Aircraft Tires: Key Principles for Landing Gear Design 1468604635, 9781468604634

Citation preview

Aircraft Tires Key Principles for Landing Gear Design

R. Kyle Schmidt

Aircraft Tires Key Principles for Landing Gear Design

Aircraft Tires Key Principles for Landing Gear Design R. KYLE SCHMIDT

Warrendale, Pennsylvania, USA

400 Commonwealth Drive Warrendale, PA 15096-0001 USA E-mail: [email protected] Phone: 877-606-7323 (inside USA and Canada) 724-776-4970 (outside USA) FAX: 724-776-0790

Copyright © 2022 SAE International. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE International. For permission and licensing requests, contact SAE Permissions, 400 Commonwealth Drive, Warrendale, PA 15096-0001 USA; e-mail: [email protected]; phone: 724-772-4028. Library of Congress Catalog Number 2022936965 http://dx.doi.org/10.4271/9781468604641 Information contained in this work has been obtained by SAE International from sources believed to be reliable. However, neither SAE International nor its authors guarantee the accuracy or completeness of any information published herein and neither SAE International nor its authors shall be responsible for any errors, omissions, or damages arising out of use of this information. This work is published with the understanding that SAE International and its authors are supplying information but are not attempting to render engineering or other professional services. If such services are required, the assistance of an appropriate professional should be sought. ISBN-Print 978-1-4686-0463-4 ISBN-PDF 978-1-4686-0464-1 ISBN-ePub 978-1-4686-0465-8 To purchase bulk quantities, please contact: SAE Customer Service E-mail: [email protected] Phone: 877-606-7323 (inside USA and Canada) 724-776-4970 (outside USA) Fax: 724-776-0790 Visit the SAE International Bookstore at books.sae.org

Chief Growth Officer Frank Menchaca Publisher Sherry Dickinson Nigam Product Manager Amanda Zeidan Director of Content Management Kelli Zilko Production and Manufacturing Associate Erin Mendicino

Dedication For my wife, Natalie, and my children, Jacob, Dylan, and Hunter.

©2022 SAE International

v

Contents Acknowledgements

ix

Preface

xi

A Note on Units

xiii

Introduction

xv

About this Book

xxi

CHAPTER 1

Tire Construction and Terminology

1

Construction Terminology

3

Tire Dimensions and Properties Inflation Pressure

8 14

Tire Temperatures

18

Tire Classification

23

Selection Between Bias and Radial Tires

24

Manufacturing, Certification, and Standardization

26

Tire Sizing

28

Tire Sizing Formulae

28

Tire Sizing Requirements

30

Tire Tables

31

CHAPTER 2

Tire Performance and Modeling Mechanics of Pneumatic Tires Rolling Behavior

53 53 54

Turning Behavior

55

Vertical Stiffness

58

Braking Behavior

59

Tire-Ground Friction

63

Wet Runways and Hydroplaning

65

Snow and Ice

72

©2022 SAE International

vii

viii

Contents

Wear

73

Tire Property and Behavior Models

75

Nasa Technical Report R-64

75

Brush Model and Fiala Model

76

Beam and String Models

77

Magic Formula Model

78

CHAPTER 3

Undesirable Tire Behavior

81

Spray

81

Debris Lofting

86

Tire Failure Modes

90

Modeling Tire Failure Events

94

Model 1: Tire Debris Threat Model

95

Model 3E: Flailing Tire Strip Threat Model

96

Model 3R: Flailing Tire Strip Threat Model

96

Model 4: Tire Burst Pressure Effect Threat Model

97

Understanding the Impact of Tire Failures

101

References

105

Index

109

Acknowledgements

T

he book you are reading, while itself a stand-alone book, originally ­constituted a single chapter of The Design of Aircraft Landing Gear. Below are the ­acknowledgements for that book—they remain true and valid for this excerpt. The idea for this stand-alone book was Sherry Nigam’s and I thank her, Erin Mendicino, Amanda Zeidan, and the other staff at SAE International Books for their assistance with this project. I would like to thank my family: Natalie, Jacob, Dylan and Hunter, for their patience, support, and encouragement, without which I would not have been able to dedicate the time to writing this book. I would also like to thank my father, Bob Schmidt, who was the first to read and comment on each chapter as it was produced. I thank my colleagues in Canada, France, the USA, and the UK who have read sections and chapters of this work and provided me with suggestions, corrections, and encouragement. In particular, I would like to thank those who gave up their time to review and comment: Bruno Aldebert, Steve Amberg, Rod Van Dyk, Andrew Ellis, Jack Hagelin, Dan Hetherington, Marianna Lakerdas, Grant Minnes, Andy Paddock, Michael Saccoccia, Jon Smith, and Peter Taylor. Monica Nogueira at SAE International has supported me from the outset of this project, gently prodding to ensure that it was completed! I would also like to thank the industry expert reviewers who reviewed portions of the book on behalf of SAE International: CB Alsobrook, Gregg Butterfield, David Brill, Bob Knieval, and Henry Steele. Finally, I would like to thank Ian Bennett and Mark Shea who reviewed the entire manuscript in detail and provided a number of excellent comments and suggestions.

©2022 SAE International

ix

Preface

T

he author has been fortunate enough to work in the field of aircraft landing gear for over twenty-five years and in three countries: Canada, France, and the UK, and to have held a variety of engineering roles relating to the development of new landing gears and the sustainment of existing landing gears in service. Landing gear provides an intriguing and compelling challenge, combining many fields of science and engineering. This book is an excerpt of The Design of Aircraft Landing Gear intended to present a specific element of landing gear design in an accessible way. The content here and in the original book was born of the author’s desire to learn ever more about landing gear — their history and the ways in which others have addressed their problems and challenges; in continuously striving to learn more about the field, it was considered advantageous to put these learnings into print in the hope that they can assist others. The book is intended, broadly, for two audiences: experienced aircraft and landing gear design engineers, for whom it is hoped that the book will act as a reference as well as an ‘idea book’, and for those new to the field who are, perhaps, working on their first landing gear design (maybe as part of their education). For the latter, it is hoped that the book provides the information needed to aid in their design and studies, and that they are as intrigued and compelled by the beautiful complexity of landing gear to consider this challenging field for their future employment. No single book can provide all the answers; throughout the chapters there are a number of references to additional documents which can aid in the design, development, and support of landing gears and their associated systems. In particular, documents produced by the SAE International A-5 committees on aircraft landing gear are widely referenced and participation in these committees is highly recommended to readers of the book and practitioners of landing system engineering. The opinions and approaches outlined in this book are those of the author and do not necessarily represent those of his employer (Safran Landing Systems). Although a great deal of care has been taken in the preparation and review of this work to ensure that the approaches, methods, and data provided are accurate, the author and publisher are not liable for any damages incurred as a result of usage of this book, for typographical errors, or for any misinterpretations.

©2022 SAE International

xi

A Note on Units

W

herever possible, units in this book follow the International System of Units (SI, also known as the metric system) approach. However, aircraft and landing gear are international in nature and many components and analysis approaches are conducted in US Customary units. In particular, some empirical formulas are based on US Customary measures and do not lend themselves to conversion to another system of measure. In general, most calculations can be performed using either SI or US Customary units, provided two different measurement systems are not mixed in the same calculation and that the units utilized are self-consistent. An area where attention needs to be paid is the use of the US customary unit of weight and force, the pound, which is often colloquially used as a unit of mass (with an implicit assumption of earthly gravity); calculations conducted in US customary units which require units of mass can employ the ‘slug’ – which is defined as the mass that is accelerated by 1 foot per second per second when a force of one pound is exerted on it. A familiarity with both systems of measure is recommended due to the international nature of the aircraft business.

©2022 SAE International

xiii

Introduction

T

he aircraft landing gear and its associated systems represent a compelling design challenge: the retractable landing gear is simultaneously system, structure, and machine; it supports the aircraft on the ground, absorbs landing and braking energy, permits maneuvering, and retracts to minimize aircraft drag. As the system is not required during flight it represents dead weight and significant effort must be made to minimize its total mass. The landing gear is one of the most complex and diverse systems on an aircraft. An article in Flight magazine [1] in 1940 expressed this, “for on no other part of the aeroplane is there such scope for engineering ingenuity and no other part can boast of so many ways of achieving the desired result”. This remains true today, many decades later. An expert in landing gear must be conversant with a wide range of engineering disciplines including materials, mechanisms, structures, heat transfer, aerodynamics, tribology, and many more. Depending on the given aircraft’s needs a landing system may be little more than wheels and tires attached to suitable aircraft structure or it may be a complicated system enabling performance on unpaved runways, steering, kneeling, retracting, and permitting further aircraft operations. Very few aircraft are designed for no other purpose than to carry the landing gear (perhaps only the Messier Laboratoire test aircraft qualifies); rather, the aircraft is designed to perform a function and the landing system must enable this function with high reliability and low mass. The aircraft landing gear and system provides a number of functions:

•• The landing gear, wheels, and tires support the aircraft on the ground •• The tires and shock absorber absorb vertical energy during landing and minimize shocks during ground maneuvering

©2022 SAE International

xv

xvi

Introduction

•• The brakes absorb forward energy and hold the aircraft when stopped and parked

•• Differential braking and steering permit turning and maneuvering on the ground

•• Specific structure and attachments permit towing, jacking, and tie down of the aircraft

•• The landing gear can retract to minimize airframe drag •• The landing gear can articulate to change the aircraft geometry – assisting takeoff or kneeling for loading

•• The landing gear can include driven wheels to maneuver the aircraft without relying on main engine thrust

•• The landing gear can comprise attachments to permit catapult launch from ships as well as airframe mounted arresting gear

•• The landing gear can include a tail bumper for protection of tail cone structure With very few exceptions, the interface between the aircraft and the ground – at least for land-based aircraft – is pneumatic tires (Figure 1). The tires not only provide a measure of shock absorption and capability to adapt to irregular ground profiles, but also are the means of ensuring an appropriate level of friction (grip) that permits other landing gear systems to steer and brake the aircraft – the tire, in most cases, is the essential interface between the aircraft and the ground.

© SAE International.

 FIGURE 1   Typical aircraft tire.

Introduction

xvii

Selection of the appropriate tires is critical to success of the aircraft: the size and number of tires (and their arrangement) determines the compatibility of the aircraft with the ground (explained further in The Design of Aircraft Landing Gear [2] and Airfield Compatibility: Key Principles for Landing Gear Design [3]), determines the space available for wheel brakes, and constitutes a significant portion of the required stowage volume for a retractable landing gear. Larger tires can carry greater loads, or carry a given load at a lower inflation and ground contact pressure, and can contain a larger wheel and wheel brake – but larger tires increase aircraft mass, aerodynamic drag, and require a larger stowage volume in the aircraft. Resolving this tension of competing requirements is a critical step in the early design stages of an aircraft. Early aircraft typically used a single tire per landing gear which worked reasonably while aircraft masses were relatively small (single tires per landing gear remains an appropriate configuration for lighter weight aircraft). As overall aircraft size and mass grew, the limits of reasonable single tire capacity were met. The peak of large aircraft on single wheel landing gears was reached with the XB-36, which first flew in 1946. With a maximum weight of around 280,000 pounds (127 000 kg), this aircraft used a single 110 inch (2.8 m) diameter main tire (Figure 2, left) and was only suitable for operation from highly reinforced concrete surfaces (the high point load exerted by the single main tires would overload most lower strength ground surfaces). Later versions of the aircraft were designed using one of the first multiple wheel units to enter service. Tracked systems (Figure 2, right) were also tested on this aircraft. Arrangements of multiple smaller wheels improved the ability of ground surfaces to support higher loads and in many cases, stowage of a grouping of smaller wheels was more readily facilitated. The production B-36, Sud Aviation Caravelle, and de Havilland Comet all used four wheel main landing gears where each pair of wheels was fitted to a lever arm, with a mechanism joining the levers to a common shock absorber. Following this brief flirtation with paired wheels on levers, most multiple wheel (more than two) landing gears have mounted the wheels to a rigid bogie beam, pivoted at the bottom of a cantilevered shock strut. Early large high speed aircraft such as the Convair B-58, Tupolev Tu-144, and Avro Vulcan utilized eight small diameter tires fitted in pairs to four wheels, mounted on a bogie beam. Advances in tire technology (as well as changing constraints on the required retracted position volume) have permitted a reduction in the total number of required tire  FIGURE 2   Convair XB-36 main wheel (left); XB-36 with tracked landing

© SAE International.

gears (right).

xviii

Introduction

© SAE International.

 FIGURE 3   Track main landing gear of XB-36.

positions; large aircraft today utilize multiple wheels on bogie beams almost exclusively (the rare exceptions being certain military transport aircraft). An early task for the aircraft and landing gear designer is to find the best configuration of tires to meet the required aircraft performance goals while minimizing weight, cost, and complexity. As was shown for the B-36 above, attempts have been made to use an alternative ground interface to pneumatic tires: skids, tracks, and air cushions have been explored with limited success. Caterpillar track designs were trialed on a number of aircraft, including the P-40, A-20, C-82, B-36 (Figure 3), and B-50 (Figure 4) with the prime

Reprinted from USAF.

 FIGURE 4   Track main landing gear of B-50.

Introduction

xix

© SAE International.

 FIGURE 5   Air cushion landing system on XC-8A.

intention to lower the ground contact pressure through a significant increase in the ground contact area. While the feasibility of tracks as alternatives to tires was demonstrated, development was halted - the weight and mechanical complexity of the track suspension and guidance mechanisms as well as increased maintenance and exposure to snow, ice, and debris rendered the tracks sub-optimal when compared to pneumatic tires. Air cushion landing systems (effectively the marriage of the aircraft and the hovercraft) have been developed and demonstrated, as shown in Figure 5. While an air cushion landing system permits aircraft alighting on virtually any surface, power is required to operate the system and the low friction created by the film of blown air results in challenges for directional control and braking, especially with the aircraft at low speed or when stationary. Advances in tire technology have rendered the pneumatic tire a lightweight and appropriate solution for almost all aircraft applications. Compared to skids, for instance, tires permit the aircraft to roll freely on the ground. Compared to the air cushion system, no aircraft power is required to provide maneuverability and support, and lateral movement is effectively restrained. Track systems were developed and tested in the 1940s, aiming to provide a significantly reduced ground contact pressure; while they worked, they proved to be heavy and noisy and were not adopted – landing gears employing multiple tires were selected as the preferred alternative. Tire companies have developed alternatives to the pneumatic tire (generally employing tread rubber attached to a flexible wheel) which have found application in off-road vehicles but are not yet in use on aircraft. The pneumatic tire is likely to be the most effective and appropriate ground interface for aircraft for some time to come.

About this Book

T

his book is designed to guide the interested reader through the key principles of aircraft tire design, selection, and integration to the aircraft landing gear. Additionally, references to further information are provided when it is available. This book is excerpted from the author’s two volume treatise, The Design of Aircraft Landing Gear [2], which provides details on the entirety of landing system design. Much of the beauty of interesting design problems such as aircraft landing gear and tires is that any one subject could fill an entire book, whether it be the tribology of wearing surfaces, the interaction of gas and oil in shock absorbers, or the kinematic arrangement and analysis of mechanisms. It is therefore impossible to provide every last detail on every problem which the landing system engineer may face, but an effort has been made to tackle many of the subjects one is likely to face when designing new products or supporting the operation of systems in service. This particular volume outlines the design details, sizing, and performance of a key element in most landing systems: tires. In the author’s experience many problems that must be confronted have already been addressed by others in the past, but the information is not widely known or shared, leading to the observation that there are few new problems, but many new people. This book is intended to share much of the information available and provide avenues for further exploration. A career in landing system design, development, and support can be spent while continually facing fresh and interesting challenges. No two aircraft are exactly alike; regulators and customers are always increasing their expectations, elevating the design challenge and making landing system engineering an exciting and rewarding discipline.

©2022 SAE International

xxi

xxii

About this Book

Chapter 1 of the book begins with an overview of the fundamentals of pneumatic tire performance and design as well as an overview of how aircraft tires are certified and standardized. The means by which tires are sized and selected are explained and summary tables of available aircraft tires are provided, ordered by increasing load carrying capacity in order to aid selection by aircraft and landing gear designers. The dynamic performance and behavior of tires being critical to aircraft operation, Chapter 2 is dedicated to this aspect. The mechanics of pneumatic tires are discussed in detail as well as tire to ground friction and tire wear properties. Chapter 2 ends with an overview of the commonly used numerical models for tire property prediction. While the pneumatic aircraft tire has secured a place as the best current solution for aircraft to ground interface, there are some undesirable aspects of tire behavior, which must be considered in the process of aircraft and landing gear design. Chapter 3 covers these aspects, including water spray, debris lofting, and tire failure modes. The specific names used for various components of the landing gear vary depending on geographic location as well as company history. A consistent set of terms is used throughout this book but as an aid to comprehension, the various components are identified and their commonly used names indicated as an aid to the reader. Further terminology is explained in document AIR1489 [4]. The common names for a variety of landing gear components that occur in this book are shown in Figure 1; further explanation of tire specific terms is provided in Chapter 1.

© SAE International.

 FIGURE 1   C-160 Transall main landing gear (cutaway).

1 Tire Construction and Terminology

A

tire provides a number of functions: it rolls, deforms over small variations in the ground profile, provides an interface with the ground that generates appropriate friction, spreads the applied load over a contact area, and provides some shock absorption. In general, all aircraft tires are pneumatic tires. Solid tires (those tires where the rubber of the tire is directly connected to the wheel without any inflation medium) are typically used only in some light aircraft tail wheels. Solid tires operate in compression, holding the vehicle off the ground in the same manner as a jack, tailskid, or other support but with the added advantages compared to these solid supports of higher traction, shock cushioning, and the ability to roll (Figure 1.2, left). However, solid tires have limited shock cushioning ability compared to pneumatic tires and their high ground contact pressure (compared to pneumatic tires) is detrimental to traction. Rubber is not a perfect spring: the energy used to compress or extend a block of rubber is not completely released when it is allowed to return to its unstressed condition. The difference is due to the hysteresis of the material, some examples of which are shown in Figure 1.1 for generic rubbers of different hardness. Solid tires are very limited in load and speed capacity as heat buildup due to the hysteresis loss cannot be easily dissipated, especially in the center of the rubber cross section. These types of tires would fail due to thermal overload if used under high load for any significant amount of time.

©2022 SAE International

1

2

Aircraft Tires: Key Principles for Landing Gear Design

© SAE International.

 FIGURE 1.1   Rubber hysteresis.

© SAE International.

 FIGURE 1.2   Solid tire (left) and pneumatic tire (right) supporting a load.

Pneumatic tires, on the other hand, operate predominantly in tension. The inflation pressure puts all of the structural components in tension with the deflected part of the carcass at a reduced tension relative to the rest of the tire. As the tire deflects (Figure 1.2 , right), the cords in the casing beneath the wheel experience both a decrease in tension and a change in angle; these effects combine to reduce

Aircraft Tires: Key Principles for Landing Gear Design

3

the vertical component of the tension acting on the bead. The wheel is supported by the bead as the carcass forces at the top of the tires are largely unaffected by the tire deflection. As a result, the wheel is supported by tensile forces rather than compressive forces. There are some rubber components which do go into compression, such as the tread and certain areas of the bead. The tread is compressed between the structural belts and the ground surface and undergoes vertical stress comparable to the inflation pressure. If the tire were a balloon, this stress would be exactly the inflation pressure, and the load would be entirely borne by the work on the inflation medium. As more reinforcement is added in the form of plies and belts, less of the load is borne by the inflation medium as the structural elements support some of the load with bending stiffness. The inflation pressure in the pneumatic tire provides the tension which is critical to supporting the load. Tire designers generally design tires to operate at optimal deflection, which has historically been 32%–35% for aircraft tires. Thus, the design inflation pressure depends on the load to be carried and is set to achieve the desired deflection (for ground compatibility, the service inflation pressure may be lower than this value, at the expense of tire life). One of the benefits of pneumatic tires is their ability to deform with very little hysteresis as the air is controlling the stiffness of the structure and the air volume is constant (during constant load rolling). Hysteresis occurs in the tread and bead areas, but the overall heating effect is much lower than that of solid or foam filled tires. A pneumatic tire is constructed by applying a tread (with or without reinforcement) to the carcass. The carcass is the structural component of the tire, fabricated from a cord rubber composite. Relatively high-modulus reinforcing cords are laid parallel to each other to form a fabric ply; various plies are then layered to build the appropriate carcass structure. There are two types of pneumatic tire construction used on aircraft: bias ply and radial ply. These methods of assembly are shown in Figure 1.3 for a bias ply tire and Figure 1.4 for a radial ply tire. The fundamental difference is in the arrangement of the reinforcing plies. In the bias ply tire, the carcass is composed of reinforcing plies arranged at an angle in the range of ±25° to ±40° to the tire circumference whereas in the radial ply tire, the carcass plies run from bead to bead with an angle 90° to the tire circumference (Figure 1.5). In the radial tire, a reinforcing belt runs circumferentially around the tire to provide stiffness to the tread area and to prevent excessive growth of the tire during inflation. In automotive tires, this belt is typically steel, but in aircraft tires this is usually a lower weight, lower modulus material. Steel was evaluated for early aircraft tires, but the extreme speeds and deflections of aircraft tires have relegated steel to some particularly specialized roles.

Construction Terminology The components of a tire are described below; the numbers in parentheses refer to the cross section shown in Figure 1.6. Bead (1): The part of a tire that comes into contact with the rim and is shaped to secure the tire to the rim.

4

Aircraft Tires: Key Principles for Landing Gear Design

© SAE International.

 FIGURE 1.3   Bias ply tire construction.

© SAE International.

 FIGURE 1.4   Radial ply tire construction.

Aircraft Tires: Key Principles for Landing Gear Design

5

© SAE International.

 FIGURE 1.5   Comparison of bias (left) and radial (right) ply orientation.

Bead Base (13): Inner portion of the bead that is seated on the bead seat. Bead Bundle (15): Also, bead coils or bead cord. A circumferentially stiff hoop made of steel wires embedded in the bead which resists the inflation pressure generated forces. Bead filler (18): Also, apex. A rubber compound fillet between the bead bundle and adjacent ply cords. Bead Heel (14): Outer portion of the bead base. Bead Toe (12): Inner portion of the bead base. Belt (10): Also, breaker. An assembly of plies located under the tread that does not extend into the sidewalls. It provides additional tread area stiffness/strength. For radial ply constructions, it restrains the overall diameter, provides circumferential tread stiffness, and is the source of cornering forces. Cap ply (21): An additional ply, under the tread and over the belt assembly of a radial ply tire, with cords oriented at approximately 0° to the circumferential line. It provides additional circumferential stiffness. Carcass (5): Also, body or casing. It is the rubber-bonded cord structure that provides the tire’s stiffness when pre-stressed by the inflation pressure. Sometimes casing is also used to describe a used or treadless tire. Carcass Cord (6): An assembly formed by twisting together textile or non-textile filaments that is the structural reinforcing element for plies. Carcass Ply (7): The ply extending from bead to bead. Chafer (16): Also, rim strip or clinch strip. A layer of rubber compound, with or without fabric reinforcement, applied to the bead for resisting damage caused by movement relative to the bead seat and rim flange. Chine: Also, deflector. It is a flared upper sidewall protrusion that deflects the spray pattern of water or slush displaced by the tire’s contact with the runway. A tire can have a single chine (one sidewall flared) for dual nose wheel tire configurations or double chines (both sidewalls flared) for single nose wheel tire configurations. A cross section of a double chine tire is shown in Figure 1.7.

6

Aircraft Tires: Key Principles for Landing Gear Design

© SAE International.

 FIGURE 1.6   Tire construction and terminology.

Fabric Tread: While not applied to all tires, multiple plies are layered throughout the tread, reducing rubber deformation under load and high speeds, and reducing heat generated by hysteresis. It also improves resistance to standing wave formation, cuts, and punctures. Innerliner (11): Also, liner. A low gas diffusion layer covering the inside of the carcass of a tubeless tire; it is typically formulated from of a blend of butyl

Aircraft Tires: Key Principles for Landing Gear Design

7

© SAE International.

 FIGURE 1.7   Double chine tire cross section.

rubber (due to its low gas diffusion properties) and other rubbers (for better low-­ temperature flexibility) and retains the inflation medium – effectively replacing an inner tube. Ply: A sheet of rubber-coated cords. Ply turn-up (17): The portion of the ply passed around the bead bundle Protector ply: A ply that provides cut resistance protection to the underlying belts and carcass plies Sidewall (2): The portion of the tire between the bead and the tread. Sidewall rubber (19): The layer of rubber compound on the outside of the sidewall; it may include molded on sidewall elements such lettering and chines. Tread (4): The portion of the tire designed to contact the ground surface in normal service. Tread Compound (20): The rubber compound which is utilized to provide the contact and wearing surface of the tread. Typically, the tread compound is predominantly natural rubber with carbon black, sulfur, and other additives. Tread Groove (9): A void that is molded or cut into the tread rubber and is relatively narrow compared to its length. Tread Reinforcing Ply: Single or multiple plies laid midway beneath the tread grooves and top carcass ply. These plies help to strengthen and stabilize the crown area, by reducing tread distortion under load, and to increase high-speed stability. They also offer a resistance to tread puncture and cutting and help to protect the carcass body. Tread Rib (8): An essentially continuous, circumferential tread element. Tread Shoulder (3): The outermost portion of the tread adjacent to the sidewall.

8

Aircraft Tires: Key Principles for Landing Gear Design

Tire Dimensions and Properties The pertinent tire dimensions are shown in Figures 1.8 and 1.9. D: Wheel Rim Ledge Diameter Df : Wheel Rim Flange Outer Diameter Do: Outside Diameter (for a new, unused, inflated tire) Dg : Maximum grown outside diameter Ds: Shoulder Diameter (for a new, unused, inflated tire) Dsg: Maximum Grown Shoulder Diameter Fh: Wheel Rim Flange Height A: Width between the wheel rim flanges H: Cross-section height (for a new, unused, inflated tire) Hs: Shoulder section height (for a new, unused, inflated tire) W: Cross-section width (for a new, unused, inflated tire) Wg : Maximum grown section width Ws: Shoulder width (for a new, unused, inflated tire) Wsg : Maximum Grown Shoulder width Do max Do min Dm: Mean tire diameter at the tire centerline Dm 2 Wmax Wmin Wm: Mean tire width Wm 2

© SAE International.

 FIGURE 1.8   Tire cross section – dimensions.

Aircraft Tires: Key Principles for Landing Gear Design

9

© SAE International.

 FIGURE 1.9   Bias ply tire clearance dimensions.

Most tire dimensions and load capabilities are provided in US Customary units. In units of inches, the radius of gyration of a new bias ply tire can be estimated (with an accuracy of ±5%) by:

Rg

Dm 2.56

The radius of gyration of a new radial ply tire can be estimated by:



Rg

Dg 2.56



The radius of gyration of the wheel assembly including the rotating brake parts (but excluding the tire) is estimated to an accuracy of ±20% by:

Rg

0.4 D

10

Aircraft Tires: Key Principles for Landing Gear Design

The moment of inertia, I, of either can be calculated with the expression:

I

2

m Rg

The static loaded radius (SLR) of a tire is calculated based on the amount of deflection, b:



SLR

Dm 2

Dm

b

Df 2



where b is the fractional deflection (35% deflection corresponds to b = 0.35). For type B and H, bias ply tires and bias ply tires rated for 160 mph or less, the value of b is 0.35. For all other bias ply tires, the value is 0.32. For radial ply tires designed for 32% deflection, use b = 0.33 for the minimum SLR and b = 0.24 for the maximum SLR. For radial tires designed for 35% deflection, use b = 0.36 for the minimum SLR and b = 0.27 for the maximum SLR. The aspect ratio (AR) of the tire is the ratio of the mean section height to its mean section width: Dm

AR

2 Wm

D

Tires are manufactured to nominal dimensions, with a production tolerance. However, they do not retain those dimensions – the inflation pressure will cause them to expand slightly but the combination of the inflation pressure stresses plus usage cause the cord-rubber composite to relax slightly, resulting in “growth” of the tire. Furthermore, when spinning, the inertial loading (centrifugal acceleration) on the tire will “throw” the dimensions even further, resulting in a larger overall shape envelope than the resting dimensions. It is imperative that the landing gear and aircraft designer consider these overall dimensions to ensure that adequate clearance is maintained between the thrown and grown shape of the tire and the landing gear bay and landing gear components. The grown tire envelope and required clearance dimensions (encompassing the grown and thrown shape) for bias ply tires are shown in Figure 1.9. These dimensions are relevant for an unloaded free spinning tire or the portion of a loaded grown tire which is above the axle centerline. The radii Ws/2 and Wsg/2 in Figure 1.9 are drawn through their respective shoulder points tangent to Do and Dg. Below the shoulder points, the radii pass through the shoulder points and are tangent to W and Wg, respectively. To compute the grown values, the following expressions are used: The section height growth factor, Gh:

Gh

1.115

0.075 AR

Aircraft Tires: Key Principles for Landing Gear Design

11

The section width growth factor, Gw, is 4%:

Gw

1.04

The grown dimensions are then calculated:

WGw

Wg



D 2 HGh

Dg



Ws Gw

Wsg



D 2 H s Gh

Dsg



H



Hs

Do

D 2

Ds



D 2



Using the grown tire dimensions, the minimum clearance dimensions that need to be respected (taking into account the maximum tire dimensions from tire tables, the service growth factors, the increase in tire diameter due to the inertial loading, and deflection above the axle due to ground loading) are given as follows. Radial clearance, Cr, in inches (for Wg in inches) of bias ply tires: V 100 1000

3.348

17.02 2.61

Cr

Wg

0.4

where V is the aircraft speed in miles per hour The lateral clearance, Cw, in inches (for Wg in inches) of bias ply tires:

Cw

0.19Wg

0.23

The grown tire envelope and clearance dimensions for radial tires are shown in

Figure 1.10. The radius Wsg/2 in Figure 1.10 is drawn its respective shoulder point

tangent to Dg. Radii below the shoulder points pass through the shoulder points and are tangent to Wg. The grown dimensions and clearance value calculations are shown in Table 1.1 for both inch code and metric tires, where Dt is the theoretical maximum new tire outside diameter and Wt is the theoretical maximum new tire width. The prime symbol is used to denote the same measurements but for metric code tires.

12

Aircraft Tires: Key Principles for Landing Gear Design

© SAE International.

 FIGURE 1.10   Radial ply tire clearance dimensions.

TABLE 1.1  Radial ply tire grown dimension and clearance calculations. Inch code tires

Metric tires

Wg = 1.04Wt

Wg

1.04Wt

Wsg = 0.9Wg

Wsg

0.88Wg

Dg = (Dt − D)Gh + D

Dg

Dt

Dsg = 0.9(Dg − D) + D

Dsg

0.9 Dg

Gh = 1.115 − 0.075AR

Gh

Dt D 2Wt

AR

SLRg

Dm 2

b

Dm

D

D D

1.115 0.075 AR Dt

25.4D 2Wt

Df 2

b = 0.33 for SLRg min, b = 0.24 for SLRg max (32% deflection tires) b = 0.36 for SLRg min, b = 0.27 for SLRg max (35% deflection tires)

© SAE International.

AR

D Gh

Aircraft Tires: Key Principles for Landing Gear Design

13

Radial clearance, Cr, in inches (for Wg in inches), of radial ply tires:



Cr

0.029 D g

D

Wg

A

V Dg

0.15

where V is the aircraft speed in miles per hour. The lateral clearance, Cw, in inches (for Wg in inches), of radial ply tires:

Cw

0.01W g ,

0.1 minimum

The distances to adjacent parts are given by the following expressions (use the appropriate values of Cw and Cr for bias and radial tires): The minimum radial distance from the axle centerline to an adjacent part, R x: Dg



Cr 2 The minimum lateral distance from the centerline to an adjacent part, Wx:



Cw 2 The permitted clearance between the tire shoulder area and an adjacent part, Sx:

Rx

Wg

Wx



Sx



Wgh

Cw

Cr

2 If using radial tires on helicopters, the following values apply (when using radial tires at loads and inflation pressures above their ratings). Note, however, that the low lateral stiffness of radial tires may render them unsuitable for helicopter use:



2

1.04 Wt

Wsgh



D gh

where:

0.9Wgh

1.04 Dt 1.04 D 1.115 0.075 AR Dsgh

0.9 D gh

D

0.1D

•• Wgh is the maximum grown section width for helicopters/rotorcraft •• Wt is the theoretical maximum new tire section width •• Wsgh is the maximum grown shoulder width for helicopters/rotorcraft •• Dgh is the maximum grown outside diameter for helicopters/rotorcraft, in inches

14

Aircraft Tires: Key Principles for Landing Gear Design

•• Dsgh is the maximum grown shoulder diameter for helicopters/rotorcraft, in inches

•• Dt is the theoretical maximum new tire outside diameter, in inches •• D is the specified rim diameter, in inches.

Inflation Pressure A pneumatic tire, by definition, is inflated with a compressed gas. Historically, this gas was exclusively compressed air, but on large aircraft, nitrogen is now used as the inflation medium. Compressed air contains all the gases found in the atmosphere and is principally nitrogen, but significant quantities of oxygen and water vapor are also found – water vapor can be between 1% and 4%, depending on the particular region and climate. The presence of water vapor in the compressed gas of a tire can lead to more significant tire pressure variation with temperature and condensed water can promote corrosion of the wheel. However, the impetus for the replacement of compressed air with nitrogen in large aircraft tires was the avoidance of explosion risk under elevated temperatures. These elevated temperatures arise predominantly from hot brakes. At elevated temperatures, the inner liner material (typically a butyl rubber blend) can generate vapors which will autoignite in the presence of sufficient oxygen. Testing determined that inner liner samples ignited in nitrogen/oxygen mixtures having 80%–90% nitrogen at temperatures between 248°C (478°F) and 270°C (518°F); with nitrogen concentrations between 90% and 95%, the ignition temperature was between 271°C (520°F) and 277°C (531°F). With concentrations of nitrogen above 95%, there was no ignition of the liner material, up to temperatures of 354°C (670°F). From these results, the FAA mandated [5] that large aircraft tires on braked wheels be inflated with an inert gas and that no greater than 5% oxygen be permitted in these tires. Rated tire pressures provided either by calculation or in tire tables are provided for unloaded tires at ambient temperature. If a tire is used at a load lower than the rated load, the inflation pressure is scaled linearly (if the maximum operating load of the tire is 90% of the rated load, then the unloaded inflation pressure should be 90% of the rated inflation pressure). Adjusting the inflation pressure in this way ensures that the tire operates at its design deflection. When a tire is loaded to its design conditions, the inflation pressure will be 4% greater than the unloaded pressure; at the bottoming load, the pressure will be on the order of 20% greater than the unloaded pressure. When a tire is inflated with nitrogen or dry air (for the condition where there is no water vapor in the tire), then it can be considered that the pressure/ temperature relationship follows the pressure law for small changes in temperature (the pressure law assumes no change in volume):

P1 T1

P2 T2

The values of temperature and pressure used in that equation must be in absolute terms (Kelvin or Rankine scale for temperature). To convert to these absolute scales,

Aircraft Tires: Key Principles for Landing Gear Design

15

the appropriate offset for absolute zero must be added to the measurement. To convert Celsius to Kelvin, 273.15° is added to the measurement in Celsius. To convert between Fahrenheit and Rankine, 459.67° is added to the measurement in Fahrenheit. Gauge pressure is converted to absolute pressure by adding atmospheric pressure, typically around 14.7 psi at sea level.

Taking an example of a 52×21.0R22 tire with a rated load of 66,500 pounds and a rated unloaded inflation pressure of 227 psi, if the tire were to be used at a maximum operating load of 60,000 pounds, then the operating pressure unloaded would be: 60,000 227 205psi 66,500



In the loaded condition, the tire inflation pressure will be increased by 4%, so the loaded pressure would be:



205 1.04 213psi

If the tire was inflated at an ambient temperature of 60°F, and then the tire temperature was raised to 85°F, then the measured pressure would be approximately:



P1 T1

P2 T2



P2

PT 1 2 T1



P2

213 14.7 85 459.67 60 459.67

238.6psia 14.7 224psig

As a general rule, a change of 5°F (3°C) results in a tire pressure change of approximately 1%. During the initial inflation of a new tire, some pressure will be lost during the first 24-hour period, not due to the loss of the inflation medium, but due to the increase in volume of the tire due to growth (stretch) of the tire. Following this period, the tire must be reinflated to the required pressure. During use, a 5% loss of inflation pressure in a 24-hour period is considered acceptable for an aircraft tire. Due to heating of the tires during use as well as variation in surface temperatures from destination to destination, the determination of the appropriate pressure at any time can be difficult. SAE document ARP5265 [6] provides the recommended practice for the monitoring and adjusting of tire service pressures. Operating a tire overinflated does not generally damage the tire. However, operating a significantly underinflated

16

Aircraft Tires: Key Principles for Landing Gear Design

tire leads to excessive heating of the tire and damage to the carcass. A tire which has been operated with significant underinflation may need to be discarded and replaced. The use and care manual provided by the tire manufacturer should be consulted for specific guidance. The internal gas volume of a tire can be calculated only with detailed knowledge of the specific tire design and the associated wheel design. However, an estimate of the gas volume can be made by assuming the volume to be formed by an elliptical toroid having a major axis equal to the width of the tire and a minor axis equal to the height of the tire. The diameter of revolution of the toroid is the rim diameter plus half the tire height, as shown in Figure 1.11. The volume of a torus is calculated by determining its area and multiplying that area by the circumference of the diameter of evolution. The area of the tire volume ellipse is given by:

A

W 2

H 2

WH 4

© SAE International.

 FIGURE 1.11   Gas volume estimation.

Aircraft Tires: Key Principles for Landing Gear Design

17

The tire gas volume can then be approximated by:

V

2 A

D 2

H 2

WH 4

2

D 2

H 2

2

2

WH 4

D H 2

Taking a 1400×530R23 tire as an example, the overall diameter, Dg is 56.85 inches, the width, Wg is 21.7 inches, and the rim diameter, D, is 23 inches. From these dimensions, the gas volume can be estimated:



H

V



2

2

2

2

WH 4

Dg D

56.85 23 16.925 inches 2

2 D H 2

91.82 19.96

2

2

21.7 16.925 4

23 16.925 2

36,177 cubic inches

This large tire (used on Airbus A330, A340, A380, and A350-900 aircraft) has a sizeable gas volume of 36,177 cubic inches (156 US gallons).

Knowing the gas volume and the inflation pressure, the mass of inflation medium used in the tire can be estimated using the universal gas formula: pV nRT where n is the number of moles of inflation gas. The number of moles of inflation gas can be determined by dividing the mass, m, of gas by the “molar mass,” M, (a constant for each different gas):

pV

m RT M

m

pVM RT

Rearranging for mass: where:

•• P is the absolute gas pressure (rated inflation pressure plus the standard atmospheric pressure, 101 325 Pa or 14.7 psi)

•• V is the volume •• m is mass of gas

18

Aircraft Tires: Key Principles for Landing Gear Design

•• M is the molar mass of the inflation gas (mass of one mole of the gas): 28.0134 g/mol for nitrogen; the molar mass of dry air is 29 g/mol approximately

•• R is the universal gas constant: 8.314 J/mol·K •• T is the absolute temperature. Calculating the mass of nitrogen in this tire when inflated to its rated pressure of 223 psi (17.2 bar) at a temperature of 15°C requires the conversion of the measurements to a consistent set of units:



Convert 223 psi to Pascals N / m2 : 223 psi 1.538 106 Pa

Convert from inflation (gauge) pressure to absolute pressure:



1.538 106 Pa 101,325Pa 1.639 106 Pa



Convert 36,177 cubic inches to cubic meters m3 : 36,177 in.3 0.5928 m3



Convert 15 C to degrees Kelvin: 15 C 288.15 K

Calculating for the mass: m



m

pVM RT

1.639 106 0.5928 28.0134 8.314 288.15

11363g 11.4kg

The large amount of compressed gas in a tire can behave explosively if the wheel separates or the tire ruptures. In the above example, the amount of stored energy (calculated in accordance with [7]) is approximately 840,000 ft-lb per tire (1.1 MJ) which is roughly equivalent to detonating a stick of dynamite. Figure 1.12 [8] shows a variety of tire applications and their associated explosive potential. Due to this high level of stored energy, it is imperative that inflation of newly mated aircraft wheels and tires be performed in an inflation cage (Figure 1.13), to protect the operator from flying debris in the case of an explosion.

Tire Temperatures During rolling of a tire, many components of the tire expand and contract, and due to the hysteresis effect of rubber and rubber-cord composites, not all energy put into the tire is returned. The energy lost is the rolling resistance of the tire, and this energy is converted to heat. There is limited ability of the tire to reject this heat: the heat can be transferred to the wheel through the bead, it can be transferred to the inflation

Aircraft Tires: Key Principles for Landing Gear Design

19

Adapted with permission from © SAE International.

 FIGURE 1.12   Explosive potential of aircraft tires.

Reprinted from http://www.352sow.af.mil/News/ArticleDisplay/Article/ 920023/352soamxsrepairandreclamationshopplaysthelonggame/

 FIGURE 1.13   Tire being loaded into protective cage for Inflation.

medium, and it can be transferred to the atmosphere. In a car or truck, the tire is designed for continuous operation at high speeds. To accomplish this, the design deflection of the tire is small compared to that of aircraft tires, and the amount of heat generated in every revolution of the tire is less than the amount of heat which can be rejected. In this arrangement, a tire starting from cold will warm up and reach a steady-state temperature during high-speed operation. However, aircraft tires are

20

Aircraft Tires: Key Principles for Landing Gear Design

designed to much higher deflection values and are operated under significantly higher loads. The geometric size of the aircraft tire being not that much greater than a car or truck tire is limited to a similar level of heat rejection; the amount of heat generated per revolution of an aircraft tire is much greater than that of a road vehicle. As a result, the speed at which thermal equilibrium is reached for an aircraft tire is much lower (typically at slow taxi speeds). Aircraft tires cannot be operated at high load and high speed for long periods of time: they require a cooling down period between operations to avoid destruction. An important part of ensuring that a tire will be appropriate for aircraft use is the creation of a load-speed-time curve: a plot which graphically shows the loading regime of the tire. These curves are generated based on the specific operation of the aircraft as the aerodynamics of each aircraft determine the loading behavior as a function of speed. For example, a supersonic aircraft like the Concorde typically has a wing which does not generate much lift until at high angles of attack. This results in the entire take-off run being conducted with the full load of the aircraft on the tires. Subsonic aircraft often have wings arranged such that as the speed increases on take-off, lift is increasing, which reduces the load on the tires. An example of this type of load-speed-time curve is shown in Figure 1.14. While acceptable tire temperatures vary slightly depending on the manufacturer (and the specific rubber compounds utilized), many tires are acceptable for use with local temperatures of the tire from –55°C to 110°C although the certification requirements typically require performance between –40°C and 71°C. In the area of the tire/ wheel interface, temperatures up to 150°C are typically acceptable. Due to heat buildup in the tire during rolling under high-load and high-speed conditions, it is typically recommended that following a long or fast taxi (prior to take-off) that the tires be allowed to cool for 5 minutes prior to performing the take-off. ARP5265 [6] identifies a long departure taxi as being more than 6.6 miles (10.7 km) and excessive

© SAE International.

Adapted with permission from © SAE International.

 FIGURE 1.14   Example rational load-speed-time curve.

Aircraft Tires: Key Principles for Landing Gear Design

21

© SAE International.

 FIGURE 1.15   Tire temperature increase with rolling at 20 miles per hour.

departure taxi speed as over 35 knots (65 km/h). The temperature increase with rolling is shown in Figure 1.15 for a tire rolling at constant speed (20 miles per hour) at close to its rated load, deflection, and inflation pressure. Whenever using a tire beyond its certified limits, it is important to involve the tire manufacturer to ensure that the planned operations will not result in unexpected consequences. The importance of ensuring correct inflation pressures (to ensure operation at the design deflection value) is shown in Figure 1.16 which shows a tire tested at three different deflection values. The tire was rolled at 20 miles per hour for 150 seconds. The sharp increase in interior temperature is evident for the tire rolled at the high deflection value (resulting from significant under inflation).

© SAE International.

 FIGURE 1.16   Temperature increase at different deflection values (20 miles per hour, 150 seconds of rolling).

22

Aircraft Tires: Key Principles for Landing Gear Design

Excessive heat buildup will lead to exceeding the reversion temperature for the rubber compounds used in the tire. At this point, the rubber “reverts” to its uncured state and loses its strength, which will lead to destruction of the tire. Tires must also withstand the temperatures generated by braking. The brake, wheel, and tire temperatures of an L-1011 aircraft during a normal stop are shown in Figure 1.17. The temperatures generated during a rejected takeoff would be much higher. Typically, three fusible plugs are provided in the wheel that are designed to melt at a set temperature in order to relieve the inflation pressure in the event of significant wheel and tire temperatures. As the strength of the tire is reduced and the inflation pressure increased by elevated temperatures, relieving the pressure in these cases is required to avoid tire burst. Operation at very low temperatures may require specific determination of the tire properties (low temperatures change the modulus of the tire materials resulting in altered dynamic performance). The certification requirements typically require operation at –40°C for civil tires and –50°C for military tires although customer

Reprinted from DOT/FAA/CT-85/32.

 FIGURE 1.17   L-1011 brake, wheel, and tire temperatures for normal stop.

Aircraft Tires: Key Principles for Landing Gear Design

23

requirements may demand operation at lower temperatures. Depending on the formulation of the liner, the resistance to gas diffusion at low temperature may be reduced, so more frequent pressure checks may be required to ensure adequate inflation.

Tire Classification Several types of aircraft tires have been developed since the beginning of aviation. The history of tire classification is provided in document AIR5487 [9], which indicates the various changes in nomenclature which have occurred over time. Modern tire size nomenclature is the three-part system, which indicates the diameter, width, and rim diameter as follows:

M N D for bias tires

where:

M N R D for radial tires

•• M is the nominal diameter in inches (for inch code tires) or in millimeters for metric code tires

•• N is the nominal section width in inches (for inch code tires) or in millimeters for metric code tires

•• D is the rim diameter in inches (for both inch code tires and metric code tires) For example, the main landing gear tire of the Boeing 787-10 is a 54×21.0R23, an inch code radial. The main landing gear tire of the Airbus A350-900 is a 1400×530R23, a metric code radial. Three part tire sizes (sometimes also called new design sizes) have a design deflection of 32% for tires designed for maximum speeds greater than 160 miles per hour. For tires with a design speed less than 160 miles per hour, the design deflection is 35%. Radial tires are designed to meet an SLR similar to the equivalent bias tire and not a specific deflection value. Historically, there were eight tire type definitions prior to the adoption of the three-part system. Of those eight types, three remain relevant:

•• Type I: typically used for non-retractable landing gear; size designation is by nominal overall diameter in inches

•• Type III: typically used for low-pressure applications giving a large footprint

(low ground contact pressure) and useful for unprepared runways. Type III tires have smaller rim diameters compared to the overall diameter compared to other tire types. These tires are designed to a deflection of 35%. Size designation is by nominal section width in inches and rim diameter in inches:

where:

N D

•• N is the nominal section width in inches •• D is the rim diameter in inches

24

Aircraft Tires: Key Principles for Landing Gear Design

•• Type VII: typically used on jet and turboprop aircraft; these tires have a narrower width and higher pressure than the type I and type III tires. These tires are designed to a deflection of 32%. Size designation is by nominal overall diameter and section width in inches:



M N

where:

•• M is the nominal overall diameter in inches •• N is the nominal section width in inches In addition to the type and size nomenclature, some tire sizes are preceded by a letter (B, C, or H). C type tires denote a cantilever type tire. This type of tire [10] has a narrow rim width compared to the tire width and is not typically used on modern aircraft. B-type tires have a rim width to tire width ratio between 60% and 70% and a 15° bead taper with a design deflection of 35%. H-type tires have the same section ratio and design deflection as B-type tires, but a 5° bead taper.

Selection Between Bias and Radial Tires In the automotive world, the radial tire has completely replaced the bias ply tire. However, both tire types continue to be relevant for aircraft, each with their advantages and disadvantages. The radial tire generally has a thinner sidewall, single bead wire, and greater reinforcement of the tread. The radial tire is typically of lighter construction (due primarily to the elimination of multiple bead wires and reduced sidewall thickness), but this effect is most noticeable on large tires with high ply ratings. On small tires, there is little difference in weight between a bias and radial ply tire. As an example [11], a bias ply tire designed to a maximum static load of 50,000 pounds could have 16 carcass plies wrapped around 3 bead wires. A radial tire designed for the same static load would only require approximately five carcass plies wrapped around a single bead wire, with eight circumferential belts. A cross section of a radial tire for an A320 main landing gear (a 46×17.0R20 tire) is shown in Figure 1.18. The single bead wires (near the rim) and a protector belt (under the tread) are clearly evident. While the radial tire offers potential advantages in weight, it can also offer some potential advantages in terms of lower heat generation; the reinforcement belt beneath the tread reduces the deformation in the tread area, resulting in increased tread life. Due to reduced slipping of carcass plies, there is lower heat generation in the carcass under load, which is an advantage in terms of overload resistance. For paired wheels, it is desirable that in the case of one tire failure, the companion tire continues to operate, carrying the combined load of both wheel positions. The radial tire can offer some advantages in this area by accepting a greater temporary overload than the bias tire. Typical tire certification requires the ability to withstand 1.5 times the rated load for a short period of time. However, it is recommended [12] that a tire be tested and able to withstand the full load resulting from failure of a companion tire (for the duration of a single flight cycle).

Aircraft Tires: Key Principles for Landing Gear Design

25

© SAE International.

 FIGURE 1.18   Radial tire cross section.

In terms of resistance to damage, the bias and radial tire each have their own strong points. The bias ply tire, by virtue of its thick and strong carcass, is typically more resistant to sidewall damage than the radial tire. This can be a particular advantage for aircraft operating to unprepared or semi-prepared runways. The potential existence of a steel protector belt in some radial tires offers improved cut resistance to these tires, which can help resist tire blowout in cases where the tire traverses a sharp object, such as occurred with Concorde. The reduced working stress in the tire tread area of a radial tire (due to the stresses being taken by the reinforcing belts) can reduce the tendency of a tire to come apart following damage to the tread area. Bias ply tires tend to have a greater radial stiffness and significantly greater lateral stiffness than radial tires. In applications where the aircraft or landing gear are sensitive to low stiffness (such as rotorcraft susceptible to ground resonance) the bias type tire may be preferred. A final area to be evaluated is the retreadability of the tires. Most bias ply tires have shown a strong capability to be retreaded – up to five or more times. Early radial tires did not have the evidence to validate such a large range of retread operations, with some tires limited to one or two retread cycles. However, knowledge and confidence in radial tires continues to grow, and the number of retread operations permitted on radial tires is increasing. Due to the weight decrease, increased wear life, and tread cut resistance of the radial tire many large modern civil aircraft are only certified to use radials.

26

Aircraft Tires: Key Principles for Landing Gear Design

Manufacturing, Certification, and Standardization Tires are designed, manufactured, and qualified according to a limited set of standards. The two most common standards are technical standard order (TSO) C62e [13] (and its European equivalent ETSO C62e [14]) for civil aircraft tires and MIL-PRF5041K [15] for military tires. Historically, some European military aircraft had tires developed to meet French standard AIR 8505/A [16], but this standard was withdrawn in 2009. To encourage standardization of tire sizes and classification within the industry, new tire sizes are agreed by the Tire and Rim Association (TRA) and the European Tyre and Rim Technical Organization (ETRTO). A manufacturer developing a new design submits their tire dimensions, load, pressure, and ply rating values to one or both of these organizations. Once finalized and approved, the new tire parameters will subsequently be published in the organization’s databook, issued annually. In parallel, an application for certification to the relevant standard is made, and certification testing is performed to validate the tire design. Tires are tested to withstand overpressure. For new civil tires, they must survive four times the rated inflation pressure for 3 seconds without bursting. For retreaded tires, the burst pressure requirement is reduced to three times the rated inflation pressure. For military tires, the historic requirement was to design land-based aircraft tires to withstand 3.5 times the rated inflation pressure and four times the inflation pressure for carrier-based aircraft tires. An aircraft tire is typically assembled predominantly by hand with limited automation (due to the relatively low number of tires manufactured compared to car or truck tires, for which manufacturing is highly automated). The tire is built up of various components and then placed in a mold where it is heated and pressurized into the mold cavity. The tire components vulcanize (cross-link) during this process which results in the final product. Upon removal from the mold, the tire must be checked to ensure acceptable balance. Balance pads (essentially weighted tire repair patches) are often added to the liner of the tire to bring the balance within acceptable tolerance limits. In accordance with TSO-C62e, an indicator of the balance location (a red dot) is placed on the sidewall of the tire above the bead in the location of the lightest point of the tire. When mounting the tire, this red dot is typically located opposite the inflation valve in an effort to achieve a balanced wheel and tire assembly. The maximum remaining unbalance on a new tire according to TSO-C62e for an auxiliary tire (not a main tire) less than 46 inches outside diameter is given by:

M 0.025Do 2 The maximum unbalance for a main tire and any tire over 46 inches outside diameter is slightly greater: M 0.035Do 2 where the moment, M, is given in ounce-inches and the outer diameter of the tire, Do, is in inches.

Aircraft Tires: Key Principles for Landing Gear Design

27

For civil tires, with a speed rating greater than 120 miles per hour (and optionally for 120 mile per hour tires), TSO-C62e requires that 61 test cycles be conducted on a single tire specimen:

•• 50 take-off cycles to a choice of a standardized load-speed-time curve or to

the aircraft’s specific load-speed-time curve (the standard curve for tires with a speed rating over 160 miles per hour is shown in Figure 1.19)

•• 1 overload take-off cycle at 1.5 times the rated load •• 8 taxi cycles at a minimum of 40 miles per hour (25,000 feet distance for tires

with a rated speed under 160 miles per hour, 35,000 feet for tires over 160 miles per hour rating)

•• 2 overload taxi cycles at the same speed and distances as above, but with the load increased to 1.2 times the rated load

Only normal abrasive wear to the tire tread is permitted following the tests (unless the overload take-off test is performed last in which case the tire tread does not need to be in good condition, but the tire should not show other signs of deterioration). Following all of the tests, the tire needs to retain the inflation pressure to within 10% over a 24-hour period. The military requirement for tire qualification is similar to the civil for load and speed testing, but it can be more aircraft specific: the detailed requirements are dependent on the procurement specification. Minimum wear life requirements are

© SAE International.

 FIGURE 1.19   Standard load-speed-time curve.

28

Aircraft Tires: Key Principles for Landing Gear Design

provided for military aircraft: 50 flight cycles for trainer and tactical aircraft, 100 flight cycles for other aircraft (transport, strategic, etc.). For a carrier-based aircraft, an arrestor cable bruise test is prescribed: at carrier inflation pressure, the tire is to be loaded against a 1.625 inch diameter cable or steel rod on two locations, 180° opposite to each other without detriment to the tire integrity. In addition to the civil and military certification requirements, a number of standards and relevant recommended practices for tires are published by SAE International, notably ARP6152 [12] on service overload capability (which recommends that the 1.5 overload factor in TSO-C62e be augmented to represent the actual expected overload in the event of a companion tire failure) and AS4833 [17] which supplements the requirements in TSO-C62e. Many aircraft manufacturers require additional testing: foreign object damage testing where the tread is damaged by rolling over a knife blade (the tire must then survive one full takeoff cycle on the dynamometer), overspeed landing, side slip during takeoff and landing, wheel compatibility testing (especially if multiple tires are to be qualified for a given wheel), thermal characterization, and cold set flat spotting.

Tire Sizing In general, the landing gear designer will typically select tires from the manufacturers’ catalogs, which contain tables of the existing tire sizes and their relevant properties. Depending on the specific need, a new or modified tire can be designed if a standard size is not available. This new design can take the form of an additional reinforcement (increased ply rating) or an entirely new size. The TRA provides a set of formulae to estimate the load carrying capability and inflation pressure of tires based on the overall diameter, width, rim diameter, deflection, and ply rating.

Tire Sizing Formulae The load carrying capacity of a tire is effectively the product of the tire inflation pressure and the ground contact patch area. As previously outlined, this would be exactly true if a tire was a balloon with no reinforcement. As additional reinforcing elements are added to the tire, a proportion of the load is taken by these elements in addition to the inflation pressure. The TRA provides a calculation of the maximum tire load, Lm, as a function of the pressure index, P, a term, Pc, which represents the load supporting capability of the tire carcass in units of equivalent pressure, and the ground contact area as a function of the design deflection, Ad: where:

Lm

Ad P Pc

•• Lm is the maximum load capacity in units of pounds •• Ad is ground contact area in square inches at design deflection, d:

Ad

0.77 d

Dm d Wm d

Aircraft Tires: Key Principles for Landing Gear Design

29

where:

•• d is the design deflection of the tire in inches (difference between the mean tire radius and the SLR) at the fractional design deflection, b:



b Dm

d

Df 2



•• b is the fractional tire deflection, typically 0.32 (for 32% deflection) •• Dm is the mean tire diameter •• Df is the diameter of the wheel flange P is the pressure index and is given by the expression:

40Re To N e S Fo

P

where:

•• N is the ply rating of the tire •• Ne is given by: Ne = N − 0.4 •• Re is the ratio of ends per inch – cured to green (a tire construction term), which is a function of the lift ratio, Lr. For values of Lr between 1.5 and 2.2, Re is given by:



Re

1.475 0.331Lr

For values of Lr between 2.2 and 5, Re is given by:

Re

0.007651Lr 5 0.14362Lr 4 1.0668308Lr 3 3.9519228Lr 2 7.4168297Lr 6.3261135

Lr is the lift ratio, the ratio of the mean diameter to the rim diameter:

Dm D

Lr

To is a constant: for type III tires, To = 4; for all other tires, To = 4.4 S is the product of a and Q (S = aQ) where:



a

Dm

Q 2.5

D 4



D 2 Dm

30

Aircraft Tires: Key Principles for Landing Gear Design

Fo is the operating factor, a function of the rim diameter, D:

Fo

1.623104 10 7 D 5 1.463062 10 5 D 4 5.607522 10 4 D 3 0.01288401D 2 0.197904D 2.567982

Pc is the pressure equivalent of tire carcass, which has a value equal to the ply rating, N, if the mean cross section of the tire is less than 5.5 inches and a value according to the following expression for cross sections greater than 5.5 inches: 10.4 N 2 Wm 2



Wm is the mean overall tire width The TRA standardizes new tire sizes in increments of 0.5 inches for the maximum outer diameter, Do and increments of 0.25 inches for the maximum width, W, for tires up to 10 inches wide; for tires wider than 10 inches, the increments are 0.5 inches. The previous calculation is always conducted at 32%. For tires with a different design deflection, the load rating is first calculated as above for the 32%, then a new P term is calculated:

P

Lm b 0.45 Ad

Pc

where Ad is calculated using the required deflection, b. The pressure index, P, determined in the expressions above is an indicator of inflation pressure, but not the actual inflation pressure. The inflation pressure, Pi, is determined from the expression:

Pi

P

XPc

3, in pounds per square inch

where for values of P greater than 100, X = 0.5 and for values of P less than or equal to 100, X = 0.01P − 0.5. These formulas are of use to the landing gear designer where an existing tire does not exist and the possibilities of an entirely new tire size need to be explored or to see the change in load rating possible by taking an existing tire size and developing a new ply rating. Typically, landing gear design work starts with tables of tire properties that are provided by the tire manufacturers in their catalogs or from the tables provided by the standardization body, TRA or ETRTO. Not every tire parameter is included in these tables, and some tires may be unsuitable for the aircraft and landing gear being contemplated. The choice of tire size should always involve the tire manufacturer.

Tire Sizing Requirements In general, the landing gear designer is seeking the smallest and lightest possible tire compatible with the load, speed, and tire life requirements of the aircraft. However, it is wise to consider during initial sizing that aircraft tend to grow in weight and capability

Aircraft Tires: Key Principles for Landing Gear Design

31

over time and that requiring a new, or larger, tire to be integrated to the aircraft at a later time may not be feasible. It has been recommended historically that the initial tire selection be done assuming 25% growth capability. However, this may result in a tire which is significantly oversize for many applications (the 25% value is potentially a good guide at the outset of a new aircraft project, where the weight of the aircraft is quite uncertain). It may be possible to gain the required additional growth capability through tire redesign at higher ply ratings; however, it is wise to ensure that the selected tire has growth potential. On some (very rare) aircraft, there may be no possibility of future weight increases (a race aircraft designed to meet rules which limit maximum weight, for instance), and in this case, the tire can be selected with no margin for future weight escalation. The selected load rating for the tire must take into account the most severe operating loads to be seen. For main landing gear tires, this is typically maneuvering and take-off at the maximum aircraft weight and most aft center of gravity position. The tire can typically be sized for this condition considering static loading conditions; transient dynamic loading of the tire during take-off greater than the load rating is typically acceptable. For nose landing gears, the most severe condition is typically braking at the maximum weight and forward center of gravity condition. Due to the transient nature of braking, the tire can withstand up to 1.5 times the maximum load rating (except type III tires, for which a maximum of 1.45 times the load rating applies). For cases where there is more than one tire on a common axle, consideration of tire load variation due to differences in tire wear, inflation pressure, and runway camber is required. For large transport aircraft, there is a mandated factor [18] of 1.07 which must be applied to the calculated static tire loads – before comparing the load to the tire rating. For rotorcraft applications, due to the reduced rolling requirements on the tire, it is generally acceptable to use a tire up to 1.5 times [19] its rated load, provided the inflation pressure is increased proportionally. If the aircraft will have significant taxi distances, this guideline may not be applicable. The inflation pressure for a rotorcraft tire can be increased up to 1.8 times the rated aircraft inflation pressure. This may be desirable to provide a stiffer load/deflection curve, which can assist with reducing ground resonance issues. It is important to note that increasing the pressure to stiffen the tire does not increase the loading capacity beyond the 1.5 factor. When using a tire on rotorcraft at increased inflation pressures compared to the rated pressure, the maximum new tire dimensions should be increased by 4% to accommodate the increase in size due to the associated increase in inflation pressure.

Tire Tables Tables of available tire sizes, along with rated loads, inflation pressures, and dimensions are available in the year books published by the TRA and ETRTO as well as in the catalogs of the various tire manufacturers. A variety of tires are shown in Table 1.2 through Table 1.5. In contrast to the typical grouping in catalogs and TRA documents, the tires are sorted in ascending order of rated load capability. As the landing gear designer is typically looking for a tire to meet a specific load capability, this format facilitates the determination of the appropriate size. The weights indicated for each tire represent a nominal weight value (often an average value). The same size tire can

© SAE International.

160

160

4

4

6

4

6

4

6

8

6

6

10

12

6

6

8

6

14

8

5.00-5

8.00-4

6.00-6

5.00-4

7.00-6

5.00-5

8.00-6

6.00-6

5.00-5

7.00-6

8.00-6

5.00-5

5.00-4

8.50-6

6.50-8

6.00-6

7.00-8

5.00-4

7.00-6

6.50-10 6

120

160

160

120

120

120

160

160

120

120

120

120

120

120

120

4

Size

2,770

2,550

2,550

2,400

2,350

2,300

2,275

2,200

2,150

2,050

1,900

1,800

1,750

1,350

1,285

1,250

1,200

1,150

1,100

800

Speed Rated rating load (mph) (lb)

Ply rating

60

54

115

46

55

51

30

95

88

35

38

70

42

23

50

23

55

29

24

31

Unloaded inflation pressure (psi)

TABLE 1.2  Type III tire table.

11

13

7

8

14

14

7

11

13

8

10

5

10

4

8

10

5

0.3

0.3

0.2

0.3

0.2

0.3

0.3

0.2

0.2

0.2

0.2

0.1

0.2

0.2

0.1

0.1

0.1

0.1

0.2

0.1

Tire mass Nitrogen (lb) mass (lb)

22.10

18.75

13.25

20.85

17.50

19.85

22.10

13.25

14.20

19.50

18.75

14.20

17.50

19.50

14.20

18.75

13.25

17.50

18.00

14.20

Do Max (in.)

21.35

18.00

12.70

20.10

16.80

19.15

21.15

12.70

13.70

18.75

18.00

13.65

16.80

18.75

13.70

18.00

12.70

16.80

17.15

13.70

Do Min (in.)

19.90

16.45

11.60

18.55

15.45

17.70

19.20

11.60

12.60

17.05

16.45

12.55

15.45

17.05

12.60

16.45

11.60

15.45

15.50

12.60

Ds Max (in.)

6.65

7.00

5.05

7.30

6.30

6.90

8.85

5.05

4.95

7.95

7.00

4.95

6.30

7.95

4.95

7.00

5.05

6.30

8.30

4.95

W Max (in.)

6.25

6.44

4.75

6.85

5.90

6.35

8.30

4.75

4.65

7.35

6.44

4.65

5.90

7.35

4.65

6.45

4.75

5.90

7.70

4.65

W Min (in.)

5.65

5.94

4.30

6.20

5.35

5.85

7.50

4.30

4.20

6.75

5.94

4.19

5.35

6.75

4.20

5.95

4.30

5.35

7.05

4.20

Ws Max (in.)

0.91

0.91

0.92

0.88

0.91

0.86

0.91

0.92

0.93

0.85

0.91

0.93

0.91

0.85

0.93

0.91

0.92

0.91

0.84

0.93

9.10

7.30

5.20

8.30

6.90

8.00

8.40

5.20

5.65

7.50

7.30

5.65

6.90

7.50

5.65

7.30

5.20

6.90

6.65

5.65

5.00

3.50

5.50

5.00

5.25

6.00

3.50

3.50

5.00

5.00

3.50

5.00

5.00

3.50

5.00

3.50

5.00

5.50

3.50

Width between flanges (A) (in.)

6.50-10 4.75

7.00-6

5.00-4

7.00-8

6.00-6

6.50-8

8.50-6

5.00-4

5.00.5

6.00-6

7.00-6

5.00.5

6.00-6

6.00-6

5.00.5

6.00-6

5.00-4

6.00-6

8.00-4

5.00.5

Static loaded radius (at rated Aspect load) Wheel Ratio (in.) size

10.00

6.00

4.00

8.00

6.00

8.00

6.00

4.00

5.00

6.00

6.00

5.00

6.00

6.00

5.00

6.00

4.00

6.00

4.00

5.00

Specified rim diameter (D) (in.)

0.81

0.75

0.75

0.81

0.75

0.81

0.88

0.75

0.75

0.75

0.75

0.75

0.75

0.75

0.75

0.75

0.75

0.75

0.69

0.75

Flange height (Fh) (in.)

0.85

0.90

1.10

1.30

0.90

0.95

0.90

0.80

0.80

0.85

0.85

0.80

0.85

0.85

0.80

0.85

0.80

0.80

0.61

0.80

Min ledge width (G) (in.)

32 Aircraft Tires: Key Principles for Landing Gear Design

© SAE International.

6.50-8

120

120

3,150

3,100

2,800

120

10

9.00-6

120

8.50-10 10

159

7,738

200

6.50-10 14

125

6,650

150

16

7.00-8

45

120

6,300

5,750

6.50-10 12

87

70

100

35

58

84

55

50

80

73

41

75

131

48

11.00-12 8

5,700

7.50-14 8

160

4,750

160

6.50-10 10

5,500

4,600

4,500

4,500

4,400

4,200

3,750

11.00-12 6

120

160

10

160

6

8.9012.50

7.00-8

160

6.50-10 8

8.50-10 8

160

10

3,600

8

5.00-5

7.00-6

14

8.00-6

3,250

8

Size

Speed Rated rating load (mph) (lb)

8.50-10 6

Ply rating

Unloaded inflation pressure (psi)

19

19

22

24

15

21

15

23

27

11

12

18

13

11

0.8

0.7

1.1

0.6

0.8

0.7

0.5

0.9

0.6

0.5

0.6

0.6

0.4

0.3

0.5

0.4

0.2

0.3

Tire mass Nitrogen (lb) mass (lb)

TABLE 1.2  (Continued) Type III tire table.

20.10

24.70

27.30

21.35

18.00

24.70

19.20

13.70

18.75

Do Min (in.)

22.10

20.85

32.20

22.10

27.75

25.65

22.10

32.20

21.35

20.10

31.00

21.35

27.00

24.70

21.35

31.00

22.40 21.40

20.85

25.65

27.70

22.10

18.75

25.65

19.85

14.20

19.50

Do Max (in.)

19.90

18.55

28.55

19.90

25.30

22.80

19.90

28.55

19.45

18.55

22.80

24.95

19.90

16.50

22.80

17.70

12.60

17.05

Ds Max (in.)

6.65

7.30

11.20

6.65

7.65

8.70

6.65

11.20

9.25

7.30

8.70

9.00

6.65

7.00

8.70

6.90

4.95

7.95

W Max (in.)

7.85

6.20

7.40

7.65

5.65

5.95

7.40

5.85

4.20

6.75

Ws Max (in.)

5.65

6.50

7.40

5.65

6.25

6.85

5.65

6.20

10.50 9.50

6.25

7.20

8.20

6.25

10.50 9.50

8.55

6.85

8.20

8.65

6.25

6.45

8.20

6.35

4.65

7.35

W Min (in.)

0.91

0.88

0.90

0.91

0.90

0.90

0.91

0.90

0.89

0.88

0.90

0.85

0.91

0.91

0.90

0.86

0.93

0.85

9.25

8.30

12.70

9.10

11.60

10.20

9.10

12.70

8.45

8.30

10.20

11.35

9.10

7.30

10.20

8.00

5.65

7.50 5.25

3.50

5.00

Width between flanges (A) (in.)

5.00 6.75

6.75

5.50

5.50 6.50-10 4.75

7.00-8

11.00-12 8.25

6.50-10 4.75

7.50-14 5.50

8.50-10 6.25

6.50-10 4.75

11.00-12 8.25

9.00-6

7.00-8

8.50-10 6.25

8.9012.50

6.50-10 4.75

6.00-6

8.50-10 6.25

6.50-8

5.00.5

6.00-6

Static loaded radius (at rated Aspect load) Wheel Ratio (in.) size

10.00

8.00

12.00

10.00

14.00

10.00

10.00

12.00

6.00

8.00

10.00

12.50

10.00

6.00

10.00

8.00

5.00

6.00

Specified rim diameter (D) (in.)

0.81

0.81

1.00

0.81

0.81

0.81

0.81

1.00

0.88

0.81

0.81

0.88

0.81

0.75

0.81

0.81

0.75

0.75

Flange height (Fh) (in.)

1.10

1.30

1.40

1.10

1.65

1.35

1.10

1.40

1.45

1.30

1.35

1.20

1.10

0.90

1.35

0.95

0.80

0.85

Min ledge width (G) (in.)

Aircraft Tires: Key Principles for Landing Gear Design 33

© SAE International.

120

160

160

160

160

160

8.50-10 16

12.50-16 10

9.50-16 12

10

14

15.0016

15.0012

12.50-16 12

12,800

12,700

12,200

11,200

10,600

9,900

9,250

8,700

14

16

14

16

15.0016

15.0016

15.5020

15.5020

160

160

24,000

20,800

19,700

17,100

16,000

160

9.50-16 10

160

120

8.50-10 14

8,700

17.00-16 12

160

7.50-14 12

8,200

8,000

15,000

160

12.50-16 14

160

11.00-12 10

Speed Rated rating load (mph) (lb)

8.50-10 12

Size

Ply rating

106

90

81

71

60

90

75

65

53

110

60

129

90

110

130

60

100

Unloaded inflation pressure (psi)

112

95

98

75

60

87

58

70

35

24

36

44

28

5.7

4.9

4.0

3.6

4.1

2.9

2.5

2.5

2.9

1.9

2.1

1.3

1.6

1.1

1.1

1.3

1.0

Tire mass Nitrogen (lb) mass (lb)

TABLE 1.2  (Continued) Type III tire table.

32.50

37.50

24.70

32.50

24.70

27.00

31.00

24.70

Do Min (in.)

37.50

37.50

45.25

45.25

8.70

9.70

8.70

7.65

11.20

8.70

W Max (in.)

0.90

0.89

0.90

0.90

9.10

8.25

0.89

16.35 14.80 0.84

12.00 10.85 0.89

12.00 10.85 0.89

18.60

44.30 40.70 16.00 15.05 13.60 0.80

16.80

16.80

17.70

15.60

15.60

14.10

16.80

13.85

15.60

10.20

13.85

10.20

11.60

12.70

10.20

18.60

15.30 14.40 13.00 0.87

15.30 14.40 13.00 0.87

39.80 17.40

37.65

7.40

8.25

7.40

6.50

12.00 10.85 0.89

8.20

9.10

8.20

7.20

0.90

0.90

14.70 13.95 12.50 0.83

34.40 12.75 37.65

7.40

Ws Max (in.)

10.50 9.50

8.20

W Min (in.)

15.30 14.40 13.00 0.87

9.70

34.40 12.75

31.95

37.65

30.25

34.40 12.75

22.80

30.25

22.80

25.30

28.55

22.80

Ds Max (in.)

44.30 40.70 16.00 15.05 13.60 0.80

42.40 41.40

42.40 41.40

45.05 43.70

38.45

38.45

36.30 35.35

42.40 41.40

33.35

38.45

25.65

33.35

25.65

27.75

32.20

25.65

Do Max (in.)

Width between flanges (A) (in.)

11.00

11.25

17.0020

17.0020

15.0016

15.0016

13.25

13.25

11.25

11.25

17.00-16 13.25

12.50-16 10.00

12.50-16 10.00

15.0012

15.0016

9.50-16 7.00

12.50-16 10.00

8.50-10 6.25

9.50-16 7.00

8.50-10 6.25

7.50-14 5.50

11.00-12 8.25

8.50-10 6.25

Static loaded radius (at rated Aspect load) Wheel Ratio (in.) size

20.00

20.00

16.00

16.00

16.00

16.00

16.00

12.00

16.00

16.00

16.00

10.00

16.00

10.00

14.00

12.00

10.00

Specified rim diameter (D) (in.)

1.63

1.63

1.38

1.19

1.38

1.25

1.25

1.00

1.19

1.00

1.25

1.13

1.00

0.81

0.81

1.00

0.81

Flange height (Fh) (in.)

2.20

2.20

1.90

1.75

2.00

1.90

1.90

2.50

1.75

1.75

1.80

1.75

1.15

1.65

1.40

1.50

Min ledge width (G) (in.)

34 Aircraft Tires: Key Principles for Landing Gear Design

© SAE International.

16

20

22

22

20

26

19.0023

15.5020

17.0020

20.0020

20.0020

20.0020

Size

Ply rating

200

200

200

120

160

46,500

46,500

38,500

34,500

29,900

29,000

Speed Rated rating load (mph) (lb)

125

125

95

130

135

85

Unloaded inflation pressure (psi)

265

13.8

13.8

10.8

8.8

7.1

8.7

Tire mass Nitrogen (lb) mass (lb)

TABLE 1.2  (Continued) Type III tire table.

W Max (in.) W Min (in.)

49.30 19.38 18.25

Ds Max (in.) 16.50 0.83

Ws Max (in.)

47.70

43.60 17.25

56.00 54.30 49.50 20.10 19.20 17.10

56.00 54.30 49.50 20.10 19.20 17.10 0.89

0.89

0.89

16.40 14.65 0.84

44.30 40.70 16.00 15.05 13.60 0.80

53.15

Do Min (in.)

56.00 54.30 49.50 20.10 19.20 17.10

48.75

45.25

55.10

Do Max (in.)

22.10

22.00

22.00

19.80

18.60

22.60

20.0020

20.0020

20.0020

17.0020

Static loaded radius (at rated Aspect load) Wheel Ratio (in.) size

15.50

15.50

15.50

13.25

13.25

14.75

Width between flanges (A) (in.)

20.00

20.00

20.00

20.00

20.00

23.00

Specified rim diameter (D) (in.)

2.00

2.00

2.00

1.75

1.63

2.00

Flange height (Fh) (in.)

3.50

3.50

3.50

2.80

2.20

Min ledge width (G) (in.)

Aircraft Tires: Key Principles for Landing Gear Design 35

© SAE International.

210

12

8

10

10

10

14

20×4.4

26×6.6

24×7.7

22×5.5

24.5×8.5

20×4.4

12

12

18×4.4

18×5.5

10

8

18×5.5

24×7.7

190

12

10

16×4.4

18×4.4

190

255

210

230

210

225

200

210

160

190

210

6

8

24×7.7

190

160

190

160

210

6,000

5,700

5,700

5,400

5,325

5,150

5,050

4,350

4,150

4,000

3,550

3,475

3,050

2,950

2,900

2,300

2,250

2,100

1,700

1,100

Speed Rated rating load (mph) (lbs)

18×5.5

8

10

16×4.4

16×4.4

6

6

18×4.4

18×5.5

4

6

16×4.4

Size

16×4.4

Ply rating

265

85

185

90

125

225

170

225

75

140

185

185

105

55

155

120

75

100

85

55

Unloaded inflation pressure (psi)

TABLE 1.3  Type VII tire table.

15

36

22

27

15

15

13

23

14

13

9

13

23

10

9

10

8

8

0.6

0.8

0.7

0.7

0.8

0.5

0.5

0.4

0.6

0.4

0.4

0.3

0.3

0.5

0.3

0.2

0.2

0.2

0.2

0.1

Tire Nitrogen mass mass (lbs) (lbs)

16.20

16.50

14.55

16.20

17.30

17.40

21.55

20.00 19.50

19.45

21.90

21.30

23.30 21.50

25.05 23.55

19.45

16.20

16.50

23.30 21.50

17.30

17.40

15.50

17.30

24.50 23.75

22.15

24.15

25.75

14.55

14.55

16.20

16.50

14.55

14.55

Ds Max (in.)

23.30 21.50

15.50

15.50

17.30

17.40

15.50

15.50

Do Min (in.)

20.00 19.50

17.90

17.90

24.15

17.90

17.90

16.00

17.90

24.15

16.00

16.00

17.90

17.90

16.00

16.00

Do Max (in.)

4.45

8.50

5.70

7.65

6.65

4.45

5.75

4.45

7.65

5.75

4.45

4.45

5.75

7.65

4.45

4.45

5.75

4.45

4.45

4.45

W Max (in.)

4.15

8.00

5.35

7.20

6.25

4.15

5.35

4.15

7.20

5.35

4.15

4.15

5.35

7.20

4.15

4.15

5.35

4.15

4.15

4.15

W Min (in.)

3.95

7.50

4.95

6.75

5.85

3.95

5.00

3.90

6.75

5.00

3.90

3.90

5.00

6.75

3.90

3.90

5.00

3.90

3.90

3.90

Ws Max (in.)

0.90

0.86

0.89

0.92

0.88

0.90

0.87

0.89

0.92

0.87

0.89

0.90

0.87

0.92

0.90

0.90

0.87

0.89

0.90

0.90

8.90

10.05

9.65

9.95

11.20

8.90

7.50

7.85

9.95

7.50

7.85

6.90

7.50

9.95

6.90

6.90

7.50

7.85

6.90

6.90

20×4.4

24.5×8.5

22×5.5

24×7.7

26×6.6

20×4.4

18×5.5

18×4.4

24×7.7

18×5.5

18×4.4

16×4.4

18×5.5

24×7.7

16×4.4

16×4.4

18×5.5

18×4.4

16×4.4

16×4.4

Static loaded radius (at rated Aspect load) Wheel ratio (in.) size

3.50

6.25

4.25

5.50

5.00

3.50

4.25

3.50

5.50

4.25

3.50

3.50

4.25

5.50

3.50

3.50

4.25

3.50

3.50

3.50

Width between flanges (A) (in.)

12.00

10.00

12.00

10.00

14.00

12.00

8.00

10.00

10.00

8.00

10.00

8.00

8.00

10.00

8.00

8.00

8.00

10.00

8.00

8.00

Specified rim diameter (D) (in.)

0.81

0.81

0.88

0.91

1.00

0.81

0.88

0.81

0.91

0.88

0.81

0.81

0.88

0.91

0.81

0.81

0.88

0.81

0.81

0.81

Flange height (Fh) (in.)

1.25

1.35

1.25

1.25

1.40

1.25

1.25

1.25

1.25

1.25

1.25

3.50

1.25

1.25

0.90

0.80

1.50

1.05

0.80

0.80

Min ledge width (G) (in.)

36 Aircraft Tires: Key Principles for Landing Gear Design

© SAE International.

6,900

160

200

200

190

10

12

12

14

26×6.6

24.5×8.5

22×5.5

20×5.5

16

16

14

29×7.7

30×8.8

40×14

14

32×8.8

12,000

14

16

16

24×5.5

26×6.6

14

11,500

12,000

14

12

28×7.7

32×8.8

30×7.7

11,000

11,000

200

14

12

26×6.6

30×8.8

30×8.8

10,200

210

10

16

32×8.8

225

210

200

200

200

8,200

14,900

14,200

13,800

13,000

12,450

10,000

9,725

9,050

8,600

24×7.7

225

14

12

24×7.7

7,200

7,100

6,900

26×6.6

210

6,200

6,800

24×7.7

275

14

12

Size

18×5.5

Speed Rated rating load (mph) (lbs)

Ply rating

90

200

230

170

177

185

270

355

140

195

139

225

165

115

185

135

230

235

90

155

110

215

Unloaded inflation pressure (psi)

53

46

42

28

35

33

33

32

29

18

20

27

30

16

3.5

2.4

2.0

2.1

2.1

1.7

1.6

1.5

1.7

1.6

1.7

1.3

1.2

1.5

1.1

1.0

0.8

0.9

0.8

0.9

0.8

0.6

Tire Nitrogen mass mass (lbs) (lbs)

TABLE 1.3  (Continued) Type VII tire table.

22.15

21.55

21.30 19.30

27.40

25.05 23.55

23.30 21.50

8.35

39.80 38.85 35.10

30.30 29.50 27.35

8.30

7.40

8.35

7.85

6.95

7.90

7.85

6.95

5.85

4.95

7.90

6.95

7.85

5.85

6.75

7.90

5.85

6.75

4.95

4.95

7.50

5.85

6.75

5.00

Ws Max (in.) 0.87

0.87

0.85

0.84

0.87

0.85

0.88

0.89

0.84

0.85

0.87

0.88

0.92

0.84

0.88

0.92

0.89

0.89

0.86

0.88

0.92

14.00 13.25 12.00 0.86

8.90

25.90 7.85

30.05 28.05 8.90

28.40 27.60

31.00

8.30

8.90

7.40

6.25

5.35

8.35

7.40

8.30

6.25

7.20

30.30 29.50 27.35

6.65

23.30 5.75

25.05 23.55

23.55

30.05 28.05 8.90

26.60 24.90 7.85

8.90

6.65

7.65

6.25

7.20

5.35

5.35

8.00

6.25

7.20

5.35

W Min (in.)

29.40 28.60 26.90 7.85

25.75

24.15

31.00

6.65

7.65

5.70

5.70

8.50

6.65

7.65

5.75

W Max (in.)

30.05 28.05 8.90

25.05 23.55

23.30 21.50

19.55

21.90

25.05 23.55

30.30 29.50 27.35

25.75

24.15

31.00

25.75

24.15

20.15

16.20

Ds Max (in.)

23.30 21.50

17.30

Do Min (in.)

24.50 23.75

25.75

24.15

17.90

Do Max (in.)

16.45

12.90

12.20

13.30

12.90

12.75

11.20

10.65

13.30

11.75

12.90

11.20

9.95

13.30

11.20

9.95

8.65

9.65

9.85

11.20

9.95

7.50

40×14

30×8.8

29×7.7

32×8.8

30×8.8

30×7.7

26×6.6

24×5.5

32×8.8

28×7.7

30×8.8

26×6.6

24×7.7

32×8.8

26×6.6

24×7.7

20×5.5

22×5.5

24.5×8.5

26×6.6

24×7.7

18×5.5

Static loaded radius (at rated Aspect load) Wheel ratio (in.) size

11.00

7.00

6.00

7.00

7.00

6.00

5.00

4.25

7.00

6.00

7.00

5.00

5.50

7.00

5.00

5.50

4.25

4.25

6.25

5.00

5.50

4.25

Width between flanges (A) (in.)

16.00

15.00

15.00

16.00

15.00

16.00

14.00

14.00

16.00

14.00

15.00

14.00

10.00

16.00

14.00

10.00

10.00

12.00

10.00

14.00

10.00

8.00

Specified rim diameter (D) (in.)

1.63

1.13

1.00

1.13

1.13

1.00

1.00

0.88

1.13

1.00

1.13

1.00

0.91

1.13

1.00

0.91

0.88

0.88

0.81

1.00

0.91

0.88

Flange height (Fh) (in.)

2.40

2.25

2.00

1.75

2.25

1.65

1.70

1.38

1.75

1.75

2.25

1.70

1.70

1.75

1.70

1.70

1.38

1.45

1.35

1.40

1.25

1.50

Min ledge width (G) (in.)

Aircraft Tires: Key Principles for Landing Gear Design 37

© SAE International.

16,500

17,025

17,200

18

16

16

16

30×7.7

32×8.8

39×13

40×14

22

22

39×13

20

40×12

40×14

22

20

36×11

42×15

210

225

22,300

20

20

39×13

40×14

21,375

18

18

40×12

42×15

20,500

25,000

24,600

23,900

23,500

23,300

22,300

21,000

21,000

22

20

34×11

20,350

36×11

225

210

19,400

18

18

39×13

44×16

18,300

18,500

20

16

34×11

17,300

40×12

210

225

230

15,000

16,100

34×11

210

14

18

Size

39×13

Speed Rated rating load (mph) (lbs)

Ply rating

155

165

170

120

200

135

150

104

150

185

185

100

130

130

165

105

115

242

270

145

100

Unloaded inflation pressure (psi)

113

89

82

87

104

89

49

80

5.7

5.1

5.0

5.7

4.3

5.0

4.6

5.0

4.5

4.0

3.7

5.1

4.1

3.9

3.3

4.0

3.6

2.9

2.4

3.0

3.2

Tire Nitrogen mass mass (lbs) (lbs)

TABLE 1.3  (Continued) Type VII tire table.

37.30

Do Min (in.) W Max (in.)

37.30

8.35

7.40

0.86

0.86

0.84

0.85

0.87

0.87 0.86

34.00 31.65

11.50

10.60 9.95

37.30

35.10

11.50

10.80 10.10

38.25

37.30

14.00 13.25 12.00 0.86

0.86

10.90 0.87

34.25 13.00 12.25 11.45

39.80 38.85 35.10

0.83

15.30 14.40 13.45 0.87

39.40 38.40 35.50 12.35 11.70

37.65

34.00 31.65

42.40 41.40

14.00 13.25 12.00 0.86

0.86

15.30 14.40 13.45 0.87

34.25 13.00 12.25 11.45

37.65

39.80 38.85 35.10

38.25

42.40 41.40

0.87 0.83

10.90 0.87

10.80 10.10

39.40 38.40 35.50 12.35 11.70

35.10

33.40 32.60 29.90 11.30

43.25 42.30 38.20 16.00 15.05 13.70 0.80

34.25 13.00 12.25 11.45

10.90 0.87

10.60 9.95

14.00 13.25 12.00 0.86

33.40 32.60 29.90 11.30 37.30

7.90

6.95

10.60 9.95

39.40 38.40 35.50 12.35 11.70 38.25

Ws Max (in.)

34.25 13.00 12.25 11.45

39.80 38.85 35.10

38.25

30.05 28.05 8.90

29.40 28.60 26.90 7.85 31.00

W Min (in.)

34.25 13.00 12.25 11.45

Ds Max (in.)

33.40 32.60 29.90 11.30

38.25

Do Max (in.)

16.45

15.80

16.60

17.30

14.70

16.45

15.80

17.30

16.60

14.70

13.90

17.90

15.80

16.60

13.90

16.45

15.80

13.30

12.75

13.90

15.80

40×14

39×13

40×12

42×15

36×11

40×14

39×13

42×15

40×12

36×11

34×11

44×16

39×13

40×12

34×11

40×14

39×13

32×8.8

30×7.7

34×11

39×13

Static loaded radius (at rated Aspect load) Wheel ratio (in.) size

11.00

10.00

10.00

11.50

9.00

11.00

10.00

11.50

10.00

9.00

9.00

13.25

10.00

10.00

9.00

11.00

10.00

7.00

6.00

9.00

10.00

Width between flanges (A) (in.)

16.00 16.00

1.63

1.25

1.50

1.50 18.00

1.38 16.00

1.63

1.25

1.50

1.50

1.38

1.50

1.63

1.25

1.50

1.50

1.63

1.25

1.13

1.00

1.50

1.25

Flange height (Fh) (in.)

16.00

16.00

16.00

16.00

18.00

16.00

14.00

18.00

16.00

18.00

14.00

16.00

16.00

16.00

16.00

14.00

16.00

Specified rim diameter (D) (in.)

2.95

2.30

2.60

2.75

2.60

2.40

2.30

2.75

2.60

2.60

2.70

3.25

2.30

2.60

2.70

2.40

2.30

1.75

2.15

2.70

2.20

Min ledge width (G) (in.)

38 Aircraft Tires: Key Principles for Landing Gear Design

© SAE International.

26,300

35,725

38,300

200

225

28

24

26

28

40×14

46×16

46×16

44×16

29,900

32

32

34

46×16

49×17

49×17

30

49×17

44,800

30

32

46×16

44×16

43,200

28

28

46×16

225

225

225

225

225

39,600

53,900

50,400

48,000

46,700

45,000

41,800

41,700

49×17

225

26

30

49×17

44×16

38,400

33,100

32,525

20

22

29,000

27,700

27,400

26,700

26,500

46×16

200

225

210

201

Speed Rated rating load (mph) (lbs)

46×16

24

24

40×14

42×15

22

24

40×12

39×13

22

24

36×11

Size

42×15

Ply rating

220

210

245

195

225

225

180

210

210

165

185

185

170

200

155

145

150

170

188

190

235

135

Unloaded inflation pressure (psi)

227

208

227

208

177

176

176

168

121

133

104

73

14.3

13.7

12.3

12.8

10.6

11.3

11.9

10.6

10.0

11.0

8.9

9.4

8.7

7.2

8.0

7.5

7.0

6.2

5.7

5.6

5.0

6.3

Tire Nitrogen mass mass (lbs) (lbs)

TABLE 1.3  (Continued) Type VII tire table.

Do Min (in.) 34.00 31.65

37.65

Ds Max (in.) W Min (in.)

37.30

11.50

37.65

14.00 13.25 12.00 0.86 0.80 0.80

0.80

0.80

43.00 17.25

16.40 14.50 0.84 0.80

16.60

48.75 47.70

48.75 47.70

43.00 17.25

43.00 17.25

16.40 14.50 0.84

16.40 14.50 0.84

0.80

16.40 14.50 0.84

45.25 44.30 40.70 16.00 15.05 14.10

43.00 17.25

20.20

20.20

19.00

20.20

17.90

48.75 47.70

19.00

20.15

19.00

17.90

20.15

17.90

19.00

19.00

16.45

19.00

19.00

17.30

16.45

15.85

0.80

16.40 14.50 0.84

45.25 44.30 40.70 16.00 15.05 14.10

43.00 17.25

17.30 14.70

43.25 42.30 38.20 16.00 15.05 13.70 0.80

48.75 47.70

45.25 44.30 40.70 16.00 15.05 14.10

43.25 42.30 38.20 16.00 15.05 13.70 0.80

48.75 47.70

43.25 42.30 38.20 16.00 15.05 13.70 0.80

45.25 44.30 40.70 16.00 15.05 14.10

45.25 44.30 40.70 16.00 15.05 14.10

14.00 13.25 12.00 0.86

45.25 44.30 40.70 16.00 15.05 14.10 39.80 38.85 35.10

0.86

15.30 14.40 13.45 0.87

45.25 44.30 40.70 16.00 15.05 14.10

42.40 41.40

0.83

10.90 0.87

10.80 10.10

34.25 13.00 12.25 11.45

39.80 38.85 35.10

38.25

Ws Max (in.)

15.30 14.40 13.45 0.87

W Max (in.)

39.40 38.40 35.50 12.35 11.70

35.10

42.40 41.40

Do Max (in.)

49×17

49×17

46×16

49×17

44×16

46×16

49×17

46×16

44×16

49×17

44×16

46×16

46×16

40×14

46×16

46×16

42×15

40×14

39×13

40×12

36×11

42×15

Static loaded radius (at rated Aspect load) Wheel ratio (in.) size

13.25

13.25

13.25

13.25

13.25

13.25

13.25

13.25

13.25

13.25

13.25

13.25

13.25

11.00

13.25

13.25

11.50

11.00

10.00

10.00

9.00

11.50

Width between flanges (A) (in.)

20.00

20.00

20.00

20.00

18.00

20.00

20.00

20.00

18.00

20.00

18.00

20.00

20.00

16.00

20.00

20.00

16.00

16.00

16.00

18.00

16.00

16.00

Specified rim diameter (D) (in.)

1.88

1.88

1.88

1.88

1.63

1.88

1.75

1.75

1.63

1.75

1.63

1.75

1.75

1.63

1.75

1.75

1.50

1.63

1.38

1.50

1.38

1.50

Flange height (Fh) (in.)

3.65

3.65

3.40

3.50

3.25

3.40

3.25

3.25

3.40

3.25

3.25

3.25

3.25

3.10

3.25

3.25

2.75

2.95

2.80

2.60

2.80

2.75

Min ledge width (G) (in.)

Aircraft Tires: Key Principles for Landing Gear Design 39

© SAE International.

3,500

4,000

H19.5×6.75-10 8

160

68

155

55

135

86

112

143

105

135

70

120

137

90

4,000

40

25

167

12

100

61

3,750

15×6.0-6

160

45

68

3,600

3,550

8

160

3,300

3,450

10

120

3,100

3,200

17.5×6.25-11

14

230

210

160

3,000

3,000

2,900

2,800

2,765

2,500

2,300

2,300

1,950

17.5×6.25-6

8

22×8.0-8

14.5×5.5-6

8

14

19.5×6.75-8

13.5×6.0-4

180

14

10

13×5.0-4

8

15×6.0-6

190

12

14.5×5.5-6

18×5.75-8

190

190

6

22×8.0-8

26×10.5-6

8

120

120

6

6

18×4.25-10

19.5×6.75-8

22×6.5-10

210

190

6

6

15×6.0-6

17.5×6.25-6

160

4

6

Size

15×6.0-6

1,250

Speed Rated Ply rating load rating (mph) (lbs)

16

11

13

10

7

17

9.5

8

14

11

14

23

13

12

8

7

0.5

0.3

0.3

0.4

0.3

0.4

0.3

0.4

0.3

0.2

0.3

0.3

0.3

0.4

0.5

0.3

0.3

0.2

0.2

0.1

18.90

17.75

14.55

14.55

Do Min (in.)

21.35

13.20

18.90

14.55

12.70

17.40

19.50

15.20

17.50

17.70

14.50

19.90 15.45

19.50

12.00

17.45

13.55

11.60

16.20

18.90

14.55

16.85 17.80

13.55

15.45

16.50

14.00 13.00 17.30

8.00

6.75

4.70

6.30

6.30

W Max (in.)

7.55

6.20

4.45

5.90

5.90

W Min (in.)

6.75

6.30

6.25

6.10

5.50

8.00

6.10

6.75

6.30

5.25

5.75

5.50

6.25

6.65

6.35

5.90

5.90

5.70

5.15

7.55

5.75

6.20

5.90

4.95

5.40

5.15

5.90

6.25

22.40 10.50 9.95

19.50

17.45

16.75

13.55

13.55

Ds Max (in.)

14.00 13.00

16.85

22.00 21.35

13.75

19.50

15.20

13.25

18.00

14.50

17.50

22.10

26.00 25.10

22.00 21.35

19.50

18.25

15.20

15.20

Unloaded inflation Tire Nitrogen Do pressure mass mass Max (psi) (lbs) (lbs) (in.)

TABLE 1.4  Three part bias tire table.

5.95

5.55

5.50

5.45

4.85

7.05

5.40

5.95

5.55

4.60

5.10

4.85

5.50

5.65

9.25

7.05

5.95

4.15

5.55

5.55

Ws Max (in.)

0.70

0.73

0.92

0.55

0.78

0.88

0.80

0.85

0.73

0.88

0.87

0.78

0.92

0.91

0.96

0.88

0.85

0.87

0.73

0.73

8.25

6.10

6.90

7.95

6.10

8.70

5.35

8.05

6.10

5.30

7.60

6.40

6.90

9.20

9.65

8.70

8.05

7.90

6.10

6.10

5.00

5.00

5.25

4.25

6.00

4.75

5.25

5.00

4.25

4.25

4.25

5.00

4.75

6.75

6.00

5.25

3.63

5.00

5.00

Width between flanges (A) (in.)

H19.5×6.75-10 4.25

6.00-6

6.00-6

17.5×6.25-11

14.5×5.5-6

22×8.0-8

13.5×6.0-4

6.50-8

6.00-6

13×5.0-4

18×5.5

14.5×5.5-6

6.00-6

6.50-10

9.00-6

22×8.0-8

6.50-8

18×4.25-10

6.00-6

6.00-6

Static loaded radius (at rated Aspect load) ratio (in.) Wheel size

10.00

6.00

6.00

11.00

6.00

8.00

4.00

8.00

6.00

4.00

8.00

6.00

6.00

10.00

6.00

8.00

8.00

10.00

6.00

6.00

Specified rim diameter (D) (in.)

0.75

0.75

0.75

0.81

0.88

0.88

0.55

0.81

0.75

0.75

0.88

0.88

0.75

0.81

0.88

0.88

0.81

0.60

0.75

0.75

Flange height (Fh) (in.)

1.50

0.85

0.95

1.25

1.50

1.10

0.94

1.25

0.80

1.25

1.50

0.90

1.20

1.45

1.10

1.25

0.85

0.85

0.85

Min ledge width (G) (in.)

40 Aircraft Tires: Key Principles for Landing Gear Design

© SAE International.

190

190

190

10

10

20.5×6.75-10

22×7.75-10

225

12

12

12

10

12

22×7.75-10

H22×8.25-10

25×7.75-10

29×11.0-10

22×5.75-12

190

10

12

24×7.25-12

210

190

10

10

23×7.0-12

22×8.0-10

21.5×7.0-10

225

14

12

17.5×5.75-8

21×7.25-10

210

120

190

190

160

210

190

10

10

22×5.75-12

22×6.75-10

210

190

10

10

21×7.25-10

257

210

160

22×6.5-10

12

12

17.5×5.75-8

18×6.5-8

10

8

22×6.75-10

7,100

7,070

6,900

6,900

6,700

6,700

6,600

6,500

6,500

6,400

6,050

5,900

5,700

5,500

5,450

5,200

5,150

5,000

5,000

4,450

4,270

Size

19.5×6.75-8

Speed Rated Ply rating load rating (mph) (lbs)

220

60

115

132

133

135

120

110

135

166

220

125

180

110

158

125

135

150

180

95

110

24

39

26

19

24

20

17

22

20

21

20

15

20

13

15

20

17

0.8

1.1

0.9

0.8

0.8

0.7

0.8

0.7

0.8

0.8

0.6

0.6

0.7

0.7

0.7

0.6

0.7

0.5

0.5

0.5

0.5

18.90

Do Min (in.)

16.95

15.80 15.95

21.35

19.90

20.60 19.25

17.45

19.85

17.45

Ds Max (in.)

15.80

19.85

20.60 19.25

16.95

19.85

8.00

7.20

7.20

5.75

6.75

21.14

7.75

7.05

20.80 8.25

19.85

18.90

22.00 21.40

29.00 28.10

20.20 5.75

25.60 11.00

25.00 24.20 23.50 7.75

22.00 21.40

22.00 21.30

21.76

24.50 23.80 22.25 7.50

22.00 21.35

7.75

6.75

6.65

7.20

6.50

5.75

6.75

6.75

W Max (in.)

20.20 5.75

19.85

23.20 22.60 21.15

21.25

17.50

22.00 21.30

22.00 21.40

22.00 21.30

20.50 20.00 19.45

22.10

21.25

18.00

17.50

22.00 21.30

19.50

Unloaded inflation Tire Nitrogen Do pressure mass mass Max (psi) (lbs) (lbs) (in.)

TABLE 1.4  (Continued) Three part bias tire table.

7.00

7.45

6.80

6.14

6.50

7.05

6.30

6.35

5.10

5.95

5.05

6.80

6.10

5.65

6.35

5.70

5.10

5.95

5.95

Ws Max (in.)

5.40

5.05

10.40 9.35

7.30

7.80

7.30

6.73

7.00

7.55

6.80

6.80

5.40

6.35

5.40

7.30

6.35

6.25

6.80

6.20

5.40

6.35

6.20

W Min (in.)

0.87

0.87

0.97

0.73

0.77

0.83

0.84

0.75

0.78

0.78

0.83

0.89

0.87

0.77

0.78

0.91

0.78

0.77

0.83

0.89

0.85

9.60

11.40

10.30

9.10

9.05

9.00

10.40

9.00

9.90

9.00

7.40

9.10

9.60

9.05

8.80

9.20

9.05

7.60

7.40

9.10

8.05

22×5.5

29×11.0-10

H22×8.25-10

6.50-10

175×254×545

24×7.25-12

22×8.0-10

23×7.0-12

22×6.6

18×5.5

6.50-10

22×5.5

6.50-10

20.5×6.75-10

6.50-10

22×6.6

18×6.5-8

18×5.5

6.50-10

6.50-8

Static loaded radius (at rated Aspect load) ratio (in.) Wheel size

4.25

8.50

6.00

5.25

4.75

5.90

6.25

5.00

6.25

5.50

4.25

4.75

4.25

4.75

5.25

4.75

5.50

5.25

4.25

4.75

5.25

Width between flanges (A) (in.)

12.00

10.00

10.00

10.00

10.00

10.00

12.00

10.00

12.00

10.00

8.00

10.00

12.00

10.00

10.00

10.00

10.00

8.00

8.00

10.00

8.00

Specified rim diameter (D) (in.)

0.88

1.00

1.00

0.85

0.81

0.75

0.70

0.63

0.65

1.00

0.88

0.81

0.88

0.81

1.00

0.81

1.00

0.88

0.88

0.81

0.81

Flange height (Fh) (in.)

1.35

1.40

1.95

2.14

0.95

1.75

1.40

1.25

1.80

1.40

1.30

1.35

0.95

1.80

1.20

1.25

1.50

1.40

1.10

1.25

Min ledge width (G) (in.)

Aircraft Tires: Key Principles for Landing Gear Design 41

© SAE International.

190

16

26×6.75-14

225

12

16

12

31×9.75-14

32×11.5-15

190

10

34×10.75-16

200

190

190

230

18

18

22×6.75-10

22×6.6-10

H25×8.0-12

135

140

200

90

315

300

101

156

164

11,900

11,300

11,200

11,100

10,870

10,700

10,600

10,300

270

187

120

115

80

260

245

199

85

10,200

160

210

12

32×10.75-14

110

160

10,000 210

9,700

9,650

9,350

9,000

8,600

8,500

8,300

8,150

7,900

7,800

250

160

225

190

250

250

190

25.75×6.75-14 14

12

16

26×10.0-11

22×8.5-11

12

12

H31×9.75-13

27×7.75-15

18

20

18×5.7-8

18×5.7-8

14

14

H22×8.25-10

22×8.0-10

24×7.25-12

25.5×8.75-10

190

190

12

12

23×7.0-12

7,250

210

10

12

Size

26×7.75-13

210

Speed Rated Ply rating load rating (mph) (lbs)

38

61

39

61

25

23

31

53

26

30

39

40

16

16

34

29

27

28

28

31

1.7

1.4

2.2

1.7

1.7

1.3

1.2

1.2

1.7

1.2

1.5

1.5

1.4

0.9

0.8

1.0

1.0

1.1

0.8

0.9

0.9

Do Min (in.) Ds Max (in.) W Max (in.)

19.85

8.00

7.20

20.80 8.25

17.40

16.20 27.70

16.20

5.75 9.75

5.75

26.30 24.85 7.75

30.10

17.40 7.30

9.20

5.40

5.40

8.25

7.80

7.00

7.55

6.80

7.45

W Min (in.)

31.65 25.10 6.75

8.10

6.40

6.35

6.35

29.00 11.50

29.30 9.85

8.80 7.50

26.00 25.30 23.85 6.75

8.85

8.85

6.00

5.95

5.95

0.86

0.88

0.90

0.89

0.87

0.84

0.65

0.76

0.77

0.93

0.87

0.87

0.90

0.73

0.84

0.75

0.78

0.84

6.35

7.55

5.95

7.20

0.89

0.82

11.30

10.50

13.50

12.80

14.20

9.45

9.10

11.05

13.25

9.40

10.85

11.80

12.40

7.55

7.55

10.25

9.10

10.40

9.00

9.90

11.00

26×6.6

H25×8.0-12

32×11.5-15

31×9.75-14

34×10.75-16

22×6.6-10

6.50-10

26×6.6

32×10.75-14

22×8.5-11

26×10.0-11

29×7.7

26.5×8.0-13

18×5.5

18×5.5

24×7.7

H22×8.25-10

24×7.25-12

22×8.0-10

23×7.0-12

26×7.75-13

Static loaded radius (at rated Aspect load) ratio (in.) Wheel size

10.80 10.50 0.74

9.25

10.45 9.80

20.00 6.80

19.85

23.65 6.75

25.00 24.40 23.70 8.00

32.00 31.10

30.90 30.15

8.50

6.85

8.30

5.10

5.10

7.70

7.45

6.50

7.05

6.30

6.95

Ws Max (in.)

28.55 10.95 10.55 9.50

19.65

34.45 33.65 31.10

22.20 21.60

22.00 21.30

25.75

32.55

22.00 21.40

26.00 25.50 23.30 10.00 9.45

27.00

31.00

18.00

18.00

25.60 24.70 22.85 8.65

22.00 21.40

24.50 23.80 22.25 7.50

22.00 21.35

23.20 22.60 21.15

26.30 25.50 23.90 7.90

Unloaded inflation Tire Nitrogen Do pressure mass mass Max (psi) (lbs) (lbs) (in.)

TABLE 1.4  (Continued) Three part bias tire table.

16.00

5.00

5.25

9.00

14.00

12.00

15.00

14.00

8.25 8.00

10.00

10.00

14.00

14.00

11.00

11.00

15.00

13.00

8.00

8.00

10.00

10.00

12.00

10.00

12.00

13.00

Specified rim diameter (D) (in.)

5.50

4.75

5.00

9.25

7.25

8.00

6.00

6.50

4.25

4.25

5.50

5.25

6.25

5.00

6.25

6.62

Width between flanges (A) (in.)

1.00

0.98

1.25

1.00

1.05

1.00

0.81

1.00

1.05

0.88

1.00

1.00

1.00

0.88

0.88

0.91

0.85

0.70

0.63

0.65

0.70

Flange height (Fh) (in.)

1.90

1.80

1.90

2.15

1.85

2.05

1.30

1.70

2.00

1.88

1.95

1.65

2.05

1.50

1.50

1.50

2.14

1.75

1.40

1.25

1.50

Min ledge width (G) (in.)

42 Aircraft Tires: Key Principles for Landing Gear Design

© SAE International.

12,500

15,500

16,200

16

20

16

20

24

34×9.25-16

34×10.75-16

H31×13.0-12

34×14.0-12

200

225

210

250

15,100

17,300

17,200

16,500

15,350

25.5×8.0-14

210

14

14,615

14,500

13,700

13,450

13,300

13,000

13,000

12,900

12,700

16

190

12,200

12,400

34×10.75-16

264

210

210

12,000

12,200

H30×9.5-16

16

20

H29×9.0-15

31×10.75-14

14

16

34×14.0-14

30×9.5-14

210

190

12

18

12

24×6.5-14

34×10.75-16

16

230

190

18

16

24×8.0-13

26×8.0-14

37×11.75-16

265

280

26

H27×8.5-14

160

242

33.5×10.75-15 12

22×7.75-9

219

210

20

Size

22×6.6-10

B24×9.5-10.5 18

Speed Rated Ply rating load rating (mph) (lbs)

155

135

145

310

155

202

110

174

197

177

108

207

80

95

375

235

285

305

100

160

270

88

68

40

53

65

44

48

42

70

65

32

37

29

23

48

40

27

4.3

2.9

2.8

2.1

2.5

2.4

2.2

3.0

2.1

2.3

3.0

1.8

2.2

1.9

1.8

1.7

1.7

1.8

2.0

1.4

1.4

Do Min (in.) W Max (in.) 8.95

6.40

W Min (in.)

19.85

7.80

36.10

33.25 11.75

9.00

0.87

0.88

0.75

0.75

0.69

0.85

0.77

8.55

8.55

8.85

8.85

6.84

8.15

8.55

27.60 13.00 12.30 11.45

10.45 9.80

7.55

8.75

8.95

0.73

0.88

0.72

0.98

0.74

0.88

0.79

0.74

0.84

34.00 32.60 30.50 14.00 13.20 12.35 0.78

30.10

34.45 33.65 31.10

8.00

30.75 9.25

25.50 24.80 23.14 31.00

0.90 0.71

10.35 0.90 7.65

10.45 9.72

8.50

8.95

10.45 9.80

30.00 29.35 28.60 9.50

34.45 33.65 31.10

30.58 28.28 11.05

29.00 28.20 27.70

34.00 33.15

11.15 8.00

8.85

5.90

6.00

7.05

7.12

9.15

8.40

6.00

Ws Max (in.)

13.70

12.40

14.20

11.00

14.30

12.85

14.20

13.20

12.30

12.65

14.10

11.40

15.05

14.20

10.60

11.20

10.45

9.20

13.70

9.80

9.35

34×14.0-12

H31×13.0-12

34×10.75-16

25.5×8.0-14

32×8.8

H30×9.5-16

34×10.75-16

31×10.75-14

H29×9.0-15

30×9.5-14

34×14.0-14

H27×8.5-14

37×11.75-16

34×10.75-16

25×6.0

26×8.0-14

24×8.0-13

22×7.75-9

33.5×10.75-15

B24×9.5-10.5

22×6.6-10

Static loaded radius (at rated Aspect load) ratio (in.) Wheel size

32.00 14.00 13.30 12.60 0.72

30.00 29.20 28.40 9.50 31.42

6.25

7.50

7.55

7.35

10.45 9.80

26.30 25.70 8.50

34.00 33.15

27.00

37.00

34.45 33.65 31.10

24.00 23.40 22.40 6.65

26.00 25.30 23.85 8.00

24.00 23.40 22.00 8.00

22.20 21.50

33.50 32.65 30.20 10.75 10.15

9.50

20.00 6.80

Ds Max (in.)

24.00 23.30 21.60

22.20 21.60

Unloaded inflation Tire Nitrogen Do pressure mass mass Max (psi) (lbs) (lbs) (in.)

TABLE 1.4  (Continued) Three part bias tire table.

11.00

8.00

8.25

5.75

7.00

6.25

8.25

9.00

6.00

7.00

10.75

5.50

9.25

8.25

4.75

6.38

5.75

6.25

8.00

6.00

5.50

Width between flanges (A) (in.)

12.00

12.00

16.00

14.00

16.00

16.00

16.00

14.00

15.00

14.00

14.00

14.00

16.00

16.00

14.00

14.00

13.00

9.00

15.00

10.50

10.00

Specified rim diameter (D) (in.)

1.38

1.20

1.05

1.00

1.13

1.10

1.05

1.25

0.95

1.13

1.25

0.95

1.00

1.05

0.88

1.13

1.00

1.13

1.00

0.88

1.00

Flange height (Fh) (in.)

3.00

2.70

1.85

2.10

2.00

2.20

1.85

3.25

2.15

2.25

2.15

2.15

1.63

1.85

1.65

2.10

2.05

2.15

1.90

1.90

2.05

Min ledge width (G) (in.)

Aircraft Tires: Key Principles for Landing Gear Design 43

© SAE International.

213

225

24

26

24

20

30×11.5-14.5

37×14.0-14

H38×13.0- 18

20

30×11.5-14.5

18

H40×14.0-19

H36×11.5-19

225

225

242

242

235

250

22

22

22

20

35×11.5-16

H35×11.0-18

32×9.75-18

255

225

18

H37×14.0-15

225

20

225

37×13.0-16

18

20

H36×12.0-18

H37×14.0-15

260

225

H38×13.0- 18

18

24

H35×11.0-18

27.75×8.7514.5

22

18

28×9.0-14

H34×9.25-18

35×9.0-17

190

177

320

192

213

280

178

154

53

25,075

172

108

73

25,000 160

67

112

82

82

67

83

52

60

25,000 243

221

145

145

69

65

25,000 245

24,925

24,100

24,100

23,700 345

23,400 216

23,000 210

22,250

22,200 165

22,000 135

21,525

21,500

20,725

19,400

18,100

17,920

17,800

210

18

16

Size

34×9.25-16

210

Speed Rated Ply rating load rating (mph) (lbs)

6.3

5.1

3.6

3.6

4.5

5.0

4.6

4.4

4.1

4.5

4.4

4.7

4.3

4.0

2.9

3.7

3.1

2.8

3.0

3.1

Do Min (in.)

27.30 25.25 9.10

9.40

27.05

33.30 11.00 24.60 8.75

36.10

36.10

36.10

8.25

33.20 13.00 12.30 11.45 11.50

0.81

9.20

8.60

10.40 9.90

0.72

0.77

10.90 10.10 0.83

0.77

11.00

11.00

10.10 0.66

10.10 0.66

36.00 13.00 12.30 11.70

0.77

36.05 32.85 14.00 13.30 12.30 0.83

28.75 27.00 11.50

10.90 10.35 0.74

36.25 14.00 13.20 12.00 0.76

33.05 14.00 13.30 12.30 0.79

29.50 9.75

33.30 11.00

31.80

36.00 13.00 12.30 11.70

28.75 27.00 11.50

38.00 37.15

37.00

29.75

29.75

0.77 0.76

10.80 0.75

7.48

0.87

0.77

0.95

0.98

15.80

15.10

12.50

12.50

15.30

16.60

15.00

14.05

14.80

14.75

15.80

15.40

15.00

15.20

11.85

14.80

14.50

12.00

14.75

14.30

H38×13.0-18

37×14.0-14

30×11.5-14.5

30×11.5-14.5

H36×11.5-19

H40×14.0-19

H37×14.0-15

34.5×9.75-18

H35×11.0-18

36×11

H38×13.0-18

36×11

H37×14.0-15

H36×12.0-18

27.75×8.7514.5

H35×11.0-18

H34×9.25-18

28×9.0-14

35×9.0-17

32×8.8

Static loaded radius (at rated Aspect load) ratio (in.) Wheel size

33.05 14.00 13.30 12.30 0.79

36.00 35.25 34.30 11.50

40.00 39.10

37.00

32.00 31.30

35.00 34.15

35.00 34.10

38.00 37.15

37.00

37.00

8.15

8.00

8.20

8.15

Ws Max (in.)

10.40 9.90

8.75

8.60

8.90

8.75

W Min (in.)

36.00 35.20 34.20 12.00 11.35

27.75

35.00 34.15

34.00 33.20 30.75 9.25

27.85

W Max (in.)

30.75 9.25

Ds Max (in.)

34.80 33.95 31.60

34.00 33.15

Unloaded inflation Tire Nitrogen Do pressure mass mass Max (psi) (lbs) (lbs) (in.)

TABLE 1.4  (Continued) Three part bias tire table.

11.00

9.75

9.75

7.50

9.00

9.00

7.50

7.00

9.00

8.50

9.00

9.00

7.75

6.00

7.00

6.00

7.25

7.25

7.00

Width between flanges (A) (in.)

14.00

14.50

14.50

19.00

19.00

15.00

18.00

18.00

16.00

18.00

16.00

15.00

18.00

14.50

18.00

18.00

14.00

17.00

16.00

Specified rim diameter (D) (in.)

1.50

1.25

1.25

1.20

1.20

1.30

1.25

1.20

1.38

1.20

1.63

1.30

1.20

1.20

1.20

1.20

1.13

1.10

1.13

Flange height (Fh) (in.)

3.00

2.75

2.75

2.60

2.50

2.80

2.55

2.80

2.80

2.40

3.20

2.80

2.40

2.35

2.80

2.40

2.25

2.25

2.00

Min ledge width (G) (in.)

44 Aircraft Tires: Key Principles for Landing Gear Design

© SAE International.

27,500

27,800

225

225

20

22

26

22

H40×14.0-19

32×11.5-15

41×15.0-18

31,400

28

24

30

40.5×15.5-16

H42×16.0-19

36×11.0-18

24

24

H40×14.5-19

H41×15.0-19

24

219

28

22

37×11.5-16

H42×16.0-19

28

31,200

225

26

22

34.5×9.75-18

41×15.0-18

225

261

225

235

225

225

225

290

29,300 220

H40×14.5-19

37×13.0-16

166

142

340

190

160

245

180

35,800 305

34,400 175

34,200 190

33,650 187

33,200 200

32,000 240

31,200

30,100

30,100

29,400 175

26

30

37×13.0-16

260

192

28,600 170

27,100

50×20.0-20

242

225

25,275

26,700 160

43×15.5-17

210

225

20

24

H37×14.0-15

Size

H38×12.0-19

Speed Rated Ply rating load rating (mph) (lbs)

85

138

145

145

134

86

143

79

112

85

126

86 36.10

10.80 0.79

Ws Max (in.)

36.25 14.00 13.20 12.00 0.76 10.90 10.50 0.75

36.10

37.00

36.10

33.20 11.50

8.40

0.85

10.90 10.10 0.92

12.80 0.73

37.90 16.00 15.20 14.10 0.72

12.80 0.73

0.81

15.50 14.70 14.00 0.79

35.80 34.90 34.10

10.40 9.85

9.35

0.86

37.90 16.00 15.20 14.10 0.72

42.00 41.10

40.10 38.80 15.00 14.25 13.50 0.73

36.25 14.50 13.75

33.20 13.00 12.30 11.45

40.50 39.50 38.10

41.00

9.15

40.05 36.90 15.00 14.25 13.20 0.77 36.10

40.00 39.10

37.00

41.00

42.00 41.10

9.75

36.25 14.50 13.75

34.50 33.70 31.55 40.00 39.10

0.81

17.60 0.75

33.20 13.00 12.30 11.45

50.00 49.00 44.60 20.00 19.10

37.00

29.00 11.50

40.05 36.90 15.00 14.25 13.20 0.77

32.00 31.45 41.00

7.6 5.7

W Min (in.)

12.00 11.35

W Max (in.)

33.05 14.00 13.30 12.30 0.79

36.10

Ds Max (in.)

15.25

17.30

16.70

17.00

16.65

15.40

17.20

17.30

15.45

16.65

14.85

20.60

15.40

17.20

12.80

17.70

16.60

15.00

16.00

36×11.0-18

H40×14.5-19

40.5×15.5-16

H41×15.0-19

H40×14.5-19

36×11

41×15.0-18

H40×14.5-19

37×11.5-16

H40×14.5-19

34.5×9.75-18

50×20.0-20

36×11

41×15.0-18

32×11.5-15

43×15.5-17

H40×14.0-19

H37×14.0-15

H38×12.0-19

Static loaded radius (at rated Aspect load) ratio (in.) Wheel size

43.00 42.05 40.40 15.50 14.75 13.95 0.84

40.00 39.10

37.00

38.00 37.20

Do Min (in.)

7.9

7.2

6.9

6.6

7.5

7.0

6.0

6.3

5.4

14.3

6.1

6.7

5.0

6.8

5.6

5.0

4.8

Unloaded inflation Tire Nitrogen Do pressure mass mass Max (psi) (lbs) (lbs) (in.)

TABLE 1.4  (Continued) Three part bias tire table.

8.50

9.50

11.50

9.75

9.50

9.00

12.75

9.50

9.00

9.50

7.50

16.25

9.00

12.75

9.00

12.00

9.00

9.00

7.75

Width between flanges (A) (in.)

18.00

19.00

16.00

19.00

19.00

16.00

18.00

19.00

16.00

19.00

18.00

20.00

16.00

18.00

15.00

17.00

19.00

15.00

19.00

Specified rim diameter (D) (in.)

1.75

1.40

1.75

1.40

1.40

1.63

1.63

1.40

1.38

1.40

1.25

1.88

1.63

1.63

1.25

1.63

1.20

1.30

1.30

Flange height (Fh) (in.)

3.20

3.10

3.60

3.10

3.10

3.20

3.00

3.10

3.15

2.90

2.55

3.95

3.20

3.00

3.00

2.80

2.50

2.80

2.73

Min ledge width (G) (in.)

Aircraft Tires: Key Principles for Landing Gear Design 45

© SAE International.

Size

235

190

26

30

28

44.5×16.5-18

H44.5×16.520

H46×18.0-20 26

50×20.0-20

225

225

225

41,000

225

225

24

H44.5×16.5-21 26

H49×19.0-22

40,600 210

225

225

26

H45×17.0-20

H43.5×16.0-21 26

39,500 195

155

150

170

198

42,800 195

42,500 195

41,800

41,500

41,100

40,000 175

39,600 187

225

28

26

40×15.5-16

38,600 215

38,500 110

38,200 140

37,800

36,800 220

36,300 180

36,200 165

H44.5×16.520

210

200

24

28

56×20.0-20

43×16.0-20

225

26

24

H42×16.0-19

50×20.0-20

225

235

26

26

40×15.5-16

225

24

H40×14.5-19

H44.5×16.520

Speed Rated Ply rating load rating (mph) (lbs)

179

200

240

186

229

173

200

155

160

226

167

153

9.8

10.3

12.4

10.2

9.7

11.1

9.4

9.4

9.4

7.8

9.5

12.2

11.6

8.2

7.6

7.3

8.4

Do Min (in.) Ds Max (in.) W Max (in.) W Min (in.) Ws Max (in.)

0.71

18.00 17.15

15.85 0.73 17.60 0.75

44.50 43.50 40.10 16.50 15.70 14.55 0.75

44.50 43.50 39.70 16.50 15.70 14.50 0.81

50.00 49.00 44.60 20.00 19.10

46.00 45.00 41.30

44.50 43.50 42.20 16.50 15.70 14.50 0.71

17.10

16.00 15.20 14.40 0.70

49.00 48.00 46.30 19.00 18.15

43.50 42.55 41.25

45.00 44.00 40.50 17.00 16.20 15.00 0.74

44.50 43.50 40.10 16.50 15.70 14.55 0.75

40.00 39.05 35.70 15.50 14.75 13.65 0.78

0.72

17.60 0.91

17.60 0.75

38.90 16.00 15.20 14.15

56.00 54.80 49.50 20.00 19.10 43.00 42.10

12.80 0.73

37.90 16.00 15.20 14.10 0.72

50.00 49.00 44.60 20.00 19.10

42.00 41.10

36.25 14.50 13.75

40.00 39.05 35.70 15.50 14.75 13.65 0.78 40.00 39.10

18.30

18.35

20.60

18.80

18.50

20.20

18.20

18.50

18.30

16.10

17.95

22.70

20.60

17.30

16.65

16.10

18.30

Width between flanges (A) (in.)

10.00

10.00

13.00

15.50

16.25

9.50

9.50

11.00 12.00 11.00 13.25

16.25 H44.5×16.5-20 10.50

44×16

50×20.0-20

H45×17.0-20

H44.5×16.5-21 10.50

H49×19.0-22

H43.5×16.0-21 10.50

H45×17.0-20

H44.5×16.5-20 10.50

40×15.5-16

43×16.0-20

20.00-20

50×20.0-20

H40×14.5-19

H40×14.5-19

40×15.5-16

H44.5×16.5-20 10.50

Static loaded radius (at rated Aspect load) ratio (in.) Wheel size

44.50 43.50 40.10 16.50 15.70 14.55 0.75

Unloaded inflation Tire Nitrogen Do pressure mass mass Max (psi) (lbs) (lbs) (in.)

TABLE 1.4  (Continued) Three part bias tire table.

20.00

18.00

20.00

20.00

21.00

22.00

21.00

20.00

20.00

16.00

20.00

20.00

20.00

19.00

19.00

16.00

20.00

Specified rim diameter (D) (in.)

1.60

1.63

1.88

1.60

1.60

1.70

1.60

1.60

1.60

1.25

1.75

2.00

1.88

1.40

1.40

1.25

1.60

Flange height (Fh) (in.)

3.50

3.55

3.95

3.35

3.30

3.95

1.24

3.25

3.50

3.20

3.45

3.40

3.95

3.10

3.10

3.20

3.50

Min ledge width (G) (in.)

46 Aircraft Tires: Key Principles for Landing Gear Design

© SAE International.

32

30

B46×16.023.5

195

223

205

34

34

28

50×20.0-20

52×20.5-20

52×20.5-23

225

235

245

34

32

49×19.0-20

H49×19.0-22

55,000 165

55,300 220

235

26

52×20.5-23

H46×18.0-20 34

53,800 190

212

276

59,500 187

185

57,000 205

57,800

259

265

191

185

245

201

257

299

280

187

56,600 205

55,700 215

54,000 215

250

32

36

50×20.0-20

53,800 260

51,900

51,500

51,100

50,900 219

49,000 160

45,800 210

47×18-18

276

279

235

47×15.75-22.1 32

49×19.0-20

225

235

30

49×18.0-22

H46×18.0-20 32

30

48,400 230

225

225

H44.5×16.5-21 30

50×21.0-20

46,700 150

225

32

28

44.5×16.5-18

50×21.0-20

44,200 180

44,700 214

225

225

H44.5×16.5-21 28

Size

H46×18.0-20 28

Speed Rated Ply rating load rating (mph) (lbs)

16.1

16.9

16.5

14.3

15.7

13.0

14.4

13.8

15.4

12.3

14.3

12.4

12.2

14.5

13.8

11.1

13.0

11.0

10.4

10.8

Do Min (in.) Ds Max (in.) W Min (in.)

18.00 17.15

W Max (in.) 15.85 0.73

Ws Max (in.)

44.50 43.50 39.70 16.50 15.70 14.50 0.81

16.20 0.75 15.85 0.73

17.90

17.25

49.00 48.00 43.80 19.00 18.15

18.00 17.15

52.00 51.00

0.71 17.60 0.75

17.10

16.70 0.77

15.85 0.73

46.80 20.50 19.60 18.05 0.71

46.25 20.50 19.60 18.05 0.79

50.00 49.00 44.60 20.00 19.10

49.00 48.00 46.30 19.00 18.15 52.00 51.00

15.75 0.81

46.80 20.50 19.60 18.05 0.71

46.00 45.00 41.30

52.00 51.00

46.90 46.00 41.60

17.60 0.75

42.20 16.00 15.20 14.10 0.71

50.00 49.00 44.60 20.00 19.10

46.00 45.10

16.70 0.77

47.20 43.40 16.00 15.20 14.05 0.82

18.00 17.15

49.00 48.00 43.80 19.00 18.15

48.10

46.00 45.00 41.30

49.00 48.00 46.30 18.00 17.15

50.00 49.00 44.60 21.00 20.05 18.50 0.72

44.50 43.50 42.20 16.50 15.70 14.80 0.71

50.00 49.00 44.60 21.00 20.05 18.50 0.72

21.30

21.30

20.60

20.20

20.30

18.80

21.30

19.25

20.60

19.65

20.30

19.95

18.80

20.60

20.20

18.50

20.20

18.35

18.50

18.80

11.00

Width between flanges (A) (in.)

13.25 13.25

13.25

12.75

11.00

13.75

13.25

52×20.5-23

50×20.0-20

50×20.0-20

H49×19.0-22

49×17

H45×17.0-20

52×20.5-23

47×18-18

50×20.0-20

13.00

16.25

16.25

12.00

13.25

11.00

13.00

14.75

16.25

B46×16.0-23.5 10.50

49×17

47×15.75-22.1

H45×17.0-20

49×18.0-22

49×17

H44.5×16.5-21 10.50

49×17

44×16

H44.5×16.5-21 10.50

H45×17.0-20

Static loaded radius (at rated Aspect load) ratio (in.) Wheel size

44.50 43.50 42.20 16.50 15.70 14.80 0.71

46.00 45.00 41.30

Unloaded inflation Tire Nitrogen Do pressure mass mass Max (psi) (lbs) (lbs) (in.)

TABLE 1.4  (Continued) Three part bias tire table.

23.00

20.00

20.00

22.00

20.00

20.00

23.00

18.00

20.00

23.50

20.00

22.10

20.00

22.00

20.00

21.00

20.00

18.00

21.00

20.00

Specified rim diameter (D) (in.)

1.50

1.88

1.88

1.70

1.88

1.60

1.50

1.75

1.88

1.25

1.88

1.75

1.60

1.88

1.75

1.60

1.75

1.63

1.60

1.60

Flange height (Fh) (in.)

3.25

4.20

3.95

3.95

3.75

3.80

3.25

3.90

3.95

3.15

3.75

3.75

3.80

3.75

3.60

3.30

3.60

3.55

3.30

3.55

Min ledge width (G) (in.)

Aircraft Tires: Key Principles for Landing Gear Design 47

© SAE International.

225

235

36

36

54×21.0-23

H54×21.0-24

235

235

38

34

235

52×20.5-20

36

30

52×20.5-20

52×20.5-23

225

235

H54×21.0-24

36

32

54×21.0-23

202

200

72,200 212

68,500 223

68,100

65,300 210

63,700 195

62,500 200

61,300

60,700 215

Size

50×20.0-20

Speed Rated Ply rating load rating (mph) (lbs)

294

281

294

334

269

20.0

21.4

18.9

19.0

16.8

18.2

19.5

17.3

Do Min (in.) Ds Max (in.) W Max (in.) W Min (in.) 17.60 0.75

Ws Max (in.)

52.00 51.00

46.25 20.50 19.60 18.05 0.79

54.00 53.00 51.00

21.00 20.10 18.90 0.72

54.00 53.00 50.90 21.00 20.15 18.90 0.74

21.00 20.10 18.90 0.72

46.25 20.50 19.60 18.05 0.79

46.80 20.50 19.60 18.05 0.71

54.00 53.00 51.00

52.00 51.00

52.00 51.00

22.20

22.50

22.20

21.30

21.30

21.30

22.50

20.60

H54×21.0-24

54×21.0-23

H54×21.0-24

50×20.0-20

52×20.5-23

50×20.0-20

54×21.0-23

50×20.0-20

Static loaded radius (at rated Aspect load) ratio (in.) Wheel size

54.00 53.00 50.90 21.00 20.10 18.90 0.74

50.00 49.00 44.60 20.00 19.10

Unloaded inflation Tire Nitrogen Do pressure mass mass Max (psi) (lbs) (lbs) (in.)

TABLE 1.4  (Continued) Three part bias tire table.

13.00

16.25

13.00

16.25

13.00

16.25

16.25

16.25

Width between flanges (A) (in.)

24.00

23.00

24.00

20.00

23.00

20.00

23.00

20.00

Specified rim diameter (D) (in.)

1.80

2.00

1.80

1.88

1.50

1.88

2.00

1.88

Flange height (Fh) (in.)

4.25

4.20

4.25

4.20

3.25

4.20

4.20

3.95

Min ledge width (G) (in.)

48 Aircraft Tires: Key Principles for Landing Gear Design

© SAE International.

18×5.5R8

10

12

10

14

26×7.75R13

26×6.6R14

32×8.8R16

23.5×8.0R12

210

190

14

12

14

25.75×6.75R14

32×8.8R16

H34×10.0R16

225

190

210

14

14

26×6.6R14

225

225

190

190

190

230

225

225

25.75×6.75R14

12

14

21×7.25R10

16

12

27×7.75R15

190

14

20×4.4R12

21×7.25R10

24×7.7R10

225

12

16×6.0R6

190

190

12

10

16×4.4R8

435×190R5

3,250

225

225

14.5×5.5R6

17.5×5.75R8

165

200

212

115

185

125

198

166

265

164

87

207

145

177

105

155

140

13,400 130

11,000

10,300 199

10,300 237

57

45

26

27

24

38

24

26

27

14

11

10

11

8

10

10

2.6

1.9

1.3

1.6

1.5

1.3

1.7

1.5

1.6

1.2

1.2

1.1

0.9

0.6

0.5

0.4

0.4

0.4

0.4

0.4

0.3 13.40

15.50

15.70

7.50

7.50

4.65

25.40 8.10

23.00 8.35

28.70 9.25

24.02 6.92

24.47 8.32

19.75

19.75

6.25

8.00

34.85

31.80

26.35

26.35

26.32 7.05

7.05

32.95 10.40

28.70 9.25

25.15

25.15

24.02 6.92

24.80 22.05 8.00

27.70

24.25

31.80

26.32

27.36

21.90

21.90

5.75 6.00

14.90 4.65

17.00

6.00

9.35

8.20

6.35

6.35

6.08

7.05

7.15

7.50

8.20

6.08

7.54

6.60

6.60

4.10

5.65

7.15

4.10

5.26

5.05

5.25

4.10

W grown Ws Max Max (in.) (in.)

14.90 4.65 16.65

20.40 19.80

16.55

18.20

16.40

18.00

15.00

18.40

16.40

Inflation Do pressure Tire Nitrogen grown Ds (unloaded) mass mass Max Max (psi) (lbs) (lbs) (in.) (in.)

10,000 225

9,725

9,650

9,425

9,000

8,600

8,100

7,600

6,400

6,000

4,375

3,600

3,525

3,375

3,050

160

2,900

10

8

Size

16×4.4R8

190

Speed Rated Ply rating load rating (mph) (lbs)

TABLE 1.5  Radial tire table.

0.84

0.87

0.72

0.84

0.78

0.78

0.90

0.81

0.90

0.83

0.77

0.90

14.00

14.75

13.60

11.60

11.20 13.00

11.60

11.60

10.50

12.20

10.55

13.60

11.60

11.39

9.40

9.40

9.05

7.00

7.30

7.20

7.88

6.45

7.90

7.05

32×8.8

32×8.8

26×6.6

25.75×6.75R14

26×6.6

24×7.7

29×7.7

23.5×8.0R12

32×8.8

26×6.6

26×7.75-13

22×6.6

22×6.6

20×4.4

16×4.4

18×5.5

16×4.4R8

Static loaded radius grown Max (in.) Wheel size

11.20

11.15

9.95

11.75

10.10

13.00

11.15

10.60

9.05

9.00

8.75

6.65

6.85

6.90

7.54

6.15

7.55

6.80

Static loaded radius grown Aspect Min Ratio (in.)

7.00

7.00

5.00

5.00

5.00

5.50

6.00

6.25

7.00

5.00

6.50

5.50

5.50

3.50

4.75

6.30

3.50

4.25

4.25

4.25

3.50

Width between flanges (A) (in.)

16.00

16.00

14.00

14.00

14.00

10.00

15.00

12.00

16.00

14.00

13.00

10.00

10.00

12.00

6.00

5.00

8.00

8.00

6.00

8.00

8.00

Specified Rim Diameter (D) (in.)

1.13

1.13

1.00

1.00

1.00

0.91

1.00

1.00

1.13

1.00

0.70

1.00

1.00

0.81

0.88

0.71

0.81

0.88

0.88

0.88

0.81

Flange height (Fh) (in.)

2.15

1.65

1.70

1.70

1.70

1.70

1.65

2.15

1.50

1.70

1.60

1.95

1.95

1.00

1.60

1.25

1.20

1.40

1.50

1.25

1.20

Min ledge width (G) (in.)

Aircraft Tires: Key Principles for Landing Gear Design 49

© SAE International.

20

20

20

24

H38×13.0R18

H38×12.0R19

H37.5×12.0R19

40×14.0R16

24

22

28

26

H40×14.5R 19

H41×16.0R20

1050×395R16

42×17.0R18

26

24

30×11.5R14.5

40×16.0R16

20

H35×11.0R18

22

24

27.75×8.75R14.5

22

20

915×300R16

H38×13.0R18

18

H34×9.5R18

H39×12.0R19

18

H33×10.5R17

250

20

16

25.5×8.0R14

H32×10.5R16.5

30×8.8R15

235

235

225

225

225

225

225

225

225

236

225

260

225

225

225

225

230

310

221

201

183

320

192

190

180

187

36,100

194

34,200 190

32,825

32,200 200

31,475

28,225 203

27,725

27,700 170

25,600 212

25,275

25,075 172

25,000 302

23,400 216

21,500

21,000 186

19,550

19,525

17,450

16,200

14,200 199

13,800

225

16

16

Size

29×7.7R15

225

Speed Rated Ply rating load rating (mph) (lbs) 2.2

5.9

5.4

5.5

5.0

4.6

3.4

4.9

3.6

3.7

3.2

2.4

2.6

131

129

137.1

115

10.4

9.3

8.4

7.8

8.5

6.1

6.0

136.4 6.9

66

52

44

40

52

31

26.55 8.20

37.05

40.00 16.15

16.65

39.05 15.10

43.50 40.95 17.70

42.65

12.50

13.55

38.90 16.65

42.40 40.15

41.30

41.45

12.50

12.50

13.55

11.96

11.44

9.19

36.08 14.56

37.05

37.05

37.05

27.82

34.17

25.31

34.90 12.30

40.05 37.95

39.15

41.02

39.10

39.10

39.15

30.75

35.97

28.68

37.00

9.65

32.25 10.95

10.95

23.28 8.04 31.30 0.85

0.77

0.85

0.77

0.80

0.84

15.95 0.71

14.20

15.00

13.06 0.73

15.00

11.25

12.20 0.77

12.48 0.86

11.25

11.25

12.20 0.77

10.50

10.30 0.78

7.85

17.42

16.60

18.33

17.55

17.40 17.90

16.60

17.40

17.15

16.50

17.30

16.50

16.65

16.50

12.65

15.40

12.30

15.43

15.05

14.55

13.90

11.35

13.50

12.70 5.75

7.00

6.00

Width between flanges (A) (in.)

40.5×15.5-16

H41×16.0R20

40×16.0R16

H39×12.0R19

H38×13.0R18

40×14

H37.5×12.0R19

H38×12.0R19

H38×13.0R18

30×11.5-14.5

H35×11.0R18

H27.75×8.7514.5

H34×9.5R18

H33×10.5R17

14.00

11.50

10.50

9.50

12.50

7.75

8.50

11.00

7.75

7.75

8.50

9.75

7.00

6.00

9.00

6.00

6.75

H32×10.5R16.5 6.75

25.5×8.0-14

30×8.8

29×7.7

Static loaded radius grown Max (in.) Wheel size

17.10

16.50

16.35

15.75

16.40

15.80

15.95

15.75

12.00

14.80

11.85

14.70

14.45

13.90

13.30

10.94

12.90

12.20

Static loaded radius grown Aspect Min Ratio (in.)

10.80 0.84

8.70

9.85

9.85

6.89

8.30

7.20

W grown Ws Max Max (in.) (in.)

29.50 9.30

34.80 33.15

33.95

32.95

26.65

31.10

29.10

Inflation Do pressure Tire Nitrogen grown Ds (unloaded) mass mass Max Max (psi) (lbs) (lbs) (in.) (in.)

TABLE 1.5  (Continued) Radial tire table.

18.00

16.00

20.00

19.00

16.00

19.00

18.00

16.00

19.00

19.00

18.00

14.50

18.00

14.50

16.00

18.00

17.00

16.50

14.00

15.00

15.00

Specified Rim Diameter (D) (in.)

1.63

1.75

1.40

1.40

1.75

1.33

1.20

1.63

1.33

1.30

1.20

1.25

1.20

1.20

1.38

1.20

1.10

1.10

1.00

1.13

1.00

Flange height (Fh) (in.)

3.30

3.50

2.80

3.10

2.96

2.62

2.40

2.95

2.45

2.73

2.40

2.75

2.45

2.35

2.60

2.28

2.28

2.11

2.10

2.10

1.65

Min ledge width (G) (in.)

50 Aircraft Tires: Key Principles for Landing Gear Design

© SAE International.

32

30

32

32

32

32

32

49×17.0R20

1270×455R22

47×15.75R22.1

H44.5×16.5R21

1270×455R22

50×20.0R22

1400×530R23

42

1400×530R23

235

235

235

38

40

54×21.0R23

235

245

235

235

235

225

235

279

225

225

235

235

225

225

235

235

36

1400×530R23

1400×530R23

38

36

45×18.0R17

52×21.0R22

30

H44.5×16.5R21

34

30

49×17.0R20

36

30

46×17.0R20

50×20.0R22

26

50×20.0R22

52×21.0R22

32

43×17.5R17

200

246

223

244

202

220

236

79,300 263

74,950 249

71,200

68,500 223

68,000 236

66,500 227

61,525

61,300

57,100

54,800 235

51,675

51,500

50,900 219

50,400 210

50,300 216

48,400 230

48,145

46,000 222

45,200 177

44,500 212

42,000 222

28

Size

45×16.0R20

225

Speed Rated Ply rating load rating (mph) (lbs)

277

302

272

281

266

222

181

29.2

27.7

25.4

25.0

23.7

22.9

21.2

22.8

19.2

18.2

13.4

13.9

17.1

15.4

14.6

12.6

14.7

13.9

15.7

12.5

11.9

43.45 17.20

17.94

44.75 17.70

56.85

56.85

55.85

56.85

53.85

53.85

51.75

56.85

51.75

51.55

45.95

49.37

51.55

17.94 0.82

15.00 0.78

15.45 0.72

11.28

15.00 0.78

15.08 0.84

16.85 0.78

15.45 0.72

15.08 0.84

15.95 0.77

19.10

0.76

53.45 21.70

19.10

0.76

0.76

19.70 0.74 19.10

52.60 21.85 53.45 21.70

19.10

0.76

19.70 0.72

19.70 0.71

53.45 21.70

50.70 21.85

50.70 21.85

48.80 20.80 18.75 0.70

53.45 21.70

48.80 20.80 18.75 0.70

48.60 18.75

43.45 17.20

47.64 16.70

48.60 18.75

50.26 44.21

46.60 43.65 18.75

45.95

16.40 0.74

48.80 20.80 18.75 0.70

50.26 44.21

47.50

51.75

18.20

22.35

22.35

22.55

22.35

21.60

21.60

20.83

22.35

20.83

20.50

18.50

20.50

20.05

18.45

18.45

20.05

19.20

20.83

17.65

18.45

Static loaded radius grown Aspect Min Ratio (in.)

14.65 0.76

W grown Ws Max Max (in.) (in.)

42.05 16.65

44.55 41.80

45.65

Inflation Do pressure Tire Nitrogen grown Ds (unloaded) mass mass Max Max (psi) (lbs) (lbs) (in.) (in.)

TABLE 1.5  (Continued) Radial tire table.

23.60

23.60

23.70

23.60

22.75

22.75

21.90

23.60

21.90

21.55

19.35

20.25

21.55

21.15

19.50

19.35

21.15

20.15

21.90

18.65

19.45

13.25

13.25

15.00

13.25

13.25

Width between flanges (A) (in.)

12.75

13.75

13.25

14.00

1400×530R23

1400×530R23

54×21.0R23

1400×530R23 54×21.0-23

52×21.0R22

52×21.0R22

50×20.0R22

1400×530R23 54×21.0-23

50×20.0R22

49×18.0-22

16.25

16.25

16.25

16.25

16.00

16.00

15.00

16.25

15.00

13.75

H44.5×16.5R21 10.50

49×18.0-22

49×17

45×18.0R17

H44.5×16.5R21 10.50

49×17

46×16

50×20.0R22

43×17.5R17

46×16

Static loaded radius grown Max (in.) Wheel size

23.00

23.00

23.00

23.00

22.00

22.00

22.00

23.00

22.00

22.00

21.00

22.10

22.00

20.00

17.00

21.00

20.00

20.00

22.00

17.00

20.00

Specified Rim Diameter (D) (in.)

2.50

2.50

2.38

2.00

2.25

2.13

1.88

2.00

1.88

1.88

1.60

1.75

1.88

1.88

2.13

1.60

1.88

1.88

1.88

1.75

1.75

Flange height (Fh) (in.)

3.50

3.50

3.98

4.20

3.75

3.75

3.15

3.80

3.15

3.95

3.40

3.75

3.75

3.95

4.20

3.40

3.95

3.70

3.15

3.89

3.75

Min ledge width (G) (in.)

Aircraft Tires: Key Principles for Landing Gear Design 51

52

Aircraft Tires: Key Principles for Landing Gear Design

have multiple versions tailored for different amounts of life, which has an impact on the weight. It is advisable to enquire with the tire manufacturers to determine the actual weight of any given tire – especially as tire technology continues to improve, resulting in reduced weights on new tire designs. The approximate mass of nitrogen (assuming inflation at 15°C) is provided for each tire in the tables. It is worthy of note that the method of dimensioning radial tires is somewhat different to that of bias ply tires; as a result, the format of the tables is not identical between these different tire types. The maximum and minimum new tire dimensions used for bias tires are replaced on radial tires by a maximum grown equivalent. This is intended to allow the designers to take advantage of the additional dimensional stability (lower growth) of radials to compensate for their somewhat lower vertical stiffness while maintaining compatibility with aircraft structures while having a compatible loaded radius.

2 Tire Performance and Modeling

Mechanics of Pneumatic Tires The intention of this chapter is to provide an overview of the mechanical behavior of pneumatic tires. What follows is only an introduction as entire volumes [20] have been written on tire performance, properties, and modeling. To permit the description of a tire and the moments and forces acting on it, an axis system must be defined. The axis system shown in Figure 2.1 is the historical system recommended by SAE International [21]. For ground vehicle applications, an alternative axis system is proposed by the International Standards Organization (which has positive Z in the upwards direction). It is important to take care when comparing approaches to ensure a common system is being employed. The origin of the axis system is the center of the tire contact patch. The X-axis is formed by the intersection of the wheel plane and the ground plane with a positive direction forward. The Z-axis is perpendicular to the ground plane with the positive direction downward. The Y-axis is in the ground plane, mutually orthogonal to the other axes, and its positive direction follows the right-hand rule. There are three forces and three moments acting on the tire from the ground. The force exerted by the tire on the ground surface is decomposed into three components: the longitudinal force, FXT, is the component in the X direction, the lateral force, FYT, is the component in the Y direction, and the normal force, FZT, is the component in the Z direction. The moments arising from the tire’s contact with the ground surface are similarly decomposed: the overturning moment, M XT, is the moment about the X-axis, the rolling resistance moment, MYT, is the moment about the Y-axis, and the aligning moment, MZT, is the moment about the Z-axis. Two key ©2022 SAE International

53

54

Aircraft Tires: Key Principles for Landing Gear Design

© SAE International.

 FIGURE 2.1   Tire axis system.

angles related to a rolling tire are similarly described: the slip angle and the inclination (camber) angle. Slip angle, α, is the angle formed between the direction of wheel travel and the line of intersection of the wheel plane with the ground surface. The inclination angle, ε, is the angle formed between the XZ plane and the wheel plane. The lateral force produced by the tire at the ground contact patch is a function of both the slip angle and the camber angle.

Rolling Behavior As a tire rolls freely (wheel torque TW = 0) such as when an aircraft is taking off or taxiing, the tire carcass is in a deflected state in the area of the ground contact. As a result of this distortion, the contact pressure in the leading part of the contact patch is higher than in the trailing part. The center of the contact pressure is shifted toward the direction of rolling (Figure 2.2). In reality, there will always be some parasitic wheel torque arising from bearing friction which will alter this behavior slightly. This shift produces a moment, MYT, about the axle (the product of FZT and the shift distance from the axle), which is the rolling resistance moment. As there is no applied torque TW, then a horizontal force at the contact patch must exist in order to establish equilibrium. This horizontal force is known as the rolling resistance. Often, the coefficient of rolling resistance is discussed, which is the ratio of the rolling resistance force to the normal force on the tire. The rolling resistance energy loss in the system arises mostly from the hysteresis in the tire materials as the tire takes on, and recovers from, the deflected shape in the carcass and in the tread area. On dry, hard

Aircraft Tires: Key Principles for Landing Gear Design

55

Adapted with permission from © SAE International.

 FIGURE 2.2   Tire center of pressure when rolling.

surfaces, this rolling resistance is predominantly a function of the tire properties and is relatively insensitive to the frictional properties of the surface. On wet or contaminated surfaces, other retarding mechanisms may predominate. On soft surfaces, the tire may need to displace material, which will exert a retarding force on the tire. In these cases, reducing the inflation pressure can result in less material being displaced and a lower rolling resistance. On hard surfaces, higher inflation pressures will result in the tire operating at less deflection, with reduced rolling resistance. A study [22] of several radial aircraft tires operating on dry, hard surfaces identified the average coefficient of rolling resistance as 0.015 with no trend to vary with speed or load. Historical evidence suggests that bias ply tires may have an increase in rolling resistance coefficient with increasing speed. An approach to modeling rolling resistance based on known tire properties is proposed by ESDU in their technical note 10015 [23]. This approach includes the influence of speed, and while based on bias ply tires, it is said to be representative of radial tire behavior. On aggregate or unprepared fields, higher tire pressures cause the tire to sink into the surface and begin displacing material. This has the impact of increasing the rolling resistance over the baseline value for a given tire on a hard surface. An estimate of this is shown in Figure 2.3 where the increase in rolling resistance (the value determined from the chart must be added to the baseline rolling resistance) is shown based on the tire pressure (in pounds per square inch) divided by the California Bearing Ratio (CBR) of the unpaved surface.

Turning Behavior In the absence of any force perpendicular to the wheel plane, a pneumatic tire will move along the wheel plane. However, if a side force is applied to a tire, a lateral force

56

Aircraft Tires: Key Principles for Landing Gear Design

 FIGURE 2.3   Increase in rolling resistance on unpaved runways [24].

0.13 0.12 0.11 0.1 0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0

0

1

2

3

4 5 6 7 8 9 10 11 12 13 14 Tire Pressure in PSI / CBR

Adapted from Ref. 24.

Delta Rolling Resistance

Approximate Increase in Rolling Resistance on Unpaved Runways

is created at the contact patch and the tire will move along a path at an angle with the wheel plane, as shown in Figure 2.4. The angle between the path of advance and the wheel plane is referred to as the slip angle. The phenomenon of side slip is mainly due to the lateral elasticity of the tire. The lateral force developed at the contact patch between the tire and the ground is the cornering force. The tire can be considered as a very complex spring which happens to roll. The spring must be deflected to develop force, and the tire must roll some distance to develop lateral force. The function describing this behavior is exponential, asymptotically approaching some final value, and is the source of another tire property, the relaxation length. The relationship between the cornering force and the slip angle governs the ability of a tire to assist in turning an aircraft and in maintaining directional stability. When the tire is moving at a constant speed along the path of advance, the lateral force, applied at the wheel center, and the cornering force (developed in the contact patch) are not typically collinear. At small slip angles, the cornering force in the ground plane is normally behind the applied lateral force, giving rise to a torque that tends to align the wheel plane with the direction of motion. This torque is called the self-aligning torque and is the primary moment that tends to return the tire to its undisturbed position following a turn. The distance between the lateral force and the cornering force is called the pneumatic trail, and the product of the cornering force and the pneumatic trail is the self-aligning torque.

Aircraft Tires: Key Principles for Landing Gear Design

57

Adapted with permission from © SAE International.

 FIGURE 2.4   Behavior of a tire subject to a side force.

The results of testing of a radial 40×14 tire (Figure 2.5) show the tire cornering force (divided by the normal force and presented as “mu side”) versus various yaw angles for both dry and wet runways. The marked reduction in available cornering force on wet runways at high speeds is visible. To generate the same side force at higher speeds, a much larger angle must be taken by the tire.

 FIGURE 2.5   Effect of speed on cornering performance of a radial 40×14 tire,

© SAE International.

1.17 MPa inflation pressure, 111 kN vertical load.

58

Aircraft Tires: Key Principles for Landing Gear Design

Vertical Stiffness Of significant importance to the landing gear designer is the vertical stiffness of the tire. As shown in Figure 2.6, the initial portion of the deflection is typically non-linear, followed by a reasonably linear amount of deflection. Finally, as the tire begins to be crushed against the rim, the load per unit deflection begins to increase sharply. The figure shows the approach [25] recommended to determine the bottoming load, whereby the bottoming load is the point of tangency between the deflection curve and line B-B. Line B-B has a slope 2.2 times the slope of the deflection curve between 28% and 48% deflected. An alternative approach is to detect the internal contact between the tire components during the test. In selecting a tire, it must be ensured that the bottoming load is sufficient for the intended application. In most cases, the bottoming load is approximately three times the rated load of the tire. Each load-deflection curve is relevant for a tire at a specific inflation pressure. Figure 2.7 shows the measured load-deflection behavior of three tires: a bias 40×14 tire, a radial 40×14 tire, and an H40×14 tire (shown at two different inflation pressures). The reduced stiffness of the radial is typical of radial tires due to the thinner sidewall construction technique.

© SAE International.

 FIGURE 2.6   Generic load-deflection curve showing bottoming point determination.

Aircraft Tires: Key Principles for Landing Gear Design

59

© SAE International.

 FIGURE 2.7   Measured load-deflection curve for three tires.

Braking Behavior As the aircraft industry is only just beginning to seriously consider adding powered wheels to aircraft for fuel burn and noise reduction, much of the interest with aircraft tires is centered on their braking performance rather than their traction behavior. Figure 2.8 shows a schematic view of a tire deflected under vertical load and braking load. It can be seen that the tread elements in contact with the ground are stretched. In addition, the tread elements prior to contact are also stretched. The distribution of the forces created by a free rolling tire is represented by line 1 in Figure 2.10; the additional shear force created by the braking torque is represented by line 2, and the resultant shear force distribution along the contact patch is shown by line 3. The specific shape of this curve for any given tire depends on the braking force, the applied vertical load, inflation pressure, coefficient of friction, and other variables. The explanation for this distribution is suggested by Figure 2.8. An extended tread element adheres to the ground on first entering the contact patch. As it moves further into the contact patch, it produces a deflection that increases linearly with increasing distance (causing an increasing longitudinal force) until the local value of limiting frictional force is reached and the tread element begins to slide back, thus reducing again the longitudinal force as shown by line 3 in Figure 2.10. The vertical force distribution along the contact length is shown in Figure 2.9 for a free rolling and a braked tire. It can be seen that the contact length of the braked tire is longer than the free rolling tire due to stretching of the tire tread.

60

Aircraft Tires: Key Principles for Landing Gear Design

Reprinted from https://nvlpubs.nist.gov/nistpubs/Legacy/MONO/nbsmonograph122.pdf.

 FIGURE 2.8   Schematic of tire during braking.

 FIGURE 2.9   Comparison of vertical force distribution between a free rolling and

Reprinted from https://nvlpubs.nist.gov/nistpubs/Legacy/ MONO/nbsmonograph122.pdf.

braked tire.

Aircraft Tires: Key Principles for Landing Gear Design

Reprinted from https://nvlpubs.nist.gov/nistpubs/Legacy/MONO/nbsmonograph122.pdf.

 FIGURE 2.10   Distribution of forces over the contact patch of a braked tire.

61

62

Aircraft Tires: Key Principles for Landing Gear Design

In dealing with the frictional behavior of tires, frequent reference is made to the “slip ratio.” The typical definition of longitudinal slip ratio taken for aircraft applications, in line with AIR1489 [26], is:

o



or : 1 o

o

where:

•• ω is the angular velocity of the braked wheel •• ωo is the angular velocity of the free rolling wheel It may be denoted as the percent slip, in which case the value determined from the formulation above is multiplied by 100. During braking the loaded tire radius, h, as shown in Figure 2.10 is reduced compared to the free rolling case due to the applied braking torque. As the tread elements stretch prior to contact, their circumferential velocity will increase. Taking the assumption that there is no sliding in the front part of the contact patch for a moderate braking force, the tread elements coming into contact with the ground will begin to travel at the ground speed. The longitudinal shear force that increases toward the rear of the contact patch, combined with the decreasing vertical force, will cause rearwards sliding of the tread elements in the rear portion of the contact patch. This is shown graphically in Figure 2.11. Increasing the braking force at a constant vertical

Reprinted from https://nvlpubs.nist.gov/nistpubs/Legacy/MONO/nbsmonograph122.pdf.

 FIGURE 2.11   Idealized Mu-slip curve for braked tire.

Aircraft Tires: Key Principles for Landing Gear Design

63

load will result in increased sliding over the contact length as shown. As the braking force increases, slip will increase and the region adhered to the ground reduces until the entire contact patch is sliding. The location of the peak value of the friction coefficient varies, but it is generally between 10% and 20% slip. The loaded tire radius, h, and the rolling radius vary as a function of applied vertical and drag loads. In many cases, the term “rolling radius” is used to denote both the distance from the axle centerline to the ground and the ratio of horizontal stopping distance to angular stopping distance. The latter is of significant importance for antiskid brake systems whereas the former is important for determining the loads on landing gear structure as well as converting from applied brake torque to drag load at the tire contact patch. Care must be exercised to ensure that the appropriate dimension is being utilized as there is a significant difference between the two values: the loaded tire radius accounts for the vertical deflection of the tire (which for aircraft tires is significant) whereas the rolling radius remains similar to the undeflected radius of the tire. While the tire rolls in a significantly deflected state, the tire tread length remains substantially the same as in the inflated, unloaded condition. For every revolution of the tire, the entire tread length traverses the ground, following a non-circular path. Methods for determining the rolling radius of the tire during braking are provided in NASA TN D-6426 [27] as well as ARP4955 [25]. ARP4955 also provides guidance for the empirical determination of “vertical sinkage” during fore-aft spring rate testing; the resulting curve can be used to determine the loaded tire radius, h, during braking.

Tire-Ground Friction The topic of the available friction coefficient between the tire and the ground surface has high importance to the aircraft and landing gear designer. In general, the highest possible friction coefficient leads to better aircraft performance in terms of ground control and stopping distance. However, high coefficients of friction during cross-wind landings could lead to control difficulties and higher coefficients of friction lead to higher loads to be  resisted in the landing gear structure. The available friction depends strongly on the ground surface and also on the tire design and composition. The presence of water or other contaminants has a very significant impact on the available friction. A dominant model [28] of  tire friction proposes two key mechanisms in the generation of friction between the tire rubber and the ground: adhesion and hysteresis as shown in Figure 2.12 . Adhesion is the frictional force that results from the small-scale bonding of the tire rubber to the pavement surface. Hysteresis is the frictional force that results from energy loss during deformation (as the tire surface locally envelops the pavement macrotexture and releases) as the tire moves across the surface. The total friction coming from the rubber to surface contact is the addition of the two values. This model is relevant when the surface can be modeled as locally rigid, and the tire is not

64

Aircraft Tires: Key Principles for Landing Gear Design

Reprinted from https://www.fhwa.dot.gov/publications/research/safety/ 14065/002.cfm.

 FIGURE 2.12   Model of rubber friction behavior.

displacing any material (such as soil, snow, slush, or water). The presence of water affects the available friction in three ways: 1. The adhesion term is reduced by the action of the water film weakening or preventing the local union of the rubber and the surface. 2. For small quantities of water, the hysteresis term is reduced as the water film provides cooling. 3. For larger water film thickness, the fluid is not readily displaced and the presence of the water between the tire and the surface asperities reduces or eliminates the local tire deformation. As a result, the hysteresis friction term approaches zero. Ensuring adequate levels of friction on wet runways requires that the water be removed or that the tire penetrate the water film to ensure adequate contact with the runway surface. While rubber, as a viscoelastic material, does not explicitly follow Coulomb’s model for friction, the phenomenon of tire/ground friction is frequently simplified as if it did. The coefficient of friction is given as:

Ffriction Fnormal

On dry pavement, the peak value of μ is typically taken as 0.8, as this value is quoted in the certification regulations for large aircraft. Individual tire test results can produce peak μ values greater than 0.8; however, in practice the available value varies with speed (higher speeds have lower values of μ) and inflation pressure and

Aircraft Tires: Key Principles for Landing Gear Design

65

© SAE International.

 FIGURE 2.13   Friction coefficient for a small rubber block sliding on concrete (speed less than 1 knot).

can range from 0.65 to 0.95. An example of the sliding friction available from a block of rubber on concrete is shown in Figure 2.13. The available friction coefficient is higher with lower contact pressure. It has been observed [29] that the adhesion portion of rubber friction is load (or pressure) dependent whereas the hysteresis term is relatively insensitive to pressure. This can result in high apparent coefficients of friction at low applied loads. The maximum value of friction coefficient available on dry pavement depends (from Figures 2.13 and 2.14) on the rubber compound used in the tread area as well as the ground contact pressure (for which the inflation pressure is a good estimator). Surface roughness and tire tread patterns reduce the area in contact with the ground, resulting in increased contact pressure and reduced available coefficient of friction. The friction coefficient on unprepared fields can vary significantly with the type and texture of the material. Aggregate surfaced runways can exhibit a coefficient of friction of around 0.6 and dry dirt strips between 0.6 and 0.68. Grass runways have a significantly reduced coefficient of friction of around 0.4 when dry. When wet, all these coefficients are reduced by a large margin.

Wet Runways and Hydroplaning The total friction force occurring with the tire (neglecting air resistance inside and outside the tire) not only includes the two rubber/ground terms, FA and FH, but also the rolling resistance, FR, and a drag term for displaced material, FD. The resulting total retarding force from the tire is:

Ftotal

FA

FH

FR

FD

66

Aircraft Tires: Key Principles for Landing Gear Design

 FIGURE 2.14   Typical maximum friction coefficient available on a dry runway at low

© SAE International.

speed (less than 1 knot).

When operating on a dry, hard runway, the term FD is effectively zero. However, if operating on soft ground, the tire may be displacing material and there will be a drag force resulting from this work performed. Equally, for tires operating on runways with water, slush, or snow, the tire must displace this material resulting in a drag force. For slush and water, this drag force has been modeled [30] as hydrodynamic drag:

Fx

1 C D hbV 2 2

where:

•• Fx is the deceleration force •• CD is the drag coefficient of the tire in water or slush (on the order of 0.7–0.75) •• h is the fluid depth on the runway surface •• V is the horizontal velocity of the aircraft •• b is the chord length of the tire cross section at the slush or water surface:

b 2W

h W

•• δ is the tire deflection •• W is the tire cross-section width

h W

2



Aircraft Tires: Key Principles for Landing Gear Design

67

For aircraft where the load of the tire is relatively constant during takeoff or landing, a fixed, nominal value of b can be used. For aircraft where there is a significant variation in vertical load during these maneuvers, then the value of b should be computed using the tire load-deflection curve, varying δ as a function of load. While this method for estimating fluid drag has been shown to be reasonable, a more refined model is available in ESDU 10015. In addition, it is advisable to consider the aircraft retardation that results from tire spray impinging on the aircraft. A model for this phenomenon is available in ESDU 98001 [31]. When operating on runways covered with water or slush, a phenomenon can occur where the tire begins to be supported by a film of the contaminant: hydroplaning. This is similar to the way a speedboat rises out of the water and planes across the surface. As this occurs, the bow wave created by the tire is suppressed, the tire can begin to slow down and stop spinning, and the friction terms (including FD) trend to zero. Extensive development activities were conducted to understand this phenomenon in the 1950s and 1960s, leading to the defining formulation of the problem [32]: Provided a smooth tire is used, or the depth of water is greater than the tread groove depth, then as the aircraft speed increases a wedge of water penetrates beneath the tire as shown in Figure 2.15 (1). The drainage capability and the macrotexture of the runway significantly impact the hydroplaning phenomenon as water (or another viscous contaminant) must be present. With water which cannot drain or be expelled present and as the speed increases, the tire will progressively ride up onto the water due to the hydrodynamic lift force that is generated until, with sufficient speed, there is no region of “dry” contact between the tire and the ground, as shown in Figure 2.15 (3). The physical confirmation of this behavior was performed with tires on test tracks passing over glass plates – high-speed camera images were used to observe the pattern of water flow created. As the speed increases, the bow wave of water pushed by the tire (and the associated hydrodynamic drag) increases until the tire is completely supported by the wedge of water, at which point the drag term drops to near zero and the bow wave disappears. In this condition, the hydrodynamic lift force equals the vertical force being supported by the tire. The hydrodynamic lift force is computed by:

F

1 C L AV 2 2

where:

•• F is the lift force •• CL is hydrodynamic lift coefficient •• ρ is the density of water •• A is the ground contact area of the tire •• V is the horizontal speed of the aircraft

68

Aircraft Tires: Key Principles for Landing Gear Design

Adapted with permission from © SAE International.

 FIGURE 2.15   Development of dynamic hydroplaning.

Investigative work done at NASA determined that for a free rolling tire, CL is approximately 0.7 and for a skidding tire (such as immediately following touch down), CL is approximately 0.95. By considering that the tire inflation pressure is a good approximation of the ground contact pressure (i.e., tire inflation pressure is a good estimator of the vertical force on the tire divided by the ground contact area), the equation can be rearranged:



V

V

0.5

2F CL A 2 CL

F A

0.5



Aircraft Tires: Key Principles for Landing Gear Design

2 CL

V



69

0.5

P



This equation can be solved in any consistent set of units, taking P as the tire inflation pressure, to determine the speed at which full hydroplaning is expected. It is typically quoted as:

V

9 P

where V is in knots and P is in pounds per square inch. This formulation uses a value of CL of 0.65, although it is typically quoted as 0.7. The formula is, at best, an estimate. It has been found to overpredict the hydroplaning speeds for modern tires, especially H-type tires. An alternative approach has been proposed that considers the aspect ratio of the tire footprint [33]. Work conducted on a number of H-type tires [34] suggests that the hydroplaning speed of these tires could be as low as that predicted by:

V

6.7 P

This is shown by some experimental test points in Figure 2.16. It is to be noted that these historical and empirical methods do not have a common definition of total planing. Typically, the values were taken as the beginning of wheel spin down. Partial hydroplaning will cause a significant reduction in the available drag force from the wheel, and the preceding formulas should be used with caution. A comprehensive model for the prediction of hydroplaning which considers the water depth and the macrotexture is provided by ESDU 15003 [35]. This method is recommended for detailed analyses of the hydroplaning phenomenon.

© SAE International.

 FIGURE 2.16   H-type tire hydroplaning.

70

Aircraft Tires: Key Principles for Landing Gear Design

© SAE International.

 FIGURE 2.17   Hydrodynamic pressures under tire against a smooth plate.

Dynamic hydroplaning, as described above, occurs when the velocity of water being driven by the tire is such that the lift force generated raises the tire partially or fully clear of the ground surface. However, hydroplaning events have been observed at low speed – typically on smooth (or bald) tires and very smooth runway surfaces. This form of hydroplaning, viscous hydroplaning, occurs when the fluid cannot be expelled from between two smooth surfaces due to the viscosity of the fluid. Figure 2.17 shows the pressures measured under a 32×8.8 type VII tire running at 90 pounds per square inch inflation pressure through water with a depth of 1 inch. The test was run against a smooth metal plate, and the pressures generated are shown against the ratio of the test speed (VG) to the calculated hydroplaning speed (VP) using the classic formula. It is of note that the pressures generated under the tire rib (smooth tire contact against the smooth plate) are almost equal to the dynamic hydroplaning pressure at speeds as low as 30% of the dynamic hydroplaning speed. Avoidance of smooth or totally worn tires and an appropriate local roughness of the ground surface are the key elements to avoiding viscous hydroplaning. The pavement microtexture must be of a sufficiently high value to permit the fluid to escape direct contact with the tire. When hydroplaning occurs due to a locked wheel on a wet runway, rapid heat generation can occur that may cause the tire rubber to revert to its unvulcanized form. This near-liquid rubber interacts with the water film on the runway to provide a very low friction surface and a form of hydroplaning occurs, which can continue down to low speeds [36]. This reverted rubber hydroplaning leaves a distinctive appearance on the tire as shown in Figure 2.18. Most reverted rubber hydroplaning events leave a path of “steam cleaned” runway, as shown in Figure 2.19, behind the aircraft. This path has also occurred in events which did not leave reverted rubber evidence on the tires, likely due to the difference between the boiling temperature of water and the higher temperature required to revert the rubber [37].

Reprinted from Aviation Investigation Report, Runway Overrun, Trans States Airlines LLC, Embraer EMB-145LR N847HK, Ottawa/Macdonald-Cartier International Airport, Ontario, 16 June 2010, A10H0004, Transportation Safety Board of Canada.

© SAE International.

Aircraft Tires: Key Principles for Landing Gear Design

 FIGURE 2.18   Reverted rubber tire appearance.

 FIGURE 2.19   Hydroplaning “Steam Cleaned” runway path.

71

72

Aircraft Tires: Key Principles for Landing Gear Design

TABLE 2.1  Hydroplaning summary [38]. Hydroplaning Viscous

Dynamic

Reverted rubber skidding

Contributing Damp or wet pavement factors Medium to high speed Poor pavement texture Worn tire tread

Flooded pavement High speed Low tire pressure Worn tire tread

Wet or flooded pavement High speed Poor pavement texture Deficient brake system

Alleviating factors

Pavement macrotexture Pavement grooving Increased tire pressure Good tread design

Good pavement texture Pavement grooving Improved antiskid

Pavement microtexture Pavement grooving Good tread design

The selection of tires with a suitably high tire pressure to avoid dynamic hydroplaning in the takeoff and landing speed range of the aircraft is an important consideration. In addition, avoidance of wheel lock is important to ensure the tire can continue to produce an effective coefficient of friction. A summary of the three forms of hydroplaning is shown in Table 2.1.

Snow and Ice Modeling the behavior of tires on snow is particularly difficult as there is no “standard snow” – snow can be loose or compacted, wet or dry, and anywhere in between. Snow can be displaced ahead of the tire in the way that water and slush are, generating hydrodynamic drag. However, snow is also compacted beneath the tire. Initial attempts to model the behavior of tires in snow followed the formulation given previously for water and slush. In general, using that model should be  conservative (providing higher drag values than for operation in snow, for the same thickness of material). Extensive winter weather testing has been conducted to attempt to improve models of the phenomenon. In order to achieve a reasonable model, extensive knowledge of the properties of the snow are required, such as density, temperature, and unconfined compressive strength. An empirical model encompassing these values and correlated against a number of aircraft testing in winter environments is provided in ESDU 10015. This model provides for operation on loose snow and compressed snow. Operation on ice will clearly provide a low available coefficient of friction. Many ice surfaces are prepared with compacted snow in order to improve the coefficient of friction (such as those in Antarctica). A formulation for predicting the available coefficient of friction in these environments can be found in ESDU 05011 [39]. Average expected values of friction coefficient in these environments would be 0.3 for snow, 0.1 for ice.

Adapted with permission from © SAE International.

Causes

Aircraft Tires: Key Principles for Landing Gear Design

73

Wear There is a wide range of wear life for aircraft tires and wear depends on a variety of factors: the energy absorbed by the tire during a given flight, the formulation of the rubber used in the tread, the amount of tread rubber available, the roughness of the runway being used, etc. Some tactical aircraft can wear a tire in as few as three flight cycles; the Space Shuttle Orbiter could wear through its tires in one crosswind landing at the Kennedy Space Center runway. However, many commercial airliner tires perform 500 flight cycles between retreads. A breakdown of tire wear by flight phase is shown in Figure 2.20, which was determined as part of the Improved Tire Life research program. The same research program identified some trends leading to increased tire wear:

•• Tire wear increases with increasing yaw and camber (lateral force) •• Braking generates more wear than other operations (cumulative energy) •• High-inflation pressures lead to higher wear than low-inflation pressures (power/footprint area)

•• High-speed yaw causes high wear (frictional power) It is worthy of note that only an estimated 5% of tire wear occurs during the touchdown and tire spin-up phase of flight. Despite the noteworthy cloud of tire smoke created on touchdown (Figure 2.21), it is estimated that only 5–10% of total tire wear occurs during this phase [41]. For aircraft that land at very high touchdown speeds (such as the Space Shuttle Orbiter), this percentage can be much higher. While the wear rate is very aggressive during the spin-up phase, the tires are typically accelerated to speed within a fraction of a second.

Adapted with permission from © SAE International.

 FIGURE 2.20   Tire wear breakdown by flight phase [40]. 12%

3%

8%

Taxi-out straight roll

2%

Taxi-out turns 2% 15%

6%

Taxi-out braking snubs Taxi-out full stops Takeoff

3%

Touchdown

2%

Landing rollout

5%

Taxi-in straight roll Taxi-in turns

42%

Taxi-in braking snubs

74

Aircraft Tires: Key Principles for Landing Gear Design

Rickshu/Shutterstock.com.

 FIGURE 2.21   Tire smoke during touchdown of Airbus A330.

Many devices have been considered to rotate the tires in advance of landing, and many have been tested. Passive systems such as rubber vanes on the tire sidewall (Figure 2.22) are producible but bring additional weight to the tire; that weight could be used instead as tread wear material (indeed, it is considered that the weight of the vanes is about equivalent to the weight of tread material required to achieve the same increase in life). While early studies (from the 1940s) indicated some success [42] on reducing tire wear, it should be noted that the landing speeds were much lower on the aircraft used at that time and that a period of tire acceleration was required with the landing gear extended at significantly higher speed than the touchdown speed in order to permit the tire to accelerate to a useful speed. Later efforts using a Boeing 727 aircraft achieved tire speeds equivalent only to about 25% of the touchdown speed. Additionally, vanes were found to be fragile and during flight testing on the Boeing 727, vane material separated from the tire and was ingested by an engine, leading to the abandonment of the effort. Additional information on pre-rotation of tires is found in The Design of Aircraft Landing Gear, Chapter 11. The driving force for tire wear is then braking and turning operations. A model that permits correlation between wear testing and in-service measurements is provided in AIR5797 [43]. This model computes the total wear energy of the tire as the sum of the side wear energy (SWE) and the drag wear energy (DWE). SWE is a theoretical quantity derived from the distance traveled in the Y-direction multiplied by the force in the Y-direction (Fy). The distance traveled in the Y-direction is approximated as the roll distance (d) multiplied by the sine of the yaw angle (ψ):

SWE

Fy d sin

Aircraft Tires: Key Principles for Landing Gear Design

75

© SAE International.

 FIGURE 2.22   17.00-16 tire with molded vanes.

Similarly, the DWE is the slip ratio (k) times the roll distance (d) multiplied by the drag force on the tire (Fx):

DWE

Fx d k

By analyzing flight data, a wear model can be built that describes the typical operating conditions. This model can then be reduced to an appropriate dynamometer test spectrum, respecting the operating conditions and wear energies. More recently, tire wear is quantified using specialist dynamometers that can replicate the profile of the expected runway and taxiway surface. A test spectrum is conducted which is representative of the expected aircraft mission. The wear observed during one or more representative missions can be extrapolated to determine the expected wear life of the tire. .

Tire Property and Behavior Models There are a wide variety of tire properties that may be of interest to the landing gear designer and analyst. Not every property is tested for every tire, and as a result a number of tire models have been developed to both explain the static and dynamic performance of tires but also to predict the performance of the tire based on a standard set of measured properties. There are many detailed models – only a few are listed here with brief descriptions.

Nasa Technical Report R-64 NASA Technical Report R-64 [44], often referred to as the “Smiley and Horne” model after the authors, is the definitive document for the generation of tire properties for bias ply aircraft tires. The document provides semi-empirical equations

76

Aircraft Tires: Key Principles for Landing Gear Design

Adapted with permission from © SAE International.

 FIGURE 2.23   Comparison of radial tire data with R-64 prediction.

for the determination of a wide variety of properties including: load-deflection curves, lateral, fore-aft, and torsional spring constants, footprint area properties, relaxation lengths, rolling radius, cornering force, cornering power, self-aligning torque, pneumatic trail, tire radial growth, and more. While this document remains very useful, caution must be taken when applying the equations to radial tires. It has been found [11] that the R-64 equations do not necessarily predict the performance of radial tires correctly (as evidenced in Figure 2.23). Notably, the radial tire footprint can differ significantly from similar size bias tires; as noted previously, radial tires tend to be less stiff than their bias counterparts, and as a result R-64 does not predict them well. Cornering parameters are also not well predicted for radial tires. At the time of writing, an activity was under way with the SAE International A-5C committee on aircraft tires to generate a modern equivalent to R-64 to encompass radial tire performance.

Brush Model and Fiala Model The brush model is for the prediction of performance between the tire and the ground surface. It describes the generation of tire forces by dividing the contact patch into regions of adhesion and sliding. The tread rubber volume between the tire and the ground surface is split into infinitesimal elements in the form of elastic rectangular blades (like the bristles of a brush) that stretch laterally over the entire contact region (as shown in Figure 2.24). Each bristle is considered to deform independently of the others to behave in a linear elastic fashion in the longitudinal and lateral directions. In the adhesion region, the bristles are assumed to adhere to the ground surface. The frictional force generated in this region is then based on static friction. In the sliding region, the bristles slide on the ground surface and kinetic friction describes the

Aircraft Tires: Key Principles for Landing Gear Design

77

Adapted with permission from © SAE International.

 FIGURE 2.24   Tire brush model.

behavior. Positions in the contact region are expressed in a reference system attached to the carcass, with the origin located in the center of the contact region. The carcass is assumed to be stiff (the compliance of the bristle elements is intended to represent the complete elasticity of the tread and carcass), and effects of carcass deformation are neglected. A parabolic pressure distribution is considered to act across the contact patch. The Fiala [45] model uses a similar approach as the brush model to represent the tire structure and its deflection in the contact patch, but with a deformable carcass. A parabolic normal pressure distribution over a rectangular contact patch is assumed. The Fiala model is available in the MSC Adams software tool and as a result may be readily employed in some landing gear applications.

Beam and String Models The beam and string approaches represent two different ways of representing the tread of a tire in models aimed at understanding the cornering behavior of tires. The string model is based on the assumption that the tread of the tire is represented by a stretched string restrained by lateral springs, representative of the sidewall, with the wheel rim acting as the base of the springs. This is shown in Figure 2.25a. In the beam model (shown in Figure 2.25b), the tread is represented by an elastic beam with continuous elastic support. A significant difference in these two models is that the stretched string model permits discontinuities in the slope of the equatorial line (the intersection of undeformed tire tread with the wheel plane). This is not possible with the beam model. The stretched-string model can provide a reasonable understanding of the lateral behavior of a pneumatic tire (for small slip angles). In shimmy analysis of landing gears, the Pacejka [46] and von Schlippe [47] models are often encountered. These models are approximate solutions to the stretched string model described above.

78

Aircraft Tires: Key Principles for Landing Gear Design

© SAE International.

 FIGURE 2.25   Beam and string tire tread representations.

Magic Formula Model The magic formula model [48], also known as the Pacejka model, is a model which has been evolved and developed to predict a wide variety of tire properties. It is based on trigonometric functions with a number of coefficients that have to be determined from experimental data. The general form of the equation is:

y x

1

D sin C tan



Y X



x

Bx E Bx tan y x

1

Bx



SV

X SH

where:

•• B is the stiffness factor •• C is the shape factor •• D is the peak factor •• E is the curvature factor •• SH is the horizontal shift •• SV is the vertical shift •• Y is the model output (Fx, Fy, or Mz) •• X is the input variable The physical meaning of the coefficients is shown in Figure 2.26. While widely used in ground vehicle applications, further development of the model is expected to model all aspects of aircraft tire behavior [49]. Nevertheless, the magic formula model can be valuable for landing gear analysis.

Aircraft Tires: Key Principles for Landing Gear Design

© SAE International.

 FIGURE 2.26   Depiction of magic formula coefficients.

79

3 Undesirable Tire Behavior

D

espite the tire being the best interface between the aircraft and the ground, there are some undesirable characteristics that must be addressed including the generation of spray in wet conditions, projection of runway debris, and failure modes of the tire itself.

Spray A tire passing through standing water will generate spray, as shown in Figure 3.1. This spray can be ingested into engines or auxiliary power unit intakes, reducing or eliminating power. In addition, the spray being ejected at high velocities impinges onto the structure of the aircraft and landing gear – this can damage small components such as harnesses and antennas; in addition, it applies a retarding force to the aircraft as the spray impacts the structure. There are three types of spray generated by tires: bow wave (water which is thrown forward of the tire, side spray (water which is projected laterally, shown in Figure 3.1), and rooster tails (water which is picked up by the tire rotation and thrown upwards behind the tire, as seen in Figure 3.2).

©2022 SAE International

81

82

Aircraft Tires: Key Principles for Landing Gear Design

Reprinted with permission from © Embraer.

 FIGURE 3.1   Embraer KC-390 water ingestion test.

Timothy Dry/Shutterstock.com.

 FIGURE 3.2   “Rooster Tail” water projection.

Research conducted by NASA [50] suggests that the amount of water in the bow wave spray is minimal and is quickly atomized. However, for some aircraft configurations this bow wave spray can still cause a concern. An example is the Concorde where the location of the main landing gears relative to the intakes (Figure 3.3) could lead to bow wave spray being aspirated into the engines. The Concorde used spray

Aircraft Tires: Key Principles for Landing Gear Design

83

Reprinted with permission from © Embraer.

 FIGURE 3.3   Concorde landing gear and intake position.

© SAE International.

 FIGURE 3.4   Concorde MLG spray deflector.

deflectors on the front portion of the main landing gears (Figure 3.4) to suppress the bow wave spray (deflectors were also used on the nose landing gear to channel spray between the intakes). While the bow wave spray does not contain the majority of the fluid being displaced by the tires, the water being thrown forward has been accelerated to a velocity greater than the aircraft [51] and has applied a significant drag force to the tire in so doing. This bow wave spray is reduced as the tire begins to hydroplane and is mostly eliminated with the tire fully hydroplaning. The side spray plume can contain two elements – a low-density spray directly to the side of the tire containing water which has been accelerated to around the same speed as the aircraft, and the main plume of high-density water which is often referred to as the “fire hose” plume. This water is lofted by the tires but not accelerated significantly (there is a small outward and upward velocity to the water, but the plume is predominantly stationary compared to the ground). As a result, it impinges on the aircraft with considerable force (the impact velocity being approximately equal to the velocity of the aircraft). The rooster tail generated from a single tire is generally a low-density spray that results from the temporary adhesion of the water to the tire which is thrown out of the tread grooves. This rooster tail can be formed over a wide range of angles and is

84

Aircraft Tires: Key Principles for Landing Gear Design

David Fossler/Shutterstock.com.

 FIGURE 3.5   Boeing 727 rooster tail spray deflector.

predominantly a low-density mist spray of water. Single-wheel rooster tails can be formed in wet conditions and do not require deep water to appear (as shown in Figure 3.2). A different type of rooster tail spray is formed where two wheels are running through deep water. This rooster tail is caused by the impingement of two side plumes from the adjacent tires, and is a high-density plume ejected rearward and upward from the tire pair. An example of a spray deflector for rooster tail spray is that found on the Boeing 727 main landing gears (Figure 3.5). Verification that aircraft and landing gear designs function correctly in standing water is performed by a full scale aircraft test. The aircraft is accelerated and traverses a water trough of appropriate water depth. An example of an aircraft undergoing this testing is shown in Figure 3.1. The primary objective of this testing is to ensure that the engines continue to operate appropriately when ingesting the quantity of water thrown by the tires. In addition, the tests serve to demonstrate the robustness of landing gear secondary fittings as well as maintenance panels and antennas which may be subjected to the water plumes. Guidance for these tests is found in the FAA Advisory Circular 20-124 [52] that recommends an acceptance test water depth of 12.7 mm (0.5 inches) and EASA AMC25.1091 [53] that requires an average depth of 19 mm (0.75 inches). However, it is in the interest of the designer to have a method of estimating the spray direction and intensity such that an analytical approach to the design can be taken. Many test programs have been conducted historically to understand the effect of a tire running through various depths of water. The spray angle is a function of the tire inflation pressure, water depth, and aircraft speed. A non-dimensionalized view of the flow rate resulting from NASA testing is shown in Figure 3.6, and the side spray angle dependency on tire pressure is shown in Figures 3.7 and 3.8. SAE International document AIR1904B [54] provides an overview of some historical testing as well as the elements to be considered when performing aircraft level tests for spray. An analytical approach for predicting the spray directions of side spray and twin wheel rooster tail spray is provided in ESDU data sheet 83042 [55]. This comprehensive method generates the spray envelopes as a function of the contaminant density and depth, tire dimensions, footprint, and deflection, as well as aircraft speed.

Aircraft Tires: Key Principles for Landing Gear Design

Adapted with permission from © SAE International.

 FIGURE 3.6   Side spray flow rate from NASA testing.

Adapted with permission from © SAE International.

 FIGURE 3.7   Side spray angle from AIR1904B.

85

86

Aircraft Tires: Key Principles for Landing Gear Design

Adapted with permission from © SAE International.

 FIGURE 3.8   Spray elevation angle from AIR1904B.

Debris Lofting As a tire rolls over loose debris, such as stones or other foreign objects, they can be lofted into the air and can subsequently impact the aircraft. This is a known issue for operations on aggregate runways but it can also arise on runways with bomb damage repairs and on nominally clean runways that have accumulated some debris. Aircraft operating regularly on aggregate or dirty airfields can suffer significant damage to the fuselage, engines, and propellers. Figure 3.9 shows the areas impacted on a Fairchild F-27 aircraft operating from aggregate runways. Typical damage is denting or perforation of skins, destruction of antennas and lights, and erosion of paint and protective coatings. Depending on placement, main landing gears can be impacted by debris lofted by nose landing gear tires. An example of this type of erosion damage is shown in Figure 3.10. In many locations, the protective coatings have been removed by the impingement of stones and fine debris. The aluminum structure is still in acceptable condition. Not every stone or piece of debris encountered by a tire will be lofted. For those that are, there is a distribution of lofting angle and speed that is dependent on a variety of factors including the shape and size of the piece. Boeing investigations [56] into operations on unpaved runways indicated that items with dimensions greater than 10 mm are projected by aircraft tires in relatively intense zones that extend behind the tire ±30° from the tire centerline and from 0° to 30° up from the runway surface. A zone with reduced intensity exists from 30° to 60° from the runway surface. The concentration of debris spray was noted to be especially dense during tire spinup at landing. Cessna has adopted a system to pre-spin the nose wheel tire before landing on aggregate runways in order to combat this phenomenon. In addition to the

© SAE International.

Reprinted from ESL-TR-81-39, The Study Of Foreign Object Damage Caused By Aircraft Operations On Unconventional And Bombdamaged Airfield Surfaces (www.dtic.mil/dtic/tr/fulltext/u2/a117587.pdf).

Aircraft Tires: Key Principles for Landing Gear Design

 FIGURE 3.9   Rock impact locations on F-27 aircraft.

 FIGURE 3.10   BAe-146 main landing gear erosion.

87

88

Aircraft Tires: Key Principles for Landing Gear Design

 FIGURE 3.11   Potential sideward lofting mechanisms: (a) hammer, (b) pinch, and

Reprinted with permission from © Cambridge University Press.

(c) spin lofting.

projection of debris, operation on aggregate runways has shown increased tire wear and tire cutting, with the possibility that tire debris can be left on the runway or discarded from the tire. A number of research efforts have been conducted to determine the mechanisms whereby stones and other debris are lofted. Several mechanisms are potentially at work: pinch lofting (where the item is rolled over by the side of the tire and “pinched” out), groove lofting (where the item becomes temporarily lodged in the tire tread groove and is then expelled), spin lofting (contact with the tire imparts a spin which permits the item to climb up the tire sidewall), and hammer lofting (where the item is struck by the tire and expelled in a manner analogous to hitting it with a hammer blow). While groove lofting is possible, it is generally not considered to be the dominant mode: debris would need to be the same size as the tire grooves and located directly in line with the groove to be lodged and then thrown. In addition, tire groove depths are not significant and in service damage indicates that most impacts are not directly in line with the tire but rather slightly to the sides of the tire path. Sideward lofting mechanisms are shown in Figure 3.11 [57]. The difference between hammer lofting and pinch lofting is effectively the duration of contact between the tire and the item being lofted. With hammer lofting, it is assumed that the tire is travelling fast enough that during the interaction with the item being contacted, the tire deflection can be treated as negligible. With this assumption, the launch velocity of the item is governed by the dynamics of rigid body collisions. The momentum of the item is then related to the momentum of the tire at the instant of contact. By contrast, pinch lofting considers that the energy stored in the tire indentation is the main source of the item’s energy. Potential energy is stored in the tread when traversing the item, which is then converted into the kinetic energy of the item upon it being released from the tire. Spin lofting is a different mechanism: contact with the tire imparts a spin on the item, the spin then causes the item to climb the tire sidewall before being ejected with the energy imparted from the rotational velocity of the tire. In research work done to date, hammer lofting [57] and pinch lofting [56] are considered to be the dominant mechanisms. In general, the velocity of the item is small with respect to the velocity of the aircraft: the lofting velocity is enough to lift the item into the air while the impact velocity comes from the speed of the aircraft. Modern work on modeling these phenomena has focused on finite-element modeling techniques. However, work outlined in Bless et al. [56] defines some ballistic calculation approaches

Aircraft Tires: Key Principles for Landing Gear Design

89

that may be relevant to make an initial approximation. It should be noted, however, that recent work by Nguyen et al. [57] strongly suggests that tire-based lofting is not the only effect at work and that once lofted, aerodynamic effects contribute significantly to lifting the item and allowing it to impact the aircraft structure. For aircraft operating on unprepared and aggregate runways, it is clear that the tires will encounter stones and other items which could be lofted. However, the issue also occurs (but less frequently) on paved runways. An analysis [58] of debris swept from a number of UK military airfields found that from a total of over 15 kg of material collected, the largest stone collected was 35 g. However, the vast majority of stones were significantly smaller than that – only 1% of stones had a mass greater than 10 g, and 3% of stones were found to have a mass greater than 5.3 g. The average density of these stones was found to be 2.7 g/cm3. The study determined that for an aircraft with a take-off velocity of 80 m/s, the probability of an impact exceeding 10, 50, and 100 J was 1.91%, 0.23%, and 0.08%, respectively. Nguyen’s work divides the impacts into three energy categories: low energy (2–10 J), medium energy (10–50 J), and high energy (greater than 50 J). While every aircraft is exposed to the possibility of debris impact due to tire lofting, there is a probabilistic nature to the problem: operation on well paved, highly frequented runways will not present a high probability of debris and debris strikes. Operation on unpaved surfaces, including aggregate surface runways and bomb damage repaired runways, will expose the aircraft to high probabilities of debris impact. In all cases, some protection of vulnerable structure is suggested. Typically for landing gear components in close proximity to tires, a polysulfide mastic applied to the component and then over painted has been shown to adequately defend against the type of erosion damage shown in Figure 3.10. For aircraft operating on aggregate runways, stone deflectors and nose wheel tire pre-spin have been shown to be effective. Combat aircraft designed to operate from semi-prepared fields or rapidly repaired runways have often been fitted with spray and debris deflectors on the nose landing gear, as shown in Figure 3.12 for a Sukhoi Su-34 aircraft. Due to the engine intake

vaalaa/Shutterstock.com.

 FIGURE 3.12   Nose landing gear deflector on Sukhoi Su-34 aircraft.

90

Aircraft Tires: Key Principles for Landing Gear Design

placement on this type of aircraft, spray suppression is required to ensure operational reliability. The European Aviation Safety Agency studied whether to define and regulate the threat of lofted debris to large transport category aircraft and decided that for this category of aircraft the threat was minimal, with tire projected foreign object damage being a very rare event [59]. It is prudent in any case to protect exposed components of the landing gear from projected debris, especially if corrosion protective coatings could be compromised.

Tire Failure Modes Despite modern aircraft tires being capable of supporting high loads at high speeds and doing so flight after flight they are capable of failing in a variety of ways, all of which need to be protected against with the design of the landing gear and aircraft. Likely the most common failure mode is shown in Figure 3.13 – a deflated tire. In multiple wheel assemblies, the adjacent tire will take the full load and the structure must be designed to accommodate this occurrence. In multiple wheel assemblies (four wheel or six wheel bogies), various patterns of tire failure can occur (including all tires being deflated or destroyed). An analysis of the critical patterns (typically all tires on one side of the bogie) should be conducted. For large civil aircraft, this is required by regulation 25.511 (c) through (f). Extended operation on deflated tires can lead to total destruction of the tire, with the aircraft load being taken directly on the wheel rims as would be the case for a shredded tire (Figure 3.14). Alternatively, tire failures can lead to local fires without the tire being completely shredded as in the example in Figure 3.15. Locked wheels due to anti-skid system failure, frozen brakes, or other causes lead to flat spotting of tires (if the duration of the wheel lock is brief) as shown in Figure 3.16. Sustained wheel lock will lead to a skid-through failure of the tire (Figure 3.17) which results in the rapid release of the inflation medium. A bias ply tire is shown in the figure – tire burst events in bias ply tires manifest themselves in an

Ismael Jorda/Shutterstock.com.

 FIGURE 3.13   Deflated tire.

Aircraft Tires: Key Principles for Landing Gear Design

91

Reprinted from NASA.

 FIGURE 3.14   Shredded tire.

Reprinted from RAF Mildenhall Airmen work to save KC-135 Senior Airman Teresa Hawkins, USAF.

 FIGURE 3.15   KC-135 tire failure and fire.

“X” shape. Radial tire bursts form more of a wedge or “Pac-Man” shape. In both cases, the carcass ruptures along the lines of the reinforcing plies. Tire bursts can also occur without a skid-through event due to foreign object damage, over heating of the tire (typically due to under-inflation), and local weakening of the tire with use. An example of a “blown out” tire is shown in Figure 3.18. It can be seen from the ruptured tire that large elements of the tire can be disgorged and propelled into the airframe. In this particular instance, a two foot by three foot hole was punched through the aircraft, destroying all tubing and wiring which was located in the area.

92

Aircraft Tires: Key Principles for Landing Gear Design

© SAE International.

 FIGURE 3.16   Tire flat spot.

© SAE International.

 FIGURE 3.17   Skid-through tire failure.

Another damaging failure mode is the shed of the tread or a portion of tread.

Figure 3.19 shows a tire where a portion of tread rib has separated from the carcass.

In some cases, a nearly complete section of the tread can be ejected from the tire (Figure 3.20) or it can be almost completely ejected but retained on the spinning carcass. This “flailing tread” can impart a significant amount of damage: often destroying flap torque tubes and hydraulics in main landing gear bays.

Aircraft Tires: Key Principles for Landing Gear Design

93

Reprinted from http://www.af.mil/News/ArticleDisplay/ Article/134456/c130maintainersaccomplishin fielddepotmaintenance/.

 FIGURE 3.18   C-130 tire failure.

© SAE International.

 FIGURE 3.19   Peeled rib.

Informational document AIR5699 [60] reviewed four decades of NTSB accident data and found 73 serious wheel and tire events, 15% of which resulted in fatalities and a further 11% resulted in complete loss of the aircraft (without fatalities). The most common cause of these occurrences was main gear tire burst, followed by main gear tire flailing tread. Tire failures not leading to aircraft damage are not captured by the NTSB and are not part of this analysis.

94

Aircraft Tires: Key Principles for Landing Gear Design

© SAE International.

 FIGURE 3.20   Tire with thrown tread.

Modeling Tire Failure Events Many approaches to modeling tire failure modes have been developed, typically by aircraft manufacturers. Prior to the existence of the EASA, the Joint Airworthiness Authority of Europe published a model in their temporary guidance material (TGM). This model was based on Airbus testing of A300 bias ply tires and has served as the baseline for aircraft design and certification for a number of years. The model approach was updated [59] in 2013 following input from an industry working group to account for differences in radial ply tires and considering a variety of worldwide tire-related accidents. The threat models cover ejected tire debris, flailing tire strips, and inflation medium release associated with a tire burst. EASA guidance material AMC 25.734 [61] provides four models that cover landing gear extended and retracted threats. It is worth noting that these tire models use the rated tire speed rather than a rational speed based on aircraft takeoff or landing speeds. This is a conscious choice and is designed to ensure adequate tire debris energies are considered. For the models, the tread depth definitions shown in Figure 3.21 and the definitions below apply.

Total tread area : Atread

D g Wsg

Minimum tire speed rating: The lowest tire speed rating certified for the aircraft. Tire speed rating: The maximum ground speed at which the tire has been tested in accordance with technical standard order C62e.

Aircraft Tires: Key Principles for Landing Gear Design

95

Reprinted from EASA AMC 25.734.

 FIGURE 3.21   Tread quantity for the tire failure model.

Model 1: Tire Debris Threat Model This model is applicable for debris released from the tire when it is in contact with the ground. Two sizes of debris are considered, and they are assumed to be released from the tread area of the tire and projected toward the aircraft within the zones of vulnerability as identified in Figure 3.22 . The “large debris” is considered to have dimensions Wsg × Wsg at Dg and a thickness of the full tread plus outermost ply (i.e., the reinforcement or protector ply). The angle of vulnerability, θ, to be considered is 15°. The “small debris” is considered to consist of 1% of the total tire mass, with an impact load distributed over an area equal to 1.5% of the total tread area. The angle of vulnerability, θ, to be considered is 30°. The debris is considered to have a speed

Reprinted from EASA AMC 25.734.

 FIGURE 3.22   Tire debris threat model.

96

Aircraft Tires: Key Principles for Landing Gear Design

equivalent to the minimum tire speed rating certified for the aircraft (the additional velocity component due to the release of carcass pressure does not need to be taken into account). These models are relevant for any fuel tanks in the threat area and ejection of the large debris can be considered to cause a fuel leak but should not also create an ignition source (e.g., by damaging electrical harnessing). Ejection of the small debris should not create a hazardous fuel leak. The large and small debris model should also be used to ensure that systems in the zone of vulnerability are appropriately segregated and, if required, armored. For the analysis of shielding or armoring, the small debris model is used. A first tire failure can also result in the failure of the companion tire (with debris being ejected from both tires). This can occur even when the tires have been designed to have double dynamic overload capability. The analysis for the segregation of systems installation and routing should take this companion tire failure into account inside the vulnerability zone defined by θ = 15° (either side of the tire centerline) and considering that both tires only release large debris. Inside zones defined by 15° < θ ≤30° only small debris from a single tire needs to be considered.

Model 3E: Flailing Tire Strip Threat Model A flailing tire strip typically results from the partial delamination of the tread from the carcass, although flailing strips can include large portions of the carcass. This model is relevant for the aircraft when the landing gear is extended. In the interests of conservatism, unless it can be demonstrated that the tire carcass will not fail as well as the tread, the thickness to be assumed in the model is the full tread thickness plus the carcass thickness, as shown in Figure 3.21. If it can be demonstrated that the carcass will remain intact (as might be the case for radial tires), then the thickness to be used is the full tread and outermost ply (the reinforcement or protector ply). The model considers that a flailing tire strip with a length of 2.5 Wsg and a width of Wsg/2 will remain attached to the outside diameter of the rotating tire at take-off speeds. The strip is to be considered to have a speed equivalent to the minimum tire speed rating certified for the aircraft. The zone of vulnerability is considered as 30°, as shown in Figure 3.23.

Model 3R: Flailing Tire Strip Threat Model This model is the same Model 3E, but for the gear while retracting and in the retracted position. The major difference is that credit can be taken for wheel spin down following takeoff and retraction brake snubbing (provided that the retraction brake system is reliable and independent from a flailing strip event). The strip is to be considered to have an initial speed equivalent to the minimum tire speed rating certified for the aircraft. Depending on the systems available, the tire can be considered to decelerate partially (wheel bearing friction and aerodynamic drag) or completely (reliable, independent retraction brake) before or during retraction. As for Model 3E, the zone of vulnerability is 30°. In the case of full retraction braking, it is advisable to assess the tread of the tire strip entering the bay with no rotational speed and at all possible radial positions.

Aircraft Tires: Key Principles for Landing Gear Design

97

Reprinted from EASA AMC 25.734.

 FIGURE 3.23   Flailing tread model.

Model 4: Tire Burst Pressure Effect Threat Model A bursting tire in the landing gear bay can cause disruption and displacement of components mounted in the bay due to the gas pressure jet released by the tire. In some cases, permanent distortion of the bay walls has been observed. This model is applicable when the landing gear is retracting or when it is completely retracted. These cases are considered to result from previous damage to the tire, which can occur at any point on the exposed surface. A review conducted by EASA of known incidents showed that all cases of retracted tire burst occurred on main landing gear tires mounted on braked wheels. While the model is applicable to all tires, EASA only considers these effects necessary to consider on braked wheels. The model assumes that tires do not release debris and that damage is only caused by the pressure release effects – the “blast effect.” Due to the construction differences between bias and radial tires, the blast effect has been shown to be different between the types. The model assumes a tire burst pressure of 1.3 times the maximum unloaded operational pressure. For multiple wheel gears, this is the unloaded tire rated pressure reduced by a factor of 1.07 (which is the design safety factor for transport category aircraft required by CS 25.733). As an example: An H44.5×16.5–21, 26 ply rating tire has an unloaded tire rated pressure of 1365 kPa (198 psig), so the maximum unloaded operational pressure is 1365/1.07 = 1276 kPa (185 psig). In absolute pressure, this is 1377 kPa (199.7 psia). The tire burst pressure is then 1377×1.3 = 1790 kPa absolute pressure (259.7 psia).

For bias tires, the burst plume model shown in Figures 3.24 and 3.25 should be used, with the blast cone axis rotated over the tread surface of the tire (± 100° as

98

Aircraft Tires: Key Principles for Landing Gear Design

Reprinted from EASA AMC 25.734.

 FIGURE 3.24   Bias tire burst pressure effect – burst location.

Reprinted from EASA AMC 25.734.

 FIGURE 3.25   Bias tire burst pressure effect – pressure cone details.

Aircraft Tires: Key Principles for Landing Gear Design

99

 FIGURE 3.26   Exponential decay functions for bias tire burst pressure effect.

(P-Pa)/(Pt-Pa)

Adapted from EASA AMC 25.734.

Bias Tire Air Jet Exponential Decay 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0

Distance from tire surface (m) 0.6 m

0.5 m

0.4 m

0.3 m

0.2 m

0.1 m

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 0.11 0.12 0.13 0.14 0.15 Radius from Centerline (m)

shown in Figure 3.24). The pressure distribution is a set of exponential decay functions shown in Figure 3.26 and following the coordinate system of Figure 3.25. Functions are provided in Table 3.1, which have been digitized from the material provided by EASA. In the figures and tables:

•• Pa is the ambient pressure •• P=P(x,z) is the pressure inside the cone, as shown in Figure 3.25 •• Pt is the tire burst pressure Due to the differences in carcass construction, a different model is used for radial tires. A burst plume model with a wedge shape is employed as shown in Figures 3.27 and 3.28. The pressure at any distance, x, from the radial tire is given by the expression:

P x

0.5283 Pt

Pa 1.4e

x 3

e

x

Pa ; if P x

Pt then P x

Pt

© SAE International.

TABLE 3.1  Bias tire burst pressure decay functions. Distance from tire (m)

Exponential decay function: (P–Pa)/(Pt–Pa) as a function of x (radius from centerline, m)

0.1

(P–Pa)/(Pt–Pa) = 325.42e–136.4x

0.2

(P–Pa)/(Pt–Pa) = 9.1038e–67.24x

0.3

(P–Pa)/(Pt–Pa) = 3.6759e–50.47x

0.4

(P–Pa)/(Pt–Pa) = 1.9686e–38.44x

0.5

(P–Pa)/(Pt–Pa) = 1.3001e–31.34x

0.6

(P–Pa)/(Pt–Pa) = 0.9621e–25.49x

100

Aircraft Tires: Key Principles for Landing Gear Design

Reprinted from EASA AMC 25.734.

 FIGURE 3.27   Radial tire burst pressure effect.

Adapted from EASA AMC 25.734.

 FIGURE 3.28   Radial tire pressure burst effect – locations.

Aircraft Tires: Key Principles for Landing Gear Design

101

where: x

C1 Wg

x

C 3 x , for W g and x in inches;

C2

C1 C2

Wg

C3

x , for Wg and x in millimeters 25.4

25.4 C1 12.478; C2

1.222; C3

0.024

•• Pt is the total or burst pressure in pounds per square inch (absolute) or bar •• Pa is the ambient pressure in pounds per square inch (absolute) or bar •• x is the distance from the grown tire surface in inches or millimeters The effect of the burst should be considered on the structure, and system components located inside the defined burst plume. As a design objective, the increase in pressure inside the landing gear bay as a result of tire burst should not be detrimental to continued safe flight and landing. In some cases, it may be instructive to conduct burst tests of tires to substantiate the modeling approach provided here. In that case, guidance material is provided in ARP6265 [62] as to how best to initiate the burst event and how to capture the relevant pressure profiles.

Understanding the Impact of Tire Failures The best defense against tire failures is to ensure an appropriate segregation of duplicated systems in the zones of vulnerability. Large pieces of landing gear structure and traditional transport category airframe structure (high aspect ratio wings built around a single torsion box manufactured of light metal alloy) have been shown, by experience, to be  robust against tire debris. However, other design approaches (composite structure or other geometric arrangements) may need to be specifically analyzed for the result of an impact of debris. In some cases, components on the landing gear may need to be shielded from ejected tire debris if appropriate segregation cannot be achieved and the components cannot be shown by analysis or test to withstand a debris impact. Test approaches include launching samples cut from tires at representative components. In addition, analytical approaches using explicit finite element solvers have been shown to model the phenomenon appropriately for some cases. An example [63], shown in Figure 3.29, is taken from an investigation into the impact of tire debris against the lock link assembly for a large transport category aircraft.

102

Aircraft Tires: Key Principles for Landing Gear Design

 FIGURE 3.29   Correlation between analysis and test for tire debris impacting a

© SAE International.

lock link.

Aircraft Tires: Key Principles for Landing Gear Design

103

The Boeing 737 aircraft has a passive hydraulic solution to avoid a flailing tire strip from entering the landing gear bay. Frangible hydraulic fittings are positioned in the bottom wing skin surface such that a flailing tread strip will rupture them during the retraction sequence before the tread strip enters the landing gear bay. Once ruptured, there is an increase in hydraulic fluid flow that trips a hydraulic fuse and depressurizes the retraction sequence. The landing gears then free fall into downlock.

References



1. Foster, B., “Undercarriages,” Flight, February 8, 1940, 131.



2. Schmidt, R. Kyle, The Design of Aircraft Landing Gear, SAE International, Warrendale, PA: 2020.



3. Schmidt, R. Kyle, Airfield Compatibility: Key Principles for Landing Gear Design, SAE International, Warrendale, PA: 2022.



4. Aerospace Information Report, “Aerospace Landing Gear Systems Terminology,” AIR1489, Revision C, SAE International, May, 2017.



5. Federal Register, “Use of Nitrogen or Other Inert Gas for Tire Inflation in Lieu of Air,” 58 FR 11778, Federal Register, February 26, 1993.



6. Aerospace Recommended Practice, “Minimum Operational and Maintenance Responsibilities for Aircraft Tire Usage,” ARP5265, Revision B, SAE International, June 2014.



7. MIL-STD-1522A, Standard General Requirements for Safe Design and Operation of Pressurized Missile and Space Systems, May 28, 1984.



8. Lay, M.K., Macy, W.W., and Baxter, A.J., “An Investigation of Aircraft Tire Blowouts,” SAE Technical Paper 961312, 1996, https://doi.org/10.4271/961312.



9. Aerospace Information Report, “Aircraft Tire History,” AIR487B, SAE International, August 2016.

10. Woodall, W.R., “Cantilever Aircraft Tires More Than a Break for Brakes,” SAE Technical Paper 720870, 1972, https://doi.org/10.4271/720870. 11. Tanner, J.A., Daugherty, R.H., and Smith, H.C., “Mechanical Properties of Radial-Ply Aircraft Tires,” SAE Technical Paper 2005-01-3438, 2005, https://doi.org/10.4271/2005-01-3438. 12. Aerospace Recommended Practice, “Aircraft Tires Service Overload Capability,” ARP6152, SAE International, December 2013. ©2022 SAE International

105

106

References

13. Technical Standard Order, Aircraft Tires, TSO-C62e, Federal Aviation Administration, September 29, 2006. 14. European Technical Standard Order, Aircraft Tires, ETSO-C62e, European Aviation Safety Agency, July 5, 2012. 15. Performance Specification, Tires, Ribbed Tread, Pneumatic, Aircraft, MIL-PRF-5041K, US Department of Defense, April 30, 1998. 16. Conditions d’homologation des pneumatiques pour aérodynes, AIR 8505/A, Direction Générale d’Armement, May 17, 1971. 17. Aerospace Standard, “Aircraft New Tire Standard - Bias and Radial,” AS4833, SAE International, November 2014. 18. Airworthiness Standards: Transport Category Airplanes, 14 CFR Part 25, Federal Aviation Administration. 19. Aerospace Recommended Practice, “Rotorcraft: Application of Existing Aircraft Designed Tires, Wheels and Brakes,” ARP5632, SAE International, April 2016. 20. Such as Clark, S.K., Mechanics of Pneumatic Tires, National Bureau of Standards Monograph 122, November 1971 and Gent, A.N. and Walter, J.D., The Pneumatic Tire, DOT HS 810 561, National Highway Traffic Safety Administration, February 2006. 21. Surface Vehicle Recommended Practice, “Vehicle Dynamics Terminology,” J670, SAE International, January 2008. 22. Daugherty, R.H., “A Study of the Mechanical Properties of Modern Radial Aircraft Tires,” NASA/TM-2003-212415, May 2003. 23. Model for Performance of a Single Aircraft Tyre Rolling or Braking on Dry and Precipitate Contaminated Runways, ESDU 10015, Revision B, July 2015. 24. From Marushko, R.A., Gravel Runway Surface Strength Measurements and Aircraft Certification Requirements, Issue 1, Transport Canada, June 30, 1997. 25. Aerospace Recommended Practice, “Recommended Practice for Measurement of Static and Dynamic Characteristic Properties of Aircraft Tires,” ARP4955, Revision A, SAE International, July 2012. 26. Aerospace Information Report, “Aerospace Landing Gear Systems Terminology,” AIR1489, Revision C, SAE International, May 2017. 27. Tanner, J.A., McCarty, J.L., and Batterson, S.A., “The Elastic Response of Bias-Ply Aircraft Tires to Braking Forces,” NASA Technical Note, TN D-6426, National Aeronautics and Space Administration, September 1971. 28. Kummer, H.W. and Meyer, W.E., “Rubber and Tire Friction,” Engineering and Research Bulletin B-80, Pennsylvania State University, December 1960. 29. Tire-Pavement Friction Coefficients, Technical Report R672, Naval Civil Engineering Laboratory, April 1970. 30. Horne, W.B. and Joyner, U.T., “Studies of the Retardation Force Developed in an Aircraft Tire Rolling in Slush or Water,” NASA Technical Note D-552, National Aeronautics and Space Administration, September 1960. 31. Estimation of Airframe Skin-Friction Drag Due to Impingement of Tyre Spray, ESDU Data Item No. 98001, April 1998. 32. Horne, W.B. and Dreher, R.C., “Phenomena of Pneumatic Tire Hydroplaning,” NASA Technical Note D-2056, National Aeronautics and Space Administration, November 1963.

References

107

33. vanEs, G.W.H., “Hydroplaning of Modern Aircraft Tires,” NLR-T-2001-242, National Aerospace Laboratory NLR, May 2001. 34. Cepic, A., “Hydroplaning of H-Type Aircraft Tires,” SAE Technical Paper 2004-01-3119, November 2004, https://doi.org/10.4271/2004-01-3119. 35. Planing of Rib-Tread Aircraft Tyres, Engineering Sciences Data Unit 15003, Amendment A, July 2016. 36. Nybakken, G.H., Staples, R.J., and Clark, S.K., “Laboratory Experiments of Reverted Rubber Friction,” NASA Contractor Report CR-1398, National Aeronautics and Space Administration, August 1969. 37. Aviation Investigation Report, Runway Overrun, Trans States Airlines LLC, Embraer EMB145LR N847HK, Ottawa/Macdonald-Cartier International Airport, Ontario, A10H0004, Transportation Safety Board of Canada, June 16, 2010. 38. Yager, T.J., “Tire and Runway Surface Research,” SAE Technical Paper 861618, October 1986, https://doi.org/.10.4271/861618. 39. Summary of the Model for Performance of an Aircraft Tyre Rolling or Braking on Dry or Precipitate Contaminated Runways, ESDU Data Item 05011, Amendment D, July 2015. 40. Lay, M.K., Macy, W.W., and Wagner, P.M., “Initial Identification of Aircraft Tire Wear,” SAE Technical Paper 951394, May 1995, https://doi.org/10.4271/951394. 41. Aerospace Information Report, “Tire Prerotation at Landing,” AIR5800, Revision A, SAE International, August 2015. 42. Schippel, H.F., “Prerotation of Landing Gear Wheels,” SAE Technical Paper 440200, October 1944, https://doi.org/10.4271/440200. 43. Aerospace Information Report, “Aircraft Tire Wear Profile Development and Execution for Laboratory Testing,” AIR5797, SAE International, October 2013. 44. Smiley, R.F. and Horne, W.B., “Mechanical Properties of Pneumatic Tires with Special Reference to Modern Aircraft Tires,” Technical Report R-64, National Aeronautics and Space Administration, 1960. 45. Fiala, E., Seitenkrafte am rollenden Luftreifen, VDI, Bd, Nr. 29, October 1954, 973–979. 46. Pacejka H.B., “Analysis of the Dynamic Response of a Rolling String-Type Tire Model to Lateral Wheel-Plane Vibrations,” Vehicle System Dynamics 1 (1972): 37-66. 47. vonSchlippe, B. and Dietrich, R., “Shimmying of a Pneumatic Wheel,” Technical Report NACA-TM-1365, National Advisory Committee for Aeronautics, 1954. 48. Bakker, E., Nyborg, N., and Pacejka, H.B., “Tyre Modelling for Use in Vehicle Dynamics Studies,” SAE Technical Paper 870421, February 1987, https://doi.org/10.4271/870421. 49. Kiébré, R., “Contribution to the Modelling of Aircraft Tyre-Road Interaction,” PhD thesis, Université de Haute Alsace, Mulhouse, December 2010. 50. Daugherty, R.H. and Stubbs, S.M., “Measurements of Flow Rate and Trajectory of Aircraft Tire-Generated Water Spray,” NASA Technical Paper 2718, National Aeronautics and Space Administration, July 1987. 51. Investigation on the use of Airjets and Chines on Aircraft Undercarriages Using Model Wheels and a Moving Belt and Water Layer, S&T Memo 10/68, UK Ministry of Technology, May 1969. 52. Water Ingestion Testing for Turbine Powered Airplanes, Advisory Circular AC20-124, Federal Aviation Administration, September 30, 1985.

108

References

53. Precipitation Covered Runways, AMC 25.1091(d)(2), CS-25 Book 2, Amendment 19, European Aviation Safety Agency, May 12, 2017. 54. Aerospace Information Report, “Tire Spray Suppression – Airplane Design and Consideration for,” AIR1904B, SAE International, May 2017. 55. Estimation of Spray Patterns Generated from the Sides of Aircraft Tyres Running in Water or Slush, Engineering Sciences Data Unit 83042A, April 1998. 56. Bless, S.J. et al., “FOD Generation by Aircraft Tires,” ESL-TR-82-47, Engineering and Services Laboratory, Air Force Engineering and Services Center, Tyndall Air Force Base, August 1983. 57. Nguyen, S. et al., “Runway Debris Impact Threat Maps for Transport Aircraft,” The Aeronautical Journal 118, no. 1201 (March 2014): 233. 58. Greenhalgh, E.S., Chichester, G.A.F., Mew, A., and Slade, M., “Characterisation of the Realistic Impact Threat from Runway Debris,” The Aeronautical Journal 105, no. 1052 (2001): 557-570. 59. Notice of Proposed Amendment (NPA) 2013-02, Protection from Debris Impacts, European Aviation Safety Agency, January 18, 2013. 60. Aerospace Information Report, “A Guide for the Damaging Effects of Tire and Wheel Failures,” AIR5699, October 2013. 61. European Aviation Safety Agency, “Protection against Wheel and Tyre Failures,” AMC 25.734, CS-25 Book 2, Amendment 19, European Aviation Safety Agency, May 12, 2017. 62. Aerospace Recommended Practice, “Tire Burst Test Methodology,” ARP6265, SAE International, December 2014. 63. Mercier, C., “Bird and Tyre Impact Analysis on Landing Gear,” SAE Technical Paper 2013-019002, December 2013, https://doi.org/10.4271/2013-01-9002.

Index

A

Airbus A330, 74 Aircraft tires air cushion landing systems, xix construction terminology, 3–7 debris, 102 dimensions and properties bias and radial tires, selection between, 24–25 manufacturing, certification and standardization, 26–28 tire classification, 23–24 tire temperatures, 18–23 engineering ingenuity, xv explosive potential of, 19 functions, 1 inflation pressure, 3, 14–18 gas volume estimation, 16 landing gear, functions, xv maneuverability and support, xix performance and modeling ground friction, 63–72 pneumatic tires, mechanics of, 53–63

property and behavior models, 75–79 wear, 73–75 pneumatic tires, 2 benefits of, 3 carcass, 3 protective cage, loaded into, 19 rational load-speed-time curve, 20 rotorcraft applications, 31 rubber, 1 hysteresis, 2 sizes manufacturing, certification and standardization, 28–30 radial tire table, 31, 49–51 reduced weights, on new tire designs, 52 requirements, 30–31 three part bias tire table, 31, 40–48 type III tire table, 31–35 type VII tire table, 31, 36–39 solid tires, 1, 2 standard load-speed-time curve, 27 temperature, 21 tensile forces, 3 track systems, xix, xvii typical aircraft tire, xvi

undesirable characteristics spray (see Spray, tires) wheel brakes, xvii Antiskid brake systems, 63 Aspect ratio (AR), 10 Avro Vulcan, xvii B

B-36, xvii B-50, main landing gear of, xviii BAe-146 main landing gear erosion, 87 Bead, 3 Bead base, 5 Bead bundle, 5 Bead filler, 5 Bead heel, 5 Bead toe, 5 Beam model, 77–78 Belt, 5 Bias ply tires, 3, 25, 52 burst pressure effect exponential decay functions, 99 location, 98 pressure cone details, 98 clearance dimensions, 9 construction, 4 “Blast effect,” 97 “Blown out” tire, 91 Boeing 727 aircraft, 74 Boeing 737 aircraft, 103 Boeing 727 rooster tail spray deflector, 84 Braking behavior, 59–63 Brush model, 76–77 109

110

Index

C

Cap fly, 5 Carcass, 5 Carcass cord, 5 Carcass ply, 5 Caterpillar track designs, xviii Cessna, 86 Chafer, 5 Chine, 5 Combat aircraft, 89 Concorde, 20, 82 landing gear and intake position, 83 MLG spray deflector, 83 Contact patch, of braked tire, 61, 62 Convair B-58, xvii Convair XB-36 main wheel, xvii Coulomb’s model, for friction, 64 C-130 tire failure, 93 D

de Havilland Comet, xvii Double chine tire cross section, 7 Drag wear energy (DWE), 74 Dry runways, 57 Dynamic hydroplaning, 68, 70 E

EASA guidance material AMC 25.734, 94 European Aviation Safety Agency, 90 European Tyre and Rim Technical Organization (ETRTO), 26, 30, 31 F

Fabric tread, 6 Fairchild F-27 aircraft, 86 rock impact locations on, 87 Fiala model, 76–77 Finite-element modeling techniques, 88

“Fire hose” plume, 83 Flailing tire strip threat model Model 3E, 96–97 Model 3R, 96 tire burst pressure effect threat model, 97–101 Flailing tread model, 92, 97 G

Generic load-deflection curve, 58 Groove lofting, 88 Ground friction, tires adhesion, frictional force, 63 friction coefficient, 64, 65 hysteresis, frictional force, 63 reverted rubber tire appearance, 71 rubber friction behavior, model of, 64 snow and ice, 72 wet runways and hydroplaning, 65–72 H

Hammer lofting, 88 Horizontal force, 54 H-type tires, 69 I

Innerliner, 6–7 International Standards Organization (ISO), 53 K

KC-135 tire failure and fire, 91 Kelvin scale, for temperature, 14 L

L-1011 aircraft, 22 Lateral clearance, 11, 13 M

Magic formula model, 78–79 Messier Laboratoire test aircraft, xv MSC Adams software tool, 77

N

NASA, 82, 84 Technical Report R-64, 75–76 P

Pacejka model, 78–79 Pinch lofting, 88 Ply turn-up, 7 Pneumatic tires, xix, xvi, xviii benefits of, 3 carcass, 3 mechanics of braking behavior, 59–63 camber angle, 54 ground vehicle applications, 53 idealized Mu-slip curve, for braked tire, 62 inclination angle, 54 lateral force, 54 measured loaddeflection curve, for three tires, 59 rolling behavior, 54–55 slip angle, 54 tire axis system, 53, 54 vertical force distribution, between free rolling and braked tire, 60 vertical stiffness, 58–59 Protector ply, 7 R

Radial clearance, 11, 13 Radial ply tires, 3, 52 burst pressure effect locations, 100 clearance dimensions, 12 construction, 4 cross section, 25 Rankine scale, for temperature, 14 Retractable landing gear, xv Retraction brake system, 96 “Rolling radius,” 63 Rolling resistance, 54, 55

Index

S

Self-aligning torque, 56 Side slip, 56 Sidewall rubber, 7 Sideward lofting mechanisms, 88 Side wear energy (SWE), 74 “Slip ratio,” 62 “Smiley and Horne” model, 75 Space Shuttle Orbiter, 73 Spin lofting, 88 Spray, tires aircraft and landing gear, structure of, 81 bow wave, 81–83 debris lofting, 86–90 direction and intensity, 84 elevation angle, AIR1904B, 86 Embraer KC-390 water ingestion test, 82 full scale aircraft test, 84 hydraulic fluid flow, 103 rooster tails, 81 Boeing 727 main landing gears, 84 Boeing 727 rooster tail spray deflector, 84

low-density spray, 83 single-wheels, 84 water projection, 82 side spray, 81 AIR1904B, 85 flow rate, from NASA testing, 85 low-density spray, 83 tire failure modes bias ply tires, 90 deflated tires, extended operation on, 90 impact of, 101–103 locked wheels, 90 modeling tire failure events, 94–101 peeled rib, 93 shredded tire, 91 skid-through tire failure, 90, 92 thrown tread, 94 tire flat spot, 92 “Steam cleaned” runway, 70, 71 String model, 77–78 Subsonic aircraft, 20 Sud Aviation Caravelle, xvii Sukhoi Su-34 aircraft, 89 nose landing gear deflector on, 89

111

T

Technical standard order (TSO) C62e, 26, 28 Temporary guidance material (TGM), 94 Tire and Rim Association (TRA), 26, 30, 31 Tire-based lofting, 89 Tire debris threat model, 95–96 Tire failure model, tread quantity for, 95 Tires. See Aircraft tires Tread compound, 7 Tread groove, 7 Tread reinforcing ply, 7 Tread rib, 7 Tread shoulder, 7 Tupolev Tu-144, xvii W

Wedge “Pac-Man” shape, 91 Wet runways, 57, 65–72 X

XB-36 main landing gear of, xviii with tracked landing gears, xvii XC-8A, air cushion landing system on, xix

Aircraft Tires

Key Principles for Landing Gear Design R. Kyle Schmidt

The author’s two volume treatise, The Design of Aircraft Landing, was the inspiration for this book. The Design of Aircraft Landing is a landmark work for the industry and utilizes over 1,000 pages to present a complete, in-depth study of each component that must be considered when designing an aircraft’s landing gear. While recognizing that not everyone may need the entire treatise, Aircraft Tires: Key Principles for Landing Gear Design is one of three quick reference guides focusing on one key element of aircraft design and landing gear design. This volume features tire construction and terminology, mechanics of pneumatic tires, tire performance and modeling as well as reviewing undesirable tire behavior. R. Kyle Schmidt has over 25 years’ experience across three countries and has held a variety of engineering roles relating to the development of new landing gears and the sustainment of existing landing gears in service.

RELATED RESOURCES BY R. KYLE SCHMIDT: The Design of Aircraft Landing Gear 978-0-7680-9942-3 Airfield Compatibility: Key Principles for Landing Gear Design 978-1-4686-0466-5

Aircraft Wheels, Brakes, and Brake Controls: Key Principles for Landing Gear Design 978-1-4686-0469-6 more related resources inside...

ISBN: 978-1-4686-0463-4

Cover image used under license from Shutterstock.com

Landing gear provides an intriguing and compelling challenge, combining many fields of science and engineering. Designed to guide the interested reader through aircraft tire design, selection, and integration to the aircraft landing gear, this book presents a specific element of landing gear design in an accessible way.