75 Years of Aerospace Research in the Netherlands. 1919 - 1994

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B.M. Spee Geilernl Uirectoi

I a m indebted t o Ir. D.J. van den Hoek for reviewing the contents in great detail. W e had many discussions on the book and he was extremely helpful in the selection of the illustrations. To both of us this was an exciting endeavor: an attempt to record what w e think the laboratory community stands for. At an early stage Ing. J.H.A. te Boekhorst supplied historical information. Dr. B.J. Meijer read the manuscript and many of his suggestions were incorporated. Parts of the manuscript were reviewed by lr. A.J. Marx, lr. W.J. Wolff, Prof. Dr. lr. H. Tijdeman, Prof. lr. J.W. Slooff and lr. W. Loeve. Dr. S. Dharmavasan of the NDE Centre, University College, London, UK, kindly read the manuscript and suggested numerous improvements. Personally I a m indebted to lng. P. Kluit for installing m y computer. Without that the book would not have been completed till the 80th Anniversary of NLR.

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The greatest gratitude I o w e to m y wife Corry, with w h o m I shared 40 exciting years in the aerospace community. In spite of her many and diverse activities, she listened endlessly to m y stories and always contributed constructively in overcoming the daily problems. Jan A. van der Bliek

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~ : o ~ o ~ > ~Producrron l o ~ l Coordinarron

HOEK MARKETING. Zoetermeer iPerer van den Hoekl Design and Lay~our

SkipDesign. Znetermeer IWinny Knenni Lrthography

DUO LITHO, Zoetermeer Printed b y Joh. Enschede, Amsterdam

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0 Copyright NLR. 1994: ISBN 90~9006909~7

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Aerorinrltics nrld nstruriniitics nre very specinl nrnorig hllrllnri endeavors.

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begirzriirfg t h e possibility ofpiglit irihigied riot orily iriveritors, visionnries, drrnrricrs, rk7w

devils, eriheprerieios mid riiechniiicnl tinkerers, but (7iSo serioiis scieritists nrid eiigirieers

who were nthncterl by the problerrrs of Pa stiiigyle 10 suwive. [Ref. 151.

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On the occasion of the 10th Anniversary of RSL, 5 April 1929, Dr. Wolff reviewed the events that had taken place during the 1920's. [Ref. 141. This celebration must have been an emotional event for the personnel and the main players. The positive remarks of Mr. Van der Vegte, then Minister of Public Works (Waterstaati. Gen. Snijders and Prof. Van Royen about the achievements of the RSL were very much appreciated by Dr. Wolff and his team. After all, they were the originators and they had guided the RSL through this difficult stage of formation. The RSL n o w was firmly established and the responsibilities between the Government and the RSL were clarified.

Altliough some form of stability had been achieved for RSL, this did not mean that an easy period had arrived. Dr. Wolff referred to the difficulty of carrying out high quality research with a minimum of staff, while at the same time having to carry out many ad-hoc investigations which had a high priority. He stated that this ad-hoc research was often of little interest to outsiders w h o are interested in the results of aeronautical research and one often heard the complaint: "what is the use of the RSL, w e never hear anything about it". Siniilar comments have been heard over the years since much of the work is carried out on contract and not published widely. But in spite of the uncertain conditions under which the personnel had to work and in spite of the fact that their work did not appear glamorous to outsiders, a small group of exceptionally talented and enthusiastic engineers and technicians gained valuable experience and laid the foundation for the laboratory of to-day.

lr. A.J. Marx' recalled that this shift of responsibilities was related to the wishes of the aircraft industry in the 1930's. Their desire was to have a national laboratory to which all interested paities would have access on an equal basis. It is very likely that this wish was based in part on the unique position of e.g. Van der Maas and Von Baumhauer w h o were responsible for carrying out the final flight tests for certification and at the same time advised the aircraft industry about flying qualities. This was probably the main reason w h y the industv insisted on converting the RSL, a Government Service, into the independent Foundation NLL.

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The RSL Main Building at the Navy Yardin Amsterdam

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lr. A J Marn joined the RSL in 1934 after having obtained his lngenieur's Diploma in Naval Architectural Engineering a t the Technical University Delft. In 1947 he~becameChief Engineer of the whole laboratory and in 1956 he was appointed Director. During the period 1 November 1956 till his retirement on 1 March 1976 he was General Director of NLR. During this twenty year period of considerable economic growth ~n The Netherlands and in Europe, the personnel increased from 280 to 650 and a completely new generation moved in. Under the able guidance of lr. Maix the lncrease in qualihi of the serwces rendered by NLR was disproponionally more than the increase in personnel. lr. Marx was Ridder in de Orde van de Nederlandse Leeuw (Knight of the Order of the Netherlands' Lion) and Officier in de Orde van OranjeNassau IOfficer of the Order of Orange~Nassaul.

lr. A.J. Marx, 797 1-1993

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As mentioned in the preceding Chapter, the RSL was located in a building a t the Navy Yard in Amsterdam. The building had t w o floors and in it were housed the Aerodynamics Department, the Materials Department and later also the Engine Department. The center piece was an Eiffel type wind tunnel. Across the road there was another building with a workshop of the Materials Department, an Instruments Shop, part of the Engine Department, and a large hall for carrying out load tests on full-scale aircraft wings.

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The Entrance Ha//o f the RSL

The Material Testing Laboratory It must have been relatively easy for Dr. Wolff to plan the Materials Department with his background, Chapter 29).He was aware of the methods of testing structures and materials. During the following years he managed to build up the laboratov with mechanical testing equipment that was available on the market. Full-scale structural static tests were carried out on e.g. wings by loading them with sand bags or lead weights.

The Materials Laboratory of the RSL

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Test on a wooden liling of i Fokker F'./I,I aircrafi

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The Chemical Laboratory of the RSL

The Chemical Laboratory A laboratory for chemical analyses of materials was installed on the second floor.

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The EngineTest Stand The engine test stand was located outside the main building. It was erected shortly after the official opening of the RSL. In Chapter 7.dealing with Propulsion, some of the engine test activities at the RSL are mentioned. By the time the laboratory was moved to the new building in 1940, these activities had been terminated for tw o reasons lack of funds and reduced demand. ~

The Instrumentation Calibration Laboratory In order to carry out the calibration of the special flight test and engme instruments. a calibration laboratory was started at an early stage.

Aircraft engine and propeller mounted in the Engine Jest Standof the RSL

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Although now the aircraft operators and the aircraft industry have their own capability to calibrate most aircraft instruments, this activity has remained important to this day and in fact the laboratory is now officially accredited as a calibration laboratory for certain types of measurements.

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The Flight lnstrunientation Calibration Laboratov of the RSL

The Wind Tunnel The construction of a wind tunnel was more complicated. Dr. Wolff had started the design in 1918 when he was still with Weikspoor. With the limited information available, he managed to produce an operational tunnel by March 1919 and it was shown a t the official opening of the RSL on that famous Saturday 5 April 1919, the official birthday of the RSL, (Chapter 21. The tunnel had an open test section and with a maximum power of 30 HP the mean velocity at the 1.6 meter diameter test section was 25 mlsec. However the uniformity of the flow across the test section was quite unsatisfactory and large fluctuations in time. 10 to 20%. occurred.

It was a wind tunnel of the Eiffel type - essentially a pipe with two open ends that is the air was drawn from the room in which the tunnel was placed and it was exhausted into that same room at the other end. This contrasted with the so-called Gottingen type whereby the air is pumped around in a closed circuit. The latter type is more energy efficient and it offers better possibilities to produce a high quality uniform flow in the test section. The first closed circuit wind tunnel had been in operation a t Gottingen. Germany, since 1908 (Prandtl's first wind tunnel). and presumably Di. Wolff had some information on that facility, although he could not visit Germany in 1918. It must be assumed that he decided on an Eiffel type tunnel because of the size and limitations of the building and on tile results published by Eiffel. Through this arrangement he achieved a t least a facility of reasonable size and Reynolds Number.' ~

After detailed investigations of the flow in the wind tunnel were carried out, several modifications were introduced. A closed cylindrical test section was installed, the flow in the room around the tunnel was examined carefully and the room was modified and also the motor was replaced by a 50 HP unit. Apparently in 1919 there was no shotiage of material anymore which had limited the size of the motor in 1918 as mentioned in Dr. Wolff's personal memoirs bee Chapter 291.

The original layout of the Wind Tunnel of the RSL

(Dimensions in mm)

fullkale situation

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The tunnel enirance of ilie RSL Wind Tunnel, around 1920

The modified tunnel entrance

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The result was that by July 1920 a fairly uniform and steady air flow of about 35 mlsec in the test section was obtained, [Ref. 161. This tunnel was used extensively for a period of 20 years and anart from smaller research facilities which were built at the Technical University Delft. it was the only wind tunnel available for aeronautical development in The Netherlands till 1940.

The validation of the measurements carried out in wind tunnels was of great concern to the wind tunnel operators all over the world and in the early 1920's the Aeronautical Research Committee (ARC) in the UK initiated tests on a 'standard model' in different wind tunnels. The RSL panicipated in this exercise and carried out a test on a simple rectangular wing (an RAF 15 model) on loan from the ARC. The model was, as 1111 models at that time, suspended upside down with thin steel wires from the top of the test section and the forces were measured with external weight balances. It was concluded that the agreement with the British results was satisfactory, [Ref. 171. This may well have been the first international cooperation in wind tunnel testing. It was the first exercise to compare the performance of test installations in aeronautics. Much later, under the ailspices of the Advisoiy Group for Aerospace Research and Development of NATO, AGARD, standard wind tunnel models were developed in the 1950's which were used by the major wind tunnel operators in the world and in the 1980's complete jet engines were tested in various engine test stands, (see Chapter 7). The AGARD Panels carried out similar comparative exercises with computational methods and structural (coupon) testing methods. During 20 years the wind tunnel was used for a variety of aeronautical tests. Some were related to actual aircraft design, some to project studies of Fokker and KCM, ideas of individuals, etc. Often the tests were Test on an RAF 15 'Standard Wind Tunnei Model' in the RSL Wind Tunnel

Model of a Fokker F I1 mounted in the RSL Wind Tunnel

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A wind tunnel model of the Pander 'Postjager', designed by ir. Th. Slot for fast mail services to the Netherlands East indies. in 1934 the 'Postjager' panicipated in the London-Melbourne race but met with an accident in Allahabad

A wind tunnel model of the Fokker 7 5 bomberaircraft, first flight 1937 related to proposals for improvements of parts of aircraft such as cockpit wind screens, engine cowlings, radiators of liquid cooled engines, undercarriage drag, aerodynamic control surfaces iflaps, ailerons, elevator surfaces).

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The tunnel was also used for non-aeronautical tests. As can be expected in The Netherlands there were many people interested in wind mills. In the 1920's and in the 1930's several wind tunnel tests were carried out on wind mills, at the initiative of both RSL personnel and others. The object was to study the aerodynamics of the wings of wind mills and to try to improve the efficiency. Without basically disturbing the original design of the 'Dutch Wind Mill' it was possible to increase the efficiency markedly by modifying the leading edge and the trailing edge as would be expected by aeronautical engineers.

One of the first tests, if not the first, dealing with the wind climate around buildings was concerned with improving the wind climate in a cattle market at Zwolle in The Netherlands; it was a covered building with open ends. The question posed in 1931 was: what is the effect of placing a fence near the open side of the building and what is the required height? A wind tunnel test gave the answer. Since that time many tests have been carried out on models of buildings, particularly high rise complexes, and urban city plans.

Sketch of a model of a Wind Mill, driving a dynamometer, mounted in the RSL Wind Tunnel, Period 1926 1929 ~

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In 1932 an engineer of the Sanitation Department of the City of Amsterdam asked for advice on reducing the nuisance of dust experlenced by the operators of the city s garbage trucks during high winds Such tests did not take much time but the results were rewarding to the personnel involved The wind tunnel was also used for tests on models of ships road and rail vehicles Some examples are shown in the photographs

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Tests on a railroad engine, without and Examples of the Research Activities with streamline covers, 1935. In 1929 Dr. Van der Maas read a paper before the British Royal Aeronautical Society, RAeS. A reduction of 90 HP [Ref. 181, in which he reviewed examples of the research activities of the RSL during its first ten could be achreved at years of operation. Some of these are: a speedof 100 KMAir. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Experiments on the effects of the wires employed to suspend models in the wind tunnel The flow around the model in a wind tunnel is influenced by the presence of the test section walls and the suspension system of the model. This has been a subject of investigation almost continuously - and still is. Shortly after the RSL tunnel was put into operation it was discovered that the wires by which the models were suspended in the tunnel could have a great influence on the flow pattern around the model. Particularly the wires attached to the upper surface of a wing model appeared to affect the drag and lift forces. In one case the drag was as much as 40% too high and the lift between 12 and 40% too low. Considering the fact that the steel wires were very thin, this was very surprising hut it alerted the staff to flow separation -triggered by the wires - at the upper surface of the model at relatively small angles of attack. Once this was recognized appropriate measures could be taken. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA

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Airfoil niodel with a rotating cylinder at the nose; with and without a streamlining nose piece

Comparison of lift coefficients obtained with a rotating cylinder at the nose and with slotted wings

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a . iiodei witlioit nosepiece. b. . I f a d d tuitli n a ~ e p i e c e .

Unstable oscillations of a wing-aileron system The unstable oscillations observed on a wing-aileron system led to the flutter investigations of Von Baumhauer and Koning, (see Chapter 91, explaining this phenomenon theoretically and experimentally and advancing the cure: mass balancing of the control surface. The iesults had been reported at the Air Congress, London, 1923.

Exaniple of a complicated joint of welded seamless steel tubing of the fuselage of a Fokker aircrah

Study of the influence of a rotating cylinder at the nose of an airfoil Wolff and Koning investigated the effect of a rotating cylindei mounted at the nose of an airfoil, [Ref. 19 and 201. It had been known for some time that by rotating a cylinder, placed in an air stream, cross forces are geneiated. However, the diag of such a cylinder is quite high. Wolff's idea was to improve the situation by placing a streamline body behind the cylinder and thus reduce the drag. The initial results were remaikable. This first results were obtained with a model without a nose piece. More sophisticated tests, also supported by detailed boundary layer measuiernents carried out in Delft by Van der Hegge Zilnen, [Ref. 211. pointed towards the possibiliw to inciease the lift substantially, be it then that the maximum lift occurred at iather high angles of attack (some 40"). It must be remembered that there were very few iesults available on airfoils with slots on the nose by which an acceleiation of the flow close to the upper suiface can also be achieved. The rotating cylinder did not make it into practical applications but it stimulated detailed investigation of high lift devices. The results are still intriguing: with an (unswept) airfoil a lift coefficient of 2.4 was obtained at an angle of attack of 40". comparable to the characteristics of modern delta wings. Airfoils with one or two slots reached maximum lift a t 26".

Testing and validation of steel tubing A specialty of Fokker was the use of seamless steel tubing in the construction of the fuselage. The testing of Steel tubing for safety and reliability became an important activity a t the RSL. Most airplane fuselage structures were made of wood and the authorities in the various countries had to be convinced that welded steel tube structures were reliable and safe. Tests on the tensile and compression strength of various kind of steel tubing were carried out. A most important part was the investigation of the welding of steel tubing and the structural behavior of the often complicated joints. In this connection an investigation was carried out to check the airworthiness of Fokker C.1 aircraft. This airplane had been in use with the Army Air Force for a long time. The fuselage of one of the aircraft was completely dissected; tensile and compression tests were carried out on all tubes and the welded joints were X-rayed, sliced and microscopically examined. No flaws were detected.

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The structural strength of w i n g s - effects of ribs and skin Over a period of roughly ten years 11925-1935) a series of papers was written by Biereno and Koch (Technical University Delfti and by Koning and Van der Neut IRSL) on the subject of the strength calculations of aircraft wings. The wooden aircraft wings consisted of t w o cantilever or semi-cantilever spars (beams) connected by ribs and covered with plywood sheets. Biereno and Koch had, in cooperation with Koning. first developed a method to carry out stress calculations for such a wing without taking into account the effect of the skin. Then Koning developed the method fuither to include the effect of the plywood skin. Biereno engaged Van der Neut, still a student, to carry out numerical calculations. But the RSL did not have the funds and so Fokker paid Van der Neut DGL. 150; per month to carry out this task. That was a very high salary for a student! After Van der Neut had graduated with Biezeno, he went to the RSL where he became the SOIE member of the Structures Group, directly responsible to Dr. Wolff, the Director of the RSL. Suitable numerical methods were adapted and develooed. The actual numerical calculations were very laborious and a group of young ladies. the Calculation Bureau, carried out the calculations mostly in tabular form using mechanical hand calculators. The analytical and numerical methods developed were meant in the first place for application in the industry, but the RSL also received many requests to carry out numerical strength calculations for the Airworthiness Authorities, the Armed Forces and KLM. During this period there were never more than t w o to four engineers available w h o could carry out such calculation~~.

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Structural failure of the front spar of the Fokker F.111wing

This multi-year program also included experimental verifications of the calculation methods. Tests were carried out on three wings which were obtained from KLM and Fokker. A not unimportant detail was that is was not easy to obtain wings for structural testing. When an aircraft crashed, the wing was often not too badly damaged and it was repaired and mounted on another aircraft,

3Pr0f. Van der Neut later said that he was constantly asked to carry out ad-hoc calculations and that lhe never had enough time to carry out more basic research. but he did also remark that it kept him on the right path: he learned to look for practical applications. This experience sewed him very well when he became Professor o i Aeronautical Engineering, specializing in structures. at Delft in 1945. During the Second World War, when there was more time ior research. he had together with Plantema. Koitei. Legger and Patrna. contributed !a the first post-war Technical Handbooi: (TechnischeVwagbaaki. \Ref. 221 This was an important publication for the engineering community iii The Netherlandsat that time

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System for measunng accurately the local deflection of a wing

ONUERZUOE VLEUGEL

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A variety o f insfrumentsusedin flight testing

During the last two tests in particular. accurate displace'ment measurements were made along the wing span to determine the deflection of the wings. The calculated bending and torsion of the wings agreed very well with the measurements.

Measurement Techniques Since there were relatively few instruments on the market to carry out the various measurements and since the funds available were very limited, the instrumentation was often developed inhouse. An interesting example is the method of measuring the displacement of the wings during the load tests described above. This was done by attaching small iesetvoirs with water to the wing at various stations along the span. These formed legs of U-tubes (communicating vessels), the other ends of the tubes were grouped together on a board. By adlusting the inclination of this board the sensitivity was adjusted.

AFSTANOSTHERMOMETER

The flight test instrumentation - and of course the calibration of the instruments required much attention. A collection of flight test instruments used during the stability tests series, mentioned in Chapter 6, is shown. These were instruments used in the 1920's. The picture shows a Pitot tube for measuring the total pressure, a static pressure tube towed by the aircraft and a thermometer for measuring the outside air temperature. The drawing on the next page shows an instrument deveioped by Von Baumhauer to measure the stick position and through this the elevator

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A dial instrument developed by

Von Baumhauer to measure the aircraft control stick position

A movie camera developed by Von Baurnhauer to record the flight path from theground

angle. With normal elevator linkage an accuiacy of better than 0.2" in elevator angle could be achieved. Von Baumhauer also developed a (manually driven) movie cameia for recording the flight path duiing take-off and landing trials, [Ref. 241. By photographing a watch (reading seconds), mounted externally on the camera, and using the known wing span as a iefeience, the distance fiom the camera to the aircraft and the altitude were deteimined from each of the pictuies. This same basic method, later refined and with modern film readers and data handling equipment, was successfully used till about 1960.

Movie pictures

Schematic of the movie camera

Propeller Slipstream Wing Interference With the advent of multi-engine aircratt the influence of the propeller slipstream on the characteristics of the wing became important. Koning published several papers on the aerodynamic properties of propellers operating in the close vicinity of a wing. His approach to this problem drew international atterltion and in 1934 he was asked to summarize the state of the art of this important subject and contribute to the six volume standard work 'Aerodynamic Theory', edited by W.F. Durand,4 [Ref. 251.This is still a classic reference on this subject. It was not till the Fokker 50 was designed (1985.1987) that more sophisticated methods were available. By then meaningful aerodynamic data on the interference of propellers and wings could he obtained by CFD (Computational Fluid Dynamics) methods. An example was presented at an AGARD meeting in 1991, [Ref. 261.

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~ ~ ~ ~for t~h e Ne.w ~ ~ 1,aborator.y r ~ ~ (NLL at the Sloterweg iii A,nnsterdain)

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As mentioned earlier, when in 1918 the RSL was planned, the location at the Navy Yard in Amsterdam was meant as a temporary site only. Prof. Van Royen intended to establish a permanent laboratory in Delft, in close association with the Technical University. However the University was apparently not too eager 10 accommodate the RSL. This may have been caused by the problems encountered in the 1920s after the transfer of the RSL from the Ministry of Defense to the lviinistv of Public Works. Also, flight testing had become an important part of the activities and several peopie felt that a location close to Schiphol and Fokker Ithe factory was still located at Amsterdam-North) was more important than being close to the University of Delft.

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In the meantime Wolff and Koning carried out studies for new wind tunnel facilities. There were several reasons why the old RSL wind tunnel with a 1.6 meter diameter test section and maximum speed of 35 mlsec was not adequate anymore to meet the requirements of that time. In a paper published in 1935, Ref. 271, they stated that the main shortcomings were: 0

in a number of cases the details of the models were too small;

* the force differences due to configuration changes could often not he measured accurately enough; the available model motors to drive the propellers were too large and could not be used for multi-engined aircraft models; a model engine could only he accommodated in the fuselage where enough space was available for mode! motors with the required power; 0 tests on many full-scale aircraft parts could not be conducted due to the size of the tunnel.

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They realized of course that Reynolds Numbers close to 25 million would be required to obtain results directly comparable to full-scale. That was the Reynolds Number for the Fokker F36 at niaximum speed, an aircraft which had been defined in 1932: 32 passengers, 4 crew, span 33 meter and indeed a very large aircraft for that period. The largest wind tunnels were the American 'full-scale' tunne! at NACA wit!?a 30x60 it' (9.1x18.3 M I test section and the French tunnel at Chalais-Meudon with a test section of 8 x 6 M. which was under construction. However even for those tunnels the Reynolds Number was only 7 to 9 million. For a given size tunnel the Reynolds Number could also be increased by operating with compressed air in the closed tunnel circuit. There were two pressurized tunnels in operation, one at NACA in the USA and one a t the National Physical Laboratory, NPL. in the UK. These tunnels were providing much basic information on Reynolds Number effects and the whole aeronautical community profited from their publications (the maximum Reynolds Number of the NPL tunnel was 11.2 millionl.

"Another author from The Netherlands contributing to this series was Prof J.M. Burgers of the Technical U n i ~ versity Delft who wrote with Prof. Th. von Karman the second volume. 'General Aerodynamic Theory Perfect Fluids'. The Durand series was sponsored by the Guggenheim Foundation. USA Interestingly enough the books were first published in Germany: there was little interest in the USA for the subject That situation changed drastically during the following ten years!

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The F36 was conceived after KLM had been veiy successful in operating the Amsterdam-Batavia IJakanaI mule during the early 1930s in spite of the worldwide economic crisis Anthony Fokker and Albert Plesman had a meeting on 6 June 1932 from which this design finally emerged The aircraft flew for the first time on 22 June 1934 Although a veiy impressive aircrafl. it was never adop led by KLM for the Far East route. The aircraft was designed along the well proven lines of Fokker. i.e. wooden wings. a fuselage of steel tubing. covered with linen and a fixed undercarriage with very large wheels 11.78 meter diameter1 for operating from soggy. unprepared airfields along the route to Batavia The range was however slioiler than that of the DC-2 and the D C ~ 3and KLM switched to the all~metalairciafr of Douglas ~

Based on their studies and keeping in mind the financial limitations with which they would be faced, Wolff and Koning decided on a 3 x 2 M' facility which was large enough to test models with a fair possibility to scale properly the geometric features and to accommodate electric model engines capable of producing enough power to simulate powered aircraft flight in the wind tunnel and a smaller, 1.5 x l . 5 M: tunnel for research purposes and non-aeronautical wind tunnel testing. As a result t w o closed circuit type wind tunnels were built in the n e w laboratory:

Power Maximum speed Reynolds Numberlmeter

600 HP 80 mlsec 5 2 million

60 HP 40 mlsec 2 6 million

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These facilities became operational in 1940. They were the main low speed aerodynamics facilities for over 40 years till the German-Dutch Wind Tunnel, the DNW (the joint venture with the German sister organization DLR, (Chapter 181, became operational in 1980. followed by the LST 3 ~ 2 . 2 5 M' of NLR. both in the Noordoostpolder. There were several other activities in connection with the n e w laboratory such as the preparation of an extended Structures and Materials laboratoiy, a laboratory for the Flight Department for calibration and instrumentation of flight test equipment, and a modern Instrument and Machine shop.

L:vaiuaiior? H o w to evaluate this period of tile RSL between the t w o World Wars.

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1918-19377 It was essentially the period (1919-19391

It was certainly a sniall effort compared to the current activity of NLR. Roughly 500 man-years were spent at the RSL during this twenty year period, that is about half the capacity that is n o w

available at NLR per year. It was however the period in which aeronautics became of age.The activities in other countries were comparable, taking into account the size of the countries. An exception was Germany, where during the 1930's an enormous growth !n aeronautical research took place. But for irlstance the total number of NACA employees was 500 in 1939 while NLL had 84 employees, whicl? was a good ratio considering the relative size of the countries. NACA produced much basic aeronautical design data of significant scope. The RSL never was in a position to cairy out elaborate systematic tests on e.g. airfoil shapes; it had to confine itself mainly to direct support of aeronautics in The Netherlands. Fortunately, most of the (few) RSL iesearcli engineers produced papers of a more fundamental engineering importance which were well received by the international community. Based on the foundations laid by this small group it was possible to build up a significant aeronautical research activity afte: the Second World Wa:, in spite of the fact that NLL had missed the impetus gained by the w i r activities. With confidence it can be stated that without the ground work and the tradition established during the RSL period, it would have been almost impossible for NLR to achieve the present status in the aeronautical engineering sciences.

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Before trnciiiy some of the ewiits nt tlie h'LL drrriiig World War I1 n few yeiiei-nl reinnrks shorild be inade.

This is the 17iost diflicirll period of the 75 y e n n of history of the lnborntoiy to repoit. The Aiiiiiinl

Re1Jorts [ire 'ciyptic' niirl rlo

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yiw i?i~rchdetail. A coiriplete nrid bnloiiced

nccouiit of this period woirld l i m e to be prorliiced by n professioiinl historinii niirl tlint is

ceit[iiiil}i oiitrirk tlie .~c(ipeof this book. Oiily s o i m of the eveiih niid ncliieveiiients related

iii

this Chripfer

mid

it dues

riot

flre

do justice to tliosc, who carrier1 the Inborntoiy

tlirorigh this tiyiiig period.

On Friday 10 May 1940, before daybreak, Nazi-Germany moved its war machine Westward. The war in The Netherlands lasted only a few days and subsequently the country was occupied by Nazi-Germany. Commencing September 1944 parts of The Netherlands were liberated. The occupation of the Western part, including Amsterdam, ended with the capitulation of the German forces on 5 May 1945. The history of the Second World War has been described extensively in the literature. Although The Netherlands was in a state of mobilization since August 1939 a t the beginning of that war, it was not very well prepared. During the First World War The Netherlands had managed to stay neutral and the government policy was again to stay neutral. There were of course several politicians who predicted that this war was different and that The Netherlands would be involved.

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The Army Air Force Although not part of the history of NLR it is noted here that on 10 May 1940 the Army Air Force had 194 aircraft in flying condition of which 144 were suitable for aerial combat. During the surprise attack of the German Air Force 44 aircraft were lost on the first day, including a large fraction of the 23 Fokker G-1's. the advanced twin-engined. twin-tail fighter-bomber.

The Netherlands armed forces were no match for the well-trained massive German forces. Nevertheless Germany lost 350 aircraft during this five-day battle including 224 Junkers Ju-52 transport planes. This was a factor in reducing the chances to carry out a successful 'Blitzkrieg' invasion of the UK as seemed to be the original idea, [Ref. 51. Wind tunnel model of the Fokker G-l fighter aircraft. The Fokker G-1 was first exhibited a t the Paris Airshow in 1936

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'B'he Move P O the Ne\v B.aI,c9raSol.y

The NLL laboiatory was located at a Navy Yard in Amsterdam. The new laboratory was under construction on the outskirts o i Amsterdam-South, on the ioad to The Hague. The building was far from complete; the construction had been interrupted from 15 December 1939 till 26 February 1940 due to adverse weather conditions. The Navy Yard was a potential military target and it was decided on 10 May to move valuable documents and instiuments immediately to the basement o i the new laboratory building. The construction of the building was completed shortly after the move. The building included the low speed wind tunnel with a test section of a 3 x 2 M' and the smaller tunnel with a 1 . 5 x 1 . 5 M?test section. These were both constructed out of reinforced concrete and were integral parts of the building. The commissioning of the first tunnel started on 17 June 1940 and the opeiation of the second tunnel began on 29 Novembei of that year. By the end of 1940 the new laboiatory was in iull ooeiation. The NLL Low Speed Wind Tunnei3xZM) in open test section configuration

The immediate effects From the iecords and the accounts it appears that in mid-May 1940 it was the intention to continue with the activities as planned as much as was practicable. There were however several important changes: all investigations related to military projects stopped and the development of civil aircraft in The Netherlands was suspended. Nevertheless, activities related to civil aeronautics, the development of equipment and measuiing techniques and studies related to future civil airciaft were continued as far as possible. Flight testing with the laboratory aircraft, a Fokker F.Vlla, had to be discontinued. The aircraft was hidden, (see Chapter 6).

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Aerialview of the NLL at the Sioterweg in Amsterdam

29

i

On 18 May 1940 Mr. Kaufl of the Aerodynamische Veisuchsanstalt, AVA (Aeronautical Research Laboratory) Gottingen and Mr. Weinitz of the Reichs LlJftfahriministerium, RLM (Ministry of Aviation) visited the new laboiatory They expressed their wish to maintain the laboiatory. Mr. Kaufl was appointed liaison officer ('Beauftragte') for the German authoiities. During the summer of 1940 Prof. Betz and Dr. Engelbrecht of the AVAvisited NLL and initiated discussions on futuie work. It was tlieii intention to involve NLL in their long-term scientific research efforts. NLL was to be excluded from research directly connected with the wai effort Their interest was focused on experimental aerodynamics and basic reseaich in structures. The NLL equipment was well advanced and particularly the investigations related to flutter problems and the possibility of developing equipment for unsteady aerodynamic measurements drew the attention of the Gottingen group. The advantage (if 'advantage' is a pioper word in this connection) of the arrangement with AVA was that NLL was declared a 'protected' organization which meant that the employees were given permits excluding them from being drafted for work in the Geirnan industry. This protection was also extended to some of the personnel from other institutions who could either be formally employed by NLL or incorporated in a list of indispensable personnel.

A personal account

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Piof. Van der Neut. who was employed at NLL till 1945, when he became Professor of Aeronautical Engineering a t the Technical University Delft, latei recalled some of his experiences, [Ref. 281: -"We spent niost of our time on our own iesearch and the majority of our reports were related to that. From that poir't of view the occupation period was 2 fine time for the researcher, without the less interesting ad-hoc type projects associated with the airworthiness oiairplanes. In fact as Iwrite this I an1 feeling guilty at having enjoyed that period as far as m y scientific work is concerned, while many others lived in a sta!e of great despair f...) The work on German contracts implied the risk tlial the results would benefit the enemy, in spite of the original intention expressed by AVA. When it seemed that an investigation would clearly benefit the German war effort lwind tunnel tests on a specific aircraft model). Koniiig, the Director, contacted Prof. Betz of AVA. Koning and Betz had known each other for a long time 2nd had had friendly scientific contacts for many years before the war. Prof. Betz understood the problem. He canceled the contract 2nd issued the following guidelines for contracts with NLL: - I f the subject was of eminent importance for the war effort i t should not be let to NLL since the Dutch were not to be t,rusted, If tile contract had no direct bearing on the war or i f it was o f 2 more general nature. it could be granted to NLL 2nd it should be labeled 'Kriegswiclitig' limportant for the war). This agreement was not recorded but the iniportant factor was that the AVA adhered to it. "

Piof. Van der Neut recalled that one rather large contract with AVA was concerned with the experimental determination of the torsion stiffness under fluctuating torsion loads of a mono-spar Me-109 wing with reduced skin reinforcements. He concluded that the major result was that two Me-I09 wings could not be used during the war. One of Prof. Van der Neut's own research projects waB concerned with theoretical investigation of the stability of cylindrical shells, with longitudinal and ciicular stiffeners. under axial loads. He found this very inteiesting and he thought this was one of his best pieces of research. When he obtained this contiact he believed that the only aeronautical application would be for the fuselage of very large transport aiiplanes. One of the conclusions of this work was that external stiffeneis were far more effective than internal ones but this did not seern piactical for aircraft. Later he understood that his work would have been very applicable to the V-2 missile. During an AGARD meeting in the US (probably in 1956)he paid a visit to Huntsville, Allabama, USA, wheie he met the designer who had woiked at Peenemunde in Germany. the site where the V-2 was designed, and asked if his

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repoits had been consulted. To liis relief Prof. Van dsr Neut learned that the design had been frozen in 1942. before his work vvas completed. The personnel Although the total contract work-load of the laboratory decreased dramatically during the five years of tile war, the personnel increased by 4096! Obviously the laboratory served as a 'legalized' hiding place. Anotlier factor contributing to that effect was also that the efficiency of the operation dropped very much as it did in the country as a wliole. The combined Annual Reports of NLL over tlie years 1944 and 1945, published in 1946, give a summary of the events during the period of 1940 -1 945. Unfortunately the information is very limited. In retrospect tliis is perhaps not very surprising. Immediately after the war the emphasis was on the future - the re~constructionof the country.

ir. C. Koning 1893 - 1952

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The laboratory, being a technical institute, carried out many jobs for resistance groups, mostly relared to the maintenance and repair of weapons. Initially this was done a t tile workshops after regular working hours. Later, when road checks became mare frequent, the activities were moved to a factory in the Haarlemmermeer and instrument technicians and machines of NLL were made available. Dr. Wolff had been seriously ill since December 1939 and on 1 August 1940, when it had become clear that he would not be able to resume his work at the laboratory the Board appointed lr. C. Koning as Scientific Director and Mr. J.L. Chaillet as Commercial Director.

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Several employees became actively involved in the undergrouiid resistance. One of those was Mr. Chaillet. He became a member of a national resistance committee. [Ref. 291. This coniniittee generated ideas and distributed pamphlets to civil servants and managers in industry, including the Railways, on how to avoid effective work for the German occiipational forces. He was arrested on 12 April 1944 and lailed in Amsterdam, moved to Vught and later deported to tlie concentration camp Sachsenhausen in Germany. Fortunately he returned after the war. Several employees were arrested and jailed for some time. Dr. Wolff. w h o was Jewish, died o n 7 February 1941, just before the massive persecution of the Jewish populations began. The young engineer A. Spits and the designer H. Groen w h o were also Jewish, were imprisoned and transported to Germany. They did not survive.

At the end of August 1944 the AVA liaison officer was called back to Gottingen. In the combined Annual Reports over the years 1944 and 1945 it is stated: -"At tlie end o f August the 'Beauftragte', Mr.Kaufl, was called back to Gottingen. He /eft on 4 September 1944, but he came back oii 18 Septeniber for a day to arrange some business. On behalf of the RLM 1Ministly of Aviation) lie took with him some equipment that had been ordered by the AVA Gottingen and manufactured, partiaiiy by NLL and partially by the industry Tliis depanure was seen as a sign of the changing circunistances and it was welcomed with joy. It niust be admitted that, during the period this man was charged with the liaison of NLL and the German authorities, he did his best to maintain the laboratoiy and prevented foreign intewention as mucli as possible. "

In September 1944, three months after D-Day 16 June 1944). the situation in Tile Netherlands changed very dramatically when the Allied Forces entered The Netherlands, near Breda on Tuesday 5 September, IDolle Dinsdag - Mad Tuesday) and Sunday 17 September, when Allied Forces landed with paratroopers and gliders near Arnhem (Operation Market Garden). The Western part of

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The Netherlands was completely cut off from the rest of the country. The food and fuel supply, already a t a bare minimum, practically stopped. It was expected that the operation of the laboratory could not be continued for long. There was the danger of war damage and plundering and so on 8 September a start was made to store machines, tools, instruments and documents in safe places. Larger pieces were taken to vegetable storage sheds of nearby gardeners and other items stored at the homes of the personnel. A substantial part was stored in the basement of NLL which was then closed with a brick wall. Later the ground water became abnormally high - presumably due to electric power shortage and the contents had t o be transferred to the large wind tunnel circuit. Due to problems of transportation, electricity supply (lighting), food supply and other problems, the working hours were reduced to the minimum of 27 hours per week in December 1944. Experimental work came to a stop. Office work continued to some extent but everybody was menially occupied with the problems of war, suwival, food and fuel. Only manual labor could be carried out in the workshops. To a large extent this consisted of the manufacture of small stoves, lamps and other utensils for the personnel. With Iaeronauticall productivity rapidly falling it would have been possible to decide to close the laboratory but it was considered prudent to continue the operation as long as possible since it would provide some protection for the personnel and the laboratory in a very uncertain situation. Also, it was still possible to organize collectively food expeditions to the rural areas, even as far as Friesland in the North of The Netherlands. The transports, 'legalized' by German papers, took place with rented trucks. It is reported that 40 tons of food was collected and distributed among the personnel.

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Now, some 50 years after World War 11, it can be concluded that the laboratory was fortunate scientifically speaking - that during this war it had a number of excellent engineers and scientists who were active, albeit under most unfavorable conditions, and that they spent their time very productively. It is difficult to single out individual activities. The research on structural stability of cylindrical shells by Dr. Van der Neut was already mentioned in this Chapter. Of great importance were the contributions of Ir. W.T. Koiter (who was detached to NLL during the war from the RLD, the Netherlands Department of Civil Aviation), on the buckling of plates (effective width of plates) and the buckling behavior of plates under shear forces. Interestingly enough Koiier later recalled, [Ref. 301, that the five years of isolation from the immense research effort in the free world and his intense occupation with the urgent practical business at the RLD in the immediate post-war period, had effectively prevented him from studying seriously the enormous stream of literature after the war. That was also true of course for all of the NLL staff, but a t least in Koiter's case, he had contributed to the advancement of the technical sciences during this period of isolation.

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The NLL Main Building with the' Entrance Hall a t the right

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The NLL Main Building wfth the two Wind Tunnels integrated in the building at the left

A few examples of the work of the NLL staff during this period are:

lr. A. Boelen, Head of the Aerodynamics Department, had initiated an extensive series of lift distribution calculations for a variety of wing planforms.

lr. A.J. Marx, Head of the Flight Department, (with Van der Maas and Van Oosteromi had compieted the lateral stability analyses and that Department did then have time to analyze the gust loads, recorded over a number of years on KLM aircraft on the route to Indonesia. Ir. T. van Oosterom, later Head of the Flight Department and Professor at the Technical University Delft, had analyzed many flight tests and further developed the measurement techniques.

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Dr. J.H. Greidanus, who later became Director of Fokker. and Ir. A.I. van de Vooren, who later became Professor of Mathematics at the University of Groningen and served as Chairman of the Scientific Committee Chapter 24)studied unsteady aerodynamics and developed methods to calculate the response of an aircraft to gust loads. During this war period several investigations took place in connection with possible new aircraft and their operation for airlines to North America and the Netherlands East lndies (Indonesia). These studies were mainly concerned with the possibility of designing and operating larger aircraft. Some of these studies were inspired by KLM's President Albert Plesman, (see also Chapter 51. Although these studies took place i n isolation from developments abroad, they were nevertheless important for the postwar development of civil aviation i n The Netherlands.

After the War a report was written summarizing the technical-scientific activities at NLL during the War, at the request of the Allied Armed Forces. From this it appears that a large number of subjects was studied in depth, including: zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFED CB methods

of calculating the strength and stiffness of cantilever wings with non-parallel spars; * t h e calculation of the 'effective width' of plates under compression, with various edge conditions; a buckling of sandwich constructions; zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJI B the calculation of lift distribution for an extensive series of wing planforms; o experimental and theoretical research on flutter and vibrations in general; o the dynamics of tailless (all-wing1aircraft; o studies of the performance of rotorcraft.

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Much of this work was published after the war but the most important aspect of it was that at least the basic activities were kept alive so that immediately after the war there was enough of a basis to absorb the new developments and apply the knowledge to the problems at hand during the post-war reconstruction period.

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The t w o n e w wind tunnels were used extensively. Curiously enough, it was reported that in 1941 a two-shift operation was starred to increase the productivity. Not all did go well: On 10 September 1941 a propeller blade of the 3 x 2 M' tunnel broke. Van der Neut recalled. [Ref. 281, that the natural frequency of the bending mode of the blades for the rotating propeller had not been calculated and compared to the flow irregularities ahead of the propeller. The blade was repaired but in 1942 a similar accident happened. Finally a properly designed propeller was installed in March 1943.

After the Liberation After the Liberation on 5 May 1945 the laboratoly was closed for 10 days, but soon after that the personnel started to collect the hidden equipment and documents and to resume normal operation. The electricity supply was restored on 13 June 1945. Most people were physically and mentally exhausred and it took several months till the performance became 'normal'. The contacts with the outside world, nationally and internationally, were resumed During the second half of 1945 several changes in personnel took place. It was not surprising that immediately after the Liberation, 5 May 1945, many employees left NLL, either to return to their former employers or to take up lobs elsewhere, their first allegiance not being aeronautics and because there was a n enormous shortage of technically trained people to reconstruct the country. M r . Chaillet returned to his former job at the Royal DutchiSheli Company and on 1 September 1945 the position of Commercial Director was filled by Mr. F.C. Beelaerts van Blokland. N e w personnel was hired and by the end of 1945 the total personnel was again at 129 the level before the end of the war - and expanding rapidly.

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linrnedintely after the ivnr' the nctivities of the InDor-ntory were resiirrieri. Altlroiiyli the

IaDoriitory clid riot iricio-plr)~sicrildrirnnyc' riirririy the w i r , it ivos riot irr the best coriilitiori,

dire to lack of firrrds arid rrinterinls, the

l l r ~ d e r p l l r ~flCtiVitiES d nliri

the pre-(Jccllpntiflllof

the perror7ne/ with S i l l v i v r i ~rilrrirly t/le wflrpel-iud.

The facilities of the aircraft companies, Fokker, Aviolanda, De Schelde, Avio-Diepen and a f e w smaller organizations had been dismantled or destroyed and much of the machinery had been taken away. The original staff was scattered over the country and abroad.

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KLM had carried out transport missions for the Allied Forces during the war and so there was an organization in operating condition. Many of the pilots had escaped to the UK at the beginning of the war. The President of KLM. M r . Albefi Plesman. (1889-19531, \Ref. 311, remained in The Netherlands, initially in The Hague. After having been taken prisoner as one of a group of hostages on 9 May 1941, he was exiled to the East of The Netherlands in April 1942. He stayed at Driene, near Enschede, where the campus of the University Twente is n o w located. The long time in jail and at Driene gave Plesman ample time to think about the future of 'his' KLM. Plesman used that time very productively to develop plans for the operation of the airline, managerial and technical concepts and also to Contemplate various forms of international cooperation. After the war he was a founder member of the International Air Transport Association. IATA, a world wide association representing the major regular airlines, promoting air transportation and dealing with a variety of subjects, including standardization and compatibility of equipment.' He remained a t Driene till t h e liberation by the Canadian Army in April 1945. As soon as the Canadian Army moved in he made his way to London to take charge of the part of KLM that had been operating for the Allied Forces and started the re-construction of the airline.

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Units of the Army Air Force and the Navy Air Service had been actively engaged in the war, mostly as pan of, or closely associated with, the (British) Royal Air Force, RAF. These groups formed the core of the n e w Air Force of the Army ILuchtstrijdkrachten. LSK), which was finally transformed into the Royal Netherlands Air Force, RNLAF (Koninklijke Luchtmacht, KLu) on 11 March 1953. In the period 1945-1946 there was no doubt about the future of the KLM and the Air Force but it was less clear that the aircraft industv would recover, at least as far as the development of civil transport and military aircraft was concerned. In the light of the enormous progress that had been made in North America and the United Kingdom many felt that the only possible activity for the aircraft industry would be maintenance, repair and possible participation in production or production of complete aircraft under license of other, foreign, manufacturers. The latter did take place and besides the development and production of a small business plane - soon after the war fighter aircraft were produced under license.

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In September 1945 the Government appointed Di. Ir. Th.P. Tromp (formerly a Director of the Philips Company and Minister of Public Works and Reconstruction during the period in 1944-1945 when

'Indicative of Plesman's activities I S the recollection of Prof. Van der Neut, lRef. 281, that Koning. Director of NLL. and he were invited by Plesman to visit him at Driene during the war to discuss the relative weight savings which could be achieved by using larger tianspon aircrafl. During the war period NLL carried out Stw dies for KLM on this and Similar subjects in preparation for the postwar period.

the Southern part of The Netherlands had been liberated1 as a special advisor to consider the reconstruction of the aircraft industry. Dr. lr. W.T. Koiter served as his Secretary. Early in 1946 Dr. Tromp invited a f e w hundred representatives of government, industry, university, etc. for what would n o w be called a 'hearing'. This helped to convince him that there were interesting opportunities for an aircraft industry with a full design and development capability. On 14 May 1946 the Government agreed in principle to support the reconstruction of such an industry. A condition of the Government was that closer cooperation should be established between Fokker and some smaller aircraft companies in The Netherlands. The Government was not well equipped to handle the complicated matter of support to the reconstruction and the development of the aircraft industry and there were also different views within the Ministries concerned as to the form this support should take. Dr. Tromp then proposed to form an intermediate body. a kind of 'trustee' between the Government and the aircraft industry. This body would advise the Government and manage the expenditures of government funds for aircraft development. Thus the Netherlands Institute for Aircraft Development, NIV (Nederlands lnstituut voor Vliegtuigontwikkelingl was founded on 19 June 1946. The signatory members were Koiter. Geudeker, Witholt, Jongsma, Gaastra and De Wolff. The Board of this Foundation consisted of representatives of the Government (Ministries, the Air Force and the Navy), the industry, the airline (KLMI and the research sector (universities and laboratories). Dr. Tromp proposed Prof. Van der Maas as the first Chairman and Head of a small executive office. Soon lr. L.L.Th. Huls (Prof. Van der Maas' second aeronautical engineering graduate1 and Mr. G.C. Klapwijk, a lawyer, joined his office, respectively as Technical Assistant and Secretary-Treasurer.

zyxwv zyxwvutsrqpo This was a positive development for the NLL.

Encouraged by the Government's intention to promote the design and development of aircraft in The Netherlands, NLL prepared plans to design and construct: 0 a high speed (transonic) wind tunnel; * a scale model of that tunnel (scale 1:5j; a supersonic blow-down wind tunnel; a low turbulence, low speed wind tunnel; * a n extension of general laboratory equipment; man extension of the office building: a hall for full-scale structural and vibrational testing

Aerial view of the Power Plant at the NLL in Amsierdam, around 1960

These were ambitious plans. The general positive attitude towards industrialization and the foundation of NIV encouraged NLL to carry on with this expansion plan. The management was strengthened: Ir. A.J. Marx, till then Head of the Flight Department, was appointed in 1947 as Chief Engineer for the whole laboratoly to suppoi? the Directorate.

When the plans were further detailed during the period 1946-1947 it appeared that the local power company (GEB Amsterdam) was not in a position to supply the electric power of around 20 MW required for the transonic tunnel. The power company would have to extend its plant and special cables would have to be laid. Also, due to the intermittent character of the envisaged wind tunnel operations, this would result in a very high price per KWH. A n e w power plant a t the NLL site, only for the laboratory was also very expensive. The solution was found when, oil-fired, steam turbine power plants of American war surplus escort vessels (destroyers) became available. Six of these units plus spares were bought for the sum of DGL. 300,000. Initially five steam boilers were installed and in 1966 a sixth was added when more power was needed for additional compressors. In 1948 additional spare parts of the H.M.S. Hotham were bought from the UK Ministry of Supply which had had in operation destroyers of the same class. At the end of 1947 a contract

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The extension of the Power Plant with a sixth steam boiler and chimney and with a n e w compressor in 1967

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was let to design and construct a turbo-electric power plant utilizing this equipment. At that tiine Government approval had been obtained for the laboratory expansion and the design of the various facilities was started.

'P'he Crisis During the course of 1949, when the design had progressed quite far and the construction of the foundations of the facilities had started, the Government re-considered the plans for the reconstruction of the aircraft industry. It must be recalled that, although the economy was recovering a t a satisfactory rate, the Government expenditures had risen to unprecedented levels, not in the least due to the military expenditures in connection with Indonesia, the former Netherlands East Indies. Immediately after the surrender of the Japanese forces in what was then the Netherlands East Indies, a group of Indonesian leaders, headed by Sukarno and Hatta, declared the independence of

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37

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Indonesia on 17 August 1945. Although the policy of the Netherlands Government was, at least in principle, to grant Indonesia gradually more independence and to move into a direction of a union of states, The Netherlands assembled expeditionary forces and ship them to Indonesia to restore law and order. This led to a political and military struggle which ended in 1949 with the recognition of the independent state Indonesia. The financial strain of these actions on the Government budget, still very much burdened by the recovery from the effects of the war in Europe, was enormous.

The result was that on 31 October 1949 N I L was informed that it had to stop all work associated with the expansion plans. After many discussions, the Ministerial Council for Economic Affairs decided on 30 November 1949 that, in principle, it would continue to support the development of aircraft in The Netherlands. However no decision was taken about the N L I expansion plans. NLL had done its utmost to build up the staff and several important financial commitments had been made in connection with the expansion plans. The laboratory was now in a very difficult financial position. Apparently the Government saw no direct link between the decision to support aircraft development in The Netherlands and the expansion and modernization plans of NLL. It is possible that the ministers and officials dealing with this matter felt that financial aid to the industry in the form of loans through NIV was a sufficient condition to give the industry a fair chance. It is also possible that it was felt that sufficient laboratory support could be given with the existing facilities. However the Minister of Traffic and Public Works did appoint a Committee to advise him on the organization, the management, the extent of the activities and equipment of the N L I required in the coming years. This Committee was also asked to advise on the need and desirability of the expansion program which had been halted. This Committee, formally charged by letter dated 7 January 1950, consisted of lr. J. Klackstone attached to the Ministry and Chairman of the Board of the Foundation NIL, Dr. lr. M.H. Damme, Director General of the PTT and Prof. Dr. lr. H.J. van der Maas, Professor of Aeronautical Engineering at the Technical University Delft. The Committee went to work immediately and completed its report by the end of March 1950. Many of the thoughts incorporated in the report were the result of debates during the months before the Committee was formed.

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This Blackstone-Damme-Van der Maas Report, which became internally known as the BDM Report. had a great impact on the operation of the laboratory. The importance of the report was perhaps not that it introduced completely new ideas about the management of the laboratory, but that it analyred in detail the possibilities and limitations for carrying out aeronautical research in The Netherlands. (The system of financial management proposed in the BDM Report had basically been in operation since the very beginning of the RSL, albeit on a less formal basis when the scale of the operation was smaller.) The KDM Report recommended in particular:

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That the annual government subsidy should be abandoned and that the interested parties [NIX lndustw, Defense, RLD, KLM, etc) should supply an equivalent amount on a contractual basis. This sum should be guaranteed and the contractors should indicate their priorities. 1 That amortization (including interest) should not be included in the rates applied for the usage of equipment and installations (including buildings, small equipment, etc. for which no separate rates existed1and that a special Government annual subsidy should be given to NLL to cover these costs. These subsidies could be used to create an investment fund. That a government subsidy should be made available for basic research (not earmarked for a particular application) amounting to 10% of the income received from contracts. .( That the original expansion plans should be executed with some a@ust~ ments and reductions.

0

At the beginning of 1950 the Board of NLL had approved the budget f o i that year, which was s u b mitted to the Government. assuming that ?he recornmendations of the BDM Report would be accepted. Howevei by mid-1950 the Minister informed the Board that no decisions had been taken yet concerning the expansion of the laboratoly and that in any case measures should be taken to reduce the personnel cost substantially in view of the expected financial shotilall in the budget. The Board then had to decide to reduce the number of personnel drastically. This led to a crisis in the Board and the vast majority of the members proposed in a meeting on 30 August 1950 that the Boaid should resign and that the members hand in their resignation to the Ministries and organizations which had appointed them, in order to create the possibility to form a new Board. The Boaid then resigned. It should be noted here that theie was no direct representation of the aircraft industry on the Boaid. In fact there was no aircraft industry representation on the Board during the period 1942-1954. The airline IKLM) was continuously iepresented.

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During the last quarter of 1950 a new Board was formed which held its lirst meeting on 5 Deceniber 1950. The Board proposed Piof. Van der Maas as its new Chairman and on 27 December 1950 he was appointed as such by the Ministei of Traffic and Public Works. Prof. Van der Maas now came into the unique position 01 heading the Aeronautical Engineeiing Department (then still a Sub-Department of the Department 01 Mechanical Engineering but soon to become a separate Department) of the Technical University Delft, the NIV (tile Netherlands Institute foi Aircralt Development) and the laboratory NLL. It was the beginning of a period of more than 25 years 01 very fruitful aerospace development in The Netherlands to which Prof. Van der Maas contributed enormously through these key positions. It still took moie than two years belore the political climate became more favorable for NLL. The laboratory was faced with a great problem. For an engineering research laboratory such as NLL, where preparations extend over many years befoie actual project support can be given, such a long delay was disappointing.

Severe measures had to be taken. In 1949 the number of peisonnel was reduced by 15 through natural attiition but in the middle of 1950 the Board had to decide that a further 59 employees had to be released before the end of 1950. Such measures had a disastrous effect on the morale of the peisonnel, particularly in a time fiame when there was a general shortage 01 technical personnel in the country. In fact by the end of 1950 there were 204 employees, compared to 304 early in 1949. A reduction of the personnel by one third in about one year is very serious indeed. The reduction was equally divided among the vaiious peisonnel categories. For many years, even to this date, this shock effect led to a vely cautious hiring policy lor permanent personnel. Another elfect was that when it was again possible to hire new personnel, it was difficult to attract suitable personnel, so badly needed for the expansion plans and the growing number of

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The recommendations of the BDM Report weie linally approved by the Government on 3 March 1952. The interruption had lasted 28 months. This delay was caused to a large extent by the linancial problems of the Goveinment but there was also another iinportant factor involved. The foundation 01 NIV in 1946 was a positive Step but it did not guarantee the viability of the airciaft industry. Many leading politicians wanted to be assured that an aircraft industry with its own design and development capability could survive. It was not till early in 1952 that this appeared to he a reasonable gamble. A maloi change was that, as a result of the critical years, the Board of NLL, tlmugh the office of the Chairman took a far more active part in the planning and decision making process. In 1953 it was decided to establish a small oflice at Delft to assist the Chairman. The staff included

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'After the Government appioval had been given. Prof. Van der Maas, through his unique position, urged promising students ~nthe 1950's to take up employment at NLL beiore they had completed their studies. They graduated while working a t NLL and several of those later made up the backbone of the engineering and research staff of NLL.

Mr. G.C. Klapwijk (who was also Secretary-Treasurer of NIV and w h o later became Chairman of the Board of Fokker and also of the Holding Company VFW-Fokkerl who served as SecretaryTreasurer of the Board, lr. J. Boel (who later moved to the laboratory and became Deputy Director during the period 1967-19711 for technical matters and Mrs. M.J.M. Janson-van Wijk itill that time Head of the Administration at the laboratory in Amsterdam) for administrative matters. With the approval of the B D M Report NLL was given a n e w lease on life. The cost of carrying out the modified expansion plans was estimated at DGL. 26.1 million. The completion date given in the repon of early 1950, was optimistically estimated as sometime in 1953. Obviously that date had to be adjusted. At the time of the interruption a total of DGL. 9.7 million had been committed of which DGL. 8.45 million had been paid at the resumption of the activities in 1952. The Power Plant was in a n advanced state of construction and the foundations of the n e w wind tunnels had been constructed.

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The changes in the plans were that the construction of the low speed low turbulence tunnel3 and the construction of the hall for vibrational and structural testing at Schlphol were canceled. One reason for the latter was probably that it was realized that for the real long term the site at Amsterdam would not suffice and that a second laboratory site had to be found. Facilities for structural testing could then be located a t this n e w site. There were also many detailed technical changes particularly for the high speed tunnel (HST). In the original plan of the HST (1947-1949) the aim was to achieve a maximum Mach Number in the test section between 0.85 and 0.90, which was the highest Mach Number attainable with a conventional, solid wall, test section. When in 1952 the construction plans were taken up again it was known to NLL engineers that it was possible to build a test section which would accommodate a flow with Mach Number larger than one, a true transonic test section. Although f e w details of the n e w transonic testing techniques, developed elsewhere, particularly in the USA, were known, a re-design of the test section of that wind tunnel was undertaken with the assistance of a Swiss firm. It became a test section with longitudinal slots in the top and bottom walls of the test section and a plenum chamber around the test section ~a 'ventilated' test section.

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Dr. Th. von Karman, Chairman of AGARD, wrote the following story about the HST transonic test section. [Ref. 321: -"They (NLL) planned a large wind tunnel going up to the speed o f sound. Transonic speeds were unattainable with design methods available in the open literature because o f a phenomenon called 'choking'. During the war, however, John Stack and his group working for the National Advisory Committee for Aeronautics in the United States had developed a transonic 'throat' which made possible wind tunnel operation in the important region just above the speed of sound. Unfortunately, this information was still classified and unavailable to The Netherlands. The Dutch scientists spoke to m e about it, and Iagreed that it would b e a waste for them to build an expensive obsolete wind tunnel when there was an urgent need on the Continent for data in the n e w speed region. I urged NACA to declassify the material, but I was told the process would take quite a while. Icouldn't help b u t believe that there was a way around this silly r e d tape, and it occurred to m e that some Swiss engineers k n e w the principle of the transonic throat because they had been working in the United States on it before the method was classified.4 Since the Swiss were unhampered b y

'The large concrete foundation of the low speed low turbulence tunnel in the middle of the NLL laboratory site became known among the personnel as the King's Tomb IKoningsgraf. perhaps referring to the Director Koningl. It resembled the coffin of a giant king. During the late 1960's an office building was constructed on this foundation. 'Note by the author: Actually the idea of a 'slotted' test section could be traced to early theoretical work of Piandtl and Glauen in Germany during the 1920's and a very specific configuration suggested by Wieselsberger in Germany in 1942, IRef 151.

The High Speed Wind Tunnel HST under construction around 1956

Sketch of the High Speed Wind Tunnel HST. as it was built

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NATO agreements, however, they were free to help The Netherlands. The drawback was that the U.S. research had progressed considerably since the Swiss left the United States. To overcome this gap l inquired in the United States whether it was possible for American engineers to criticize the designs of our NATO partners, even if they were not allowed to pass out information on U.S. designs. The authorities said this was possible, so I arranged for U.S. experts to visit The Netherlands and constructively criticize Dutch drawings of designs based on Swiss information. This worked. Instead of a ‘lemon’ The Netherlands has one of the best facilities on the Continent and has made outstanding contributions to the design of European aircraft. ”

Staning from this ‘Swiss design’ the adjustable throat ahead of the test section, the test section itself and the second throat after the test section were further developed and the HST is now indeed a superb transonic wind tunnel.

41

The latest modifications, completed in 1992, include adjustable top and bottom test section walls-from2.00xl.60M'to2.00x1.80M2-,a n e w model support system, modification of the control system and data handling system.

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The High Speed Wind Tunnel HST conipleted

The n e w test section, with increased length and variable height, of the High Speed Wind Tunnel H S I 1992

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An Irsterrlatiolaal ~hcr,szaier

One of the annexes of the BDM Report was a letter (dated 10 February 19501 of Prof. Maurice Roy, the Director of ONERA, the Office National d'Etudes et de Recherches Aeronautiques (the French Aeronautical Research Organization), to lr. C. Koning, the Director of NLL, indicating ONERAs interest in some form of cooperation with respect to the variable density transonic tunnel under consideration a t NLL. The French interest in the project was used in the BDM Report as supporting evidence for the NLL plans. In retrospect it is difficult to determine h o w much influence this had on the final decision of the Government to approve the plans. It may not have been important for the direct decision, but it was the beginning of international cooperation and 'cross utilization' of facilities. In January 1950 Mr. R.A. Wiliaume' of ONERA visited NLL and discussed the wind tunnel plans of NLL. In France ONERA was involved in a large construction activity a t Modane-Avrieux in the French Alps. The major wind tunnel under construction was a high speed wind tunnel with a test section diameter of 8 M. This facility originated in Germany during the Second World War and was under construction at Otzal. Austria, at the end of the war.' The plans of ONERA also included a transonic tunnel with a test section of approximately 2 M7.However France was also faced with financial limitations and ONERA realized that the plans to construct a transonic facility might be retarded. That must have been Prof. Roy's motivation to explore some form of cooperation with NLL. In return he could offer the use of the large 9-Meter high speed wind tunnel at Modane.

'MMIWillaurne's trip report of January 1950 was made available to the author by IGA M. Benichou. President of ONERA M i Willaume was External Relations Officer at ONERA. Later he jolned Dr Th. "on Karrnan when AGARD was established in Paris He sewed as AGARD's Director of Plans and Programmes during the period 1952-1980 and assisted Von Karma" and Wartendod. respectively Chairman and Director of AGARD. in the liaison with the French authorities Through his position a t AGARD he was also instrumental in assisting in the cooperation

between several other countries. 'The highly interesting story of the transfer to France of this facility and the subsequent construction of the facilities a t Modane was described by Marcel Pierre who was the engineer in charge of the development at Modane. IRef. 331.

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A model of the French-British Concorde in the High Speed Wind Tunnel HST

A modelofan Airbus in the High Speed W h d Tunnel HST

At that point in time (1950) no further progress in international cooperation could be made since NLL had not received government approval to proceed with its expansion plans. However some time later, a i the end of 1953, the Association lnternationale des Constructeurs de Material Aeronautique, AICMA, (European Association of Aircraft Manufacturers), established the Commite Internationale Permanent des Souffleries, ClPS (Permanent Committee on Wind Tunnels). This Committee made an inventory of the need for development facilities in Europe and on 26 March 1954 a meeting was held at the Paris' office of AICMA. The ClPS representatives discussed with Prof. Van der Maas and Prof. Zwikker (who then was the Director of NLL) a proposal for the utilization of the HST which was then under cotistruction and also for the supersonic tunnel, the SST which was in the design stage. On 9 and 10 April 1954, during a meeting in The Netherlands. various modes of cooperation were further discussed with representatives of some aircraft manufacturers. Finally these discussions led to the signing of a contract between AICMA-CIPS and AILL, which stipulated that NLL would make available the HST to members of AICMA for up to 50% of the available testing time. This contract, signed on 23 February 1955, included details about the minimum occupancy by AICMA members, AICMA fees, the principles of the wind tunnel charges and details on the reservation of testing times.

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During the following decades this agreement resulted in a v e v fruitful utilization by various AICMA members of the HST and later also of the SST. It also served as a stimulant to further cooperation across the borders although this was a rather slow piocess.

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The panicipants in the ClPS planned to go much farther and their plans included a large blow-down facility, with a 3 x 3 M' test section, for up to Mach Number 3 and suitable for engine tests at supersonic speeds. In the period 1956-7958 the French company SESSIA built an 0.85x0.85 M' pilot facility, with a high pressure (65 aim.) hot water (270°C)injector after the second throat.

A model of the Caraveile in the High Speed Wind Tunnel HST

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Aerial view of NLL in Amsterdam around 1960 with the uncovered High Speed Wind Tunnel H S J f n the rear

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Members o f the Board, Directorate and Staff of the NLL, 1959

It was hoped that at least five countries would pamicipate in the full-scale facility. It was apparently too early.

Since the 1950's many cooperative aerospace projects were carried out in Europe whereby companies of different countries worked together closely during the design, development and manufacturing stages. However it was not till 1976 when a two-nation (Germany and The Netherlands) aeronautical test facility, the DNW, (Chapter 18). became a reality, and it took till 1988 when finally a four-nation (France, Germany. the UK and The Netherlands) aeronautical test facility, the ETW, (Chapter 191, was started. The best that could be achieved in the 1950's in the area of cooperation in planning and operation of facilities was the AICMAINLL-contract.

Even before the RSL was officially founded on 5 April 1919, Dr. Wolff managed to hire lr. J.C.G. Grase', an engineer w h o had graduated from the Technical University Delft. lr. Grase wanted to go to England to join the Army and learn to fly but he was persuaded to join RSL instead. Dr. Wolff made arrangements with the LVA of the Army a t Soesterberg for lr. Grase to receive a pilot's training. It was the only place in The Netherlands where one could learn to fly properly. Later Dr. Wolff managed a similar arrangement for lr. Van der Maas, who joined the RSL in 1923 and who succeeded Ir. Grase. For lr. Wynia, w h o worked at the RSLiNLL from 1932-1952. and also for lr. Marx, who joined RSL in 1934, similar arrangements were made.

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The RSL engineers were very dependent on the instructors and of course on the weather. The pilots a t Soesterberg thought, at least initially, that it was perhaps useful that research engineers knew something about flying, but it seemed to them research ought to be carried out in a laboratory on the ground and they (the LVA) would do the flying. Dr. Wolff recalled later that lr. Grase became one of the best pilots. Anthony Fokker, w h o himself was an excellent pilot, appreciated lr. Grase's opinion and he often took him along on trips and so lr. Grase had the opportunity to fly many planes which never became available at Soesterberg or anywhere else in The Netherlands.

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Tile enaineer-uilot zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA How 11. Grase came to work at RSL was later recalled. IRef 341. by lr J C G Grase in Dr Wolff. the cockpit I

'

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-"For fhght testing and the study of the airplane in general I had engaged If. Benus Giase. He was the son of my former English teaciier and he had been a good student a1 Delft. I received a letter from iiis father with an urgent

request to employ hmi Grase wanted to go 10 the UKandjoin the Armyand become a pilot. He was at home with the flu and liis failier tried to convince him not to go abroad and panrcipate in the war. I employed him since liis references from the Technical Universiiy Delfl were excellenr and I was c o n ~ vinced that we needed an engineer-piloi. Thrs was of crucial rmponance to me Most 1ahmtorie.s were not much concerned wrth flvino and soecralned . , .. .:/ . . . .I : ., . . , . .. ., .. . .. , . .... , . . . . .,.. .. . . . - > . . ... -. . , . . . . .:, , . irals were secondary subjects The problem was that it IS much more difitcult - and more dangerous - to caiiy out ilight tesis than laboratory tests. One needs excellent pilots with a scienriiic mind who are able to recognize the phenomena occurring durrng fhght, to analyze them and then 10 cariy out iiight tests with a lrmited number of parameters. I was lucky in that r l was easy to convince Prof Van Royen of this poirir o i view and that I found Grase and later Van dei Maas who fully understood lheir task ~~

~

.

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li. Grase 11891~19291stayed with the RSL till June 1923, when he went to Fokker. It was rumored that Fokker found him too difficult as the certifying government official a t the RSL and offered him a higher salaiy There may be some t w l i in tliat but Dr. Wolff recalled that Fokker appreciated very much the technb cal knowledge and flying skills of Giase and they had cooperated Several times in flight demonstrations. Giasb and Roosenschoon 1wlio was the first lecturer in Aeronautical Engineering in Deiftl. designed the wing for the so successiul Fokker F.Vlla, working under Platr. Fakker's chief design engineer.

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During the 1920'sand the 1930's RSL personnel participated as pilots and observers in m a n y hundreds - perhaps thousands - of flight tests for KLM, the Army. the Navy and the Dutch aircraft manufacturers Fokker, Van Berkel, Koolhoven, Pander, De Schelde, Spijker and several foreign aircraft manufacturers who wanted to demonstrate their aircraft. Many of the flight tests dealt with the take-off and landing characteristics, the climb performance, the performance at altitude, stability and control, spin characteristics, stall performance, maneuverability and very often with undesirable vibrations. Different aircraft of the same type often exhibited different vibration characteristics. The flight tests were often carried out for the aircraft manufacturers and for the users in combination with tests for airworthiness certification. There was also a constant demand to measure the performance (speed, fuel consumption, range, etcl of aircraft, often based on the desire to increase the range and the payload. The handbooks supplied by manufacturers were in general not very complete. The RSL was requested frequently to advise on a possible cure of an undesirable characteristic of an aircraft or on the effect of changing to another engine or propeller.

A major activity in support of flight testing was t h e calibration of instruments and t h e positioning of sensors o n aircraft Much attention was paid to the positioning of Venturi tubes, used in the early days, Pitot tubes, static pressure measurements and the measurement of fuel consumption. The RSL and later NLL carried out aircraft instrument calibrations for many aircraft users. The laboratory built up and maintained a complete calibration laboratory for this purpose. After World War II when the malor users acquired their own facilities, this activity was more and more limited to the calibration of the instruments used by the laboratory itself. The reports were short and clear, mainly reporting the results and the conclusions, often only on one page. This conciseness must have been due - in part - to the fact that there were only a f e w engineers involved in the flight testing at the RSL. They were the only authoritative persons around and little further explanation was needed. There was only one layer of approval: the Director of the RSL! It must also be remarked that many of these fiight tests reports did not have a long lasting effect. During the 1920'sand the 1930'sthe aircraft types and the various versions of each type succeeded each other very rapidly. Modifications were often made overnight and it was very hard to stay current with the characteristics of a particular type of aircraft.

RSL was also occupied with aircraft accident and incident investigations. Many emergency landings -relatively easily carried out in the early days had to do with engine failures; some accidents were related to structural problems and often the cause could be traced. An example of an aircraft accident investigation in 1934 is mentioned in Chapter 29.Other accidents gave rise to a more thorough investigation with a long lasting effect, for example the flutter investigation described in Chapter 9. ~

A speed and altitude record During 1949,when NLL had oniy the Siebel aircraft available for flight testing, the opportunity arose to carry out measurements with a high performance aircraft. The Air Force2 decided to carry out a series of flights to estabiish a Netherlands' speed and altitude record with one of its Gloster Meteor Mk.lV fighter aircraft. The Air Force had received its first Meteors in 1948.The Air Force received a total of 266 Meteors in various versions. The Royal Netherlands Air Force operated the Meteors tiil 1959.Fokker built till 1953 a total of 330 Meteors under license - f o r the Air Forces of Belgium and The Netherlands. ~

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'Actually the Air Force was still pan oi the Royal Netherlands Army and did not become a separate Farce till 11 March 1953 when the Royal Netherlands Air Force was formed. It was almost 35 years aiter the Royal Air Force of the UK was formed A consolation was that the United States Air Force was also formed i a t l w late. on 26 July 1947.

47

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The Gloster Meteor Mk.lV with which the Netherlands' speed and altitude record was establishedin 1949

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The flights were cariied out in August 1949 by Maj. J.L. Flinterman3 over the island of Ameland in the North of The Netherlands. NLL carried out the measurements and adapted the instrumentation in the aircraft and on the ground. Apart from the fact that this was a welcome and stimulating exercise for the NLL personnel, it also was an exercise in which the technical staff of the Air Force and NLL became acquainted with each other's capabilities. This first major post-War joint activity laid the foundation for a much broader cooperation between the Air Force and NLL.

Stal1iiity and i:tani-i.oi N o w again going back to the pre-World War I / period. The extensive experience gained in flight testing and the many observations of the aircraft characteristics, panicularly the aircraft stability, led lr. Van der Maas to an investigation of the longitudinal static stability of aircraft. For this he carried out many measurements on a Fokker F.VII with one, t w o and three engines and with a Pander type EC aircraft. He analyred the longitudinal stability using the concept of constant stick position lines (lines of constant elevator angle1 for various angles of attack and throttle positions. From this he developed criteria to judge the longitudinal stability of aircraft. This work led to his dissertation for which he was awarded the degree of Doctor at the Technical University Delft in 1929. This was one of the first attempts to formulate a scientific basis for aircraft flight testing, [Ref. 351. The stability criterion based on stick position was later superseded by the criterion of stick force stability as it was developed paniculariy in the USA during the 1940's. [Ref. 361. Without going into details, it seems that with the current development of 'fly-by-wire' and computer controlled flight systems - whereby unstable aircraft are made to fly -, stick position stability becomes again a relevant criterion. These investigations were later extended to the lateral static stability characteristics. Again using the concept of constant stick position lines, criteria were developed to judge the lateral stability and control of aircraft. Although this work, authored by Van der Maas, Marx and Van Oosterom, [Ref. 371, was essentially completed several years before, due to the pressure of contract work it was not published till 1940. The study of stability and control of aircraft remained one of the most essential parts of aeronautics. The problem always was: h o w to determine quantitatively the desirable and acceptable flying properties and h o w to determine these propenies in flight. With the advent of large computers and flight simulators many studies on the behavior of aircraft aie carried out in the laboratory. In addition, with the introduction of flight control systems the emphasis is often on developing the proper control laws long before the aircraft flies.

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3Maj Jan L. Flinterman had escaped to the UK during the Second World War. From there he had flown over 400 missions with Spitfires. After the war he served with the Royal Netherlands Air Force and after his retirement from the Air Force he seNed for some time with the NIVR. managing space progiams. With the Gloster Meteor he established in 1949 the Netherlands' speed record of 953 KMiHR and the altitude record of 14.821 M.

An associated problem is that accurate flight data are needed to be able to model the aircraft properly on a computer or flight simulator. The information needed for an accurate mathematical model is often not avaliable from Wind tunnel tests and calculations and so once the aircraft is built, flight tests are carried out to complete the mathematical model to be used in a flight simulator and of course also to prepaie the final aircraft manual.

NEW measurement techniques and instrumentation for carrying out its flight tests were continuously developed at RSL. During the first years after the Second World War, when the need arose to measure more parameters simultaneously during one flight, a so-called automatic observer was developed. It consisted of a panel on which many dial gauge instruments were mounted. During flight tests this panel was photographed by a movie camera.

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The first digital flight data recorderdevelopedai NLR. the DR28

When digital recording equipment became available, special magnetic tape flight recorders were developed and the measurements were increasingly carried out with sensors with digital outputs. The first complete digital recording installation, the DR28, was used during the flight tests of the Fokker F28.

During the 1970s and the 1980s the demand for flight testing increased considerably and a new, modular system was built up which could handle flight tests for a variety of aircraft. This system called MRVS -the Dutch acronym for System for Measuring, Recording and Processing Flight Test Data (Meet, Registratie- en Vetwerkingssysteem voor Vliegproeveni included an autoland camera, telemetry equipment and also a quick-look system for use on board and many other practical features.

.-

zyxwvutsrqpon zyxwvutsrqpo zyxwvutsrqp zyxw The system was developed in close cooperation with Fokker, the prime user, and Fokker developed a specific part of it. Agreement was reached on a division of tasks between Fokker and NLR. This created a unique situation in aircraft flight testing whereby both partners were fully dependent on each other. The NIVR, the organization providing a substantial part of the funding, played a crucial role in this arrangement. During the 1990's a new version of the MRVS is being developed, again in close cooperation with the Fokker Aircraft Company.

Schedule of fiight tests using an MRVS in various configurations, with an indication of the relative size of the tests

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~~

AIRCRAFT

CLASS

'79

'80

'81

'82

'83

'84

'85

'86

'87

0

METRO I1 F27 - F83

LOCKHEED ORION

FZ7 F555 ~

OUEEN AIR .. . .. .. .. . ..... ... .....

F16 METRO / I FZ8 A1 - ATB ~

FOKKER 5011 FOKKER 5012 FOKKER 10011

FOKKER 10012

;' n

~~~~~~~~~~~~

from airciafl systems

40 20 25 5 40 15 4000 350 350 7500 7500

from MRVS

transducets

30 35 20 125 20 40 60 300 450 450 700 900

i o t a ) numbei of measured VaIueSperseconl

1250 3000 2000 6000 550 6500 3500 22000 10000 10000 30000 30000

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., c> c ,. .. ., ,,

,.

=

SMALL

=

MEDlUM~SiZED

=

LARGE

=

VERYLARGE

, ,"

=

(PLANNED1 OPERATIONAL PERIOD

.,,.,,

=

EXPECTED EXTENSION OFTHE OPERATIONAL PERIOD

M'RVS equipment mounted in a Fokker F28 Feliowshio

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Operatork console of the flight test instruments in the Fokker 100Avionics Test Bed

NLR flight test equipment installedin the Fokker 50 prototype

Airflow measuring probes in the intake of a P&W 124 engine of the Fokker 50 prototype

NLR flight test instruments on the main landing gear of the Fokker 50 prototype

NLR Atitolaiid caniera hatch and images of the runway taken during landing with the camera

I.ab0ratcHy Aircraft

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Although from the start flight testing was a major element of the R S L i N L L i N L R activities, the laboratory was never abundantly equipped with airplanes. It was not until 1931 that the laboratory obtained for the first time its o w n airciaft, in spite of the fact that I:. Grase and Ir. Van der Maas had cariied out hundreds of flight tests with aircraft of other organizations. This first laboratory aircraft was a Fokker F.II. This specific aircraft was originally built in Germany in 1918 as a prototype for Fokker's first passenge: plane. It was smuggled out of Germany in the Spring of 1920 because Fokker wanted to demonstrate it on the day Plesman's KLM made its first flight to London with a converted De Havilland military plane, 17 May 1920, and so attract the attention of the authorities and KLM. A f e w months late: KLM did place an order for t w o Fokker F.Il aircraft and the aircraft which later became the first laboratory aircraft of the RSL was one of those t w o . Besides with KLM it had also served with the Belgian Aiiline SABENA before it was registered as PH-RSL. During a period of 5 years it was used for the development of flight test instrumentation and for various flight tests, particularly in the aiea of stability and control. Interestingly enough this aircraft did not have a vertical stabilizer and the rudder was directly mounted at the tail end of the fuselage. Presumably the square fuselage provided enough directional stability. Another peculiarity was that the ailerons extended beyond the wing tips. In 1936 the aircraft was returned to Fokke: for incorporation into a museum collection, but in 1940 it was destroyed during the bombardment of Schiphol Airport.

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The Fokker F.i/ Laboratory Aircraft

In 1936 the RSL acquired a Fokker F.Vlla through the cooperation of Fokker and KLM. Fokkei built 3 6 airciaft of this type. Oddly enough KLM also built four Fokkei F.Vlla's f i o m spare parts and parts retrieved from crashed airplanes. The RSL aircraft was one of those aircraft built or assembled by KLM. When the RSL acquired it, it had flown more than 7 years with KLM. The main usage of this airplane was also in the context of stability and control research. During the war it was hidden at the yacht haibor of Van Dam, Oude Wetering. It had been damaged by gun fire during the war. For quite some time there were plans to restore it, but finally in 1960 it was sold to a scrap dealer. The Fokker F.Viia Laboratory Aircraft

lmrnediately after the Second World War, May 1945, it was extremely dilficult for the laboratory to obtain an aircraft suitable for flight testing. In retrospect this seems strange since there was an enormous surplus of military aircraft. This may have been due to the lack of funds and the shortage of tuel. It must be remernbered that in 1945 many essential items were still in short supply even though the economic conditions improved very rapidly. The laboratory did have a glider, the Tromp Govier, for flight testing but that was a very limited flight testing capability. Then in 1946, H.R.H. Bernhard Prince of The Netherlands olfered the use of his aircraft, a Siebel 204-D-1. This aircraft, a military version, had been built in 1942. In 1955 the ownership was transferred to NLL. It was extensively used for comparison 01 wind tunnel data with flight test data, including the effects of propeller wakes.

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The Siebel 204-0-1 Laboratory Aircraft

Also with this aircraft the first performance measurements in non-stationary iacceleratedl flight were carried out, [Ref. 381. The tests were inspired by a report 01 the Centre d'Essais on Vol (CEV), France, 1947, whereby flight data were taken during a symmetrical dive or climb. In principle such a mode of flight testing would result in an important saving in llight test time. Various flight paths were flown with the Siebel aircraft. The results were encouraging but with the type of instrumentation available then, the accuracy of the test results was far less than those obtained in stationary flight. The development of this llight test technique was to become an important activity at the Technical University Delft, when under the guidance and inspiration 01 Professor Dr. lr. O.H. Gerlach? suitable instrumentation arid data reduction methods were developed. The Siebel was also used for flight test exercises 01 students of the Aeronautical Engineering Department of the Technical University Delft. An interesting detail is that during the first days of February 1953 the aircraft was used to transport sand bags to plug the holes in the dikes in the disaster area during the floods in Zeeland. The Siebel had to be scrapped finally in 1964 due to lack of spare parts.

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There were fortunately other opportunities to become involved in llight testing. For example a group 01 organizations in The Netherlands had banded together in 1947 to purchase a Sikorsky S51 helicopter to investigate the applications of helicopters in The Netherlands. NLL staff had the opportunity to carry out performance measurements on this helicopter. It was at that time that lr. Meyer Drees, w h o later designed the Kolibrie helicopter (see Chapter 121 became interested in

'Prof. Geilach, an aeronautical engineer and pilot, the successor of Proi. Van der Maas. became Lector (Associate Professor) in 1958 and lull Professor of Aeronautical Engineering in 1965 a t the Technical University Delit He had written his Doctoral dissertation an the measurement of performance, stability and control characteristics in non~steadyflight. [Ref.391. He introduced several new and important ideas in this emerging tech nique which became known as Aircraft Parameter Identification.

53

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The Sikorsky S51 helicopter used for various experiments in The Netherlands

the flow through rotors. Although the helicopter had been purchased mainly to investigate the possible applications for military operations, postal sewices, rescue operations, city-center to city-center passenger transportation, etc. it provided NLL the opportunity to obtain first hand experience with helicopters. It is to be noted that futurologists at that time expected that helicopters would soon be used extensively for short haul transportation.

In the late 1940's Fokker designed its first jet aircraft, the Fokker S14, a side-by-side jet trainer. It made its first flight on 19 May 1951 and it was probably the first jet aircraft designed from the start as a trainer. Finally only 20 aircraft of this type were sold to the Royal Netherlands Air Force, because at that time many countries were provided with Lockheed T . 3 3 ' ~ a. two-seat version of the F.80 jet fighter, iinder the Mutual Defence Assistance Program, MDAP. In 1961 NLL obtained an 5 1 4 - the first one built - f r o m the NIV, the Netherlands Institute for Aircraft Development. Till 1966 it was often used as a calibration aircraft (pacer) for other aircraft. It was the laboratory's first direct experience with the operation of a jet aircraft. In 1971 it was handed over to the National Aeronautical Museum AVIODOME at Schiphol Airport

The Fokker S14 Laboratow Aircraft

The Beechcraft Queen Air 80 LaboratoiyAircraft

In 1963 the NLL was in a position for the first time to buy a n e w aircraft. It was a Beechcratt Queen Air m o d e l 80. On 7 November 1963 it arrived at Schiphol Airport. after a flight of 8000 k m in 5 stages, from Kansas, Wich. USA. lr. F.E. Douwes Dekker, the NLL engineer-pilot and a pilot from Beechcraft made the trans-Atlantic crossing. For this flight an extra fuel tank with 1200 liter of gasoline had been installed in the cabin. This aircraft was used for a variety of tasks. It was used for both developing n e w measurement techniques and testing of flight test instrumentation. This included the flight testing of individual instruments such as radio altitude gauges, airborne computers, and complete flight test instrumentation systems as developed for flight testing of the Fokker aircraft and aircraft of the Air Force. Over the years this aircraft was used as a real laboratory aircraft. a flying laboratory.

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These tests were continued several years. At the time there was no immediate application in sight for an aircraft developed in The Netherlands, but the knowledge and experience gained was useful for the evaluation of applications in e.g. the General Dynamics F16 and later the Airbus family of aircraft.

The NLR side-stick controller was also tested in 1976 in a series of flight tests with the Fokker F28-A1 (the first prototype of the Fokker Fellowship that was used for a variety of development flight tests). It was used in a program to investigate the positive stick force stability in attitude stabilized aircraft. The results of this advanced research were communicated to the international community through specialist meetings such as organized by AGARD.

In the 1 9 6 0 s the laboratoiy aircraft were increasingly used for applications which were not strictly aeronautical, particularly remote sensing. This included infrared and radar measurements of tile sea state, measurements of pollution, particularly oil at sea, agricultural growth monitoring, ship movements, infrared measurements for military and civil purposes, e.g. the dispersion of cooling water from power plants, etc. Many of these flights were carried out under the auspices of a national interdepartmental program for the application of remote sensing INederIandse lnterdepartemeintale Werkgemeenschap voor het Applicatie-onderzoek van Remote Sensing technieken, NIWARS), (see also Chapter 171. In most cases the flights involved very accurate navigation. recording and analyses, and the upgrading of existing equipment to acceptable airworthiness standards. The development of the instrumentation was carried out in cooperation with other, national and international, organizations. In 1966 the Royal Netherlands Air Force transferred to NLR t w o Hawker Hunter T Mk-7 dual seat jet fighter aircraft, one in flying condition and one for spare parts. The last Hunters were phased out by the Air Force in 1968. During more than 13 year this aircratt was also used for a variety of investigations. It was one of the aircraft with which extensive test flights were made for the development of the non^ Stationary Method (NSM)for measuring performance characteristics of aircraft.

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The Hawker T Mk-7 Hunter Laboratory Aircraft

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With this aircraft many flights were made in the 1960's with the ORPHEUS day and night reconnaissance system. This system was developed by Delft instruments in cooperation with Fokker and NLR and later used by the Netherlands and Italian Air Forces. In fact for NLR it was the stimulant for the activities in the area of remote sensing, (Chapter 171.

The Hunter aircraft was employed in the validation of the moving base research flight simulator, which was then under development at NLR. It was an aircraft for which the mathematical model (the characteristics or coefficients of the equations of motions1 was known and also the NLR engineer-pilots could judge the motion fidelity as incorporated in the fllght simulator.

zyxwvutsrqpo This aircraft was flown by NLR till 1980 when it was sold to an aircraft dealer

The Swearingen Metro il Laboratory Aircraft

The arrivai of the Swearingen Metro li Laboratory Aircraft at Schiphoi Airport, 29Aprii 1979 Flight testing of complete systems became more and more important in the 1970's and after careful considerations it was decided to purchase a somewhat larger aircraft than the Queen Air. On 29 April 1979 a new laboratory aircraft arrived a t Schiphoi Airpoit with an all NLR crew. It was the Swearingen Metro 11, which they had flown from San Antonio, Texas, USA, via Goosebay and Iceland to Amsterdam. This aircraft had been specially modified to accommodate laboratory equipment, including a camera dome in the cabin floor, extra electrical power supplies and 'hard-points' for carrying external instrumentation pods. In the 1980's this aircraft was used extensively both for testing of the flight test instrumentation of the Fokker 50, the Fokker 100 and militaiy aircraft and for remote sensing experiments.

For a short period NLR had three laboratory aircraft in operation The thrcc laboratory

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Aircraft in 1979

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The operation of laboratory aircraft is a relatively costly aflair. The number 01 actual llying hours is seldom more than 100 per year. That is very low compared to the number of flying hours in commercial operations and even compared to military or general aviation operations. Very little routine flying is carried out with laboratov aircraft: practically every flight is a test flight. It is not surprising then that the number of occupancy hours, that is the number of liours required for preparation of the test flights, is 10 to 20 times the number of flight hours. Over the years attempts have been made to realize more flight hours so as to reduce the cost per eflective flying hour. It was thus not surprising that the laboratory. with never more than three fully qualified engineer-pilots. had to dispose of the Hawker Hunter. An agreement was made with the Royal Netherlands Air Force whereby NLR could make use of high speed aircrait of the Air Force for occasional flight tests if these were thought to be of national interest, thus obviating the need lor NLR to maintain and operate a fighter type aircralt. In order t o maintain the flight proficiency of the NLR pilots and - what proved to be even more important - to have available at the laboratory first hand experience with the operation of current airliners, arrangements were made for the engineer-pilots to fly with commercial airlines on a part-time basis. During the last few decades such arrangements have been made for the pilots of NLR and the Technical University Delft, mostly with charter airline companies. The advantages are obvious: the engineers stay current on airline practices which is important when dealing with air traffic problems and when teaching students. The airlines concerned have the part-time service of highly motivated and capable pilots.

For many years the Siebel and later the Queen Air were used for flight test exercises with students of the Department of Aerospace Engineering of the Technical University Delft. Also in other aspects the cooperation with that Department was pursued over the years through the execution of joint research projects. When it became clear at the end 01 the 1980's. that the University had to replace its more than 30 year old laboratory aircraft, a De Havilland DHC-2 Beaver, and the Queen Air of NLR would have to be phased out within a few years, the Department of Aerospace Engineering and NLR decided to purchase and operate jointly a new laboratory aircraft, a Cessna Citation Il. The aircraft was flown across the Atlantic Ocean by lr. Kleingeld and Mr. Groeneveld 01 NLR and Ir. Hosman of the Technical University Delft and landed at Schiphol on 19 March 1993.

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With the joint ownership and operation of a new laboratory aircraft in 1993 this cooperation between the Depaiiment of Aerospace Engineering and NLR will be further intensified,

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The Hangars at Schiphol During the 1980's it became more difficult to maintain hangar space at Schiphol Airpon the airport closest to the laboratory. NLR had been very fortunate to have had access to an airport only a few kilometers distance from Amsterdam and adjacent to the Fokker Flight Test Center. Due to the increased pressure from the ever growing commercial aircraft operations it became almost impossible to lease a secure hangar space at Schiphol and NLR lost its rented hangar space when a mapr re-construction program was carried out. Fortunately the Dutch Dakota Association (DDAI took the initiative to construct a hangar at Schiphol in 1989 and this Association was interested in leasing part of the hangar to NLR since obviously it would strengthen its case to maintain a hangar space at Schiphol Airport ~

The DDA was founded in 1982 under the energetic leadership of Capt. A.C. Groeneveld. The Association is a private organization and it operates a Dakota (the PH-DDAI and plans to have a second Dakota (the PH-DDZI operational in 1994. Groeneveld managed in 1988-1989 to build a hangar at Schiphol from where the DDA aircraft are maintained and operated by professional volunteers. The DDA, run by volunteers, organizes tourist flights over The Netherlands. It is a great pleasure to watch a DC-3lDakota 'touring' over The Netherlands, often during week-ends. There is a growing, nostalgic, interest of the public in those remarkable planes which contributed so much to fhe development of civil aviation and of course also to the transport needs during the Second World War and even later. It is nice that through this arrangement the connection of this historical Douglas aircraft and NLR is continued.

NLR instrument pod (left) installed on the NF-5A Test Aircraft K-3001 of the Royal Netherlands Air Force

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During the 1960's the technical cooperation with the Royal Netherlands Air Force was again intensified. One reason was the purchase of the Northrop F-5. The particular version was produced by Canadair. Montreal, Canada. It became known as the NF-5. The NF-5 aircraft 105 in all - were flown from Canada to The Netherlands (Air Force Base Twente, near Enschedei during 1969-1972. This aircraft had been modified to accommodate the requirements of the Royal Netherlands Air Force. The first aircraft of this series, the K-3001, was assigned to the Air Force Test Group at the Twente Air Force Base. This Test Group consisted of an Air Force test pilot, a ground crew and a permanent support group of NLR engineers and technicians. This aircraft was used as a test aircraft for a variety of experiments such as flutter testing with various external loads (bombs, fuel tanks, dispensers, etc.), fatigue monitoring and various electronic installations. The flight tests were carried out by the Air Force and NLR prepared and installed the instrumentation and carried out the analyses of the flight test data. This joint Air Force-NLR team operated during the period when the NF-5 was operational with the Air Force. ~

Preparing a flight plan with the CAMPAL Svsteni Computer AidedMissionPlanning at Air Base Level)

When the RoVal Netherlands Air Force purchased the General Dynamics F-16 (deliveries began in 1979) the aim was to achieve a high degree of commonality with the USAF and the other three European Air Forces (Belgium. Denmark and Norway). A separate Netherlands test aircraft would then not be necessary for the investigations of such matters as new external store configurations, new mission patterns, etc. This goal was largely achieved during ?he first few years of operation of the F-16. The task of NLR shifted towards the participation in field trials, mission preparation and evaluation of the effectiveness of the aircraft in a changing environment. After some years there arose the need for further special instrumentation and NLR became more involved with the Air Force operations of the F-16 aircraft. An extensive task was the development of a mission planning system - CAMPAL Computer Aided Mission Planning at Air Base Level, in close cooperation with the RNLAF, (Chapter 161.

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Around 1990 the Royal Netherlands Air Force decided to maintain the F-16 for several more years and to carry out a Mid-Life Update (MLUI. In this undertaking the Air Forces of the USA, The Netherlands, Belgium, Norway and Denmark participated. Here NLR is carrying out several tasks in close cooperation with the U.S. Companies and the RNLAF. The Mid-Life Update may eventually include: 0 0

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a modernized cockpit; digital terrain following equipment; a n upgraded radar; an advanced IFF (Identification Friend or Foe) system; provisions for night vision.

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The fixed base WSTOL F/ight Simuiator

Chapter 15 mentions that a t NLR the first complete anaiog computer was installed in 1955. With this computer it became possible to 'fly' an aircraft in the laboratory in real time in a simplified form. Gradually more functions were added and with the so-called ViSTOL simulator it was possible to study take-off and landing characteristics of aircraft.

In 1972 the construction of a flight simulator with a moving base was started in a separate building at the laboratory in Amsterdam. The moving base of this simulator was driven by special 'frictionless' hydraulic cylinders. These cylinders were developed by Prof. Dr. lr. T.J. Viersma and his associates of the Department of Mechanical Engineering of the Technical University Delft in close cooperation with the Department of Aerospace Engineering of that University. The cylinders are made 'frictionless' by means of hydrostatic bearings - an oil film leaks constantly between the piston and the cylinder and the piston does not make contact with the cylinder. This means that 'sticking' and 'littet are down to a level that cannot be felt by the pilot in the cockpit mounted on the moving platform.' The flight simulator was provided with two, interchangeable, cockpits: a single seat F-I04 cockpit obtained from the Air Force and a dual seat DC-5 cockpit obtained from KLM. The visual system consists of mirrors projecting an image on the cockpit windscreen obtained by a small camera moving above a venically placed board with a landscape which includes an airiield. Around 1970, when the system design was frozen and the major components were ordered, the capability to generate 'landscapes' with computers was still in its infancy and certainly not suitable for application in a comprehensive research simulator system as envisaged by the NLR simulation group. The visual system was very useful in research concerned with such widely different subjects as take-off and landing procedures and the development of low altitude high speed flight control characteristics for fighter aircraft. 'Around 1970 it was felt that such a refinement was not necessary for ordinaly flight simulators as used by the airlines for pilot training But as the importance of training simulators and the demands for better quality increased, this type of motion system became also common for pilot training simuiators. For the second SIX degrees of freedom - motion system of NLR. the iirm Hydraudyne Systems & Engineering produced the motion system and platform, with technical advise from the Technical University Delft. Since that time a substantial number of motion systems was produced ior simulator manufacturers.

Tile moving base Flight Simulator with four degrees of freedom (Research Fligh? Simulator RFSi

The model landscape board with moving camera of the RFS

The outside view presented to ?hepilots of the landscape' board illuminated for simulation of the night situation

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Duai seat cockpit (transpon aircraf? configuration1 of the RFS

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The development of a research flight simulator proved to be a very challenging task. Although many components were obtained from vendors, there still was an enormous amount of work to be carried out in-house, particularly since the simulator incorporated many new features. For the validation of the simulator mathematical models of the DC-9 and tile Hawker Hunter laboratory aircraft were installed. Pilots of NLR and external pilots carried out the validation.

During more than 20 years of operation the facility has been used for several different research and development projects. NLR was also very fortunate to find a large number of civil airline and military pilots prepared and interested to panicipate in these programs. zyxwvutsrqponmlkjihgfedcbaZYXWVUT F-16 cockpit of the NSF

Moving base of the NSF

Artist view of the moving base Flight Simulator with six degrees of freedom (National Simulation Facdity, NSfi

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Examples of projects in which the flight simulator was engaged are:

'. Simulations

of MLS (Microwave Landing Systems) and related Air Traffic Control problems sponsored by the RLD of The Netherlands, Eurocontrol (the European organization concerned with air traffic control), the FAA (the US Federal Aviation Administration responsible for air traffic control) and research projects within the cooperation framework with DLR. A mathematical model of the Boeing-747 was used for many of those simulations. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDC

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Simulations in connection with the development of the Fokker 100 civil aircraft. Those sirnulations were obviously of a different nature. They were concerned with the flying characteristics and the development of the flight control systems of this aircraft and the development of syrnbology on the display screen ('the full glass cockpit').

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During the selection of a new fighter aircraft for the Royal Netherlands Air Force in the first half of the 1970's. the 'riding qualities' of the four competing aircraft types were investigated and particularly the F-I6 riding qualities were investigated with the NLR flight simulator. Later a complete mathematical model of the F-16 was implemented which was used in connection with the Air Force operations and also for accident investigations.

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Following this the simulator was engaged in an extensive research and development program of the Lavi aircraft of the Israel Aircraft Industry - IAl - and particularly the flight control laws for the flight control system, under development with the US company Kearfoot. This program was very demanding for the, very few, members of the NLR flight simulator staff, charged with several other tasks during this period. The final result and the experience gained proved to be extremely useful in the further development of the 'art' of flight simulation at NLR.

Following these experiences it became possible to define the next generation of research flight simulators: a new simulator with six degrees of freedom. This facility was developed into a 'National Simulation Facility', NSF.

The NLR Air Traffic Control Research Simulator NARSIM

The installation has a fully computer-generated visual system and several cockpits, including an F-I6 cockpit. At the time of writing this book the plans were to employ the installation for the further development of the F-I6 and to develop programs for low altitude high speed flight training, which became an important subject in the late 1380's when the aircraft noise associated with low altitude flight training became an important environmental problem in certain areas of Europe. The simulator will also be employed in research of Air Traffic Control and air routing around airports. The studies carried out during the last several years in connection with helicopter operations will also be continued with this simulator. Obviously the an of simulation has now progressed so far that for any new civil and militaiy aircraft development the installation will be of great use Air traffic simulation. As explained above the moving base flight simulator was used to carry out research in connection with the possible use of different approach and take-off procedures, mostly motivated by the increasing air traffic at several airports. A closely associated technical problem is

Derailed view of The Netherlands' en-route airsoace structure

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that of the air traffic control; the control of many aircraft approaching an airport in a given period of time and the control of many, civil and military, aircraft overflying a certain area simultaneously. NLR assisted the RLD and the industry (Signaall in this field over a period of many years. This led to the development of the NLR Air Traffic Control Research Simulator INARSIM) with which various ATC-scenarios can be studied.

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Currently developments have progressed to the point that the combination of an aircraft in the air (the Metro II laboratory aircraft), a laboratory air traffic simulator (NARSIMI and possibly the flight simulator will be coupled to create a 'laboratory environment' in which future Air Traffic Control scenarios can be studied.

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That could have been the title of this Chapter. Finally all that counts is the contribution to safe and effective flight. The process is complicated but there was never any doubt about the goals of NLR.

For this book the choice was made not to describe systematically the activities of all the Departments but to select certain topics. This Chapter is therefore not an account of all the achievements of the Flight Division. Some laboratories in other countries are organized differently in that often a Systems Division is incorporated dealing with the aircraft as a total system. At NLR this need did not arise since the laboratory seldom was involved directly in the development of a total aircraft system. That was and is the responsibility of the aircraft industry. Nevertheless in research related to civil and military aircraft operations all aspects of the system are often imponant. It is remarkable to note here that in the context of AGARD - basically an organization for exchange of information and cooperation in the area of aeronautical research - t h e total system aspects are usually assigned to only one of the nine AGARD Panels, namely the Flight Mechanics Panel. That is a reflection of the opinion of most people involved in aircraft research and development. The most successful aircraft designers do involve their test pilots in the design process. This does not mean the aerodynamicists, propulsion engineers. structural engineers, avionics engineers, etc., are less important in this process. The ideal chief designer combines all these aspects with those of economics, manufacturing and a multitude of other elements which together make a successful aircraft design.

There remained a keen interest a t NLL in the performance of aircraft engines and often aircraft operators were advised on the performance of aircraft engines. e.g. operating under various circumstances such as in tropical climates and at high altitudes. Engine Noise Measurements In 1929 the Engine Depaitment of the RSL started to develop methods for measuring noise. Although the external aircraft noise measured on the ground (flyover noise1 was not yet a problem, the internal cabin noise certainly was. The measurement techniques developed were reported and several comparative measurements were carried out, but it seems that around 1930 there were f e w attempts to reduce the internal noise level drastically. Much later, during the 1960's. engine noise became a major problem area in aeronautics and various activities were started at NLR to tackle this problem as is summarized in Chapter 11

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Example of calculated contours of constant noise nuisance levels around Schiphol Airporl

Models were developed to calculate the 'noise loading' around airports. Contours of constant noise loading ~a measure of the degree of nuisance experienced on the ground - were calculated for all airports, civil and military, in The Netherlands. Here the sound level, the duration and the time of the day are taken into account to arrive at a number which characterizes the integrated noise nuisance level.

Such contours are important for urban planning. With the computer programs developed for this purpose, predictions are made of the effects of different runway usage, projected new runways, the changing composition of aircraft types making use of a particular airport, etc. Over a period of years this model has been refined to such an extent that it can be reliably applied in city and airport planning. Models such as these can also he used to assess the effect of aircraft noise rulings which prohibit older, more noisy, aircraft from using a particular airport. Testing of Propeller Powered Aircraft Models At NLLiNLR as at other aeronautical laboratories - techniques were developed for wind tunnel testing of aircraft models with powered propellers. Small direct current electric motors were installed in the aircraft model and driven by a Ward-Leonard electric generator located outside the wind tunnel -converting alternating current to direct current. ~

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Wind tunnel test with eiectrically powered Model Engines of the Fokker F27, 1955

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Wind tunnel test with compressed air-driven Model Engines of the Fokker 50, 1983

More recently, as turbo-powered model engines became available - see below under Turbofan Engine Simulation propeller driven aircraft (models have also been supplied with turbo-powered model engines, driven by compressed air. 7he advantage is that they can deliver more power to the propellers for a given size of the model than electric motors.

Ramjet Engine Testing During the development in The Netherlands of the Kolibrie helicopter, (see Chapter 121, which was provided with ramjet engines at the rotor tips, various tests were carried out in a static test stand constructed a t the Noordoostpolder laboratory. The development of this helicopter was terminated at the end of the 1950's and the facility was used later for testing small model jet engines, including testing of exhaust noise suppressors. The ramjet engines at the tip of the rotor blades did introduce special problems such as the operation of the fuel system under the load of veiy high centrifugal forces and the problem of ingestion of the exhaust gases of one engine into the engine of the opposite blade. This called for an experi-

Test of the R

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mental investigation and a rotary test stand was built at the laboratory in Amsterdam. The noise was not acceptable to the surrounding community and the test stand was moved to the newly acquired laboratory site in the Noordoostpolder. There it was placed in the middle of the 200 HA site and it was surrounded by a wall for safety reasons and to reduce the noise.

The Rotary Jest Standat the Noordoostpoider in the mid-1950's

Jet Engine Exhaust Simulation The exhaust flow of let engines and rockets interacts with the external flow and greatly affects the performance. The mixing of the jet with the surrounding flow is characterized mainly by the ratio of the exhaust flow velocity to the surrounding flow velocity and the density ratio (and temperatures) of these two flow streams. The after-body drag of an aircraft with the exhaust a t the tail (e.g. a single engine fighter plane) can amount to as much as 20 to 50 percent of the total drag. In order to simulate the proper conditions in wind tunnel testing it is therefore necessary to duplicate not only the proper velocity ratio but also the proper density ratio. The latter can be achieved by heating the exhaust gas of the model engine. Another factor that plays a role in this is the ratio of the specific heat of the two gas streams. At NLR a jet simulation system was developed whereby the ratio of the temperatures and the ratio of specific heat are simulated by means of an H,O,-gas (hydrogen peroxide) generator. The liquid hydrogen peroxide is pumped to the engine model installed in the aircraft or rocket model to be tested. It flows through a small-mesh silver wire netting which acts as a catalyst and the hydrogen peroxide decomposes into water and oxygen while releasing heat. The gas, a mixture of superheated steam and oxygen simulates the hot exhaust gas of the engine. By varying the ratio of hydrogen peroxide and air flowing through the engine model exhaust gas temperatures between 225°C to 1000°C can be achieved. For obtaining higher temperatures, such as may be required for the simulation of rocket exhaust gases, NLR used hollow polyethylene cartridges through which hydrogen peroxide was fed. Temperatures up to 3000°C can then be achieved with ratios of specific heat close to those of that of rocket exhaust gases. The hydrogen peroxide installation was mounted on a trailer so that it could be used a t various wind tunnels in Amsterdam and in the Noordoostpolder.

The mobile Hydrogen Peroxide H107 instailation

Turbofan Engine Simulation In the 1970's high bypass engines were introduced for application in civil aircraft. These engines have a lower fuel consumption and the engine noise is greatly reduced compared to the previous generation of low bypass engines. The simulation of the flow around the larger diameter engines and the aircrait-engine combinations required new wind tunnel simulation techniques. In the USA small Turbine Powered Simulators - TPS - were developed. NLR and DNW purchased several of these model engines of different size and power. They are small turboian model engines where the fan is driven by a turbine, mounted inside the model engine. This turbine is in turn driven by high pressure air from a pressure vessel outside the wind tunnel and piped through the aircraft model to the model turbine. The emphasis in measurements on aircraft models with high bypass engines is often on the interference drag of the relatively large engines and the flow around the aircraft model, particuiarly the wing. In order to determine the thrust of these model engines under the correct operating conditions. a special calibration facility is required. This installation consists oi a tank which is evacualed and in which the model engine exhausts. The front of the engine is open to the ambient air and the pressure difference corresponds to the stagnation pressure of the air stream in the wind tunnel. The engine operates in the same way as when it is installed in the wind tunnel model, that is the turbine inside the engine is driven by compressed air. By carefuliy mounting the model engine on a balance and compensating for extraneous iorce effects, it is possible to calibrate the model engine lhrust to within a small fraction oi a percent. This TPS calibration installation was put into operation in 1982, and is used for calibration of model engines for the NLR wind tunnels and for the DNW.

There are only a limited number of similar calibration installations in the world. Accurate calibration of TPS engines proved to be quite complicated due to the difiiculty of carrying out accurate force measurements while high pressure air has to be ducted into the engine, the difficulty of simulating accurately the inlet flow conditions, etc. Compressor and Turbine Blade Testing The atmosphere in Western Europe and in The Netherlands in particular is rather corrosive. This is caused by a relatively high atmospheric humidity, moderate air temperatures, frequent rain, salt from the sea in the atmosphere (chloride-ions)and industrial air pollution, especially sulfur-dioxide. Through these factors the life-time of some engine components may be reduced by a faclor of two

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as compared with operating in an environment where these effects are of no importance. These effects, combined with the corrosive effects of the let combustion products on the turbine rotor and stator blades have led to the development of various coatings to protect the expensive blades.

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The 'Burner Rig' for testing Jet Engine Turbine Blades

In order to provide a realistic test environment a 'Burner Rig' was developed and put in operation by the Structures and Materials Division at NLR-NOP in 1975, in which turbine blades are exposed to hot exhaust gases produced by a let enqine combustion can. Controlled auanti. ties of contaminants are introduced in the hot gas stream. This installation was later replaced by a commercially available, more economical, combustion chamber especially designed for this type of testing. By moving the turbine blades in and out of the hot and cold gas stream - in a pre-programmed manner thermal cycling as occurs in reality can be simulated. The gas temperature is typically 1000°C. ~

A similar installation for testing compressor blades with temperatures up to 600°C was also built at the Structures and Materials Division. Here the gas is supplied by a centrifugal compressor and heated by a natural gas burner. With an electro-magnetic excitation device the blades can be subjected to fatigue tests at their natural frequency. Several test programs were carried out in these facilities in close international cooperation under the auspices of the Structures and Materials Panel of AGARD and of other international groups.

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(21 BLOCKTEMPERATURECONTROL 131 MECHANiCALFATiGUE

The 'Compressor Rig' for testing Jet Engine Coinoressor Blades

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The Hunter T Mk-7 Laboratory Aircraft, pacing a KLM DC-8 aircraft, 1974. The cone trailing the tail of the Hunter was used to measure the static oressure.

Tests on an early Bypass Engine Model in the High Speed Wind Tunnel HST. 1960

Other Activities During the last several decades NLR carried our many ad-hoc investigations associated with engine performance and operational problems. pafliculariy for the Royal Netherlands Air Force and the Royal Netherlands Navy. An interesting problem was to determine why some of the DC-8's of the KLM had a higher fuel consumption (up to 5%) than others. The major cause was finally traced to modifications which had been executed a t the rear end of the engine, causing flow separation. lr. J.P.K. Vleghert of the Flight Division of NLR came to that conclusion after photographing the behavioi of wool-tufts attached to the rear part of the engine during an uncomfortable airfreight flight from Amsterdam to Teheran, Such experimentation during a passenger flight might have been discomforting to the passengers! The DC-8 was also photographed from the NLR Hawker Hunter laboratory aircraft which was used as a pacer for speed caiihration.

During the period 1980-1987 specially prepared and instrumented turbine engines (Pratt & Whitney J57-P-lSW) were tested in eight different test bed and ground test facilities in five different countries. This very extensive program, under the auspices of AGARD's Propulsion and Eiiergetics Panel, resulted in an in-depth assessment of the quality of the engine test facilities and it formed the basis for improving the accuracy of turbine engine testing. Ir. Vleghert contributed to this program by heading an international group to assess the measurement uncertainties, [Ref. 401. zyxwvutsrqponmlkjihg

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The Materials Department was headed by Dr. li. L.J.G. van Ewijk from the start in 1919 till he retired from NLL in 1945. He was succeeded by l i . J.H. Palm and when Palm left NLL in 1950 the Materials Department was merged with the Structures Department. From 1919 structural analyses were carried out by li. C. Koning, who was also responsible for Aerodynamics. till lr. A. van d e i Neut came to work at the RSL in November 1928. Among the others w h o later joined him were Ir. F.J. Plantema, Ir. W.T. Koiter and Ing. J.H. Rondeel.’ The group was called: the Aircraft Department B with the task to provide the data of the structural part of aircraft for airworthiness certification. The Department also carried out many investigations related to aircraft accidents and incidents. When the Government Service RSL was converted into the Foundation NLL in 1937 the Aircraft Department B became the Structures Department, with Dr. li. A. van der Neut’ as the Chief till he became a full-time Professor at the Technical University Delft in 1945. His successor was li. F.J. Plantema. who had joined the RSL in 1934. Ir. Plantema advanced the state of knowledge of constructions made out of sandwich materials [ t w o thin sheets of a high strength material with a thick layer of a low density material, of relatively low strength, sandwiched between the t w o sheets), particularly for aircraft structures. Theoretical studies of sandwich constructions at NLL had started in 1943 and some of the results had been presented at the Vllth Congress for Applied Mechanics, London, 1949. He wrote his Doctoral dissertation in 1952 on the theory and experiments on the overall elastic stability of flat sandwich plates. Dr. Plantema summarized his work in 1966 in a book on sandwich construction, [Ref. 411. Dr. Plantema passed away untimely on 13 November 1966.

To complete the story of the organization: The Structures and Materials Division was moved from Amsterdam to the Noordoostpoldei in 1966. Around this time the laboratory was re-organized into the Divisions Fluid Dynamics, Flight, Structures and Materials, and Space - with effect from 1967.

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’lng. Rondeel started a t the RSL in 1931. When the Structures and Materials Division moved to the NOP in

1966 he stayed in Amsterdam and was responsible for the liaison with Fokker in connection with the structural testing o i the Fokker F28 Fellowship In 1969 he retired after more than 38 years of service When the RSL became the NLL in 1937, he was one of the iew employees who elected to remain a civil servant and so for 32 years he was employed by the Netherlands Depanment of Civil Aviation IRLDI but worked a t NLLiNLR. Van der Neut received his Doctor’s degree in 1932. HIS dissenation was on the problem of hucklmg of spherical shells. Prof. C.B. Biereno was his promotor.

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Prof. Dr. Ir. J. Schijve3 became Head of the Structures and Materials Division. In 1971 he divided the Division into four Departments: zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA 0

Loads;

* Structures; 61 0

Materials; Testing Facilities

This is on the one hand an expression of the distinctive disciplines with which the Division is occupied and on the other hand it expresses the close relations of these activities in aircraft reseaich 2nd development and also in aircraft operations. When Prof. Schijve became a full-time Professor at the Technical University Delft on 15 November 1973, he was succeeded by lr. H.P. van Leeuwen as Head of the Structures 2nd Materials Division. Dr. Van Leeuwen obtained his Doctor's degree in 1976 with a thesis on 'A Quantitative Analysis of Hydrogen-induced Cracking'. This work pertains particularly to the phenomenon of hydrogen embrittlement of high strength steels. His contributions, clarifying and quantifying these effects, had also applications outside aeronautics, e.g. for pressure vessels and piping. Dr. Van Leeuwen ietired on 1 August 1989 and Dr. li. G. Bartelds became his successor. At foreign - larger aerospace laboratories the research on structures (including loads) 2nd on materials is organized in separate Divisions or Departments. At NLR the combination of Structures and Materials has been maintained since 1950. A major reason was that the number of people in the Division was and still is - relatively small. It is about 10 percent of the total personnel of the Divisions of Fluid Dynamics, Flight, Structures and Materials, Space, and lnformatics together. This does not include the support activities of the Services, but as a first approximation that support is equally divided over the Divisions. As time progressed much of the research requested by the customers required inputs from all four Departments of the Division and with this combination it was possible to serve a variety of customers' with a relatively small group. This became even more important with the advent of research on composite structures - e.g. carbon fiber re-inforced plastics - where the properties of the material and the shape of the structure are closely linked and the optimization of the stiucture is dependent on inputs of all the Departments. So perhaps NLR is fortunate to have these Isubldisciplines represented in one Division of Structures and Materials. ~

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The facilities and accommodations of the Structures and Mateiials laboiatoiy at the RSL site at the Navy Yard in Amsterdam - 1919-1940 are shown in Chapter 3. After moving to the laboratory site Sloteiweg (now Anthony Fokkerweg) in Amsterdam and when planning the post-war expansions for the 1950's the intention was to construct a hall for full-scale testing a t Schiphol, jointly with the n e w Fokker aircraft plant. After the work stoppage of the expansions, 1949.1952. this plan was not realized. Finally, after the laboratory site at the Noordoostpolder (the NOP) had been acquired, 2 structural testing hall was built at the NOP. It was completed in 1960. The construction was similar to the local agricultural storage buildings.

3Prof Schijve had been employed at NLL since 1953 and had already made many valuable contributions related to mateiials research, research of structures, non-destructive testing and accident investigations. In 1964 he wrote his Doctoral thesis on the fatigue phenomenon in aluminum alloys. [Ref. 421. Praf 1. P. Jmgenburger was his promotor. In 1964 he was appointed part-time Professor of Aeronautical Engineering (Aircraft Mateiialsl at the Technical University Delft.

contractors (Chapter 231 about the effectiveness of the support rendered by NLR The response was veiy positive and for example the Head of Scientific Research of the Royal Netherlands Air Force stated invariably that the Structures and Materials Division was the most effective part of NLR as far as the support of the operations of the Air Force was concerned zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA

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The Structural Jesting Building a t tlie Noordoostpoider, 1960

Several years later, in 1966, a n e w combined laboratoly and office building was completed and the whole Structures and Materials Division moved to the NOP. During the following years the offices and laboratory space were expanded. The last major expansion included the addition of a composites laboratory which included an autoclave for the manufacture of test articles made of composite materials (Carbon Fiber Re-inforced Plastics) and an ultrasonic installation (C-Scan) for inspecting test articles for irregularities or flaws.

The laboratory was equipped with a variety of mechanical test installations including machines for servo~controiiedfatigue testing whereby the varying loads, as they occur during the service life of an aircraft. are applied.

Microscopic investigations are important to study the fracture surfaces. From such studies the cause of a fracture can often be determined and the propagation of cracks under varying loads can zyxwvutsrq

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An Electron Microscope for scanning the microstructure of surfaces o f metalaiioys lmagnification up to 1 millioni Fracture Surface photographed by an Electron Microscope, showing the growth of a fatigue crack under periodic loading

zy zyxwvutsrqp be studied. This is done with the aid 01 optical microscopes, transmission electronic microscopes, surface scanning reflection microscopes and X-ray diffraction and fluorescence machines.

In Chapter 3 an impression is given 01 the research on the wooden structures of wings and lhow this problem area was approached theoretically and with experiments. This included the contribution of the wooden (plywood1 skin to the strength of the wings. With the introduction of all-metal wings in the 1930s the idea of stressed skins became important. The wing structure was no longer composed 01 two spars (beams1 with heavy flanges. The function of the flanges were partially replaced by many stiffeneis relatively closely spaced, to stabilize the thin skin. This re-inforced skin largely took over the lunction of the flanges of the spars. The Douglas DC-2 was the first aircraft operating in The Netherlands in which these principles were applied.

The Netherlands' certilication authorities were laced with a new type of aircralt construction and Di. Van d e i Neut was the only person who could be consulted for this ceitilication. He had often critically examined stress calculations submitted by the aircraft industry for certilication. It was therefore not surprising that Plesman, the President of KLM, when tile first DC-2 was unloaded in 1934 a t the haibor of Rotterdam. snapped at Van der Neut: "Don't you dare touch it!" IReI. 281. This did not mean that Plesman did not appreciate Van der Neut's technical-scientilic capability, but he did not want any delays in getting this aircraft in operation for KLM. The RSL did contribute soon alterwards to this Douglas aircraft by locating the most critically stiessed parts, some 01 which were thought to be prone to fatigue due to stress concentrations. In January-February 1935 Di. Wolf1 and Dr. Van der Neut went to Inglewood, Calif., USA, and discussed their findings with representatives of the Western Office of the Department of Commerce, the Douglas Company, KLM and Fokker (Presumably the Fokker representative, lr. Van Meerten, participated since Fokker was European sales representative of Douglasl. This visit resulted in an agreement 'Structural changes in the DC-2 aiiplane made in order to satisly the requirements of the RSL 01 The Netherlands', [Rel. 431. Undoubtedly this exercise introduced the RSL very rapidly into aluminum aircraft structures and lrom then on much of the research was concerned with all-metal aiicralt. Dr. Van der Neut, who was then 27 years old, later recalled that the confrontation with the Douglas engineers was 01 great importance to his further work. For him it was the liist time he was conlronted with the 'New World' and although he was impressed, he was also critical and stayed in

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The Netherlands in spite of the fact that there were many opportunities to move to the USA. For The Netherlands this was fortunate: In 1945 he became the second Professor of Aeronautical Engineering at the Technical University Delft and his influence on the (post Second World War) generation of aeronautical engineering students till his retirement in 1973, was profound. After moving to Delft he kept contributing to NLR as an advisor, through specific projects such as the stress calculations for the High Speed Wind Tunnel, HST, and through his panicipation in the Scientific Committee NLRiNlVR.

The problem of metal fatigue can be defined as the failure of metal components subjected to many cyclic forces which are much smaller than the forces that would be required for a failure under a static loading. As early as 1839 Poncelet appears to have recognized the problem of metal fatigue, [Ref. 441. The phenomenon was studied extensively by those involved in railroad engineering and for a long time the criteria developed by the railroad engineer A. Wohler (1819-1914) were used to design parts subjected to cyclic loadings. In aeronautics the introduction of aluminum as a construction material gave a n e w dimension to metal fatigue research. Around 1950 NLL carried out many fatigue investigations - i.a. various aluminum alloys and bonded aluminum structures - in close cooperation with the aircraft industry and material manufacturers. This researcli drew international attention.

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In M a y 1951 NLL (Plantemai and Fokker (Van Beek) proposed to the RAE (UKi and to the FFA ISwedenl to cooperate in the area of fatigue research and a first meeting was held at Cranfield (UK).Plantema was appointed Coordinator. The cooperation was extended to include laboratories in Belgium and Switzerland and on 25-26 September 1952 a conference was held at NLL in which representatives of these five countries participated. It constituted the foundation of the lnternational Committee on Aeronautical Fatigue, ICAF. Later institutes of other countries joined the Committee. Dr. 11. F.J. Plantema was tile General Secretary till his untimely death at the age of 55 in 1966. To honor his contribution to ICAF. the Committee instituted the F.J. Plantema Memorial Lecture to be given by a distinguished engineering scientist a t the bi-annual ICAF Congresses. Prof. Schijve, Plantema's successor as Head of the Structures and Materials Division a t NLR, became the National Delegate to ICAF in 1967 and since 1979 he serves a s General Secretary. Aeronautical fatigue really came to the fore-ground after the accidents with the De Havilland Comet. This first operational', four-engined, jet transport aircraft received its Airworthiness Certificate on 22 January 1952 and on 2 May 1952 the Comet left London for its first operational flight to Johannesburg, South Africa. The following quotation, [Ref. 461, summarized the events: -"The subsequent story o f the Comet is weii-known. The rapid spread o f j e t airliner routes was halted in the Spring o f 1954,when following unexplained accidents over the Mediterranean the Comets were grounded. The subsequent investigation b y the Royal Aircraft Establishment, Farnborough, discovered the cause o f the disasters - metal fatigue and as a result changed the entire nature of large l e t airliner manufacture for the rest of the world to follow. The Comet design was revised .... and entered on 4 October 1958 the first regular trans-Atlantic j e t airliner service .... Britain's overall lead in j e t airliner development had been overfaken b y the US with the development of tile Boeing 707and Douglas DC-8.... " ~

5

The De Havilland Comet made its first flight on 27 July 1949 but accordlng to iRef 451 it rose only a few feet above the runway to become the first commercial jet to fly. Only two weeks later, on 10 August 1949, Canada's Jetliner. the AVRO C-102,flew over an hour up to an altitude of 13,000 feet. On 18 April 1950 the Jetliner delivered the first jet mail between Toronto and New York Llke the De Havilland Comet it also did not - but for different reasons become a commercial success. ~

zyxwvutsrqp zyxwvutsrqp Following the tragic events with the Comet, NLR gained considerable expeiience by fatigue testing of 13 full-scale wing centei section panels of the Fokker F27.

Fatfgue tests on Fokker F27 Wing Panels around 1960. partially sponsored b y the USAF

The system loracquisition data olAircraft Loadsduringactual /light operations

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Clearly, fatigue of aircraft structures is of great importance to flight safety and the subject tianscends peisonal, company and national interests. Therefore the participants in ICAF regularly exchanged reports among each other and at the Congresses national ieviews of the results of reseaich were presented.

8-747 FATIGUE DATA ACQUISITION

The recording and t h e analysis of loads o n aircraft structures duiing actual operations provides the input foi research on fatigue of metals and structures. At NLR activities in this aiea can be tiaced back to the time of the pioneering flights of KLM's DC-2 and DC-3's f i o m Amsterdam to Batavia iJakarta.lndonesiai duiing the 1930's. when gust loads were recorded and finally analyzed during the Second World War period. The measuiements were reiined and the statistical analysis of the data resulted in standard load spectra for designing airciaft and testing components and full-scale aircraft stiuctures. The load spectra contain the different loads and the fiequency of occurrence of the loads that can be expected during tile operational life of an aiicraft. It was found that the sequence of the loads o i difierent magnitudes is important for the fatigue life of aircraft structures. Much o i this work during the last decades took place in inteinational groups in which the Stiuctuies and Materials Panel of AGARD plays an impoitant role.

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Several programs were initiated to develop standard load spectra for civil aircraft, iighters and helicopters. The load spectra were used for many detail tests o i components, joints, notched parts and for comdete structures.

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Computer-generated modei of a criticaiiy stressed p a n - a lug connecting the wing to the fuselage o f the NF-5 Fighter Aircraft used in the laboratory for service-iife assessment o f the NF-5

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SERVICE~LIFE ASSESSMENT

An example, developed a t NLR during the 1970's. is shown in the Figure above. A structural component was subjected to the loads as experienced during flight operations of an NF-5 fighter. The test specimen was designed and shaped such that it experienced a t the critical points the same stresses as occurred in the actual component of the aircraft. In turn, when the fatigue propenies of critical parts of an aircraft are known. it is possible t o determine the remaining life of a paiticular aircraft. For the Royal Netherlands Air Force extensive programs were run to determine the remaining life-time of fighter aircraft using recorded data from operational aircraft - as time progressed and the mission profile changed. Often aircraft experience loads of a magnitude and frequency different from the design loads used during the design of the aircraft. This is particularly true for military aircraft which are in service for a long-time period when often the standard maneuvers change, while also the external loads carried by the aircraft change during its life-time. ~

Similarly the service-life of civil aircraft was extended far beyond the design-life as it was originally conceived. The airlines were then confronted with the problem of 'aging aircraft'. This called for detailed analysis of the flight history of aircraft and during the 1980's a world wide activity developed to determine standards for safe life and to develop reliable inspection methods and also acceptable reDair methods.

The full-scale testing of aircraft structures is basically the task of the aircraft industry developing the aircraft. The designer has to prove the validity of the structural design. Although numerical stress calculations are now very elaborate and are of great assistance in designing efficient structures, final full-scale testing is still carried out by the aircraft industry except perhaps when it concerns derivatives of proven structures. Since the Second World War NLR has obtained contracts from NlVR to carry out a part of the structural testing of Fokker aircraft. This participation in full-scale structural test programs is important for the laboratory since NLR is then directly confronted with the problems of testing full-scale structures. The benefits for the laboratory are that it offers an opportunity to obtain first hand experience with the possibilities and limitations of current test techniques and from it ideas for further research result. NLR also cooperated with Fokker in specifying the load spectra and the loading, recording and data handling equipment for the full-scale tests at Fokker.

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BASIC DESIGNS

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1975

Supercritical Wing investigations in the High Speed Wind Tunnel HSI. Period

1975-1981

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zyxwvutsrqpon Investigations on Flap Systems Parallel to this research in the HST, experiments were carried out in the Low Speed Wind Tunnel LST 3 x 2 M', on supercritical wings with flap systems designed by Fokker. It appeared that aircraft with supercritical wings and properly designed flap systems would have considerably better takeoff and landing characteristics than aircraft with 'conventionally' designed wings.

Instationary Flow / Vibration Research Starting in 1975 research was carried out on the effect of instationary air forces on supercritical wings and on the vibrational behavior of these wings. Initially investigations of the aerodynamic characteristics of oscillating supercritical airfoils and airfoils with oscillating flaps were carried out in the Pilot Tunnel of the HST (PHST) and then a method was developed to predict the instationary air forces on supercritical wings and its effects on elastic wings. The design method was verified by flutter test in the HST with a speciaily designed half-model of a supercritical wing-body configuration. Basic Research / Feed-Back Already starting in 1973 and parallel to this Project-Oriented Research, financed by the NIVR, several more basic research projects were carried out. These projects were also largely supported by NIVR through its 'General Research Program'. They concerned the development of computer programs for wings at transonic speed which could replace Some of the semi-empirical elements in the design procedure and methods for the calculation of the instationary flow over wings.

Development (1979 -1984) Development o f t h e F29 (1979-1980) During 1978-1979 Fokker started the development of a new civil airliner, first announced as the FZ8-Super and later called F29, as the design evolved further. The experimental work at NLR was determined to a very large extent by the specific needs of the Fokker design team.

zyxwvuts zyxwvut zyxwvutsrqpo zy Development of the MDF 100 (1980-1982) During the early 1980'sFokker and McDonnell-Douglas cooperated in a joint design project which became known as the MDF 100. This led towards a further intensification of the aerodynamic design activities. Although it was a joint project in which the best engineering capabilities ot the partners were combined, it also had an element of competition since the partners were faced in detail with each other's design capabilities. In February 1982 the project was canceled for other than purely technical reasons. The Fokker/NLR-team certainly had gained contidence through this confrontation. For the FokkeriNLR-team there was an important change in that the engines of the MDF 100 were planned under the wing instead ot at the rear of the fuselage as had been the case since the F28 and the subsequent Fokker design studies.

Model of the Fokker F29rnounted ii? the test section of the High Speed Wind Tunnel HST

Development of the Fokker 100 (1983-1984) The supercritical wing technology and the aerodynamic computational capability developed at NLR since the 1960's had been applied in several European and American colitracts and in various projects carried out for the Royal Netherlands Air Force, but the Fokker 100 was a case in which all the

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Test of a inodel of the Fokker 100 in the High Speed Wind Tuiinel HST

experience gained was applied to a civil airliner. The design of the Fokker 100 wing was constrained by certain production and economical considerations. One of the constraints was that the design of the wing torsion box Ithe center part of the wing) of the F28 had to be retained. External form changes of the leading edge and trailing edge of the wing and of the wing tip could be accommodated. With the design methods available and the experience gained in the F29/MDF 100 projects, it was possible to design in a very short time an optimal supercritical winR within the constraints set bv the Fokker designers

The expenditures at NLR related to the development of Supercritical Wing Technology

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NLR : IN-HOUSERESEARCHICOV SUBSIDY1

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PROJECT ORIENTED RESEARCH PHASE

DEVELOPMENT PHASE

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The Cost of this Innovation Process The annual expenditures a t NLR involved in "Supercritical Wing Technology" during a period of over twenty years are as shown. (Quotation marks are used here since the cost involve besides the 'supercritical' part the development of computer programs, the manufacture of wind tunnel models and the wind tunnel tests). The first phase of the process - Basic Research, 1960.1972 - w a s funded a t a level of DGL. 300,000 per year till 1968 and DGL. 400,000 per year till 1974.

The Project-Oriented Research was funded at a average level of DGL. 3,750,000 during the period of 1973-1978. The higher cost level was associated with the use of more expensive equipment (wind tunnels, computers) and the design and manufacture of wind tiinnel models. During the Development Phase zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA 1979-1984 the expenditures increased very rapidly t o the level of DGL. 10 million per year. During that five year period Fokkei went through the evolution of the designs of tlie F29, the MDF 100 and finally the Fokker 100.Had the design goal in 1980 been the Fokker 100, the total expenditures would probably not have been much less.

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I:iri itel As a second example of NLR contributions to theoretical and experimental aerodynamics the solution of the Flutter problem is selected. Flutter is an aeio-elastic phenomenon in which the elastic and the inertial forces interact unfavorably with the unsteady aerodynamic forces generated by the oscillatory motion of the structure itself. Flutter occurs when the oscillatory motion is reinforced and this can lead to destruction of the structure. The elastic and the ineitial forces are determined by the properties of the aircraft or p a r k of the aircraft such as wings, ailerons, flaps and tail surfaces. That 18 the structural p a r t The aerodynamic forces due to the oscillatory motion form the aerodynamic pan and so flutter is an aero-elastic phenomenon. In general t w o or more structural vibration modes are involved - for instance bending and torsion of a wing which, under the influence of the unsteady aerodynamic forces, interact with each other such that the vibrating structure extracts energy from the passing air stream. This leads to a progressive increase of the amplitude of the vibration and this may lead to a structural failure. ~

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Flutter played an important role in t h e development of t h e airplane o r rather it was a major hurdle t o be overcome by m a n y aircraft designers, often without t h e designers being aware o f the phenomenon. Collar contributed t h e failure of S.P. Langley's flying machine (launched w i t h a catapult f r o m a house-boat on t h e Potomac River, USA) t o aero-elastic problems: ''...It seems, therefore, ihat, but for aero-etasiicity, Langiey might have displaced the Wright brothers from their place in hisfor,..", [Ref. 531. Note that Mr. Langley's attempt t o fly his airplane took place o n 8 December 1903, nine days before t h e Wright brothers' first powered flight. In 1916 F.W. Lanchester et al. repotted on t h e problems of a Handley Page biplane bomber, where a combination o f vibrations of t h e tail plane with t h e torsional vibrations o f t h e fuselage caused t h e fuselage t o twist as m u c h as 15 degrees, [Ref. 541. They probably carried o u t t h e first analytical investigations o f aero-elastic stability.

'iSee page 941 The story of the Van Berkel aircraft 1s sum^ marized in lRef 71. During the first World War the purchase of aircraft from abroad was vew difficult and so the Government looked for natio~ nal companies to manufacture aircraft. One of those was, the 'N.V. Maatschappil tot vewaardtging van snijmachines "01gens Van Berkels Patent' iCompany for the manufacturThe Van Berkel WB aircraft rilevanBerke/ WA aircraft ing of food cutting machines according to Van Berkels' Patent1 a t Rotterdam. The export of cutting machines and commercial weighing scales Was restricted due to the war and since this company had an excellent reputation. the Government awarded i l a contract to produce aircraft for the Navy. On 18 April a German aircraft, a Hansa-BrandenburgW-12, was captured after having made an emergency landing near the isle of Rottuni. in the North of The Netherlands. The aircraft was still in perfect condition and Van Berkel was asked to copy this aircraft. That IS how the Van Berkel WA model was created The WB model was definitely a different aircraft as indicated above. Both models served with the Navy till 1933 in The Netherlands and in the Netherlands East lndies In the early 1920'sVan Berkel terminated the aircraft division due to lack of orders and presumably since its 'core business' was more profitable.

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The experin-rental arrangement of 2 Wing Aileron Wind Tunnel Model

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In The Netherlands, in the early 1920's violent unstable oscillations were observed on the wing of a Van Berkel WB semi-cantilever monoplane of the Royal Netherlands Navy. The Navy had purchased six aircraft of this monoplane equipped with floats: the aircraft were delivered in 1921 and 1922. Earlier Van Berkel had received an order from the Navy for some 40 biplane aircraft, designated Van Berkel WA. which were delivered between 1919 and 1924. The introduction of a single wing version (the WB) with a 360 HP Rolls Royce engine compared to a 180 HP Mercedes engine on the WA, changed the aircraft to such an extent that flutter conditions Ir. Von Baumhauer and Ir. Koning of the RSL investigated various possible causes for the problem. A wind tunnel test was carried out on a half wing with an aileron and coupled oscillations were observed. This two degrees of freedom system (bending of the wing and rotation of the aileron) showed unstable oscillations due to aerodynamic forces. It was shown that the problem could be eliminated by moving tile center of gravity of the aileron towards the center of rotation (through mass balancing of the aileron). In the first instance wing torsion was neglected in the experiment and also in the analysis. The Figures show the principle of the experimental set-up and the results of the calculations for this two-degrees of freedom vibrational svstem. for the case of an unbalanced aileron and a balanced aileron, [Ref. 551. Although this was not the first time flutter had been observed and studied, it was certainly the most effective - and elegant analysis and experimental investigation of aerodynamic flutter.

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The oscillalions of the Wing-Aileron system. wilhoutand with Aileron Mass Balancing

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The above referenced report of Von Baumhauer and Koning was dated August 1923. Unforiunately this did not mean that from then on all aircraft in The Netherlands were free of flutter. Flutter accidents occurred when aircraft were flown under extreme conditions such as on 15 January 1932 when a Fokker D.Wl ended in a crash after the pilot carried out a series of tests to determine whether or not wing vibrations would occur in a steep dive. From the brief RSL report it does not appear that the pilot was aware of the flutter phenomenon and Von Baumhauer, after having reviewed the evidence of the accident, had to recommend to provide the ailerons with balance weights [Ref. 561, some ten years after he and Koning had carried out their pioneering investigations! The basic mechanism of flutter was now uncovered. This laid the foundation for an enormously fruitful series of investigations and a school of experts on unsteady aerodynamics and flutter

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developed at NLLiNLR. Major contributions were made by Timman, Van de Vooren, Greidanus, Bergh, Tijdeman, Zwaan and several others. In 1956 Dr. lr. A.I. van de Vooren of NLL became a part-time Professor of Unsteady Aerodynamics a t the Technical University Delft before he became a full-time Professor of Applied Mathematics at the University Groningen, September 1958. lr. H. Bergh continued the lectures at Delft and later a special Chair on the subject of Aero-Elasticity was created, first occupied by Prof. lr. H. Bergh and from 1985 bv Prof. lr. R.J. Zwaan of NLR.

When high speed aerodynamics became more important at NLR the emphasis shifted over the years via the calculation of the aerodynamic coefficients of airfoils in oscillatory motions and many intricate experiments, to transonic phenomena. Detailed investigations of oscillatory motions of shock waves over airfoil surfaces a t transonic speeds were carried out and methods were developed to determine the safe boundaries of the combination of speed and angle of attack, [Ref. 571'. A very fruitful area of application of unsteady aerodynamics is the investigation of flutter behavior of fighter aircraft with external stores. During the life-time of these aircraft many different stores and combinations of stores under the wings and the fuselage are used. Each configuration has to he cleared for safe operation, that is the range of operation (speed, altitude, angle of attack. mass, etc.). A summary of more recent investigations carried out by NLR on several aircraft of the Royal Netherlands Air Force and foreign Air Forces, [Ref. 581 shows that there was and still is a need for careful testing whenever the external configuration of a fighter aircraft is changed.

zyxwvutsrqp An additional problem is that high performance fighter aircraft carry out 'high g' maneuvers at transonic speed (high accelerations due to rather abrupt maneuvers) causing separations of the air flow

Example o f a Fighter Aircraft carrying a varjerv of stores

When Prof. Dr. lr. H. Tildeman who worked at NLR for 25 years before he became Professor of Technical Mechanics a t the University Twente in 1986 - defended his Doctoral dissertation at the Technical University Delft he posed the proposition'-The prominent position NLR has achieved in the field of aero~elasticityis for a substantial pan due to the fact that the Aero-elasticity Depanment is pan of the Aerodynamics Division and not of the Structures and Materials Division, as in most other aeronautical laboratories. zyxwvutsrqponmlkjihgfedcba ~

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over the wing. This type of flow causes aircraft buffet and in some cases transonic nonlinear oscillations of limited amplitude. This is known as Limit Cycle Oscillations ILCO). These oscillations may affect the performance of the aircraft and of the pilot. It is therefore necessary to determine the allowable limits of the amplitude and frequency of these oscillations and the limits of operation of the aircraft with various external stores combinations. During the 1980's NLR (in cooperation with the USAF and General Dynamics) carried out a series of experiments on an oscillating delta type wing with sharp leading edges and strakes. Detailed pressure and force measurements were made and with the aid of a stroboscopic laser light sheet the behavior of voitices, emanating from the leading edges and strakes was studied so that comparisons could be made with numerical calculations, both a t low speed and at high speed. The knowledge and experience gained at NLR with aircraft aeio-elasticity has been applied over the years to a large number of other engineering structures, including many bridges, tall structures such as chimneys, and offshore oil and gas platforms.

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Mode/ o f a wing for investigations of Limit Cycie Osciliations

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Over a period of many decades theoretical analysis and wind tunnel tests on scale models have been made for all n e w major bridges in The Netherlands and also in some other countries. Combined with the measurement of the vibration frequencies and amplitudes on the full-scale bridges, a considerable body of knowledge and experience has been built up in this field.

Visualization o f flow on upper wing surface in the High Speed Wind Junnei H S J

Isobar pattern on upper wing surface calcuiated by N L R b Euler method on the Supercomputer of NLR

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Wind tunnel model of a Bridge

For the t h i r d example of NLR contributions to aerodynamics the design of a keel for a sailboat is chosen. In fact it is not aerodynamics but hydrodynamics. Although the NLR contribution was rather limited in terms of man-hours it is an interesting example of applying knowledge and experience gained in aeronautics to non-aeronautical problems.

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Example ofa Computer Grid used to calculate the hydrodynamic forces on the Keel of the

'AUSTRALIA /I'

In 1983 the 'AUSTRALIA /Ii, owned by Alan Boiid, w o n the America's Cup ii? the 12-meter yacht race at Newport, R.I., USA. This race, organized by the N e w York Yacht Club, had always been w o n by Americans, since its very beginning, 132 years earlier.

The success of the AUSTRALIA I1 was attributed to a n e w and revolutionary keel design. The keel was provided with end plates or 'wings', giving the yacht considerably better side force and drag characteristics than yachts with conventional keels. It resembled an inverted T-tail as used on some types of airplanes. The main keel is inversely tapered with little or no sweep, a rounded iorward tip and trapezoidal. downward sloping winglets at the rear half of the foot or 'tip' of the keel. In an integrated ship design the concept results in a more slender hull with a smaller wetted area, [Ref. 591.

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This type of winged keel was conceived in 1980 by lr. J.W. Slooff, w h o was then Chief of the Theoretical Aerodynamics Department at NLR and a cruising yachtsman.' He had been developing computational methods and computer programs for aircraft design purposes. In fact his Department contributed greatly to and worked closely with the Fokker design team in several aircraft design studies and research projects, some of which involving winglets small surfaces mounted at the tip of a wing. He also cooperated with Slooff was appointed part-time Professor of Aerodynamics at the Technical University Delft and Head of the NLR Fluid Dynamics Division in 1986

'I1

97

The 'AUSTRALIA 11

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The Keel of the 'AUSTRALIA 11'

Dr. P. van Ossanen of the Netherlands Ship Model Basin, MARIN, at Wageningen. in a Study Group for Advanced Ship Design for the Royal Netherlands Navy. It was in the Spring of 1981 when Ben Lexcen, Mr. Bond's designer, was supervising model tests at MARIN, when the concept of the winged keel was discussed with him. The result was that NLR received a contract to carry out computer simulations of the flow over a number of hull-keel configurations using the NLR lifting potential flow computer programs. The calculations confirmed that the side force and resistance characteristics of the winged keels were superior to those of conventional keels. This was verified by model tests in the towing tank of MARIN in the summer of 1981 After sizing and fine-tuning the design of the AUSTRALIA I1 the final result was that in 1983 the America's Cup went to Australia. Early in 1983 rumors circulated that the Austraiians had a revolutionary design with a 'Dutch connection' and MARIN and NLR were approached by competitors with offers for contracts. However the agreement with the Bond Syndicate was that no information would be released and that similar work would not be carried out for possible competitors till after the race. It was also questioned whether this was an original Australian design, which seemed to be part of the rules of the New York Yacht Club. Unlike 'normal' sailboat races of a cenain class, where all panicipating boats must have the same dimensions, the rules of the N e w York Yacht Club for the 12-meter racing yachts stipulated a certain number of design parameters which can be varied according t o a certain formula. The parameters relate to length and beam of the hull, the depth of the keel, the displacement, the mast height, the sail area, etc. The yachts are specifically designed for the race: specified trajectory and location with an expected wind force, sea state, wave height and patterns.

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The impact on the design practice of yacht designers was enormous. During the preparations for the 1987 race in Australia. 17 syndicates all resorted to computer modeling and analysis. The team of the STARS & STRIPES, the winner of the 1987 America's Cup competition. wrote, [Ref. 601: -"It was our ambition first to duplicate and then to exceed the AUSTRALIA I1 achievement...... Although we dreamed up and modeled several other keel appendages, none proved to be as promising as 2 refinement of Lexcen's design.... " What more can one desire than such praise from a competitor!

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There seem to be endless possibilities for the usage of wind tunnels. In Chapter 3 some examples of non-aeronautical tests were given. This type of activity continued to this day. In some areas a considerable expertise was built up, e.g. the simulation of tlie wind climate around high-rise buildings 2nd built-up urban areas, and the smaller of the two low speed tunnels in Anisterdam, the LST 1.5x1.5 M' with an open test section was used almost exclusively for this type of testing. After the termination of the two low speed wind tunnels in Amsterdam and the transfer of all experimental low speed aerodynamics to the NOP, the new L S T 3 x 2 . 2 5 M' in the NOP continued to carry out non-aeronautical testing and the DNW was used for larger scale (and more expensive) tests. The photographs present typical nonaeronautical tests.

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Jan de Vries, World Champion Motorcycle 5Occ. in tlie Low Speed Wind Tunnel LST. 1971

Model of a Train being prepared for tests in the Low Speed Wind Tunnel LST 3 x 2 25 M

Model for an Urban Development Plan in the Low Speed V l h d Tunnel LST 1Kurhaus Sclievenrngeni

The NLR (Erdnianni Supersonic Nozzle Design

adjusted. (The 'throat' is the narrowest pan of the nozzle; it is where the Mach Number becomes one and after the throat the flow expands into the supersonic regime.) For a larger Mach Number range this still required many adjustments to achieve a reasonable Mach Number distribution across the test section. Dr. Erdmann devised a system whereby the additional corrections were achieved by means of a series of pie-adjustable 'cross members' and a llmited number of jacks. [Ref. 611. The Mach Number uniformity was better than 0.0015 M over a Mach Number range of 1.2 to 4.0 in the 1.2 x 1.2 M: facility, the SST, and in the smaller 0.27 xO.27 M: facility, the CSST, up to M=G.O.The C stands for continuous: with the large compressor and air storage vessel this smaller tunnel can run almost continuously.

zyxwvutsrqp The large blow-down supersonic facility. the SST, became operational in 1963, four years after the transonic facility, the High Speed Wind Tunnel, HST.

The Supersonic Wind Tunnel SST with the Continuous Supersonic Wind Tunnel CSST in the rear

A model of an ELDO Launcher

iii

the Supersonic Wind Tunnel SST

A conibination of a Herrnes Re entry Vehicle and an Ariane 5 Launcher inodel in the Supersonic Wind Tunnel SST

All this finally resulted in a capability with which The Netherlands through NLLiNLR was in a position to contribute substantially to the development of the ELDO series of launchers and later to the development of the Ariane rocket launchers and the Hermes vehicle. The SST was designed such that the same model (same size) could be used in the HST and in the SST. Thus it is possible to use the same model for testing continuously from subsonic speeds up to Mach Number 4 with an overlap around Mach Number 1.2. This feature proved to be very effective; not only for the ELDO and Ariane rocket series but even more so for the French-Briiish Concorde, various fighter aircraft and missiles. zyxwvutsrqponmlkjihgfedcbaZ

Schlieren photograph of the cornbination Herrnes/Ariane 5 at Mach Number2

The flow quality of both the HST and the SST was high by any standard. Also much effort was spent to increase the productivity of the two tunnels and the data handling equipment was periodically upgraded. NLR was proud of tile fact that the Concorde aerodynamic data obtained in the HST-SST wind tunnels compared very well with flight data and that the tunnels were often used for the final check of the aerodynamic data to confirm aerodynamic data of the Concorde obtained elsewhere. Only fifteen Concorde supersonic airliners were produced in spite of the fact that it was technically a very successful project. The main reasons for this limited production were the drastic increase in fuel costs and the increased concern about the environmental effects: pollution, noise, supersonic bang, possible effects on the ozone layer, etc. These developments were not foreseen in the 1960's when the aircraft was conceived. Nevertheless there is now a considerable experience in supersonic airline operation: close to twenty years of trans-Atlantic operation of 150,000 passengers per year. A successor with a reasonable price per passenger-kilometer would find a growing market! It is not surprising then that major aircraft manufacturers (Aerospatiale, Boeing. British Aerospace, Deutsche Aerospace-DASA and McDonnell Douglas) have been studying for some time the possibility to design and develop the next generation of supersonic airliners. Some of the maior aerospace research laboratories also have active research programs to tackle the problems mentioned above.

It is conceivable that the SST, still one of the best supersonic wind tunnels, will play a role in the development of the next generation of supersonic airliners around the turn of the century. zyxwvutsrqponmlkjihg

102

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The French-British Concorde tested in the Suoersonic Wmd runnel SST

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In this Chapter only the name of Dr. Erdmann was mentioned in connection with the development of the SST, but it must be clear that many experts contributed to this achievement. Dr. trdmann who l?ad been a part-time Professor at the Technical University Delft since 1960, became a fulltime Professor of High Speed Aerodynamics at Delft in 1969 till he retired in 1983.

Pilot tests in the CSST of an insert for the SST to achieve high Reynolds Numbers at transonic speed

During the 1970's. when testing at high Reynolds Numbers at transonic speed became more and more important, 1. J.P. Hartzuiker developed the idea of placing an insert in the SST test section. It was a kind of supersonic inlet with transonic flow inside. The advantage of the scheme was that a liigh stagnation pressure land thus a high Reynolds Number) could be achieved, the pressure level of the air storage vessel being 40 atm. Pilot tests were carried out in the smaller supersonic blow-down tunnel, the CSST, and it was shown that this was a feasible idea. However due to technical complications and high pressure of other (contract) work, this insert was never developed for the SST and so it remained an interesting idea.

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103

--L

The Acoustic Flow Duct Facility for measuring the noise attenuation characteristics of

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A n instrumented Engine Inlet o f the Fokker 100 for flight testing

in which the material was embedded in a wall along which the intake flow was simulated. At the downstream end of this flow duct a powerful noise source (powerful loudspeakers) was located, simulating the fan noise of the engine. By measuring the sound level before and after the ponion of the wall in which the test article (sound absorbing liner1 was mounted an impression could be gained of the effectiveness of the liner material to suppress the fan noise.

With this facility it became possible to compare effectively the acoustic absorption properties of various liner materials. This capability also stimulated the research into the mechanism of sound absorption. One result was the development by the industry of a n e w sound absorption material, Perfolin. Having .gained experience in determining the acoustic properties of liner material, NLR was in a position to contribute to a series of flight tests carried out by Fokker on the engine inlet duct - made by Grumman - f o r the Fokker 100. Contributions to the understanding of propeller noise were made at NLR as early as 30 years ago when a theory of propeller noise was presented by Van de Vooren and Zandbergen, [Ref. 621. More recently Schulten of NLR provided a theoretical background for fan noise calculations, [Ref. 631. A basic experiment with a specially designed model, [Ref. 641, was used to provide experimental data. The theoretical and experimental capability was gainfully applied to civil aircraft development and in the support of tests carried out in the DNW. With these aero-acoustic studies and experiments, a considerable experience had been gained in this field by the mid1970's. It is therefore not surprising that it was clear to the aerodynamicists that any future large scale facility for aircraft model testing should be suitable for aero-acoustic experiments. The facility under consideration at NLR was a large

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Cross-sectional view of fan noise wind tunnel model

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ROTOR SPINNING DIRECTION

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PRISSURETRANSOUCIRS INSiRUMENiEO VANE

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VAN1 WITH STATIC PRISSURETAPS

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Pressure measurement stations at stator vane

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A wind tunnel model for basic studies of the Fan Noise of a High By-pass Jet Engine

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DIRECTION O f ROD MOVEMENT

VANE LOWIR SIDE

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low speed wind tunnel with a test section cross-sectional area of 8 x 6 M'. At the NOP a wooden 1 : I 0 scale model of the design had been built. That pilot facility came into operation in 1972 and by 1974 the investigations had shown that this design resulted in a very high flow quality. In the UK, Dr. John Williams of the Royal Aircraft Establishment, RAE, had been studying the noise problem in wind tunnels for quite some time and he had generated ideas to reduce the background noise in wind tunnels. In 1976 he summarized the state-of-the-art in [Ref. 651. Based on his work and that of others it was then decided to make the LST 8 x 6 suitable for aereacoustic testing of aircraft and engine models. This tunnel design was the basis for the German-Dutch Wind Tunnel, the DNW. which was designed in detail and constructed during the period of 1976-1980. The acoustic features of the DNW proved to be extremely valuable, (Chapter 18).

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The ori'yiri of tlie Iielicopter ririylit be tmced back to the niicierit Cliiriese, wliose 'flyiris tops' were recorded as early as tlie 4th Cerihrry H.C., [Re6 661. 117 ii sketch rrinrle

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Leorimrio dfl Virici ir7b-udircerl (I liftiriy screw, which is liow 1-egflrrferlfls tlie oriyirr of the ~iiorleiiihelicopter.

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I t was however riot till n1011iiil 1900 tliot the fir-stntternpt.5 were riinde

these ideiis iritu n flyirig

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riot till the 1940's

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lielicopters b e c m i i ~

pmctical flyirig rnnchbres. This Clinpter rlenls with the iiivolvernerit of the Inborntoiy

the rleveloprnerit arid npplic(itiuris of helicopters iri vririoirs ways,

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The Van Baurnhauer Helicopter When the RSL was founded lr. A.G. von Baumhauer 11891-19391 was a designer with the aircraft factory Trornpenburg. He joined the RSL in 1921 and when the RSL became the foundation NLL in 1937 he moved to the Netherlands Department of Civil Aviation, RLD. At RSL he headed for some time the Engine Department and also became Deputy Director. On 18 March 1939 lr. Von Baumhauer and Mr. P. Guilonard. Technical Director of the KLM, died in an accident with a Boeing 307 Stratoliner while on a test flight near Seattle. USA. lr. Van Baumhauer was an exceptional engineer and scientist. While a student at the Technical University Delft he became interested in aeronautics and worked a t the small aerodynamics laboratory of Mr. A.P. Kapteyn, [Ref. 81 and Chapter 2. When he came to the RSL he was 30 years old and he had accumulated a considerable aircraft design experience with the aircraft divisions of the factories Trompenburg and Van Berkel. In 1920 he had already sketched the first outline of a helicopter in his notebooks. He was a typical inventor, often rapidly shifting his attention and he did not always conform to the requirements of the organization, which made it sometimes difficult for his colleagues. One of his colleagues at that time, Prof. Van der Maas. remarked to the author that lr. Von Baumhauer never wrote proper reports - a strict requirement at the RSL. That may have been true from the point of view of the RSL, but Von Baumhauer did keep a very extensive diary, starting on 15 March 1906, when he was only 14 years old, [Ref. 671. During the period 1924-1930, while employed at the RSL, Ir. Von Baumhauer experimented with a helicopter of his own design. In 1922 the British Air Ministry had offered a prize of €50,000 for the design and construction of a helicopter' with demanding requirements, including vertical autorotation and landing from a height of 500 feet. Apparently this stimulated the start of the Society 'De Nederlandsche Helicoptere' of which lr. Von Baumhauer became the technical advisor. The Society received support from industry and government. The construction of the helicopter started in the Fall of 1924 and in June 1925 the first tests began at Soesterberg. Von Baumhauer's helicopter (total weight 1195 KG), lifted off the ground for the first time on 17 September 1925, and early in the Spring of 1926 Capt. Van Heyst of the Army Air Force, LVA, flew the helicopter for five minutes.

'It is reported that the British Air Ministly withdrew this prize in 1926 since there had been too many accidents in trying to meet the requirements.

107

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The experimental Von Baumhauer Helicopter, Period 1924 -1930

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The 15.4 M diameter main rotor of the helicopter had t w o blades with a large chord (1.2 M at the root). Tlie rotor blades were constructed of four spars and many ribs and each blade weighed 54 KG. The rotor was provided with a collective pitch control and a swash-plate for cyclic pitch control, much the same as present day helicopters. Power was initially provided with a 160 HP rotary Ober Ursal engine, later replaced by a 200 HP Bentley Rotary BR2. The power was transmitted to the rotor through a worm-wheel gearing arrangement. The main rotor turned at the rather low speed of 100 RPM and the tip speed of the blades was correspondingly low at less than 300 KMiHR.

Another impoiiant novelty was the introduction of a tail rotor, driven by first a 40 HP Anzani motor and later by an 80 HP rotary Thulin motor. There were five vertical tail surfaces and three horizontal tail surfaces operating in the slip stream of the tail rotor, providing directional and longitudinal control respectively. All-in-all the Von Baumhauer helicopter resembled the helicopters of to-day. However it was not very reliable mechanically and tlie machine was heavy and complicated through the use of a separate tail rotor engine.

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Tlie Voii Baunihatier Helicopter after tlie crash on 29August 1930

From October 1926 the tests took place at Schiphol Airport, and several RSL employees participated in the flight testing. Many flights were made by the engineer-pilot lr. J.C.G. Grase of the RSL (see Cliapter 6).There were several structural failures due to excessive vibrations and after each flight repairs had to made It is reported that in 1930 Jhr. P.J. Six flew freely over the whole of Schiphol Airport, albeit in a somewhat uncontrolled manner. Unfortunately on 29 August 1930, a blade failure occurred a f e w meter above the ground. The pilot was unharmed but the helicopter was totally lost. After the crash the project was terminated due to lack of funds. With this helicopter with collective pitch control, the swash-plate for cyclic pitch control and the tail rotor valuable contributions were made to the development of the helicopter of to-day.

Rotor Aerodynamics Shoitly after the Second World War theie was a great inteiest in helicopteis. lr. J. Meyei Drees, who had already started studies of the flow through rotors while working towards his degree (he graduated Cum Laude in 19481 at the Technical University Delft in Prof. Burgers' laboratory, came to NLL in 1949. He completed there a series of wind tunnel tests on a simple rotor model with smoke visualization. Through these experiments he gained an excellent understanding of the flow through rotors with and without vertical and horizontal speed and also of the transition of powered flight to the state of auto-rotation.

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A sample of the fiow through a Helicopter Rotor

lr. Meyei Diees analyzed the longitudinal and lateral non-uniform distribution of the induced velocity in the rotor plane. He set up a schematic and a manageable simplification of the fixed and fiee line voflices of the blades. This led to a calculation method to take into account the uneven distiibution of the induced velocity encountered by a blade during rotation. His papei describing this woik was awarded the La Cierva Memorial Piize in 1949 for the hest author under the age of 35 iMeyei Diees was 26):it was published in the Journal of the Helicopter Association of Great Biitain, [Ref. 681.

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Another contribution to the understanding of rotor aerodynamics was made by Piof. R . Timman, at that time employed in the Fluttei Department of NLL, when he analyzed the unsteady aerodynamic lift on rotoi blades, in paiticular as affected by the free vortices shed by the blades at eailier rotations below the rotor plane, [Ref. 691. The result, in the form of a modified Theodorsen function, was useful in explaining certain flutter regimes that had been observed. Theodorsen's work was related to piopelleis. A 16 m m movie was made at NLL of the flow through a rotor, showing the changes in flow pattein with changes in forwaid and vertical speed and under auto-rotation conditions. Many copies of this film were used in vaiious countries to gain a better understanding of the flow thiough helicoptei rotors.

The 'Kolibrie' A second helicopter development in The Netherlands took place during the period 1950-1960 undei the technical leadeiship of Ir. G.F. Verhage and li. J. Meyei Drees, iwho went to Bell Helicopters in 1959 wheie he later became Vice President of Technology) with Mr. R.J. van Harien (later Deputy Director KLM Helicopters) as the test pilot. A more complete stoiy is given in [Ref. 701. The initiative came from a group who formed the Foundation for Development and Construction of an Experimental Helicoptei (Stichting tot Ontwikkeling en Bouw van een Experimenteel Hefschioefvliegtuig, SOBEH) in 1951. After a n experimental period the Netherlands Helicopter Industry, (Nederlandse Helikopter lndustrie NHII, was formed in 1955 in which the companies Aviolanda (fuselage), Kromhout irotor head and engines) and Fokker (rotor blades) participated.

In 1954 the research related to helicopters justified the formation of a Helicopter Department a t NLL, headed by lr. L.R. Lucassen? There were now several helicopter activities in which the NLL became involved.

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The Rotary Test Stand at NLR Amsterdam

The Kolibrie had a number of novel features. The two rotor blades had ramjet engines at the tip and the blades were self-adjusting. In 1948 lr. Verhage. employed by the P n , showed theoretically how a blade with torsionally flexible pockets could lead to low induced power required. by striving towards a uniform induced velocity through the rotor plane. (The idea was based on the fact that a uniform induced velocity along the span of a wing results in a minimum induced drag for a given lift condition.]

The NLL built a rotary test stand for the ramjet tip engines. This test stand was located at the laboratory at Amsterdam. The complaints of the neighborhood about the noise were one reason to accelerate the search for new premises, (Chapter 261. That test stand was the first facility to become operational at the NOP in 1958. Another facility was erected to study the combustion in the ramjet. NLL was very inuch involved in the development of this helicopter through analysis, experiments and of course also through the fact that some of the NLL personnel participated directly in the project development group.

The Kolibrie Helicopter

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The Kolibrie had some unusual characteristics. Since ?he power was provided by ?he tip ramjets, leaving no reaction torque at the fuselage, only a small tail rotor was required. The high kinetic energy of the rotor made it possible for the helicopter to take-off and land safely within seconds in the event of enaine failure durina take-off. The 'unsafe' altitude

motor was required to produce the initial velocity for the ramjet eiigines to work A small series of the Kolibrie was built The applications were finally mostly in the agricultural sector, e g crop spraying Helicopters on ships An interesting aspect of helicopter operations is the problem of the qualification of the ship-helicopter combination. The problem is to determine the safe operating limits and the procedures for specific ship-helicopter combinations a t various wind and sea state conditions. NLR developed qualification methods, in close cooperation with the Royal Netherlands Navy. Starting with takeoff and landing tests on land, under various weather conditions, the qualification tests have to be carried out with helicopters a t sea under various sea states, wind force and wind directions. Usually this type of operation is much more complicated than landing on and take-off from land or even from an oil platform in

'In 1943 lr. Lucassen was the Delft.

first to receive the Diploma of Aeronautical Engineer at the Technical University

the open sea. Apart from the fact that the ship motion in a storm makes the operation more difficult, there is also the problem of the 'wind climate' on a ship, that is the large-scale turbulence caused by the superstructure of the ship. This wind climate on a ship is determined in a wind tunnel using scale models of the ship. This capability to determine the safe operating limits, built up with the assistance of the Navy, has been applied for the qualification of several helicopter-ship combinations for Navies of many countries. Typical operating limits for a particular combination are indicated in the Figures below, [Ref. 71 and 721.

The Operating Limits of a Helicopter-Ship combination for take-off and landing during shore-based operations and at sea

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SHIP INDICATED RELATIVE WIND SPEED ktl

PORT 1 609

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Other Helicopter activities Dr. J.P. Jones, Technical Director and Chief Engineer of Westland Helicopters once said that helicopters weie perfect vibration machines. They were very noisy machines and aerodynamics, apart from the aerodynamics of the rotoi, seemed of little importance to the designers of helicopters. Most helicopters were developed without any wind tunnel test during a period when the designers of aircraft already paid much attention to the external shape of their aircraft. But during the last twenty years, as the speed of helicopters was increased, this seems to have changed.

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Aerodynamic testing of the fuselage of the NH-90 Helicopter in the Low Speed Wind Tunnel LST

A mock-up of the NH-90Heiicooter

The NH-90 After an extensive series of studies and evaluation of several available and planned helicopters, the Governments of Germany, France, Italy and The Netherlands decided to undertake the development of a helicopter for the Navies and the Armies, mainly for tiansportation of troops and equipment. For this helicopter an initial requirement of over 700 has been identified. Apart from aerodynamic model testing NLR contiibuted to the development of this helicopter by assisting the Netherlands industrial participants (Fokker, DAF-SP) in the project team. The expeiience gained in evaluating heiicopter operations under difficult circumstances piovided a valuable basis for participation in the NH-90 pioject.

Rotor Noise At the instigation of the US Army a very extensive series of experimental investigations was carried out in the 1980's in the DNW. The aim was to study the noise produced by helicopter blades. The DNW, with its unique acoustic testing capabilities, was the ideal facility to carry out such investigations. The program was carried out by the US Army, NASA, and several American helicopter companies. DNW was strongly supported by the DLR Helicopter Group of Braunschweig. NLR engineers contiibuted through project support to DNW. This extensive international program definitely established the value of the aero-acoustic testing in wind tunnels.

A noise test on a rotor and tailroto,r combination of a Helicopter in the German.-Dutch Wind Tunnel DNW

In several countries free flight model testing had been used to study aerodynamics and stability and control characteristics with the aid of free flight models, launched by rockets. Paiticularly at transonic and supersonic speeds there was a need for reliable data which could not (yet) be obtained in wind tunnels. Another motivation for pursuing this technique was to gain practical experience in launching rockets and in guidance and control techniques.

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During 1954 some fife flight models were launched by NLL with boosters made available by the Commission for Experimental Testing of the Army Kommissie van Proefneniing'). The launchings took place at the North Sea coast near Petten, in the Province Noord-Holland. The flights took place at night with mndels illuminated with flares and tracking was done with optical cameras. The first models fired were simple bodies of revolution of the shape of the NACA R M - I 0 model. This model was adopted by AGARD as a standard for testing in wind tunnels and data were being collected from various wind tunnels and from free flight tests. The drag coefficients in tile Mach Number range of 0.9-1.5 obtained from these first free flight tests compared reasonably well with published data. Encouraged by these results the technique was developed further.

The Rocket Launch installation at the beach

11.3

,

zyxwvutsrqpo The free flight model activities started a t the laboratory in Amsterdam but soon after 1957. when the new laboratory in the Noordoostpolder began to take shape, the activities were moved to the NOP.

The Mobfle Rocket Launcher of NLR

Par? of the Mobile Ground Equipment

During the following years more elaborate models were built, which were provided with programmed control surfaces and telemetry for on-board

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When the models became more sophisticated The Flying Models were and costly it was decided to develop a pararecovered by helicopter chute recovery system which had the addifrom the mud-flats tional advantage that malfunctions could also at low tide zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA be better analyzed. A semi-permanent launch site was acquired at the North of the Isle of Texel. Permission was obtained to use an area with a diameter of about 17 KM, East of Texel, as a test range. This area, consisting of tidal mud flats whlch become largely dry during low tide, was very suitable for recovering both the models and the boosters During this development there was a close cooperation with the industry (Fokker, Philips, the munitions and gun powder industry) and the Air Force and the Army. Much of the development was sponsored by the NIV.

I

By 1965 the need for free flight model testing at transonic and low supersonic speed had diminished. The quality of wind tunnel testing techniques had improved considerably and, world wide, free flight model testing was only used for special tests such as ballistic tests around Mach Number 20. The last launching by NLR took place in June 1966. With the experience of more than eighty launches and the development of the equipment an inteiesting capability had been built up. There was no immediate interest and support in The Netherlands to develop guided missile techniques, for which the experience would have provided a good background.

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The development had been funded partially out of the NLR subsidy and by the NIV. A few tests were carried out f o i customers but with other higher national priorities this was not sufficient to maintain the capability in the long run. The experience gained did provide a basis for participation in various tasks in the international context of ELDO the European Launchei Development Organization. ~

Following this period 11954.1966) of free flight model testing an attempt was also made to apply the knowledge and experience gained very directly. A feasibility study was carried out for a twostage sounding rocket for high altitude research with a very small impact dispersion. Theie was a desire to launch high altitude research rockets in areas where only a limited area for impact on the ground is available. It was argued that the major factor contributing to the impact dispersion of vertically launched and spinning sounding rockets is the influence of the wind and some form of compensation for the deviations from the nominal flight path due to the wind had to be piovided.

A two-stage iocket system was designed f o i a small impact area of 17 KM diameter. This was the test range of NLR East of the Island of Texel. Based on this impact area an apogee of 150 KM was chosen for a system with horizontal velocity control. The rocket had a total mass of 285 KG and a gross payload of 33 KG (net payload 15 KG). The first stage was unguided and designed such that it would always impact within the designated area. The second stage would only be ignited aftei it had been determined that the horizontal velocity was within certain boundaiies. If this were not the case or if during the sustained flight of the second stage a failure of a vital component would occur, a safety system (air brakes on the second stage) would be activated so that the rocket would impact in the designated area. The second stage was controlled in such a way that during the powered flight - up to an altitude of 30 KM -the horizontal velocity component had to stay within certain, safe, boundaries. The position and velocity of the rocket were to be measured with a tracking system and the horizontal velocity would be continuously compared with the desired horizontal velocity. The effect of the wind on the impact dispersion was thus compensated during this controlled part of the flight. It was shown that for such a guided sounding iocket the radius of the aiea in which the impact occurs with a probability of one million-to-one was 6.3 KM as compared to 21 KM for attitude stabilized rockets and 63 KM f o i unguided, uncontrolled rockets.

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Sketch of a guided Sounding Rocket

115

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The projected impact area of the guided Sounding Rocket at the Test Range a t Texel

The systems study was carried out in the period 1967-1969 when there was an interest in high altitude sounding rockets with small impact dispersions. They were of interest even for the rocket launching base Kiruna in the North of Sweden, an area with a very low population density. The Committee for Geophysics and Space Research of the Royal Netherlands Academy of Sciences (Geofysica en Ruimte Onderzoek Commissie, GROC, van de Koninklijke Nederlandse Akademie voor Wetenschappen, KNAW) gave partial financial support to the feasibility study of this system. The study included a market survey, carried out with the Space Division of Fokker. and potential partners from Germany and Sweden. Unfortunately the market for sounding rockets had stabilized and no definite development plans materialized for this interesting idea which was basically developed by lr. G. Boersma, [Ref. 731, w h o worked at the Space Division of NLR. Elements of this idea were applied later in other sounding rocket systems.

A comprehensive international sounding rocket program was planned to collect data on the earth's atmosphere. The USA program included the launch of a satellite for which a US Navy proposal, the Vanguard, was chosen. The USSR, participating in the program, surprised the world by launching the lirst artificial earih satellite sputnik 1 on 4 October 1957, exactly 40 years after the beginning of the Communist Revolution. The impact of this event on the world was enormous.

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Although the USA responded rapidly by launching the Vanguard within a l e w months, the USSR seemed to be well ahead of the rest of the world. Only t w o years later in 1959 again on 4 October the USSR launched a spacecralt (Luna 3) to orbit the moon and it transmitted the lirst pictures 01 the far side of the moon. The USA set up a broad space program and much of the Western World prolited l r o m it. The rest of the story is well known. The USA organized a great space program. culminating in the first manned landing of Apollo 11 on the moon on 20 July 1969.

Much of the technology l o r space flight was available, parricularly through the development programs 01 guided rockets and ballistic missiles. There had been a great interest in space flight in many countries but outside the military there were no organized space programs. The contributions of The Netherlands were very modest': there was no industrial rocket activity.

'One notewonhv cantiibution was Prof. Dr. ~

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lr. J M J Kooy's book which he wrote with Prof. J.W H. W e n bogaari in 1946: 'Balhstics of the future'. This elaborate work on space mechanics served as a standard space flight dynamics textbook in many countries in the period after the Second World War This book was written for the most part during World War l l when Prof. Kooy observed the launchings of the V-2 rockets near his home in The Hague. During many years he contributed to the space flight literature. ,.a. the stability of lunar orbits. and he contributed to the lnterna~ tional Astronautical Federation. the IAF, as Chairman of the Netherlands Astronautical Society.

However at the universities there were several very active groups 01 astronomers interested in employing the n e w technical means which were becoming available through the development of space flight technology. On 2 March 1960 the Royal Netherlands Academy of Sciences - t h e KNAW - formed a Committee lor Geophysics and Space Research, the GROC', which was to coordinate the space research carried out by the astronomers in The Netherlands. Through this Committee The Netherlands was represented internationally and this Committee also had the task to manage the government funding lor space research carried out by the universities. The GROC consisted mainly 01 the Astronomy Working Groups of: a the University Utrecht (Solar and Stellar Space Research

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* the University Leiden Cosmic Rays under

van de Hulst), Prof. Dr. H.C. the University Groningen (Photometry under Prof. Dr. J. Borgnian) and a the Working Group on Satellite Geodesy of the Technical University Delft (under Prof. li. G.J. Biuinsi.

'This Committee operated vet? successfully and managed. amongst others. all the aspects of the instrument development and the scientific experiments of the ANS and the IRAS satellites mentioned in this chapter Prof. Dr. H C. van de Hulst of the University Leiden was its Chairman till the Committee was replaced by the Space Research Organization of the Netherlands - SRON a on 10 June 1983.

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The GROC Working Groups participated in several rocket and balloon campaigns and flew experiments in American (NASA1 and European (ESRO1 satellites. The instruments were designed and developed by the university laboratories with assistance of the industry and other technological laboratories.

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In 1960 several European countries, among which The Netherlands, decided to iorm the European Space Research Organization - ESRO - t o carry out space research by means of high altitude rockets and satellites. ESRO became effective in 1964 and through this organization the Netherlands' astronomers were able to participate in several projects.

In the period 1960-1961 the UK started to discuss with France the possibility to develop a satellite launching system in Europe. The UK had decided to stop the development of the (military1 strategic rocket the 'Blue Streak. The Blue Streak was proposed as the first stage o i a three-stage rocket to be launched irom Woomera, Australia. In February 1961 an agreement was reached and a year later, April 1962, seven countries signed a convention to design, construct and launch rockets for spacecrait. The new organization was called ELDO, European Launcher Development Organization. There was a global division of work:

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: t h e Blue Streak (first stage), guidance equipment; : the Coralie (second stage). already under development; 0 Germany :third stage, still to be developed; :t Italy : experimental satellite; 0 Belgium : ground guidance station, various equipment items; 0 Australia : launching facilities at Woomera; : ,The Netherlands : the development and manufacture o i telemetiy equipment, program units and ground installations (Philips), systems testing of the attitude reference system and later the inenial guidance system (NLRI. The UK

c3 France

NLR also carried out a large part of the aerodynamic wind tunnel testing and the analysis of aercdynamic data.

An experiment in the High Speed Wind Tunnel HST to determine the effects o f high ground winds on ELDO and Ariane Launchers

A major task of NLR was to carry out ground testing of the Attitude Reference and Programme Unit - ARPU and to develop the protocols for the launching of the rockets. This ARPU had a gyroscopically stabilized platform providing a reference frame from which the attitude of the rocket was derived. ~

The ground testing system, located at NLRNOP, consisted of a hydraulically controlled rocking table with three degrees of motion on which the reference unit was mounted. Thus the rotational motions of the rocket were simulated. The hydraulic cylinders, actuating the motion of the platform, were controlled by an analog computer on which the equations of motion and the characteristics of the rocket steering mechanism were simulated, The signals from the reference platform on the rocking table were fed back to the analog computer. The reference platform was placed in a closed loop. It was thus possible to simulate a complete launch and to carry out the testing at a systems level. In later versions of the ELDO rockets the gyroscopically stabilized platform was replaced by an inertial system using accelerometers. For this inertial system NLR also carried out the systems testing before shipment to the launching site. The inertial sensors, very sensitive accelerometers, were provided with signals derived from the analog computations, to simulate the accelerations that would be sensed during an actual flight.

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Laboratory test on a stabilized Attitude Reference Platform Unit of an ELDO Launcher

It is interesting to note here that, at that time, the speed of digital computers was not fast enough to process the equations of motion and the control equations in real time. Initially fully analog computation was used, later a hybrid (analog-digital]. but a fully digital computer could not cope with the real time requirements. For the last ELDO flights the launching site was moved from Woomera (Australia)to Kourou (French Guyana1 near the equator, favorably located for launching satellites into a geostationary orbit. NLR employees also panicipated in the testing before launch and in the actual launching procedure. The design and operation of this test system was a very useful experience for the laboratory. Unfortunately, although the guidance system worked perfectly during all ELDO launches, during the period of 1962-1973 no fully successful launch was achieved. This is not the place to analyze the reasons why this experiment in international cooperation was not successful.3 but a major reason was undoubtedly that the panicipating countries acted quite independently, the central management was weak and there had not been a joint systems study. The development of various versions of the launchers, the Europa I, /I and 111, was continued till 1 May 1973 when it was decided definitely to terminate the activities. However for NLR: The experience gained and the laboratory facilities for guidance and control testing laid the foundation for the participation in many ESA satellite projects, usually under contract from a (foreign) main contractor.

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3A first attempt to analyze the failure of ELDO is made m [Ref. 741

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Other organizations in Europe had similar experiences. Apparently ELDO was an (expensive)experiinent in international cooperation that did not work out too well but from which valuable lessons were learned. At the initiative of France the development of the Ariane launcher was started, and in 1972 it was decided to form the European Space Agency - ESA, combining the activities of the former ESRO and ELDO organizations. During tile ELDOiESRO period NLR carried out several other interesting tasks. One of these was a full mission analysis for the projected ELDO-PAS satellite (Perigee-Apogee Satellite). This was a system which would carry a payload, launched from Kouiou near the equator, into an elliptical orbit with the apogee, the highest point, at the altitude for a geostationary orbit from where the satellite would be injected into a geostationary orbit. This was a useful experience when later NLR was given the task of the ground operations of the ANS. Fokker, Philips and NLR jointly carried out the task to develop the attitude control system, including the sensors, for the ELDO-PAS satellite under contract from an Italian consortium which was to develop the satellite. Although this satellite was also canceled when the ELDO operations were terminated, the project did provide valuable experience for the industry and NLR for the development of the first Netherlands satellite. the ANS.

The Astroiioniical

Netlieriands Sateiiite,

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In 1966 representatives of Fokker and Philips presented a proposal to the Minister of Economic Affairs for the development of an astronomical satellite. The proposal was tile result of a close cooperation between the industry and t w o of the GROC Working Groups: the Kapteijn Observatory of the University Groningen and the Laboraton/ for Space Research of the University Utrecht. The Dutch astronomers had taken advantage of flight opportunities on American (NASA) and European IESRO) satellites, but their scientific standing and their ambitions exceeded the limited opportunities. The ANS was to make a complete survey of ultra violet and X-ray sources in the sky. For this the satellite had to be placed in a special near-polar, so-called sun-synchronous, orbit. By a judicial choice of the orbital parameters the plane of the satellite can be made to rotate at the rate of one degree per day, making use of the oblationes of the eaith. The satellite can then almost continuously be exposed to the sun and the telescopes in the satellite, when always pointing outward, will have viewed the whole sky after 6 months.

zyxwvu zyxwvuts zy The ANS prolect was approved in early 1969. The industrial consonium Fokker-Philips obtained the cooperation of General Electric, USA, as an advisor. The ANS project was presented to NASA and NASA offered to launch the satellite with a Scout rocket from the Western Test Range. NASA also sponsored an additional experiment from the Massachusetts Institute of Technology, MIT, Cambridge. Mass. for incorporation in the satellite.

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Tile overall program management was entrusted to NlVR. It acted as the official representative of the Netherlands Government and concluded the contracts with the industry and the agreements with the American oartner.

The satellite was unique in that it employed for the first time an on-board computer which could be programmed from the ground. Twice a day the data collected were transmitted to the Operations Center and also twice a day the computer was loaded with a new observation program.

SCHEOULE

OETLRMINATION

MONITORING

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OPERATION PROGRAM GENERATION

EVALUATION

The major task of NLR in the development and operation of this satellite was to develop and test the computer programs for the ground operations, the software for the execution of the scientific measurements, and the programs to control the on-board computer. Finally software was developed to translate the observations into useful astronomical data. The ground operation took place a t the European Space Operation Centre, ESOC, Darmstadt, Germany. A team of 12 experts was involved. This team was stationed at Darmstadt from the middle of 1973 till the end of the operation.

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TARGET LIST

1

ORBITAL DATA

The ANS satellite was launched by NASA with a Scout rocket from the Western Test Range, California, on 30 August 1974 and was kept in operation till 12 December 1975. It was turned on again during a brief period, 1 March 1976 19 April 1976, to observe some special X-ray sources.

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HISTORY EVALUATION

EXPERIMENTORS PROCESSINGCENTER

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Diagram of the ANS Orbital Operations

The NLR crew operating tlie ANS SateSre froin the European Space Operations Centre iESOCl at Darmstadt, Germany

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Static test of the Sandwichconstruction of the frame oi ANS Sateliite

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The development and operation of the ANS satellite was extremely successful. The teams paiticipating were small compared to international standards. The participants were very capable and enthusiastic, the lines of communications were short and there was a minimum of 'red tape'. The total expenditures on the Netherlands side were DGL. 81.5 million, including DGL. 1 6 million paid by the industry and excluding DGL. 12 million born by the experimenters for their instruments. These amounts are given here because for many involved in space activities they were so unbelievably low for the development of such an advanced system. The ANS satellite was technically very advanced as is evident from the following data: Height Width Depth Mass breakdown Instruments Structure Attitude Control System Power Supply On-board Computer Telecommunication System Remainder Total

123 61 144 73

CM CM (solar panels folded) CM (solar panels deployed) CM

42 3 KG 40 3 KG 146KG 105KG 7 8 KG 3 5 KG 21 0 KG -__ 140OKG

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Sensors:

13 in all (coarse. intermediate and fine solar sensors down to 0.01' accuracy, star trackers (Plumbicon), magnetometersl

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Actuators:

yo-yo system for de-spinning. reaction wheels, magnetic coils

On-board Computer: Mass 7.8 KG Power consumption a Watt Task: data storage and execution of 12 hours observation program attitude control data handling

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Apart from the fact that the ANS project provided the astronomers wlth a wealth of data, it 'qualified' the industry as full fledged spacecraft developers and indeed it did help to acquire several interesting contracts. The problem of the relatively small size of the contribution of The Netherlands in the European context remained and it did not lead towards contracts in which the Dutch industry was given the overall system responsibility as was the case in the ANS project. It was therefore not surprising that proposals were made for a second national satellite. Again the astronomical community of The Netherlands and the industry proposed a satellite, now of a much larger size than the ANS.

The lnfra-Red Astronomical Satellite IRAS - w a s a cooperative effoit of The Netherlands, the USA and the UK. The dans of the Dutch astronomers to suivey the sky for infra-red sources resulted in the design of the IRAS satellite by a consortium of Fokker and HSA (Signaall - a division of the Philips Company where Philips had concentrated its space activities. This design was presented to NASA. In a similar way as with the ANS satellite the plans were merged with American plans into the IRAS satellite. This satellite, which was much larger than the ANS (mass of 1080 KG as compared to 140 KG for the ANS), was launched by NASA - on 26 January 1983 - w i t h a Delta rocket from the Western Test Range, California, USA, as the ANS, in a near-polar sunsynchronous orbit. ~

The Netherlands contribution included the systems design, manufacturing of the structure, integration and a large part of the instrumentation. The USA contributed a major pan: the liquid helium cooled (at 4'Kelvin = -269°C) part of the infrared telescope. The operation of the IRAS was terminated on 22 November 1983, when the helium was fully used. The satellite was also operated from a sun-synchronous earth orbit (near polar) and it was designed to survey the complete sky in six months, the orbital plane rotating one degree per day. It more than accomplished its mission. The IRAS Ground Operations took place from the UK. under the responsibility of NLR and in close cooperation with the Rutherford Appleton Laboratory, at Chilton in England. The lnfra-Red Astronomical Satellite, lRAS

The contributions of NLR to this most successful satellite project included a variety of tasks such as:

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testing of the Attitude Control System in the laboratory, the integration and systems responsibility for the Ground Check-out System and assistance in testing of the electrical systems, the Ground Operations and its preparations, the development of Data Reduction Systems for the enormous stream of data, in close cooperation with the University Groningen.

The final results were compiled in the IRAS catalogue which provided basic information taking astronomers many years to analyze.

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IRAS was a much larger project than the ANS satellite and several more companies and organizations in The Netherlands contributed to the development of this satellite. Also the contribution of NASA was much larger, not in the least due to the large cryogenic vessel containing the infrared telescope.

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After the successful completion of this mission several more studies were carried out for application satellites in which The Netherlands would have overall systems responsibility. These included a study together with Indonesia for a remote sensing satellite specially designed for tropical conditions. But although the industry - and NLR and other laboratories in The Netherlands - did obtain many more highly interesting research and development contracts, mostly from ESA, a n e w 'national' satellite project did not appear feasible.

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Nevertheless, the t w o 'national' satellite projects. the ANS and the IRAS. had provided the industry. and also NLR, with a good background for future research and development in space technology. Testing the Attitude Control System o f IRAS at NLR

For NLR the participation in these t w o satellite projects also resulted in a solid basis for the development of several other information systems, (see Chapter 161.

Fluid iiyriainics and Heat '1i.ansport in Space The advent of the NASA Space Shuttle Transportation system and the European participation with the Spacelab created the opportunity for scientists of the ESA countries to prepare experiments under near zero-gravity conditions. There are several groups in The Netherlands participating in this program, e.g. in the ;area of biology, physiology, metallurgy. The Spacelab is essentially a laboratory, built for ESA by the European industry, which can be mounted in the NASA Shuttle vehicles. The original idea was that ESA would regularly provide (a f e w time3 per year) Spacelabs, fully instiumented t o carry out a series of experiments in space, and that NASA would fly the Spacelab with American and European astronauts performing experiments. Unfortunately, for various reasons, only a f e w Spacelab flights have been carried out. NLR carried out experiments on the behavior of fluids in partially filled containers. The first preliminary experiments were carried out during parabolic flights with the Hawker Hunter laboratory aircraft but there it was only possible to achieve a period of about 15 seconds under '0-gravity' conditions. These experiments were later complemented by participation in 'zero-g' flights organized by ESA in a Caravelle and an American KC-130.

Fluid in a container under Weightless Conditions during a zero-g flight with the Hunter Laboratory Aircraft

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The Dutch €SA Astronaut Dr. Wubbo Ockels carrying out an experim e n t in Spacelab with the Fluid Containers of Dr. Vreeburg of NLR

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During the first operational flight of the NASA Space Shuttle ISTS 51 in November 1982, a small demonstration model of the NLR experiment was carried during that flight. In November 1983 (launch date 28 November, flight duration 10 days) the NLR experiment was carried in the first Spacelab flight and again in the first German (Dli Spacelab flight in November 1985' (launch date 30 October, flight duration 7 days). During these flights the NLR experimenter. Dr. lr. J.P.J. Vreeburg. interacted with the Dutch astronaut Dr. W.J. Ockels' and the German astronaut Dr. U. Merbold via a N connection with the ground station. The experiments were of great importance to refine the theoretical work of Dr. A.E. Veltman and others of NLR on the behavior of fluid under 0-gravity conditions. In preparation of other Shuttle flights NLR participated in the design of a Fluid Physics Module. Also preliminaly experiments during the ballistic part of the flight with ESA high altitude rockets and a proposal and a design for a so-called 'Wet Satellite' were made.

Mock-up of an experiment with a Two-Phase System for heat transpoit to b e carried out in Smcelab

Another aspect of the behavior of fluids under zero-gravity conditions is the transport of heat in pipes filled with vapor and fluid. Through the mechanism of vaporization on one end and condensation on the other end of a tube, heat can be transported through a spacecraft. This subject has been studied by NLR over a period of several years. The potential is very great, especially for large space systems.

In 1994 a two-phase experiment will be flown as a 'Get Away Special' in a NASA Shuttle flight. This experiment designed by NLR with the assistance of four industries. will provide experimental data on the behavior of the vapor and fluid and the capillary pumping system under 0-gravity conditions. The beauty of heat transport systems like this is that there are no moving parts. zyxwvutsrqponmlkjihgfedcbaZYXWVU

' h e D1 Spacelab was carried by the Shuttle 'Challenger' which met w t h a fatal accident on 28 Janualy 1986, shortly aiter launch. The events following this accident resulted in a long delay of ilights with the NASA Shuttle and this also meant fhat the ilight opportunities for this type of testing were almost nonexislenl for a long time

In 1993 Dr. Ockels. employed as an ESA astronaut. ithe first astronaut from The Netherlands) became part-time Pioiessor In the Aerospace Engineering Department Of the Technical University Delft. zyxwvutsrqponmlkjihgfe

125

In connection with the NASA plans of deveioping a Space Station and the European participation in this station, the ESA organization started studies for the Hermes shuttle which was to be launched by an advanced version of the Ariane launcher: the Ariane 5. Hermes is essentially a small manned shuttle, launched by the Ariane and returning to earth in a manner similar to the NASA Shuttle. This concept was developed in the early 1980's. mainiy by the French industry, and adopted by ESA in 1987. Since that time many technicai and political changes took place, in Europe, the USA and the former USSR. When this book was wiitten, the future of the Space Station and the Hermes vehicle was not clear. For NLR the project did result in its involvement, together with Fokker Space &Systems, of studies of a Hermes Robot Arm (HERAI. For this space manipulator a simulation facility for training purposes was developed.

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Jhe Space SNnubtor of the Hernies Robot Arm (HERAi

This project formed the basis for seveial space robotics studies, often in cooperation with other companies and oiganizations in Europe. The ultimate application of these studies is uncertain, but it is clear that space robotics in manned and unmanned vehicles wiil inciease in impoitance. Through exercises iike these, valuable expeiience is being gained in the development and application of mathematical algorithms for the manipulation of robots. At the beginning of the 'Space Age' it was clear t o the Chairman of the Board, Prof. Van der Maas and the Director, lr. Marx. that NLR had much to offer in the area of technology (aerodynamics, flight mechanics, guidance and control, structures, systems testing, etc.) and in turn, NLR had much to gain by participating in space technology projects. They both spent a considerable amount of their time to become acquainted with the problems at hand and they also became very much involved in the national and international discussions. Prof. Van der Maas convinced one of his prize students, Ir. P. Kant, to join NLR even before he graduated. He was employed by NLR on 4 October 1959 and first sent to Cranfield in the UK to take a guided missile course. After that Kant acted more or less as a personal assistant to lr. Marx for several years. He worked at the

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Flight Division but reported mostly directly to lr. Marx. Since there was n o national space technology program, they concentrated on the ELDO organization. Under the guidance of lr. Kant NLR built up the capability for the systems testing of the guidance and control system for the ELDO launchers. In later years the reputation Ir. Kant‘ had gained and the connections he made formed a solid foundation for NLR to operate i n the European context.

One aspect of the task of NLR i n the area of space was to advise the Ministry of Education and Science, the Ministry of Economic Affairs, and also on occasion the Ministry of Foreign Affairs. This requirement diminished i n the 1970s when the NlVR was given the task to supervise space programs and when the Ministries became better equipped to handle technical matters. Since a separate Space Department was formed at NLR in 1967 a rather extensive spectrum of subjects has been treated. In almost all cases this took place in close cooperation with other NLR Divisions, other laboratories and the national and European industry often stimulated by the opportunities offered by ELDO/ESRO/ESA and other international organizations involved i n some aspects of space.

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The subjects for in-house research had to be selected very carefully. which was not always easy since the forecast for medium term applications (always a good guideline for engineering research) was quite uncertain i n the national and the international context, Also the more or less traditional division between the tasks of the aircraft industry and the laboratory did not always apply, since for the space industry the emphasis was far more on research and development than on design and production as it was in aeronautics.

The Space Environmental Simulator with Solar Simulator of NLR

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Finally the matter Of test facilities deserves attention. Traditionally the aeronautical laboratories operated special test facilities of sufficient size to carv out experiments in support of the industry, the Armed Forces and other government organizations (wind tunnels, structural test facilities, flight simulators, laboraton/ aircraftl. The develop rnent of these facilities is usually subsidized by the governments: they are to be available for government and industry. Since the ESROiESA central test facilities were being built up in The Netherlands (the ESTEC laboratories at Noordwijki and since it was not to be expected that the national requirements would justify the construction of large space technology facilities, it was clear that NLR’s role in space technology would not be exactly the same as in aeronautical technology. With these constraints NLR did purchase a space chamber in 1966 and added a solar simulator later, but the size (1 M diameter and 1.5 M long) was such that full-scaie space simuiation for sateilites was not possible. The facility is however very useful for more basic engineering research.

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6 0 n 21 June 1985 Ir. Kant was involved in a very Serious car accident. After a long period he did recover remarkably well. However it was not possible for him to continue as Head of the Space Division of NLR a demanding position he had held since 1971. li. C.A Schmeitink succeeded him.

127

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Experimental set-up to measure the heat conduction of sandwich-constructions in the direction perpendicular to the piates under vacuum conditions

The Guidance and Control Laboratory of the Space Division was initially developed specially for the ELDO program. It was paitially financed by ELDO. During its thirty years of existence several more motion tables and other simulator equipment were added. The laboratory was engaged in the systems analyses and testing of many European satellite attitude control systems, among others for the SAX and I S 0 satellites. Testing the Attitude Control System of the European Comniunication Sateliite OLYMPUS

It would seem that a special chapter on this subject related to the activities of NLR would not be different from historical chapters of any other organization. However aeronautics land since the 1960's particularly space technology) was a major stimulant for the development of computer technology. At NLR, as at other aerospace laboratories, the latest developnients of computers were applied whenever the human and financial resources could he made available. W e have n o w reached a state where in many organizations every employee has available a computer. This is certainly so in many university departments and in research laboratories. The word 'computer' n o w often has a meaning which is quite different from what it meant some decades ago. It must be recognized that the majority of computers is used as advanced word processors and filing systems, but at the same time the capabilities of the n o w standard personal computers IPC'sl are orders of magnitude larger than the digital computers of only a f e w years ago. That is not only due to the spectacular development of tile computer hardware but also due to the continuing development of software. Computers have become an integral part of education at schools of all levels and therefore the story of the application of computers at NLR is less impressive to younger than to older readers, w h o will undoubtedly remember their first struggles will? computers.

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The Numerical Calculation Office in the 1930's

The aeronautical engineering sciences were faced from the beginning with the problem of carrying out large scale numerical calculations to obtain e.g. the pressure distribution around airfoils and wings, the oscillatory motions of aircraft due to atmospheric and pilot induced disturbances and of course the stress calculations of the complicated wing and body structures of airplanes. It is n o w difficult to imagine that it took several manlwoman months to carry out an accurate calculation of even the first f e w periods of a purely symmetrical longitudinal motion of an aircraft. This made it almost impossible to calculate in detail the stability and control characteristics of an aircraft by numerical methods. The numerical methods were reduced to calculations in tabular form and then handed to the Numerical Calculation Office, where ladies carried out intiinerical calculations, using simple hand operated calculators. 'The slide rule IS now almost archaic and unknown to the current generation. A slide rule E - according to Webstei's Dictionary a device for rapid calculation, consisting essentially of a rule having a sliding piece moving along It. both marked with graduated. usually logarithmic. scales. ~

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Usually the same numerical calculation was carried out by two different persons or groups to eliminate human errors. This (double check) procedure was also used for the reduction of the vast amount of data produced by flight tests and wind tunnel tests. During the 1940's and 1950's the Flight Department and the Aerodynamics Department started to incorporate elementary computational components as they became available. However it was not till the mid-1960's that the application of computers penetrated all corners of the laboratory. In the issue of 'De Ingenieur', commemorating the 50th Anniversary of the NLR in 1969, [Ref. 11. there is only a shorl description of the computational facilities although at that time a central computer facility had been established. During the 1970's this activity became a dominating factor in almost all research activities.

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The Numerical Calculation Office, started as a part of the Flight Department, grew from a complement of about 20 in the 1950's to some 70 personnel in the early 1970's when digital computers were really incorporated in the laboratory and further to more than 150 in the 1990's when the supercomputers were introduced. The introduction of computers definitely did not lead to fewer jobs at NLR!

Before describing some of the highlights of the digital computational facilities a t NLR it is of interest to pay attention to the analog computational facilities. In the early 1950's these were the only computational facilities commercially available and of practical engineering use. Paiticularly in North America computer systems and elements of systems became available with which motion systems could be simulated. Shortly after that the first digital computers became available. For some time the analog computers were favorite for engineering applications and in the beginning it seemed that digital computers were only useful for accounting purposes. The access to the digital computer was cumbersome at first - card punch machines, separate interfaces, often difficult to handle outputs, etc. - but that soon improved. The speed, and the input and output mechanisms, of digital computers improved rapidly and for most applications analog computers were replaced by digital computers.

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An earlyapplication of an Analog Computer to simulate the flight o f a Free Flight Model a t NLL, 1956

At NLR the Flight Department stimulated the application of analog computers. In 1955 a Short analog computer was installed at NLL. The first interest was in the use of analog computers 'in the loop', that is computers directly connected to hardware whereby the analog computer solved continuously the equations of motion, as illustrated by an application in the mid-1950's.

The analog computer was used here to simulate the flight of a free-flight model (solving continuously the equations of motion) and it was connected to the electro-pneumatic sew0 control system of the model. When reliable and accurate integrators, function generators and multiplier units, etc. became available analog computers were used mostly for this type of arrangements. It became possible to 'fly' an airplane in the laboratory by connecting a control stick and engine controls to the analog computer which would then solve rapidly the programmed equations of motion and present the new flight status to the 'pilot'. Thus the analog computer not only opened the possibilities of obtaining rapidly solutions to the equations of motion but it also provided the possibility to study the response of an aircraft with the pilot in the loop. The road was opened to sophisticated flight simulation in the laboratory.

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The most important applications of analog computeis at NLR were in flight simulators for aircraft and in the testing of guidance and control systems for rockets, Chapters 6 and 141.

The main advantage of analog computers ovei digital computeis was the speed of computation at the desired accuracy. Most of the applications were with a pilot in the loop or hardware in the loop which had to he tested in real time. Only in a limited number of cases, analog computers were used for purely computational problems. Although most analog computers were relatively easy to use, the number of applications diminished when the capacity and speed of digital computers grew very rapidly in the 1960s and 1970's. This was accompanied by the development of more efficient and user friendly computer codes.

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Application of an Analog Computer to simulate the f/ight mechanics of V/STOL aircraft at NLR, 1963

In the beginning of the 1960's Vertical and ShortTake-Off and Landing IVISTOLI aircraft became an important subject of study'. A simulator was developed by the Flight Division to study the flight characteristics and the requirements for aircraft in tliat category. This was a so-called fixed base flight simulator, meaning that the cockpit did zMuch attent,on paid to V,STOL a,icra,, not move, in contrast to the moving base flight simulators as described designs since It was believed that it would help solve the noise problem around aiiiields and paRiin Chanter - - , - - - 6- . culaily since there existed various schemes to Open up a,ipon facilities at o1 neal city centers Another major application of analog computers was the simulation of the An example is the trial operation between Mon. flight of the ELDO (European Launcher Development Organisation) treai and Ottawa In Canada I n the 1970s. rockets. The simulation was set up to test the guidance and control sysFokker also studied the prospects of adapting the Of the ELDO iauncheis, iCi'apter 14). Fokker F27 Friendship to short take~offand landing operations to and from city centeis. In fact That simulation system, gradually refined and extended, was conveited the sublect was so Prom'nent that 'he studies for into a 'hybrid system' in 1972. Hybrid in this context meant that the systhe new low speed wind tunnel of NLR. Chapter a large extent by the t e m consisted of a digital part and a n analog part. The analog part was were reauirements of ViSTOL aircraft. Obviouslv an? used for those elements of the computation that required a fast aircraft having that addltlonai capability w'ill be response which could at that time not be m e t by digital computation, heavier than its counterpart operating from a 'norThis was also an application with actual hardware in the loop - an i n e r h mal' and the fuel consumption w,Il be h,g. platform of the Europa Launcher. An EAI 640 digital computer provided her. After the first 'energy crisis' the market did

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and the improvements in Qround~transportation pushed back further the aPPllcatlon Of Civil VISTOL aircraft

The PACE Analog Computer used in the Guidance and Control Laboratow at NLR-NOP

The analog cornputer systems were used also for other purposes by individuals in the laboratory on an ad-hoc basis The idea in the late

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1960's - t o concentrate the analog computer activities (aircraft, space flight and others) in one building at the NOP never came to fruition. This was of course also influenced by the fact that the ELDO operations ceased and the analog Computers of the Space Division were used for different purposes. As time went on it became more efficient to instal dedicated computer facilities for a particular research installation.

Developments like this made it difficult to chart a long-term plan for computational facilities, in a period where the computers themselves developed very rapidly. The development of computers - not a part of the NLR research program -has a great influence on the long-range planning of the laboratory. For decades it was a major problem that required the full attention of the Management. zyxwvutsrqp

Digital Computers In 1954 it was reported that Mr. Th. Burgerhout, then Head of the Computation Office, carried out numerical calculations on boundary layers over a swept-back wing at the Mathematical Center of the University Amsterdam (ARRA computer). These and similar trial calculations resulted in ordering the first digital computer for the laboratory. It was the ZEBRA (= Leer Eenvoudige Binaire Reken Automaat = Very Simple Binary Calculation Machine), installed at the laboratory in Amsterdam in 1958.

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Jhe first Digital Computer ZEBRA installed at NLL-Amsterdani in 1958

ZEBRA Operator Panel The small scope showed the contents of accumulators 2nd counters in binary form, suitable to follow the progress o f the prograni execution

The ZEBRA machine was developed by the Netherlands PTT. As the name implied, it was a very simple machine hut it was the start at NLR of the 'computer era'. The name of the Computation Office was changed - it became the Mathematical Problems and Numerical Calculations Department and under the leadership of Dr. E. van Spiege13 this Department used the computer for a large variety of numerical problems: data reduction for flight tests and wind tunnel tests, the development of nozzle contours for wind tunnels, the development of numerical methods for aerodynamic force calculations, pressure distributions and forces on oscillatingairfoils, etc. The computer was used almost continuously. Wind tunnel data reduction took up a very large part of the available time. The personnel included eight university graduates in 1959 as compared to only one a few years earlier.

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// i..':'i2:.I . .. : '. ,. . . . , . . .... ... ..-. , < 1 . ' : ,... . . . .I ./' '. . . I .. . . . . .. , . < . I . c : . Committee. concerned with the planning and purchase of large-scale computers and as a member of the sub^ Committee for Applied Mathematics and lnformatics of the Scientific Committee, till he became director^ General for Science Policy of the Miristw of Education and Science.

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The read and write heads on the Drum Memory of the ZEBRA

The Electrologica Digital Computer X- 1 installedat the NLL-NOPin 1962

In 1962 the ZEBRA was replaced by an Elliott 803b computer. This computer was mostly used for the data reduction of wind tunnel and flight tests.

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The Central Computer Control Cat2 CDC-3300 installedat the NLR-NOP in 1967

Also in 1962 a digital computer of Electrologica (The Hague) X - I was installed at tile NOP. The number of numerical computations at NLR had expanded considerably and the Department - n o w headed by Dr. lr. J.P. Benthem' - also made use of three other ZEBRA and t w o X-1 computers located at other institutes in The Netherlands. By then there were also t w o analog computers in full use at NLR.

The X-1. the more general purpose computer in the NOP, was succeeded by a Control Data Corporation CDC-3300 in 1967. At NLR this was the end of computers made in The Netherlands. The computer industry had developed very rapidly and there were only a f e w computer manufacturers left on the market for large-scale scientific computations.' The next major operation was the installation of a CDC1700 computer at Amsterdam in 1971. It had a fixed line connection with the CDC Computer Center at Rijswilk, near The Hague, for the data reduction of wind tunnel tests and flight tests. The older Elliott computer had become unserviceable and aparl from the capacity - the transportation of data tapes by car to the NOP became too cunibersome; there was not yet a fast line connection available between the NOP and Amsterdam. ~

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'Di. Benthem stayed in that position till 1970 when he went to the Technical University Delft where he later became Professor of Applied Mechanics i1979~19861.For a while it seemed that with the introduction of every new computer generation NLR contributed a professor to the universities Fortunately for NLR. after li. W Loeve took this position, tlxs brain drain process has been discontinued. 5

This did not mean that the capability of producing advanced digital computers was lost in The Netherlands Only a few years later Philips produced the first on~boardsatellite computer for the ANS satellite, followed later by the on-board computer +or the IRAS Satellite These were marvelous Computers but they were special purpose - one of a kind -developments.

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It is often difficult to identify important mile stones in organizations like NLR where there is a continuous development of ideas which sometimes come to fruition instantly and sometimes much later or unfortunately - never result in any particular action. In retrospect the period 1970-1972 may be noted as a mile stone in the application of computer technology a t NLR. On 1 June 1970 lr. W. Loeve became Head of the Scientific Services at NLR. Since the major re-organization in 1967 (Chapter 221 lr. J. Boel, Deputy Director, had been Head of this group on an interim basis. This Group of Scientific Services also included the Space Technology Department which later also became a separate Division. ~

The Group of Scientific Services included: Applied Mathematics and Data Reduction c Electronics I- Library, Documentation, Photography and Reproduction

The last activities of the Group were later separated and became the responsibility of Ir. W.F. Wessels. The cornputer activities and all the interactions with the rest of the laboratory became the responsibility of lr. Loeve. One could argue that all these organizational aspects are of less interest than the actual work carried out by the personnel. While that is certainly true, it was also important that the computer activities were represented directly on the Management Team. After all this was the body where the - uilen heated debates took place about the deployment of manpower and the financial resources. ~

It was clear that in order to support the aerospace community and to stay abreast with developments in other countries, strategic plans had to be developed, even though the financial means were limited. There were plans to extend the computer networks in The Netherlands and NLR extensively investigated the possibilities to establish connections with the national network(s1 for which the plans were then in progress. The Ministry of Education and Science stimulated this and in fact there was a Committee which had to sanction new (major) computer acquisitions in which government funding - directly or indirectly - was involved. Discussions took place with universities and other engineering laboratories which received government subsidies.

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Finally it was decided by NLR to install a large Central Computer at the NLR-NOP site, operating independently from other computers in The Netherlands. The arguments were, i.a.: NLR woulrj use tile facility to its full capacity after a short introduction period (a f e w years): c security could not be guaranteed when the computer was part of a national network; 0 the networks in The Netherlands were still not reliable and cumbersome in use; 0 it was expected that the cost effectiveness would be greater for a separate coniputer.

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In the Spring of 1972, after having discussed the matter extensively at the Board meeting, Prof. Gerlach, the Chairman of the Board of NLR, took the bold step of ordering a Control Data Cyber 72 system. This step was bold, not in the sense that he did something for which he did not have the mandate, but becaiise several Board members and people in other organizations were still not in agreement and felt that the NLR computers should be part of the national network (which did not yet really exist1 and that the main computer should be located somewhere else. It turned out to be a wise decision to place the contract. Reporting on computers is often very dry and uninteresting. The Annual Report of NLR of the year 1973 says: "As a result of the installation of the n e w Central Computer C D C Cyber 72). a large number of programs was converted from the CDC-3300". In reality this involved hard work of many people who had to work under constant pressure of internal and external users who really did not care about the details of the introduction of the new computer system.

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In 1974 a 48 kHr line connection was established between the laboratory in Amsteidam and the Cyber in the NOP. There were also fixed lines introduced with the Fokker computer system. Although the first (quick look) data reduction of wind tunnel tests became gradually more and more possible on relatively inexpensive - local computers, more extensive analysis, using a data base compiled in the Central Computer, took place via terminals of the Central Computer. For quite some time the data reduction of the flight tests took place at the Central Computer in the NOP. A real compute: network was developed. The ideal was: no matter where one would be working within the laboratory 0:outside the laboiatoiy i f connected to the nftwork, it would not make any diffeience as fa: as the access to the Central Compute: is concerned. Theie was on the one hand the tendency to channel all computations to the Central Computer but on the othei hand gradually a new generation of engineers and scientists moved in. They were educated in the 'compute: age' and less dependent of the expertise of the personnel operating the Central Computer. This also coincided with the advent of less expensive smaller computer systems with which many day-to-day problems could be solved. This new generation also understood bettei the advantages and possibilities of large scale computeis and so the net iesult was - besides a considerable increase in special purpose and personal computers - also an increasing demand on the central computing facilities. This development at N L R was of course not unique. By 1978 there were 22 terminals directly connected to the Central Computer, including one from Fokker. The 'standard' data reduction associated with the various expeiimental facilities was mostly carried out on dedicated computers directly linked with the test facilities. ~

In 1980, when the lnformatics Division was formed (Chapter 161, 18.5% of the total NLR personnel of 760 was employed in this Division. The employment of the then five Divisions - that is excluding the Administrative, Technical, and General Selvices - was: Aerodynamics 151 Flight 125 Structures and Materials 46 Space 26 lnformatics 140

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The Control Room with the Control Data Cyber 73 and Cyber 170-855installedat the NLR-NOPin 1982

Total Divisions 488 The personnel employed in the lnformatics Division thus was 28.7% of the personnel directly employed in the Divisions.

In 1980 the Cyber 72 was further extended to make it equivalent to a Cyber 73-configuration and the number of computer teiminals was funhe: increased.

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During 1981 the demand for computei capacity rose very iapidly, mainly due to design activities at Fokker and also in connection with project studies carried out jointly between Fokke: and McDonnellDouglas. Teiminal connections with the CDC computer Cyber-176 at Brussels and the CDC computer Cyber-760 at Rilswijk were implemented. During the following year the internal capacity was adjusted when a Cybei 170-855 was installed at the NOP and the computer speed was increased by a facto: of 12, while the thioughput became 4 times larger. In 1983 the line connection between the laboratories in Amsterdam and the NOP was increased from 50 kbitsisec to 150 kbitsisec.

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The hardware of that computer configuration was extended periodically during the following years: the Central Computer memory was doubled till 32 Megabytes and several disc memories were added. This continuing story of hardware extension must be supplemented by the story of develw ping data base management systems specifically geared towards aerospace applications. A first atteinpt was made to design a software infrastructure - a Computer Aided Engineering (CAE) infrastriicture to include aerodynamics, flight mechanics, structures, etc. ~

Besides the software developments associated with data handling, data reduction and the handling of engineering design data in general, there were also other software activities in which the NLR contributed. Specific examples are: zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDC

zyx zyxwvutsrqpo zy e the development of Expert Systems and Artificial Intelligence Systems for aeronautical applications; * data compression, in particular for satellite and remote sensing applications; a cryptography with a variety of applications; * the participation in a national effoir to develop an Information System for the solution of the Navier-Stokes equations IISNaSI.

Tile latter refers to numerical methods to solve the basic equations of motion of fluids, hopefully

Schernatjc of the Computer Network with the NEC SX-2 Supercornputer i~istalledin 1987

finally to its full extent. These partial differential equations have been used for over a hundred years witl? various degrees of simplification. It is assumed that full solution of these equations might finally be possible when digital computers become available with several orders of magnitude larger computing speeds and memory than the present supercomputers. Wind tunnels will then remain the installations in which the basic physical phenomena are studied, but they will also seNe as installations to produce the final physical check at selected operating conditions.6

'This prospect of numerically solving the fiil Navier-Stokes equations. with real physical turbulence models -that IS to be able to calculate truly the flow around aerospace vehicles without any simpli~ fyiny assumptions was an element in the discussion as to whether or not a European high Reynolds Number transonic wind tunnel facility. costing hundreds of million of guilders. should be constructed. Finally it was decided to construct the E l V J (European Transonic Wind Tunnel, Chapter 191. This IS the only facility In Europe (and i o i that matter the only real production facility In the world) producing the correct Mach Number and Reynolds Number combination f o i aircrait operatiny at transonic speeds and it will - at the veiy least - provide physical checks of numerical computations for decades to come ~

zyxwvutsrqp zyx zyxwvutsrqpo zyxwvutsrqpon Supercomputers In the 1980's there were several aerospace centeis employing so-called supercomputers. NLR, one of the smaller aerospace laboratories in Europe, had made use of supercomputer facilities elsewhere for some time. Based on this experience and in view of the increasing demand the computer network was extended in 1987 with a Japanese supercomputer, the NEC SX-2.

The conversion of existing programs to this computer was relatively easy and on 6 April 1988 the Minister of Traffic and Public Works officially started the operation of this supercomputer.

Mrs. Drs. N.Smit-Kroes, Minister of Traffic and Public Works, officially started the operation o f the NEC SX-2 Supercomputer on 6AoriI 1988

The use of the Central Computer had grown enormously, as indicated in the Figure where the production during the 1970's an 1980's is shown -expressed in units of computation per year.

The use of the Central Computer Facilities at NLR

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This computer was also made accessible to universities and other groups in The Netherlands through a Working Group Supercomputers (WGSI which had obtained a budget from the Ministry of Education and Science for carrying out large scale computations by university groups

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Configuration of NLR's NEC SX-3 Supercomputer 1993

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The NEC SX-3 Superconiputer installedin 1991

During the following years, 1990 and 1991 the computer network was further extended and a variety of new, outside, users became involved. The Cyber 855 in the network was replaced by a Cybei 962 and a contract was signed to replace the NEC SX-2 by a NEC SX-3/12. This configuration was installed in 1991. without any loss in productivity during the installation period. This computer has a speed of 2.75 Gigaflops (one Gigaflop is 1000 million floating point computer operations per second). a central memory of 51 2 Megabits and an extended memory of 1 Gigabits. In 1993 the maximum speed and the central memory of the SX-3 were doubled. An extension of the computer, increasing the speed to 22 Gigaflops, is likely to be introduced later The computer is embedded in the NLR cornouter network covering both the laboratories in the NOP and Amsterdam.

When considering the developments as sketched above, the question arises when the end is in sight. From the point of view of the aerodynamicist there is still a long way to go. In the Figure. after [Ref. 751, an estimate is given of what would be required in terms of computer speed and memory to solve the Naviei-Stokes equations for complete practical airplane configurations within a reasonable time frame (hours). The final solution may be found in massively parallel computing systems, combined with some orders of magnitude increase in speed and memory capacity. This will introduce complicated communication software of the various subsvstems. Estimates of required Computer Speedand M e n i o i y ior the calculation of the flow around an Aircraft with and without any amplifying assuiiiptioiis

Great strides have been made and with the present programs in the hands of capable aeiodynamicists realistic design calculations can be made. Indeed Computational Fluid Dynamics (CFDI is now a very essential element in all efforts to refine the aerospace vehicle designs in spite of the fact that the ideal computer installation is still far away.

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The change from a Service into a Division meant that this group gradually had developed from a pure sewice, mostly for internal support, to a group with its own 'products' and customers as the other Divisions had.

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The Scientific Services comprised four Departments: :.> Electronics; Mathematical Models and Methods; a Numerical Mathematics and Application Programming; Computing Center and Systems Programming. These Departments were retained when the name was changed into lnlormatics Division . j

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Practically all the information systems mentioned in this and other Chapters were not developed exclusively by the lnformatics Division. They often resulted from activities started in other Divisions, but in most cases the lnformatics Division became involved. The work of the Electronics laboratory, which had started in the Flight Division, had evolved lrom building and repairing instruments into dealing with electronic systems, not only for internal use such as lor the laboratory aircraft and the wind tunnels, but also electronic systems for aerospace applications A major development undertaken by the Electronics laboratory was the development ot the DR28, the Digital Recorder tor the flight testing of the Fokker F28 Fellowship, which flew for the first time on 9 May 1967. Similar developments took place in the other Departments of the Scientific Services. By 1980 a considerable part 01 the activities of these Sewices was related to the realization of Information Systems. Those were systems whereby specific aerospace knowledge was essential. Examples at that time were: c> a Ground Operation System for the IRAS satellite; c' an Operational Management Information System iOMlSI for the Royal Netherlands Air Force; 0 a System for Measuring, Recording and Processing Flight Test Data (MRVSI; 0 a Receiver and Data Reduction System lor Weather Satellites IKOSMOSS) lor the Royal Netherlands Meteorological Institute (KNMII; 0 a Data Reduction System for Remote Sensing Data (RESEDA).

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In all cases close cooperation in project teams was necessary with members of the more 'classically' oriented Departments of the other Divisions. Often there was - and still is - Some degree of competition between the various Depaitments and project leadership for the development of aerospace intormation systems is not always placed within the lnlormatics Division. This is understandable since the degree ot specialized knowledge and operational background experience differs from system to system. Similar considerations apply when computer programs have to be developed and whether the Central Computer or a local

computer should be used. Needless to say that during the last decades many changes took place as a n e w generation, grown up with the use of computers, moved in and the costs of computers decreased drastically. It is worth noting here that, when the proposal to change the name of the Scientific Services into the lnformatics Division was discussed, some members of the Scientific Committee NLRiNlVR pointed out that it was important for the laboratory to maintain a group of engineers and scientists ltypically 8 to 121 active in applied mathematical methods, the Department Mathematical Models and Methods. Traditionally this Department had been concentrating most of its efforts, but not all. on applied mathematical problems related to fluid dynamics. As part of a Division concentrating on information systems in a somewhat broader sense it was felt that there would be some spin-off to other applications in aerospace. The Depanment of Numerical Mathematics and Application Programming supports practically all other Departments in the laboratory with their numerical problems, while the Department Computing Center and Systems Programming is responsible for the Central Computer and the Computer Network, Chapter 15). The experience gained with the specification, acquisition and operation of large-scale computer systems is in itself valuable and has been applied to the design of other information systems.

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Tile development of aerospace information systems has thus become a major product during the last 25 years of the 75 years history of NLR. The examples of the systems given below - designed during this period are the result of merging the knowledge and experience gained in aerospace technology and the efficient use of (large-scale! computers. ~

Wiaieliize Grolrnci. Slat i O i 1 4 The ANS Ground Operations The Astronomical Netherlands Satellite, a cooperative effort between The Netherlands INIVR! and the USA INASAI. was launched on 30 August 1974 by a Scout rocket into a near-polar, sunsynchronous orbit, lsee also Chapter 141. The satellite was designed for a six months period of operation, but when it had suiveyed the complete sky. the operation was extended a f e w times till the operation was definitely terminated in April 1976. It was conceived by Dutch astronomers and designed and developed by an industrial consortium formed by Fokker and Philips. It carried an UV-telescope (1500 -3300 "A! and soft and hard X-ray experiments, including an American experiment.

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The nearpolar, SunSynchronous Orbit of the ANSSateSte

NLR developed the computer programs for the operations of the ANS during its mission. The operations were carried out by an NLR team headed by lr. M. Lamers - of the Space Division - from the European Space Operations Center, ESOC, a t Darmstadt, Germany and in close cooperation with that center. This satellite with a mass of onlv 140 KG was comaletelv comautei oaerated zyxwvutsrqp from the ground station. A small onboard computer (power consumption 8 Watt, mass of 7.8 KG), developed by the Physics Laboratory of Philips, was

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employed to control the satellite and to store the data which were read out a t the ground station every 12 hours. The computer was programmable from the ground and instruction packages for the observation program for the coming period were transmitted daily. This almost directly interactive system was a novelty in unmanned satellites at that time.

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The IRAS Ground Operations For the second 'national' satellite, the lnfra Red Astronomical Satellite - IRAS - a similar task was carried out by NLR, (Chapter 141. The operations took place in 1983 from the Rutherford Appleton Laboratory a t Chilton in the UK by a crew of NLR in close cooperation with the British.

The KNMl Ground Station KOSMOSS The acronym KOSMOSS stands for KNMl (Royal Netherlands Meteorological Institute! Ontvangst Station vooi Meteorologische Omloop en Stationaire Satellieten a receiving station for meteorological satellites Signaal then a Division of the Philips Company was selected by the Ministiy of Traffic and Public Works to design and manufacture a

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Jhe Antenna of the KNMl Weather Satellite Receiving Station, KOSMOSS

The Indonesian Weather Satellite Station COSMOSS (Combined Operating Station for Meteorological Operating Stationary Satellites!. This Ground Station, located near Jakarta, Java, was again developed by Signaal and NLR, whereby NLR was responsible for the data handling and data reduction system. It was particularly geared towards the Indonesian requirements suitable for handling of data from the American NOAA low orbit satellite and the Japanese Geostationary Meteorological Satellite, IGMS!. This station began operation in 1987. Apart from the then common information about the weather development, this station was also to be used for geophysical phenomenon such as the observations in connection with volcanic eruptions and also the measurement of the water temperature of the oceans.

Tlie Antenna of the Indonesian Weathei Satellite Receiving Station. COSMOSS

Ground Station equipment of COSMOSS

Mr. Bleekrode of NLR amidst students of the introductory course for COSMOSS

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The ARTEMIS' Ground Station In 1985 NLR reached an agreement with the Food and Agriculture Organization ithe FAO) of the United Nations to develop a ground station for receiving and processing remote sensing data of Northern Africa, in particular the Sahel area. The project was a cooperative effort between the FAO, the NASA Goddard Space Flight Center and universities in the UK and The Netherlands, whereby the Netherlands Government Department of Development Cooperation assisted in financing the project. One of the objectives of this project was to monitor the soil conditions (moisture content), the vegetation and the temperature development over a large area and to predict the probability of insect (locust) plagues. Systems like this offer a real possibility to apply aerospace technology in tackling large-scale world problems. The Figures below give an iinpression of the system and the type of gross information.

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The Antenna o f the Africa Real Tinie Environm e n t Monitoring using Iniaging Satellites Ground Station, ARTEMIS, of the FAO, Rome

A photograph of Africa wit!i Qross information o f Agricultural Data Although the NLR contributions to all the above satellite information systems was vested in the Space Division, the involvement of the lnformatics Division was extensive. This was a feriile arrangement since often similar implementation problems were encountered after having defined the requirements and the preliminary design of the system.

While during the early days flight testing brought about the development of specific measuring techniques and the development of specific instrumentation, during the last 25 years tile emphasis was on the design, development, construction and operation of complete flight test systems. The following t w o examples illustrate this. Flight Test System A major effort of the Flight Division was the development of the system for the measurement of flight parameters, the registration and the data handling during the 1980's. In close cooperation

'ARTEMIS stands for Africa Real Time Environment Monitoring using lmaging Satellites The proliferation of acronyms to designate systems and activities IS often annoying to tllose who are not part of tile often limited group directly associated with the system. In tiiis case the name IS not mappropriate Artemis, in classical mythology a Greek goddess identified with the Roman Diana. was a Oelty of the woods and a specjal goddess of women and childbinh Her celebrated temple is located in Ephesus. Turkey

with the Fokker Aircraft Company a system was developed with the ultimate goal to flight test the Fokker 50 and the Fokker 100. A clear division of tasks between the two organizations was agreed. Many of the elements developed at NLR were tested with the NLR laboratory aircraft, the Queen Air and the Metro 11. Some of these developments were applied to other projects in which NLR panicipated, (see Chapter 61.

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Schematic of the FANOMOSFIight Track andAircraftNoise Monitoring System

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The Flight Track and Aircraft Noise Monitoring System FANOMOS installed around andat Schiphol Airport ~

With this system the Airport Authorities are able to determine the deviation of the actual flight path from the prescribed path, dictated by environmental requirements. It gives the Airpon Authorities the possibility to warn or penalize the offenders. The system was combined with noise monitoring stations located around the airpoii and thus a true environmental control station was develooed.

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Subsequent to the application at Schiphol Airport several European Airport Authorities ordered their specific version of this system and applied it successfully, i.a. the airports of Maastricht. Oslo, Zurich and Manchester.

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From the beginning of wind tunnel operations at NLR most of the wind tunnel data handling systems, including the wind tunnel control systems, were developed in-house, as has been the case also in other aeronautical laboratories. In fact there is usually a constant development activity to meet the demands for special testing. Occasionally this capacity was applied to provide other institutes with a wind tunnel data handling system. In most cases the actual manufacturing was contracted to the industry

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The Control Desk and Data Handling System of the Low Speed Wind Tunnel LST at NLR-NOP

The renewed Control Desk and Data Handling System of the High Speed Wind Tunnel HST at NL R-Amsterdam

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In the 1960's an infrared reconnaissance system was developed for the Royal Netherlands Air Force. An infrared line Scanner 18-14 micrometer wave length1 was installed in a 'pod' mounted under the reconnaissancelfighter aircraft. In The Netherlands Locklieed F-104 Slarhghteis were used for this purpose. The pod, developed by Fokker and NLR, contained equipment developed by Delft Instruments lforrnerly known as 'Oude Delft'). The task of NLR was to assemble the system, to test it for airworthiness and to carry out flight tests with the laboratory aircraft. Thls infrared reconnaissance system. called Orpheus, was used by the Air Forces of The Netherlands and Italy.

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An infrared Reconnaissance Pod mounted under an F-104 Starfighter of the RNLAF

instaiiation of Sensors and Recording Equipment in a Pod to be mounted under an aircraft for Remote Sensing flights

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This system was later used for civil applications. A governmental working group for the application of remote sensing, called NIWARS, was formed. During the period of 1971-1977 this working group sponsored a large number of experiments, involving many groups who had a potential interest in the application of data obtained by remote sensing. The equipment was mounted in a pod under the laboratoly aircraft. Remote sensing activities can be divided into four areas: (a) the development o f the instrumentation; (b)the operation of the instrumentation platforms (first for aircraft but later also in the context of ESA satellites); (c1the registration and reduction of the data; (d)the interpretation and utilization of the data. NLR contributed to the first subject (a) through assisting in the development of the instrumentation, to adapt it to safe and reliable flight operations and to package the instrumentation in the pods mounted under the Queen Air and the Metro II laboratory aircraft. The second item (b) is concerned with the execution of flight tests. This often includes vely accurate navigation and recording of the aircraft position and that was an area in which NLR could contribute. Many flights with the laboratory aircraft were carried out for a variety of applications such as to observe the discharge of cooling water, to locate pollution at rivers and at the North Sea, to locate features under the earth surface which result in small temperature differences a t the surface (ancient foundations, seepage through dikes), etc. The participation of NLR in the registration and reduction of data (c) led to the development of a Remote Sensing Data reduction and data handling station IRESEDA).This station became a national center for handling remote sensing data for a wide variety of purposes. including land use

zyxwvutsrqp zyxwvutsrqp The Orpheus Pod mounted on the Queen Air Laboratovy Aircraft

An early infraredphotograph 119731 o f an agricultural test area, niade in cooperatioii with the Aqriculturai University Waqeninqen, . . . usino - the oodmounted equipment on the Queen Air Laboratory Aircraft

management, hydrology, cartography, etc. The station started its activities at the Flight Division in Amsterdam but was later transferred to the Space Division in the NOP. Througli this activity NLR also became the logical place to deal with the satellite remote sensing data as they hecame available from first the NASAINOAA satellites and later on a regular, commercial, basis from the French SPOT satellites. NLR became an agency for the utilization of the products of SPOT IMAGE, the French company charged with the sale of remote sensing data obtained with tile SPOT satellite. The actual commercialization of remote sensing pictures was carried out by companies producing geographical maps and pictures. The task of NLR became to handle the digital information produced by the satellites.

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A piiotograph of the Noordoostpolder, derived irom data obtained with the SPOTSateiirte, 1986

A composite photograph of the Frisian islands and the Wadden Sea, taken by the Landsat Sateilite over a period o i 13 years 119751988)

A photograph of The Nerheriands taken by the Landsar Sareiiire. 1989

zyxwvut zyxwvutsrqpo This became a maior activity and NLR made contacts with a different part of the scientific community. The interpretation and utilization of the remote sensing data id) is not a task of NLR but through the handling of large amounts of remote sensing data it IS not surprising that a certain expertise was built up.

A Side-Looking Airborne Radar (SLAR) installed under the Queen Air Laboratoory Aircraft

After the experiments with remote sensing equipment in the visible and infrared regime had met with some success, similar tests were carried out to investigate the applicability of RADAR for remote sensing purposes. A Side-Looking Radar System ISLARI was mounted under the laboratory aircraft. NLR's role was again to integrate the instrumentation, to carry out flight tests, to register and carry out the data reduction and presentation.

A Scatterometer niounted under the Queen Air Laboratory Aircraft After the initial experience with the infrared equipment (Oipheus), inherited from the Royal Netherlands Air Force, and the radar experiments with the SL4R. obtained from the UK, several more advanced instruments were developed by the Technical University Delft and TNO. In the framework of the national remote sensing program, funded by the government, an advanced airborne phased array radar system for remote sensing purposes, PHARS (Phased Array Synthetic Aperture Radar), was developed. The Technical University Delft developed a multi-band wave scatterometer. Because of its size, NLR had to develop a complicated retractable mechanism to suspend the sensor underneath the Beechcraft Queen Air laboratory aircraft.

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Jhe IYiased Array Syiithetic Aperture Radar (PHARSI mounted under the Metro 11 Laboratory Aircraft

During many years a phased array synthetic aperture radar was mounted under the Swearingen Metro II laboratory aircraft. Nominal resolutions of about 5 meters were achieved. Several of the flight tests carried out by NLR were concerned with providing basic i'calibration'l data for the European Remote Sensing Satellite, the ERS-1

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The Gemmrr-Diitcli Wirid Tiiririel, D N W , was the resirlt of twu project pru/Jusa"l: the

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Dutch NLR Low Speed Wirid Tiirii7el LST 8x 6 aiid the Germnii DLR (tlieri ciilled

DFVLRj hirzfiel called 'GI-osserUfiter-.sclinll-Kaiinl,GUK' free also Cliapter 27, ivliers' the

pie.si.s oftlie D N W is .showri iri relntiori witl7 the DRG Aerotest Gr-oiip arid the ACAKU La Ws Groiipj.

H o w the Low Speed Wind Tunnel LST 8 x 6 M' was developed The two low speed wind tunnels at NLR, with test sections of 3 x 2 M' and 1.5x1.5 M' and maximum speeds of respectively 70 and 35 mlsec were designed in the period 1935.1938. and some 30 years later the need for more modern facilities became urgent. There were new technical requirements that could not be met by the older wind tunnels.

World-wide predictions indicated that there was a necessity to develop aircraft with shon take-off and landing distances. This idea was inspired by the desire to take-off and land in the middle of cities and by the need to increase the capacity of existing airports and the requirement to reduce the noise around airports. Fuel costs did not yet dominate the operational cost of aircraft and it was expected that the additional power needed for shorter take-off lengths and thus greater mass and fuel consumption of the aircraft would be acceptable. ~

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In 1963 studies were started at NLR on the elements of a low speed wind tunnel which would allow the testing of models for Veitical or Short Take-Off and Landing, VISTOL aircraft. A special aspect of testing VISTOL aircraft models of a fair size in relation to the test section dimensions was the problem of how to cope with the downwash effect which is much larger than with conventional aircraft models of the same size. Much attention was paid to the contraction The Airline desjgn of the LST8x6, 1971

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The wooden Pilot Tunnel ofthe L S T 8 x 6

section before the test section and the diffusor after the test section which had to designed such that highly non-uniform flows emanating from the test section would not cause flow separation in the diffusor and introduce flow instabilities in the wind tunnel circuit. The project studies were initiated in 1963 but only limited manpower and funds were available during the fiist f e w years. In 1968 the design studies had piogressed so far that external engineering consultant firms and an architect could be engaged for the preliminary design and cost estimates. One of the studies was concerned with a comparison of using steel or concrete f o i the tunnel circuit.

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Over a number of years various elements of the wind tunnel were studied in great detail and finally in 1971 a 1 : l O scale model of the tunnel - t h e Pilot Tunnel with a test section of 0.8x0.6 M'- was built in the laboratory in the NOP. This high quality wooden pilot tunnel, built in-house by the Modelshop carpenters in a very short time, proved to be of great value. It was used in the first place to check the aerodynamic design of the LST 8 x 6 and to make final corrections to the design of the circuit and the propeller. Later it was used intensively when an aero-acoustic test section was incorporated in the plan and when vaiious decisions on modifications resulting from the merger of the LST 8 x 6 with the GUK project had to be taken in a very short time. Some of the change proposals were implemented in the Pilot Tunnel practically oveinight. The result of all this was an aerodynamic ciicuit design that was nearly perfect and, as far as can be ascertained, still is the best design of a circuit of this type of low speed tunnel. It is basically the same as that of the DNW, it was used for the Indonesian Low Speed Tunnel -the ILST - at Serpong, near Jakarta and it was applied to the NLR 3x2.25 M