 Their FS 24 Phönix model was the first glider made of a fully supporting shell of balsa wood and glass-fibre-reinforced plastic. This glider was presented for the first time in November 1957 on the airfield in Schwaighofen.8 The requisite new calculation methods, e.g. for wing profiles with different wing-spans, were carried out by Richard Eppler, who would later be appointed to the chair for technical mechanics at the just renamed University of Stuttgart. This pioneering work by Nägele and Eppler can be seen as the grounding upon which fibre-reinforced plastic (FRP) was applied to gliders and attracted attention world wide.9 The way to success was not without its problems, though. Originally, a composite material with inlaid cellulose tape—not glass fibre—had been foreseen as the reinforcement material for the FS 24 Phönix. The sponsor, the State 5 Bollenrath (1946). 6 Achermann (2016), p. 41, Löwer (2011), p. 699 f., Reinke (2004), p. 38, Fabian (2001), p. 55 f. 7 A dissertation on the Stuttgart Akaflieg is currently being written by Katharina Fuchs at the

Stuttgart GNT. 8 See the statements by Richard Eppler made in the context of the patent dispute about issues in

materials technology from 1962 (case file on the patent dispute “FS 24 Phönix”, APS). 9 Gersdorff (1981).

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of Baden-Württemberg, had set as a condition for its funding that a patent be filed on the aircraft. In order to raise the patent level sufficiently, the cellulose tape was ultimately exchanged with glass fibre. Bölkow-Entwicklungen in Ottobrunn stepped in as manufacturer for the State of Baden-Württemberg and also hired Eppler and Nägele on its staff. The already submitted patent had to be suitably adapted to take the glass-fibre modification into account. This, however, caused problems as a similar patent had already been filed. The joint applicants for this patent were Ulrich Hütter (1910–1990), the later director of the Institute of Aircraft Design at Stuttgart and at that time head of the design department of the engine and vehicle manufacturer Allgaier-Werke GmbH in Uhingen, which also built aircraft parts and wind turbines, and his colleague there Eugen Hänle (1924–1975). The result was a patent dispute which could only be ended by settlement in 1968.10 The dispute was about the roving11 manufacturing process, on which Hütter and Hänle wanted to secure the rights. The legal suit was not trivial to Hänle, having founded the glider company Glasflügel Segelflugzeugbau GmbH shortly after submitting the patent application. It built the glider model Glasflügel Hütter H 301 Libelle. The final settlement also granted Bölkow Entwicklungen the freedom to produce rovings without having to pay license fees. This phase also includes the development of a synthetic fibre, but which would not come to fruition until the early 1970s. This invention by the US-American of Polish descent, Stephanie Kwolek (1923–2014), dates back to 1965. The material in question was aramide which was later marketed by the company DuPont in the USA under the name kevlar.12 Its very good mechanical properties, especially its tensile strength and excellent tear length, make the material very tough. As a result, aramide has a high energy absorption capacity and was therefore later increasingly used in the field of body armour and armoured plating for vehicles. Not infrequently, mixed forms were also used, whereby carbon and aramide fibres were combined into blended fabrics to form new, more efficient composites sharing the properties of both fibres. At this point in time, this development contributed insignificantly toward consistent implementation of GFRP, since the initial aim was to put into practice the experiences gained from glider construction. This implementation happened in 1968 with the four-seater civilian small aeroplane LFU 205, which was built by Leichtflugtechnik Union (LFU) in cooperation with the German Aviation Research Institute (DVL) and by the three shareholders—Bölkow, Rheinflugzeugbau and Pfützer-Kunststofftechnik—and financed with funds from the Federal Ministry of Defence (BMVg) and a number of other ministries.13 The BMVg was motivated to act as the financial backer because it wanted

10 See the letter from the patent litigation by Richard Eppler at Bölkow Entwicklungen in Ottobrunn

of 18 Mar. 1958 and the decision of the Federal Patent Court of 12 Mar. 1968 (APS). 11 Roving = a defined bundle of fibres. 12 Wyckoff (2008). 13 Weather (1982).

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eventually to certify GFRP as a material for defence applications. Initially, polyester was used as the supporting matrix and later epoxy resin.14 Glass-fibre-reinforced plastic can be seen as the template for the modern fibre composite, which henceforth replaced presstoff as the commonly used material, even though the reinforcing fibres in presstoff, too, were inlaid to suit the load along a defined course determinable by calculation. The considerably higher strengths of glass fibres, however, transformed the reinforcing material embedded in the plastic matrix into a finely definable structure. The filaments of a roving were the key to a numerically controllable work arm. The caesura of 1945 also became a verbal caesura for fibre composites. The paper by Franz Bollenrath from 1946 is a good indicator of this: With reference to GFRP the old term Preßstoff is abandoned in favour of Kunstschichtstoffe mit Glasfasern—syntheticresin laminate with glass fibres—thus singling out the reinforcing material as the defining factor in determining a new type of material.

5.2

New Load Horizons from “Black Gold”—Early 1970

5.2.1

Student Involvement Leads to Serially Produced CFRP

Although GFRP is still a central and important fibre-composite material today and is used in a wide variety of applications, the search for alternatives began promptly after its development and application in such areas as aircraft construction,15 boat building, container construction, sports equipment and quite a few other fields. This was not surprising, as many new fields of application were anticipated. The new fibre materials would make new load horizons feasible. The step from glass fibre to a higher-quality, more durable and robust fibre was taken when the load limits of the former were reached. In Germany this step was taken by the Akademische Fliegergruppe in Braunschweig. This Braunschweig Akaflieg had run up against a limit in glider construction in 1969 with its glider model SB 9.16 Clarity had already been reached about designing the wing geometry and good aerodynamic fuselages. Only the wing-span still offered potential for optimization. The problem was that the existing GFRP did not permit the envisaged wing-span. An unacceptable wing deformation was predictable for a wing-span of 30 m. Therefore, it was necessary to find a new material for the spar of the wing mid-section.

14 Kluge (2018), p. 18 f., Füller (2005), p. 15 f., Grüninger (1968), p. 341 f., Niederstadt (1968),

p. 847 f. 15 This also included engine construction. In the 1960s, for example, the compressor housing and

compressor blades of the RB 162 engine by Rolls-Royce were made of GFRP. 16 Haka (2012), p. 1 f.

5.2

New Load Horizons from “Black Gold”—Early 1970

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The available alternative materials were boron-fibre-reinforced plastic (BFRP) or carbon-fibre-reinforced plastic (CFRP).17 In the end, the decision favoured CFRP. It was expected that CFRP would behave similarly to GFRP in processing. Boron fibre was much more brittle to work with, but that was not the only reason for its rejection. It was also far more costly to produce and consequently little use was made of boron fibre in aircraft construction. Examples of its successful application include various components in the US fighter aircraft Grumman F-14 Tomcat manufactured by Grumman Aerospace Corporation,18 which was put into service in 1970, and the short-range passenger aircraft VFW 614 of Vereinigte Flugtechnische Werke (VFW) in Bremen.19 The cost factor was duly drawn into account in choosing the new reinforcement fibre, but the student project idea was in danger of failing because carbon fibre was still very expensive at the time. For this reason, the Akaflieg applied to the Technical University (TU) in Braunschweig and the German Research and Testing Institute of Aeronautics and Astronautics (DFVLR) also in that city, which later became the German Aerospace Centre (DLR), and relied on their network (Fig. 5.1).20 The latter was headed from 1969 to 1972 by Hermann Blenk (1901–1995). Blenk had directed the Hermann Göring Aeronautical Research Institute from 1938 to 1945 and also headed the Institut für Aerodynamik at the TU at the same time. He took an interest in the ambitions of the Akaflieg.21 This sympathy was due to his having formerly worked closely with his then deputy at the Luftfahrtforschungsanstalt and director of the Institut für Motorforschung, Ernst Schmidt (1892–1975), on new, more efficient materials for solid-fuel rocket technology.22 After the collapse of the national socialist regime, having then worked for the British Ministry of Supply and subsequently for the Landtechnisches Institut für Grundlagenforschung, Blenk had managed to become director of the Institute of Flight Mechanics at the newly founded German Aeronautical Research Institute (DFL) in 1953.23 As a member of the board of the DFVLR, Blenk joined forces with his fellow board member Hermann Schlichting (1907–1982), another aviation expert from the pre-war period, who at the time was head of the DFVLR’s large wind tunnel, to advocate for the Akaflieg project. Like Blenk, Hermann Schlichting also held a professorship at the TU in Braunschweig and had begun his career as an assistant to Ludwig Prandtl at the Kaiser Wilhelm Institute for Fluid Dynamics Research and from 1937 headed the wind tunnel department of Dornier-Werke 17 “CFK” has become established in German usage for kohlenstofffaserverstärkter Kunststoff , even

though it is not an exact translation of the term into German. It is a mixture of one English and two German words: “C” for “carbon”, “F” for “faserverstärkter” and “K” for “Kunststoff”. The English abbreviation of “carbon-fibre-reinforced plastic” is CFRP. 18 Chawla (1998), p. 22. 19 Wentzel (1977), p. 1 f. 20 Haka (2011), p. 86 f., Akaflieg Braunschweig (1972). 21 Haka (2014a), p. 80 f. 22 Ibid., p. 131 f. 23 Gerke (1991a), p. 17 f.

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in Friedrichshafen on Lake Constance. Thus, he knew how indispensable technical examinations of the fluid dynamics were.24 He made it possible for the outcome of the Akaflieg project, the SB 10 glider, to undergo testing in the DFVLR’s wind tunnel.25 The SB 10 (Fig. 5.2) was manufactured with wing-spans of 26 and 29 m. Its successful maiden flight in 1972 provided proof of the great rigidity of CFRP. Thus GFRP, the hitherto most efficient structural material in glider design, was replaced. The promptness with which the project was implemented was not least due to the willingness of the company VFW-Fokker to donate the central fuselage tube for the SB 10. Heinrich Doetsch (1910–2003) was another sponsor of the SB 10.26 In 1936 Doetsch had taken over the management of the DVL’s Flight Characteristics Department and in 1947 worked together with his colleague Hermann Schlichting on commission of the British Royal Aircraft Establishment in Farnborough. There he was instrumental in drafting the design of an electric primary control system for the later Anglo-French supersonic aircraft Concorde. In 1961, despite his nazi past, Doetsch was easily appointed to Braunschweig as full professor and director of the Institute of Flight Guidance and simultaneously also directed the DVL institute of the same name. He was thus able to provide the SB 10 with the complete instrumentation.27 The financing of the SB 10 was assumed by the German Federal Ministry of Defence (BMVg). This speedy federal funding of this project was because the aircraft manufacturer Dornier was working almost simultaneously on its Alpha Jet light fighter-bomber, and CFRP also played an important role there. It was not an easy task for Dornier to certify CFRP as a new lightweight material either. Manfred Flemming (1930–2015),28 head of the Structural Engineering Department from 1967 and head of the Structural Calculation, Structure Testing and Acoustics Department from 1972, had already been 24 Gerke (1991b), p. 231 f. 25 Akaflieg Braunschweig (1972). 26 Karl Heinrich Doetsch (1910–2003) studied mechanical engineering at RWTH Aachen, joined

the NSDAP on 1 May 1933 (membership number: 1 760 263) (according to an NSDAP survey of 1 July 1939, Doetsch also belonged to the paramilitary National Socialist Flying Corps, NSFK). In 1936 he headed Abteilung Flugeigenschaften at the DVL, 1943 earned his doctorate at TH BerlinCharlottenburg, 1961 was appointed full professor and director of Institut für Flugführung and the DFL institute of the same name, and 1977 was awarded an honorary doctorate by Cranfield Institute of Technology (BArch NSDAP-Zentralkartei, PK, Doetsch, Karl, 4 Oct. 2010). See Völckers and Schänzer (2003), p. 9 f. 27 Gersdorff (2004), p. 325 f., Völckers and Schänzer (2003), p. 9 f., Akaflieg Braunschweig (1972). 28 Interview with Manfred Flemming on 27 May 2010 and 22 June 2011 in Markdorf [hereafter abbreviated as IMF] as well as telephone interviews from 2011 and 2012. Vita: Prof. Dr.-Ing. E.h. Dr.-Ing. Manfred Flemming (born 28 Jan. 1930 in Mittweida–died 1 Aug. 2015 in Markdorf), 1953– 59 studies in the field of aircraft design at TH Darmstadt, 1959 structural engineer at the Dornier company, there 1967–68 head of Abteilung Statik and from 1972 department head of Strukturberechnung, Strukturversuch und Akustik, 1975 doctorate at TU Berlin, 1985 professor of construction and structural engineering at the Swiss ETH in Zurich, 1996 award of honorary doctorate (Dr.-Ing. E.h.) by TU Chemnitz.

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New Load Horizons from “Black Gold”—Early 1970

German Federal Ministry of Defence (BMVg)

German Federal Armed Forces

Ministerialdirigent Dipl.-Ing. Hans Ambos

Air Force Inspekteur air marshal Johannes Steinhoff

263

research programmes: “future – technology – air” “components and experimental programme”

development contract on the Alpha Jet (1 May 1969)

Vereinigte Flugtechnische Werke Fokker supply of central fuselage tube for SB 10 glider free of charge

BWB Federal Office for Defence Technology and Procurement

Forces armées françaises

IABG

Commandant de la Défense aérienne

IndustrieanlagenBetriebsgesellschaft mbH flight testing and certification of CFRP air-brake flap on the Alpha Jet

Général de corps d'armée François Maurin

Akademische Fliegergruppe (Akaflieg) Braunschweig Segelflugzeug SB 10 (funding by BMVg)

research project: testing of load-bearing parts in aircraft design made of CFRP

Dornier GmbH Friedrichshafen main department director of structural calculation, structure testing and acoustics Dr.-Ing. Manfred Flemming department head of construction methods with FRP Dipl. Ing. Helmut Conen department head of theory of component parts and construction methods Dipl.-Ing. Siegfried Roth (first application of the finite element method to calculate CFRP structures) development of the CFRP manoeuvring air-brake flap for Alpha Jet (first serially produced CFRP component in aircraft design) development of CFRP tail plane, verticle stabilizer and rudder for the Alpha Jet

DFVLR Braunschweig German Research & Testing Institute of Aeronautics and Astronautics Prof. Wilhelm Thielemann Prof. Hermann Blenk Prof. Heinrich Doetsch Prof. Hermann Schlichting Technical University of Braunschweig Institute of Aircraft Design Prof. Wilhelm Thielmann Institute of Flight Guidance Prof. Heinrich Doetsch

DFVLR Stuttgart German Research & Testing Institute of Aeronautics and Astronautics Prof. Ulrich Hütter

Messerschmidt-Bölkow-Blohm Ottobrunn

University of Hanover Institute of Plasma Physics

University of Stuttgart

lightning-protection testing of the CFRP air-brake flap, tail plane, verticle stabilizer and rudder of the Alpha Jet

study group on lightningprotection simulation

Institute of Aircraft Design Prof. Ulrich Hütter

Fig. 5.1 Reconstruction of the network of clients, developers and testers for the commissioning of the world’s first serial component made of CFRP in aircraft design: the manoeuvring air brake for the Alpha Jet light fighter-bomber (1968–1972). This network flow chart is based on the interview with Prof. Manfred Flemming and worksheets from the Luftfahrttechnisches Handbuch (LTH) by Arbeitskreis Faserverbund-Leichtbau29

29 Thiele (1984), Altpeter (1984b/1984c), Andersen (1984a/1984b), Ames (1977b), Conen (1977).

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Fig. 5.2 The SB 10 glider by Akaflieg Braunschweig, the first civil aircraft in the world whose wings were made of carbon-fibre-reinforced plastic, here as a single-seater with a wing-span of 29 m. The maiden flight occurred in 1972. Source Courtesy of Akaflieg Braunschweig

pursuing the idea of certifying CFRP as a material for serially produced components in aircraft construction since the mid-1960s.30 In order to be able to implement his idea, Flemming entered into a series of intense discussions with the management of Dornier at the end of the 1960s.31 The management approved that the material be introduced in Alpha Jet development after Flemming had explained the advantages of CFRP, such as weight reduction and the elimination of time-consuming chemical shaping work on the planking panels in the rear fuselage area.32 In cooperation with the BMVg, represented by Hans Ambos for the development of the Alpha Jet, who later also became the systems representative for the Tornado multirole combat aircraft, the development commenced at Dornier at the end of the 1960s. Within the framework of the research programme “Future—Technology—Air” (Zukunft— Technik—Luft, ZTL), and continuing with the Component and Experimental Programme (Komponenten- und Experimentalprogramm, KEL), the BMVg approved substantial grants for the extensive developmental research to qualify CFRP as a material for the Alpha Jet, in order to be able to manufacture the appropriate components later on.33 The finite element method (FEM), which was relatively new at the time, was used for the first time 30 Flemming et al. (1996), p. 13 f. 31 On Alpha Jet development, see also Haka (2011), p. 86 f. 32 IMF, 27 May 2010. 33 IMF, dated 27 May 2010 and 22 June 2011.

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265

Fig. 5.3 Manfred Flemming (1930–2015) next to the CFRP brake flap he had developed for the Alpha Jet. This air-brake, mounted on a marble base, was an original that he had received as a gift from his employees at Dornier and was displayed in his front garden. Photo A. Haka, 22 June 2011, Markdorf

to calculate the CFRP component parts. In two departments which had been founded at Dornier under Flemming and which were headed by Siegfried Roth and Helmut Conen, intense work was conducted on the material CFRP as well as on questions concerning component parts and construction methods. The first component to be developed in CFRP for serial production of the Alpha Jet was the manoeuvring air-brake flap (Fig. 5.3). Although it was not a primary component, it was particularly well suited as a demonstration object because, besides for braking, it was also used for special flight manoeuvres and for flight stabilization prior to a missile launch and therefore had to endure high levels of stress. Originally, the air-brake was supposed to be made of a magnesium casting with an aluminium sheath.34 The first design of the air-brake in CFRP was completed in June 1971. Dornier itself assumed major portions of the developmental work on CFRP for the Alpha Jet. Nevertheless, Flemming involved the leading German universities in the field of fibre-composite research at the time, in Stuttgart and Braunschweig, in the extensive developmental process. Cooperations with them already existed on other topics. Later, other universities were involved in the development, e.g. in lightning protection measures for the CFRP rudder. Tests were performed on it in June 1977, for instance, at the Institute of Plasma Physics in the University of Hanover in collaboration with the

34 Conen (1977), p. 1.

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companies VFW-Fokker and Messerschmitt-Bölkow-Blohm (MBB).35 Whilst at the university location in Braunschweig the above-mentioned aviation experts Doetsch, Blenk and Schlichting took care of the framing conditions for the development of the SB 10 glider, at TU Braunschweig the aircraft manufacturer Wilhelm Thielemann (1908–1985)36 acted as an information turnstile between the university and the decision-maker, Flemming, at Dornier. Thielemann in Braunschweig had decisively promoted the approval by the BMVg of the research project attached to the SB 10, on: “testing carbon-fibre-reinforced plastics on supporting parts in aircraft design”. Thielemann arranged for the study of various technical questions at Braunschweig affecting both the SB 10 and the Alpha Jet, within the framework of project reports and Diplom theses.37 The other site, Stuttgart, which was far more involved in the development of the Alpha Jet, was also the starting point for a further line of development in the early application of FRP in German aviation and in helicopter development. In 1953, the Baden-Württemberg Ministries of Commerce, Culture and the Interior founded the Deutsche Studiengemeinschaft Hubschrauber (DSH), which united two already existing helicopter study groups at that time. The DSH was the origin of the current Institute of Structures and Design at the DLR in Stuttgart.38 The DSH initially began its work in two departments. At the turn of the year 1958/1959, an additional department became necessary due to the breadth of its tasks. Ulrich Hütter (1910–1990)39 was appointed director of the new Applied Flight Physics Department.40

35 Institut für Plasmaphysik der Universität Hannover. Cf. the reported results in Ergebnis-

bericht 1976, Schwerpunkt 5: Energietechnik und andere fortschrittliche Technologien, Vorhaben 586: Holmkasten in Faserverbundbauweise mit Hybridverbunden, 32–34. Ad 48 1976/1972, DLRBibliothek Köln [hereafter abbreviated DLRB] and Altpeter (1984b). 36 Wilhelm Thielemann was full professor of aircraft and lightweight construction at TU Braunschweig 1960–76 (UAB: B7: 487, curriculum vitae Prof. Dr. Wilhelm Thielemann); for a detailed biographical account of Thielemann see Sect. 4.4.2.1. 37 IMF, 27 May 2010. 38 Institut für Bauweisen und Strukturtechnologie der DLR. Ibid. 39 Ulrich Hütter studied mechanical engineering and shipbuilding at the Viennese polytechnic 1930– 1936, thereupon studying aeronautical engineering at TH Stuttgart, 1939–1943 he headed the aerodynamics department at the Ingenieurschule Weimar, from 1940–1943 additionally employed as chief designer at Ventimotor GmbH in Weimar; 1943–1945 initially a lecturer at FGZ, he then became a designer there. He had earned his doctorate at the TH in Vienna 1942 and thus in 1944 obtained a lectureship on fluid mechanics and flight mechanics at TH Stuttgart, accepting another lectureship there 1952–1953. 1957 he was awarded his habilitation degree, 1958–1959 headed a department at the DSH, since 1959 was extraordinary professor and in 1965 appointed director of the Institut für Flugzeugbau at TH Stuttgart; 1965–1968 he directed the DFL Abteilung Bauweisen und Konstruktionsforschung, followed by a directorship of Institut für Bauweisen und Konstruktionsforschung at the DFVLR 1969–75; see Füller (2005), p. A5, Assmann et al., eds. (2002), p. 53 f. 40 Abteilung Angewandte Flugphysik, Füller (2005), p. 1 f.

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Fig. 5.4 Ulrich Hütter, from 1965 director of the Institute of Aircraft Design at TH Stuttgart and director of the Institute of Construction Methods and Design Research at the DFVLR. Photo Dangl family, courtesy of Peter F. Selinger

One of the department’s first projects was the development of a miniature helicopter with ram jet engines for the BMVg in 1959. The goal was to produce a helicopter consisting almost completely of GFRP. This project was the prelude to further research and development of GFRP for helicopters, especially for rotor blade systems. One year later, the DSH was renamed the German Research Institute of Helicopter and Vertical Flight Technology.41 Hütter (Fig. 5.4) was also the contact person for Dornier in the context of Alpha Jet development. His many years of experience in aviation made him a sought-after interlocutor and he was therefore engaged by Dornier as a consultant as early as 1962 and entrusted with developmental projects on FRP, such as shock-absorbing legs out of GFRP for the landing gear of the Do 27 multi-role aircraft.42 Later, this cooperation between Hütter and Dornier was extended to a wide variety of topics related to FRP.43 Although Hütter dealt extensively with aeronautical engineering issues and concentrated on topics in the area of FRP, it was his development of wind turbines that primarily attracted notice at home and abroad.44 In particular, the topic of

41 Deutsche Forschungsanstalt für Hubschrauber und Vertikalflugtechnik. Rößler (1965), p. 115 f.,

Hütter et al. (1960). 42 See Ulrich Hütter’s honorarium contract dated 16 Oct. 1962 concerning the Dornier research com-

mission “Kunststoff (GFK-Federbeine)-Fahrwerk für die DO 27” or the one dated 31 July 1974, cf. Archivsig. 153/397, 153/353, Universitätsarchiv Stuttgart [hereafter abbreviated as UAS]. 43 Cf. meeting minutes of 12 June and 21 Apr. 1967 as well as meeting minutes No. EF 10/B 76/67 from 1976, drawn up in the context of Hütter’s visits to Dornier, as well as the letter dated 3 Aug. 1967 from Dipl.-Ing. Hermann Rieger (Dornier System GmbH) to Hütter, cf. Archivsig. 153/397, UAS. 44 Cf. the report on German-American cooperation in the field of wind turbines, cf. Archivsig. 153/ 210, UAS, Hütter.

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looping technology on rotor blades to introduce loads and the application of GFRP are closely associated with his name.45 In 1940 Hütter, at 30 years of age, headed the aerodynamics department at the Weimar School of Engineering and as chief designer at Ventimotor GmbH was the dominant employee who set the first accents in the field of wind turbine systems. Ventimotor GmbH, which had been founded as a subsidiary of the Gustloff concern by the area commander of Thuringia, Gauleiter Fritz Sauckel (1894–1946), and by the NSDAP Gau advisor on economics, Walther Schieber (1896–1960), gave the loyal party member Hütter a great deal of freedom in his work on wind turbines, which were later used in the occupied eastern territories.46 The fact that Hütter was merely classified as a “fellow traveler” after 194547 was probably not really thanks to Hütter’s activities and statements during the nazi era. Its purpose was rather to gain acquire Hütter’s expertise sooner. Closer consideration of his past yields a much more complicated picture of this engineer. Ulrich Hütter and his brother Wolfgang Hütter (1909–1990) both joined the nazi party in Vienna as early as 1932. A letter by him dated April 1938 to the NSDAP’s central membership office in Berlin48 shows that he wanted to be perceived as more than a regular party member at this time and was therefore certainly not just a “fellow traveller” in the sense of the denazification process. In this letter he requested that his early membership in the Viennese chapter of the nazi party be duly reflected in his membership record in Germany, explaining that the NSDAP had been banned in Austria between 1932 and 1935. Hütter stated that, despite these adverse conditions as a Viennese party member, he had served as a block warden in the Wieden local group of the fourth Viennese party district and had looked after approximately 25 to 30 members of the wounded veterans association Kampfopferring of the Austrian NSDAP.49 In addition, Ulrich Hütter pointed out in this letter that he and his brother had already publicly declared their allegiance to the NSDAP in 1931 during an election of the Student Council. In this context he added that the Berlin NSDAP was welcome to enquire of his superior and his party comrades about their conduct and attitude as nazi party members.50 During the tribunal proceedings which Hütter had to face in 1948, he concealed this early party membership and indicated 1938 as his entry date to get a more favourable judgement. However, having access to part of his NSDAP file, the tribunal convicted Hütter of making false allegations.51 Hütter also 45 Hütter (1960), p. 5 f. 46 Assmann et al., eds. (2002), p. 53 f., Heymann (1995), p. 264 f. 47 Mitläufer. On the topic of denazification or inconsistent denazification, see Ash (2010), Becker

(2004), Kappelt (1997), Frei (1996), Pollmann (1995), Vollnhals (1991), among others. 48 Mitgliedersammelstelle der NSDAP, cf. Ulrich Hütter NSDAP membership number: 1 205 381,

Wolfgang Hütter NSDAP membership number: 1 205 379 BArch, PK, Hütter, Ulrich, 18 Dec. 2010. 49 Blockwart in der Ortsgruppe Wieden der NSDAP IV. Bezirk Wien, Haka (2011), p. 100. 50 On Ulrich Hütter in the nazi system, see: BArch, PK, Hütter, Ulrich, 18 Dec. 2010. 51 See the verdict by the Spruchkammer proceedings on 10 June 1948 on the individual Dr.-Ing.

Ulrich Hütter (Staatsarchiv Ludwigsburg: StAL EL 902–18_Bü).

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269

declared that he was completely penniless, that his savings were blocked in the Eastern Zone, and that he had only joined the NSDAP under the pressure of the ongoing political debates of the time. He added that at the age of 21 he had misjudged the implications of his actions. His arguments and his obligation to provide for his wife and children persuaded the court to only sentence Hütter to pay a penalty for his false testimony.52 What the tribunal’s verdict would have been if the complete correspondence with the reich leadership of the NSDAP membership office had been available in the Document Centre at that time is a matter of speculation. Although Hütter put much effort into his engagement with Ventimotor, his employment ended abruptly in 1943. After a short period of military training, he was assigned to the Graf Zeppelin Research Institute (Forschungsanstalt Graf Zeppelin, FGZ) in StuttgartRuit.53 The FGZ, which had emerged in 1941 from the Institute of Flight Technology (Flugtechnisches Institut) at the Stuttgart polytechnic and had been established by the RLM as a national institution, was primarily concerned with questions of bomb aerodynamics, parachute and brake-chute development, the physics of underwater explosions, aeroplane take-off and landing aids, and the aerodynamics of external attachments to aircraft. Under the direction of Georg Madelung (1889–1972),54 Hütter took over the direction of the working group on catapult development and flight mechanics.55 A report which Hütter was required to write in Völkenrode in 1946 for ‘Operation Surgeon’ of the British Ministry of Supply, is ambiguous about his activities there as his contributions to various developments are clearly exaggerated. The report suggested that he had been one of the most important developers at the FGZ and concealed the fact that he had initially only been employed by his teacher Georg Madelung as a lecturer for training courses for the staff. Only later, due to a lack of personnel, was he called upon to do development and design work, and that only to a very limited extent. Hütter’s background knowledge of war equipment was extensive and may well have played a significant role in the development of the Alpha Jet. However, a decisive conversation with Manfred Flemming triggered the original assignment of various “work packages” on the Alpha Jet to Stuttgart. During a train ride after an event that both had 52 Sühnegeld, literally: atonement fee. The penalty imposed on Hütter was 200 marks. 53 Elsässer (2016), p. 9 f. 54 Prof. Dr.-Ing. Georg Hans Madelung, studied mechanical engineering, earning his Diplom at

TH Berlin 1919 and his doctorate (Dr.-Ing.) at TH Hannover 1921; 1921–1924 he was an aircraft designer in the USA, from 1926 full professor at TH Berlin, from 1929 full professor at TH Stuttgart (Flugtechnisches Institut) and head of the aircraft department at the Deutsche Versuchsanstalt für Luftfahrt and later board member there; in 1937 he joined the NSDAP, in 1941 he became the founding director of the FGZ, 1946–54 he spent a leave of absence from TH Stuttgart on working in the Naval Medical Research Institute in Bethesda, Maryland, returning afterwards to his professorship at TH Stuttgart, cf. Klee (2005), p. 386. 55 Arbeitsgruppe Schleuderentwicklung, Flugmechanik. Cf. Ulrich Hütter’s report from 1946: Organisation, Arbeitsgebiete und Berichte der FGZ Stuttgart-Ruit. Archivsig. KPAR: Ad 558, ZADLR.

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attended, Hütter told Flemming that he feared his Institute of Construction Methods and Design Research at the German Research and Testing Institute of Aeronautics and Astronautics (DFVLR) would have to be closed down for financial reasons.56 The network around Hütter, his deputy Gerhard Grüninger and Flemming took action. The cooperative “bridge”, which had been established in 1967 by the transfer of the head of construction methods from Hütter’s department, Helmut Conen, to Dornier as department head under Flemming, may have contributed to Flemming’s strong support for the Stuttgarters. Flemming intervened at the DFVLR after this conversation with Hütter, arguing that the Stuttgart location and expertise were indispensable for the future development of FRP and aircraft design.57 In order to strengthen Hütter’s position as well as that of his Stuttgart institute, Flemming awarded research contracts to Stuttgart in the context of Alpha Jet development, such as testing the CFRP air-brake flap, as well as assigning related thesis topics and project work to graduate students, which were primarily supervised by Gerhard Grüninger.58 Thus, research on Alpha Jet issues was performed at both institutes in which Hütter was employed in Stuttgart. The first component for the Alpha Jet, the air-brake made of CFRP, was designed in June 1971, and the flight testing took place in July 1974. This was not without problems, since the German Federal Office for Defence Technology and Procurement (Bundesamt für Wehrtechnik und Beschaffung, BWB) had not yet agreed upon whether a flight testing with a CFRP component should be done or not. Something then happened that would probably be impossible today: The first CFRP air-brakes were ultimately installed by the relevant specialists on Flemming’s instructions without first informing the BWB.59 The Federal Office of Defence Technology was probably reluctant about this because at that time there were no regulations on the certification of CFRP in flight operations and none of the officials wanted to bear the responsibility for such a flight. Only the Federal Ministry of Defence (Bundesministerium der Verteidigung, BVMg) knew about Flemming’s bold “go-it-alone” move, because it was noticed during an examination when the Alpha Jet had to make an emergency landing due to a failure of the engine lubrication system and CFRP debris was found. The BWB and the French project management—the test flight had taken place in France—perceived this singlehanded decision as a grave violation. It was thanks to the Federal Ministry of Defence, in particular, to Hans Ambros, that Flemming did not suffer any further consequences as a result. Once the development of the CFRP air-brake (Fig. 5.5) had been completed, work was begun in 1974 on designing the rudder, the verticle stabilizer and the wings in CFRP, 56 IMF, 27 May 2010. 57 Ibid. 58 Engineering theses for the Diplom degree. Memorandum on a conversation between Kammerer

(chancellor of the University of Stuttgart) and Günther concerning contracted research on 21 Dec. 1973. The conversation regards research on the Alpha Jet air-brake at Prof. Hütter’s institute, cf. Archivsig. 153/114, UAS. 59 IMF, 22 June 2011.

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271

Fig. 5.5 Alpha Jet with installed CFRP air-brake version III (deployed). Source LTH. Arbeitsblatt, Conen, FL 25 400–05. Courtesy of Arbeitskreis Faserverbund-Leichtbau des LTH

although not all these components made it later to serial production. The German Federal Armed Forces (Bundeswehr) introduced the Alpha Jet into its air force in 1978/1979.60 The development of the Alpha Jet with the world’s first serial use of a CFRP component in aircraft design can be seen as path-breaking for further aircraft models with CFRP components, especially in Germany. This applies both with regard to the development of fixed-wing aircraft for the military, such as the multi-role combat aircraft Tornado, as well as with regard to developments in the civil sector, such as the twin-engine commercial aircraft Do 328 or the twin-jet wide-body aircraft from Airbus—the A310. Parallel to the Alpha Jet development, an interest group was founded in 1974 composed of the aviation companies and institutions: VFW-Fokker GmbH in Bremen, the MBB’s Rotary Wing Division in Ottobrunn, Dornier Luftfahrt GmbH in Immenstaad and the Stuttgart Institute of Construction Methods and Design Research (Institut für Bauweisen und Konstruktionsforschung) at the DFVLR. The aim of this interest group was, to draft the design criteria for fibre-composite methods for a manual on fibre-composite lightweight construction. Employees from the founding enterprises were engaged to convert information of relevance to FRP from their respective current projects into handling regulations similar to DIN standards. Because many of the topics discussed and documented there were of military relevance, it was funded by the BMVg. When this funding was discontinued in 1984, the manual was incorporated into the aeronautical engineering handbook Luftfahrttechnische Handbuch (LTH) in 1985 as the volume: Faserverbund-Leichtbau.61 The current highlight of fibre-composite structures in flying equipment is the NATO helicopter NH 90, 85% of which are FRP structures. Its fuselage, made almost exclusively of carbon-fibre and aramide-fibre composites, has properties especially suited to military purposes, such as very high safety in the event of a crash and a low radar signature.62 60 Altpeter (1984a), Andersen (1984a), Conen (1977), Dornier (1983). 61 AK-FL (2009), p. 1 f. 62 Majamäki (2007), Frommlet (1997), Nitzschke and Müller (1995).

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The manufacturer of the NH 90 is NHIndustries, whose majority shareholder is Airbus Helicopters. This company, which until 2014 was still called Eurocopter and emerged from the MBB company, was instrumental in pushing forward the second development line of FRP in German aircraft design, which, as already mentioned, had begun with Hütter’s development of miniature helicopters. The first GFRP rotor-blade prototypes for the BO 105 helicopter63 was followed soon afterwards by the development of applications in CFRP and aramide-fibre-reinforced plastics (AFRP) for further components by MBB.64

5.2.2

A New “Era in Materials Engineering” for Civil Aviation

Almost simultaneously with the integration of CFRP in military applications came its certification in the field of civil aviation. For example, the manufacturer Deutsche Airbus GmbH planned to use GFRP combined with CFRP in its A300 model as early as 1969.65 For cost reasons, Airbus designed for this model the seal of the three-part tailplane cover as a GFRP shield, which consisted of three cover lips. CFRP prepregs were used to strengthen the contact surface between the sealing lip and the fuselage planking against friction as well as anticipated air forces and potential icing. In 1977, a CFRP spoiler (Fig. 5.6) was installed in the A300 for testing purposes as part of the preliminary development of the model A310.66 The first serial CFRP production for model A310 occurred in 1981 at the Airbus plant in Stade within the framework of a conversion of production from metallic aerospace materials to CFRP. The rudder was the first series product out of CFRP and was first delivered in 1983.67 With the introduction of the A310 product family, an almost continuous rise in the number of CFRP and GFRP series components used is observable, at least at Airbus. However, a very significant increase in use in the number of CFRP components of design relevance was required, such as in the manufacture of the centre wing box for the A380,68 before CFRP could eventually be regarded as a legitimate material.69 How do we understand this delayed perception? Aeroplanes are the largest means of transport, in terms of their dimensions, in daily use by a large number of people, and general reliance on them has been increasing steadily in recent years. Therefore, safety issues regarding this conveyance are perceived by the public as particularly relevant. The step to manufacture a very large proportion of such a 63 BO 105 = Bölkow Bo 105, light helicopter of the company Messerschmitt-Bölkow-Blohm GmbH. 64 Bansemir (1996), Wetter (1981). 65 Ames (1977a), p. 3 f. 66 Günther and Berg (1981), p. 2 f. 67 AIRBUS Operation (2009), p. 11 f. 68 Flügelmittelkasten = centre wing box. 69 Haka (2012), p. 1 f.

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Fig. 5.6 Verall view of the CFRP spoiler and its installation locations on the Airbus A 300 B2/B4. Source LTH—Arbeitsblatt FL 25.400–30, p. 7. Arbeitskreis Faserverbund-Leichtbau des LTH

sensitive means of transport out of a “young” material represented a radical turning point both for the rather conservative sector of the aviation industry and for aircraft designers. Its properties in public awareness as well as in the eyes of many experts had not yet stood the test in large-scale technical projects. The general public and experts alike focused primarily on the CFRP used in the A380, even though in civil aircraft design this material was not an innovation. By contrast, the relatively new aluminium lithium alloys were hardly noticed at all.70 The type of design of the upper outer skin of this wide-bodied aircraft was also a premiere in materials technology. It is made of the laminate composite material Glare® (Fig. 5.7), which is a combination of glass-fibre-reinforced components and aluminium. This novelty only accelerated this process.71 It was a development of the Delft University of Technology in the Netherlands and the National Aerospace Laboratory (NLR) there and represented a new quality in hybrid aeronautical materials as a quasi-functional material, not only due to its fire retardancy, but above all to its cracking behaviour. Whereas in aluminium the cracking speed and thus the crack length increases rapidly, the glass-fibre layer in Glare significantly inhibits this behaviour, which was also the reason behind its strategic use in the structure of the A380. The A380 and its high percentage of fibre-composite components opened a door through which aircraft manufacturers, the supply industry and design engineers from many 70 Campbell (2008), p. 497 f. 71 Bock and Knauer (2003), p. 2005, Müller (1995), p. 41.

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Fig. 5.7 Glass-fibre reinforced aluminium = Glare (acronym for Glass Laminate Aluminium Reinforced Epoxy), shown here in various material thicknesses. The matchstick indicates how thin the glass-fibre-reinforced laminates between the aluminium sheets are designed to be. Photo A. Haka, 21 Sep. 2017

sectors have been passing for some time. The path to using FRP components was cleared for a completely new generation of aircraft, including the A350 XWB and the Dreamliner from Boeing. The proportion of the structural weight of FRP in these aircraft exceeded 50% for the first time. Until the A380 entered into service, the use of CFRP or hybrid material structures had often been met with scepticism. Whereas the general public hardly paid any attention to hybrid materials and CFRP in particular, many engineers and designers were rather cautious about handling and using these materials. Just as in the 1930 and 1940s, at the beginning of the 2000s the clearly defined metallic materials dominated especially among designers and materials engineers along with the associated classical understanding of their role in materials technology with regard to stability and large load carrying capacities. As the present investigations have shown, it took almost a century—if the first layered presstoff materials of the 1920s are considered—for engineers and designers, who were accustomed to isotropic behaviour of materials, to warm to the idea of anisotropic strength in FRP. It was a matter of avoiding a direct confrontation between different material structures, surfaces and chemical potentials among the various materials and at the same time adjusting to the not infrequently different material characteristic values. A number of regulations, standards and, above all, calculation methods, such as the classical laminate theory, the failure criterion according to Stephen W. Tsai (*1929) and Edward Ming-Chi Wu (1938–2009), the fracture criteria according to Alfred Puck (1927–2021) or

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the inter-fibre failure criterion72 by Ralf Cuntze and others were available. Nevertheless, a number of companies created their own calculation bases for their product assortments.73 The dynamics in this area are accelerating due to the strong demand and the knowledge since gained about FRP. The important topic of the inter-fibre failure criterion will be briefly discussed here as an example.74 Mathematically describing fracture risk by means of failure criteria is an important instrument in the dimensioning of structures because it is not possible to check all arbitrary multiaxial states of stress experimentally. A number of fracture criteria have been developed in fibre-composite engineering. In the German-speaking realm—including the GDR with Berthold Knauer and Alfred Wende75 —the most frequently used criterion was published by Alfred Puck (1927–2021)76 in 1969 (Fig. 5.8).77 It formulates the basic element of a lamina, the unidirectional single layer, in a flat tensile state. The distinctive aspect was that Puck—probably for the first time—distinguished between fibre failure and inter-fibre failure. That is, he posited two mutually independent criteria, thus taking these really different events in a fracture into account. This differs from the more general failure criteria which provide no information about whether the failure occurs in the fibre or in the area between the laminae. Puck also developed a suitable testing procedure to check the strength values of the failure criterion with precision: the strain/stress torsion test on tube-shaped UD78 test samples. It is particularly unfortunate that many failure criteria formulate “anisotropic” flow criteria. This contradicts the brittle fracturing of fibre-composite materials. Recognizing this, the Israeli materials scientist Zvi Hashin (1927–2017)79 proposed the Mohr80 brittle-fracture criterion to describe inter-fibre failure events. Mohr’s criterion required knowledge about the position of the fracture surface. The particular challenge was, to determine the unknown fracture surface in which the failure risk is maximal. Puck achieved this in 1992 based on Hashin’s concept and earlier studies by the French physicist Charles Augustin de Coulomb (1736–1806) and the inter-fibre

72 In the case of an “inter-fibre failure”, a break or crack occurs in the matrix or in the interface

between fibre and matrix. Contrary to a fibre fracture, an “intermediate fibre fracture” does not result in a severing of the fibre. 73 Tsai and Wu (1971), Puck (1996), id. (1992), Hinton et al. (2004), Knops (2008). 74 I am grateful to Helmut Schürmann and Ralf Cuntze for the opportunity to discuss this topic of fracture criteria with them. 75 Knauer and Wende (1988). 76 Alfred Puck, German scientist, 1979–89 professor of design engineering/fibre-composite engineering at the University of Kassel. 77 Puck (1969), p. 780 f. 78 UD = unidirectional lamina (characterization of a FRP in which all the fibres are laid in a single orientation). 79 Hashin (1980). Zvi Hashin’s professorship was at Tel Aviv University. 80 Mohr (1900). This engineer and structural analyst became professor of technical mechanics and strength-of-materials theory at TH Dresden in 1894.

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Fig. 5.8 Alfred Puck (1927–2021). Foto Courtesy of Hannelore Puck

failure criterion for the action cross-section formulated by the American engineer Burton Paul.81 Puck’s formulations were a substantial advance in the area of physics-based inter-fibre failure; it is applicable to spatial states under tension and also yields the direction of the fracture. Puck’s action cross-section (Wirkebene) criterion became known to an international audience on the occasion of the World-Wide Failure Exercise (WWFE).82 Compared to other fracture criteria for calculating experimental results on laminates it did very well. The organizers of this competition evaluated it with the words: “Overall we consider Puck to be best at capturing the qualitative characteristics of lamina and laminate behaviour.”83 It should be mentioned, though, that this quantitative ranking in the competition depended not only the type of fracture criterion but also on the ability of the used stress analysis computing programme to describe the behaviour of the material before and after inter-fibre failures (“degression calculation”) non-linearly and precisely. The Puck criterion is now used around the world. It is frequently the point of departure for modifications, for instance, by Cuntze. He formulated the failure event on the basis of invariants. The basic ideas of the inter-fibre failure criterion were first presented in 1996 by its author, Ralf Cuntze (*1939), who directly referred to the paper by Alfred Puck from 1992 entitled “A fracture criterion points out the direction”—along with Hashin’s and his own 81 C. A. de Coulomb was the founder of electrostatics. Paul (1961). 82 The World-Wide Failure Exercise (WWFE), also known as the “failure olympics”, was a British

initiative in the scientific community of composite specialists to compare the progress made by methods under development and to assess the remaining challenges in the way of accurate predictions of the strength of laminates. The origin of the WWFE is a meeting among the experts on the topic: “Failure of polymeric composites and structures: Mechanisms and criteria for the prediction of performance”, which convened in 1991 in St Albans, just a few kilometres away from London. See Hinton et al. (2004), p. 2 f. 83 Hinton et al. (2002), p. 1725 f.

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work accomplished over many decades, turning Cuntze into one of the most influential scientists to write the theory of fibre composites in Germany.84 An extension of Cuntze’s concept with regard to the range of applications of the three material families: isotropic, transversal isotropic (UD) and orthotropic, followed two years later. Cuntze’s model won the 2004 World-Wide Failure Exercise,85 which significantly increased awareness of this criterion as well as its implementation, albeit Cuntze entered the competition late.86 A more conservative interpretation of the competition could certainly have been conceivable here. A consolidation of this model of a sort, or a final, simpler formulation of the criterion, followed in 2012.87 Although in Cuntze’s case the immediate development of the inter-fibre failure criterion lasted just under two decades, it is based on the findings of several stages in materials engineering which began with the German engineer Christian Otto Mohr (1835–1918). His observation that the strength of a material is determined by the stresses on the fracture plane was the starting point. However, de Coulomb’s work was also decisive and merged to form the Mohr–Coulomb hypothesis.88 Although this hypothesis actually regards isotropic materials, Burton Paul applied it to unidirectional materials in the early 1960s. A similar path was also taken by Zvi Hashin, who applied Mohr’s former fracture hypothesis to inter-fibre fracture in unidirectional layers of FRP. But none of the afore-mentioned included the fracture angle in their considerations or determined it. This was finally done by Alfred Puck,89 based on Hashin’s work. Cuntze’s approach could be regarded as a provisional intermediate state—if the state of research on this topic may be called that at all, since this complex of topics is a permanent work-in-progress. Cuntze could also determine a fracture angle with his invariant-based approach. This means that he was probably the first to translate a strength condition in structural stresses into Mohr stresses in a very elaborate mathematical procedure. With this approach, he was able to formulate his inter-fibre failure strength conditions directly into friction values that engineers could understand. This facilitates applying this approach and reduces errors. Analysis of FRP in this context has significantly expanded over the years and, in turn, has raised new questions. As already mentioned in the introduction to this book, this applies in particular to problems in the field of mechanics and its subdisciplines, such as fracture mechanics. One example is the issue of stress concentrations foreign to isotropic materials (higher stress concentration factors due to elastic anisotropy, the laminate edge

84 Cuntze (1996); Ein Bruchkriterium gibt die Richtung an: Puck (1992); My thanks go to Ralf

Cuntze and Helmut Schürmann for their assessments, comments and advice on this subject. 85 Hinton et al. (2004), p. 2 f. 86 Cuntze (2004). 87 Cuntze (2012). 88 Cf. Coulomb (1773). 89 Cf. Puck (1996), Knops (2008).

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effect and corner effect, etc.), and the frequently associated problem of delamination.90 A further problem area is the load introduction into a component. Comprehensive solutions are also being sought in chemical and mechanical joining technology in connection with FRP. Compromises are still being made here, and in aircraft construction it is not uncommon to add the so-called “anxiety rivet” (“Angst-Niet”) to secure bonded seams, or to take appropriate tolerances into account. Furthermore, the topic of FRP fatigue under static and dynamic stress is currently the subject of intensive investigations. Corrosion, in the form of contact corrosion in joining CFRP to classical metallic structures, as well as behaviour in a fire and recycling concepts are further topics which still require more directed solutions. Finally, the many open questions in connection with topics related to the structural mechanics of textile fibre composites must be mentioned. Due to the complexity of the materials, only a step-by-step numerical approach is currently possible for many of these still outstanding tasks. The wave of euphoria about FRP had hardly subsided when efforts were already being made to “breathe life” into a new variety of FRPs, thus endowing these material constructions with their own specific designs and functions. For example, the potential of carbon fibre from its conductivity (Fig. 5.9) was put to use. The thermoelectric de-icing of a slat is based on the conductivity of this fibre (Fig. 5.10).91 As in many phases of aircraft development, especially in modern aviation and increasing globalization with its steady rise in traveling rates, the hunt to reduce costs has become a priority and is being pursued both for business reasons and from an engineering point of view. Cost efficiency is a special motivator toward further exploitation of human and material resources. In the case of flying equipment, few epoch-making innovations are being made in structural design. Apart from the propulsion aggregates, the focus is henceforth on the “adjustment screws” afforded by materials engineering, here in particular on ever-better materials or material combinations.92 This applies to metallic alloys just as to hybrid material systems. The current highlight in CFRP applications in civil aircraft construction is the A350 XWB from Airbus and the 787 Dreamliner from Boeing. Both aircraft not only have the usual CFRP components, such as tail planes and vertical stabilizers as well as control and high-lift surfaces, but their wings and fuselage are also made of carbon-fibre components. The associated increased production of FRP structures inevitably necessitates the development of new dimensions with regard to the design, materials and manufacturing of hybrid material structures, especially CFRP. Composite-adapted architecture is a prerequisite for commercially viable production in large quantities.93 So-called black metal construction does use components suitable for fibre composites. But ultimately it implements them conceptually according to the design and manufacturing principles 90 On the understanding and application of numerical problem domains in the context of FRP, see

Mittelstedt (2017), Mittelstedt and Becker (2016). On delamination, see Cuntze (2019), p. 22. 91 Orawetz and Gliesche (2009). 92 Statistisches Bundesamt (2019). 93 Hermann et al. (2005), p. 13 f.

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Fig. 5.9 Internal structure of the CFRP slat, where textile technology and electrical engineering meet. This material design is based on the tailored fibre placement technology developed at the Institut für Polymerforschung in Dresden. Source Courtesy of Qpoint Dresden

of old-fashioned metallic construction methods, which will have to be redefined. In the 1930s, the change over from metallic construction methods to applications suitable for presstoff materials made it indispensable to explore new design principles, load horizons and, above all, technical parameters for those engineered materials, thus opening the way to hybrid materials, and in particular to fibre-reinforced composites, which would otherwise not have been accessible. Today, just as in the past, hybrid materials and material structures are at a crossroads awaiting solution. Looking back on the development from glass fibre to aramide fibre to boron fibre and finally to carbon fibre as a composite reinforcement, we see that in 1972 the CFRP in a glider by the Akaflieg in Braunschweig became one of the most efficient lightweight materials certified for aviation to date. The network in this context was funded by the state and dominated by industrial interests, which strongly influenced university and nonacademic research over long periods at various university locations. This example of the development of fibre-reinforced composite materials clearly shows that a large proportion of the actors from the field of German aeronautical research, such as Ulrich Hütter or Karl Heinrich Doetsch, were able almost effortlessly to follow a straight course in their biographies and use their pre-war professional connections despite the caesura in 1945 and convey their ideas and research topics to the post-war generation. The integration of CFRP in the development of the Alpha Jet is probably due to the persistence of Manfred Flemming and his team vis-à-vis the management of Dornier, which initiated a turnaround in aircraft design. Flemming was only able to take this path

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Fig. 5.10 Prototype of a CFRP slat by Airbus Germany and Qpoint Composite in Dresden, here fixed on a stand as a demonstration object. Source Courtesy of Qpoint Dresden

thanks to the ambitions of the BVMg and its desire to design new weapons technology. As was the case with a number of other technologies, such as later the Internet, the military took on the role as technology driver. It is meanwhile ascertainable now that a large number of military technologies have found their way into civilian applications, such as in the automotive industry. The FEM, just recently conceived, exemplifies a piece of engineering development which enabled the engineers at Dornier to calculate anisotropic materials according to specific load cases. Even now, the field of fracture mechanics, for example, is still faced with a wide-ranging catalogue of questions needing answers with regard to FRP. The path for engineers and scientists from isotropic materials such as steel to anisotropic FRP was long and not easy. Not only purely technical barriers had to be overcome, but also the reservations of sceptics from among their own ranks as well as among simple consumers, who often dismissed FRP under the catchword plastic and rather tended to associate material stability with materials such as steel and titanium. The publicity with considerable involvement by the media when the wide-body aircraft by Airbus—the A380—was first put into service presented FRP and especially CFRP as acceptable high-performance materials. This paved the way for the A350 XWB of the Airbus family and, together with the further development of FRP components in production technology, also paved the way for the Megacity vehicle, a series product made of CFRP, which thus slowly began to become financially manageable. This made it possible to reduce the consumer’s inhibitions about using designed materials further and to promote the development of hybrid materials. The fact that this trend is likely to continue

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is shown, for example, by the 970 orders recently placed by 51 customers of the aircraft manufacturer Airbus for all variants of the A350.94

5.3

Research with Limited Prospects—GDR Composite Materials Development, 1954 to 1980

A study of the development of hybrid materials in the German Democratic Republic (GDR), particularly of fibre composites for structural applications, generally focuses on one of the best-known natural-fibre composite products—namely, the Trabant passenger car with its duroplast cladding on a steel frame. Phenolic resin was the supporting matrix of this panelling, into which several layers of cotton fleece were inserted as the reinforcement material. The exhaustive investigations into this vehicle in recent years95 give adequate cause not to discuss its materials development, production and associated overall conditions in the present book. Four studies allude only cursorily to the further developments or sector-specific applications of hybrid structural materials in the GDR. Elke Genzel’s thesis briefly discusses the topic of composite materials within the context of the rating and design of loadbearing structures in the GDR building industry.96 The other three studies mention the development of this group of materials within the field of aircraft construction in the GDR. The first of these is the strongly autobiographical account by Berthold Knauer (1935–2017),97 in which he glances at his time as an East German academic teacher at the Technische Universität (TU) in Dresden in the field of polymer technology. He mainly broaches institutional decisions taken within a political context or explains student education at that time, but without pursuing concrete questions about the developments in materials engineering at the university or made by non-academic research.98 The book by Reinhard Müller, a former lecturer at the college for air force officers: Offiziershochschule der Luftstreitkräfte “Franz Mehring”, of the East-German Nationale Volksarmee (NVA), attempts to fathom the ups and downs of the GDR aircraft industry. This takes the form of a biographical account of Brunolf Baade (1904–1969), the technical director and chief designer of the GDR aviation industry and later director of the Institute of Lightweight 94 Airbus (2020). 95 See, among others, Breuninger (2017), Möser (2012), Merkel (2009), Kirchberg (2000), Bauer

(1999), Zepf (1997), Reichelt (1993). 96 Genzel (2006). 97 Berthold Knauer studied aeronautical engineering at TH Dresden and became a research assis-

tant at the Institute of Machine Elements there in 1961. In 1962 he served as secretary of the SED party leadership at TU Dresden, earning his doctorate in the economic sciences in 1966 (Dr. rer. oec.). In 1969 he was lecturer on the design of Plaste components and in 1971 was appointed professor of design engineering there and later a professorship in lightweight construction and polymer technology in 1991. See Petschel (2003), p. 465. 98 Knauer and Salier (2006).

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Construction and Economical Use of Materials at TU Dresden.99 Just a few cue words serve as its reappraisal of aspects in materials engineering. This also applies to the coauthored book by Lothar Brehmer and Jochen Werner, who as contemporary witnesses of the GDR aircraft industry mainly recall technical facts in a variety of ways.100 With the exception of the thesis by Elke Genzel the other studies are largely based on recollections. There are essentially no links drawn between the statements made and the sources cited, which virtually precludes verification and deeper analysis of various references to the technical history. The existing studies on East German mechanical engineering as well as the more extensive investigations on the short-lived aircraft design in the GDR almost universally mention the often-limited availability of technical materials and the restricted application options. The focus of the investigation on aircraft construction in the GDR is largely concerned with a discourse on the design aspects of the aircraft models as well as on the institutional, political and economic framing conditions.101 Just one book which includes the development of GDR mechanical engineering broaches a comparative contextualization of the contemporary state of technical developments on the subject of materials research, thereby allowing an evaluation to be made of the conditions in this field in the GDR.102

5.3.1

The “Reinvention” of Lightweight Design

As early as 1952, planning began in the GDR to develop its own aviation industry.103 Far away from the GDR metropolises, in “provincial” Pirna in the region known as the “Saxon Switzerland”, work commenced on the development of the first German jet-turbine airliner model 152. The home-coming in 1954 of a large number of German aviation experts who had been living in the USSR since 1945, including the future technical director and chief designer of the GDR aviation industry, Brunolf Baade, provided the pool of personnel to initiate the engine development for model 152.104 Special factories were founded primarily in Saxony to build aircraft components, and suitable staff were hired. The socialist brother countries, first and foremost the USSR, were preferentially envisaged as the target clientele for these aviation products. Dresden’s entry into the aircraft manufacturing 99 Institut für Leichtbau und ökonomische Verwendung von Werkstoffen. Müller (2010). 100 Brehmer and Werner (2010). 101 Cf., e.g. the studies on GDR aircraft design: Müller (2010), Schultze (2008), Lorenz (2003),

Mewes (1997), Ciesla (1997), Barkleit (1996), Dienel (1996), Barkleit and Hartlepp (1995), Michels and Werner (1994). On aspects of developments in materials technology in GDR mechanical engineering, see Buschmann (2012), Heymann (2005). 102 Haka (2014a). 103 Werner (1994), p. 74 f. 104 Strahlturbinen-Verkehrsflugzeug 152. Barkleit and Hartlepp (1995), p. 49 f.

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Fig. 5.11 Cover of the 96-page technical description and specifications of the improved prototype of the GDR’s jet turbine airliner 152 II V4. Source VEB Flugzeugwerke Dresden (ed.), 1959. Technische Beschreibung. StrahlturbinenVerkehrsflugzeug152 II. Dresden

business came in 1956 with the licensed serial production of the Soviet airliner Iljushin Il-14P. The East German federation of publicly owned enterprises in aviation design, VVB Flugzeugbau, was founded in 1958. This association of GDR companies formed a network of enterprises in aircraft design, production and supply. The first domestically made product was the jet-turbine airliner 152-I V1, which was completed in 1958 but crashed in 1959 during its second test flight, presumably due to the engines stalling. It killed the crew of four. The improved prototype152-II V4 (Fig. 5.11), also performed two test flights but was grounded shortly afterwards due to technical problems. The permanent delays in the development and production of these aircraft models, the lack of personnel and financial resources, but also the lack of a viable market and the obsolescence of their aeroplane model, finally led to the cessation of aircraft construction in the GDR in 1961. This also included glider construction.105 The latter was located in the VEB Apparatebau in Lommatzsch. Several glider models of the Lommatzsch Libelle—i.e. dragon-fly—series had been successfully developed and produced there.106 105 Cf. Schultze (2008), Lorenz (2003), Mewes (1997), Ciesla (1997), Barkleit (1996), Dienel (1996), Barkleit and Hartlepp (1995), Michels and Werner (1994). 106 VEB Apparatebau Lommatsch (1960).

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One central aspect of GDR aviation was the lack of an aviation infrastructure, especially with regard to training of appropriately skilled personnel and the requisite established development centres. This deficit was countered by converting the academic Faculty of Lightweight Design at the nearest academic institution, the TH Dresden, into an Aeronautics Faculty in 1956, and in the same year redesignating the Dresden trade school on lightweight design: Fachschule für Leichtbau, into one for aviation engineers: Ingenieurschule für Flugzeugbau Dresden.107 The deployed specialists trained there would have an impact on the R & Din aviation and provide decisive impulses for the GDR aircraft industry. In the start-up phase, the GDR not only consulted a large number of aviation experts originating from aviation companies and the armaments industry of the pre-1945 era, but also copied their R & D structures. This had the advantage that those structures were already familiar to the majority of the experienced aviation experts. They were also known to have already stood the test of time. The DVL in Berlin as well as the former Hermann Göring Luftfahrtforschungsanstalt in Braunschweig served as models. Based on these structures, the Research Centre of the Aviation Industry (Forschungszentrum der Luftfahrtindustrie, FZL) was founded.108 The following constituent research institutes were established at Dresden over a period of several years, determined by the demand and available personnel, as well as the material and institutional means: • • • • • •

Institute of Materials Institute of Aerodynamics Institute of Strength of Materials Institute of Hydraulics Institute of Vibrations Institute of Technology.

The area of materials science for aircraft was the basic branch of aviation development and set the pace for the options afforded designers. That was why the Institute of Materials (Institut für Werkstoffe) was founded very early on, in 1954, in Pirna-Sonnenstein on the edge of the Saxon Switzerland region. The materials engineer Heinz Eitner was appointed director of this institute. He had worked in the Junkers-Werke in Dessau until 1945 and had a wealth of experience in the field of industrial materials development.109 Eitner tried to delegate his staff onto the expert panels of the individual development institutes and companies in the aviation industry which were exploring topics in materials technology, i.e. steels, light metals, Plaste, elastomers, textiles, paints and heat-resistant materials,110 107 Buchwald (2016), p. 8, Schulz (1959), p. 369 f. 108 See Institut für Werkstoffe, Institut Verteiler (UA TUD: 94 vols. 1 and 2, Forschungs- und

Informationsberichte. Fakultät für Luftfahrtwesen, Forschungszentrum der Luftfahrtindustrie). 109 Landesarchiv Sachsen-Anhalt [hereafter LASA]: I 410 Nr. 781 Junkers-Werke Dessau. Flugzeug- und Motorenbau; it also includes information on Heinz Eitner. 110 Ceramic materials and iron.

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in order to gather information on current issues.111 In addition, the Materials Working Group, Arbeitskreis Werkstoffe, was founded as a specialist forum of the central Working Group on Research and Technology in Aircraft Design, Arbeitskreis für Forschung und Technik des Flugzeugbaues, at the Research Centre of the Aviation Industry of the GDR. This working group (AK) comprised the department heads of the Institute of Materials and special representatives of various industrial and GDR supplier companies in aircraft design (Table 5.1). The working group, which met once a month, dealt with all relevant questions in materials technology in the fields of aeroplane air-frame construction and engine and equipment construction. All information on the status of materials development in the GDR aeronautical industry converged on this working group, which also evaluated current and planned materials research and development projects. The fact that only about 30% of the materials required by the aviation industry could be supplied domestically by the GDR and the remainder had to be imported affected all areas involving materials technology, and this issue was specifically addressed in the working group. The materials provided by the CMEA states112 often did not meet the specified requirements suited to their intended use.113 Filing a complaint in the manufacturing countries cost time and was usually not successful. Thus, a number of domestic endeavours in materials engineering were quickly needed, which took shape as various R & D projects, often cooperations between academic research and companies. Examples include the development of new or modified types of tempered114 and case-hardened steel,115 high-strength weldable cast steel and the corresponding welding technology.116 In this context, an R & D programme was set up between TH Dresden and Hochschule für Maschinenbau in Karl-Marx-Stadt, together with the technical college for materials engineering also located there,117 as well as the Institut für Technologie und Organisation in Dresden. The companies VEB Rheinmetall in Sömmerda, VEB Härtolwerk and VEB Karl-Marx-Werke, both in Magdeburg, and VEB Hermann Schlimme in Berlin served as practical partners. The outcome was a new weldable tempered steel, a directly case-hardenable steel and a high-strength temperable cast steel, all of which could be introduced in 1958 along with a new welding technique. These materials were produced 111 Eitner (1958), p. 2 f. 112 CMEA = Council for Mutual Economic Assistance (also known as Comecon), a compact among

predominantly socialist states to create a mutually beneficial division of labour. Under the leadership of the then USSR, this compact included, among others, the following states: GDR, Poland, Romania, Bulgaria, Hungary and Czechoslovakia. Later, Cuba and a number of African states joined as well. 113 Etiner (1958), p. 6 f. 114 Tempered steel = steel given high tensile and fatigue strength by “hardening” and “tempering”. 115 Case-hardened steel = steel with a low-percentage alloy, which is preferentially used for the production of machine elements. 116 Tauscher (1958), p. 28. 117 Hochschule für Maschinenbau and Fachschule für Werkstofftechnik, both in Karl-Marx-Stadt, i.e. Chemnitz, before that city readopted its historical name.

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Table 5.1 Members of the Materials Working Group, subordinated under the central Working Group on Research and Technology in Aircraft Design in the Research Centre of the Aviation Industry (FZL). The meeting place was Pirna-Sonnenstein. The status in 1958118 Member’s name

Affiliation

Position

Eitner

Institute of Materials (FZL)

Director

Freytag

VEB Flugzeugwerke, Dresden (production of the air-frame of aircraft)

Director

Kalthoff

VEB Flugzeugwerke, Dresden (production of the air-frame of aircraft)

Dhief metallurgist

Prof. Scheinost

VEB Entwicklungsbau, Pirna (testing of engine and gas turbines)

Director

Rossner

VEB Entwicklungsbau, Pirna (testing of engine and gas turbines)

Dhief metallurgist

Böhme

VEB Industriewerk, Karl-Marx-Stadt (air-frame and jet-engine equipment production, aeroplane engines)

Chief metallurgist

Haubner

VEB Maschinen und Apparatebau, Head of department Schkeuditz (development) (aircraft repair, tail unit construction and aircraft seating)

Dubnack

VEB Industriewerke, Ludwigsfelde (production of the jet engine Pirna-014)

Chief metallurgist

Ebert

Aircraft Testing Station of the GDR (PfL) in Dresden

Head of department (materials)

Mädebach

Institute of Materials (FZL)

Main department head

Tauscher

Institute of Materials (FZL)

Head of department (iron and steel)

Sternkopf

Institute of Materials (FZL)

Head of department (heavy metals)

Weller

Institute of Materials (FZL)

Head of department (light metals)

Quaiser

Institute of Materials (FZL)

Head of department (non-metals)

Wiedemann

Institute of Materials (FZL)

Head of department (textiles)

Wesser

Institute of Materials (FZL)

Head of department (plastics) (continued)

118 Compiled from the remarks by Heinz Eitner, which were written during the meetings of the

Arbeitskreis Werkstoffe in April and May 1958.

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Table 5.1 (continued) Member’s name

Affiliation

Position

Baumann

Institute of Materials (FZL)

Head of department (surface protection)

Radtke

Institute of Materials (FZL)

Head of department (fuels)

Schmidt

Institute of Materials (FZL)

Head of department (standardization)

in the foundries VEB Edelstahlwerk “8. Mai 1945” in Freital and VEB Elektro-Stahlguß in Leipzig-West.119 In the area of hybrid materials, composite materials based on phenolic resin systems were already available as mature products. In accordance with my methodological approach, the products mentioned here must be identified by their technical materials. These composites were compressed moulding materials which, depending on the product variant, had a reinforcement of cotton fabric or sodium-cellulose paper layers; in the GDR they were mainly used in early glider design. A glass-fibre-reinforced plastic (GFRP) was likewise available, which was based on epoxy resin and was reinforced with woven fabric out of glass silk.120 The technical term for East German GFRP was glasfaserverstärkte Plaste.121 This version of the material was a unique development which, motivated by the poor quality of woven glass-fibre imports from the USSR, had been promoted as a central project in materials engineering by the Institute of Materials (FZL) and came to fruition as early as 1957. Judging from the work by the Dresden research network led by Paul-August Koch in the 1940s, it can be assumed that glass-fibre-reinforced Plaste products had already been available to a certain extent shortly after 1945. However, as a result of raw material shortages and the dismantlings of many industrial plants at the end of the war, the young German Democratic Rrepublic had initially purchased glass fibre or glass-fibre fabrics from the USSR, which had originally confiscated the know-how for manufacturing glass-fibre structures as a reparations payment. The provision of an epoxy resin of higher quality by VEB Chemische Werke Buna in 1958 led to an improvement in quality of the GFRP, especially with regard to its processing, but also with regard to glass corrosiveness and plastic brittleness. This GFRP material was used in the aviation sector for panelling or cladding and was promptly deployed in 1957 in the glider Libelle-Laminar built by VEB Apparatebau in Lommatzsch.122 Although the quality of this GFRP material was considered sufficient for glider construction in the GDR, there was still considerable room for improvement for larger 119 Tauscher (1958), p. 13 f. 120 Wesser (1958), p. 79 and 85. 121 (Abbreviated in German as GFP). On the term Plaste and its use in the GDR, see Schrader

(1959). 122 On the GFRP in the glider “Libelle Laminar” see VEB Apparatebau Lommatzsch (1960), p. 3.

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aeroplane models, especially in terms of fibre strength and aspects of processing technology. That was why a research consortium on glass-fibre reinforced Plaste was established, composed of the following institutes123 : • • • • • •

Institute of Fibre Research of the Academy of Sciences of the GDR in Teltow-Seehof Institute of Fibre Technology at TH Dresden Institute of Textile Technology at TH Dresden Institute of Technology of Chemical Fibres in Rudolstadt Research Institute of Textile Technology in Karl-Marx-Stadt Institute of Glass Technology of the glassworksVVB Ostglas in Weißwasser.

The details of the commissioned R & D work were complex, with the priority placed on the development of high-performance glass fibres or glass-fibre fabrics for load-bearing aircraft structures. For such supporting structures the following components out of GFRP were designed for the aircraft industry124 : Fuselage noses, wing tips, wing noses and trailing edges, main structures, landing gear fairings, engine cowlings, doors, bulkheads, rudders, propellers, and compressor blades. Furthermore, in the context of GFRP materials in aviation, the research consortium studied aspects of electrical insulation, materials for the interior of aircraft, as well as the finishing of technical textiles and their coatings.125 Another research focus was on production and manufacturing aspects, such as the production of different semi-finished products, in particular rovings, mats and woven fabrics, as well as, in the case of the latter, refinements in interlacing techniques in the weaving process.126

5.3.2

From Garland to Lightweight “Honeycomb” in Aviation

Parallel to the R & D work on glass-fibre reinforced Plaste, the development of loadbearing hybrid support materials for aircraft construction began as early as 1956. This involved the development of honeycomb sandwich materials, which today are known as sandwich panels with a honeycomb core, or honeycomb for short. Patenting, and above all financial reasons, prevented the GDR from importing honeycomb materials, which ultimately made it imperative that it develop its own. The Division on Design Development

123 Wesser (1958), p. 91 f. 124 Wiedemann (1958), p. 112 f. 125 Wesser (1958), p. 91 f. 126 The research consortium investigated the following weaving techniques for glass-fibre fabrics: plain weave, twill and satin weave.

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289

of the Main Department for Production Development in the company VEB Flugzeugwerke in Dresden was in charge of this development.127 The research was divided into two large topical complexes, on the one hand, the development of the honeycomb core and the materials for the covering layers as the segments of a sandwich element, and on the other hand, the development of the technology of synthetic-resin impregnation of a honeycomb material. The starting point of the paper honeycomb core design was the East German brand Wawepa, a product by the papermill VEB Papierverarbeitungswerk in Engelsdorf.128 This honeycomb core product made of corrugated cardboard had hitherto been used in the GDR in the furniture and construction industries and constituted the core material of lightweight furniture as well as of doors covered on both sides with hard fibreboard. This honeycomb hexagonal shape of the GDR lightweight honeycomb was used as the basic honeycomb shape for the aviation industry. The developers were also guided by the patent from 1901, which Luxuspapierfabrik Heilbrun & Pinner in Halle an der Saale had filed for the manufacture of a “paper net”.129 Today this paper net is used in many ways for decorative purposes and is called a garland (Girlande). The research plan for this development was scheduled in three one-year stages from 1956 to 1959 and was subdivided into paper honeycomb development (completed in 1957), sandwich construction, part 1 (1958) and part 2 (1959).130 The last stage also included the development of an appropriate testing regime for honeycomb materials and sandwich components as well as a wide-ranging numerical study with regard to design, stress analyses and failure models. The identification and testing of suitable materials followed as a follow-up project. The aim of this project was the certification of the developed sandwich components for concrete aeronautical applications. This task was assumed in April 1960 by the Institute of Technology and Organization of the Research Centre of the Aviation Industry (FZL). Manufacturing of the lightweight honeycomb core materials finally started in May 1959 at VEB Apparatebau in Lommatzsch, where a large-scale production plant for impregnated honeycomb cores (Fig. 5.12) for the aviation industry had been installed. However, a honeycomb system for aircraft components was already being manufactured in small series at the beginning of 1957. The honeycomb material was sodium kraft impregnated with a cresol resin. The honeycomb core material (sodium paper) of the first honeycomb systems in a sandwich structure with a GFRP coating came from VEB Papierfabrik Wolfswinkel in Eberswalde. The cresol as well as the polyester resin later used were supplied 127 Abteilung Bauweisenentwicklung der Hauptabteilung Fertigungsentwicklung. See the final

report: Entwicklung von Wabenkernen für Sandwichbauelemente. Technologische Entwicklung von Wabenkernen aus kunstharzimprägniertem Papier für die Luftfahrtindustrie. 1957–1959. (UA TUD: 94 vol. 1, Forschungs- und Informationsberichte. Fakultät für Luftfahrtwesen, Forschungszentrum der Luftfahrtindustrie). 128 Authorenkollektiv (1961), p. 4. 129 Papiernetz. See Heilbrun & Pinner (1901). 130 See the final report: Entwicklung von Wabenkern für Sandwichbauelemente. (UA TUD: 94 vol. 1, Forschungs- und Informationsberichte). On design principles and numerical materials analysis, see Hintersdorf (1965), id. (1963), Auguszt (1965).

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Fig. 5.12 Component parts of a wedge-shaped honeycomb core system (hexagonal) with a GFRP coating (matrix: polyester resin) for the auxiliary rudder of the soviet commercial airliner Ilyushin Il-14P, which was built in 1959 at VEB Apparatebau in Lommatzsch. Source Courtesy of the University Archive of TU Dresden, 94–2-11_6

by VEB Plasta Kunstharz- und Pressmassewerk in Espenhain near Leipzig. The later paper honeycomb-cell core production was done by the publicly owned enterprise VEB Eloplast in Micheln. The honeycomb production still posed a problem to some extent, because the paper strips had to be stretched out, i.e. the honeycomb cells pulled apart again after gluing, which was an intricate business. Bleed-through from the honeycombs occurred where the individual paper strips had been glued together by machine. This finicky manual task was reserved for women as supposedly having the necessary experience in this area (Fig. 5.13). The honeycomb sandwich panels developed in this way were eventually used in the model152-II V4, the improved jet turbine airliner, before it was retired in 1960 after only two test flights. The aircraft components involved were as follows: • Tail unit tips, tank compartment cowling (Fig. 5.14), flooring, partition walls, interior and ceiling panelling, wardrobe and baggage compartment, interior cladding, doors, toilet area. The honeycomb-sandwich construction developed by the GDR in Dresden was carefully designed not to impinge upon any patents in the USA, Great Britain and the FRG, insofar as the material composition and manufacturing were concerned. This meant that such sandwich components, which were produced in series as of 1959, could be sold to socialist countries as well as to capitalist countries without posing any legal problems. A

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291

Fig. 5.13 Female employees of VEB Apparatebau in Lommatzsch stretching honeycombs for the aviation industry. A metal pin was used to “stretch” glued honeycomb chambers, into which the adhesive (“Plastacol”, a pure phenolic resin from VEB Plasta Kunstharz- und Pressmassewerk in Espenhain) had penetrated, and the material was then mounted on an immersion frame for resin impregnation. Source Courtesy of the University Archive of TU Dresden, 94–2-10_5

Fig. 5.14 Female employees of the production department of VEB Apparatebau in Lommatzsch laying out a honeycomb mat for the tank compartment panels, a sandwich composite with glassfibre face sheets on either side and used in the jet-turbine airliner 152-II V4. Source Courtesy of the University Archive of TU Dresden, 94–2-10_7

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5 Development of Hybrid Material Systems in the Second Half …

Fig. 5.15 Experimental house as a honeycomb structure by VEB Flugzeugwerke in Dresden, which was tested out by employees in Graal-Müritz in the Rostock Heath on the Baltic Sea. Source Courtesy of the University Archive of TU Dresden, 94–2-11_8

patent expert opinion of the Central Office for Patents and Proposals also provides this information.131 The sandwich panels developed in this way were available in various configurations from 1960 onwards. The base material was synthetic-resin-impregnated sodium paper with a hexagonal or square cell shape. Paper, steel, aluminium and GFRP could be used as face sheets. The deliberately broad configuration of these honeycomb sandwich panels allowed them later, after the official dissolution of the GDR aviation industry, to find other applications elsewhere. That was no makeshift solution. This R & D project had envisaged a broader range of applications for the materials from the outset. The original research project was still underway when the Division on Design Development of VEB Flugzeugwerke Dresden drafted a prototype house made of honeycomb panels (Fig. 5.15), which was conceived as a holiday and weekend cottage for GDR citizens and was easy to assemble. The design of a special flexible honeycomb shape was one of the developments made by this project.132 One problem in designing these honeycombs was that bending the honeycomb structure leads to stretching, resulting in the formation of a saddle shape (Fig. 5.16, see the honeycomb structure on the left), which results in larger cell cavities on the outside than on the inside. By means of numerical analysis, a possibility was found to 131 See the expert opinion in the final report “Entwicklung von Wabenkernen für Sandwichbauelemente” (UA TUD: 94 vol. 1, Forschungs- und Informationsberichte). 132 See the explanations on the special honeycomb shape in sheet 28 of the report “Entwicklung von Wabenkernen für Sandwichbauelemente” (UA TUD: 94 vol. 1, Forschungs- und Informationsberichte).

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293

Fig. 5.16 Comparison of the classical honeycomb shape (left) and the custom reshapable honeycomb (right) with no cell deformation when in a cylindrical curve. Source Courtesy of the University Archive of TU Dresden, 94-2-14_15

design a regular honeycomb for cylindrical or spherical shapes. This custom honeycomb shaping was later used in numerous fields, e.g. in the building trade, shipbuilding and wagon construction.

5.3.3

Composite Materials Development Compared—FRG and GDR

Allied Control Council Directive No. 25 of 1946 initially prohibited direct aeronautical research in the western and eastern zones of Germany alike. The Akaflieg groups in the Federal Republic of Germany (FRG) were able to fill this gap promptly with glider construction at a number of technical universities. In the eastern zone, initially, only the Dresden polytechnic existed as an established academic institute of technology which dealt with this topic and whose personnel and technical proficiency were comparable to those of the academic institutions in the FRG after 1945. Two further academic institutions with a similar profile emerged with the upgrading of the engineering college of heavy machinery Hochschule für Schwermaschinenbau in Magdeburg in 1961 to a Technische Hochschule (TH) and likewise the Hochschule für Maschinenbau in Karl-Marx-Stadt in 1963. However, these polytechnics in the German Democratic Republic (GDR) were assigned specific technical orientations.133 A gliding culture as in the Akaflieg groups in the West did not develop at the polytechnics in the eastern zone. 133 Cf. Haka (2014a), p. 299, 338 f.

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Many of those persons interested in gliding initially joined the model aeroplane and glider flight section of the Freie Deutsche Jugend (FDJ), the communist youth association of the GDR. This section was founded in 1950 but had to be handed over to the Sports and Technology Association (Gesellschaft für Sport und Technik, GST) in 1954.134 The GST was a mass organization created by the state that trained young GDR citizens in various activities in a pre-military framework to commit them to the political doctrine. Wearing military-like uniforms, they could learn various recreational sports, such as diving, sailing, and motoring, including amateur radio broadcasting and a shooting club. Flying and parachuting were also offered.135 In the latter fields it was also possible to practice gliding as a sport. The gliders were not just flown. Technical modifications were also made on the aircraft. In addition, the maintenance of the gliders was taken as an opportunity to experiment with materials. Various escapes from the East German republic in the 1970s, however, led to the imposition of very rigid controls of the people and aircraft involved. Company-operated glider groups also existed in the east. One of the most active of such groups was organized by VEB Nagema in Dresden, a packaging-machine manufacturer.136 A GDR equivalent to the work by Hermann Nägele and Richard Eppler in the Stuttgart Akaflieg, did in fact exist nevertheless. The Stuttgart model FS 24 Phönix with its fully supporting shell made of balsa wood and GFRP flew for the first time in 1957. The student endeavours at TH Dresden under the chair for lightweight construction can be regarded as comparable, even though only a restricted number of people and just one academic institution were involved. As in the FRG, a number of East German R & D establishments were opened within the context of commercial aviation development, with their staff members sharing very similar backgrounds. In 1954, for example, Hermann Landmann (1898–1977) (Fig. 5.17) received an appointment to Dresden who had already been active in the field of aircraft construction before 1945.137 After studying mechanical engineering at RWTH Aachen and working for a time as assistant in the Institute of Flight Technology at TH Stuttgart under Georg Madelung (1889–1972), Landmann had been employed since the 1930s as a lecturer at various institutions in the field of aircraft design and as an aerodynamicist for Ernst Heinkel Flugzeugwerke AG in Rostock.138 His first appointment to a tenureship was at the University of Rostock. In connection with the decision to locate GDR aircraft design in Dresden and its environs, he was appointed director of the Institute of Aircraft Design and to the chair for lightweight construction at TH Dresden. As was the case with very many university teachers in the FRG and the GDR alike, his political past no longer played a part, as his professional competence was what counted. Thus, in the Dresden appointment proceedings there was no mention 134 Diedrich et al. (1998), p. 196. 135 Wagner (2006), p. 134 f. 136 Lemke (2018), p. 27 f. 137 Haka (2014b), see the entry on Hermann Landmann. 138 At the end of the 1920s he worked in Bonn as an instructor in the field of aviation and thus also

became the first teacher of aircraft design for the Horten brothers, see Sect. 4.6.2.

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295

Fig. 5.17 Hermann Landmann (1898–1977), director of the Institute of Aircraft Design and holder of the chair for lightweight construction at the Dresden polytechnic. Source Courtesy of the Archive at TU Dresden

of Hermann Landmann’s memberships in the nazi party, the National Socialist Teachers League and the National Socialist Flying Corps.139 As chair-holder, Landmann developed his Landmann—La 16 V1 “Lerche”—literally, “lark”—in collaboration with a number of students as early as 1954. This motor glider was made of wood and had a distinctive V-shaped tail. It first took to the skies in 1955. The successor model, the La 16 V2 “Heidelerche” (Fig. 5.18)—“woodlark”—was developed in 1958.140 The original “Lerche” was already supposed to have been made of GFRP. However, the scarcity of technical materials dictated that wood be used. In the case of the “Heidelerche”, Landmann at least succeeded in having it built as a mixed wood-GFRP structure (Fig. 5.19). Thus, the motor glider, which could be flown either as a glider or as a power glider by simply attaching or detaching an engine, was given a GFRP fuselage back and a GFRP engine cowling. This material was composed of a woven glass fabric embedded in a polyester-resin matrix. The frugal usage of GFRP here had another reason besides the chronic shortage of materials. The East German aircraft testing station Prüfstelle für Luftfahrtgeräte der DDR (PfL) in Dresden barred the way to more liberal usage of this material because aircraft manufacturers were unable to claim long-term experience with GFRP and no reference models were available. These student activities finally led to the establishment of a student study group on plastic gliders called Arbeitsgruppe Kunststoff-Segelflugzeug (AKUS). It can be considered a counterpart to an Akaflieg group in the FRG. By 1959 at the latest, the GFRP method of building gliders at Landmann’s academic institute was being widely applied and had become an established method in glider design in the GDR. In the same year, work 139 See the NSDAP, NSLB, and NSFK card catalogue entries in the German Federal Archives

(BArch): R 9361-IX Kartei 2461 0405 Landmann, Hermann; (Slg BDC) NSLB Landmann, Hermann; NS 12/8697 Landmann, Hermann. 140 Weber (1960), p. 91 f.

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Fig. 5.18 The Landmann La 16 V2 “Heidelerche”, which Hermann Landmann had developed together with students as holder of the chair for lightweight construction at TH Dresden in 1957. This motor glider was built as a wood-GFRP mixed structure. Source Flieger-Jahrbuch, 1961, p. 91

Fig. 5.19 Central part of the wing of the model FL 60 with a shell made of glass-fibre-reinforced plastic and wood as a mixed construction. Source Kautschuk und Plaste, 1963, p. 497

began on the Landmann La 20. This engine-powered aeroplane had been designed as a GFRP sandwich construction. All the main load-bearing structures, such as the wing unit and fuselage tube, were made of resin-impregnated paper honeycomb cores with a GFRP surface layer.141 Just a few connecting structures were still based on the method of 141 Lemke (2018), p. 142.

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297

metallic construction. In the middle of 1961 work stopped, however, when in the context of the dissolution of the East German aviation industry the aircraft manufacturer VEB Flugzeugwerke in Dresden cancelled its funding. It had also been supporting this project as a developmental study on GFRP structures. The model Felde FL-60 from Dresden suffered a similar fate. It had almost identical material parameters to the La 20 (a resin-impregnated paper honeycomb core with a GFRP top layer).142 The construction of the Felde FL-60 had commenced in collaboration with students under the direction of Willi Felde, an engineer and workshop head at the Institut für Flugzeugkonstruktionen of the Dresden polytechnic. Its intended purpose was to be shown at international glider competitions. Especially in the case of the Landmann La 20, a direct comparison can be drawn with developments in the FRG—namely, with the first GFRP small aeroplane by Leichtflugtechnik Union, the LFU 205, which was completed in 1968. Although these two designs are not comparable and the step towards GFRP small aircraft was taken in the FRG almost ten years later than in the GDR, conceptual parallels with regard to GFRP applications are clearly visible. Access to a free (materials) market in the Federal Republic and funding by various companies or the Ministry of Defence gave aircraft builders in the west far greater freedom of action, which ultimately led to final assembly and actual completion of an aeroplane. In the GDR, despite great enthusiasm among recreational glider pilots and developers, shortages of materials and financing often prevented aircraft development and construction. The dissolution of the aviation industry in the GDR put a halt to many areas of aeronautical research and the unused resources were later redirected into other channels and areas of expertise. Honeycomb structures and GFRP then found their way into East German shipbuilding, wagon construction, car manufacturing and antenna and insulation technology, for example.143 At the beginning of the 1970s, there was an almost simultaneous exploration of boron fibre, carbon-fibre-reinforced plastic (CFRP) (the East German terms were kohlenstofffaserverstärkte Plaste—KFP or kohlenstofffaserverstärktes Epoxidharz—KEP) and aramide-fibre-reinforced plastic (AFRP) (the East German term was aramidfaserverstärkte Plaste—AFP) and the associated development of mixed laminates made of glass and carbon fibres or carbon and aramide fibres.144 Carbon fibres for CFRP were preferably imported from Great Britain and Japan and aramide fibres from the FRG, whereas GFRP was produced domestically in the glass silk works VEB Glasseidewerke in Oschatz. The supporting matrix was, on one hand, a polyester resin, which was produced by VEB Kombinat Chemische Werke Buna in Schkopau and, on the other hand, epoxy resins, which belonged to the product line of VEB Leuna Werke “Walter Ulbricht” in Merseburg. The GDR had achieved almost complete self-sufficiency in developing and manufacturing glass-fibre-reinforced plastic. 142 Felde (1963), p. 495 f. 143 Institut für Leichtbau (1966), p. 61 f. 144 Lauck (1978), Wilhelm (1973).

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Through joint conferences and international aeronautical exhibitions, chosen individuals from the aeronautical community and materials research in the GDR were able to compare notes with their professional colleagues in the FRG until the early 1960s.145 Foreign exchange-devouring conference fees and growing isolationist tendencies in the GDR very quickly restricted this exchange of knowledge. For this reason, GDR materials researchers increasingly relied on international publications to learn about developments in the field of composite materials, which were only accessible to a select group of people. Only a small selection of specialist publications appeared in the bibliographies of publications by their colleagues in the FRG. Some of these exceptions are the researches on the design and numerical analysis of honeycomb structures by Gert Hintersdorf, which can still be regarded as pioneering work today.146 Due to the shortages, GDR materials research sought a way out and found it in a series of symposia on reinforced plastics “Verstärkte Plaste”, which were organized from 1970 onwards by the Kammer der Technik, the GDR equivalent of the Association of German Engineers (VDI). This series of conferences brought together materials scientists from a number of socialist countries, mainly from the USSR, Poland, and Czechoslovakia to discuss issues connected with developments in composite materials and fibre-reinforced plastics.147 The subject matter spanned a wide technical spectrum. They ranged from materials design, their numerical analysis and application examples, to materials testing scenarios, and were on a par with specialist topics at international conferences outside the community of socialist states. In the pioneering period of GFRP between 1945 and the 1960s, the technological developments of composite materials made in the two German states were at the same level. One reason is the transfer of knowledge by aviation experts, who had already been active in aircraft design or in the armaments industry prior to 1945. They subsequently applied their knowledge in the service of the FRG or the GDR. It should be noted, however, that the resources needed in materials engineering in the GDR were already dwindling by the mid-1950s, not least owing to the different currencies in the two Germanies. The essential self-sufficient developments that East Germany was able to achieve in this context were highly advanced, e.g., the development of honeycomb-core sandwich components with GFRP. In the FRG, the development of boron, aramide and carbon fibres and the resulting fibre-composite structures opened up new load horizons primarily in aircraft construction. This quickly came to fruition, including the production of the CFRP brake flap as a series product of the aircraft manufacturer Dornier. The aerospace industry and university research were the driving forces behind the development of composite materials in the FRG. Not only materials with a polymer matrix were looked at, but also composites with matrices made of ceramic or metal. 145 Baade (1958), Forschungszentrum der Luftfahrtindustrie (1958). 146 Oehler and Weber (1972), p. 146, Hintersdorf (1972), id. (1969), id. (1965), id. (1963). 147 Kammer der Technik (1978), id. (1978).

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Research with Limited Prospects—GDR Composite Materials …

299

Since the aircraft construction sector ceased to be an area of application in the GDR, many composite materials were used in a wide range of mechanical engineering, chemical engineering and the building materials industry. However, the development of hybrid materials continued unabated in the GDR, primarily by academic applied research. In many cases, research projects were carried out in cooperation with various important specialized companies. Thus, such developed products could also be transformed into applications.148 However, these applications were modest in number, not least because of the drastic shortages of materials in the GDR. Whilst GFRP products could in actual fact be regarded as standard products in the GDR, aramide and carbon fibres had to be imported. In conclusion, it can be stated that the parallel developments of composite materials in the FRG and the GDR can be regarded on the whole as equivalent.149 In the FRG, many composite materials could be developed promptly into high-quality products, thereby often entering new terrain. In the GDR, this was similar in many respects up to the dissolution of its aviation industry, albeit on a much smaller scale, hampered by the limited availability of materials. The contemporaneous state of knowledge about composites in both German states can thus be assessed as approximately the same, with analytical and numerical aptitude being a focal point of composites research in the GDR.150 In this context, the work by Gert Hinterdorf of the Institute of Lightweight Construction at the Technical University of Dresden deserves particular mention.151 The use of technical textiles as reinforcing materials evidently appeared earlier in the GDR than in the FRG. It can be traced back to the mid-1950s.152 At this point, the key question posed at the outset about the way developers and engineers handled composite materials can be answered in that they were largely ambivalent. The developers at DVL in the 1930s, for example, initially had to struggle hard to rouse awareness about composites as a structural material compared to metallic materials. This had changed only minimally by the time the Airbus 380 entered service. Neither in the public perception nor in the purview of the technical experts were composites, especially fibre composites, seen as real alternative technical materials. The certification of the CFRP air-brake flap is good evidence of this. The autonomous initiative of the chief developer Manfred Flemming to install the component even without official approval was needed to 148 Lauck (1978). 149 Nikolai Ingenerf comes to the same conclusion from his interviews with West German materi-

als scientists. However, no reliable surveys are currently available to allow more detailed and more extensive statements to be made, see Ingenerf (2017), p. 129 f., 140. 150 Schwarz and Schlegel (1966), Hintersdorf (1965), id. (1963). 151 Hintersdorf (1969), id. (1965), id. (1963). Hintersdorf summarized his extensive work on GFRPs in 1969 in a collection of instructional sheets, which contained in particular the dimensioning and testing of GFRPs for engineers in industry. A comparable work at this theoretical level could not be found for the FRG. 152 Wiedemann and Müller (1965), p. 724 f., Wiedemann (1958).

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open the way for fibre composites to be used as structural materials in the technical highperformance sector. Although many areas of application have since emerged for these “material structures”, their initial reception among developers and engineers as reflected in their practice was ambivalent in materials science of the twentieth century.

5.4

Beast of Burden for the Ether—The SOFIA Project, 1985 to 2009

Carbon-fibre-reinforced plastics (CFRP) can be regarded as an established material in aviation by the mid-1970s even though this fact went virtually unnoticed by the general public. The first modern fibre-composite ceramics entered this market almost contemporaneously but were primarily reserved for aerospace companies.153 The search for new materials with specific designs and defined load horizons had already started within the context of engine systems but only attained a purpose-oriented level once concrete characteristic values had been specified. The initial impetus came from a cooperative project between the utility vehicles division of the German company Maschinenfabrik AugsburgNürnberg (MAN), located in Augsburg, and the French company Société Européenne de Propulsion on the subject of engine emission filters. The ceramic components and processes envisaged here flowed into the French Hermès space project.154 The demand for more efficient materials had arisen there in connection with heat-shield issues in the context of re-entry scenarios for a spacecraft. Although the project was eventually scrapped, a number of feasibility studies were conducted on new materials, particularly hybrid ceramics. The first large-scale endeavour to design advanced ceramics with carbon fibres emerged at the end of the 1970s. It produced the hybrid composite C/SiC, silicon carbide with inlays of carbon fibres via the liquid polymer infiltration process, or else C/ C materials, where molten silicon is incorporated into a carbon–carbon composite. Today, the term CMC materials—for ceramic matrix composites —is used as a keyword, which now comprehends many ceramic composites. The actual utilization of these materials did not occur until the end of the 1980s, however, and represented a new performance level of hybrid material systems. Although CMC materials were developed for a different range of applications, these materials dethroned fibre composites which had been in use for only a few years, especially CFRP with its load limits, and heralded in a new design generation of engineered materials. My investigations into hybrid materials revealed that technically demanding projects either generated a prototype that was innovative in terms of materials technology but was not implemented until much later, or else only came into play when there were no alternatives. Classical ideas in materials technology were initially preferred and only discarded when the anticipated loads proved to be too much for them. The latter case was 153 Mühlratzer (2008), p. 377 f. 154 Hermès = a spaceplane by the French space agency Centre National d’Études Spatiales.

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found upon examining the SOFIA project. This project fell exactly within the time frame in which materials technology was undergoing the transformation just described and even found its conceptual beginnings in the area of metal-based materials. SOFIA is the acronym for Stratospheric Observatory For Infrared Astronomy, a project involving the integration of a telescope into an aeroplane.155 Ultimately, its implementation was not new. Its design was based on two precursor models. The first flying observatory was a reflecting telescope (with a 30-cm-diameter mirror) installed in a Learjet at the Ames Research Center on NASA’s Moffett Field in 1965. This observatory was replaced in 1975 by the Kuiper Airborne Observatory (KAO), a converted military transporter of the type Lockheed C-141 Starlifter, which was equipped with a Cassegrain telescope (with a mirror 90 cm in diameter). KAO can be considered the direct predecessor of SOFIA. One of the scientists who flew in this observatory was the German physicist and radio astronomer Hans-Peter Röser (1949–2015), the later founder of the Deutsches SOFIA Institut (DSI) at the University of Stuttgart and initiator of the Baden-Württemberg aeronautical centre on its campus. He can be seen as the central link in the collaboration between the German Aerospace Centre (DLR), which was the German research sponsor of the SOFIA project, and NASA. The latter was the initiator of the SOFIA project. The research motivation behind equipping an aeroplane with a telescope is the wish to be able to “see” into the Milky Way and its surroundings in the infrared range. The SOFIA project uses a Boeing 747 SP as the carrier aircraft. This project is the attempt to determine parameters that provide information about the birth of stars and to analyse interstellar space, i.e. the matter found between the stars in the form of large gas and dust clouds, which often block the view to other stars or their light. These regions can be made analytically visible primarily by their different temperature fields, but only by means of infrared technology. Such observations with a telescope on the ground, irrespective of its performance class, are futile because the atmosphere is not permeable enough and the view from Earth would be comparable to a view through milk glass. There is a possibility to escape this milk-glass effect, however, by taking advantage of the visibility afforded by an aeroplane at an altitude of 15 km. The design model for the SOFIA telescope was the Hubble space telescope, which has a vibration-free mounting. During flight the Boeing is almost vibration-free and comes very close to the conditions created by the Hubble telescope. Two vibration isolation systems suppress the vibrations caused by the aircraft. Previous studies on the SOFIA project have generally yielded popular science accounts in magazines or specialist articles on individual topics associated with the research mission. A comprehensive description of all aspects of the project would go beyond the scope of this book. The present study thus focuses on the most important developments in materials engineering and design. This analysis is based on archival material: the papers of the leading systems engineer and main designer of the telescope, Hans Jürgen Kärcher

155 Kunz (2016).

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(*1941),156 who attended the entire developmental phase from the beginnings in 1986 until the final commissioning in 2002; and the researches by the engineer responsible for the development of the hybrid-material systems, Dieter Muser.

5.4.1

First Steps and Historical Obstacles

The German Agency for Space Affairs (Deutsche Agentur für Raumfahrtangelegenheiten, DARA),157 together with the later renamed German Aerospace Centre (Deutsches Zentrum für Luft- und Raumfahrt, DLR), and NASA’s Ames Research Center, developed preliminary ideas for the SOFIA project in late 1985. Both project partners were to be involved in setting up SOFIA.158 The distribution of tasks resulted in NASA providing the aircraft, a Boeing 747, and modifying it to accommodate the telescope and the scientific operations. DARA was assigned the task of designing and building the telescope. In the end, NASA provided 80% of the financial outlay, and DARA 20%. This division was later also applied to the observation times allocated to the scientists from the USA and the FRG while the aircraft was in operation. Within the framework of an initial study of the plan, which DARA had put out to tender in 1986, MAN Gute Hoffnungs-Hütte (MAN GHH) in Mainz (now MT Mechatronics) and MAN Neue Technologie in Karlsfeld near Munich joined forces as experts in the field of telescope construction, their competencies being in the design and manufacture of CFRP structures. A short time later, an invitation arrived by the German Federal Ministry of Research and Technology (BMFT) to participate in a technology conference of the SOFIA project in Ames, California. Hans Jürgen Kärcher, representing MAN GHH, and Dieter Muser, representing MAN Technologie, attended it. The project outline presented at that conference proposed the utilization of CFRP instead of an aluminium and steel structure. This attracted quite some attention because CFRP made it possible to reduce the weight of the overall structure considerably. This conference resulted in the formation 156 Hans Jürgen Kärcher (*1941), 1961 took up studies in mechanical engineering at TH Darmstadt

(up to the preliminary exam), from 1964 he changed his majors to mathematics and physics, earning his degree as Dipl.Ing. in 1968 and working as assistant there. In 1972 he taught in Darmstadt as lecturer in lightweight design, earning his doctorate in engineering at the chair of lightweight design in 1973. In 1974 he became a structural engineer at the MAN-Werk in Gustavsburg of MAN-GHH (a mining and metallurgical corporation). The project area “communications antennas and telescopes, bridge devices and theatre construction” was transferred to MAN Technologie AG. There he became head of engineering in 1997 and in 2005 was assigned to Augsburg within the context of its affiliation with MT Aerospace AG. (Archiv—Projekt SOFIA—Dr. Kärcher [hereafter APSK], data gathered from documents on the SOFIA project). 157 DARA (an offshoot of the DFVLR in 1989) was merged with the DLR in 1997, simply retaining the acronym “DLR”. On the structure and fields of activity of DARA as well as its political embedding, see Mennicken (2007), p. 405 f. 158 See NASA system drafts, document no. PD-2001 (APSK).

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German Federal Ministry of Research and Technology (BMFT) Thomas Otterbein

German Research & Testing Institute of Aeronautics and Astronautics (DFVLR) Alois Himmes

MAN Technologie Dieter Muser

MAN GHH Gustavsburg

MAN Technologie Munchen

Dr. H. J. Karcher Dr. Lautner

Adleff Dreher Ehrhardt Hobauer Jobst Petzoldt

Steward Observatory Tucson Powell

Eastman KODAK Rochester

Dr. Angel Harvey Dr. Hoffmann Dr. Martin Nagel Dr. Olbert Young

DeClerck Forster O'Brien Dr. Snavely

Fig. 5.20 Initial structure of the SOFIA project 1987 (compiled by A. Haka)

of an initial consortium among the attendees on the development of the SOFIA telescope. This consortium (Fig. 5.20)159 included the two MAN enterprises as well as the Steward Observatory in Tucson, Arizona as the American experts on telescopes, and the Eastman Kodak Company in Rochester, New York, for the imaging. The fact that German expertise was chosen here rather than restricting participation to Americans was due to the players involved and their know-how. No US company could offer the competence combination of telescope construction and fibre-composite structures, for instance. The actors in the MAN companies had been involved in both fields since the 1970s.160 In addition to a number of technological aspects, the use of high-modulus CFRP was instrumental in reducing the weight of the aeroplane. The original proposal by NASA envisaged the telescope hatch in the Boeing 747 to be located behind the cockpit (Fig. 5.21) and the telescope structures to be made of aluminium and steel. The idea by Kärcher and Muser to make a large part of the telescope elements out of CFRP made it possible to rearrange the entire aircraft. Furthermore, a telescope of a different type and dimensions could be chosen. This made the observatory developed in the SOFIA project 159 Compiled from the Project Organization. RL/1–3. SOFIA-Project. 5 May 1987 (APSK); graphically laid out by the author. 160 Interview with Dieter Muser on 19 July and 10 Oct. 2017.

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Fig. 5.21 First system concept for the installation of the telescope in the Boeing 747 from 1987, which envisaged that it be positioned directly behind the cockpit. Source Document No, PD-2001, APSK

different from NASA’s previous flying observatories, which also distinguishes it in terms of materials and construction. This was followed by a series of definition studies, which resulted in the cooperation between the companies Carl Zeiss West and Dornier. Carl Zeiss West would be responsible for the optical components of the telescope, and Dornier for the control systems and a number of electronic components.161 Implementation of the work was to begin in 1991. A total financial volume of DM 100 million was planned, with MAN GHH assuming a share of DM 25 million. In the context of the reunification of Germany, the Federal Ministry of Research and Technology made some budget cuts. This was compounded by miscalculations on the part of Carl Zeiss West, which led to the federal ministry slating the continuation of the project to 1995 at the earliest. In consultation with the federal ministry, NASA attempted to set up a corresponding alternative project in the USA, in order to be able to secure its share of the know-how independently of Germany. This step never came about because NASA itself was faced with budget cuts shortly afterwards. The project was finally continued in Germany in 1994 in a cooperation between MAN GHH, MAN Technologie and the company Erwin Kayser-Threde GmbH in Munich. Erwin Kayser-Threde GmbH is still engaged in science-based systems solutions in the aerospace 161 Internal letter from MAN GHH on the progress of the definition study within the SOFIA project, November 1991 (APSK).

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sector following its merger with OHB System AG into OHB SE, which is headquartered in Bremen.162 Following the resumption of the project, the focus was on the design of the telescope as well as on issues relating to the materials used, the interior design of the working cabin for the scientific personnel in the aeroplane and the air-flow conditions in the telescope cabin. A company reorganization caused Boeing to lose interest in redesigning the aircraft, especially as regards the telescope cabin. Consequently, a new way had to be found on the part of the Germans in particular, which ended up in a complete overhaul of the SOFIA project. For this purpose, NASA signed a new framing agreement with the FRG in 1996 that DARA had drafted. Research and Development Contract 50 OK 9602 specified the development, manufacture, testing and transport of the SOFIA telescope as well as the support in its integration into the aircraft and in-flight testing. A subcontract by DARA united MAN GHH, MAN Technologie and the systems service provider Erwin Kayser-Threde GmbH in Munich in a research alliance.163 MAN GHH was responsible for systems design, mechanics and the associated assembly work of all mechanical parts on the telescope as well as its position controls and functional testing, which accounted for forty per cent of the services to be provided (i.e. a service share of 40%). MAN Technologie (at 20%) was exclusively responsible for structural and aircraft integration issues and Kayser-Threde (at 40%) dealt with issues involving the optics and electronics. In line with this division of labour, the parties initially shared DM 80 million. As a performance incentive, approximately DM 3 million was available in addition as bonus payments for improvements.

5.4.2

“Black” Decision and New Ways Along Old Paths

The document written by Nans Kunz (1956–2016), the Chief Engineer of the NASA Engineering and Safety Center (NESC), describes in typical NASA style a number of technical developments in the SOFIA design and provides insight into a number of scientific details on the system’s performance.164 Unfortunately, there is virtually no information in this documentation about material structures or the resulting technical design. Dieter Muser, chief developer of fibre composite structures for the German SOFIA project at MAN Technologie, reported in this context that the path to the later CFRP structures had not been smooth, and that around 10 years elapsed from the initial ideas to their implementation.165 Implementing the telescope structures in metallic materials was a pragmatic solution envisaged by NASA. When Kärcher and Muser presented their ideas for a CFRP solution at the afore-mentioned technology conference, they were welcomed 162 See here Project Paper, SOFIA-Project. Phase B1 of 1994 (APSK). 163 See the SOFIA framing contract on telescope phases B2/C/D dated 16 Dec. 1996 (APSK). 164 Kunz (2016). 165 Interview with Dieter Muser on 19 July and 10 Oct. 2017.

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by NASA, since the material CFRP material provided a solution to several problems at the same time, such as reducing the weight of the aeroplane and minimizing vibrations. Moreover, CFRP provided a great deal of freedom in the design. Having Hans Jürgen Kärcher and Dieter Muser, two experts in telescope construction and the design and manufacture of fibre composite structures together as part of the project team proved to be an ideal constellation. This enabled them to develop a novel design for an airborne observatory. By this point, Kärcher had already designed a large number of telescopes world wide, and Muser had not infrequently provided CFRP structures for them. The starting point had been their work on the radio telescope Mount Korek in Iraq with a mirror diameter of 30 m in 1984.166 That collaborative effort started within the context of a warranty claim. Climatic conditions in Iraq had caused signs of wear on the radio telescope. CFRP components were therefore retro-fitted for the reflector. This was followed by CFRP developments for MAN GHH. Kärcher additionally developed antenna panels made of CFRP. Here it was possible to draw on the knowledge gained from manufacturing the fuel tank for the Ariane 4 rocket, such as the observations made on flat CFRP components under tension.167 The first CFRP reflector component in a sandwich construction was developed out of these observations. Aluminium honeycombs were used as the material core enveloped in fabric layers of CFRP. A separately applied, easily meltable metallic alloy provided the necessary reflectivity. First came the CFRP lattice stiffening, coating and application of an anti-rust primer. Then the reflector was finally applied. These CFRP structures, which had been successfully installed for the first time on a telescope, were only in use for a short time, however, as this telescope in Iraq was destroyed by Iranian air strikes during the Iraq war.168 The equipment was not rebuilt. Other telescopes with CFRP structures were developed by IRAM (Institut de Radioastronomie Millimétrique) in Grenoble, which is economically coupled with the MaxPlanck-Gesellschaft in Munich. The initial observations formed the backdrop for CFRP structures coming increasingly into use in the area of telescope technology. The six antennae of the IRAM radio interferometer are one example. At the IRAM facility (Fig. 5.22), the 176 reflector panels, arranged in six rings over a total area of 214 m2 , were designed as a CFRP sandwich structure. In the subsequent years, there followed radio-telescope developments in La Silla/Chile, the Heinrich Hertz Submillimeter Telescope on Mount Graham, Arizona, the PRONAOS balloon telescope (Programme national d’observations submillimétriques) and the Antarctic telescope.169 With the exception of the last telescope, where the mirror and frame 166 Muser (2008). 167 See the layout, designs of tank systems and boat elements for the Ariane rocket in the techni-

cal documentation of the Luftfahrttechnisches Handbuch issued by the Arbeitskreis FaserverbundLeichtbau: Fröhlich and Diem (2006); Wächter (1997). 168 Interview with Dieter Muser on 19 July and 10 Oct. 2017. 169 Interview with Dieter Muser on 19 July and 10 Oct. 2017.

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Fig. 5.22 One of the seven antenna units with a mirror diameter of 15 m at IRAM Observatory, on Plateau de Bure at 2,550 m altitude in the French Alps. Astronomers there observe interstellar molecules and cosmic dust, or else are on the lookout for “black holes”. Mounted on rails, these telescope antennae can change their position relative to one another or can be moved into a maintenance hangar. The photo on the left shows an antenna in front of such a hangar. The photo on the right shows an antenna inside the maintenance hangar with the mirrors and paneling removed; the black CFRP supporting frame is visible. Source APSK

structure were designed in a sandwich construction of glass-fibre-reinforced plastic and a plastic foam, the above-mentioned telescopes with reflector surfaces and support structures designed in CFRP can be grouped in the same generation. This applies to both their design and the framing conditions in materials technology. Over the years, Kärcher and Muser developed a large number of CFRP application parameters which are now used as standard guide-lines in telescope construction. They thus ushered in a new generation of telescopes which were far lighter than their metal predecessors and could be steered and positioned more quickly and precisely. These structures are also far less susceptible to interference from wind loads and to effects caused by chemical media. Nevertheless, the protocols and development reports indicate that individual adaptation was necessary for almost every one of these telescopes. In particular, the extreme site conditions, combined with the demand for high precision, called for adjustments to be made to the fibre-composite structures.170 It was necessary to avoid focal point effects above the melting point of the polymer matrix in order to prevent damaging it. Stress 170 See the collection of material by Dieter Muser and his comments on the individual stages of telescope development from the 1980s onwards (APSK).

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concentrations resulting from thermal interactions, which are classic disadvantages of fibre-composite structures, also had to be reduced as far as possible. In the end, though, the significant improvements in quality outweighed the disadvantages.

5.4.3

The “Black-Frame” View into the Past and Future

Taking the CFRP structures developed for use in telescope construction as a basis, Kärcher began to plan the structure of the SOFIA telescope. The radio telescope owned by the Swedish Astronomical Institute in La Silla in Chile, which is known as the SEST telescope (Swedish ESO Submillimetre Telescope),171 served as the design model. It had also been designed by Kärcher and Muser and the IRAM team.172 However, this telescope was shut down by the operator in 2003 due to cuts in its research budget. The La Silla telescope was anchored in a stationary position. The question of how to anchor the SOFIA telescope inside the Boeing 747 first had to be resolved. Not least for the sake of telescope manoeuvrability, Kärcher decided to anchor the telescope to the aircraft bulkhead (Fig. 5.23). The bulkhead separated the cabin segment accommodating the working astronomers and the scientific equipment from the cabin containing the telescope.173 This included the decision to abandon the original concept of placing the telescope behind the cockpit. This was possible because of the low weight of the CFRP structures and the resulting positive distribution of mass inside the aircraft. It had to be decided whether a cage structure or a dumbbell structure would be expedient for the suspension of the telescope. The latter had the advantage that the load of the bearing point of a “dumbbell handlebar” could be introduced directly into the structure of the aircraft, i.e. in the area of the aircraft’s centre of gravity. That was why this solution was favoured.174 There were two model telescope structures to choose between, the more massive solidwall design and the truss construction. Kärcher opted for the truss construction because it weighed less. The telescope suspension in the bulkhead (Fig. 5.24) divides and links together two worlds with a temperature difference of approx. 60º Celsius and a pressure difference of 0.6 bar. While the telescope’s counterweight and control units are located on the left side with the scientific personnel, the actual telescope with the mirror units is located on the other side. Both sides are connected by the Nasmyth tube,175 which carries 171 ESO = European Southern Observatory. 172 See Hans Jürgen Kärcher’s conceptual studies from 1986–1997, overhead transparencies com-

pilation from November 2010 (APSK). 173 See the concept drafts by Hans Jürgen Kärcher from 1986, 1995 and 1997 as well as Kärcher (2002) (APSK). 174 See the explanations or sketches on the principle of the telescope suspension in Document No. PD-2001; Kärcher (2014), Sust et al. (2002), Schönhoff et al. (2000) (APSK). 175 Named after the Scottish engineer James Nasmyth (1808–1890), who had developed a special reflecting telescope (Nasmyth telescope) with two auxiliary mirrors extending the incoming beam and leading it out of the telescope tube.

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Fig. 5.23 Cross-sectional view of a fuselage section of the Boeing 747 of the SOFIA project, showing the subdivisioning of the aircraft into the cockpit, visitor’s area, working area of the researching astronomers along with their scientific equipment, the separating aircraft bulkhead and the telescope cabin with the telescope behind it. Source CAD drawing: MAN Technologie, APSK

the weight of the telescope and has a cladding thickness of about three centimetres. This tube is made of CFRP and is connected to a CFRP strut frame, which acts as a support for the mirror units. It is currently probably the largest CFRP component in the world to have been manufactured in one piece. The stiffness of the CFRP material in these structures as well as its temperature stability allow for a much higher operating precision than a metallic structural solution could ever have achieved. The temperature stability of CFRP structures was a much more important consideration when drafting the SOFIA design than the weight reduction they offered. In addition, there is another vibration damper, which compensates for vibrations during take-offs and landings as well as any turbulence caused by the aircraft. Whereas the majority of the CFRP structures were manufactured by subcontractors of MAN Technologie the CFRP tube is an in-house production of that company.176 The mirror units were supplied by the French company REOSC becauseCarl Zeiss had dropped out of the project due to the discontinuation of its relevant business branch. The mirror assembly made of glass ceramics was supplied by Schott AG from Mainz, the mirror diameter is 270 cm. All these structures, not least the CFRP mirror cell and the mirrors themselves, had to be custom adapted to the aircraft configuration. The telescope-cabin hatch in particular, which is ajar during flight to be able to provide a view of such objects as the Milky Way, is regularly exposed to special environmental influences. The gaping “hole” in the aircraft creates roughly the same acoustical effect as a flute hole when the flotist blows air through the tube. It is exposed to pressure, changing temperatures and weather conditions. Air currents in the telescope-cabin shaft can generate the organ-pipe effect, which had to be avoided. A complex simulation procedure was employed to aid in designing the components involved in a suitably stable way and reducing noise generation and 176 Telephone conversation with Dieter Muser on 19 July and 10 Oct. 2017.

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Fig. 5.24 Later mirror version of the reflector telescope. The dumbbell shape can be seen with its “handlebar” embedded in the bulkhead of the aeroplane structure. The right-hand part of the telescope is incorporated into a light truss-type structure. The counterweights and the control units for operating the telescope can be seen on the left-hand side behind the bulkhead where the scientific staff is also located along with suitable IT recording equipment. Source CAD drawing, telescope design by H. J. Kärcher, APSK

the associated vibrations. All the component parts and aggregates in the telescope were compatibly adjusted to create tolerable aeroacoustics. Just like the different resonances produced inside the body of a violin by the individually vibrating strings, all the component elements inside the telescope shaft had to be conformed to one another to generate compatible aeroacoustics.177 The technical components were integrated into this simulation to verify mutual harmony, most importantly the strut frame with the mirror units, before being installed in the telescope shaft. The assembly and installation of all these components and aggregates was done in Waco, Texas, in 2002.178 The first flight with the hatch open (Fig. 5.25) finally occurred on 14 December 2009 above the Mojave Desert in California. Despite the large number of new developments achieved by the SOFIA project, the companies MAN Technologie and MAN GHH, in particular, perceived considerable deficits in the organization and financial handling of the project by the contracting agencies. In assessing the SOFIA project, several aspects have to be considered. First of all, remarkable technical solutions were developed, which make the project a technical milestone in airborne astronomy. In addition, the now available means within the context of 177 Kärcher et al. (2008), Krabbe and Kärcher (2004) (APSK). 178 Kärcher et al. (2008), Schubach et al. (2002) (APSK).

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Fig. 5.25 SOFIA, the Boeing 747 with its hatch open during flight. The telescope mirror is protected from direct sunlight by a special textile tarpaulin without, however, impairing the mirror quality. Source APSK

prospects gained and insights made about the universe must be evaluated as positive. But there were also deficits. The permanent subsequently posed demands by the clients made with regard to the performance scope of the overall structure or the telescope, as well as delayed disbursements of project funding and considerable decision-making weaknesses with regard to approval procedures in the relevant German ministries, had the consequence that on average ten percent of the development costs incurred by SOFIA had to be borne by the companies involved to avoid contractual penalties.179 It would not have been possible to implement this ambitious project without the basic technical knowledge about hybrid materials, such as CFRP, GFRP or C/Si. In designing the fibre-composite components, MAN Technologie in particular was able to break new ground with its numerical methods of devising hybrid structures and improving design accuracy. The same applied to issues concerning the manufacturing process involving prepreg technology and autoclave procedures. Decisive knowledge could likewise be gained on the machining of CFRP components in particular, whose material characteristics lend them high wear potential. These findings proved useful in later contracted work in the aerospace sector. Finally, the SOFIA project also casts a line back to the origins of manned spaceflight, which once sparked early interest in the universe for all astronomers. Buzz Aldrin (*1930), 179 Audit by the board of directors: Wir haben uns übernommen. Mehrkosten im Bereich Entwicklung des SOFIA-Projektes, 22 June 1999; letter by MAN Technologie on the formation of reserves in the amount of 2 million to cover development costs, dated 22 July 1999 (file memorandum on additional costs incurred by MAN GHH from its development services for the SOFIA project, 6 Feb. 1997) (APSK).

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Fig. 5.26 Meeting between the past and future of astronomical research, in two senses. This photo depicts astronomers of the SOFIA project at the rear of the cabin section of the SOFIA Boeing, standing right next to the counterweight of the telescope, in conversation with the second man to have walked on the Moon, astronaut Buzz Aldrin (centre, in a red shirt). Source APSK

the second man to have been on the Moon paid a visit to the SOFIA team in 2007 (Fig. 5.26).

5.5

Hybrid Materials with Other Matrices and Reinforcing Materials

The range of hybrid materials has become so large by now that a comprehensive exposition would probably only be possible by going through the developments in stages. New hybrid materials are constantly being added all the time, and their couplings with other materials turn them into new “material constructions”. This applies to all the materials used for reinforcement, supporting strength, layering and as a matrix. One of many examples of new hybrid materials and hybrid material constructions is the current subject of a large-scale project in Dresden, which deals with the design of so-called Dresden carbon concrete (Dresdner Carbon-Beton) for applications in building construction.180 In the building industry, the roots of composite materials can be traced back to antiquity. As explained in Sect. 2.2.1 above, straw-reinforced mudbricks were in use as early as about 3000 B.C. About the modern building industry, an intensified academic debate arose in the early 1980s. It was initiated by Antoine E. Naaman (*1940) and 180 Al-Jamous (2015), Genzel (2006).

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Hans W. Reinhardt (*1939) at the University of Michigan and the Technical University of Delft, who later came to the University of Stuttgart. It inspired the international workshop series called Fiber Reinforced Cement Composite, which conveyed a number of impulses to the field, thereby strongly shaping the image of hybrid materials in civil engineering.181 Today, we find more advanced concepts in construction and materials design, which are based on the design possibilities afforded by hybrid materials and can also be combined with construction forms inspired by bionics.182 Polymer nanocomposite materials are another large field, which has its own variety of composites and is becoming increasingly differentiated. Nanocomposites are used, among other things, for designing surfaces and coatings, but are now also being used in medicine, chemistry, biology and other fields of application.183 Closely linked to nanocomposites is the large field of biocomposites. They must contain a certain proportion of natural substances such as natural fibres (jute, flax) or a biopolymer matrix to be classified under this category. As with most hybrid materials, a whole range of composite combinations can also be created here. The best known are the natural-fibre-reinforced plastics (NFRP). They find applications as cladding materials or as load-bearing lightweight structures in the interior of automobiles, in shipbuilding and in the recreational sector.184 Durable carbon fibre can currently be viewed as the most versatile reinforcing fibre. It can be considered an established structural material in numerous product applications, such as the BMW i3 electric car by the auto-maker Bayerische Motoren Werke (BMW), whose passenger tonneau was made of CFRP as the first-ever series product. Another example is the Airbus A350 XWB, whose airframe is made of 53% carbon-fibre-reinforced plastic.185 Carbon fibre has replaced glass fibre, which had dominated for a long time, and is used in the area of high-performance composites. The increased use of carbon fibre in prestigious products can also be seen as a kind of consolidation phase of this group of composites. It is constantly being developed further and refined, involving a continuous technical presence. For example, carbon fibres serve as reinforcement in an aluminium or ceramic matrix, which, in turn, is incorporated into textile semi-finished products which are ultimately used for the production of fibre-reinforced plastics.186 Ceramic composites, in particular, are often used in the chemical industry because of their inert and temperature-resistant material behaviour. In combination with carbon fibres they are a strong composite material used, for example, in the aerospace industry. The development of ceramic composites began in the 1960s with the introduction of chemical vapour infiltration to produce ceramic fibres or for coating surfaces. The fields of application of 181 Naaman and Reinhardt (2015), p. 3 f. 182 Knippers and Speck (2017), Knippers (2016). 183 Schulte et al. (2006). 184 Pickering (2008). 185 Airbus (2020), BMW (2020). 186 Gude and Boczkowska (2014), Cherif (2011), Morgan (2005).

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ceramic fibres include the aerospace, automotive and chemical industries, robotics and the manufacture of prosthetics.187 The most important hybrid material systems at present are as follows: • • • •

fibre-reinforced plastics, FRP for short ceramic fibre composites, abbreviated as CMC materials (ceramic matrix composites) metal matrix composites, i.e. MMC materials biocomposites: natural-fibre-reinforced plastics (NFRP) and wood-polymer materials: wood-plastic composites (WPC) • polymer nanocomposites, in short PNC materials. The hybrid material systems listed above are examined with the emphasis variously placed in my research project in the history of science, technology and materials. Its aim is, to offer insight into the field of artificial materials which by their combination of two or more material groups are subsumed under the designation composite materials. In closing, the question addressed: Who were the central actors to appear in particular in the second half of the twentieth century? They supplement the names mentioned at the end of Sect. 4.3.2.1 for the first half of the twentieth century. For the evaluation of this period, the interviews I had conducted were used in addition to primary and secondary sources. The following central actors in the sense of this guiding question are: Hermann Nägele (TH Stuttgart), Richard Eppler (TH Stuttgart), Manfred Flemming (Dornier), Ulrich Hütter (TH Stuttgart), Stephen W. Tsai (Stanford University), Gert Hintersdorf (TH Dresden).

187 Mühlratzer (2008), p. 377 f.

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My book outlines in excerpt different developmental stages in hybrid materials engineering and focuses on the two major classes of composites: laminates and fibre composites. The developments in Germany and Europe as well as in the USA are featured. The antecedent developments sketched in Chap. 2, which extend from antiquity to the Middle Ages, serve both as a historical introduction and as exemplary proof of the early appearance of fibre composites. Furthermore, the actors working within the context of development are illuminated here along with their social and institutional networks. These early developments also provide the groundwork leading to the later developments in materials technology. The knowledge base, which has been passed down to the present day via the oral tradition, craft conventions and design guide-lines, is the foundation upon which the manipulation of materials, especially hybrid materials, is based. The methodological challenge Methodologically, the present study comprises a mixture of approaches in the histories of materials and objects, biographical, institutional, social and economic history, thereby essentially concentrating on the histories of materials, companies and biography. Whilst numerous groups of materials have already been well studied—as we have seen in Sect. 1.3 on the state-of-the-art in research—hardly any historical work is available on composites or hybrid material systems. One reason for this is certainly owed to the fact that this group came into industrial use as a relevant structural material relatively late, in contrast to metallic materials, for example, although, as explained above, the underlying principle of composite materials has been used in various forms and to different extents since antiquity. The main focus of this work was directed on the development of hybrid materials in the nineteenth and twentieth centuries. The approach of typology, which I had chosen for the present examination to sort the materials encountered in the primary

© The Author(s), under exclusive license to Springer Fachmedien Wiesbaden GmbH, part of Springer Nature 2023 A. T. Haka, Engineered Stability, https://doi.org/10.1007/978-3-658-41408-5_6

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and secondary sources, some of which are individualistic and alter over time, has proved its merit. The development of composite materials in the nineteenth century My study was able to show that the dwindling colonial material resources motivating the search for alternatives in materials technology led in a new direction: the chemical modification of natural materials. Increasingly refined and extensive chemical analyses and methods of processing in the late eighteenth century made it possible, along with industrialization beginning in the early nineteenth century. As shown in Sect. 3.1, these materials can be outlined with reference to the key material points: chemical modification, plastic consistency and final technical forming under pressure and heat. In materials science this group of materials is distinguished or typologically identified as the plastic masses. Classifying the early synthetics among the group of plastic masses, together with materials such as cement and ceramics, expanded this group considerably. Two of the most important early plastics were, on one hand, celluloid as the first semi-synthetic polymeric plastic and based on the natural material cellulose; and, on the other hand, casein-formaldehyde resin, which was marketed under the brand name galalith. Taking up where the publications by Günter Lattermann on the development of galalith left off, my investigation concentrated on the second synthetic of this generation, celluloid. It became apparent that the development of this material had two aspects: the innovative idea and ultimately its commercially successful implementation. The inventor of celluloid, the metallurgist Alexander Parkes, was not endowed with the latter competence. Thus, his invention, which he had named parkesine, only became successful through the efforts of the industrialist John Wesley Hyatt in the 1860s. His Albany Billiard Ball Company manufactured billiard balls made of parkesine, but this material by Parkes was advertised under the name celluloid. As recounted in Sect. 3.1, this entrepreneur succeeded in generating the world’s first industrially manufactured plastic composite material. It was designed as a layered composite material and reinforced with bone meal for stabilization. As this study has indicated, many kinds of plastic masses appeared on the market or were used industrially in the middle or late nineteenth century. Within the context of the methodological approach of typology, a number of these basic and manufacturing materials could be depicted in a classificatory diagram (Fig. 3.2). It would have exceeded the scope of the present exposition, however, to survey all the plastic masses in circulation at that time—even if limited to those based on chemically modified natural materials. My investigation therefore concentrated on one of the most important, primarily industrially and economically successful materials in this period: vulcanized fibre. It was a milestone in materials technology at the end of the nineteenth century and has hitherto only been treated in technical and sector-specific studies. But none went into its historical development in science or technology. As the analysis in Sect. 3.1.2 has shown, from the point of view of materials engineering, cellulose-based vulcanized fibre was a key

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composite material in the waning nineteenth century. Although it was originally developed in France in the middle of that century, it was patented later in Great Britain. With regard to the dimensioning of the material, vulcanized fibre has all the attributes of a modern laminate composite, even though its mechanical stability is not designed for use as a structural material. Thus, typologically speaking, it can be placed in the portfolio of composite materials without objection. Fibre webs are compressed under heat and pressure at the core of the material, but it has no true supporting matrix. The bonding of the fibre webs is achieved by a moist rolling process and subsequent thermal pressing without any bonding agent being added. Other composites are produced in a very similar manner, particularly fibre composites, by means of prepreg technology as already discussed in this study. The material ultimately produced in this way has found many uses. The vulcanized fibre suitcase is most commonly associated with this material in the minds of many consumers, but the product portfolio is much wider and extends into mechanical engineering, where gears are made from vulcanized fibre. Just as with vulcanized fibre, the development of the most important industrially manufactured wood-derived materials can also be attributed to the end of the nineteenth century, as described in Sect. 3.2.1. The natural form of composite material, wood (or woodderived materials), served as the basic model for all hybrid materials, in particular the industrially manufactured composites made of wood. That is why light had to be shed on the drafting, design and sometimes also manufacture of this material. Radkau’s books on wood were the point of departure of this examination. Many parallels to fibre composites, especially with regard to design details, could be ascertained and classified. One example is star plywood, a special form of plywood, whose laminates are stacked relative to one another at angles of 15º and 45º, producing a star-shaped structure with corresponding fibre-load angles. This form of fibre layering can be found today in multiaxial noncrimp fabrics,1 the underlying design principle of which was probably originally taken from an adaptation of star plywood. The invention and patenting at the time brought the Thuringian entrepreneur Carl Wittkowsky great economic success at the end of the nineteenth century. The plywood principle brought similar success to the Dresden company Deutsche Werkstätten Hellerau, which used plywood for the world’s first mass-produced furniture, so-called machined furniture, which was designed in 1903 by the architect and designer Richard Riemerschmid. Temporarily, plywood was also an important—if not the most important—aeronautical material or lightweight construction material. Many aircraft models fall under this category, including the so-called rigid airships, the equivalent of Zeppelin airships. Plywood can thus be considered the first serially produced composite material in aircraft construction. A further important finding of my study was demonstrated within the context of the development of chipboard in Sect. 3.2.2. For a short time, chipboard was also known as artificial wood (Kunstholz). This investigation of its development was able to clarify 1 Multiaxial non-crimp fabric = a laid web of unidirectional layers with orientations “constructed”

at a defined angle.

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its origin and usage under patent law. Radkau places the first chipboards and their production principles in chronological order in his book, but does not delve into its direct development. Therefore, my investigation was able to focus on the first patenting in 1936 in Switzerland. Within the context of typological classification, the chipboard could be categorized under the plastic masses as a borrowed concept. As the investigation has also shown, this type of board was essentially initiated by the German engineer Max Himmelheber and the Swiss physical chemist Alfred Schmid. Especially after his return from British captivity in 1943, Himmelheber pushed ahead with the technical development of chipboard. During the war he had primarily produced chipboard for the German air force and entered into numerous cooperations with companies in the German timber industry. The conclusion of my investigation into developments in the nineteenth century is a case study that was remarkable both with regard to the idea of the project and the choice of materials made in that context and is presented in Sect. 3.3.1. According to this analysis, Ulfers, an engineer from Berlin, wanted to use for his stern-tube bearing arrangement, bearing shells made of a technically robust material with a broad thermal spectrum. Until then, plain bearings had mainly been made of white metal. This was a lead or zinc alloy, which, however, required a considerable amount of maintenance. Ball bearings were not yet an option at this time, as the technology required for their production was not yet available. The decision to use parchment paper as bearing-shell material was innovative at the time, because parchment paper was not produced industrially in Germany until 1861, under British license. Ulfer’s reaction propeller did not come into general use, though, because the efficiency of its propulsion fell short of expectations. As a result, not only his development of the propeller and engine were forgotten, but also the plain bearing developed in this context with its composite-material structure and which can be classified as an early laminate presstoff. This investigation was able to show that it was ultimately the Dresden thermodynamicist and university lecturer Gustav Anton Zeuner, in cooperation with the shipbuilding engineer Ewald Bellingrath, who succeeded in designing and implementing a reaction propeller. Composite materials in the context of 20th-century polymer chemistry Leo Hendrik Baekeland changed the world of materials permanently with his “process for the production of condensation products from phenols and formaldehyde”, as the German patent reads, which he had originally submitted in 1907. Bakelite, as its inventor and namesake called it, was a phenol–formaldehyde mixture to which a filler was added. The admixture of fillers made bakelite a composite material, and it was the prelude to numerous products, world wide. The incorporation of fillers to specifically manipulate mechanical properties, as was later done in designing fibre-reinforced plastics in order to accommodate special load horizons, did not exist yet in the case of bakelite. This is where my investigation began in pursuit of the question of when this first massproduced plastic in the world was first used for a sophisticated product, in particular

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as a structural material, and whether this was a decisive technical step in the development towards modern fibre-reinforced plastics. This inquiry led to the research by the US American Robert Kemp and his colleague Frederick Johnson at the Westinghouse Electric Company in 1916 (presented in Sect. 4.1.1). Its aim had been to use the new material in aircraft construction. The patent they submitted described a new material that was to be used as a plate-shaped material for components of a propeller aircraft. This material was presented in four variants, the supporting matrix of which consisted in each case of condensation products of phenol and formaldehyde and could contain alternatively for reinforcement: paper, fabric, wood fibre and wood. The Kemp-Johnson patent and the subsequent Kemp patents were in line with the trend of technical practice at the time to find new approaches for aviation in materials technology. It can thus be stated as a central finding of this investigation that the patented project idea by Kemp and Johnson was probably the first description of the principle underlying modern fibre-reinforced plastic. It has not been possible to determine how this project idea was implemented, presumably because many of the related prerequisites for technical materials and their manufacture were still lacking at that time. The fact that Kemp was able to develop a project idea with such a material at all at that time is presumably due to the close interconnections and associated network of his employer Westinghouse Electric Company with Baekeland as well as the Eastman Kodak Company. The latter had used the branded micarta composite material developed by Westinghouse as the housing material for one of its cameras. In this context, it was possible to identify other early applications of composite materials in aircraft construction, which were elaborated in my analysis as case studies in Sect. 4.1.2— namely, the researches by the British aircraft manufacturer, John Dudley North of Boulton and Paul Aircraft, and by the technical autodidact, Albin Kasper Longren. These investigations revealed that by turning to lightweight construction, North entered new terrain in aircraft construction. Deviating from the foregoing model, the airframe of his designed aircraft was made of rolled steel elements instead of wood; and the rear fuselage consisted of a monocoque, i.e. a fuselage made as a stressed-skin construction. This form of construction had hardly been used until then and was a novelty. But so was the fuselage sheathing made of load-supporting dilecto plates, a bakelite-licensed product, which had hitherto been used for door panels and table tops. According to this typological evaluation, dilecto panels can be identified as an early fibre-reinforced plastic. North had thus for the first time undertaken a multi-material design consisting of metallic materials and a fibre composite. The second case study, on Longren, in Sect. 4.1.2.2, shows that the aircraft he had developed differed considerably from the one by North. He designed the fuselage as two complete shells and employed an existing composite material. Longren developed probably the first composite fuselage shells ever for an aircraft by modifying vulcanized fibre for his application, that laminate composite material patented in 1859 by Thomas Taylor in Britain. He developed a mould for the fuselage shells into which he inserted vulcanized cellulose-fibre sheets in three layers and pressed them together with rotary-cut

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veneers on both faces. In 1922, Longren secured the idea of a modular aircraft design as well as the production of fibre-composite fuselage shells with two patents. The plastic masses versus presstoff Hermann Staudinger’s entry into polymer chemistry opened a door for the group of fibre composites in particular, because the supporting matrix gained a new quality. This inspired me to explore the scope afforded by these new supporting systems in this investigation and what this signified for the development or design of the embedded materials. This analysis shows that a definite change occurred. Precisely designed reinforcing materials henceforth replaced the typical fillers in bakelite, e.g. wood flour, crushed shells or coal dust, whose ratio in the mixture had been used to define the stability of the material. In the new product assortments, rough filler quantities thus gave way to precisely defined fibre tapes. The presstoff manufacturer Heinrich Römmler AG in Spremberg in Lower Lusatia was identified as the central industrial player in this field and is described in Sect. 4.2.1. The phenolic formaldehyde condensation process that Römmler AG developed in parallel to the Bakelite Company gave it a considerable technical lead over other companies in the synthetic-resin products business. The German company started to develop its product range further as early as 1920 within the context of the expansion of its machine installations, especially its press technology. Römmler AG was also the first company to insert and press defined layers of fibrous tapes into resin systems. This transition from the pressed masses to laminate compression moulding material or presstoff , represents the birth of modern fibre-reinforced plastics. The company thus became the first manufacturer of such composite materials in Germany. Pre-impregnated paper and fabric tapes were used as reinforcing materials, which were applied according to a defined load pattern, taking the values of metallic materials as a guide. The utilization of pre-impregnated webs is a standard production technique today known as prepreg technology and can thus be traced back to a historical model. As my investigations have shown, this form of production was also associated with a surge in the development of compression technology, which had a significant influence on product quality. In this context, Römmler AG coined the term Preßmasse or “pressed mass” in professional circles, the end product of which was referred to as Preßstoffe, literally, “pressed materials”. This technical term was used for such materials until the 1960s. By supplying the fittings to the rigid airship LZ 127 Graf Zeppelin, which was put into service in 1928, Römmler AG was able to present layered presstoff fabrics to a wider public. “Fibre-materials pioneers” and secret alliances The streamlining of machines and higher shaft speeds put conventional machine elements inevitably to the test. In the course of new machine dynamics, new questions arose in engineering, particularly as regards load and the associated wear. As my investigations have shown, good material characteristics in the context of abrasive wear permitted

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presstoff to be applied as a material for plain bearings at an early stage. A mechanical engineer who recognized this advantage early on was Enno Heidebroek, a research specialist in the area of plain bearings. He was first employed in Darmstadt and later in Dresden. An earlier study of mine presented his direct research on bearings and his theoretical explorations within the context of hydrodynamics. My survey of some 4,000 mechanical engineers retraced their social networks in academic and industrial research. Setting out from this state of the science, I undertook to evaluate his family estate, which was reunited for the first time at the end of 2015, along with various secondary sources. Assuming a completely new focus of investigation, I completed an examination of the role of presstoff materials in bearing systems. The copious findings added considerable detail to the portrait of this versatile mechanical engineer, who pursued his research interests on the basis of a thorough study of fields beyond his expertise. Heidebroek’s private correspondence with his family reveals that he had close ties to the steel industry through a family business. Thus, he came into contact with rolling mill technology and encountered early presstoff bearing shells and recognized their potential. In this environment, I was able to determine by means of network analysis his early involvement with Römmler AG, which had led to a series of contracts to perform research and verificational work during the 1930s. Until then, Heidebroek had concentrated on the individual components of a plain bearing. My investigation was able to show that he changed his analytical attitude in the context of the utilization of presstoff materials by beginning to study their mutual affinities. He realized that a plain bearing with a bearing shell made of presstoff required less maintenance and thus incurred lower costs, because high-quality lubricants could be dispensed with in favour of water enriched with some grease. This finding was a central insight for the subsequent development of plain bearings. It has since defined the use of fibre-composite plain-bearing systems around the world. Heidebroek’s analyses of presstoff materials represented a turning point in his research on bearings up to that point and is an essential addition to the previous state of knowledge about his research. A number of letter exchanges with his colleagues from the 1920s and 1930s reveals that the research on machine elements was directly related to research on tribology and lubricants. Heidebroek’s research on presstoff materials throughout a period of over 30 years steered him towards lubricant research, particularly synthetic lubricants, only towards the end of his career as a researcher and emerged from the quintessence of his presstoff bearings research. A reappraisal of his extensive research on lubricants is still pending. As I have stated earlier, Heidebroek ventured beyond the boundaries of his field of expertise and until 1945 was mainly concerned with mechanical engineering design and physics. One result of my present investigation is that the field of chemistry can now be added to this list, as shown in Sect. 4.2.3. There is no doubt that Heidebroek was already considered one of the leading plainbearings researchers at the beginning of the 1930s, who also had extensive expertise in bearing materials and presstoff in particular. It is therefore not surprising that companies such as Römmler AG awarded research and verification contracts to him. Römmler

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AG had been a leader in this field since the 1920s due to its in-house development of production technology, which granted it the liberty to offer the same kind of products as Bakelite Company. With the expiry of the heat-pressure patent, Dynamit Nobel AG entered this market segment in 1933 at the latest, backed by its superior capital and resources. My evaluation of the correspondence between Heidebroek and the company revealed that the latter requested almost the same research services as Römmler AG within an interval of two years. The irritating thing about this was that Heidebroek passed on to Dynamit Nobel AG data on characteristic values of various presstoff materials stamped with the company logo of Römmler AG and even explicitly referred to that company. It was not until I had located the company’s files that this inexplicable research practice of Heidebroek’s was explained. Those papers also contain a secret cooperation agreement between Römmler AG and Dynamit Nobel AG. Thus, I was able to prove that the German presstoff market had been divided up amongst the companies involved by means of a common trust, sharing the interests and production. Their direct agreements on products and pricing largely determined entire market segments and enabled both companies to specialize in manufacturing and production. This gave Dynamit AG the ability to push ahead with demanding projects and develop further presstoff varieties as structural materials. Its corporate affinity as a manufacturer of explosives had already brought the company long-standing connections with the military. In this context, the development and production of vehicular body parts and even an entire car body for the DKW F8 occurred between the mid and late 1930s. In cooperation with Auto Union Chemnitz, a small series was initiated with the aim of conducting military field testing on this DKW model. This finding provided an answer to the two central aspects of my first guiding question. Firstly, when composite materials were first considered as lightweight materials and, in particular, as structural materials for industrial use; and secondly, in which product group they are to be found. Public perception, especially in industrial circles, was initially shaped by the necessity for presstoff materials to prove their worth against classical metals and other materials. It should be mentioned that the military intended to use these materials for technical equipment already by the end of 1934. This was possible due to an overriding quality inspection by the Berlin Materials Testing Office (MPBD) and the DIN standard 7701, which was issued in 1936, since standardization is generally a prerequisite for military equipment in order to facilitate rapid and reliable replacement. With the outbreak of war in 1939, the first step was the founding of the Independent Special Ring on Plastics and Presstoff , which later became the “Main Ring” in that specialty. Within the framework of my study, a network analysis was performed on these intertwined professional relationships in order to be able to identify the actors involved in German armaments production. The result is displayed in the graph on the network of the most important German compressed thermoplastics manufacturers, their expert bodies, testing and trials facilities, in the context of German armaments production in 1940/41 (see Fig. 4.22 in Sect. 4.3.2). My analysis showed that university professors, such as the above-mentioned mechanical engineer Enno Heidebroek or the plenipotentiary on synthetic materials, Richard Vieweg, were involved

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in this network as technical experts. The fact that there were also discrepancies in content and expertise could be illustrated by the dispute between Enno Heidebroek and Gerhard Lucas, chairman of the Main Ring on Plastics and Presstoff. Fibre research as the basis for fibre composites The performance of composites, as found in particular in the variously used fibrecomposite materials, depends on the supporting matrix and even more so on the quality of the load-bearing fibre inserts. Therefore, it was necessary to investigate German fibre research in greater detail, starting from the publications by Günther Luxbacher, who investigated technical botany within the context of the German efforts to achieve autarky in the period between 1914 and 1938. In particular, a closer look at the researches by the botanist Friedrich Tobler was necessary, since Luxbacher’s work has not focused on them. Tobler was one of the most important German researchers and experts on raw materials in this field in the first half of the twentieth century. One of the main reasons for me to focus my investigation on this was that Tobler’s work influenced the materials technology of a large number of textile products, including the hard fabrics found in laminate presstoff. In order to better assess Tobler’s work, I conducted a network analysis, based on Luxbacher’s account, ending with Tobler’s acceptance of the Dresden chair in botany. Two important findings emerged, which are presented in Sect. 4.4. On the one hand, it was possible to establish that already during World War I, in the context of the debates about substitute materials at the time, Tobler had called for a reappraisal of the work by the scholar and botanist Georg Rudolph Böhmer, who had published a two-volume work on this very topic in 1794,Technische Geschichte der Pflanzen—the “technical history of plants”. Tobler’s efforts to avoid duplicating this research during both the World Wars failed, leading to frustration on his part, which is why he then concentrated more on local research. The second finding, which I presented in Sect. 4.4.1, was that there was a tight intermeshing with two other professorial chairs and their staffs at the Dresden polytechnic. This network with Tobler also involved the mechanical engineer Heidebroek and the materials researcher Paul-August Koch, the latter of whom held the chair for fibrous materials science at the Dresden polytechnic. In the course of this study, it was possible to establish that these three chairs were interconnected both on a private and a professional level. On a private level, the chair holders or their assistants were linked to each other through their memberships in student fraternities, and on a professional level through their specialty in fibrous materials or composites. However, not all these technical issues or research could be identified at the respective chairs, as no usable correspondence or project documentation could be found about every one of these topics. It can be established, though, that Tobler was involved as a sought-after expert on fabrics in numerous armaments-related topics almost until the end of 1945, even though he was at odds with the political authorities because of his wife being Jewish. The research topics pursued by Paul-August Koch were of particular interest to my study. Until now, it has been assumed that glass-fibre-reinforced plastic had first been

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tested in the USA in the early 1940s within the context of military applications as a substitute for aluminium alloys, which were in very limited supply at that time. However, the decisive fundamental researches on glass fibres and glass-fibre fabrics had not been conducted in the United States, as has also been shown in Sect. 4.5.5, but at Koch’s chair in Dresden, where the Reich Office of Economic Expansion and the Reich Ministry of Aviation acted as clients. The glass-fibre research for the reich ministry was at the forefront and had the goal of generating glass fibres or glass-fibre fabrics as a technical textile in glass-fibre-reinforced plastic. The network analysis disclosed a contact with the already described manufacturer Römmler AG. This Spremberg company took on the task of transfering the glass fibre or fabric designed by Koch into a composite and performing the corresponding preliminary tests on it as a structural material. As early as the beginning of 1942, Römmler AG was able to provide the Luftwaffe with glass-fibre-reinforced plastic based on the developments made at the chair held by Paul-August Koch. It was plate material in secret serial production under the brand name Harex. In conclusion it is thus establishable that the Dresden researchers on fibrous materials can be considered pioneers not only in the area of basic research, but also in the area of applied research on glassfibre-reinforced plastic. Documentary evidence shows that the USA only began to focus more on such development in 1941 upon receiving instructions to do so within the context of a military restructuring of the Air Force. My findings on the work of Paul-August Koch, presented in Sect. 4.4.1.1, show that the development of glass-fibre-reinforced plastic did not originate from American research intentions but had been initiated much earlier in Germany. However, the USA was able to expand this branch in industry after World War II because unlike Germany the economy there did not first have to be completely rebuilt. Classical knowledge about materials put to the test—Two aeronautical research facilities This evaluation of primary and secondary sources has revealed that two research institutions in particular were engaged in research on composite materials or closely related applied fibre research. The network analysis on the DVL’s Institute of Materials Research, which was also performed in this context, has revealed that its long-time director, the national conservative engineer Paul Brenner, moved between state authorities, researchers and the military, and had a reliable network at his disposal to be able also to promote unconventional topics, such as presstoff materials, during this period. The results of my investigation collide with the biographical account by Helmut Maier, which interprets him as an ideal, typical researcher and developer.2 As early as the beginning of the 1930s, unbeknownst to the expert world, prototype trials were commenced under Brenner’s aegis to certify presstoff as a structural material. This can be viewed as a novelty for the time. These attempts failed because decisive fundamentals on the behaviour of composite materials with joining technology were lacking. With the production of prototype components for a Heinkel aeroplane, the fabrics 2 Maier (2019), p. 111 f.

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department (Stoffabteilung) took a further step forward towards a better understanding of construction with presstoff materials. Contrary to the trend in the specialist community, which adhered to the doctrine of designing all-metal aircraft, Brenner’s employees succeeded in working out the characteristic parameters of very many composite materials and technical fundamentals about their manufacture, including arrangements of composite systems. Thus, an abrupt turn-about in materials technology in the area of flying equipment would have been conceivable as early as the mid-to-late 1930s. The reasons why this did not happen were complex, starting with the political doctrine on metallic materials, moving onwards to conventional technical knowledge about the strength of materials, and ending with the persistence of engineering principles in practical training. Although the Association of German Engineers (VDI) tried to change the direction by offering training for engineers in the field of mechanical design to further a better understanding of presstoff materials, little progress was made in reducing the scepticism towards this material in the offices of design engineers and in the technical community generally. It would have meant a radical rethinking about the teachings and practical experience guiding an engineer. As the present analysis has shown, a number of engineers put passeddown knowledge to the test in order to explore the extent to which a rethinking was needed in the field of engineering design. In my investigation, I was able to demonstrate in Sect. 4.4.2.1 that numerical designing of composite materials, in particular laminate presstoff, was already underway to a very considerable degree already by the end of the 1930s and parallels can evidently be drawn here with currently held criteria on strength testing of composites, such as the classical laminate theory. One of the beneficiaries of fibre research in composites development was the Graf Zeppelin Research Institute (FGZ). The rapid incorporation of fibres in composite materials for reinforcement as well as the application of research results from Dresden in the field of glass-fibre fabrics were based on sound knowledge gained and active research being conducted on fibres and textiles at the DVL’s Institute of Materials Research. Three dominant themes could be identified, foremost the broad topic of cloth coverings. It included analyses of linen, flax and cotton fabrics and their application as an outer skin for aircraft wings and also as winding and adhesive tapes. Another focus was on the use of fabrics in parachute development. The work at the Graf Zeppelin Research Institute has been examined in greater detail in a dissertation submitted to the Section for History of Science (GNT) at the University of Stuttgart.3 Case study—Fibre-aligned shell construction of the Hü 211 by Wolfgang Hütter This case study was selected to show the extent to which wood, that classical aviation material which itself is a natural form of fibre composite, was introduced in an optimized form into the modern method of fibre-composite construction and therefore also into lightweight construction. This occurred at a time when duralumin was the 3 Alsatian (2022).

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favourite lightweight material, and presstoff and also the first glass-fibre-reinforced plastics were known amongst well-informed aviation circles to be alternative materials with good prospects for the future. Albeit, initially they were prevented from moving into the applications portfolio by the prevailing dogma supporting all-metal aircraft. Wolfgang Hütter was well informed about these alternative technical materials, however, the driving force behind the developments for the Hü 211 model were scarce materials in Germany and time constraints, embedded in the uncertainties of the final phase of World War II. In addition, this period was characterized by staffing shortages, which were countered by the deployment of foreign and forced labourers. Creative in-house production attempted to compensate for supply bottlenecks in machine technology. This research was motivated by armament goals, but also by the wish not to fall at last under the wheels of an increasingly eroding political system, if it wasn’t already in the process of disintegrating, led by ill-considered erratic measures often bringing destruction. As Wolfgang Hütter described in his preamble, on one hand, a construction method had to be sought that enabled the construction of a wing under the adverse circumstances of the war to meet the requirements of a nocturnal fighter plane. On the other hand, a working method had to be developed which was able to transfer such an ambitious design into serial production. Although it was clear early on in the planning that his original concept, which the Reich Aviation Ministry considered “audacious”, could not be implemented, Wolfgang Hütter nevertheless focused on the basic shell-construction concept. In particular, he attempted to refine the fibre-aligned plywood architecture by means of additional blocking angles and to further differentiate them statically by means of various cuts of the fibrous material and various quality grades of wood. It represented an entirely unique design quality in materials engineering. The conception of a modern laminate composite or fibre composite and the partial use of aspects in modern material statics reveal how Wolfgang Hütter had attempted to adapt wood, that classical aeronautical material, to the new requirements in materials engineering, stretching the available means to meet those ends. The numerical reliance on the classical laminate theory or the integration of layout strategies used not only for fibre-aligned presstoff, which was just emerging at that time, but also for the first glass-fibre-reinforced plastics, is clearly apparent here. In addition to his focus on fibre orientation by moulding the wood to shape, Hütter cast a bridge in aviation not only to individual custom shaping in presstoff technology but also to lightweight construction. A meticulous engineering approach is recognizable in his finely tuned treatment of the classical aeronautical material, wood or wood-derived materials, within the framework of a comprehensive definition of characteristic values determined by a large number of different methods in materials testing. The approximately 1,000-page project documentation that has been preserved show the discovery phase, which is characterized by repeated inquiries into the pros and cons or readjustments for lack of resources overall. Although time and the framing conditions spoke against an implementation of his ideas,

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he was nevertheless largely able to carry out his method of fibre-aligned shell construction; documentary evidence exists on many prototype components. Hütter was embedded in a network of cooperation partners, such as the aircraft manufacturers Schempp-Hirth or Wolf-Hirth as well as the moulded-wood company Erwin Behr in Wendlingen on the Neckar and the Materials Testing Institute in Stuttgart (MPA). Hütter’s wing dummy with attached engine and landing-gear segment, came the closest to his conception of the aeroplane. The versatility and segmentation of this commissioned work by the small circle of developers headed by Wolfgang Hütter can also be seen in the conception and design of the press for the wing shells. It was designed with serial production in mind. From the point of view of industrial engineering, it was finely executed and even had logistical prospects, having a railway line in close proximity. The improvisation motivated by the lack of a supplier for the engine technology demonstrates the versatility of the know-how about the work at hand and Hütter’s clear notions about aircraft production. How well Hütter’s network leading to the developmental project on the Hü 211 would have functioned without the foreign and forced labour force cannot be determined. Nevertheless, it must be noted that Wolfgang Hütter approved of the deployment of these workers, because they helped him to achieve his ambitious engineering goals as well as to fulfil the task set before him—to develop a long-range reconnaissance aircraft for the Reich Ministry of Aviation. Ultimately, with this project, Hütter joined the long line of war-matériel developers who knowingly or unknowingly supported the national socialist war machine. Case study—Flying wing development by the Horten brothers There were several reasons for selecting this case study and presenting it in context. On one hand, to examine the extent to which it was indeed possible at that time for self-taught aviators to develop and manufacture a flying wing from presstoff materials. On the other hand, to examine more closely the partly strongly diverging publications on the subject, to identify the elements of truth. The research for this case study lasted four years, the results of which are presented in Sect. 5.4. The search for usable primary sources, which were eventually located with the assistance of various branches of the Horten family, was considerably protracted by the hesitation of selected family members to provide information about the family during the nazi era or to verify their statements. Some technical points, especially concerning the material used for the Horten model H IX, could be clarified with the assistance of the Smithsonian Institution, which preserves the last surviving Horten flying wing amongst its holdings. First of all, it was necessary to sift through the existing works on the Horten flying wings, most of which turned out to be useless, as crucial points of historical fact and on aeronautical aspects were very flawed. As with many other main topics of my study, network analysis was carried out here for the first time, the most important findings of which are summarized in the present book.

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The brothers Walter and Reimar Horten were already committed to gliding and showed considerable interest in aircraft construction as amateur adolescents. In admiration of the technical achievements of their role model Alexander Lippisch, they quickly took up flying-wing design and model building. By participating in flying competitions, they were able to build a network of like-minded people and supporters amongst the circle of aviation enthusiasts, including their elder brother Wolfram, who died in World War II without enemy involvement as a result of a fellow soldier’s faulty operation of a weapons system. One of their early supporters was General Luftzeugmeister and confidant of Hermann Göring, Ernst Udet. They had met Udet at a flying competition and sparked his interest in flying-wing aircraft. Walter Horten later married Udet’s secretary, Sabine von der Groeben, who was acquainted with many nazi celebrities and aviators including Hanna Reitsch, who was also implicated in the nazi system as a pilot. For the Horten brothers, von der Groeben served as the information gateway into the nazi aviation bureaucracy. Another sponsor of the brothers was the operations director of Dynamit Nobel AG, Gustav Leysieffer, whom they had met within circles interested in aviation. Reimar Horten’s particular interest in materials technology led Leysieffer to donate small amounts of material from his company to construct aircraft. The relationship between Leysieffer and the Horten brothers intensified to the extent that Leysieffer offered them the opportunity to test various material products from his company free of charge as part of a trials programme and also made a workshop available to them along with the tools located there for this purpose. This resulted in the idea of developing a presstoff all-wing aeroplane. Whilst their flying-wing model already existed on paper, its construction turned out to be much more difficult than expected. However, their model-making experience, which had taught them the skill of improvisation, came in handy. The brothers realized that the special properties of presstoff materials and their anisotropic material behaviour called for a complete rethinking in the manufacturing process compared to the way metallic materials are treated. In many cases, the climatic conditions inside the workshop led to failure, as presstoff occasionally behaved hygroscopically, causing the glue to unstick or rivets to tear through the material. TROLITAX, one of the most advanced composite materials of the time, was made available to them for their all-wing construction. This material is definable as a thermosetting plastic consisting of a phenolic formaldehyde resin matrix with several layers of hard paper tapes as reinforcing material. As these investigations have shown, the work with this material led to the development of many now clearly defined manufacturing and joining concepts for fibre-composite materials and ultimately to their successful application. In this context, it should be noted that the Horten brothers were able to rely on the help of a small workshop team. The maiden flight of the Horten V-a finally proved that presstoff was suitable as a structural material, meeting the goal of plant director Leysieffer. Applications of presstoff in aviation were then discussed at a secret meeting of the Lilienthal Society on the premises of Dynamit Nobel AG, which was also attended by Walter Horten and all the important representatives of German aeronautics, state agencies and

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the Luftwaffe. The Horten brothers’ presstoff flying-wing was exhibited on that occasion and presstoff was evaluated as superior to foregoing aeronautical materials. A rethinking or change of course in German aviation did not take place, however. My investigations indicate this even though some aviation companies, such as Focke-Wulf , subsequently successfully developed their own presstoff materials, and patents exist documenting as much. Nonetheless, a real turn-about in German aircraft construction did not occur due to the factors already mentioned. At the outbreak of war, Reimar had followed his brother Walter into the German air force, who became a professional pilot, but they served in different units. It was in this context that the brothers eventually developed a wooden flying wing (the Horten IX), which was supposed to be powered by a jet engine that had just been developed. Through sponsoring and useful contacts inside the Luftwaffe as part of their network, the Horten brothers managed to dodge the regular military structures and thus were able to initiate a small group of developers to work on their afore-mentioned project of conceiving a flying wing. In order to be able to work autonomously on this project or only implement conditions they themselves had formulated, they also chose illegal pathways. This conduct relates to the procurement of materials, for example, which was difficult due to the war. It also involved the “diversion” of material stocks of the air force and the manipulation of superiors with ambiguous statements. The brothers’ pronounced technical and personal ambitions seemed boundless. This is clearly evident in the preserved documentation including correspondence, the as-yet-unpublished autobiography by Walter Horten and records by their brother-in-law Karl Nickel. Quite apart from this questionable behaviour, they ultimately succeeded in implementing this very innovative project. After World War II, this advanced model for its time became the subject of a number of exaggerations and implausible statements about the technology involved. One of these contentions was that Reimar Horten had perspicatiously taken radar signatures into account in his original design. Reimar Horten confirmed this allegation and allowed the American historian David Myhra to cite him accordingly in a subsequent entire series of books and a documentary film on the subject. Analyses of the technical materials on the only existing model at the Smithsonian Institution provided proof to the contrary. This flying wing concept can be regarded as aerodynamically very advanced, but the original idea can be traced back to the Austrian aircraft designer Ignaz “Igo” Etrich, who drafted and built the first flying wing at the beginning of the twentieth century, basing his design on the seed-leaf of the Javan cucumber. The all-wing design was thus not an invention of the Horten brothers; they had merely developed their own models. Their membership in the nazi party (NSDAP) opened many doors in governmental entities and among players interested in aviation, and the brothers took full and even unethical advantage of these opportunities. The Horten all-wing H IX models as well as the model H V-a were products of their day. In both incidences, we must note that they were originally supposed to be built differently. The prevailing circumstances, such as a lack of funding for high-quality

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materials or a lack of materials due to wartime shortages and political restrictions, led to these famous designs. Composite materials in the second half of the twentieth century—The legacy of armaments research With Allied Control Council Directive No. 25 of April 29, 1946—on the regulation and monitoring of German scientific research—aircraft construction also came to a standstill. However, ways and means were found to continue to pursue research topics from prior to 1945. The work by the Aachen materials scientist Franz Bollenrath is a case in point. As a former Professor im Reichsdienst, he had also been responsible for all confidential research reports in the field of materials from the 1940s onwards as editor of the technical publication Ringbuch der Luftfahrttechnik. His first publication after the war, from 1946, dealt with synthetic resin laminates with glass fibre. All the footnotes in the publication cite sources from the 1930s and 1940s and primarily refer to research reports by the DVL as well as the central researches by Paul-August Koch in Dresden on glass-fibre fabrics and their textile properties. Thus, this article by Bollenrath can also be considered a commentary of a sort on the latest state-of-the-art in research on GFRP at the DVL during that period. It also shows how far materials technology had already advanced. GFRP quickly established itself in glider construction in the young Federal Republic. Prompt applications in larger aircraft, whether civilian or military, could only be considered, if at all, after Allied Control Council Directive No. 25 was repealed in 1955. Pioneering work on applications of the first GFRP structures in aircraft design was carried out in Germany by the Akafliegs, as those flying groups at leading technically orientated universities and polytechnics were called. The developments described by Philipp Hassinger in his dissertation are incomplete as far as the aeronautical technicalities are concerned, neither is the canon of influential actors in the field of composite materials development during this period identified. This is supplemented by the results of my study. One of the most important projects on GFRP structures at this time was conducted by the designers Hermann Nägele and Richard Eppler of the Akaflieg in Stuttgart. Their FS 24 Phönix was the first glider developed with a fully supporting shell of balsa wood and GFRP. However, as described in Sect. 5.1, there were obstacles along this path. A composite material with inlaid cellulose tapes was originally planned as the reinforcement material, not glass fibre. By using glass fibres instead, they may have reached the more elevated patent level they wanted but thereby impinged on the interests of another patent applicant. This rival was the former employee at the Graf Zeppelin Research Institute and later director of the Institute of Aircraft Design at the University of Stuttgart, Ulrich Hütter, who at that time was head of the design department of the engine and vehicle manufacturer Allgaier-Werke GmbH in Uhingen, which built aircraft parts and wind turbines. The resulting patent suit ended later, in 1968, with a settlement.

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One application that arose out of these students’ research work on GFRP was a small four-seater civilian aeroplane in 1968, the LFU 205, which was built in cooperation with the Leichtflugtechnik Union, the German Aeronautical Research Institute (DFL) and the three corporations: Bölkow, Rheinflugzeugbau and Pfützer-Kunststofftechnik, with funding by the German Federal Ministry of Defence (BMVg). The motivation behind this sponsorship of the BMVg was, to accelerate the certification process of GFRP as a material for other technological projects of the military. These early applications superceded presstoff as a composite material system. Although presstoff already had fibre alignment adjusted to a given load and a defined fibre course for the reinforcement material, which was also determinable mathematically, glass fibre prevailed, if only because of its far higher load limits. The caesura of 1945 also became a conceptual caesura for fibre composites. The already mentioned paper by Franz Bollenrath abandoned the old term Preßstoff in referring to GFRP, in favour of “synthetic-resin laminate with glass fibres”, thus emphasizing the reinforcing material as the defining factor in determining this new type of material. GFRP is still one of the most common composite materials today and has found and continues to find countless applications within its load class. The search for alternative fibres already started when the first fields of application for glass fibre already existed. The immediate trigger for this was the student glider construction project at the Akaflieg in Braunschweig. In the course of developing one of their models, the students ran up against the load limits of glass fibre. The constraints imposed on the model’s design left its material as the only remaining adjustable parameter with some promise. These glider architects from Brauschweig then focused on two fibre systems: boron fibre and carbon fibre. A series of material tests followed, which ultimately led to the choice of carbon fibre because of its load limit, but foremost because of its material dynamics. Although this was the right choice as a technical material, the project was almost doomed to failure since despite its superiority carbon fibre was also much more expensive than any of the alternative materials. As my investigation has shown, once again a network of academic teachers came into play, such as the aircraft structural engineer Wilhelm Thielemann, the aerodynamicist Hermann Blenk, who had formerly directed the Hermann Göring Aeronautical Research Institute, and the BMVg. This development was not straightforward but rather a lengthy searching process which lasted over a year. Philipp Hassinger’s dissertation only describes it as a normal transitional process from one fibre to another. The fact that the BMVg became involved in this exploratory process as well was due to its renewed interest in certifying another composite material. In this case, there was also a special research interest behind it—namely, the development of the Alpha Jet light fighter bomber by the aircraft manufacturer Dornier. It was spearheaded by the engineer Manfred Flemming who was a keen experimenter. My interview with Flemming on the development of the Alpha Jet was especially fruitful because he was able to provide documentation from his private files to back up many of his assertions, which made it possible to compare facts about the materials and technical details against his personal recollections. His account of

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the developmental work was interesting in many respects, as it revealed the personal freedoms Flemming enjoyed as chief developer. The use of the finite element method and the application of PC technology in the late 1960s shows that the company made good use of all the resources available at the time. But in the end, Flemming personally had to take the decision to install the CFRP air-brake flap on the Alpha Jet, without the knowledge of the regulatory authorities. Flemming’s good networking in the BMVg made this possible. It gave its nod of approval to the developer’s single-handed move, and thus data on the use of fibre composites as load-bearing structures in aircraft construction could be generated. Such a process would be unthinkable in current-day aircraft construction. Flemming’s solo performance ultimately smoothed the way for the use of CFRP in aircraft design. Composite materials development in the GDR In the German Democratic Republic (GDR), the planning for the establishment of its own aviation industry began as early as 1952. Just as in the Federal Republic of Germany (FRG), former aircraft builders and technicians had also returned to the GDR after 1945 and formed the first generation of aircraft builders in East Germany. The chief designer of the aviation industry in the GDR was Brunolf Baade upon his return from the USSR. VVB Flugzeugbau, founded in 1958, was an association of GDR enterprises that established a network of companies in aircraft design, production and supply. The first domestic product was the jet-turbine commercial aircraft model 152-I V1, which was completed in 1958 but crashed in 1959 during its second test flight, presumably due to engine failure. Plagued by perpetual delays in the development and production of their aircraft models, shortages in personnel and economic resources, but also a lack of demand for their aircraft model which had meanwhile become outdated, aircraft construction in the GDR was doomed and was finally discontinued in 1961. During the start-up phase, not only were a large number of aviation experts from the former aviation companies and the armaments industry from before 1945 hired, but earlier R & D structures were also copied. The Research Centre of the Aviation Industry in the GDR (FZL) was established, taking the structures of the former Hermann Göring Aeronautical Research Institute as its guide. From the canon of its new institutes, I chose the Institute of Materials for network analysis within the context of my study. This institute brought forth the Materials Working Group (Arbeitskreis Werkstoffe), whose members were able to move freely between all the agencies of GDR aircraft construction. In 1958, this group also produced the East German research association on GFRP, Forschungsverbund glasfaserverstärkte Plaste, an alliance of research institutions, research academies, and industrial companies, with the common goal of producing load-bearing structures made of GFRP for aircraft construction in the GDR. Linked to this was another project: to develop honeycomb sandwich materials, now known as sandwich panels with a honeycomb core. Their honeycomb structure was made from sodium paper with a GFRP surface. However, the honeycomb core systems developed there did not last long in the

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field of aircraft design. Model 152-II V4 of the jet turbine commercial aircraft only completed a total of two test flights before the entire national development programme was discontinued. Nevertheless, this development was still useful because the honeycomb systems had been originally developed with equivalent applications already in mind. This material was used in special holiday and weekend house models. The design and numerical analysis of honeycomb structures originated from Gert Hintersdorf at the Dresden polytechnic, whose work is still valid in this field today. Here another one of the guiding questions is pertinent: How did the development of hybrid materials occur in the two German states? Allied Control Council Directive No. 25 of 1946, alluded to many times in the above, naturally also applied to East Germany. In the FRG this research gap could be bridged quite quickly by glider construction within the framework of the Akaflieg groups, but there were none in the GDR. A similar flow of ideas emerged, nonetheless, with the founding of the model aeroplane and glider flight section of the Freie Deutsche Jugend (FDJ), the communist youth association of the GDR in 1950. Genuine materials engineering with regard to CFRP development was unthinkable, if only for cost reasons. But a kind of “hobby constructor culture” emerged which, among other things, made technical alterations to the materials used for their aeroplanes. However, glider flight eventually became heavily regulated in the GDR for fear of political escapees and it was transferred into the paramilitary Sports and Technology Association (GST). In the present study in Sect. 5.3.3, a GDR equivalent to the researches of Hermann Nägele and Richard Eppler in the Akaflieg in Stuttgart and the production of their FS 24 Phönix could be identified. This was the aircraft manufacturer Hermann Landmann, who came from the armaments research and development department of the Heinkel factory in Rostock. When he was appointed to the chair for lightweight construction at the Dresden polytechnic, his party membership in the NSDAP was not mentioned, certainly due to a lack of personnel with Landmann’s qualifications. The Landmann—La 16 V1 “Lerche” is the aircraft equivalent of the FS 24 Phönix, although the use of GFRP was not used until its successor model, the La 16 V2 “Heidelerche”. The GFRP was a woven glass fabric enveloped in a polyester-resin matrix. Here Willi Felde, an engineer and workshop manager of the Institute of Aeroplane Constructions at the Dresden polytechnic, also deserves mention. In cooperation with students, he developed the Landmann La 20, built of a paper honeycomb-core material impregnated in resin with a GFRP facing. The abandonment of the aviation industry in the GDR brought many areas of aviation research to a standstill that were later channeled and redirected into other fields. Honeycomb structures and GFRP later found their way into the GDR industries of shipbuilding, wagon construction, car manufacturing and antenna and insulation technology, for example. The development of boron fibre, carbon-fibre-reinforced plastic and aramide-fibrereinforced plastic in the early 1970s occurred almost simultaneously. These high-quality fibres were imported into the GDR, provided there was enough foreign currency available there to pay for them. Professional exchanges among engineers dried up when the funds

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in foreign currency for conference attendance could no longer be raised. As a result, GDR materials research began increasingly to rely on international publications for reviews of the latest developments in the field of composite materials, and personal exchanges only took place with countries of the Warsaw Pact. Contacts were thus lost. Responses to technical findings on both sides petered out, apart from analyses of honeycomb structures by Gert Hintersdorf, which are still regarded as pioneering work in the field. In the pioneering period of GFRP after 1945, a parity in materials technology on the development of composites in the two German states existed until the 1960s. One reason for this is the transfer of knowledge by aviation experts. It should be noted, however, that in the mid-1950s technical materials were already dwindling in the GDR, not least due to the exchange rates of the different currencies. When the aircraft construction sector in the GDR fell away as an area of application, many composite materials found uses in a broad spectrum of areas, spanning from mechanical engineering to chemical engineering and the building materials industry. However, the development of hybrid materials continued unabated in the GDR, primarily in academic research. In many instances, research projects were carried out in cooperation with various relevant specialized companies. Thus, the developed products could also be transferred into applications. In conclusion, it can be said that the development of composite materials in the FRG and the GDR can be regarded as parallel over a considerable stretch of time. In the FRG, a large number of composite material developments were promptly incorporated into high-quality products, thus opening up new territory in many cases. In the GDR, this was partly similar up to the dissolution of the aeronautical industry, although on a much smaller scale due to the limited amounts of utilized materials. The SOFIA project, analysed in Sect. 5.4, is a persuasive example of the importance that hybrid material structures have now acquired in technical fields. In all my previous studies on composite materials, the focus has always been on the reception of a material, its design, layout, construction and processing as compared to metallic materials, but never on the technical properties making a material unique. From this point of view, my study of the technical criteria of materials for the SOFIA project was important, in order to be able to assess the current significance of this group of materials on the threshold between the twentieth and twenty-first centuries. The discussions and interviews with the chief systems engineer and main designer of the SOFIA telescope, Hans Jürgen Kärcher, and with the engineer responsible for the development of the hybrid-material systems, Dieter Muser, were amongst the sources for this account about the project, as presented in Sect. 5.4.1. The trigger for a closer examination of this project was a statement made by the engineer responsible for the development of the hybrid-material systems, Dieter Muser, during the preliminary stage of my research, that the utilization of fibre-composite materials had been the defining factor in making the project feasible. Whereas the latter arranged to have his records on the project, which contain information on the materials engineering in particular, preserved in the MAN archives, almost all

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the relevant data on the construction of the telescope were only locatable among HansJürgen Kärcher’s private files. My depiction of the SOFIA project profited from both these archival sources. My conversations with Kärcher and Muser produced a multifaceted picture of a project that took more than twenty years to complete, from the initial conceptual idea to its successful implementation. From the outset, this project was to be a partnership between the USA and the FRG, with the German Agency for Spacecraft Affairs (DARA), later renamed the German Aerospace Centre (DLR), and NASA’s Ames Research Center being the key national institutions of each country to carefully develop the original idea. NASA assumed the responsibility of providing the aeroplane and its conversion. The DLR was responsible for constructing the telescope. The decisive factor here was that, initially, metallic materials were chosen to build all the supporting systems of the telescope. Dieter Muser, the chief developer of fibre-composite structures at MAN Technologie, reported in this context that the journey from the initial ideas to their implementation as CFRP structures took around ten years. Building the telescope structures out of metal was a pragmatic solution envisaged by NASA and also had prototype predecessors. However, the developers in the USA soon realized that metallic materials exceeded their weight limits, which almost led to the failure of the entire project. In the end, at a decisive technology conference, Muser and Kärcher presented a “black solution”: CFRP as the load-bearing material. This technical solution made it possible to reduce the weight of the aircraft as well as minimize vibrations. CFRP even granted great leeway in the overall design. This consideration was crucial. In addition, the sources reveal that a reunited old network of technical experts provided the needed reassurance and promise of success: Hans Jürgen Kärcher and Dieter Muser, who had already successfully worked together on other projects. Both brought into this collaboration their expertise in telescope construction and fibre-composite structural design and manufacture. This interaction between the two can also be gathered from the perused correspondence and became the decisive factor in the materialization of this project. In particular, the German decision-makers at DLR were convinced that the link between these two experts could persuade their American project partner, NASA. The implementation of this ambitious project would not have been possible without the fundamental engineering know-how on hybrid materials, such as CFRP, GFRP or C/Si. In designing the fibre-composite component parts, primarily MAN Technologie was able to explore new avenues in numerically laying out hybrid structures and in design precision. The same applied to the manufacturing process involving prepreg technology and the handling of autoclave processes. Likewise, for the machining of CFRP components in particular, which have a high wear potential determined by their material characteristics. Decisive knowledge was gained in this respect which later found applications in other orders in the aerospace sector as well. Building an airborne telescope to explore the Milky Way was per se an exceptional project.

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Despite the considerable developmental gain generated by the SOFIA project, the involved companies, such as MAN Technologie in particular, noted considerable deficits in the organization and financial handling of the project by the contracting agencies. In evaluating the SOFIA project, several aspects have to be considered. For one, remarkable technical solutions were found, which distinguish the project as a technical milestone in in-flight astronomy. For another, tools to look into the universe were created. However, it is also necessary to point out the problems encountered throughout the execution of the project. There were constant alterations to the technical demands made by the clients with regard to the efficiency parameters of the overall structure or the telescope as a scientific instrument. The disbursements of project funds were often delayed and there were considerable decision-making weaknesses in the approval processes in the relevant German ministries. All of this resulted in an average of ten percent of the developmental costs having to be borne by the private companies involved in order to avoid contractual penalties. The key to this project was the pooling of technical expertise, however. The network dynamics moved the project forward and allowed various weaknesses to be overcome. The political will in the USA and Germany as well as an appropriate development budget also contributed towards its implementation but was partly dispensed to the disadvantage of German companies. The SOFIA project clearly demonstrates the product quality that can now be achieved with composite materials and hybrid material structures. Although there is still an information deficit about the versatile “world” of composites among the broader public, it can be established that this group of materials need not shy away from any comparison with other materials, not even with metals. On the contrary, the integration or combination of different materials into a new material with more advantageous properties will lead to even more individuality and precisely fitted custom-made solutions in the future. Summary of my answers to the guiding questions First guiding question—When and where were composite materials first developed and utilized with industrial application as the specific purpose in order to attain new performance thresholds especially as lightweight or high-performance structural materials? Plans for industrial exploitation of presstoff materials were drawn up for the first time with an eye to the product divisions of lightweight construction and structural materials within the framework of the strategic alliance between Römmler AG and Dynamit AG. The conception of a serially produced presstoff-based car body, as presented in Sect. 4.3.1, identifies the product and the location sought by this guiding question. Second guiding question—Is it possible to identify central players in this context who drove the development process forward as key figures? The individuals identified as central actors by means of network analysis for the first and second half of the twentieth century have already been presented (see Sects.

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4.3.2.1 and 5.5) and are summarized below. It should be noted here that this is a selection of people who were identified through the sources available for this study, and therefore no claim can be made to completeness. In the following are listed actors from the first half of the twentieth century, who are to be regarded as central within the context of the developmental process of composite materials, in particular fibre composites, in various areas. Due to the volume of data, only German actors could be considered here, exceptions being Baekeland for the first half of the century and Tsai for the second half. Leo Hendrik Baekeland (entrepreneur, Bakelite Gesellschaft), Eberhard Römmler (entrepreneur, Römmler AG), Albert Kuntze (Römmler AG), Gustav Leysieffer (Dynamit AG), Paul Müller (Dynamit AG), Enno Heidebroek (TH Dresden), Paul-August Koch (TH Dresden), Friedrich Tobler (TH Dresden), August Thum (TH Darmstadt), Richard Vieweg (TH Darmstadt), Gerhard Lucas (AEG), Paul Brenner (DVL), Wilhelm Küch (DVL), Kurt Riechers (DVL). For the second half of the twentieth century, according to my network analysis, this central position applied to the following individuals: Hermann Nägele (TH Stuttgart), Richard Eppler (TH Stuttgart), Manfred Flemming (Dornier), Ulrich Hütter (TH Stuttgart), Stephen W. Tsai (Stanford University), Gert Hintersdorf (TH Dresden). Third guiding question—How did developers and engineers treat composite materials within the context of the processes of design and application? The attitude of developers and engineers towards composite materials can largely be seen as ambivalent. For example, in the 1930s the developers at the DVL initially had to fight for acceptance of composites as a suitable structural material compared to metallic materials. This had changed only minimally by the time the Airbus A380 entered service. Neither in the public perception nor among technical experts were composites, especially fibre composites, seen as real alternatives in materials technology. The certification of the CFRP air-brake flap, described in Sect. 5.2.1, is a good example of this. It took the bold personal initiative of the chief developer Manfred Flemming to install the component without official approval for the way finally to be paved for fibre composite materials into the field of structural high-performance engineering. Although there are now many fields of application with these “material constructions”, a certain ambivalence about 20thcentury developments in materials technology can still be observed among developers and engineers and the manner in which they should be handled and applied, as was also evident in the interaction between Kärcher and Muser within the SOFIA project. Fourth guiding question—How do the developments of hybrid materials in the two German states—the Federal Republic of Germany (FRG) and the German Democratic Republic (GDR)—compare with each other? The level of knowledge on either side after 1945 can be regarded as equivalent until into the 1960s, as I have argued in the expositions in Sects. 5.3 and 5.3.3. This is because it was furthered by specialists who had been employed in aircraft and armaments production

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within the nazi system. The growing isolation and lack of materials and resources in the GDR upset this constellation. Although research in the field of composite materials continued to be pursued, the research there increasingly concentrated on theoretical issues or numerical problems. The GDR produced its own GFRP. High-quality fibres had to be imported. The Federal Republic was additionally capable of generating high-quality products in the context of CFRP in particular. Fifth guiding question—Are key stages in the development of composites or hybrid material systems identifiable? My study on hybrid materials has revealed numerous overlapping developments, particularly in the research fields of fibre materials and plastic materials. But it has also presented a multifaceted wealth of fields of application and products. Despite fluid transitions between them, they can nevertheless be clearly depicted in a series of developmental phases from the initial beginnings in this area in the early nineteenth century to the present day. The stages set up here are identical only in a few points with the categories presented in the publication from 2002 by Tim Palucka and Bernadette Bensaude-Vincent (see Sect. 1.3), because their paper has focused exclusively on the US materials market of the twentieth century. Thus, a number of the materials examined in the present study, such as the plastic masses or the early work on GFRP in Germany of the 1940s, were not the focus of their study at that time. First phase—Generating the base substance—the plastic masses, ca. 1820–1910 The plastic masses constitute the base of modern composite materials. In the nineteenth century they already manifested the product-specific characteristics of the material classes of laminate composites and fibre composites which are still current today, as described in Sect. 3.1.1. However, the carrier matrices of these materials were mainly still modified natural products or semi-synthetic resin systems. The market for plastic masses was already crowded at the turn of the century, with around twenty base materials falling under this category of plastic compounds. Depending on the base material, up to forty chemically modified special products were produced under a wide variety of brand names. Second phase—Supporting matrices, ca. 1910–1930 The second phase of composite materials was dominated by bakelite products, which controlled the market until the 1930s together with the first products of polymer chemistry. The expiration of the heat-pressure patent led to a differentiation of bakelite products, as shown in Sect. 4.3, which gained momentum with an upswing in the press technology. This is where the step from bakelite to the particle composite was taken, which finally qualified as a high-performance laminate composite.

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Third phase—Reinforcing materials, ca. 1930–1945 The period up to 1945 can be regarded as the third phase of hybrid materials. The generation of reinforcing materials came into particular focus. The definition of glass fibres, as described in Sect. 4.4.1.1, introduced a new quality into the field of composite materials. An emancipation also occurred with the new-found ability to exploit glass fibres. The second and third phases of composites thus also cast a bridge to modern high-performance materials. The supporting matrix was decisively improved within the context of polymer chemistry and ended up with carbon fibre as its high-performance reinforcement. Fourth phase—Restart and exploitation of GFRP—numerical analysis, ca. 1945–1965 In this phase, the knowledge gathered from multiply validated research findings of the final years of World War II began to be implemented. In particular, as described in Sect. 5.1, glass-fibre-reinforced plastic became the new high-performance composite material. At the same time, within the context of the Sputnik shock of 1957, the search began for new materials for space travel. Ceramic composites thus experienced a quite considerable boost and were the subject of targeted research. The finite element method (FEM) was applied to structural calculations, which led to a streamlining of technical equipment and ultimately brought the aspect of lightweight construction into the focus of research and development. Fifth phase—Development and differentiation of composites, ca. 1965–ca. 1990 As described in Sect. 5.2.1, during this period FEM was largely used to redefine design requirements for technical equipment. FEM was first applied to fibre composites at the end of the 1960s, which ultimately dynamized structural lightweight design and computerbased layout of composite materials. Many developments of the 1970s came to completion during this period, and the search began for new applications, especially in the field of vehicle construction, but also in classical mechanical engineering. At the same time, glassfibre-reinforced plastics used in products for the recreational and sports industries came under scrutiny and underwent further developments, e.g. CFRP frames for bicycles. In this phase, there was a turn within the scope of intra- and extra-university research towards nature’s hybrid principles of action. Bionic applications and questions about nanostructures gained growing academic importance in the 1980s, and were profitably implemented in product technology, e.g. the lotus effect. At the end of the 1980s and the beginning of the 1990s, more and more specialized research fields emerged from these areas, such as nanotechnology and biotechnology. This was accompanied by technical imaging of biological systems. In this context, polymer nanocomposites were also the subject of a large number of theoretical and practical research projects.

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Sixth phase—Establishment of hybrid materials as high performers, ca. 1990–2005 The entry into service of the long-haul aircraft A380 built by the aviation company Airbus (see Sect. 5.2.2) marked the end of the fifth phase of hybrid materials. Its technical dimensions and augmented use of CFRP turned heads not only amongst technology enthusiasts, but also in society at large. In addition, its maiden flight was also the premiere for the new aerospace material Glare® , a laminate composite material made of glass-fibre-reinforced components and aluminium. The development of CFRP as the most efficient composite material up to that point with an above-average serial scope ended a long period of searching for a high-performance and widely applicable hybrid material. Seventh phase—Consolidation, ca. 2005 to date Since the deployment of the A380, materials research and numerous application industries have been particularly focused on lightweight construction. As explained in Sect. 5.5, the high load horizons and design freedom granted by hybrid materials, which technical textiles in particular make feasible, make them virtually indispensable in conceptions of new products. Sophisticated technical products that have appeared on the market after 2005 reflect this especially. Over fifty percent of their load-bearing structures consist of hybrid material systems. Examples include the BMW i3 electric car or the Airbus A350 XWB. In conclusion, it can be established that, as in many phases of the development of high-quality technical products, the quest for alternatives in materials technology often concentrated on hybrid materials, although the causes for this must be evaluated in a differentiated manner. The complex issue of shrinking colonial resources was the motor behind the plastic masses along with modernization, that is, the accelerating process of industrialization at the beginning of the nineteenth century, attended by many developments in mechanical and process engineering in the field of chemistry. Amongst other things, natural resins took on the function of supporting matrices and the bakelite boom ultimately spurred this trend on. The thirst for synthetic “plastic” (Kunststoff ), which was easy to manipulate and conveyed modernity, stimulated many industrial companies in this area to find ever more novel products and introduce new variants and individualized renditions of this material. The targeted use of such good moulding and individually workable materials as composites in prestigious industries like aviation was unstoppable. The search for structural materials on this basis, especially within the spectrum of presstoff materials, was undoubtedly attributable not only to their good shapability but also to the far more cost-effective use of machining techniques. This latter aspect became a lucrative alternative, especially in view of the otherwise so cumbersome and costly technology required for moulding metallic materials. Concentrated scientific exploration of the potentials offered by materials engineering led to advances in the joining technology in particular, that “Achilles’ heel” of fibre composites. This diachronic longitudinal study represents the first attempt to periodize the genesis of composite materials in the nineteenth and twentieth centuries. The knowledge

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gained in materials technology in each of its main specialties is considered and evaluated within its relevant socio-economic environment. Although exact material-technical requirements for the performance parameters of a given technical product often defined these developmental stages, the overall development proceeded in spurts and not in a targeted manner. May this study provide an impetus for further historical research into this large, multifaceted and increasingly important group of materials.

Appendix

Participants of the workshop on flying-wing aircraft in Cologne on January 18 and 19, 1937 of the Lilienthal-Gesellschaft für Luftfahrtforschung, Aerodynamics Section. Participant’s name

Institution

Dipl. eng. Alpers

Reich Ministry of Aviation (RLM)

Dr. eng. Lorenz

Reich Ministry of Aviation (RLM)

Dipl. eng. Kirchof

Reich Ministry of Aviation (RLM)

Dr. phil. Braun

Testing Station for Aircraft, Berlin (Prüfstelle für Luftfahrzeuge)

Kensche, engineer

Testing Station for Aircraft, Berlin

Dipl. eng. Ballerstedt

Central Testing Facility for Aircraft, Rechlin

Dr. eng. Kramer

DVL, Berlin

Dr. phil. Kupper

DVL, Berlin

Scheibe, head of aircraft building

Proving Ground for Troops, Zeithain

Dipl. eng. Kohler

Aerodynamic Testing Station, Göttingen (AVA)

Dipl. eng. Muttray

Aerodynamic Testing Station, Göttingen (AVA)

Dipl. eng. Seiferth

Aerodynamic Testing Station, Göttingen (AVA)

Dr. phil. Stüper

Aerodynamic Testing Station, Göttingen (AVA)

Dittmar, pilot

German Research Institute of Glider Flight, reg.assoc., Darmstadt

Dipl. eng. Hubert

German Research Institute of Glider Flight, reg.assoc., Darmstadt

Dipl. eng. Krämer

German Research Institute of Glider Flight, reg.assoc., Darmstadt

A. Lippisch, engineer

German Research Institute of Glider Flight, reg.assoc., Darmstadt

© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Fachmedien Wiesbaden GmbH, part of Springer Nature 2023 A. T. Haka, Engineered Stability, https://doi.org/10.1007/978-3-658-41408-5

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Appendix

Participant’s name

Institution

Dipl. eng. Roth

German Research Institute of Glider Flight, reg.assoc., Darmstadt

Prof. Dr. Scheubel

Professorship for aeronautics and flight technology Darmstadt polytechnic (TH)

Commander Dinort

Cologne Airport

Lt. W. Horten

Cologne Air Base

R. Horten, Non-commissioned officer

Cologne Air Base

Dr. eng. Barth

Dornier Metallbauten GmbH, Friedrichhafen on Lake Constance

Berger, grad. eng

Gothaer Waggonfabrik

Richter, constr. eng

Gothaer Waggonfabrik

Wengrich, engineer

Gothaer Waggonfabrik

Dipl. eng. von Doepp

Junkers Flugzeug- und Motorenwerke AG, Dessau

Dipl. eng. Quick

Junkers Flugzeug- und Motorenwerke AG, Dessau

Prof. H. Focke

Focke-Wulf Flugzeugbau AG, Bremen

Dipl. eng. Günther

Heinkel Flugzeugwerke GmbH, Rostock

Dr. Hertel, director

Heinkel Flugzeugwerke GmbH, Rostock

Dipl. eng. Horn

Siebel-Flugzeugwerke KG, Halle (Saale)

Regelin, engineer

Henschel Flugzeugwerke GmbH, Berlin

Stender, engineer

Hamburger Flugzeugbau GmbH, Hamburg

Dr. Leysieffer, operations director

Dynamit AG, Troisdorf

Ludewig, operations manager

Dynamit AG, Troisdorf

Dipl. eng. Dominke

Lilienthal Society

Dipl. eng. Rackow

Lilienthal Society

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Name Index

A Aldrin, Buzz, 312 Alfeis, Carl, 178 Ambros, Hans, 270 Aristotle, 84 Arndt, Paul, 165 Arnold, Henry Harley, 254 Asplund, Arne Johan Arthur, 90

C Cahn, Robert W., 7 Chamberland, Charles, 252 Charles, Lewis, 73 Clay, Henry, 72 Comte de Buffon, Georges-Louis Leclerc, 108 Conen, Helmut, 265, 270 Coulomb, Charles Augustin de, 275 Cuntze, Ralf, 275–277

B Baade, Brunolf, 281, 282 Bachmann, Johann Georg, 71 Baekeland, Leo Hendrik, 9, 113, 160, 318, 337 Baeyer, Adolf von, 113 Balfour, Herny, 67 Beck, Adolf, 19 Beck, Georg, 158 Bellingrath, Ewald, 111, 318 Bensaude-Vincent, Bernadette, 7, 338 Bergmann, Max, 170 Betz, Albert, 245 Blenk, Hermann, 261, 266, 331 Bobeth, Wolfgang, 181, 182 Böhmer, Georg Rudolph, 166, 323 Bollenrath, Franz, 59, 171, 257, 331 Braun, David, 39 Braun, Dietrich, 9 Brehmer, Lothar, 282 Brenner, Paul, 13, 14, 41, 160, 170, 324, 337 Brügmann, Alfred, 95 Buchli, Viktor, 37

D Dederichs, Matthias, 10 Dell, Christian, 41, 43 Doecker, Johann Christian Clemens, 102 Doetsch, Heinrich, 262, 266, 279 Dubus-Bonnel, Ignace, 178 Duhamel du Monceau, Henri Louis, 108

E Edison, Thomas Alva, 89 Ehrenstein, Gottfried W., 25 Einstein, Albert, 94, 101 Eitner, Heinz, 284 Endres, Wilhelm, 59 Eppler, Richard, 258, 314, 333, 337 Eresos, Theophrastos of, 84 Escales, Ernst Richard, 116 Etrich, Ignaz (Igo), 225, 329

F Felde, Willi, 297, 333 Figuier, L., 82

© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Fachmedien Wiesbaden GmbH, part of Springer Nature 2023 A. T. Haka, Engineered Stability, https://doi.org/10.1007/978-3-658-41408-5

393

394 Fischer, Friedrich, 111 Flemings, Merton C., 7 Flemming, Manfred, 5, 28, 32, 44, 262, 266, 269, 270, 299, 314, 331, 337 Föppl, August, 94 Ford, Henry, 255 Franz, Anselm, 241 Frisch, Otto Robert, 222 Fronius, Stefan, 23

G Gabriel, Karl, 106 Gaine, W. E., 82 Gajewski, Fritz, 148 Genzel, Elke, 25, 281, 282 Gordon, J. E., 11 Göring, Hermann, 226, 228 Graf, Otto, 206–208 Grassmann, Wolfgang, 170 Gregorie, Eugene, 255 Grüninger, Gerhard, 270

H Haber, Fritz, 169 Hackett, Alfred George, 130 Hahn, Otto, 222 Haka, Andreas T., 1, 61, 75, 113, 257, 315 Hänle, Eugen, 259 Hanstein, Hans von, 157, 163 Hartmann, Carl, 178 Hashin, Zvi, 275, 277 Hassinger, Philipp, 18, 330, 331 Hatshepsut, Pharaoh, 65 Heidebroek, Enno, 16, 21, 23, 26, 41, 107, 141, 144, 150, 156, 157, 160, 174, 177, 183, 321, 322, 337 Hentschel, Klaus, 7, 11 Herbert, Ulrich, 215 Herzog, Alois, 168, 173 Herzog, Reginald Oliver, 169 Heydrich, Reinhard, 98 Hicks, Joseph Skean, 23 Himmelheber, Max, 41, 49, 93, 96, 97 Himmler, Heinrich, 98 Hintersdorf, Gert, 314, 333, 334, 337 Hirth, Wolf, 217 Horten, Dirk, 27, 222

Name Index Horten, Elisabeth Antoinette (née. aus dem Kahmen), 221 Horten, Helmut, 221 Horten, Klaus, 44 Horten, Max, 221 Horten (Mrs. Nickel), Gunilde, 218, 222 Horten, Reimar, 4, 27, 32, 50, 218–221, 223, 225, 231, 232, 235, 238, 244, 248, 328, 329 Horten, Sabine (née von der Groeben), 229, 328 Horten, Ursula (née Hoffmann), 221 Horten, Walter, 4, 27, 32, 44, 218–221, 223, 225, 231, 232, 235, 244, 245, 328, 329 Horten, Wolfram, 27, 221, 224 Huber, Maksymilian Tytus, 192 Hubert, Emil, 195 Hughes, Howard, 252 Hütter, Ulrich, 32, 197, 207, 259, 266–270, 279, 314, 330, 337 Hütter, Wolfgang, 50, 197–200, 206, 207, 209–211, 214, 268 Huyton, Corry, 215, 216 Huyton, Peter, 216, 217 Hyatt, John Wesley, 76, 316

J Jaeggi, Rahel, 42 Junkers, Hugo, 184, 225

K Kammler, Hans, 244 Kärcher, Hans Jürgen, 5, 302, 303, 306, 308, 334 Kármán, Theodore von, 254 Karmasch, Karl, 108 Keller, Friedrich Gottlob, 73 Kemp, Robert, 122, 123, 319 Kirchhoff, Gustav Robert, 191 Klein, Ursula, 7 Knacke, Theodor, 171, 195, 197, 242 Knauer, Berthold, 275, 281 Koch, Paul-August, 32, 160, 179, 180, 182, 183, 323, 330, 337 Kränzlin, Friedrich Wilhelm Ludwig, 168 Krische, Wilhelm, 9

Name Index Krüger, Franz August Otto, 169 Küch, Wilhelm, 160, 337 Kühnel, Reinhold, 21 Kuntze, Albert, 160, 337 Kunz, Nans, 305 Kwolek, Stephanie, 259

L Landmann, Hermann, 294, 333 Lattermann, Günter, 9 Lauche (Mrs. Menzel), Annemarie, 174 Lauer, Karl, 171 Leeuwenhoek, Antoni van, 85 Lefèvre, Wolfgang, 7 Leysieffer, Gustav, 149, 160, 205, 231, 235, 328, 337 Lippisch, Alexander, 225, 244, 328 Longren, Albin Kasper, 41, 49, 130, 134, 319 Lucas, Gerhard, 153, 160, 323, 337 Luxbacher, Günther, 15, 17, 323

M Macintosh, Charles, 78 MacKenzie, Donald, 39 Madelung, Georg, 206, 269, 294 Maier, Helmut, 7, 11, 324 Marten, Heinz, 24 Martin, Joseph D., 26 Martire d’Anghiera, Pietro, 78 Mason, William H., 89 Mehdorn, Walter, 20 Meirowsky, Max, 74 Meitner, Lise, 222 Melkus, Heinz, 31 Menzel, Klaus, 174, 183 Milch, Erhard, 229, 244 Mody, Cyrus, 26 Moebes, Wolfgang, 24 Mohr, Christian Otto, 275, 277 Müller, Ernst, 168 Müller, Paul, 151, 160, 337 Muser, Dieter, 29, 302, 303, 308, 334, 335 Mutschmann, Martin, 173 Myhra, David, 219, 236, 329

395 N Naaman, Antoine E., 312 Nägele, Hermann, 258, 314, 333, 337 Nickel, Karl, 27, 220, 223, 231, 244, 329 North, John Dudley, 41, 49, 127, 128, 319

O Obermiller, Julius Rudolf, 169 Opitz, Herwart, 156 Ostwald, Wilhelm, 169

P Pabst von Ohain, Hans Joachim, 241 Palucka, Tim, 7, 338 Papin, Denis, 252 Parkes, Alexander, 76 Parkyn, Brian, 24 Patterson, Gary, 9 Paul, Burton, 276 Payen, Anselme, 80 Pietsch, Edgar, 23 Pinten, Peter, 205 Pohl, Oswald, 106 Poumarède, J. A., 82 Prandtl, Ludwig, 244, 245 Puck, Alfred, 274–276

R Radkau, Joachim, 10 Regener, Erich, 196 Reißner, Hans Jakob, 192 Reinhardt, Hans W., 313 Reitsch, Hanna, 28, 227, 229 Rekhmire (vizier), 64 Richthofen, Manfred von, 88 Riechers, Kurt, 160, 187, 337 Riemerschmid, Richard, 87, 317 Rommel, Erwin, 226 Römmler, Eberhard, 160, 337 Roth, Siegfried, 265 Ruth, Dirk, 211 Ruth, Frits, 211, 215

S Satlow, Günter, 179, 180, 183

396 Sauckel, Fritz, 268 Sauerbier, Gerhard, 210 Schäfer, Jakob Christian, 72 Scheidhauer, Heinz, 220 Schieber, Walther, 268 Schiebold, Ernst, 17 Schiffer, Michael, 39 Schilling, Ernst Carl Magnus, 168 Schlack, Paul, 195 Schlichting, Hermann, 261, 266 Schmid, Alfred, 49, 92, 93, 95, 98 Schmid, Erich, 22 Schmidt, Ernst, 261 Schmitz, Hermann, 148, 151 Schürmann, Helmut, 25 Scott, Mackay Hughes Baillie, 103 Seddon, John W., 130 Segond, Alfred Léon, 109 Selinger, Peter F., 219 Sierakowski, Robert, 25 Skibo, James, 39 Smith, Cyril S., 6 Spitteler, Adolf, 9 Staudinger, Hermann, 9, 49, 80, 116, 134 Stock, Alfred, 222 Straßmann, Fritz, 222 Strebel, Hermann, 223 Stüper, Josef, 245 Sudrow, Anne, 36

T Taylor, Thomas, 319 Teinský, Elisabeth, 178 Thielemann, Wilhelm, 191, 193, 266, 331 Thoma, Johannes, 94 Thonet, Michael, 210, 214 Thum, August, 21, 41, 160, 337

Name Index Thutmose III, Pharaoh, 64–66 Thutmose II, Pharaoh, 65 Tobler, Friedrich, 32, 160, 166, 168, 170, 172, 174, 176, 177, 183, 323, 337 Tsai, Stephen W., 192, 274, 314, 337 Tutankhamun, Pharaoh, 85 Tylecote, Ronald Frank, 7

U Udet, Ernst, 95, 226, 228, 229, 232, 328 Ulfers (engineer), 108 Ungewitter, Claus, 153

V Vidal, Eugene Luther, 252 Vieweg, Richard, 156, 160, 190, 193, 322, 337 Vinson, Jack, 25 Voigt, Pamela, 25

W Wachsmann, Konrad, 101, 102 Wajcman, Judy, 39 Weigel, Wolfgang, 22 Weltzien, Wilhelm, 169 Wende, Alfred, 24, 275 Werner, Jochen, 282 Westinghouse, George, 121 Wittkowsky, Carl, 85, 86, 317 Wolff, Gertrud, 173 Wu, Edward Ming Chi, 274 Wyss, Oswald F., 95, 97

Z Zeuner, Gustav Anton, 111, 318

Index

A Actien Gesellschaft der Gerresheimer Glashütte, 180 Action cross-section criterion, 276 Aeroacoustics, 310 Aerodynamische Versuchsanstalt (AVA), 227, 245 Aeromold process, 252 Aeronautical material, 19 Aeronautical research, 185, 194, 231, 279 Aeroplane tailless, 221 wing, 205 Aeroplane (magazine), 128 Aerospace sector, 311, 314 Agave fibre, 188 Aggregate 4 (V-2 rocket), 196 Airborne astronomy, 310 Airbus A310, 271, 272 A350 XWB, 274, 278, 280, 313 A380, 34, 272, 280 A400 M, 28 Aircraft bulkhead, 308 Aircraft construction, 83, 88, 98, 99, 118, 121, 122, 125, 128, 130, 185, 204, 221, 226, 278, 289, 294 Aircraft design, 220, 223 Aircraft designer, 207 Air vessel, 212 Akaflieg, 258, 261 Braunschweig, 260, 279, 331 Karlsruhe, 96 Stuttgart, 258, 294, 330, 333

Akalit, 78 Albany Billiard Ball Company, 76 Albatros Flugzeugwerke GmbH, 88 Albumine, 80 Aligned-fibre shell construction, 205 Alkali glass, 178 Alkali-lime glass, 178 Allgaier-Werke GmbH Uhingen, 259 Allgemeine Elektricitäts-Gesellschaft (AEG), 117, 153, 179, 201 Allied Control Council Directive No. 25, 194, 257, 258, 293 All-metal aeroplane, 184, 189 All-wing aircraft (see Flying wing), 45 Aloe fibre, 188 Alpha Jet, 5, 28, 50, 59, 262, 265, 266, 270, 271, 279 Alte-Herren-Vereinigung, alumni association, 174 Alumina, 80 Aluminium, 52, 185, 237, 313 Aluminium lithium alloy, 273 American Institute for Conservation of Historic and Artistic Works, 248 Ames Research Center, 301 Anisotropic material, 280 Anthropology, 38 Apollo mission, 197, 242 Aramide, 53, 259 Aramide fibre, 259, 279, 297, 299 Aramide-Fibre-Reinforced Plastic (AFRP), 272, 297 Arbeitsgruppe Kunststoff-Segelflugzeug, 295 Arbeitskreis für Faserverstärkte Kunststoffe, 14

© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Fachmedien Wiesbaden GmbH, part of Springer Nature 2023 A. T. Haka, Engineered Stability, https://doi.org/10.1007/978-3-658-41408-5

397

398 Arbeitskreis Kunststofftechnik der VDI-Gesellschaft, 52 Archaeology, 38 Archaeometallurgy, 7 Archiv der Faserforschung, 176 Armament, 150, 154, 184 Armaments industry, 215 Army, 160 Art, 8, 64, 65, 69, 70, 116, 120 Artefact, 37, 38 Artificial wood (Kunstholz), 91 Asbestos, 81, 115, 180 fibre, 180 Aspect ratio, 202 Assault rifle MP 43, 161 MP 44, 162 ASTRALON, 235, 249 Asymmetrical shell geometry, 206 Attire accessories, 118 Auschwitz, 104 Blechhammer (satellite camp), 104 Heydreck (satellite camp), 104 Autarky, 150, 171, 176 Autoclave, 71, 311 Autographic Kodak Special, 124 Automobile design, 118, 314 Auto Union AG, 58, 151, 322 Aviation, 319 Aviation expert, 98

B Bakelite, 9, 12, 47, 53, 57, 74, 114, 115, 121, 124, 134, 146, 185, 319 Bakelite Company, 116, 117, 320 Bakelite Gesellschaft, 43, 116 Bakelite resin, 47 Balloon material, 195 Balsa wood, 251 Bank der deutschen Luftfahrt AG (Aerobank), 95 Bankhaus Kapff, 95 Bark, 67 Barracks, 98, 103 construction, 100 type 20 601 (BfH), 104 type 260/9 (OKH) horse stables, 104

Index type 263/9 (OKH) vehicle and equipment shed, 104 type 265/9, 106 type RL IV, 103 Barring layering, 86 Baryte, 81 Basic materials testing, 206 Bast fibre, 168 Bauhaus, 43, 101, 120, 184 Bayerische Motoren Werke Aktiengesellschaft (BMW), 34 Bearings, 16, 82, 140 plain or slide, 21, 76, 107, 111, 140 Bearing shell, 110 presstoff, 20 Becker van Hüllen (press manufacturer), 213 Beech, 86 Beech veneer, 201, 205, 206, 208 Bending, 206 load, 208 stress, 195, 205 test, 208 Bentwood process, 210 Betweenness centrality, 32 Bevollmächtigter für Holzbau, 103 Bible, 66 Billard ball, 76 Billiard Ball Company, 316 Binder, 107 Bionics, 2 Biopolymer matrix, 313 Bisterfeld & Stolting Radevormwalde, 153, 187 Blended fabric, 259 Blocking angle, 210 Blocking layering, 85 Blohm & Voss BV 246 (“Hagelkorn”), 99 Blood, 80 Blumberg & Co, 161 Boeing, 133, 278 747, 303, 308 747 SP, 301 Bölkow, 259 Bolt, 130, 212 Bonding, 122, 126 agent, 317 temperature, 211 Bone, 68 Bone meal, 61, 76 Boron fibre, 18, 279

Index Boron-Fibre-Reinforced Plastic (BFRP), 261 Botanischer Garten Dresden, 174 Boulogne-sur-Mer, 222 Boulton & Paul aircraft, 128 P.3 Bobolink, 128 Boundary friction, 144 Brake parachute, 197 Brick, 63 British Plastic Federation, 24 Brömel & Söhne, 208 Bronze, 140 Brückner, Kanis & Co., 111, 145 Building industry, 25, 48, 49, 62, 64, 65, 69, 73, 84, 88, 180, 293, 312 Building material, 63 Building paper, 73, 74 Buna rubber, 79 Bundesamt fürWehrtechnik und Beschaffung (BWB), 270 Bundesministerium der Verteidigung (BMVg), 259, 264, 266, 267, 271, 280 Bundesministerium für Forschung und Technologie (BMFT), 302 Bundeswehr, 271 Bündische Jugendbewegung, 94 Bursting test, 195

C Cabin-floor panel, 100 Calibration, 206 Carbamide resin, 120 Carbon concrete, 312 Carbon fibre, 63, 64, 259, 278, 279, 299, 313 Carbon-Fibre-Reinforced Plastic (CFRP), 11, 18, 34, 63, 261, 264, 265, 272, 274, 278, 297, 300, 302, 306–308 Cardboard, 69 Carinhall, 228 Carl Zeiss West, 304 Carpentry, 84, 246, 247 Casein, 9, 80, 88, 91, 117, 134 Casein formaldehyde, 9, 76 Casein glue, 86 Cassegrain telescope, 301 Caustic soda, 80 Celluloid, 8, 76 Celluloid Manufacturing Company, 76

399 Cellulose, 49, 75, 76, 79, 84, 117, 136 Cellulose derivative, 118 Cellulose plastic, 74 Cement, 76, 80 Centre wing box, 272 Ceramic matrix, 313 Ceramic Matrix Composite (CMC), 54, 300, 314 Ceramics, 7, 51, 76 C. G. Haenel, Suhl, 161 Chaîne opératoire, 39 Chalk, 71 Chemical joining technique, 209 Chemisch-Physikalische Versuchsanstalt der Marine, 160 Chipboard, 10, 19, 49, 91, 92, 94, 108 Christoph & Unmack, 49, 100–104, 106 Classical laminate theory, 34, 191, 192, 274 Classification, 48 Clay, 71, 73 Climate-chamber testing, 26 Closeness centrality, 32 Cloth covering, 195 Clothing, 73, 78, 118, 165, 171 CMEA states, 285 Coal powder, 116, 135, 320 Coal tar, 114 Colloid, 9 Colonial raw material, 75, 165 Colour analysis, 169 Compensatory payment, 215 Composite-adapted architecture, 278 Composite bow, 67, 69 Composite material, 5–8, 11, 16, 18, 24, 30, 33, 35, 37, 38, 47, 48, 50, 51, 55, 60, 61, 73, 78–80, 113, 194, 258, 298, 314, 317, 319 expert panel on, 14 hares, 120 Compressed thermoplastic, 161 Compressed thermoset material, layered (laminate presstoff), 253 Concentration camp, 106 prisoner, 215, 228, 229 Concrete, 64 Concrete foundation, 212 Coniferous wood, 165 Conservation product, 204 Construction, 62

400 Construction approach, 199, 202, 205 testing, 207 Contact corrosion, 278 Continental-Diamond Fibre Co., 129 Core material, 53, 58 Core wood, 67 Cork, 80, 96 Corps Altsachsen Dresden, 174, 183 Corrosion, 278 Corrugated cardboard, 289 Cotton, 51, 79, 81, 136, 165, 195 Crafts, 72, 92 Craftsman, 65 Cresol, 96 Cresol formaldehyde, 143 Cresol resin, 136, 163, 289 C/Si, 311 Cutocellulose, 80 Czechoslovakia, 298

D Defence logistics, 106 Defibrator process, 90 Deformation, 206 Degree centrality, 41, 45, 159 De Havilland Aircraft Company, 251 DH.91 Albatross, 251 DH.98 Mosquito, 251 De-icing, thermoelectrical, 278 Denazification, 229, 268, 269 Design, 158, 231, 240, 278 Desk lamp (Christian Dell), 120 Deutsche Agentur für Raumfahrtangelegenheiten (DARA), 302, 305 Deutsche Airbus GmbH, 272 Deutsche Forschungsanstalt für Hubschrauber und Vertikalflugtechnik, 267 Deutsche Forschungsanstalt für Luftfahrt (DFL), 259, 261 Deutsche Forschungsanstalt für Segelflug, 197, 227 Deutsche Forschungs- und Versuchsanstalt für Luft- und Raum fahrt (DFVLR), 261, 270, 302 Deutsche Gesellschaft für Materialkunde (DGM), 13

Index Deutsche Institut für Textil-und Faserforschung, 169 Deutsche Luftwacht. Luftwissen, 30 Deutsches Forschungsinstitut für Textilindustrie, 168, 173 Deutsches Institut für Textilstoffe, 168 Deutsches Patentamt, 204 Deutsches SOFIA Institut Stuttgart, 301 Deutsche Studiengemeinschaft Hubschrauber, 266 Deutsches Wollforschungsinstitut (RWTH Aachen), 179, 180 Deutsches Zentrum für Luft- und Raumfahrt (DLR), 261, 301 Deutsche Versuchsanstalt für Luftfahrt (DVL), 13, 14, 30, 59, 137, 160, 170, 183–185, 187, 188, 193, 194, 227, 232, 239, 240, 253, 258, 262, 284, 299, 324, 325, 330, 337 Deutsche Werkstätten Hellerau, 87, 91 Deutsche Werkstelle für Farbkunde, 169 Diagnostics, 17 Diagonal plywood, 205 Diagonal veneer angle, 208 fibre of, 201 proportion of, 208, 209 Die billige Wohnung, 87 Digression calculation, 276 Dilecto, 130, 134, 319 DIN 4076, 94 4850, 232 7701, 57, 107, 147 7702, 107 7703, 107 EN 309 f., 92 Dornier, 28, 44, 213, 239, 262, 266, 314 Do 328, 271 Double-trapezoid wings, 225 Douglas Aircraft, 133 Draping, 71, 134, 151 Dr. Frenzel-Hahn principle, 182 Dry process, 90 DuPont, 259 Duralumin, 189, 190, 237, 242 Duramold process, 201, 251, 252 DYNAL, 151, 235, 237

Index Dynamit AG, 10, 43, 107, 148, 151, 159, 187, 193, 218, 232, 234–236, 242 Dynamit Nobel AG, 204, 205 DYNOS, 235, 249

E Eastman Kodak Company, 123, 319 Edge, 159 Egypt, 63 Eidgenössisch Technische Hochschule Zürich, 28, 44 Elasticity, 67 Elasticity modulus, 188, 208 Elastomer, 51 Elberfelder Farbenfabriken, formerly Friedr. Bayer & Co., 79 Electrical engineering, 114, 118 Electrical industry, 73, 147 Entwicklungsgemeinschaft Homogenholz GmbH, 95 Epoxy resin, 260, 287 Ergolith, 78 Ernst Heinkel Flugzeugwerke AG, 294 Erprobungsstelle Rechlin, 227 Ersatzstoffkultur, 15 Erwin Behr Wendlingen/Neckar, 206, 208 Erwin Kayser-Threde GmbH, 304 Esterification, 134 Ethnology, 38 Experimental equipment, 207 Extension, 206 Extermination camp, 106 Extruder, 78

F Fabric, 11, 47, 69, 140, 172 Fabric, reversed bending stress of, 195 Face material, coating, 53 Fachschule für Leichtbau, Dresden, 284 Fachschule für Werkstofftechnik, 285 Failure criterion, 274 Faraday Society, 9 Faserverstärkter Kunststoff (FVK), 113 Fatigue, 3 Fatigue strength, 195 Federal Republic of Germany (FRG), 6, 290, 297, 298, 305

401 Felde FL-60 Dresden, 297 Fiber Reinforced Cement Composite (workshop), 313 Fibre, 81 milled, 81 semi-synthetic, 171 Fibre-aligned construction, 208 Fibre-aligned lightweight wood-derived material, 214 Fibre-aligned shell construction, 206 Fibre alignment, 50, 53, 206, 208, 214 Fibreboard, 10, 89, 96 Fibre breakage, 195 Fibre chemistry, 169 Fibre composite, 59, 107 Fibre Composite Material (FCM), 3, 6, 19, 24, 48, 52, 130, 134, 252, 279 Fibre fabric, 165, 188 Fibre failure, 275 Fibre-load angle, 86, 107, 108, 317 Fibre mat, 165 Fibre material, 63, 72, 73, 80, 166, 172, 188 Fibre-matrix bond, 62, 177 Fibre plant, 65, 79, 172 Fibre-plastic composite, 52 Fibre-reinforced composite material, 14, 202 Fibre-Reinforced Polymer (FRP), 49, 64, 71, 74, 81, 121, 124, 125, 135, 165, 258, 267, 274, 275, 277, 278, 298, 303, 314 Fibre reinforcement, 4, 6, 54, 62, 65, 178 Fibre research, 173 Fibre substitute industry, 165 Fibre suspension, 90 Filament, 69, 165 Filler, 12, 81, 114, 115, 120, 123, 135, 187 Finite element method, 264 Fish bladder, 68 Fish bone, 68 Flax, 72, 79, 165, 313 Flight equipment, 207 Flying wing, 5, 44, 50, 219, 221, 225, 228, 231, 236, 239, 240, 248 Foam wood, 96, 99, 100 Foam wood–plywood sandwich, 99 Foam wood-sandwich rotor, 100 Foam wood–textile sandwich, 99 Focke-Wulf, 189, 239, 240 Forced labourer, 98, 211, 215

402 Ford, 255 Foreign labourer, 211, 215, 217 Formaldehyde, 78, 96, 113, 117 Formholz, 206 Forschungsanstalt Graf Zeppelin, 171, 195, 197, 207, 269 Forschungsinstitut für Textiltechnologie Karl-Marx-Stadt, 288 Sorau des Verbandes Deutscher Leinen-Industrieller, 170 Forschungsstelle für Physik der Stratosphäre (Friedrichshafen am Bodensee) in der Kaiser-Wilhelm-Gesellschaft, 196 Homogenholz, 96 Forschungs- und Konstruktionsgemeinschaft der Reichsleitung des Reichsarbeitsdienstes und der Deutschen Holzbau-Konvention (FOKORAD), 102, 104 Forschungszentrum der Luftfahrtindustrie, 284–286 Forstliche Hochschule Eberswalde, 100 Four-Year Plan, 150 Fracture criteria, 274, 275 Fracture mechanics, 3, 277 Freie Deutsche Jugend (FDJ), 294 FS 24 Phönix, 258 Fuel containment, 204 Furniture industry, 118 Fuselage design, 98

G Galalith, 9, 76, 78, 316 Garland, 289 Gartenstadt (Hellerau), 103 Gas mask, 83 Gauwirtschaftsberater (economics expert), 268 Gearwheel, 76, 82 Gebrüder de Trey AG, 177 Gebrüder Himmelheber MöbelParkettbodenfabrik AG, 94 Gebrüder Spindler, 161 Gebrüder Thornet Bugholzmöbelfabrik, 210 Gelatine, 70 Gemini mission, 197, 242 General Bakelite Company, 116 Generalluftzeugmeister, 95, 227

Index German Democratic Republic (GDR), 6, 12, 42, 50, 52, 137, 281, 282, 285, 289, 294, 298 Gertrude device (Regener barrel), 196 Gesellschaft für Sport und Technik (GST), 294 Gestapo-Arbeitserziehungslager Oberleutensdorf-Maltheuern, 104 GFP (Glasfaserverstärkte Plaste, East German abbreviation for GFRP), 287 Glare®, 53, 273 Glasflügel Hütter H 301 Libelle, 259 Segelflugzeugbau GmbH, 259 Glass, 1, 7, 51, 76 Glass corrosion, 178 Glass fabric, 178 Glass fibre, 182, 194, 254, 258, 260, 288 Glass-fibre quality, 178 Glass-Fibre-Reinforced Plastic (GFRP), 8, 18, 24, 31, 50, 52, 63, 80, 171, 177, 178, 182, 183, 194, 253–255, 259–261, 267, 288, 295, 298 Glass-fibre woven fabric, 178, 179, 182, 194, 288 Glass-fibre yarn, 179 Glass filament, 178 Glass silk, 178, 179 Glass thread, 178 Glass wadding, 178 Glass wool, 178 Glass-wool presstoff sheet, 179 Glider, 31, 225, 250, 258, 287 construction, 50, 197, 293 Glue product, 204 Gluing, 207, 210 Gluten glue, 68 Goldmann AG, 205 Göller & Boshart, 204 Gothaer Waggonfabrik, 248 Grade quality, 206 Grahame-White Aviation Company, 128 Grasses (tropical), 96 Great Britain, 8, 251, 253, 290 Gross & Pertun, 204 Grumman Aerospace Corporation, 261 F-14 Tomcat, 261

Index H Half-timbered construction, 84 Han dynasty, 178 Hard fabric, 160, 162, 172, 182, 187, 188, 190 Hard fibre, 168 Hard fibreboard, 98–100 Hard paper, 53, 57, 188, 190, 237 Hardwood, 67, 189, 206 Hares, 120 Harex woven-glass plate, 183, 324 Haskelite Manufacturing Corporation, 252 Hauptring Kunst- und Preßstoffe, 13, 153 Heater wire, 212 Heat-pressure patent, 114, 115, 122, 138, 146, 185, 218, 233 Heeresabnahmestelle Velten, 161 Heeresbekleidungsamt, Army Clothing Office, 171 Heeresversuchsanstalt Bad Saarow, 196 Peenemünde, 196, 227 Heereswaffenamt, 156, 157, 161, 162 Heinkel, 239, 241 He 110, 99 He 219, 199 He 45, 185 Heinrich Diehl GmbH, 161 Heinrich Hertz Submillimeter Telescope, 306 Hemicellulose, 84 Hemp, 72, 165 Henschel, 239 Hermès, 300 Hide, 69 High-frequency heating, 212 High-voltage current, 118 Hille Motoren AG, 144 Hirth Motoren GmbH, 232 Historia plantarum, 84 Historiography, 35 Hochschule für Maschinenbau Karl-Marx-Stadt, 23, 285, 293 Hochschule für Schwermaschinenbau Magdeburg, 293 Hole-face strength test, 208, 209 Holig Homogenholzwerk Görlitz, 95, 98 Neustrelitz, 99 Hol’s der Teufel, 225, 232 Holz-Zentralblatt, 30

403 Home leave, 217 Homogeneous wood, 49, 93, 94, 98 Homogeneous wood material, 100 Homogenholz-Syndikat, 95 Honeycomb, 288–290 Honeycomb-sandwich construction, 290 Honeycomb sandwich panel, 290 Horn layer, animal, 67 Horten V-a, 219, 232–234, 236, 237, 239, 247 IX, 219, 246–248 IX V2, 219 IX V3, 247 Horten, Walter, 50 Hubble space telescope, 301 Hughes H-4 Hercules, 252 Hütter GmbH, 198, 206, 213 Hütter Hü 211, 197, 198, 200–202, 204, 210, 214, 215 Hybrid material, 6, 25, 55, 59, 60, 108, 194, 249, 279, 300, 312, 315 Hydrate cellulose, 82 Hydrochloric acid, 113 Hydromotor, 109 Hygroscopic property, 85, 86, 130, 161

I I.G. Farbenindustrie AG, 135 Auschwitz, 104 Iljuschin Il-14P, 283 Indene-coumarone resin, 114 Industrialization process, 6, 75 Industrial Revolution, 2 Ingenieurschule für Flugzeugbau, Dresden, 284 Insect infestation, 204 Insert, 208 Institut de Radioastronomie Millimétrique (IRAM), 306 Institut für chemische Technologie synthetischer Fasern an der TH Breslau, 171 Institut für die Technologie der Chemiefasern Rudolstadt, 288 Institut für Faserforschung der Akademie der Wissenschaften der DDR, 288 Institut für Glastechnik des VVB Ostglas, 288 Institut für Technologie und Organisation, 285, 289

404 Institut für Werkstofforschung der Deutschen Versuchsanstalt für Luftfahrt, 171 Instruments and apparatus, 118 Insulation, 76, 100, 115, 130, 147, 178, 180, 190 Intercellular gaps in wood, 85 Interessengemeinschaft Deutscher Sperrholzfabriken, 88 Inter-fibre failure, 275 criterion, 275, 276 Inter-fibre fracture, 277 Interior component, 210 Interior design, 118 Iron, 51 Iron-reinforced concrete, 96 Isotropic material, 191, 277, 280 Ivory, 75, 76 dust, 76

J Jagdgeschwader Richthofen, 97 Jet engine, 200, 219, 241, 246 Jet turbine airliner, 282 Joining element, 209 Joining technology, 103, 122, 125, 130, 209, 238, 278 Junkers, 99, 239, 241 Jumo 004, 241 Jumo 222 AB-3, 199 Jute, 81, 165, 313 Jute–glass-fibre mixed fabric, 180

K Kaiser-Wilhelm-Gesellschaft, 15 Kaiser-Wilhelm-Institut für Arbeitsphysiologie, 83 Kaiser-Wilhelm-Institut für Bastfaserforschung, 15, 168 Kaiser-Wilhelm-Institut für Chemie, 169, 222 Kaiser-Wilhelm-Institut für Faserstoffchemie, 169 Kaiser-Wilhelm-Institut für Lederforschung, 170 Kaiser-Wilhelm-Institut für Strömungsforschung, 227, 261 Kammer der Technik, 12, 298 Kaolin, 81

Index Kaurite glue, 91, 96 Kelle und Hildebrandt Gm, 111 Kevlar, 259 Klepzigs Textil-Zeitschrift, 30 Kofferfiber, 82 Komponenten- und Experimentalprogramm, 264 Kriegsrohstoff-Abteilung des Kriegsministeriums, 165 Kuiper Airborne Observatory, 301 Kunstholz, artificial wood, 91, 116, 317 Kunststoffe, journal, 30 Kunststoff, terminology, 116

L Laid web, 64 Lamina, 275 Laminate, 53 Laminate composite, 53, 59, 131, 134, 237, 240 Laminated blockwood, 96 Laminated veneer furniture, 85 Laminate material, 59 Laminate presstoff, 136, 320 reinforced, 58 Landing flap, 201 Landing gear, 201 Landing parachute, 197 Landmann La 16 V1 Lerche, 295 La 16 V2 Heidelerche, 295 La 20, 296 La Silla telescope, 308 Layered composite, 53, 67 Layered material, 58, 60 Layered moulded material, 137 Layered moulded wood, 210 Layered presstoff, 82 Lead glass, 178 Leading edge, 99 Leather, 51, 170 Legion Flying Meeting, 132 Leichtflugtechnik Union, 259 Les cellules, 80 Libelle-Laminar, 287 Life-cycle assessment, 35 Light metal, 213 Lightweight construction, 84, 121, 129, 319 Lightweight fibre material, 237

Index Lightweight material, 5 Lightweight metal, 171 Lightweight wood composite, 50 Lightweight wooden construction, 204 Lignin, 84 Lignocellulose, 79 Lilienthal-Gesellschaft für die Luftfahrtforschung, 239 Lime, 80 Limewood, 206, 208 Linen, 79, 81, 168, 195 Linen industry, 170, 173 Linoleum, 96 Liquid polymer infiltration process, 300 Load, introduction of, 278 Lockheed, 133 C-141 Starlifter, 301 Longitudinal-fibre veneer, 201 Long-range reconnaissance aircraft, 197, 214 Longren AK, 131 Lower shell, 201, 205, 206, 212 Lubricant, 26 Ludwigsluster carton, 70, 71 Luftfahrtanlagen GmbH Berlin (LAG), 95, 100 Luftfahrtforschungsanstalt Ainring, 196, 197 Luftfahrtforschungsanstalt Hermann Göring, 261, 284 Luftfahrttechnisches Handbuch (LTH), 5, 53, 271 Luftkriegsschule 3 Wildpark/Werder, 231 Luftschiffbau Zeppelin GmbH, 208, 213 Luftwaffe, 160, 177, 182, 233 Luxuspapierfabrik Heilbrun & Pinner Halle an der Saale, 289 LZ 127 Graf Zeppelin, 137

M M35 Stahlhelm, 83 Mâché, 69, 73 Machined furniture, 87, 91 Machine element, 16, 140, 160 Mackintosh, 78 Macromolecule, 135 Magnesium, 19 MAN, 29 GHH, 302 Technologie, 302, 305, 309 MAN Augsburg, 300

405 MAN GHH, 310 Manoeuvring air-brake flap, 265, 270, 298, 299 Manufacturing process, 200 Marble flour, 81 Maschine element, 140 Maschinenfabrik und Eisengießerei Ing. J. Vlatavský, 162 Masonite process, 89 Masse, plastische, 81 Masses, the plastic, 48, 49, 57, 75, 79, 80, 89, 91, 117, 135 Mat, 136, 288 Matchbox Program, 231 Material, 2, 3, 5–7, 11, 37, 61, 62, 69, 80, 82, 121, 285, 306 Material behaviour, 208 Material composite, 16, 52 Material constructions, 312 Material culture, 38 studies, 37, 39, 40, 46 Materiality, 38, 39, 46 Material, manufacturing, 16, 55 Material parameter, 3, 61, 108, 136, 182, 189, 208, 232, 240, 311 determination, 202 Materialprüfungsamt St. Gallen, 175 Materialprüfungsanstalt Berlin, 100 Materialprüfungsanstalt Stuttgart, 206–208 Materials group of, 35 Materials design, 70, 135, 219, 221 Materials diagnostics, 17, 195 Materials failure, mechanical medial, 195 Materials, group of, 48, 75 Materials science, 1, 6, 7, 11, 17, 47, 298, 299, 307 Material statics, 214 Materials testing, 17, 195, 202, 210 Materials testing station, 17, 169, 174 Material stiffness, 309 Material systems, 315 Material turn, 37 Matrix, 30, 47, 54, 63, 107, 121, 135, 137, 165, 237, 249, 317, 319 Matrix material, 80, 81, 113 Mauser firm, 200 Max-Planck-Gesellschaft, 306 McCook Field, 131

406 Mechanical engineering, 16, 20, 83, 118, 133, 141, 190, 282 Mechanical joining technique, 209 Mechanical wood pulp, 237 Medium quality grade, 206 Megacity vehicle, 34, 280 Meister des Sports, 31 Mercury mission, 197, 242 Messerschmitt AG, 99, 244 Me 108, 99 Me 109, 99, 202 Me 109 G-6, 217 Me 109 K, 198, 210 Me 110, 213 Me 321, 204 Me 323 (Gigant), 204 Messerschmitt-Bölkow-Blohm, 266 Metal construction, black, 278 Metal inlay, 125 Metallography, 7 Metallurgical industry, 84 Metallurgist, 316 Metallurgy, 7, 11 Micarta, 124, 127 Microscope, 85 Military, 132, 151, 167 Milkweed, 72 Milky Way, 301, 309 Mining industry, 84 Ministry of Supply, 269 Mixed-method design, 32 Mixed methods of construction, 237 Möbelwerken Niesky, 104 Modernity, 2, 48 Modern Plastics (journal), 30 Mohr-Coulomb hypothesis, 277 Mohr’s criterion, 275 Moisture, 208 Mojave Desert, 310 Monocoque, 129, 131, 202 Mother material, 55 Moulded-fibre part, 99 Moulded plywood, 210, 214 Moulded wood, 206, 208, 210, 214 Mud, 163 Mulberry-silk-moth silk, 195 Multiaxial non-crimp fabric, 86 Multilayer composite, 202 Multimaterial design, 122, 237

Index Musical instrument, 118

N Nasmyth tube, 308 National Aeronautics and Space Administration (NASA), 193, 301–303, 305 National Air and Space Museum - Smithsonian Institution, 28, 248 Nationale Volksarmee (NVA), 281 National socialism, 173, 175, 194, 227, 250 Nationalsozialistische Deutsche Arbeiterpartei (NSDAP), 21, 98, 225, 228, 268, 269, 295, 333 Nationalsozialistische Fliegerkorps (NSFK), 295 Nationalsozialistischer Bund Deutscher Technik (NSBDT), 190 Nationalsozialistischer Lehrerbund (NSLB), 295 Nationalsozialistisches Fliegerkorps (NSFK), 97 NATO-Helicopter NH 90, 271 Natural fibre, 170, 171, 313 Natural-Fibre-Reinforced Plastic (NFRP), 313, 314 Natural material, 10, 35, 51, 75, 76, 313 Natural resin, 75 Natural silk, 195 Navy, 160 Neolithic, 61 early, 69 final, 61 Nepera Chemical Co., 124 Nettle cloth, 166 Nettles, 72, 166 Network, 5, 50, 124, 154, 156, 173, 206, 261, 270, 279 Network analysis, 31, 50 Network star, 32, 45 New Longren Airplane, The, 131 New Zealand flax, 177 Nile mud, 62 Nitric acid, 80 Nitrocellulose, 134 Node, 32, 159 Non-woven fabric, 90 Northrop, 134, 248 Nuclear fission, 222

Index Nuremberg Laws, 173

O Oberbefehlshaber der Luftwaffe, 228 Oberkommando der Marine (OKM), 111 Oberkommando der Wehrmacht (OKW), 106 Oberkommando des Heeres (OKH), 154, 157, 161, 162, 207 Oberschlesische Hydrierwerke AG, 104 Object, 37, 38 Observatory, 301 Occupying force, 216 Oeffentliche Seiden-Trocknungs-Anstalt zu Crefeld, 169 Öffentliche Prüfstelle für die Spinnstoffwirtschaft, 169 Omaha meeting, 132 Ontology, 7 Operational strength, 208, 210 Operation surgeon, 269 Optical industry, 118 Oral history, 41, 43 Orthotropic material, 192, 277 Osmosis, 9 Ostarbeiter, 217 Outdoor weathering, 26 test, 100, 232 Owens-Corning Fiberglas, 23, 253

P P-600 (glue), 205 Palaeolithic Age, 84 Panel structure, 103 Paper, 1, 69, 72, 122, 319 Paper-making, 72 Paper mill, 72 Paper net, 289 Paper pulp, 69 Paper ware, 72 Paper yarn, 166, 177 fabric, 195 Papier-mâché, 71, 72, 89 Parachute fabric, 195 Parchment paper, 82, 111 Parkesine, 76, 316 Particle composite, 53 Particulate composite, 53

407 Patent, 57, 58, 72, 76, 82, 92, 100, 109, 114, 115, 122, 179, 202, 235, 255 office, 204 secret, 204 PeCe fibre, 195 Pectocellulose, 79 Perlon, 195 Perlon fibre, 196 Pertinax, 74 Pertunol, 204, 205 Pflanzenkautschuk-Forschungs-und Anbaugesell, 176 Pfützer-Kunststofftechnik, 259 Phenol, 113, 117 Phenol formaldehyde, 74, 80, 88, 114, 115, 117, 118, 123, 130, 237 condensation process, 117, 146 Phenolic resin, 113, 116 Philosophy, 94 Photographic camera, 124 Pine wood, 205, 206, 208 Pitch, 80 Plant fibre, 171 Plaste, 20 aramidfaserverstärkte (GDR term for AFRP), 297 glasfaserverstärkte (GDR term for GFRP), 287 Plaste und Kautschuk (journal), 30 Plastic, 1, 7, 9, 30, 49, 51, 54, 76, 117, 138, 177, 252, 280, 318 boron-fibre-reinforced, 261 carbon-fibre-reinforced, 261 fibre-reinforced, 2 glass-fibre-reinforced, 287 semi-synthetic, 75 synthetic, 75 Plastic masses, the, 316 Plate theory, 191 Plenipotentiary on plastics, Bevollmächtigter für Kunststoffe, 156 Plywood, 10, 49, 50, 85, 86, 208, 214, 237, 248 composite, 206 panel, 98 plate, 201 Poland, 298 Polymer chemistry, 9, 11, 30, 49, 74, 80, 116, 127, 134, 165 Polymer matrix, 298, 307

408 Polymer Nanocomposites (PNC), 314 Polysaccharide, 9 Polystahl, 205 Poplar wool, 72 Porcelain, 1 Preßmasse, 57 Prepreg, 35, 272, 311 technology, 317 Press, 117, 119, 136, 140, 210, 211 Pressed mass, 117, 136, 161, 187, 320 Pressed material, 116, 214 Pressing duration, 117 Pressing pressure, 117 Press technology, 81, 89 Presstoff, 12, 18, 22, 57, 96, 116, 117, 143, 145, 149, 151, 160, 161, 163, 185, 202, 218, 232, 238, 240, 253, 260, 320 bearing, plain, 138, 140, 144, 156, 163 bearing, shell, 143 laminate, 137, 218 layered, 187–189 layered moulded, 137 panel, 202 reinforced, 58, 188–190 Pressure rams, 212 Pressure test, 208 Principle of composite materials, 315 Prisoner-of-war, 96, 97 Production, 48, 63, 65, 69, 81, 85, 89, 117, 119, 126, 127, 131, 134, 136, 140, 141, 149, 151, 188, 212, 254, 272, 278, 283, 311 Production technology, 206 Product life-cycle management, 2, 35, 39 Product-line analysis, 36, 40 historical, 36 Product series, 204 Professor im Reichsdienst, 257 PRONAOS balloon telescope, 306 Proportioning, 206 Prosthetics, 314 Protectorate of Bohemia and Moravia, 96, 156, 161, 162 Protein, 80 Prüfstelle für Gleitorgane des OKH, 154 Prüfstelle für Luftfahrtgerät der DDR, 286, 295 Puck criterion, 276 Pulp, 69

Index Pump jet propulsion, 109

Q Quality, 48, 62, 69, 119, 132, 136, 201 Quality grade, 206, 208

R Radar camouflage, 221 Radio telescope Mount Korek, 306 Rags, 72, 82, 136 Rag trade, 72 Raw material, 165 Raw materials card catalogue, 176 Reaktion propeller, 108 Recycling, 70, 278 Regener barrel, 196 Reich Ministry of Aviation, 171, 180, 188, 194, 197–200, 232, 236, 239, 240, 246, 269, 324 Reich Research Council (RFR), 177 Reichsamt für Wirtschaftsausbau, 153, 176, 180, 324 Reichsarbeitsdienst (RAD), 98, 103 Reichsbeauftragter für Homogenholz, 49, 97 Reichsbekleidungsstelle, 165 Reichsbeteiligte Homogenholz-Gesellschaft, 95 Reichseigne Hochdruckprüfanlage des OKM in Dresden, 111 Reichsforstamt, 96 Reichsleitung des NSDAP Mitgliedschaftsamt, 269 Reichsluftfahrtministerium, 28, 96 Reichsminister der Luftfahrt und Oberbefehlshaber der Luftwaffe, 100 Reichsminister für Bewaffnung und Munition, 95 Reichsminister für Rüstung und Kriegsproduktion, 158 Reichsministerium für Bewaffnung und Munition, 153 Reichsministerium für Rüstung und Kriegsproduktion, 156 Reichsstelle Chemie, 153 Reichswerke Hermann Göring, 104 Reinforcement material, 194 REOSC, 309 Research

Index history of materials science, 314 Resin canal, 84 Resin pocket, 117 Resin, rapid-press, 119 Resin system, 238, 252 Resin Transfer Moulding (RTM), 126 RESOPAL, 137 Rheinflugzeugbau, 259 Rheinisch-Westfälische Sprengstoff AG, 148, 233 Rheinmetall-Borsig, 99 Rib, 201, 205 Ribbon parachute, 197, 242 Rib web, 205 Rifle grenade, 161 Rigid airship, 317 Rigidity, 140 Ringbuch der Luftfahrttechnik, 188, 257 Rivet, 126, 130 Robotics, 314 Römmler AG, 43, 117, 120, 135, 137, 138, 143, 148, 150, 151, 158, 160, 162, 177, 183, 187, 193, 218, 234, 237, 320–322 Roving, 69, 136, 165, 288 Royal Aircraft Establishment, 262 Royal Flying Corps, 128 Rubber, natural, 9, 78 Rubber-plant research, 176 Rudder unit, 185 Rütgers AG, 116 RWTH Aachen, 294

S Salon de l’Aéronautique, 129, 134 Sand, 163 Sandwich composite, 100 Sandwich construction, 53, 67, 288–290, 292, 296, 298, 306 Sängerschaft Erato Dresden, 174 Sateen fabric, 99 SB 10, 262, 266 SB 9, 260 Schalenflügel, 206 Schempp-Hirth, 198, 207, 215, 217 Schmidt & Müller, Dresden-Striesen, 87 Schnellaktion Schweinfurt, 16, 23, 158 Schott AG, 309

409 Schütte-Lanz Holzwerk AG, 88 SL 1, 88 Schwachstellenauswertungszentrum (S.A.Z.), 163 Science Museum, London, 8 Screw anchor, 208 Secret agreement, 207 Seddon Mayfly, 130 Segmental construction method, 252 Selbstständiger Sonderring Kunst- und Preßstoffe, 153 Semi-finished fibre-composite, 233 Semi-finished product, 35, 47 Semi-monocoque construction, 202 Serial furniture, 88 Serial production, 212 Serum, 134 albumin, 88 Servotechna AG, 161 SEST telescope, 308 Shaping, 206 Shell, 205 Shellac, 80, 114 Shell body, 201, 206 Shell construction, 129, 202, 205 Shell curvature, 207, 208 Shell design, 205 Shell geometry, 206 Shells, crushed, 53, 115, 135 Shell thickness, 208 Shell wing, 206 Siebel-Flugzeugwerke Halle/Saale, 99, 191 Siebel Si 204, 100 Siemens-Schuckert AG, 100 Siempelkamp, 117 Silk, 81, 165, 169, 195 Sinew, 67 Sisal fibre, 188 Slat, 278 Slate flour, 81 Société Européenne de Propulsion, 300 Sodium paper, 289 Softwood, 206 Solid state physics, 11 Solid-wall design, 308 Solid wood furniture, 85 Sonderkommando IX, 223, 229, 231, 246 Sonder-Kraftfahrzeug 9, 162

410 Sonderpreßmasse Nr. 3721, 161 Soybean car, 255 Space research, 197 Spar flange, 205 Spitfire, 253 II, 253 Sports car RS 1000, 31 Sprelacart, 137 Spun glass, 178 SS (Schutzstaffel), 104, 216, 229 SS-Wirtschafts-Verwaltungshauptamt, 106 Staatliches Materialprüfungsamt, 147 Stanford University, 314 Star plywood, 86 Statics, 206 Stationery, 118 Statuary pasteboard, 73 Steel, 51, 280 Steward Observatory, 303 Stiffness, 202 Stoffgeschichte, 33, 35, 40 Stoffökonomie, 15 Stone, 84 Stone dust, 81 Strahlstoßmotor, jet thrust motor, 110 Strahlturbinen-Verkehrsflugzeug 152, 282 Stratospheric Observatory For Infrared Astronomy (SOFIA), 5, 28, 51, 301, 302, 310 Straw, 62, 63, 72, 96 Strength, 202, 206 Strength anisotropy, 3 Stress-number curve, 189 testing, 232 Stretching, 290 Structural material, 5, 171, 182, 188, 190, 202, 218 Structural mechanics, 278 Studiengruppe Homogenholz, 95 Submarine, 161 Substance, 114, 115 Substitute, 150, 165, 166 fibre, 166 material, 15, 76 Sudetenländische Treibstoffwerke AG, 104 Sühnegeld, 269 Sulphuric acid, 82 Swept-back wing shape, 225 Symmetrical shell geometry, 206

Index Synthetic fibre research, 171 Synthetic material, 51 Synthetic panels, 202 Synthetic-resin presstoff, 20

T Tail unit, 99 Tank Panzerkampfwagen III, 163 Panzerkampfwagen V “Panther”, 163 Panzerkampfwagen VI “Tiger”, 163 Taylor, Thomas, 82 Tear-out test, 208 Technical Committee on Plastics and Presstoff, 13, 58, 153 wood issues, 107 Technische Geschichte der Pflanzen, 323 Technische Hochschule Breslau, 171 Technische Hochschule Dresden, 17, 23, 100, 225, 284, 285, 288, 293, 294, 297, 314, 323 Technische Hochschule Karlsruhe, 94 Technische Hochschule Magdeburg, 17 Technische Hochschule Stuttgart, 207, 294, 314 Technisches Amt der Luftwaffe, 227 Technische Universität Dresden, 281 Technology, 38, 46 Technology transfer, 197 Tego film, 205 Telescope, 29, 301, 303, 307, 311 Tensile and flexional strength, 117 Tension brace, 212 Tension test, 208 Testing technology, 206 Textile, 168 technical, 64, 71, 180, 288, 299 Textile industry, 168, 171, 173 Textilforschungsanstalt Krefeld, 169 Theory, hydrodynamic, 141 Thermography, 17, 26 Thermoplastic, 51, 80 Thermoset, duromere, 51 Thing, 37, 38 Thüringische Glaswollindustrie, 178, 253 Timber, 51, 73 Timber construction, 50, 84, 101, 202, 214 Timber construction problems, 204 Timber material, 49

Index Toiletries, 118 Topeka, 131 Tornado, 28, 264, 271 Torpedoversuchsanstalt Eckernförde, 160 Torsion moment, 205 Torsion test, 208 Tortoiseshell, 75 Toys, 118 Trabant, 24, 281 Transversal isotropic material, 277 Treaty of Versailles, 184 Tribology, 140 TROLITAX, 149, 233, 237, 238, 249 SUPRA, 233 TRONAL, 235–237 Truss construction, 308 Tsai-Wu criterion, 274 Tussah silkworm silk, 195 Twist cap, 161 Typology, 41, 43, 47, 49, 79, 315

U Übigau-AG Schiffswerft, Maschinen- und Kesselfabrik, 111 Unidirectional, 180 layer (UD layer), 69 material, 277 Union of Soviet Socialist Republics (USSR), 298 Universität Basel, 93 Universität Rostock, 294 Upper Palaeolithic, 61 Upper shell, 201, 205, 206, 212 Urea-formaldehyde resin, 120 Urea resin, 120, 137 USA, 251–254, 259, 290, 304 US Army, 133 US Navy, 133

V V-2 rocket, 196, 228 Vapour infiltration, chemical, 313 Varnishing system, 204 VEB Apparatebau Lommatzsch, 283, 287, 289 VEB Chemische Werke Buna, 287 VEB Edelstahlwerk „8. Mai 1945“, Freital, 287 VEB Elektro-Stahlguß Leipzig-West, 287

411 VEB Eloplast Micheln, 290 VEB Entwicklungsbau Pirna, 286 VEB Flugzeugwerke Dresden, 286, 289, 292, 297 VEB Glasseidewerke Oschatz, 297 VEB Härtolwerk Magdeburg, 285 VEB Hermann Schlimme Berlin, 285 VEB Industriewerk Karl-Marx-Stadt, 286 VEB Kombinat Chemische Werke Buna, 297 VEB Leuna Werke „Walter Ulbricht“, 297 VEB Maschinen- und Apparatebau Schkeuditz, 286 VEB Nagema Dresden, 294 VEB Papierfabrik Wolfswinkel, 289 VEB Papierverarbeitungswerke Engelsdorf, 289 VEB Plasta Kunstharz- und Pressmassewerk Espenhain, 290 VEB Rheinmetall Sömmerda, 285 VEB Sprela-Werke Spremberg, 137 VEB Werk für Technisches Glas Ilmenau, 180 Velox photographic paper, 113 Venditor Kunststoff-Verkaufsgesellschaft, 149, 234 Veneer, 10, 85, 201, 206, 207 layer, 206, 208 stacking, 208 Veneer layer, 210 Veneer thickness, 208 Ventimotor GmbH, 268 Venus of Vˇestonice, 61 Verein Deutscher Chemiker (VDCh), 12 Verein Deutscher Ingenieure (VDI), 4, 12, 52, 58, 107, 146, 153 Vereinigte Flugtechnische Werke, 261 Vereinigte Leichtmetallwerke GmbH Hannover, 171 Vereinigte Walz- und Röhrenwerke AG, 83 Versuchs-und Materialprüfungsamt der TH Dresden, 174 VFW-Fokker, 262 Vibration resistance, 140 Vidal process, 252 Volkswirtschaftliche Abteilung der Reichsbekleidungsstelle, 165 Von der Front für die Front (info sheet), 163 Vulcanized fibre, 49, 83, 131, 133, 134, 235, 237, 249, 317, 319 helmet, 83

412 VVB Flugzeugbau, 283

W Waffen-SS, 156, 244 Wagon building, 100 War economy, 197 War effort, 215, 216 Waste paper, 74 Wawepa, 289 Wax, 75 Web, 205 central (beam), 201 outer (beam), 201 Wehrmacht, 106, 144, 145, 156, 159, 229 Weight reduction, 206, 309, 313, 317 Weimarer Bauhaus, 101 Werner & Pfleiderer, 117 Western Paper Company, 74 Westinghouse Electric Company, 121, 123, 319 Wet process, 90 Wet wood, 88 Whiting, 73 Wind turbine, 100 Wing, 2, 232 design, 200 shell, 214 statics, 202 wooden, 198 Winglets, 2 Wolf-Hirth, 206–208 Wood, 1, 10, 79, 80, 84, 100, 106, 122, 130, 200, 240, 251, 319 Wood composite, 200, 201 Wood composite, lightweight fibre-aligned, 50 Wood-core plywood, 96, 98

Index Wood-derived material, 10, 89, 214, 251, 317 Wooden shell, 199, 210 Wooden wing, 200 Wood fibre, 214, 319 Wood flour, 47, 53, 71, 89, 114, 115, 135, 320 Wood industry, 92 Wood-Plastic Composite (WPC), 314 Wood pulp, 89, 96 ground, 81 Wood-saving building method, 84 Wood screw, 209 Wood veneer, 202 Wool, 51, 81, 165 Wool research, 179 Working principle, 62 World Exhibition, 76 World War I, 82, 151, 165 World War II, 107, 145, 166, 176, 189, 251, 254 World-Wide Failure Exercise, 276, 277 Woven fabric, 53, 64, 116, 122, 136, 288, 319 coarse, 177 fine, 177 Wright-Patterson Air Force Base, 254 WUMAG, 117

Z Zanonia (Javan cucumber), 225 Zeitschrift des Vereins Deutscher Ingenieure, 30 Zeitschrift Faserforschung (journal), 173 Zentralstelle für Patent- und Vorschlagswesen, 292 Zeuner turbine, 111 Zinc chloride, 82