A E R O N A U T I C A L R E S E A R C H C O U N C I L

Review of the Workof the Aeronautical Research Council

1939-1948

HTH JANUARY, 1949This review divides naturally into sections covering the war and post-war

periods. Parts 1 and 3 give surveys of the work which came within the purviewof the Aeronautical Research Committee until its reconstitution as a Council in1945, and of the Council since that date, respectively. Part 2 describes mattersconcerned with the formation of the Council.

There are four Appendices :—(i) The membership of the Council at December, 1948.

(ii) The changes in the membership of the Council during the years1939-1948.

(iii) The membership of the Committees and Sub-Committees at December,1948, and

(iv) A numerical list of papers published in the Reports and MemorandaSeries.

During the period under review a very large number of technical papers havebeen discussed. The fourth Appendix lists the papers published since 1938,most of them since the conclusion of the war. There are about 500 of these,which is about 5 per cent, of the technical material which has been communicatedto the Council's Committees. An equal number of papers is either in the pressor has still to be sent to H.M. Stationery Office for publication.

CONTENTS

PART 1.1. Introduction

THE PERIOD 1939-1945

2. Policy of the Committee .3 . Aerodynamics . . . .

(a) High speed research(b) Low drag wings(c) Fluid motion research(d) Performance tests .(e) Stability and control(f) Flutter . . . . .(g) Wind tunnels . . . .

4 . Power plants . . . .( a ) Fuels . . . . .(b) Piston engines(c) Special problems on piston engines( d ) G a s turbines . . . .( e ) Propellers . . . .

5 . Structures . . . .( d ) General . . . .(b) Electrical strain gauge(c) Vibration problems .( d ) V - g recorder . . . .

6 . Materials . . . .7 . Meteorology . . . .8 . Naval aircraft . . . .9. Equipment for post-war research

10. Post-graduate School of Aeronautics1 1 . Liaison . . . . .

(a) The Aircraft Industry(b) The Royal Aeronautical Society( c ) Canada . . . .( d ) Australia . . . .(e) United States of America

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PART 2. THE CONSTITUTION OF THECOUNCIL

12. Introductory13. Terms of Reference14. Membership

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Page15. Organisation . . . . . . 1 416. The Aircraft Industry . . . . 1 517. Commonwealth Advisory Aeronautical

Research Council . . . . . 1 518. Universities . . . . . . 1 5

PART 3. THE PERIOD 1945-194819. Introductory . . . . . . 1 520. Equipment for research . . . . 1 62 1 . Aerodynamics . . . . . . 1 7

(a) Supersonic research . . . . 1 7(b) Research at high subsonic speeds . . 1 8(c) Stability and control . . . . 1 9(d) Research on boundary-layer control . . 20

2 2 . Power plants . . . . . . 2 1(a) Trends of research and development . . 21( b ) Special problems . . . . . 2 2( c ) Rocket research . . . . . 2 2(rf) Piston engines . . . . . 2 3

23. Structures and aero-elasticity . . . 2 3( c ) Structures . . . . . . 2 3(£>) Aero-elasticity . . . . . 2 4(c) Vibration problems. . . . . 2 6

24. Special problems . . . . . 2 6( a ) Seaplanes . . . . . . 2 6( b ) Helicopters . . . . . . 2 7( c ) Meteorology . . . . . . 2 7

Glossary of abbreviations . . , . 2 8Appendix I

Membership of the Council, December, 1948Appendix II

Changes in membership of the Council, 1939-1948

Appendix IIIMembership of the Council, its Committees and

Sub-Committees at 31st December, 1948Appendix IV

Numerical List of Reports and Memorandapublished between 1939 and 1948

PART 1. THE PERIOD 1939-19451. INTRODUCTION

The last report of the Aeronautical Research Com-mittee which was published dealt with the year 1938.During the war a very brief secret report was submittedto the Secretary of State for Air early in 1940 ; sincethat time, with the approval of the responsible Ministers,no report has been written. An attempt is now made tobridge the intervening gap—in so far as this is nowpossible—so as to give continuity to the reviews on theprogress of aeronautical research which have beenpublished since the first Committee, then the AdvisoryCommittee for Aeronautics, reported to the PrimeMinister in 1910.

Throughout the-long history of the AeronauticalResearch Committee a chief, subject studied has beenthat of aerodynamics, including both the experimentaland theoretical aspects of air flow as applied, in the main,direct to aircraft problems. This subject has continuedto be of first importance. The power plant to drive theaircraft has provided a second main subject and aircraftstructures a third. These three are now considered to beof equal importance, and they and their inter-relationswith each other have been the main themes of theCommittee's work throughout the war period. Problemsconnected with them have arisen from time to timewhich have resulted in discussions and recommendationson other subjects—such as materials, meteorology,navigation, etc.—in so far as these have affected the mainproblem.

2. POLICY OF THE COMMITTEEThe Committee has acted throughout solely in an

advisory capacity. The procedure has been to sendrecommendations on research problems direct to theexecutive officer first at the Air Ministry, next at theMinistry of Aircraft Production and latterly at theMinistry of Supply. The presence and the help of repre-sentatives of Government departments on the technicalsub-committees has helped in the day-to-day problems.In time of war this loose type of contact between theresearch workers and the advisory sub-committees didnot lead to such effective action as was found necessary.Thus, soon after the outbreak of war, a small executivecommittee was appointed by the Director of ScientificResearch, Air Ministry, to ensure that the best use wasmade of facilities at the Royal Aircraft Establishment andthe National Physical Laboratory, and to discuss theprogress of urgent work on aerodynamics. We wererepresented on this committee and found it reciprocallyof value to our work. This Aerodynamics ExecutiveCommittee is still vigorously functioning.

After the first three months of the war, the AeronauticalResearch Committee met regularly to discharge itsnormal duties of initiating and advising on work of lessimmediate urgency. The value of this advice became

apparent with the rapid development of aircraft, especiallyin the problems associated with the much higher topspeeds and higher ceilings of 1945 compared with thosenormal at the outbreak of war.

3. AERODYNAMICS(a) High speed research. We wish first to draw

attention to the general problems arising from theincreasing speed of aircraft. Even in 1939 difficultieswere being experienced on aircraft in high speed dives.These were due to the formation on the aircraft of wavesof compression at high speeds which are commonlycalled ' shock waves'. These waves have been wellknown for years, occurring as they do on 'shells projectedat speeds greater than the speed of sound or on propellersrunning at high rotational speeds, but they had notpreviously been experienced on aircraft wings duringflight. Shock waves are accompanied by an increase indrag which is so rapid that a great increase in enginepower gives only a very small increase in top speed.At the same time large and often dangerous changes instability and control characteristics occur. Theseobstacles to progress become increasingly serious as thespeed of sound is approached. Great efforts were madeduring the war, and still continue, in an attempt topostpone the difficulties to as high a speed as possible.These efforts have taken three forms

(1) Theoretical work aimed mainly at the design of the mostsuitable wing sections for high speed flight.

(2) Wind tunnel tests on models to investigate the character-istics of wing sections and of complete aircraft at highspeeds and to check the theoretical work.

(3) Experimental work in flight at high speeds.

On the theoretical side the National Physical Labora-tory initiated methods for the rational design of lowdrag aerofoils in a series of reports which were circulatedto designers and will be published. The first (A.R.C.No. 5804) bears the date 14th May, 1942, and" wasfollowed by six others. Earlier in the same year theresults of this theory were already being tried out bytesting aerofoils at the N.P.L. : the results of some ofthis work have already been published by the Councilin the Reports and Memoranda Series.

Tests at high speed were first made at the N.P.L. in asmall tunnel 1 ft. in diameter. This tunnel could be runat a wind speed of 900 ft./sec., or, as it is better described,at a Mach number of 0-85, where this number is theratio of the wind speed to the speed of sound in thetunnel. All the high speed subsonic tunnels in thiscountry had a working section about 1 ft. wide or less,until the construction of the R.A.E. High Speed WindTunnel which was opened on 10th November, 1942.This tunnel has a working section 10-ft. wide and cantherefore be used for tests on much larger models. Agreat deal of valuable work on the lift, drag, stability and

control characteristics of aircraft at high Mach numbershas been done in this tunnel and a large body ol usefuldata has been provided on specific designs for high speedaircraft. The smaller tunnels continued, however, toprovide valuable systematic information on aerofoildesign for high speeds.

We wish to put on record our appreciation of the goodengineering design and excellent organisation involved inthe provision of the R.A.E. High Speed Wind Tunnelin war time. Its rapid construction and the attainmentof more than the predicted performance was made thesubject of letters of congratulation to the R.A.E.

The work in flight has involved the development ofnew and difficult techniques of flight testing in steepdives, since this was at the time the only way of reachingsufficiently high speeds. Mach numbers as high as 0-9were achieved in some of the tests. Much valuable workwas done in this way, particularly in investigating thelarge changes in trim which occur at high Mach numberand in finding practical solutions to problems such as theviolent longitudinal' porpoising ' which occurs on manyaircraft at high Mach numbers. The flight tests were alsoused to provide a check on high speed tunnel measure-ments and close collaboration was maintained with thetunnel work in the development of various improvementsto existing aircraft. Modification to the engine nacellesof the Meteor, for example, eventually enabled anincrease in speed of over 30 m.p.h. to be obtained.

(b) Low-drag wings. We drew attention in our reportsfor the years 1937 and 1938 to the two types of air flowwhich are found near the surfaces of good streamlineshapes such as wings : first, a smooth type, free ofeddies and called laminar, near the leading edge of thewing ; this type changes at a certain point, called thetransition point, some way back on the wing to thesecond, which is an eddying or turbulent type. Theposition on the surface of a wing of the transition pointwhere eddies start to form is affected by size, by speed,and by the shape and conditions of the wing surface.The drag caused by the laminar flow is only a fractionof that due to the turbulent flow and an extensivetheoretical and experimental investigation was thereforeundertaken to discover how wings can best be designedand constructed to secure the maximum area of laminarflow over their surfaces.

During the whole period it has been realised that flighttests are an essential part of the development of wingswith extensive laminar flow. Special wings were builtfor three Falcon aeroplanes which showed up theimportance of surface waviness : extensive laminar flowcould only be obtained with metal sleeves fitted locallyon the wings because of the waviness of the plywoodcovering. In 1942 the need for experiments correspond-ing more closely to service conditions was apparent andtests were begun on a King Cobra which had been fittedwith a wing of a suitable basic shape. Successful resultswere obtained only after much work had been done in

improving the surface condition of the wings so as to beas good as the surface of a high class motor car and thiswas very difficult to attain on an aeroplane. A notableadvance in the technique of flight testing was providedby chemical methods of detecting the transition betweenlaminar and turbulent flow. By suitably treating thewing and flying through a trail of chlorine gas, transitionwas indicated by a change in colour of the wing surface.This enabled the whole surface to be studied and showedup the effect of local disturbances such as specks orflies which might become attached to the leading edgeduring take-off or at low heights.

Practical advances were made during the war byreducing the surface roughness. As an example of theinterest we have continuously taken in this matter wemight refer to the wide difference in finish for day andnight fighters to which attention was drawn in the earlypart of 1942. The night finish then in use decreased thetop speed of the Mosquito by 24 m.p.h., a figure confirmedby N.P.L. experiments : this finish increased the normalroughness three times. Co-operation between the R.A.E.and the aircraft industry resulted in further improvementsin camouflage paints and the technique of applying themto the wing surfaces.

Another side of the low drag development has beenstructural and here the advance has been slow. It isextremely difficult to make a wing surface of the desiredsmoothness which will remain free from the small wavesthat cause transition from laminar to turbulent flow.A first start came as the result of tests in the N.P.L.13-ft. x 9-ft. wind tunnel of a series of special largeaerofoil models constructed by aircraft firms. Thistunnel was suitable because the turbulence of the air-stream was low so that the eddies in the stream were toosmall to trigger the laminar flow over the surface andcause it to become turbulent. The first model fromMessrs. Armstrong Whitworth tested in January, 1943(6436) was most satisfactory and was followed by modelsmade by other firms. The R.A.E. also made measure-ments of the distortions of an aeroplane wing under theloads experienced in flight to give some measures ofwhat had been, and could be, achieved in practice. Theproblem of designing wings which will retain, in generalservice, the very low drag associated with extensivelaminar flow has not yet been finally solved, but experi-ments in flight at the R.A.E. have already shown thatthese low drags can be realised on wings speciallyconstructed and carefully maintained throughout theexperiments.

(c) Fluid motion research. We have also paid a greatdeal of attention to the general problems of fluid motion.In 1938, the members of the Fluid Motion Panel co-operated with a few other scientists in the production of abook entitled Modem developments in Fluid Dynamics.This was edited by Prof. Goldstein on the Committee'sbehalf and was published by the Clarendon Press. Thebook dealt with the flow of fluids in boundary layers, inturbulent motion and in wakes behind wings and bodies.

The treatment was both theoretical and experimental,covering the whole range of the subject and comparingthe results from all known sources. The book provideda landmark from which further advances were madeduring the war. We can do little,more in our reportthan draw attention to the continued valuable work ofthis Panel (now a Sub-Committee). Not only how manysolutions of new problems been found for flow at subsonicand supersonic speeds, but the results deduced therefromhave made easier the interpretation of the experimentsconducted on small models in the available high speedwind tunnels of that period. Most of this work will bepublished with the dates when the original papers werecommunicated ; a little has already appeared in theReports and Memoranda Series ; a great deal more isin the press ; and a few papers of special interest havebeen published externally.

Methods of finding approximate solutions of theequations of fluid dynamics have been greatly improved.We wish to mention, in particular, the simplified methodsof calculation which depend on the representation of theflow over an aerofoil wing by a number of horseshoevortices. We were indebted to many outside workers forpapers and assistance on computational work.

The experiments at Cambridge University which, in1938, had shown that the boundary layer on a wing inflight can be made to retain the laminar form to aconsiderable distance from the leading edge werecontinued in 1939 and communicated to the Council inReports and Memoranda 2187 (A.R.C. No. 4193) inwhich it was shown trial, by modifying the distributionof pressure, the laminar form can be maintained over thegreater part of the wing surface. This pioneer work wasfollowed by many studies at N.P.L. and R.A.E. of thelaminar boundary and the region where it changes to theturbulent form, on wings and under more simpleconditions on flat plates and in pipes.

Methods of control of the boundary layer by suctionthrough slots—also by blowing—were and still are ofgreat interest to us. One marked advance in our ideasof its possibilities came from Dr. A. A. Griffiths in 1942.Experiments were made at his suggestion and showedthat separation of the flow from a wing surface of specialdesign can be prevented by sucking a relatively smallquantity of air at a single chordwise position. Theeffective drag coefficients thus obtained, including anallowance for the power required for the suction pump,are of the same order as for a normal low drag aerofoilof considerably smaller thickness.

Compressibility problems and the study of shockwaves have been in the forefront and new evidence wasobtained in the high speed wind tunnels on the applicationof laws previously formulated by Ackeret, Glauert andothers. In addition to photographic and pressureplotting work, a valuable series of experiments over avery wide range of speeds was made on a faired double-wedge and a biconvex aerofoil. Successful interpretationof the experiments depended on correct allowances for the

wind-tunnel walls shaped to give as small an effect aspossible and on a knowledge of blockage due to thepresence of a model in the stream of air. Theory andexperiment were combined to clear up the difficultieswhich were experienced. Valuable assistance on shock-wave studies was rendered by the staffs of the OrdnanceBoard and of the Engineering Division, N.P.L.

(d) Performance tests. The steadily increasing speedsof aircraft brought new problems of performancemeasurement and estimation. One difficulty which stillremains is that of knowing the power of an engine at agiven height and speed on the day of a test. Improve-ments in methods of performance reduction have beendevised including one originating from the N.P.L. andbased on theoretical considerations, which provided aconsiderable advance in the early part of the war. Mostof the advances, both theoretical and experimental, havecome from the staff at the Aircraft and ArmamentExperimental Establishment, Boscombe Down, who havecontinued to improve their technique to meet each newneed. The standard attained by this establishment incareful measurement of aeroplane performance has beenvery high. A number of research aspects of performancetesting were also examined by the R.A.E. staff whocollaborated with the A. & A.E.E. The reports describingthis work are being published in the R. & M. Series.

The need for improving performance early in the warled to the appointment of a High Altitude Sub-Committee. One of the matters discussed was thedevelopment of more power for a short time by the useof methanol or rockets. The improvement came notwith the aid of special devices but by a general cleaningup of aircraft, a decrease in cooling drag and an increasein engine power particularly at the greater heights.Short bursts of much higher power were also obtainedwith certain engines and this was of great value to fighteraircraft. In connection with this matter, flight tests forthe estimation of engine power were made on a Spitfirewhich towards the end of 1941 frequently flew at44,000 ft.

The next requirement was the need for reducing thespeed of fighters, especially when approaching an enemyaircraft at night. This was effected by fitting variousforms of drag flaps. It was one of the subjects discussedat conferences arranged by the Royal AeronauticalSociety to which reference is made elsewhere (p. 11).

(e) Stability and control. In the past the theory andpractice of longitudinal stability and control has sufferedfrom too academic a treatment. During the war periodthe urgent necessity to get the handling qualities ofmilitary designs satisfactory in the shortest possible timeprompted a more realistic approach to the subject. Thiswas supplied at the R.A.E. by recasting the theory insuch a way that it concentrated on the types of instabilitythat really were dangerous, related the stability character-istics to stick movements and forces required for variousflight conditions, and provided a workable basis for a

practical and fairly comprehensive technique of flighttesting. The theory thus developed gave, to the firstorder, a general framework within which the mostimportant handling qualities of an aircraft could bestudied, even when distortion effects produced by highspeed had to be allowed for. It elaborated the earlierconception of the neutral point for static stability andintroduced another :—the manoeuvre point The theoryof the static margin related the static stability to theangular settings and hinge moments of the controlnecessary for trim at various speeds ; while the theoryof the manoeuvre margin related the control movementfrom a trimmed state to the response which followed, interms of stick force or stick travel per g. This approach,combined with the allied researches on control balanceand tab design, has proved useful in several ways :—

(1) a clearer insight was obtained into the general problemof design for good handling qualities, particularlyat high speeds,

(2) the diagnosis of handling defects by flight testing hasbecome quicker and easier,

(3) much firmer design requirements for handling can nowbe laid down.

Throughout the war years ever increasing demandswere made on flying controls, lightness and effectivenessbeing demanded owing to the need for violent evasiveaction. Much important theoretical and wind tunnelwork was done at the N.P.L. on the fundamentalproblems of control effectiveness and balance, while agreat deal of flight testing was undertaken at the R.A.E.The importance of stiffness of control covering wasestablished, as exemplified by the change from fabric tometal covering on the Spitfire ailerons—a change whichenabled the Spitfire to compete successfully in rollingmanoeuvrability with the German fighters. Methodswere developed—notably the spring tab—of makingcontrol forces less sensitive to minute manufacturingerrors or to panel distortion.

As speeds rose during the war, elastic deformation ofthe aircraft structure under the applied loads—wingtwist, fuselage bending, tail plane twist, etc.—began toexert a large influence on the stability and controlcharacteristics of military aircraft. A great deal ofexperimental work in flight was undertaken, with con-siderable success, in order to check the theory which hadbeen developed to cover these effects.

From time to time available information on controlpower and balance has been analysed and broughttogether in the form of design charts. Such generalisedcharts have been greatly appreciated by the aircraftindustry.

(f) Flutter. With the coming of tabs, a new risk offlutter was introduced to aircraft design. We drew theattention of aircraft firms to the importance of carefuldesign, construction and maintenance of tabs, theirhinges and their operating mechanism, with a view to theminimisation of backlash, both initially and throughout

the service life of the aircraft on account of its importancein connection with flutter. A good deal of theoreticaland experimental work was undertaken on this subjectat the N.P.L. and R.A.E. and many papers were promptlycommunicated to the aircraft industry. We are glad tosay that the theory indicated the dangers and theremedies with the result that no serious difficulties arosewith the introduction of this type of auxiliary.

Many other aspects of aeroplane flutter were investi-gated during the war. These covered extensive theoreticaland experimental work on aerodynamic derivatives(including some consideration of supersonic flight),mass balancing of controls and the study of the numberof degrees of freedom to be considered in flutter investiga-tions. The outstanding need was, and still is, for asimple method of predicting the flutter speed of anaeroplane in order to make sure in the design stage thatthis speed will exceed any speed at which the aircraft islikely to fly. The complete set of equations to solve anyparticular condition of flight is very complicated and agreat volume of computation is necessary to obtain anydesired result. We have therefore considered manycomputational machines such as the Hollerith, theMallock, the Biot and the differential analyser. No finalconclusion has yet been reached owing to the complexityof the problem, the requirement of very large and costlymachines of any chosen type and the lack of adequatestaff to undertake the work. A possible way out maycome from wind-tunnel tests on properly proportionedmodels made of Xylonite or other material and trialswith simple models are to be made to test the value of thisproposal. Another suggestion has been for the construc-tion of a special large wind tunnel solely for flutterresearch, but this is at present ruled out, together withother experimental construction, owing to lack offacilities. We expect that it will be a very long time beforeeither theory or wind-tunnel work will provide sufficientdata to make flutter calculations both simple and entirelyreliable.

The technique of ground resonance testing has improvedconsiderably in recent years with the employment ofelectrical and electronic recording apparatus. (Resonancetests are now mandatory for all prototype militaryaircraft.) These tests provide a check on the effectivenessof the mass balancing arrangements, and an inspectionof the modes of vibration enables the most dangerousmodes to be selected and used in flutter calculations.

(g) Wind tunnels. During the war a number of newwind tunnels and a whirling arm were brought into useat the R.A.E. and N.P.L. We have already mentionedthe R-.A.E. large and the N.P.L. small High SpeedTunnels. In addition, there were new tunnels of lowerspeed, the 111 ft. X 8£ ft. at the R.A.E., the 13 ft. X 9 ft.at the N.P.L., the N.P.L. Twin Tunnels each 9 ft. X 7 ft.and the Low Turbulence tunnel also at the N.P.L.More experiments at very high speeds were madepossible by a second small photographic tunnel 20 in. x8 in. in the Aerodynamics Division at the N.P.L. and a

supersonic 11 in. tunnel in the Engineering Division,mainly used in connection with work for the OrdnanceBoard. The N.P.L. whirling arm was completed at theend of the war for special work on stability which cannotbe undertaken in a wind tunnel ; in particular, forstability investigations on tailless aircraft types.

We have found this new equipment of great value.It was mainly designed eight to ten years ago and owingto great delays in construction much of it has alreadybecome obsolescent since neither the scale and speed(Reynolds number) nor the top speed (Mach number)are sufficiently high for present-day needs. In a subse-quent section (section 9) we refer to a Committee reportwhich drew attention to the way in which we were beinghandicapped by lack of up-to-date research apparatus,and recommended steps which should be taken to remedythis defect in the future.

During the earlier period the standards of low turbu-lence and steadiness of flow in wind tunnels wereprogressively raised, and this led to the investigation ofways of improving both existing and future wind tunnels.For existing wind tunnels these include the use of wind-mills in the return circuit, the division of the returncircuit into a number of channels, and the introduction ofwire gauze screens. In new wind tunnels the favouredscheme is to make the expansion in the return circuitvery gradual and to fit a number of gauze screens in themaximum section.

Improvements have also been made in wind-tunneltechnique and new methods of measurement have beendevised ; the influence of the wind-tunnel walls on theforces on the models in high speed tunnels has beencarefully studied ; visualisation of air flow and satis-factory methods of indicating transition have beenperfected.

To assist in the new developments a special committeeon wind-tunnel design was appointed in 1944 to considerproblems associated with design and operation and toadvise on a number of special matters in this field. Onesuch special matter was the types of wind tunnel whichwould be of most use to aircraft designing firms. ThisCommittee continues to do useful work, especially inconnection with the design of modern wind tunnels andother equipment for the National Aeronautical Establish-ment and the N.P.L.

4. POWER PLANTSDuring the period reviewed in this report the specific

power output of piston aero-engines was increasedenormously, in the cases of the Merlin and Sabre engines,for example, by over 100 per cent. This was achievedby the application of the intensive research work carriedout during recent years.

(a) Fuels. The limiting factor controlling the poweroutput and the efficiency of the spark ignition engine isthe tendency of the fuel to detonate under high pressures.Intensive research has therefore been devoted to the

improvement of aircraft fuels with a view to reducingthis tendency. Though even to-day little is known of thechemical changes responsible for detonation duringcombustion, much is now known both about themechanism of detonation and the physical factorscontrolling it.

It is still impossible for the chemist to predict theoctane number of any new fuel from a knowledge of itschemical constituents, for this engine tests alone willreveal. Once it has been determined, however, andfound favourable, the chemists have been remarkablysuccessful in devising means for bulk production withthe result that during the period 1939-1945 the generalimprovement in aircraft fuels available for spark ignitionengines has been such as to permit of potential powerincreases of well over 100 per cent.

While the chemical problems involved in the produc-tion of high octane fuels have been left to the oilcompanies to solve, researches into fuel testing and intothe modifications to the engine necessary to takeadvantage of higher octane fuels have, for the most part,been the concern of the A.R.C.

(b) Piston engines. During the years preceding thewar, the A.R.C. had advised on a research into thepossibilities of the compression ignition engine, bothtwo-cycle and four-cycle, for aircraft propulsion. Withthe outbreak of war, however, this relatively long-rangeresearch was interrupted in favour of more immediateproblems. Though it had produced no acceptablecompression ignition aero engine, yet the experiencegained proved to be of great value in the developmentof spark ignition engines of high output. The researchon compression ignition engines had, for example,brought to light the need for improved bearing materialsto stand up to high pressure loads, improved lubricationsystems, the importance of controlling air swirl, moreespecially in sleeve valve engines, and the need for moreefficient piston cooling. All of these problems had beeninvestigated and many of them solved before the improvedfuels involving the use of pressures similar to those of thecompression ignition engine rendered them equallyinsistent in spark ignition engines.

Throughout the last twenty years the A.R.C. hassupported research into the possibilities of the sleevevalve for aircraft engines. This has borne rich fruitduring the period under review in the development ofthe whole range of Bristol air-cooled radial sleeve valveengines, in the Napier Sabre and in the latest Rolls-Royceengines. Research on the main problems peculiar to thesleeve valve has been continuous and intensive during theperiod under review. Chief of these has been the findingof a material for the sleeves having both suitable wearingproperties and such a coefficient of expansion as to allowof its being used directly in a light alloy cylinder. Otherproblems have been the control both of turbulence andair swirl which play so important a part in the per-formance of sleeve valve engines.

The compression ignition engine research alreadyreferred to had revealed the great advantage of thetwo-stroke cycle in high specific output and at the sametime had shown both how to time and how to meteraccurately the injection of very small quantities of fuelat very high revolution speeds.

With the termination, therefore, of the research oncompression ignition engines, attention was turned to thedevelopment of a sleeve valve two-stroke petrol aero-engine of very high specific output. Most of themechanical problems had already been encountered andcoped with during the research on compression ignitionengines and those which remained were such as arecommon to any type of piston engine when very highoutputs are aimed at. A number of both single andtwin-cylinder experimental units were built and had beensubjected to prolonged and severe endurance testing andabout six complete 12-cylinder full-sized aero-engineshad been completed before the conclusion of the war.With the cessation of hostilities and the advent of thegas turbine, further development of this project wasabandoned. The research had however revealed thatthe two-stroke sleeve valve cylinder was capable of amaximum power output of nearly double that ofcontemporary four-cycle engines, nearly 200 h.p. perlitre of cylinder capacity or slightly over 18 h.p. persquare inch of piston area.

It seems probable that had the turbine not materialised,the two-stroke petrol injection engine would have provedthe next step in the development of the aero-engine.

(c) Special problems on piston engines. With therapidly rising power output of aero-engines the problemof piston cooling became very insistent and a great dealof research was carried out in this direction. The firststep was to devise accurate means of measuring thepiston temperature under actual operating conditions,the next to ascertain the safe limiting temperature forthe various areas of the piston, and the third to findpractical means of keeping these areas below the safelimits by carefully directed oil cooling. The researchproved very successful to tho extent that it becamepossible to double the power output from a given piston,while still keeping within the same temperature limits.

A great deal of research was devoted to the problem ofcylinder cooling, with the minimum of drag, in bothair- and liquid-cooled engines. Here again one of thefirst essentials was to measure the temperature gradientthrough the cylinder walls at various points, by means oftraversing thermocouples, and to concentrate the flow ofcoolant over those areas where the gradients weresteepest.

The very high altitude performance called for during thewar demanded, and the high octane number of the fuelpermitted, the use of superchargers with a very highpressure ratio. Much research was therefore devoted tothis aspect of the problem, as also to that of intercoolingbetween the supercharger and the engine cylinders.

The high altitude and high ground boost, renderedpossible by other fuel and engine developments, increasedenormously the difficulty of maintaining a uniformmixture strength under all conditions with existingcarburetters, and resulted in a great lack of uniformityin the fuel consumption of identical machines in any onesquadron. This led to new research into the furtherdevelopment of fuel injection, either metered individuallyto each cylinder, as favoured by the Germans, or. directly,and as a continuous spray, into the eye of the super-charger, as favoured by ourselves and the Americans.

The war brought into prominence the need for shortbursts of high power substantially in excess of thatnormally obtainable. This was required, on the onehand for take-off with heavy loads, and on the other forcombat use by fighters, usually at high altitude.

At low altitudes the supercharger can always supplymore oxygen than the engine can consume, within thelimits set by thermal and mechanical conditions. Excesspower can, however, be obtained by the injection ofwater, or water with methanol as an anti-freeze. Theaction of this is twofold. In the first place the highlatent heat of evaporation of the water serves to cooldown the supercharged air and so lowers greatly theinduction temperature and with it that of the wholecycle. In the second place, the presence of steam in theworking fluid serves both as a diluent to lower themaximum temperatures and pressures and, at the sametime, as an anti-detonant ; by such means it provedpossible to increase the power output by about 20 percent, without any increase either in the heat flow to thecylinders or to the peak pressures. Though this methodof power augmentation has long been well known andwidely used in other spheres, it needed the stimulus ofactual warfare to introduce its use in aircraft.

At high altitudes, i.e. above the rated altitude, theengine is starved for lack of oxygen and power augmenta-tion can be obtained only by the admission of additionaloxygen in some form or another.

The first and most obvious method was the use ofliquid oxygen and a considerable amount of researchwas involved in devising ways and means of adaptingthis. At the same time other researches were devoted toexploring the possibilities of oxygen carriers. Of thesethe best appeared to be nitrous oxide. Although the useof nitrous oxide involved carrying an additional weightof nitrogen, this drawback was more than offset by othercompensating advantages. In the first place nitrousoxide is highly endothermic and was found to- dissociateand liberate heat at the most appropriate stage in thecycle, thus providing a very substantial power augmenta-tion, over and above that obtained from the additionaloxygen. In the second it proved, somewhat surprisingly,to be an anti-detonant. In the third it could be storedand carried in the liquid state at atmospheric tempera-tures, in relatively light pressure vessels, thus reducinggreatly the difficulties in the way of handling, storage andtransport.

The thrust obtainable from piston engine exhaust bydirecting them rearwards was the subject of theoreticaland experimental study, and it was found possible todesign exhaust systems to provide a thrust equivalent tofrom 5 to 25 per cent, of the total engine power accordingto aircraft speed and altitude. The development ofexhaust systems for military aircraft was, however,restricted by the necessity for exhaust flame damping atnight. The scientific study of the origin and causes ofred and blue flames contributed to the practical solutionof this problem.

(d) Gas turbines. In the pre-war years the Aero-nautical Research Committee had a considerableinfluence on the progress of gas turbine research,particularly in the axial compressor field. In the post-warperiod, through its Power Plants Committee, the Councilis again playing a part in gas tUrbine research activity.During the war years, however, the Committee was ableto do little more than keep in touch with the work inprogress which during this period flowed from two mainsources. One was Power Jets Ltd., the company whichwas exploiting Sir Frank Whittle's invention of the jetpropulsion and gas turbine with centrifugal compressor ;the other was the Turbine Division-of the Royal AircraftEstablishment. The pioneer work of these organisationsspread out into the aero-engine industry with resultsthat are now well known. The two organisationsreferred to were united during the war into a singleorganisation, which later became the National GasTurbine Establishment.

(e) Propellers. Propeller research during the periodhad two principal objects ; the collection of experi-mental data necessary for the design of propellers forhigh speed aircraft, and trie development of a series ofcharts for the rapid computation of propeller performanceby persons without specialized knowledge. To achievethese objects a large number of research propellers andtypical production designs were tested at high tip speedsin the 24-ft. tunnel of the R.A.E. by means of a1,500 h.p. electric motor of exceptionally small size andweight, installed for this purpose in 1939. The resultsof these tests were made available to the propellerindustry as soon as they were obtained, and after carefulanalysis were made available to a wider field in the formof simplified charts and in reports giving rapid numericalmethods of design.

A large number of detailed design studies were madeboth by the N.P.L. and the R.A.E. These includedcalculations to show the advantages of variable pitch(the variable-pitch propeller was far from universal in1939), two-speed propeller gearing, and improved bladeshapes and experiments at R.A.E. and N.P.L. oncontra-rotating propellers and models of them.

5. STRUCTURES(a) General. Throughoutthewarwewereincreasingly

concerned with problems relating to the structure ofaircraft. Great strides have been made in accumulating

knowledge both by long-range research and by day-to-dayinvestigations. New methods of construction, newmaterials, and improvements in the use of old materialsas well as invention have all played a part in the advance.The field of aero-elasticity has broadened because of itseffects not only on construction and flutter but also on thestability and control of aircraft. The greatly increasedvolume of work, especially at the R.A.E., can be seenfrom the much higher percentage of the Council'sReports and Memoranda which describe researches onstructural problems. A valuable contribution has beenmade by the N.P.L. and R.A.E. in the fields of stressed-skin construction and of sandwich structures and in thetheory of structures ; also by the N.P.L. and ChemicalResearch Laboratory jointly on plastics. There has beenuseful co-operation with Aero Research Ltd., wheremany new developments on plastic materials and theiruse have started, and with the Forest Products ResearchLaboratory of the Department of Scientific and IndustrialResearch on plywoods. Most of this work was discussedby the Structure Sub-Committee and that on plastics bya Plastics Sub-Committee, which latter has since beendissolved. The results of our work have been handed tothe Royal Aeronautical Society to help in the preparationof the valuable series of data sheets which are issued fromtime to time.

We have welcomed the opportunity of assisting forseveral years in the application of relaxation methods tothe solution of many problems, including those ofstructural strain and stresses. This was done by thepayment of grants from the special fund available to theCouncil for helping individual investigators.

(b) Electrical strain gauge. A great advance in thetechnique of the measurement of the stresses in structureshas been made possible by the invention of the electricalresistance strain gauge. This tiny gauge can be stuck toany part of a structure and readings are taken at aconvenient place of the change in electrical resistance ofthe long length of fine wire which forms a grid embeddedin the insulating adhesive surface of the gauge. Changesin the resistance are correlated with strains and so cangive a simultaneous measure of the stresses in variousparts of an aircraft, either in the laboratory or in flight.This instrument is finding an extended use in fieldsoutside structural research.

Its advent in the early part of the war proved singularlyopportune as it enabled many urgent structural problemsto be solved that otherwise would have proved intractable.Among these the following may be mentioned :

(i) It becams possible to measure the distortion of thefuselage skin of a bomber under the deterioratinginfluence of repetitive blast impacts from the rapidfire of a 20-mm. cannon with barrel almost flush withthe skin. By coupling the resistance gauges with acathode ray oscillograph and so obtaining a faithfulrecord of the transient stresses in the skin, the wholeaction was made clear and the appropriate designchanges determined.

(ii) The stresses in the tailplane structure of a fast fighterunder severe manoeuvring loads and particularly thedegree of asymmetry present at one time presented anurgent problem. Here, by attaching resistancegauges to the tailplane spars and taking oscillographreadings under such flight conditions, a body of dataon tailplane loads was quickly built up which couldhardly have been obtained in any other way.

(iii) Another problem arose from fatigue failures in the sparsof certain bomber aircraft. By using the resistancestrain gauge to record in flight the oscillating stressescaused by gusts, the amplitudes of stress variation atthe critical sections of the spars were found, and thusthe first step taken in the task of modifying thedesign to suit the stress conditions.

(iv) Before the war destruction tests on full-scale majorcomponents like wings and fuselages gave little moreinformation than the magnitude of the breaking loadunder a chosen load distribution. By the end of thewar a new strain gauge technique had been developedinvolving the use of anything up to a thousand gaugeson one test component and of enabling the corre-sponding thousand readings between each localincrement to be taken in a matter of seconds. Thesubsequent analysis of the records gave a clearpicture of the stress distribution in the test specimenat every stage of loading to be drawn.

(c) Vibration problems. Much work, both theoreticaland practical, has been directed to the reduction of thedeleterious effects, both on the pilot and on the aircraftstructure, of vibrations excited by the engine-propellercombination, with the result that the whole subject is nowmuch better understood.

The increased size and speed of bombers during thewar years made it necessary to study the dynamic effectof transient forces which arise when landing and throughthe action of gusts. The problem involves the naturalvibration modes of the aeroplane and the degree to whicheach mode is excited. Theoretical methods have beendeveloped which enable a rapid estimate of the aircraftresponse to be made on the basis of its vibrationcharacteristics as found by full-scale resonance tests.

One structural problem deserves special mention. Thiswas the investigation of the ' shimmy' of undercarriagewheels at the R.A.E. A careful theoretical analysisexplained the main causes of the trouble and led to thedesign of efficient shimmy dampers. A special referenceshould also be made to the use of double wheels anddouble-tread tyres, successfully adopted for the suppres-sion of shimmy.

(d) V-g recorder. It was realised early on that theaccelerations suffered by a bomber under operationalconditions, which involved not only flying under adverseweather conditions, but the frequent resort to violentevasive action, might very well be more severe than werefully allowed for in the design. A practice was thereforestarted of fitting bombers, and particularly Lancasterbombers, with instruments called V-g recorders whichregistered, as a trace on smoked glass, the acceleration on

a velocity base. By the end of the war something like10,000 operational flying hours were covered in this wayand a very valuable body of data collected. There isunfortunately no means of separating the effects of gustsfrom those due to evasive action, but it is possible to saythat the records, in so far as they indicate gust loads,must err on the severe side.

6. MATERIALSWe have not, in our deliberations, considered materials

as a subject of primary importance to us, because theadvances here come mainly from industry with a widerapplication than aircraft. From time to time specialneeds, especially in the turbine field, have been pointedout and the interaction of materials on the strength ofaircraft structures gave rise to certain problems.Throughout the war we maintained an Alloys Sub-Committee which kept in touch, by yearly visits, withresearches on light alloys at the R.A.E. and the N.P.L.at the same time advising on the programme at theseestablishments. The position was changed by theappointment in the Ministry of Aircraft Production ofa Materials Committee directly responsible to theDirector of Scientific Research, after which the AlloysSub-Committee was dissolved. This Committee has nowbeen replaced by the Inter-Services MetallurgicalResearch Council.

In other directions the Structure and Plastics Sub-Committees took a direct interest in materials and thestrength which they provided for construction. TheN.P.L. Engineering Division carried out the firstresearches on the mechanical properties of fibre-filledsynthetic resin materials and have done much work onspecial materials for use as fillers between sheets ofmetal and of plywood. Much of the later work hasprovided valuable knowledge for aircraft designers.

7. METEOROLOGYA limitation is imposed on structural design by the

need to make an aircraft strong enough to withstandgusts met in flight. After the war special steps weretaken to review our scanty knowledge of this subjectand we refer to these in Part 3. The subject was,however, in our minds although pushed to one side bythe greater risks of war, which brought more importantproblems to the fore. V-g recorders, previously men-tioned in the section on Structures, were fitted to anumber of aircraft and some special flights were madeat the R.A.E. to investigate the gust distribution in theatmosphere. A great number of results from V-grecorders were also communicated from the U.S.A. andcontributed to our knowledge of gusts, which is stillscanty.

Another meteorological subject was the accretion ofice on aircraft in flight. Some experiments have beenundertaken in a special 3-ft. square de-icing tunnel runin a cold room at the Ditton Laboratory. An importanttheoretical contribution to the subject is given in a paper

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on the deposition of water drops on a body in an airstream (R. & M. 2024). The R.A.E. have collected alarge number of observations in flight under a greatvariety of weather conditions and their conclusions haveemphasized the importance of the presence of super-cooled drops in the atmosphere in the formation of themost dangerous type of icing. Numerous trials ofdifferent forms of de-icing devices have been made.The greatest progress came from the MeteorologicalOffice developing methods of prediction of the range ofheights where icing was likely to be experienced at agiven place and time. The whole problem is not yetsolved and the present outlook suggests that thermalde-icing may provide the best preventative against theaccretion of ice.

The production of condensation trails by aircraftflying at greater heights came to the fore towards theend of the year 1940 when an explanation of thephenomenon was unknown. We now know thatcondensation trails formed by the exhaust are dependenton the amount of moisture in the atmosphere and themuch shorter ones are due to suction from the wingtips of heavily loaded aircraft. Experiments on a dew-point instrument were started early in 1941 and it wasultimately possible to determine accurately the moisturecontent of the atmosphere either in the form of vapouror ice crystals. Condensation trails were thus shown tobe associated with the tropopause and not to occur in thestratosphere above it. The Meterological Office devisedmethods for forecasting the height of the base of thestratosphere and the height in the tropopause belowwhich trails would not be formed. Aircraft thus learntwhich range of heights to avoid. In all this work wehad the close co-operation of the Meteorological Office.

During the latter part of .the war we ceased to bedirectly concerned with meteorological problems becausethis work was taken over by the Meteorological ResearchCommittee of the Air Ministry. Contact has beenmaintained by common membership and by the discussiononce a year with the Director of the MeteorologicalOffice of the Report of this Committee. We have beenglad to learn the results of several meteorologicalinvestigations in this way, including the fog dispersionwork of the Petroleum Warfare Department, themeasurement of winds at great heights and the increasinguses of radio-sondes.

8. NAVAL AIRCRAFTWe have for many years interested ourselves in those

problems which are peculiar to aircraft that operatefrom aircraft carriers. Our interest was renewed by avisit to H.M.A.C. Ark Royal in May, 1939, and withthe formation shortly afterwards of a Special Committeeto deal with the problems of the Fleet Air Arm. Oneof the most important functions of this Special Com-mittee was that it encouraged discussions between thoseresponsible for operations under the Admiralty andscientists in the A.R.C. Organisation who had specialisedknowledge.

During the early part of the war full-scale scientificinvestigations had to be made on service carriers and theChairman of the Special Committee spent some days atsea during the war to keep in direct touch with what wasbeing done. We have pressed from time to time forbetter full-scale research facilities and in 1944 H.M.S.Pretoria Castle was allocated solely for scientificinvestigations. We advised on the programme andrecommended that it be directed towards laying thescientific and technical basis for the next step forwardin aircraft and carrier design. The permanent avail-ability of a carrier in the future for such a purpose wasconsidered by us to be essential for satisfactory progress.We also recommended that work on assisted take-offand arrester gear was of the greatest importance andshould be carried out by a group of workers in closetouch with full-scale experimental work, as also theprovision of new wind tunnel facilities for work on theair flow over carriers. Effect has been given to theformer by concentrating this work at the R.A.E. andconsiderable progress was made in assisted take-offmethods—including the introduction of R.A.T.O.G.—and in the study of deck-landing and arresting problems.Action on the wind tunnel work has been postponed,however, because of the building programme. In themeantime wind tunnel tests on model carriers haveproceeded at the N.P.L.

A large number of model carriers have been tested toinvestigate the air flow conditions over the flight deckand it was shown how this could be improved in severalways even when the carrier was not steaming head towind. These methods were successfully applied by theN.P.L. and the R.A.E. to the problems of catapulting inside winds up to 30 knots. A close co-operation betweenthe N.P.L. and the Directorate of Naval Constructiondid much to correlate successfully the actual conditionson the carrier with the tunnel results.

At an early stage the advantages of an aircraft with ahigh maximum lift were discussed from many angles ;in particular it would enable an aircraft, other thingsbeing equal, to land at a slower speed on the deck.Maximum lift coefficients as high as 3 had been shown tobe possible with the aid of flaps and slots and the designof a special aircraft was approved by the Ministry in1940 solely to try out what was the best that could beobtained with high lifts. However, the performance ofland-based aircraft improved so rapidly that the develop-ment of special high-lift designs and other very specialisedmachines could not keep pace and was thereforeabandoned. Exceptions occurred in the cases of certainvery manoeuvrable strike aircraft like the Swordfish andthose needed for communication work such as theWalrus.

The Committee were able to direct attention to themuch better performance of R.A.F. aircraft and tosuggest certain ways hi which advantage could be takenthereof. As an example, the first fleet fighters were ofslow speed, but a practicable demonstration showed

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that under favourable conditions a Spitfire of greatlysuperior top speed could be operated successfully froma carrier. The adaptation for Naval use of aircraftoriginally designed for the R.A.F. started with theHurricane and Spitfire, proceeded by way of the Mosquito,Fury and Hornet, and culminated with the Vampireexperimental trials in 1945. The knowledge gained fromthe successful operation of these aircraft from carriers,together with the results of a series of deck landingexperiments with typical Naval aircraft, has allowed aconsiderable relaxation in design requirements whichwere peculiar to ship-based aircraft. On the other handthe severity of some design requirements has had to beincreased ; for instance, the minimum standard offorward view provided for the pilot must be greater onaircraft operating from carriers than for those operatingfrom aerodromes and the strength of the undercarriagemust also be greater.

9. EQUIPMENT FOR POST-WAR RESEARCHEarly in 1943 the Minister of Aircraft Production

asked us to prepare a report on the research equipmentwhich would be required after the war to keep thiscountry to the fore in aviation. In our report (A.R.C.No. 7500) we pointed out that the anticipated greatincreases of flight speed, operational height, and aircraftsize would call for much larger and more expensiveresearch equipment than in the past. We recommendedthe formation of a National Research Establishmentcontaining very large and powerful wind tunnelstogether with extensive equipment for testing gasturbines and for structural tests on large aircraft. Wealso stressed the need for experimenting in flight and inthat connexion recommended the construction of a widerunway of some five miles in length from which largeprototype or experimental aircraft could be flown withreasonable safety. The anticipated capital expenditureat that date for the equipment recommended was in theneighbourhood of twenty million pounds. Financial.difficulties have since made it necessary drastically toreduce the items scheduled for construction in theimmediate future. We are, however, of the opinionthat research equipment of the order of magnituderecommended in our report will be necessary if thiscountry is not to fall behind in both civil and militaryaviation.

10. POST-GRADUATE SCHOOL OF AERONAUTICSIn May, 1943, the Minister also asked us to advise on

the establishment of a post-graduate School of Aero-nautical Science. The intention was to provide highercourses of training and opportunities for research workfor able students drawn from appropriate universitydepartments ; this would ensure an adequate supply offirst class technical men to satisfy the needs of theServices, civil aviation and the aircraft industry in theperiod of rapid aeronautical progress to be expectedafter the war. We replied on the 10th August, 1943, andthe main conclusions of our report are here enumerated.

We felt that one main point had to be settled : wasthere a case for establishing a new school ? The answerdepended upon the national importance and magnitudeof the aeronautical industry after the war. In view ofthe ever growing difficulty and complexity of aeronauticswe considered that the industry and the Governmentresearch establishments would require to maintain largeaeronautical and technical staffs, and, to ensure a con-tinuing supply of the right quality and training, wereported in favour of the establishment of a school.

Our view was that this proposed school should be ofuniversity standing, enjoy the same liberties as a university,be financed by the State and be controlled by a board ofgovernors. It should not compete with universities byteaching undergraduates and it should be affiliated toone of the great universities whilst retaining a largemeasure of autonomy. The staff of the school shouldcarry on research primarily to maintain its own freshnessand vigour. The subjects taught should be aerodynamics,aircraft structures, systems of propulsion and aircraftdesign with a number of subsidiary subjects. Thestudents should have a previous knowledge of engineering,physics or mathematics of graduate standard and thenormal course of instruction should cover two years.We considered that the training of higher grade scientificand technical staff for the industry was one of theprincipal reasons for founding the school, that aero-nautical design should be a principal subject and thatstudents should preferably have spent at least one yearin industry before entering the school. In addition to thenormal course of two years, specialist and refreshercourses should be provided for men from the aircraftindustry. The school would need adequate equipmentboth in the laboratory and for flying, with an airfield.

In the main our recommendations were adopted by theinterdepartmental committee set up later by the Govern-ment to put the scheme into effect. The school is knownas ' The College of Aeronautics' and is situated atCranfield, Bedfordshire.

11. LIAISON(a) The Aircraft Industry. We have maintained close

contact with the aircraft industry and the Society ofBritish Aircraft Constructors. Before the formation ofthe Council the Society was not represented on any ofour committees but we are glad to record that we hadmany valuable meetings on special subjects with technicalrepresentatives of the Society's committees and ofaircraft, engine and airscrew firms ; we were invariablyassisted by individuals when their special knowledge wasrequested in the solution of difficult problems and ourcollaboration on propellers with the de Havilland andRotol Companies was close. These cordial relations led?to an easy transition from attendance on special mattersto regular membership when our constitution was soaltered as to permit the change.

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Reciprocally, we have had a number of problems putto us by engine, aircraft and airscrew firms, and on alloccasions we were able to render some help and in a fewto give the solution. We have also welcomed severalpapers describing researches conducted by members offirms' staffs and where the subject matter was suitablehave published, or are publishing them in our Reportsand Memoranda Series. These contributions have beenin the fields of performance, stability and control,airscrews and structures.

(b) Royal Aeronautical Society. We co-operated withthe Royal Aeronautical Society on a number of mattersand have welcomed the steps which they have taken,first in the structural and next in the aerodynamic field,to provide for the designer a series of reliable datasheets. In this way the Society has condensed andassimilated in a suitable form a large volume of resultsscattered through scientific papers available from Britishand other sources. This link is most valuable as abridge between the research worker and the constructor.

The Royal Aeronautical Society arranged a number ofmost valuable week-end conferences in 1941, at whichpilots, designers and scientists exchanged views both informal conference and in friendly chats. The subjectswere chosen because of their immediate interest to thewar effort and included Airscrews (Hatfield), Manoeuvra-bility and Stressed-skin Structures (Hanworth), PowerPlants (Bristol), Serviceability (Slough), Undercarriages(Cheltenham), Maintenance and Operation of Aircraftunder picketed-out conditions (Hatfield). The membersof many of our committees thus came into personalcontact with members of the Fighting Services. TheSociety kindly supplied us with detailed accounts of theinteresting discussions.

(c) Canada. At an early date in the war Sir GeorgeThomson was stationed in Canada to keep the Dominionin touch with scientific progress in this country. Hismembership of some of our committees enabled him tospeak at first hand on aeronautical matters and he wassupplied continuously with such of our technical papersas he required. On his return to this country his placewas taken by Prof. G. T. R. Hill who again took withhim a personal knowledge of our work which wasrefreshed at intervals by visits to London.

In the early summer of 1941, eighteen representatives ofCanada came over to discuss research work and tookback with them certain British proposals for investiga-tions to be carried out in the Dominion. This wasfollowed by many visits exchanged between the twocountries.

During the autumn of 1944 we had a meeting withspecial representatives from Australia and Canada andwe forwarded to both a memorandum on Common-wealth and Empire Collaboration in Aeronautical

Research. This was the inception of the conference onaeronautical research with the Dominions held inLondon in 1946 to which reference is made in section 17of this report.

(d) Australia. The Australian Advisory Committee,formed in 1941, led to a closer co-operation in aero-nautical research between the United Kingdom and theCommonwealth. By that time the aeronautical equip-ment planned at the beginning of the war after a visitby Mr. H. E. Wimperis was nearing completion underthe Australian Council of Scientific and IndustrialResearch. Mr. Wimperis became their scientific adviserin London and with his wide knowledge of aeronauticalresearch was most helpful in starting and maintainingour contacts. We have continued to receive from theDominion the individual reports of researches and themore general reports of the C.S.I.R.

Sir Henry Tizard visited Australia in 1943 specially todiscuss aeronautical research. As a result of his visitarrangements were made for exchanges of staff whichhave continued since that date. This was followed in thenext year by a visit from Mr. Coombes, Chief of theDivision of Aeronautics, C.S.I.R., who attended anumber of meetings of our committees. As a result ofthis visit we sent to Australia during the summer of 1944,in answer to requests, our recommendations on aero-nautical research including stability and control, powerplants and a special programme on fluid motion. Aboutthis time the C.S.I.R. commenced the publication of theirseries of aeronautical publications called A.C.A. Reports.We have welcomed this step, which agrees with thepolicy of the A.R.C. that scientific work should be freelypublished because of its mutual benefit to all workers inthe same field.

(e) United States of America. Sir Henry Tizard,Chairman of the A.R.C., visited the National AdvisoryCommittee for Aeronautics, Langley Memorial Aero-nautical Laboratories and Langley Field, in September,1940, and was accompanied by Mr. J. H. Parkin of theNational Research Council, Canada. This was thebeginning of a closer contact between the N.A.C.A. andA.R.C. including the exchange of numerous visits betweenthe two countries during the war to discuss aeronauticalresearch. Arrangements were then made for the earlyexchange of confidential papers between the twocountries. A British Scientific Office was shortlyafterwards set up in Washington with Sir Charles Darwin,Director of the N.P.L., as the first Director. Thisoffice facilitated the exchange of scientific papers betweenthe two countries and helped forward the preliminaryarrangements made by Sir Henry Tizard. Thesepreliminary arrangements were followed by exchangesof visits between the two countries throughout the war.

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PART II. THE CONSTITUTION OF THE COUNCIL12. INTRODUCTION

The Aeronautical Research Committee was reconsti-tuted as a Council in April, 1945, when Sir Melvill Joneswas Chairman. The Council immediately arranged todepute some of its authority to Standing Committees tolessen the need for a continued detailed discussion in theCouncil of a great number of subjects and so to leavetime for the Council to consider more carefully majorquestions on research policy, which are frequentlyreferred for its opinion by the Ministry.

13. TERMS OF REFERENCEThe Council has been appointed with the following

terms of reference :—(1) To advise the Minister responsible on scientific problems

relating to aeronautics.(2) To keep under review the progress of aeronautica

research and to advise the Minister on the programmeand the planning of aeronautical research carried outfor the Government of the United Kingdom.

(3) From time to time, to make recommendations to theMinister on research which the Council considers itdesirable to initiate.

(4) When requested to do so, to tender advice upon anyresearch carried out by or on behalf of the aeronauticalindustry.

(5) Subject to the needs of security, to make the results ofBritish research generally available, by the publicationof research reports.

(6) To advise upon aeronautical education in the UnitedKingdom in so far as it is relevant to research.

(7) To maintain contact with similar, bodies or institutionsin the Dominions and foreign countries.

(8) To make an annual report to the Minister.

14. MEMBERSHIPThe members of the Council are appointed by the

Ministry of Supply. The Council is made up ofequal numbers of independent members and of officialrepresentatives of Government departments with anindependent Chairman. The Chairman and the eightindependent members are appointed for periods ofthree years ; these members are not eligible for re-appointment until the lapse of one year after thecompletion of their period of service. The officialmembers are : the Chief Scientist of the Ministry ofSupply ; the Principal Director of Scientific Research(Air), Ministry of Supply ; the Chief of the Royal NavalScientific Service ; the Director of the N.P.L., represent-ing the Department of Scientific and Industrial Research ;the Director of the Royal Aircraft Establishment; the

Director of the National Gas Turbine Establishment anda representative of the N.P.L., at present the Superin-tendent of the Aerodynamics Division.

15. ORGANISATIONThree Standing Committees as well as a number

of Special Committees have been appointed. The Stand-ing Committees deal respectively with aerodynamics,mechanics and power plants, and are empowered to sendforward recommendations on aeronautical researchdirect to the Ministries concerned unless they affectmatters of major policy. They have also the right toaccept recommendations from their Sub-Committees forpublication in the Council's series of technical papersentitled ' Reports and Memoranda ' and to endorse andforward recommendations for external publication tothe Ministries concerned. The Special Committees areappointed to do special work and, in the first instance,have covered the subjects of helicopters, seaplanes andwind tunnel design. These Committees put forwardtheir recommendations through the Council with theexception of those dealing with publication, upon whichthey have beer, given authority to act. The Council hasalso appointed three Special Committees dealing withoperational problems ; in all three, the membersrepresent operators, technicians and scientists under anindependent Chairman.

The Chairman of the Standing Committees areappointed by the Council from amongst its independentmembers to serve for a period of two years. Independentmembers of Standing Committees are appointed by theCouncil and each Chairman presents, for the approvalof the Council, suggestions for membership andnominations from Government departments after dis-cussion with the Government departments concerned.The Chairman of each Standing Committee, afterdiscussion with his Committee, puts forward proposalsfor the Chairmen and independent members of itsSub-Committees for the Council's approval. Theindependent members of all Committees and Sub-Committees serve for a period of three years on a rotasystem and are eligible for immediate reappointment onthe completion of a period of service.

The Standing Committees review their activities in areport to the Council two or three times a year and givetherein a list of all the recommendations which they havemade direct to the various Government departments.Many of these recommendations have originated withthe Sub-Committees who usually report to their respectiveStanding Committees after each meeting. The StandingCommittees also review periodically the progress ofresearches resulting from their recommendations anddraw attention to those which are not making satisfactoryprogress. A similar procedure applies to the Special fCommittees which report to the Council at more frequentintervals.

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16. THE AIRCRAFT INDUSTRYThe aircraft industry is represented on the Standing

Committees and their Sub-Committees and on some ofthe Special Committees. The procedure is for theSociety of British Aircraft Constructors to put forwarda number of nominations which are considered by theCouncil from which two are chosen for each Committeeand after acceptance nominees become members in theirown right and serve on a rota in the same manner asindependent members. The final selection of each pairof the Society's nominees is made to provide as wide arepresentation from firms in Industry as is possible. Thisunderlying principle has resulted in a wide representationfrom the various firms and the Council wishes toacknowledge the valuable help it has reczived from theknowledge and experience which the industrial membershave placed in the common pool. The industrialmembers have reciprocally helped the aircraft industryby the dissemination at an early stage of the technicalinformation which has been considered by the variousCommittees and Sub-Committees.

17. COMMONWEALTH ADVISORYAERONAUTICAL RESEARCH COUNCIL

In June, 1946, a Commonwealth Conference onAeronautical Research was held in London. It wasconvened- to discuss and make recommendations on theco-ordination of aeronautical research throughout theCommonwealth and was attended by delegates from theUnited Kingdom, Canada, Australia, New Zealand andthe Union of South Africa. The delegation from theUnited Kingdom was nominated by the AeronauticalResearch Council and included the Chairman of Con-ference, Sir Melvill Jones. At some of the meetingsrepresentatives of the United States of America attendedas observers.

The Conference reached unanimous agreement ona number of recommendations to the appropriateauthorities in the different countries. The most importantof these was a recommendation for the formation of aCommonwealth Advisory Aeronautical Research Council.The formation of this Council has been confirmed by theparticipating countries.

The terms of reference of the C.A.A.R.C. include thepromotion of progress and encouragement in the widest

practical sense of aeronautical research throughout theCommonwealth and the review of the progress ofaeronautical research therein, involving advice on thebroad planning of programmes and on the facilitiesrequired. Consideration will also be paid to means ofdisseminating information on aeronautics and of pro-moting interchange and visits of scientists within theCommonwealth. Action on these recommendationshas already taken place with reference to the main itemson the programme in the respective countries and someinterchanges of personnel. In general, the programmecovers the subjects of aerodynamics, structures, powerplants and operational research. It is intended that theCommonwealth Advisory Aeronautical Research Councilshould meet alternate years with the place of meetingto be in each Dominion in turn. The first meeting tookplace in Australia in April, 1948.

The Aeronautical Research Council has maintainedthe direct contact with those in charge of research inCanada and Australia and a number of the workers inthese Dominions, which was first initiated by theAeronautical Research Committee. There has beenco-operation in both the aerodynamic and structuralfields of research and the Council has welcomed a varietyof questions on aeronautical subjects put to them by thetwo Dominions concerned. It is expected that opera-tional research will start in all four Dominions and theUnited Kingdom will welcome this co-operation. TheCouncil has been informed of the first steps taken tocollect information and review the whole subject inAustralia. This and other aeronautical work of commoninterest came under consideration at the first meeting ofthe C.A.A.R.C.

18. UNIVERSITIESThe Council wishes to encourage research on aero-

nautical matters at universities. The Mechanics andthe Power Plants Committees have had special meetingsto which many members of university staffs were invitedto be present. In each case a brief outline of the researchquestions needing solution were placed before thevisitors and as a result some additional research hasstarted at universities. The Council is informed that theMinistry of Supply is willing to assist aeronauticalresearch which is undertaken at universities and technicalcolleges.

PART III. THE PERIOD 1945-194819. INTRODUCTORY

The change in the constitution of the Council reportedin Part 2 give it more time to deal with major questions,while leaving detailed discussion of most of the technicalproblems and action thereon to its Committees andSub-Committees. The scope of discussion throughoutthe organisation has also widened considerably during

the period 1945-48 due to the appointment of the newOperational Special Committees. In addition to thecontacts with the Admiralty which go back over a greatnumber of years, similar contacts are now maintainedwith the Air Ministry, the Ministry of Civil Aviation andto a lesser extent with the War Office on matters affectingaeronautical research and aircraft operation. The much

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closer contact with the aircraft industry has already beenreferred to in Part 2. The three civil aircraft Corpora-tions are represented on the Civil Aircraft ResearchCommittee.

An increasingly close liaison with the Dominions ofCanada, Australia, New Zealand and the Union of SouthAfrica has followed the first meeting of the Common-wealth Advisory Aeronautical Research Council held inAustralia in April, 1948.

We deal briefly in subsequent sections with our moreimportant activities during the period 1945^48. Thesecover the main subjects of aerodynamics, power plantsand mechanics, and also include seaplanes, helicopters,meteorology and wind tunnel design, in addition tomatters on aircraft operation already mentioned above.From amongst these subjects we have drawn specialattention to the two following matters.

There are revolutionary possibilities opening up in theaeronautical sphere of to-day. These can only berealized if the large and powerful research tools recom-mended in 1944, and since partly planned, are providedquickly for the National Aeronautical Establishment atBedford. The United Kingdom has in the intervallagged lamentably behind other countries in the provisionof adequate research tools. If the new tools are notforthcoming in the immediate future, this country willnot have a chance to catch up in research and theconsequence will be that development of new aircraftwill be both much more costly and very much slower.We have commended this matter for most seriousconsideration.

The second matter relates to the whole of the presentresearch activity. At the request of the Chief Scientistthe Council reviewed with care in 1946 the wholeprogramme of aeronautical research under his directionand made definite recommendations about the prioritiesof different subjects. This matter continues to be of firstimportance, particularly in relation to the availability ofstaff. The best progress in research can be expected onlyfrom investigations of a few specific designs combinedwith a study of the fundamental physical problems whicharise in the course of development and construction. Wehave also commended this for serious consideration.

20. EQUIPMENT FOR RESEARCHThe requirements for Aeronautical Research and

Development were reviewed and set out in a report(A.R.C. No. 7500) to the Minister in 1944 (see Part 1),and following the adoption of this report by the Govern-ment, preliminary plans for a new AeronauticalEstablishment were drawn up and a survey of possiblesites for the Establishment was undertaken.

Early in 1945 a decision was reached to build the newEstablishment (National Aeronautical Establishment) ona site three miles north of Bedford, taking in the war-time

airfields of Twinwood, Thurleigh, and, as an ultimatepossibility, Little Staughton in addition.

In April, 1945, a mission led by Mr. Perring left thiscountry to study the aeronautical research equipment inAmerica ; in that country many ambitious tunnelprojects had been started as the result of the War, andmuch of the equipment had come into operation or wasin the final stages of construction. The ending of theWar in Europe also afforded an opportunity of studyingthe many developments that had gone on in Germany inthe years preceding as well as during hostilities.

The rapid post-war developments and the emphasis ontransonic and supersonic research, together with thedecision to set up a National Gas Turbine Establishment,brought about a revision of the original plans as set outin the report A.R.C. No. 7500. These changes resultedin first priority at Bedford being directed towards theprovision of supersonic research equipment, whilst theequipment required to meet the future needs of gasturbine research would be planned for the Gas TurbineEstablishment at Pyestock.

Work at Bedford started in June, 1946, and progress onthe roads and services went ahead satisfactorily. Planshave also gone ahead and are well advanced, but noconstruction has started, to provide a High SpeedLaboratory, a new Spinning Tunnel, and two generalpurpose tunnels.

A small experimental tunnel has been constructed atFarnborough to investigate the design of tunnels, andexplore those features in design likely to lead to steadyand uniform flow and low stream turbulence. Thistunnel was completed in April, 1946, and tests haveshown that the longitudinal turbulence expressed as apercentage of the velocity in the tunnel working sectionis only 0-004 per cent, at 50 ft. per second, rising toabout 0-01 per cent, as the speed increases to 250 ft.per second. Measurements of the noise level in thetunnel and study of the spectrum of the turbulence haveshown that most of this apparent turbulence rs reallysound vibration which is generated by the fan and by thewall friction.

The Council has reaffirmed the importance of providingthese research facilities, and urged that staffs should bestrengthened and priorities on labour and materialsshould be arranged so that all phases of the work can beaccelerated.

It is perhaps important to stress that the new andalmost revolutionary possibilities opening up in aero-nautics to-day are only likely to be realized if the largeand powerful research tools being planned for Bedfordare provided quickly. Without this vital equipment,development will be both costly and slow.

The existing facilities for gas turbine research anddevelopment at the National Gas Turbine Establishmentprovide a variety of air supplies for combustion andaerodynamic work.

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21. AERODYNAMICS

(a) Supersonic researchA major part of the business of the Fluid Motion

Sub-Committee has been concerned with problems ofhigh-speed flight, and particular attention has been paidto flows which are either wholly supersonic or whichcontain regions of both subsonic and supersonic speed.The latter type of flow is characterised sooner or lateras the speed is raised by the appearance of shock waves,and is particularly important as it is that encountered atthe top speeds of many current aircraft. No satisfactorytheory has yet been advanced to predict either theappearance of these shock waves or their effects upon theperformance and stability of aircraft, and most of ourpresent knowledge is derived from experiments made inwind tunnels. These experiments have in many casesbeen assisted by the development of optical methods offlow exploration. Fundamental experiments made atthe N.P.L., in Switzerland and in America on theinteraction of shock waves with boundary layer have beenparticularly valuable. In addition to investigating theinfluence of the shape of the wing section on its per-formance at high speed, it has been necessary toinvestigate also the effect of the planform, for it wasfound in Germany and confirmed in this country thatthe high-speed effects mentioned above and in Part 1 ofour report can be postponed by sweeping back the wings.

Linearized flow equation. The theory of flows which,apart from some regions of the boundary layer, arewholly supersonic has been considerably advancedalthough only hi very few cases have experimental checksbeen'attempted. The most notable advances have,perhaps, arisen from solutions of the linearized flowequation. This linearized equation is based on thesupposition that the disturbances introduced by a bodytravelling at a supersonic speed are small in comparisonwith the speed of the body itself. In this respect it issimilar in character to the linear theory which has beenused extensively in the past for determining the flowaround bodies at subsonic speeds. The principalapplication of the linearized supersonic theory has beento the detailed study of the flow over wings, and, inparticular, to swept-back planforms. The solution forthe flow over the triangular, or so-called delta wing,has been the genesis of this work. The lift, pitchingmoment, profile drag and induced drag, as well as theaerodynamic derivatives in pitch and roll which areessential to stability calculations, have all been evaluatedfor the delta planform ; by a simple extension thesolutions can be.applied to a family of similar planformswhich have swept-back trailing edges, in addition toswept-back leading edges. The aerodynamic character-istics of fuselages have also been studied with the aid ofthe linearized flow equation and comprehensive solutionshave been obtained for shapes including the solid shelland the open duct, the latter being of the type requiredfor a ramjet or gas turbine air intake. Moreover, the

interaction between the fuselage and the wing has beenexamined and solutions have also been obtained for thedownwash behind wings.

It is clear from these examples that the linear supersonictheory is a powerful and productive tool which hasallowed some considerable progress to be made in theunderstanding of the behaviour of the flow around bodiesat supersonic speeds ; but there are extremely importantreservations which must be made at this stage. The lineartheory is essentially only an approximation to the flowof an ideal fluid, which is in itself unreal since boundarylayer effects are ignored. The degree to which theseapproximations represent real events can only bedemonstrated by experiment. So far experimentalverification of the results of the theory have been sporadicand much more systematic work remains to be done.

Wind-tunnel techniques. During the period underreview experimental work has developed rapidly, but,since the techniques of supersonic wind tunnel testingwere relatively undeveloped in this country at the end ofthe War, the start was slow and work is only now gettinginto its stride.

Much experimental work has gone into the develop-ment of supersonic wind tunnels. The provision of auniform airstream demands tunnel wall shapes dependingon the speed desired, the boundary layer growth and thenature of the flow ahead of the tunnel throat. Varioustheoretical designs have been tested with varying success,and a method for redesigning wall shapes to give improvedflow uniformity after an initial test has been made, hasbeen developed. Using this method satisfactory resultshave been produced.

As the air in a wind tunnel is accelerated it becomescooler. At supersonic speeds this effect is so marked thatany water vapour present usually condenses. The effectsof condensation of the moisture present in the tunnelair have been investigated and correlated satisfactorilywith theoretical work. Methods of avoiding trouble dueto condensation have been investigated, but in generalthe only safe solution is so to dry the air that the effectsof condensation become negligible.

Boundary layer effects.—As the experimental work hasdeveloped it has become more and more clear thatboundary layer effects often seriously limit the applicationof theoretical solutions in which viscosity is neglected.Some theoretical and experimental investigations ofboundary layers in supersonic flow have been made.The laminar boundary layer has been treated theoreticallyfor the cases with and without pressure gradients withsimplified laws for the viscosity variation. No experi-mental verification is yet available. The experimentalwork has been largely on turbulent layers and hasindicated that in certain circumstances the velocitydistribution is roughly independent of Mach number.The most marked difference between supersonic andsubsonic boundary layer effects arises from the fact that

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in supersonic flow a pressure rise outside the boundarylayer often occurs discontinuously through a shock wave.In this case the assumptions of boundary layer theoryare not satisfied and an experimental approach isnecessary. The detailed nature of the flow and thequestion of whether the boundary layer will separate ornot in any given case are the subject of experimentalinvestigation but no conclusions have yet been published.

Some checking of linearized potential wing theory hasbeen done and in general severe discrepancies due toboundary layer effects have been found, but the mainprogramme on this subject, which includes wing-bodyinterference, is still in its early stages and few results areavailable as yet.

Engine intakes. Efficient air intakes are absolutelyessential to the working of turbo-jets or ram-jets atsupersonic speeds. All available data have beencorrelated and tests on several forms of intake have beenmade. Efficient intakes for use at Mach Numbers (M)up to 2 and above have been developed. The problemsof maintaining efficient operation over a wide range ofoperating conditions, and of reducing the drag of theintakes are absorbing a great deal of effort at the moment.

Transonic flight work. At and near the speed of sound,interpretation of wind-tunnel results becomes difficultowing to the effects of the tunnel walls, and piloted flighttesting is necessarily hazardous. For these reasonsvarious free flight testing techniques have been developed.

A series of tests were planned using rocket-propelledaircraft models controlled by an auto-pilot and launchedfrom an aircraft at about 35,000 ft. The aircraft shouldthen accelerate in level flight through the transonic speedrange and decelerate to subsonic speeds again. Theflight path was to be observed by radar, while speed,acceleration and the movement of the tailplane weretelemetered to the ground. Despite many difficulties inrocket ignition, fuel system and controls, a successfulflight was achieved. By this time it was, however, clearthat, considering the accuracy and extent of the resultswhich could be obtained, the effort required for suchtests was uneconomic, and other simpler techniques arebeing used for future work. Of these techniques themain ones are (1) observing the path of relatively simplemodels propelled by solid fuel rockets and launchedfrom the ground, and (2) observing by radar and bytelemetering the trajectory of heavy models freely fallingfrom an aircraft at high altitude. With this secondtechnique, drag measurements on wings up to aboutM = 1 • 1 have been made, though some technicaldifficulties in accurate telemetering caused by thetemperature change as the body is taken up to highaltitude have caused work to be slow.

Experimental supersonic aircraft. The accumulateddata, both theoretical and experimental, on supersonicflow have recently been applied to the study of possible

designs for an experimental supersonic aircraft. Withsuch an aircraft it is hoped to be able to penetrate andfly well beyond the sonic region and, in so doing, providesome insight into the many complex transonic problemswhich up to the present have eluded treatment boththeoretically and in the wind tunnel. It is consideredthat this full-scale approach to the problem of pilotedsupersonic flight is likely in the near future to be the mosteconomical and fruitful of any of the methods proposed.

(b) Research at high subsonic speeds »Swept wings. Towards the end of the War, the

possibility of achieving a considerable improvement inthe performance of high speed aircraft by the use ofhighly swept-back wings and other unconventional wingshapes had begun to be realised, and a large proportionof our work since 1945 has been concerned with thedevelopment of these ideas. German experimental andtheoretical work had already shown that the rapidincrease in drag which occurs on existing aircraft atspeeds around 0 • 7 to 0 • 8 of the speed of sound could bedelayed to higher speeds by sweeping the wings forwardor backwards. Tests in the high speed tunnels at theR.A.E. and N.P.L. soon confirmed this, and showedthat the dangerous changes which occur in stability andcontrol at high speeds could also be delayed in this way.The improvements obtained were much greater thancould also be delayed in this way. The improvementsobtained were much greater than could have beenachieved by other methods such as a practicable reductionin the wing thickness or by modifying the wing section.Sweeping the wings back through 40 deg, for example,seemed to make possible an increase of the order of50 m.p.h. in speed, and similar gains seemed possiblewith wings of triangular planform.

It soon became clear, however, that these advantageswere accompanied by several new and difficult problems.Among the most important of these was the problem oftip stalling which at first appeared to constitute a seriousobstacle to further development. This problem wasunfortunately important, not only at low speeds, wherecertain partial solutions had already been considered,but also at high speeds. It still remains one of the mostdifficult problems in the design of aircraft with swept-back wings, but tunnel tests and theoretical considera-tions have in the meantime suggested methods by whichthe difficulty can at least partially be met. This andother problems associated with swept-back wings arediscussed in more detail in the section on stability andcontrol.

A considerable amount of theoretical work has beendone on the design of the body-wing junction on swept-back wings. The air flow in this region is normally suchas to prevent the maximum advantage being obtainedfrom the sweepback. It has been shown that by carefuldesign of the junction and of the wing itself the lossesin this region can be reduced and an appreciable gainin speed obtained.

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All the work discussed so far has been either theoreticalor on models in wind tunnels. It has of course beenclear from the outset that confirmation of this work onfull-scale aircraft in flight would be desirable beforeproceeding far with the construction of operationalaircraft. Several experimental aircraft with swept-backand triangular wings have therefore been initiated, andwill shortly be tested. The work on these aircraft willconstitute a vital link in the high speed research pro-gramme, not only in providing a check on the model andtheoretical work, but also in investigating those handlingcharacteristics which are not amenable to theoreticaltreatment or model testing. In the meantime the highspeed characteristics of several existing aircraft have beencarefully measured in flight for comparison with highspeed tunnel tests, and promising agreement found inmost cases. Extensive project calculations and designstudies have also been made, at the R.A.E. and ataircraft firms, to determine the best designs for futurehigh speed fighters and bombers, and some of thedesigns proposed have been tested in the High SpeedTunnel at the R.A.E.

Control at high speeds. The development of controlsfor high speed aircraft has received considerable attention.High speed tunnel tests had at an early stage indicatedthe possibility of a large reduction or even a completereversal of control effectiveness at speeds near the speedof sound. The reasons for this loss of effectiveness havebeen investigated and some possible solutions suggested.Measurements have also been made, mainly in flight,of the large variations in stick force characteristics whichoccur at high speeds. The fact that these variations aredifficult to predict and often dangerous has led to theconclusion that power operation will be essential onfuture high speed aircraft, at any rate whilst they are inthe experimental stages. The work already in progresson the development of power controls for large aircrafthas therefore been extended to the high speed field.

Problems at great heights. The importance of certainnew problems associated with high speed flight at greatheights became apparent soon after the end of the War.The most important aerodynamic problem in this fieldarises from the limitations imposed on maximum liftunder these conditions. These limitations are of coursepartly due to the low density, but at high speeds thiseffect is very much accentuated by the reduction inmaximum lift caused by compressibility effects. In somecases the maximum lift which can in practice be utilisedis substantially less than the true maximum owing tothe onset of severe buffeting. Wind-tunnel tests have^>een made to determine the wing section characteristicsneeded to minimise the reduction in maximum lift athigh speeds. Measurements of the maximum liftobtainable have also been made on complete models ofhigh altitude aircraft designs proposed by variousaircraft firms. Tests have been made in flight on existingaircraft such as Meteor, Vampire and Spitfire, to checkthe reliability of the high speed tunnel measurements,

and to investigate buffeting limitations. Attempts havealso been made in flight to assess the margin needed inpractice between the maximum lift and the normalcruising lift, and to determine the characteristics ofaircraft operating near the limiting lift. Some progresshas been made in investigating the precise nature oflimitations, observing the flow over the wing by meansof wool tufts.

Experimental technique. The investigation of many ofthe problems of high speed flight discussed above hasnecessitated the development of new experimentaltechniques, both in wind tunnels and in flight. In thecase of the R.A.E. High Speed Tunnel, for instance, itbecame necessary to develop new methods of measure-ment, using smaller models and a strain gauge balance,in order to enable the effect of speeds up to 0 • 95 of thespeed of sound to be investigated, but only with a seriousreduction in the values of the Reynolds numbers at whichthe experiments are made. In flight the technique ofmeasurement in dives and in level flight has been verygreatly improved. Methods of obtaining a clearerphysical picture of the air flow at high speeds have alsobeen developed, including a method of photographingshock waves in flight which is capable of wide application.

(c) Stability and controlSwept-back wings. Since 1945 the major new problem

in stability and control research has arisen from theacceptance in this country of large sweepback to ease theproblems of transonic and supersonic flight (seesection 21 (b)). This brings in its train a series of adverseeffects in incompressible flow :—

(1) There is premature stalling at the wing tip, partlybecause the swept tip carries more than its share oflift in inviscid flow, and partly because of the pilingup of the boundary layer at the tip. This tends toproduce longitudinal instability, and to impair theeffectiveness of a control at the rear of the wing tip,as the stall is approached.

(2) When a swept wing bends up under load, the incidencefalls near the tip, thus bringing into play an aero-dynamic moment tending to increase the incidence ofthe whole wing, and therefore the load. This is atroublesome form of aero-elastic instability.

(3) The sideslipping characteristics of a swept wing varygreatly with its incidence. Thus it is unusuallydifficult to arrange fin surface and dihedral so as toavoid persistent lateral oscillations in some part of theflight range.

(4) Sweepback impairs the maximum lift coefficient, whichis further reduced by the low aspect ratio with whichit is commonly combined, and it is not so easy as instraight wings to make flaps supply the deficiency.The provision 01" a reasonably low approach speedwith good control (see (1)) is not an easy matter.

Work on these problems is in the pioneer stage and,with our limited resources, is- proceeding mainly by thecollection of essential data through theory and experi-ment on specific design projects. Items 1 and 2 above

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indicate a complex of intricate problems in which theinteraction between good handling qualities and theefficiency of the aircraft as a whole could hardly be closer.In the circumstances, some playing for safety is inevitable.Thus the conventional wing tip control, and well triedmethods of wing construction, are retained, and a solutionis sought, at least cost in structure weight, by combininglarge sweep with low aspect ratio and high taper. It isrecognised however that more radical departures, on theone hand by using novel methods of stressed-skinconstruction, and on the other by developing wing tipcontrols which are aerodynamically more effective andstructurally less costly, would probably lead to a plan-form which was stiff enough without being so stubby*Such possibilities are now under review.

Aerodynamics of trailing edge controls. For manyyears the design of trailing edge controls for non-sweptaerofoils has rested on data whose systematisation hasbeen largely empirical. Since 1945 the foundations ofthis subject have been more securely laid down at theN.P.L. by intensive study by theory and experiment ofthe mechanism by which a flap provides lift and theassociated hinge moment. A great advance has thusbeen made in our knowledge of the flow near the trailingedge under various conditions of the boundary layer, andhow this influences the design parameters. The problemremains rather intractable in its detail and its applicationto practical design, because of the many parameters.But it has led to a scheme for the basic estimate of controlcharacteristics which a designer can use with much moreconfidence than formerly.

Flight research. The following items, mainly of flightresearch, represent partly consolidation of work startedduring the War, and partly advances into new problems:—

(i) The flight techniques and analysis suggested by theextended theory of longitudinal stability and control(see Part 1) have been developed in testing a numberof aircraft, including cases with large distortioneffects. This work has gone far to establish themethod as a reliable tool for research and development.

(ii) In pursuance of safety, particularly for large civiltransport aircraft, our research handling work hascontinued to stress the need for larger tail and finsurfaces than are willingly adopted in this country.This has accentuated the problem of balancing thecontrols and has involved the wide use of spring tabs,including schemes to avoid overstressing the structureat high speeds.

(iii) In very large aircraft the power to move the controlsmust be obtained either from an auxiliary source(e.g. the engines' batteries), or, in the servo tabsystem, from the airstream. The choice in such acase as Brabazon I between powered and servo tabcontrol means a major and difficult decision. Researchon the merits of the two systems is being suppliedin much detail by tests of Lancaster installations. Thechoice rests on the relative weight and safety of thetwo methods. To be safe, powered controls musteither be duplicated or provided with reversion to

manual control ; the increase in weight is to bebalanced against the possibly greater initial weightof the servo tab system. The prevalent opinion isthat the servo tab is certainly the safer, and may alsoprove the lighter, of the two types.

(iv) Passage through a gust may be eased and the wing loadreduced if there is anticipatory movement of a controlat a signal from a gust detector ahead of the wing.A successful gust alleviator would much increase thepayload of civil aircraft, but account would have tobe taken of its effect on the stability and controlcharacteristics. The general problem is beingexamined, and a particular study is being made of aLancaster installation of the Brabazon I gust alleviator.

Efforts are being made to reduce the intricatecalculation of longitudinal response to a gust toreasonably accurate formulae which are simpleenough to be handled by designers.

(d) Research on boundary-layer controlBoundary-layer control continues to be a live issue.

Besides its application to thick low-drag wings, slotsuction can also be used for providing the increases inmaximum lift which the thin wings of high-speed aircraftneed for take-off and landing and for high-speedmanoeuvres. Applied to the outboard parts of the wings,it can be used for the prevention of tip stalling. Wind-tunnel tests at low speeds have confirmed that increasesof lift are obtained, although the suction quantities haveproved to be rather larger than was hoped.

Much theoretical work has been done on an alternativemethod of boundary-layer control in which the air iswithdrawn through an area of porous surface instead of ata discrete slot. The suction quantities in this alternativemethod (known as ' distributed' suction) promise to bevery much less than those for suction through slots.This prediction has been confirmed by preliminary testson the stalling properties of a thin symmetrical aerofoilwith a porous nose.

An application of distributed suction has beensuggested for producing lift independently of incidence.The suction keeps the boundary layer thin and preventsit from separating ; the lift obtained depends on theposition of a trailing edge flap which fixes the position ofthe dividing streamline at the rear of the aerofoil and sothe lift. This method has been applied in the wind tunnelto the extreme case of a circular cylinder.

The general problem of the design of suitable aerofoilsection shapes, including those for use with the variousmethods of boundary-layer control, has been greatlyfacilitated by the development of rapid numericalprocesses for application to the theory given in papersreferred to in Part 1 of this report, and by a powerfulexact method which is used in the final stages of design.Theories have been put forward for estimating the suctionquantities required in the several cases, and experimentalinvestigations have shown how to design the internalducting within the wing in such a way as to minimise thepower needed for leading the sucked air to the pumpingsystem which discharges it into the atmosphere.

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The value of many wind-tunnel experiments has beenincreased by the development of techniques which enablethe position of transition from laminar to turbulent flowto be visualized over the whole of the surface. Atechnique which permits this to be done in flight ismentioned in Part 1 of this report.

22. POWER PLANTS(a) Trend of research and development

At the beginning of the period under review the simplejet engine of the centrifugal type had reached service in theR.A.F., and subsequent developments have been mainlyin greater mechanical reliability, increase in thrust byscaling up, and reduced specific weight, especially for thelarger thrusts. There has been practically no change inthe simple basic design and only a very small reduction inspecific fuel consumption. The achievements in mechani-cal developments are indeed remarkable when comparedto the history of the piston engine and have proved thatthe jet engine is quicker in development and requires lessoverhaul. The fundamental reasons for this are of coursethe revolutionary simplicity of the power plant in whichthe available power is developed entirely as fluid energy,mechanical power transmission being confined to a singleshaft, with no rubbing surfaces.

The axial compressor engine has now also madeconsiderable progress in mechanical development, bothas a jet engine and as a propeller turbine. The poten-tialities of the axial jet engine are generally accepted tobe much greater than those of the centrifugal jet enginefor two main reasons ; namely, inherent lower frontalarea for a given thrust and adaptability for higherpressure ratios. The first advantage is associated withthe axial direction of flow and the efficient use of thecross sectional area of the compressor annulus, althoughthere are indications that reducing the diameter of theinner hub is beginning to introduce new problems incompressor aerodynamics. The combustion chamber orthe turbine may also limit the diameter of the wholeengine, bringing problems of pressure loss in the com-bustion system, or design of the turbine if it is to rotateat the same speed as the compressor rotor The secondadvantage is bound up with how far the number ofstages or the pressure rise per stage can be increasedw ithout unduly affecting the flexibility of the compressor,and it may be necessary to divide the compressor intotwo rotors running at different speeds. Some concernhas been felt that the axial compressor might be parti-cularly sensitive to deposits on the blades and also toicing effects, although its advocates are confident thatthese problems will be overcome by normal development.Research has recently been started on the separation ofparticles from the air before it enters the. compressor.

The flight conditions under which the various forms ofapplication of the turbine principle—the simple jetengine, propeller turbine, ducted fan, and compoundpiston engine plus turbine—show to advantage, have been

the subject of a great many papers and discussions by theCouncil's Power Plants Committee. It is now possibleto form a fairly clear picture, although the border linesbetween zones of application of each type cannot bedecided with any certainty because they are so sensitiveto the precise values of the fuel consumption, weights,etc., which in turn depend on progress in efficiencies ofcomponents and in mechanical design. As is well known,the simple jet is most suited to high flight speeds and highaltitudes and has an inherent weakness at take-off andduring climb, which may, however, be countered eitherby extra fuel burnt after the turbine known as reheat, orby injection of an evaporating liquid such as methanolso as to cool the inlet temperature or by use of auxiliaryrockets. The propeller turbine shows to best advantageat the lower speeds and has a very good take-off andclimb. The upper limit of speed of the propeller turbine,at first thought to be in the neighbourhood of 450 m.p.h.,is now believed to be considerably higher in view ofimprovement in propellers and may reach 550 or600 m.p.h.

The propeller turbine. Progress in the development ofpropeller turbine engines since 1945 has been consider-able. They have now reached a stage of reliability andare beginning to be flown. It is of special interest thatsome of these have axial compressors.

The ducted fan. The ducted fan has a logical place inthe speed range intermediate between the propellerturbine and jet engine and has considerable potentialitiesfor increasing thrust by extra fuel burned after therotating parts, but on the other hand it tends to be largein diameter and involves special constructional problems.

The compound engine. The compound piston engineplus turbine arrangement is attractive primarily as itshould give a very high fuel economy and have theimportant advantage that this is attained at low altitudesand is maintained at the lower flight speeds. This enginewould have possible application for very long-range andlong-endurance aircraft. Possible disadvantages are itscomplexity and weight ; also, it would be unwise toassume that it will ultimately be less reliable merelybecause of its more complicated fundamental principle.The Power Plants Committee has recommended thatwork on the free piston gas generator for aircraftpropulsion should be continued only to clear up certainpoints and that a vigorous policy should not be adoptedfor this power plant.

Fuel economy. The outstanding future need in turbineengines is improvement of fuel economy. Amongst thevarious means to achieve this, increased pressure ratioseems the most promising. Of other methods the use ofheat exchangers has been almost ruled out for aircraftengines on the score of size, weight and pressure loss,and the improvements of component efficiencies do notappear likely to be sufficient to solve the problem,especially when other requirements such as small frontalarea must be met at the same time.

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The Council has strongly advocated the constructionof higher compression jet engines. It considers that suchan engine should be of the double compound type andwould justify a research engine for experimental purposes.It has been informed that under present conditions, theMinistry of Supply finds it impracticable to arrange forany firm to build an engine for research, and that enginesmust always be built for a definite aircraft application.While appreciating the difficulties from the firms' pointof view the Council has felt that this state of affairs mustresult in conservative designs being put forward andengines of advanced new types not being built. Since theturbine engine lends itself to prior development of thecomponents and a subsequent bringing of them togetherto form an engine, many of the research problems,although not all, can be solved by building compressorsand turbines of advanced design.

Frontal area. The other outstanding need is forengines of smaller frontal area for a given thrust,especially for the propulsion of supersonic aircraft otherthan those for research purposes which may be propelledor boosted by rockets. It has been agreed that someincrease, estimated variously at from 30 to 100 per cent,in the present thrust per unit frontal area, is available bydevelopment of existing engines and this will go someway to solve the problem. The Power Plants Committeeare at present endeavouring to decide how much furtherincrease in specific thrust is desirable and whether anynew research is needed in order to arrive at a design ofengine which will be satisfactory for supersonic flightlooking ahead a number of years.

Suction wings. The arrangement of suitable enginesfor an aircraft employing boundary-layer suction hasbeen the subject of several deliberations and it has notbeen possible to say definitely whether it is better tofeed all the sucked air from the boundary-layer slots intothe engine intake, or to use an engine driving a separateturbo-pump to suck the boundary-layer air. Thedecision is likely to rest on further knowledge of the flowand pressure loss between the slots and the engine intake,and the Committee has strongly recommended that adesign layout be immediately investigated and anexperimental aircraft be constructed and flown.

In connection with the various power plants beingdeveloped at firms, considerable testing facilities havegrown up, and a large amount of research is now beingdone there, in addition to that at establishments.

(b) Special problemsCompressors. More knowledge is required of the

actual flow inside compressors and the increased provisionof test plant should provide this. It is important thatsome of these facilities be devoted to work of a funda-mental analytical kind, aided by cascade tests, todetermine the limiting factors in design for futurecompressors.

Axial-flow turbines. Strong recommendations weremade in 1945-46 for increased provision of turbine testplants, as it was felt that efficiencies of turbines had notbeen adequately measured and research was needed onthem, especially in view of the sensitivity of the efficiencyof the whole engine to variations in the turbine efficiency.The position is now improving.

Combustion of fuels. New fundamental problems havearisen when operating combustion chambers at lowpressures and temperatures associated with high altitudein which chemical as well as physical limitations tocombustion appear : research is active in this field.Combustion systems have now been run on a range ofdifferent fuels and the whole field of possible substancesfor use as fuels has been surveyed. This has led to theconclusion that with the exception of somewhat freakishsubstances there is little to be gained in departing fromhydro-carbons either on a heat per unit mass or a heatper unit volume basis. Nevertheless, work on unusualfuel substances has been encouraged especially in viewof ram-jets, where there is no turbine to follow thecombustion chamber.

Materials. Increased turbine operating temperaturesare desirable for improved economy in the propellerturbine and for improved specific power output for thejet engine, the latter being particularly important lookingahead to the use of jet engines for supersonic flight.While the alloys at present used are giving good results,improved methods of manufacture of blades are needed.The rising pressure ratios for compressors necessitatehigher temperatures and new light alloys may be required.It has been recommended that a study should be madeon new materials and interest is also being shown in theuse of sintered materials.

Blade cooling. The cooling of turbine blades is oneof the most important subjects of research. In the pastblade cooling systems have been unsatisfactory requiringexcessive amounts of cooling air, and more knowledge ofthe fundamentals is required before successful applicationcan be made. One method is the release of air through-aslit in the blade to form a cool boundary layer oralternatively the use of porous blades for the samepurpose. It has been recommended that experimentalresearch be pursued on the heat transfer and flow withsuch blades. Interest has also been shown in the Schmidtwater-cooled blade system.

Fundamental physical research on high speed flow. Theimportance of physical research on flow at high speedsunder conditions of shock wave formation and especiallynear the boundary layer, which has been referred to insection 21 (a), is also emphasized in the design of turbinesand compressor cascades operated at high Mach numbers.

(c) Rocket researchThe part to be played by the rocket in aircraft propulsion

has been considered in the light of encouragement torocket development which followed the German war

22

work and the increased attention given to rocketdevelopment in many countries in connection withguided missiles. It appears that there are two aircraftapplications for which the rocket is almost indispensable ;namely, climb boost and assisted take-off. The rocketis also a very convenient and fairly readily availablemeans of propulsion of research aircraft to pass throughthe sonic barrier to reach supersonic speeds, as has beenshown in America. Where any considerable duration offlight is required the rocket is always at a disadvantagecompared to a jet engine with reheat, on account of itshigh fuel consumption. Considerable increase infacilities for rocket research and development in thiscountry have been recommended.

The design and development of rocket motors is stillnecessarily carried out in the absence of fundamentaldata and it has been recommended that research becontinued on such problems as heat transfer at high gasspeeds and temperatures in rocket nozzles and combustionsystems, boundary layer cooling using porous materials,search for high energy rocket fuels, and the study of thefundamental ignition and combustion phenomena.

(d) Piston enginesApart from some further investigations into piston

cooling and an investigation into the mechanism of heattransfer from the piston to the cylinder walls, researchon piston engines during the period under review hasbeen limited to the development of a high pressuretwo-cycle piston engine.

A number of both single and twin cylinder units of theengine have been built and tested, both of the valvelessloop scavenged type and with end to end scavengingusing a single sleeve valve. So far as performance isconcerned, the results show a substantial improvementover the target figures both in thermal efficiency and in theamount of fuel that can be burnt in a given size ofcylinder (which latter consideration alone determines thesize of the piston engine).

23. STRUCTURES AND AERO-ELASTICITY(a) Structures.

The work on structures has fallen into the followingmain divisions :—(1) Determination of external loads onaircraft, (2) Materials, (3) Stress analysis, (4) Methodsof construction, (5) Test methods, (6) Aero-elasticproblems.

Determination of external loads on aircraft. Knowledgeof the external loading on aircraft structures is beingaccumulated steadily, but is still scanty, particularly forflight at high Mach numbers. From time to time theStructure Sub-Committee has received results fromV-g recorders, and the development of the electricalresistance strain gauge and methods of recordingtransient strains has given the research worker a tool ofgreat value in determining the instantaneous distributionof stresses in a structure and thence by deduction themagnitudes and distribution of the air loads themselves.

This latter work is still in an early stage, and progress islimited by the numbers of research staff available. Theeffect of gusts upon modern aircraft has received attentionfrom two Gust Panels. Aircraft have hitherto beendesigned to resist occasional heavy loads, but with ademand for increased life of the structure considerationof fatigue and effects of repeated loading have emphasizedthe importance of knowing the frequency of occurrenceof forces of different magnitudes ; it seems that a readilyobtainable number of repetitions of comparatively smallforces may produce more serious effects upon thestructure than an occasional very heavy load.

Materials. Research in metallurgy may consist offundamental investigations into the behaviour of metals,or investigations to solve immediate problems confrontingthe engineer. Although naturally reluctant to impedefundamental research, the Structure Sub-Committeefeels that the trend of aircraft design indicates certainrequirements which could with advantage find a placein the programme of the metallurgist. The close controlof physical properties is of great interest to the aircraftdesigner, and when it is realized that the ultimate strengthof aluminium has been increased ten-fold by alloying,and that this depends upon a complex and sensitiveprocess, the importance of such work is evident.Improvement of one property is usually accompanied byloss in others, e.g., high strength aluminium alloys havea lower ductility, a lower ratio of fatigue strength toultimate strength and a lower absolute resistance tofatigue than those of lower strength. Any improvementin this direction would be desirable. Very high strengthaluminium alloy accounts only for about 10 per cent, byweight of the aircraft structure and the greatest need isfor alloys with improved physical properties in the sheetform. Material with a greatly increased Young's moduluswould be very valuable and experiments in progress givehope that a material will be produced having an ultimatestrength- of 28 tons per square inch and a Young'smodulus increased by 20 per cent. The development ofstructural materials to withstand high temperatures isalso a matter of importance since they would enable thehot-gas ducts used with thermal de-icing to be incor-porated in the fabric of the aircraft.

The importance of knowing the frequency of occurrenceof loads of different magnitudes is equalled by theimportance of knowing the effects of such loads onstructures and structural elements. Essential design datacan be obtained by tests on standard material testspecimens incorporating known stress concentrationsand by tests on typical examples of main aircraft joints.

Stress analysis. A most important development is thepossibility of experimental examinations of stressdistribution under transient conditions by electricalstrain gauges, to which reference has already been made.

A valuable contribution to theoretical analysis hasbeen made in a paper giving a method for the treatmentof dynamic loads, allowing for the vibrational response

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of the structure of the aircraft. This method has foundan immediate application in the treatment of gust loadsand landing loads in large aircraft.

Methods of construction. The two main problemsunder this heading have been sandwich construction andthe production of smooth wings.

Several discussions have been held on sandwichconstruction and the numerous possibilities both for theskin and for the core. These range from foamedalginates to paper and metal honeycomb for the core,while the skin materials investigated have ranged fromply-wood to light alloys and steel. Considerable workon the theory of this construction has been done and itis now on a satisfactory basis. Practical development,particularly of suitable core material, nowneeds attention.

The aerodynamic importance of a high degree ofsmoothness in wing surfaces has resulted in discussionsof the structural problems involved. It has beensuggested that the structural part of the wing should bemade reasonably smooth and the final surface obtainedby a moderately thick plastic covering, cut to thenecessary contour by a milling or grinding cutter. Othermethods of construction have been tried by differentfirms and sections of wings have been measured andtested at the R.A.E. to determine the degree of accuracyachieved and the behaviour under load.

Test methods. The development of the electricalresistance strain gauge has provided the structuralengineer with an important research tool. Problems ofconstruction of the gauges themselves, their applicationto the test body, the bridge used for measuring thechanges of resistance which they experience whenloaded, and the methods of recording results particularlyfor transient loads have all been under review. Workhas been in progress in a number of laboratories, and onedevelopment has been the production of a wire whichkeeps linear electrical characteristics even when strainedas much as 13 per cent. The normal measuring device isthe simple Wheatstonebridge, but other circuits claimedto have special value are in use. Work in this field hasalso led to a keener realisation of the possibilities oferrors arising in the measurement of stress by straingauges.

When strain gauges are used in flight, it is necessaryto obtain practically simultaneous readings of a largenumber and this requires a multiple channel oscillograph.The major problem is to produce a high-speed switchgear. A mechanical switch has been produced at theR.A.E. capable of scanning 24 signals 25 times persecond. While such a device is not essential for statictests, much time will be saved by its use, and the introduc-tion of an extra switch in the R.A.E. instrument makes600 readings per second possible during static tests.

Aero-elastic problems. The importance of aero-elasticproblems in connection with swept-back wings led to acombined meeting of Structures, Oscillation, and

Stability and Control Sub-Committees. They felt thatthe problems in connection with swept-back wings weresevere but not intractable, and that invaluable data mightbe obtained by the use of flexible models. Before thesemodels could be made, research would be necessary intothe properties of the material and into the technique ofmanufacture. The first use of these flexible modelswould be to determine the distribution of aerodynamicloads in the wind tunnel, and measurements ought to bemade both on rigid and flexible models. Deflexion ofmodels under load should be obtained whenever possibleand deformations of actual aeroplanes during flightshould be measured. The Structure Sub-Committeelater discussed a proposal for designing the structure ofa swept-back wing to overcome aero-elastic troubles,such as control reversal, divergence and decrease ofstability. This design incorporates all-moving wing tipswith a wing structure designed so that the changes inincidence due to bending nullify those due to torsion.It is considered that a case has been made out forexperimenting on all-moving wing tips, and althoughaware of certain troubles which may arise, the promiseof reduction in structure weight is sufficiently attractiveto justify further work.

General. In addition to the work falling under themain headings, a number of other matters have beenconsidered. These include statistical methods of deter-mining the strength of materials and components foraircraft structures, the detailed specification of a researchprogramme for the Canadian Associate Committee onAeronautics on the buckling of curved plates, and anumber of special problems connected with experimentalphoto-elasticity.

(b) Aero-elasticityAero-elasticity. This heading covers all the effects on

the behaviour of an aircraft due to the interaction ofaerodynamic and inertia forces with the elastic forcesarising from structural distortion ; and since, consequenton the great increases in speed of recent years, theaerodynamic forces are very large, structural distortionhas naturally tended to become a significant factor inmany more fields of work than was the case ten years ago.For example, at that time the subjects of flutter and ofaeroplane stability were only beginning to becomeinter-related ; the mass-balance weights required forflutter prevention had to be taken into account instability studies. But the past decade has seen anappreciable overlapping and merging of interests ; toquote the same example, in the study of elevator flutter ithas become necessary to include many bodily freedomsof the aircraft, while the study of longitudinal stabilityhas required the introduction of distortion effects ; thetwo studies are now no more than phases of the sameproblem. The Council has recognised this merging ofinterests and has taken appropriate steps to secure theintegration of effort and the interchange of informationwhich the situation demands.

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The widening and deepening of the already complexproblems of aero-elasticity has made and will makecontinually greater demands on mathematical science ;accordingly, considerable attention has been devoted tothe development of new mathematical methods andmathematical aids.

Two matters of general interest should be mentionedhere. The first concerns the special problems in theaero-elastic field posed by the swept-back wing, and bysimilar unconventional wing planforms, a matter brieflymentioned in the previous section of this report. Inthe case of the ordinary unswept wing, pure flexureproduces insignificant changes in aerodynamic loading,and in consequence flexure is unimportant in problemsof divergence, loss of control, and stability, and playsonly a minor part in flutter. But flexure of a swept wingdoes change the aerodynamic load distribution con-siderably, and this case has therefore set a variety of newproblems : severe loss of dynamic stability, considerablecomplication of the phenomenon of control reversal, andflutter in new combinations of modes. The difficulty oftreating these questions is much accentuated by thefundamental lack of knowledge on the manner in whicha swept wing distorts and on the distribution of airloadscorresponding to the distortion. The Council has givenmuch attention to these matters, and has stronglyencouraged the investigations, both fundamental andapplied, into them.

The second matter relates to research into aerodynamicderivatives ; in this field special mention must be madeof the work of the N.P.L. Valuable contributions havebeen made, in a series of researches, to the theory of theair forces on a wing of any planform in unsteady motion,at low, high subsonic, and supersonic speeds. In windtunnels, a series of elegant experiments has been carriedout on the forces acting on an oscillating profile, over asimilar range of speeds ; and apparatus has been devisedfor recording the complete time history of the forces onan aerofoil which is deforming in any manner.

Loss and reversal of aileron control; rolling power.A high rate of roll is an exceedingly important militarymanoeuvre and structural deformation at high speedsseriously detracts from the efficiency of an aeroplane inthis respect. The phenomenon has been well understoodfer some years. Recently, however, the rapid approachtoward sonic and supersonic speeds, and the consequentdemand for more and more structural stiffness, hasnecessitated a re-examination of the phenomenon and ofthe methods for avoding it. At the R.A.E., appropriateaerodynamic theories have been evolved, and a newmethod of treatment of the problem given ; comparisonwith experiment has proved very satisfactory. It appearsthat at supersonic speeds this phenomenon may wellrequire the use of control surfaces differing radicallyfrom those now in use.

Distortion effects on longitudinal stability. The generaltheory of these effects had been stated, and to someextent used, during the war years. Since 1945 attention

has mainly been directed towards a careful and systematicflight study of these effects. This has been carried outon a Mosquito aircraft, and measurements have beenmade of fuselage distortion tailplane twist, and elevatortwist in flight. These measurements have given generalconfirmation to the theory and have besides pointedseveral important conclusions.

Flutter. Effort in the field of flutter investigations hasbeen divided mainly between prediction, prevention, andthe study of the relevant air forces. In the prediction offlutter and the estimation of critical speeds, it has beenfound that many degrees of freedom require to beintroduced to give satisfactory results ; this has involvedgreat complexity. Attention has therefore been paid toinverse methods of solution and to the choice of the vitaldegrees of freedom ; but much remains to be done, andthe Council is urging forward these investigations asrapidly as possible.

Although flutter prevention is well understood,continual efforts are needed to see that no unnecessarypenalties, in the form of mass-balance weights or materialfor structural stiffness, are incurred. With this end inview, and with the special case of the Brabazon I in mind,a new study of the possible use of artificial damping forflutter prevention has been made. However, it has beenconcluded that this method will not be satisfactory andthat a conventional method must be used.

With the rapidly extending use of spring tabs forcontrol balance, there have been a number of occurrencesof spring tab flutter, and a thorough study of thisphenomenon has been necessary. A simple criterion hasbeen evolved by the R.A.E. for use by designers, and hasproved satisfactory in application.

The question of flutter at supersonic speeds is compli-cated by a theoretical prediction that negative dampingmay occur ; in this event, the normal methods of flutterprevention (which might otherwise be expected to proveefficacious) would be of no avail. An experimentalinvestigation of this question has been recommended.So far, the experimental evidence conflicts with thetheoretical prediction, and modifications to the theoryare evidently necessary. The situation is slowly beingclarified ; but much further work is still required.

The development of stiffness criteria. In almost allaero-elastic phenomena, it is necessary to prescribe somestandard of structural stiffness to give satisfactoryqualities. For this purpose it is most helpful—indeedalmost essential—to give designers simple criteria bywhich the necessary standards of stiffness for an aeroplanemay be estimated at a very early stage in design. In thelast five or six years many such criteria have been evolvedby the R.A.E. ; they define the stiffness in terms of thedimensions, equivalent airspeed, and Mach number,and they provide for the avoidance of such phenomenaas, for example, wing flexure-torsion flutter, tailplaneflutter, reversal of elevator control, and loss of

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longitudinal stability. The possibility of extension ofthese criteria to cover swept-back wings is the mosturgent problem in this field at present.

Resonance testing. Not only for flutter studies, butalso for the understanding of the dynamics of gusteffects and of landing impacts, it is necessary to know thenatural frequencies and modes of vibration of an aircraft.These are normally determined by ground resonancetesting ; and such tests are now mandatory for prototypemilitary aircraft. The large volume of work involvedhas necessitated the development and simplification ofthe technique of such tests, so that aircraft firms mayundertake them. This development has proceeded at theR.A.E. and has been endorsed and encouraged by theCouncil. Attention is now being directed toward thepossibility of conducting resonance tests in flight. Thedifficulties are exceedingly great, but the informationwhich might be gained on air loads in such circumstancesis most important. It is difficult to conceive of any othermethod which will give data on oscillatory air forcesat the correct Reynolds and Mach numbers ; and theflight tests should be pressed forward as urgently aspossible.

(c) Vibration problemsAirframe vibrations. This subject has been investigated

by a method of replacing the airframe by a finite numberof isolated masses with suitable elastic connections.In many cases there is good agreement between theresults of this theory and experiment, but a few dis-crepancies remain to be cleared up. A beginning hasbeen made in the application of the admittance conceptto airframe vibrations. The use of models for the studyof vibrations of aircraft at the design stage has beenconsidered but the difficulties in achieving accuracy areformidable.

An interesting new theoretical approach to problemson the motions of structures and the stresses in themcaused by shock loads has been made using the concep-tion of elastic waves. This work has served to drawattention to possible dynamic stress concentrations atany discontinuities in the structure and at the wing tips.A useful simple treatment of shock problems has beenput forward.

Experiments on shock loads on aircraft have beendiscussed and the conclusion reached that reliable resultscan only be obtained by tests on full-scale aircraft makinglandings, etc. It is thought that the results of hangartests on landing shocks are of doubtful validity althoughsome help may be obtained from such tests provided thatdue care has been taken with the experiments themselvesand that the results are interpreted with discretion.

Engine vibrations. A considerable amount of work onthe vibration of piston engines has been carried out.This has served to emphasise that the flexibility of gearsand their mountings has an important influence on the

vibrations of the engine and of the engine-airscrewsystem. Some of the special problems arising on engineshaving two crankshafts have been studied and elucidated.

A valuable review of the subject of the blade vibrationsof turbines and compressors has been made; Someattention has also been given to flutter of blades incascade.

General theory. The Monograph R. & M. 2000gives a general account of mechanical admittances andtheir applications to oscillation problems. Some usefulgeneralisations of the admittance concept are included.

24. SPECIAL PROBLEMS(a) Seaplanes

Large flying boats. The main interest of the SeaplaneCommittee has been directed to problems of the largeflying boat in view of the Government's decision to buildthese aircraft. A comparison between large seaplanesand landplanes has shown that at a weight of 200,000 Ibor less a flying boat can be designed to be as good as alandplane of the same weight. At greater weights theflying boat is superior and the structure weight is expectedto be at least 2 per cent less than that of the correspondinglandplane at an all-up weight of 300,000 Ib.

The greatly increased size and weight of flying boatshas necessitated a consideration of the handling of suchcraft. The best solution for very large sizes is to providedocks and in general to treat the boat like a ship. It isconsidered essential that an adequate flying boat baseshould be provided for operational use when the largeSaunders-Roe flying boats are available. If an existingwaterway were used, dredging would probably have tobe resorted to in order to provide the necessary depthand width of channel for satisfactory operation, and thegreater these are, the greater will be the cost of construc-tion and maintenance. It will therefore be necessaryfrom the economic view-point that the depth and widthshould be as small as possible. Experience has shownthat the effect of changes in depth of water on the take-offof flying boats is very small, and the minimum depth istherefore that required to avoid fouling the sea bottomor submerged obstacles, or to avoid excessive damage tothe banks through wave making.

The conclusion has been reached that the minimumdepth of water for flying boats. up to a weight of500,000 Ib is 15 ft. This is mainly determined by thestatic displacement with an allowance for contingencies.The width of the channel required is about 400 ft. andit may be necessary to protect the banks from destructionby inclining them at the natural angle of repose, or byproviding a shallow fringe on which the wave energy canbe dissipated, or by both expedients.

For overseas bases it will be necessary to providemeans of repairing the flying boats in an emergency.For this purpose some form of floating dock will be

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necessary. Some thought has been given by Messrs.Saunders-Roe to the design of such a dock as well as toquick means of getting flying boats moored up after aflight.

A high-speed towing tank for testing models of largeseaplanes is needed. It should be such as to give a speedof 70 ft. per second for the testing of models to bemaintained for 20 seconds and this would suffice formodels of large flying boats from 150,000 Ib to 500,000 Ibloaded weight. This implies a length of 2,000 ft., awidth of 20 ft. and a depth of 6 ft. Two carriages shouldbe built, one for dynamic model tests and the other forforce measurements on models. On both carriages meansshould be provided for regulating the airflow past themodel. The value of a tank of this kind for otherpurposes such as testing hydrofoils would be increased bya greater depth and speed.

Water drag. One of the most important problems inthe design of large seaplanes is the interaction of the airand water flows around the hull, particularly when thehull has been streamlined to the maximum amount inorder to reduce air drag. This subject has been investi-gated by experiments in the R.A.E. Seaplane TestingTank and by full scale tests at the Marine AircraftExperimental Establishment on the Sunderland and onthe Saro half scale R.5/39 model with long faired stepsand aeration. An alternative to tank tests is the use offree flight tests of models. The Seaplane Committeehas recommended that pending the provision of a tank,work on free flight models should be given high priority.

Impact forces and pressures. The stressing require-ments for"seaplanes during take-off and landing and forlandplanes during ditching have been under discussion byI.C.A.O. Some theoretical and experimental work onthe subject has been undertaken in this country by theM.A.E.E., Felixstowe, by the R.A.E. and by Messrs.Saunders-Roe. As a result of this and similar work inthe United States of America, a much better theoreticalmethod of deducing seaplane loads has been obtained.Further experimental evidence is, however, needed fromthe Hull Launching Dock and from full-scale tests inorder to complete the theory.

Ditching of landplanes. The problems arising duringthe ditching of landplanes are similar to those experiencedby seaplanes in landing, and it has therefore beenregarded as suitable for consideration by the SeaplaneCommittee.

The question of future equipment for ditching tests isone which needs to be settled, because the existingequipment at R.A.E. which consists of a small catapultand pond, is inadequate for present requirements. InAmerica this method of test is not favoured ; instead,tests have been made on radio-controlled models,including apparatus for the measurement of waterpressures and accelerations. Although the Americanlarge models can take apparatus which cannot be fitted

to the smaller catapulted models, the conditions of testcannot be controlled with the same accuracy. The casefor the less costly type of experiments proposed in thiscountry is therefore a good one. A further point infavour of the catapult tests is that the weather in thiscountry is much less suitable for free flight testing thanin America.

The Seaplane Committee and the Structure Sub-Committee at a joint meeting have recommended theconstruction of a new ditching tank with catapult :it could be used for testing both landplanes andseaplanes.

(b) Helicopter researchThe advances made in helicopter design in the United

States of America between 1942 and 1945 showed thatthe helicopter was then becoming a practical flyingmachine. In accordance with this trend a HelicopterCommittee was appointed in 1946 to encourage researchon this type of aircraft. While the basic theory of thelifting rotor has been long established, more experimentaldata on rotor characteristics were, and still are, badlyneeded. The main sources for these data are flightresearch at R.A.E. and at A.F.E.E. ; model tests in theR.A.E. 24-ft. wind tunnel, and full-scale rotor tests onthe rotor tower at Bristol.

Compared with a stable aeroplane the flying charac-teristics of present helicopters are rather unsatisfactoryand improvements are desirable before regular blindflying and night operation will be possible. Largerhelicopters are now being built with more than onelifting rotor : the provision of adequate stability formulti-rotor helicopters has been the subject of pre-liminary investigations but is still not assured.

A tower for the testing of full-scale rotors was con-structed under Ministry of Supply contract at the worksof the Bristol Aeroplane Company in 1946. Theprogramme of research on the tower has been discussedand it is hoped that it will become a valuable tool forresearch. It has already proved useful in the eliminationof rotor flutter on one new type of helicopter.

(c) MeteorologyNow that the Meteorological Office is not represented

directly on the Council or on any of its Committees, theDirector of the Meteorological Office communicatesyearly the report of the Meteorological Research Com-mittee and its programme of research. These have bothbeen discussed each year by the Council with repre-sentatives of the Office. In addition, one representativeof the Office was made a member of Gust Panel No. 1,which was appointed in July, 1947, to consider and reporton all investigations needed to obtain a reasonableknowledge of gusts. The general discussion on meteoro-logy in the Autumn of 1948 took the form of a jointmeeting of the Council with the Meteorological ResearchCommittee and this practice will be continued next year.

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The deliberations were helped by a number of papersprepared by the Meteorological Office and the Reportof Gust Panel No. 1.

Meteorological investigations are required :—(a) to extend wind and temperature statistics to great

heights over the whole world ;(b) to investigate the nature and intensity of gusts likely to

be encountered by aircraft;(c) to examine drop size distribution and liquid water

content in the most severe icing conditions likely tobe encountered.

As regards (a), maps exist of upper wind distributionfor heights up to 200 mb. (about 40,000 ft.) and anextension up to 50,000 ft. is needed within the next threeyears for both temperature and wind in connection withthe design of aircraft and power plants.

As regards (b), the magnitude of the gusts assumedwhen calculating the strength of aircraft is a limitingfactor in design and the experimental basis for theassumed figures is scanty. Gust statistics have been

collected by aircraft on routine flying in England by theBritish European Airways over Europe and in theUnited States of America, but much more needs to bedone. We have recommended that machinery bedevised for the co-ordination of the United Kingdomeffort on gust research, that the production of certaininstruments in quantity be considered and that someliaison be arranged with the work being undertaken on alarge scale in America to investigate turbulence incumulo-nimbus clouds.

As regards (c), there is enough information to enabledesigners to deal with the problem of ice accretion onairframes, but the position is very unsatisfactory withregard to the protection of engines against ice accretion.The Council are informed that the physics of clouds isbeing carefully studied by the Meteorological ResearchFlight and this seems to be the most profitable activityin connection with this problem for the near future.It seems doubtful whether it will be possible to protect allaircraft against hail, which occurs only in the conditionsassociated with cumulo-nimbus clouds : the solution isto avoid such clouds.

GLOSSARY OF ABBREVIATIONS

A. and A.E.A.F.E.E.A.R.C.

C.AA.R.C.

C.S.I.R.

I.C.A.O.M.A.E.E.N.A.C.A.N.P.L. . .R.A.E.R.A.F.R. &M.R.A.T.O.G.

E. Armament and Aircraft Experimental Establishment.Airborne Forces Experimental Establishment.Aeronautical Research Council.Commonwealth Advisory Aeronautical Research Council.Council for Scientific and Industrial Research (Australia).International Civil Aviation Organization.Marine Aircraft Experimental Establishment.National Advisory Committee for Aeronautics (America).National Physical Laboratory.Royal Aircraft Establishment.Royal Air Force.Reports and Memoranda.Rocket Assisted Take-off Gear.

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APPENDIX IMembership of the Council. December, 1948

Prof. S. Goldstein, M.A., Ph.D., F.R.S., F.R.Ae.S. (Chairman).Mr. E. F. Relf, C.B.E., A.R.C.S., F.R.S., F.R.Ae.S. (Vice-

Chairman).Prof. L. Bairstow, C.B.E., D.Sc., F.R.S., Hon. F.R.Ae.S.Mr. F. Brundrett, C.B., B.A.*Mr. H. Constant, M.A., F.R.S., F.R.Ae.S.Sir Charles Darwin, K.B.E., M.C., M.A., Sc.D., F.R.S.fMr. A. Page, A.R.C.S., D.I.C., F.R.S., F.R.Ae.S.JMr. H. M. Garner, C.B., M.A., F.R.Ae.S.Prof. A. A. Hall, M.A., F.R.Ae.S.

Sir Ben Lockspeiser, M.A., F.C.S., F.R.Ae.S.Mr. W. G. A. Perring, R.N.C., A.M.I.N.A., F.R.Ae.S.Sir Harry Ricardo, LL.D., B.A., M.I.Mech.E., A.M.Inst.C.E.,

F.R.S., F.R.Ae.S.Prof. O. A. Saunders, M.A., D.Sc.(Eng.), A.M.I.Mech.E.,

F.Inst.P.Sir Geoffrey Taylor, M.A., F.R.S., Hon. F.R.Ae.S.Prof. G. Temple, D.Sc., F.R.S., F.R.Ae.S.

Secretary : Mr. J. L. Nayler (N.P.L.).Assistant Secretary : Mr. R. W. G. Candy (N.P.L.)

' Representing the Admiralty. t Representing the Department of Scientific and Industrial Research.} Representing the National Physical Laboratory.

APPENDIX IIMembership of the Council or its Predecessor, the Aeronautical Research Committee, 1939-48

The following were Chairmen of the Council or its predecessor,the Committee, during the period :—

Sir Henry Tizard .. .. January, 1939-March, 1943Sir Melvill Jones .. .. April, 1943-March, 1946Prof. S. Goldstein .. April, 1946

The following have beenSir Edward AppletonProf. L. Bairstow

Prof. P. M. S. Blackett

Mr. F. Brundrett ..Mr. H. ConstantDr. H. Roxbee CoxSir Charles DarwinProf. W. J. DuncanMr. A. PageMr. W. S. FarrenProf. R. H. FowlerMr. H. M. GarnerProf. S. GoldsteinDr. H. J. Gough

members during the period:—, February, 1939-March, 1945

January, 1939-March, 1939April, 1940-March, 1946April, 1947January, 1939-March, 1941April, 1943-March, 1945May, 1947September, 1948April, 1945-August, 1948February, 1939 ..April, 1939-March, 1945January, 1946July, 1941-December, 1945January, 1939-March, 1941April, 1947April, 1945January, 1939-August, 1945

Prof. A. A. Hall ..Mr. A. H. HallProf. G. T. R. Hill

Sir Nelson JohnsonSir Melvill Jones ..Sir John Lennard-JonesSir Ben LockspeiserMr. W. G. A. PerringProf. A. G. PugsleyDr. D. R. Pye

Mr. E. F. Relf ..Sir Harry RicardoProf. O. A. SaundersSir Richard SouthwellSir William StanierSir Geoffrey Taylor

Prof. G. Temple ..Sir George ThomsonSir Henry Tizard ..Sir Charles Wright

April, 1946January, 1939-June, 1941January, 1939-March, 1939April, 1941-March, 1944January, 1939-March, 1945April, 1939-March, 1948September, 1945-March, 1946January, 1943January, 1946April, 1945-March, 1947January, 1939-December, 1942April, 1943-March, 1946April, 1945April, 1946April, 1947April, 1940-March, 1943April, 1944-March, 1947January, 1939-March, 1940April, 1941-March, 1947April, 1948April, 1947January, 1939-March, 1941January, 1939-March, 1943January, 1939-April, 1947

In the above list, leaders after a date indicate that the individual was a serving member at December, 1948, when the list was compiled.

APPENDIX IIIMembership of Committees, Sub-Committees and Panels. December, 1948

Aerodynamics Committee.—Prof. L. Bairstow (Chairman) ;Mr. E. F. Relf (Vice-Chairman) ; Mr. L. W. Bryant (N.P.L.) ;Mr. F. S. Burt (Ad.) ; Mr. R. M. Clarkson (S.B.A.C.) ;Dr. G. P. Douglas (M.o.S.) ; Prof. W. J. Duncan ; Mr.A. Page (N.P.L.) ; Mr. H. M. Garner (M.o.S.) ; Prof.S. Goldstein (ex officio) ; Prof. A. A. Hall ; Mr. S. ScottHall (M.o.S.) ; Prof. G. T. R. Hill ; Dr. L. Howarth ;Mr. H. B. Irving (M.o.S.) ; Mr. W. G. A. Perring (M.o.S.) ;Mr. H. L. Stevens (M.o.S.) ; Sir Geoffrey Taylor ; Prof.G. Temple ; Prof. A. Thorn ; Mr. H. F. Vessey (M.o.S.);Mr. B. N. Wallis (S.B.A.C).

Secretary : Mr. J. L. Nayler (N.P.L.).Assistant Secretary : Mr. R. W. G. Gandy (N.P.L.).

Fluid Motion Sub-Committee.—Dr. L. Howarth (Chairman) ;Sir Geoffrey Taylor (Vice-Chairman); Prof. L. Bairstow(ex officio) ; Dr. G. K. Batchelor ; Prof. W. G. Bickley ;Mr. W. F. Cope (N.P.L.) ; Mr. A. Fage (N.P.L.) ; Prof.S. Goldstein ; Mr. H. B. Irving (M.o.S.) ; Mr. W. P. Jones(N.P.L.) ; Mr. M. J. Lighthill ; Mr. C. N. H. Lock (N.P.L.) ;Dr. J. W. Maccoll (M.o.S.) ; Mr. W. A. Mair ; Mr. L. F.Nicholson (M.o.S.) ; Mr. P. R. Owen (M.o.S.) ; Prof.L. Rosenhead ; Prof. O. A. Saunders ; Mr. A. G. Smith(M.o.S.) ; Mr. H. B. Squire (M.o.S.) ; Prof. G. Temple ;Prof. A. Thorn ; Mr. G. W. Trevelyan (S.B.A.C.) ; Mr.A. D. Young.

Secretary : Mr. D. W. Holder (N.P.L.).29

Performance Sub-Committee.—Mr. E. F. Relf (Chairman ) ;Mr. A. Page (Vice-Chairman) (N.P.L.) ; Prof. L. Bairstow(exofficio) ; Mr. J. A. Beavan (N.P.L.) ; Mr. F. S. Hurt (Ad.);Dr. D. Cameron (M.o.S.) ; Dr. G. P. Douglas (M.o.S.) ;Prof. W. J. Duncan ; Mr. S. B. Gates (M.o.S.) ; Prof.S. Goldstein ; Prof. A. A. Hall; Prof. G. T. R. Hill ;Mr. R. Hills (M.o.S.) ; Mr. P. A. Hufton (M.o.S.) ; Mr.W. A. Mair ; Mr. P. R. Owen (M.o.S.) ; Dr. R. C. Pankhurst(N.P.L.) ; Dr. J. H. Preston ; Mr. E. J. Richards (S.B.A.C.) ;Prof. A. Thorn ; Mr. B. Thwaites ; Mr. C. O. Vernon(S.B.A.C.) ; Mr. H. F. Vessey (M.o.S.).

Secretary : Mr. E. W. E. Rogers (N.P.L.).

Stability and Control Sub-Committee.—Prof. A. A. Hall(Chairman) ; Prof. A. R. Collar (Vice-Chairman) ; Prof.L. Bairstow (ex officio) ; Miss F. B. Bradfield (M.o.S.) ;Mr. L. W. Bryant (N.P.L.) ; Mr. F. S. Burt (Ad.) ; Mr. A. N.Clifton (S.B.A.C.) ; Group Capt. R. G. Dawkins (M.o.S.) ;Prof. W. J. Duncan ; Mr. D. L. Ellis (S.B.A.C.); Mr.V. M. Falkner (N.P.L.) ; Mr. S. B. Gates (M.o.S.) ; Mr.J. Hanson (M.o.S.) ; Prof. G. T. R. Hill ; Mr. P. A. Hufton(M.o.S.) ; Mr. H. B. Irving (M.o.S.) ; Mr. M. B. Morgan(M.o.S.) ; Dr. J. H. Preston ; Group Capt. G. Silyn-Roberts(M.o.S.).

Secretary : Mr. R. W. G. Gandy (N.P.L.).

Mechanics Committee.—Prof. G. Temple (Chairman) ;Prof. A. G. Pugsley (Vice-Chairman) ; Prof. L. Aitchison ;Prof. A. R. Collar ; Prof. W. J. Duncan ; Mr. D. J. Fajrar(S.B.A.C.) ; Dr. R. A. Frazer (N.P.L.) ; Mr. H. M. Garner(M.o.S.) ; Prof. S. Goldstein (ex officio) ; Mr. H. Grinsted(M.o.S.) ; Mr. H. B. Howard (M.o.S.) ; Prof. R. L. Lickley ;Mr. W. G. A. Perring (M.o.S.); Prof. A. J. Sutton Pippard ;Dr. S. C. Redshaw (S.B.A.C.) ; Dr. D. G. Sopwith (N.P.L.) ;Sir Richard Southwell ; Mr. H. L. Stevens (M.o.S.) ; Dr.P. B. Walker (M.o.S.).

Secretary : Mr. E. A. Poulton (M.o.S.).

Engineering Physics Sub-Committee.—Prof. G. Temple(Chairman) ; Prof. L. Aitchison ; Mr. R. Graham (M.o.S.) ;Prof. O. A. Saunders ; Mr. K. T. Spencer (M.o.S.) ; SirGeoffrey Taylor ; Mr. B. N. Wallis.

Secretary : Mr. L. H. G. Sterne (M.o.S.).

Oscillation Sub-Committee.—Prof. A. R. Collar (Chairman) ;Prof. W. J. Duncan (Vice-Chairman) ; Prof. L. Bairstow ;Mr. J. B. Bratt (N.P.L.) ; Mr. J. R. Forshaw (M.o.S.) ;Mr. H. Grinsted (M.o.S.) ; Mr. J. Hanson (M.o.S.) ; Mr.W. S. Hemp ; Dr. S. Hollingdale (M.o.S.) ; Mr. H. B.Howard (M.o.S.) ; Mr. W. P. Jones (N.P.L.) ; Mr. M. B.Morgan (M.o.S.) ; Capt. J. Morris (M.o.S.) ; Prof. A. G.Pugsley ; Prof. G. Temple (ex officio) ; Mr. R. G. Voysey ;Dr. W. Ker Wilson (S.B.A.C.) ; Mr. J. C. Wimpenny(S.B.A.C).

Secretary : Mr. N. C. Lambourne (N.P.L.).

Structure Sub-Committee.—Prof. A. J. Sutton Pippard(Chairman) ; Prof. G. T. R. Hill (Vice-Chairman) ; Prof.L. Aitchison ; Mr. H. L. Cox (N.P.L.) ; Mr. H. H. Gardner(S.B.A.C.) ; Mr. W. S. Hemp ; Mr. H. B. Howard (M.o.S.) ;Mr. E. D. Keen (S.B.A.C.) ; Dr. D. M. A. Leggett ; Mr.E. A. Poulton (M.o.S.) ; Prof. A. G. Pugsley ; Mr. L.Rotherham (M.o.S.) ; Sir Richard Southwell ; Prof. G.Temple (ex officio) ; Dr. D. Williams (M.o.S.).

Secretary : Mr. R. J. Atkinson (M.o.S.).

Power Plants Committee.—Prof. O. A. Saunders (Chair-man) ; Mr. F. M. Green (Vice-Chairman) ; Prof. L.Aitchison ; Mr. J. F. Alcock ; Capt. (E) N. J. H. d'Arcy(Ad.) ; Prof. A. R. Collar ; Mr. H. Constant (M.o.S.) ;Dr. H. Roxbee Cox ; Dr. J. W. Drinkwater (M.o.S.) ;Mr. H. M. Garner (M.o.S.) ; Prof. S. Goldstein (ex officio) ;Dr. A. A. Griffith ; Prof. C. H. Lander ; Mr. W. H. Lindsey(S.B.A.C.) ; Mr. P. Lloyd (M.o.S.) ; Mr. C. N. H. Lock(N.P.L.) ; Mr. I. Lubbock ; Capt. (E) M. Luby (M.o.S.) ;Mr. H. C. Mansell (S.B.A.C.) ; Mr. E. S. Moult (S.B.A.C.) ;Mr. W. G. A. Perring (M.o.S.) ; Sir Harry Ricardo : Mr.J. Rosen (Ad.) ; Mr. H. Sammons (S.B.A.C.) ; Sir WilliamStanier ; Mr. H. L. Stevens (M.o.S.) ; Air Cdre. Sir FrankWhittle.

Secretary : Mr. A. F. C. Brown (N.P.L.).Assistant Secretary : Mr. F. G. Code Holland (M.o.S.).

Combustion and Fuels Sub-Committee.—Prof. C. H.Lander (Chairman) ; Mr. P. Lloyd (Vice-Chairman) (M.o.S.) ;Mr. J. F. Alcock ; Mr. S. Alien (S.B.A.C.) ; Mr. A. D.Baxter (M.o.S.) ; Dr. J. S. Clarke (S.B.A.C.) ; Dr. J. W.Drinkwater (M.o.S.) ; Sir Alfred Egerton ; Dr. H. R.Fehling ; Prof. W. E. Garner ; Dr.'A. G. Gaydon ; Dr.T. P. Hughes (M.o.S.) ; Mr. I. Lubbock ; Miss E. J. Macnair(Ad.) ; Prof. O. A. Saunders (ex officio) ; Sir GeoffreyTaylor ; Mr. M. W. Thring ; Dr. D. T. A. Townend ;Dr. C. G. Williams.

Secretary : Mr. G. A. E. Godsave (M.o.S.).

Engine Aerodynamics and Propellers Sub-Committee.—Prof.A. R. Collar (Chairman) ; Mr. F. M. Green (Vice-Chairman) ;Mr. D. M. Cockburn (S.B.A.C.) ; Mr. E. H. Cole ; Mr.K. V. Diprose (M.o.S.) ; Mr. J. Edwards (Ad.) ; Mr. L. G.Fairhurst (S.B.A.C.) ; Mr. G. B. R. Feilden ; Dr. A. A.Griffith ; Mr. C. H. Griffiths (M.o.S.) ; Mr. A. B. Haines(M.o.S.) ; Mr. A. R. Howell (M.o.S.) ; Mr. G. H. Lean(N.P.L.) ; Mr. C. N. H. Lock (N.P.L.) ; Mr. I. Lubbock ;Mr. J. Mullin (S.B.A.C.) ; Mr. A. J. Penn (S.B.A.C.) ; Mr.J. Remfry (M.o.S.) ; Prof. O. A. Saunders (ex officio) ;Mr. A. G. Smith (M.o.S.) ; Mr. R. G. Voysey.

Secretary : Mr. A. B. Haines (M.o.S.).

Piston Engine Sub-Committee.—Mr. F. M. Green (Chair-man) ; Dr. H. Moss (Vice-Chairman) (M.o.S.) ; Mr. J. F.Alcock ; Dr. F. P. Bowden ; Mr. B. G. Markham(S.B.A.C.);Mr. A. W. Morley ; Sir Harry Ricardo ; Major A. A. Ross ;Mr. A. A. Rubbra (S.B.A.C.) ; Prof. O. A. Saunders (exofficio) ; Miss B. Shilling (M.o.S.) ; Mr. W. L. Taylor(M.o.S.).

Secretary : Mr. A. F. C. Brown (N.P.L.).

Rockets Sub-Committee.—Prof. O. A. Saunders (Chair-man) ; Prof. L. Rosenhead (Vice-Chairman) ; Prof. L.Aitchison ; Mr. J. F. Alcock ; Mr. S. Alien (S.B.A.C.) ;Dr. C. E. H. Bawn ; Mr. A. D. Baxter (M.o.S.) ; Mr. A. V.Cleaver (S.B.A.C.) ; Mr. W. R. Cook (Ad.) ; Air Cdre.C. L. Dann (M.o.S.) ; Mr. W. G. Heatley (Ad.) ; Mr.I. Lubbock ; Dr. W. G. Parker (M.o.S.) ; Mr. R. P. Probert(M.o.S.) ; Mr. J. M. F. White (M.o.S.).

Secretary : Mr. J. Humphries (M.o.S.).30

SPECIAL COMMITTEESCivil Aircraft Research Committee.—Prof. A. A. Hall

(Chairman) ; Sir Melvill Jones (Vice-Chairman) ; Mr. F. S.Barton (M.o.S.) ; Dr. G. E. Bell (M.C.A.) ; Prof. A. R.Collar ; Dr. H. Roxbee Cox ; Dr. T. E. Easterfield ; Mr.A. Page (N.P.L.) ; Mr. H. M. Garner (M.o,S.) ; Prof.S. Goldstein (ex officio) ; Mr. F. M. Green ; Mr. S. ScottHall (M.o.S.) ; Prof. G. T. R. Hill ; Mr. J. W. Kenny(B.S.A.A.) ; Prof. R. L. Lickley ; Mr. P. Masefield (M.C.A.) ;Mr. A. E. Woodward Nutt (M.o.S.) ; Mr. A. C. CampbellOrde (B.O.A.C.) ; Mr. W. G. A. Paring (M.o.S.) ; Mr.H. C. Pritchard (M.o.S.) ; Sir Harry Ricardo ; Mr. N. E.Rowe (B.E.A.) ; Mr. P. A. Sheppard ; Mr. H. L. Stevens(M.o.S.) ; Prof. G. Temple ; Mr. R. H. Walmsley (M.C.A.).

Joint Secretaries : Mr. J. L. Nayler (N.P.L.).Mr. R. W. G. Gandy (N.P.L.)

Helicopter Committee.—Mr. H B. Squire (Chairman)(M.o.S.) ; Prof. L. Bairstow (Vice-chairman) ; Dr. J. A. J.Bennett (S.B.A.C.) ; Mr. F. S. Burt (Ad.) ; Prof. A. R.Collar ; Prof. S. Goldstein (ex officio) ; Mr. R. Graham(M.o.S.) ; Mr. R. Hafner (S.B.A.C.) ; Mr. W. G. Jennings(M.o.S.) ; Capt. R. N. Liptrot (M.o.S.) ; Mr. C. N. H. Lock(N.P.L.) ; Prof. A. G. Pugsley ; Mr. H. Roberts ; Mr.N. E. Rowe ; Mr. W. Stewart (M.o.S.) ; Mr. H. Templeton(M.o.S.) ; Mr. A. H. Yates.

Secretary : Dr. R. C. Pankhurst (N.P.L.).Naval Aircraft Research Committee.—Prof. P. M. S.

Blackett (Chairman) ; Prof. L. Bairstow (Vice-Chairman) ;Mr. L. Boddington (M.o.S.); "Lt.-Cdr. E. M. Brown (M.o.S.);Dr. R. Cockburn (A.M.) ; Dr. G. P. Douglas (M.o.S.) ;Mr. R. R. Duddy (M.o.S.) ; Mr. A. Page (N.P.L.) ; Capt.H. L. St. J. Fancourt (M.o.S.) ; Mr. H. M. Garner (M.o.S.) ;Prof. S. Goldstein (ex officio) ; Mr. F. M. Green ; Mr.S. Scott Hall (M.o.S.) ; Prof. G. T. R. Hill ; Mr. F. Holroyd(M.o.S.) ; Sir Charles S. Lillicrapp (Ad.) ; Rear-AdmiralL. D. The Mackintosh of Mackintosh (Ad.) ; Air Vice-Marshal C. B. R. Pelly (A.M.) ; Mr. W. G. A. Perring(M.o.S.) ; Mr. J. E. Serby (M.o.S.) ; Capt. E. H. Shattock(Ad.) ; Dr. I. G. Slater (Ad.) ; Mr. O. Thornycroft (Ad.).

Joint Secretaries : Mr. J. L. Nayler (N.P.L.).Mr. F. S. Burt (Ad.).

R.A.F. Aircraft Research Committee.—Prof. P. M. S.Blackett (Chairman) ; Prof. A. G. Pugsley (Vice-Chairman) ;Dr. H. J. J. Braddick ; Dr. W. E. Burcham ; Dr. D. Cawood(M.o.S.) ; Dr. R. Cockburn (A.M.) ; Mr. H. Constant(M.o.S.) ; Dr. G. P. Douglas (M.o.S.) ; Mr. A. Page

(N.P.L.) ; Mr. G. W. H. Gardner (M.o.S.) ; Mr. S. B. Gates(M.o.S.) ; Prof. S. Goldstein (ex officio) ; Prof. A. A. Hall;Mr. S. Scott Hall (M.o.S.) ; Air Vice-Marshal J. D. I.Hardman (A.M.) ; Rear-Admiral L. D. The Mackintosh ofMackintosh (Ad.) ; Air Vice-Marshal C. B. R. Pelly (A.M.);Mr. W. G. A. Perring (M.o.S.) ; Air Commodore T. G.Pike (A.M.) ; Prof. H. R. Pitt ; Mr. W. J. Richards (M.o.S.) ;Prof. O. A. Saunders ; Mr. J. E. Serby (M.o.S.) ; Dr. I. G.Slater (Ad.) ; Mr. H. L. Stevens (M.o.S.) ; BrigadierN. P. H. Tapp (W.O.) ; Dr. O. H. Wansbrough-Jones(W.O.) ; Prof. S. Zuckerman.

Joint Secretaries : Mr. J. L. Nayler (N.P.L.).Mr. A. Walker (A.M.).

Seaplane Committee.—Mr. H. M. Garner (Chairman)(M.o.S.) ; Prof. L. Bairstow (Vice-Chairman) ; Mr. A. M.Binnie ; Mr. F. S. Burt (Ad.) ; Mr. H. R. P. Chatten (Ad.) ;Mr. A. W. S. Clarke (S.B.A.C.) ; Mr. A. Emerson (N.P.L.) ;Mr. R. H. Francis (M.o.S.) ; Prof. S. Goldstein (ex officio) ;Prof. A. A. Hall ; Mr. H. Knowler (S.B.A.C.); Air Cdre.D. F. Lucking (M.C.A.) ; Mr. A. G. Smith (M.o.S.) ; Mr.H. C. B. Thomas (M.o.S.) ; Dr. D. Williams (M.o.S.).

Secretary : Mr. L. J. Jones (N.P.L.).

Wind Tunnel Design Committee.—Prof. L. Bairstow(Chairman) ; Sir Geoffrey Taylor (Vice-Chairman) ; MajorG. P. Bulman (M.o.S.) ; Dr. G. P. Douglas (M.o.S.) ; Mr.D. L. Ellis (S.B.A.C.) ; Mr. A. Page (N.P.L.) ; Prof. S.Goldstein (ex officio) ; Mr. M. S. Hooper (S.B.A.C.) ;Mr. H. B. Irving (M.o.S.) ; Sir Melvill Jones ; Mr. W. A.Mair ; Mr. P. R. Owen (M.o.S.) ; Mr. W. G. A. Perring(M.o.S.) ; Mr. E. F. Relf; Prof. A. Thorn ; Mr. J. S.Thompson (M.o.S.).

Secretary : Mr. R. W. G. Gandy (N.P.L.).

Gust Panel No. 1.—Sir Geoffrey Taylor (Chairman) ;Mr. P. A. Sheppard (Vice-chairman) ; Dr. A. H. R. Goldie(D.M.O.) ; Prof. S. Goldstein (ex officio) ; Mr. H. B.Howard (M.o.S.) ; Mr. M. B. Morgan (M.o.S.) ; Mr.W. Tye (A.R.B.).

Secretary : Mr. E. A. Poulton (M.o.S.).

Gust Panel No. 2.—Prof. A. A. Hall (Chairman) ; Prof.S. Goldstein (ex officio) ; Mr. H. B. Howard (M.o.S.) ;Mr. F. A. Kerry (S.B.A.C.) ; Mr. D. J. Lyons (M.o.S.) ;Mr. E. A. Poulton (M.o.S.) ; Mr. J. K. Reid (S.B.A.C.) ;Mr. W. Tye (A.R.B.) ; Mr. H. R. Watson (S.B.A.C.) ;Dr. D. Williams (M.o.S.).

Secretary : Mr. F. Grinsted (M.o.S.).

Representation of various departments has been indicated above as follows :—Ad.A.M.A.R.B.D.M.O.D.S.I.R.

M.C.A.

Admiralty.Air Ministry.Air Registration Board.Director, Meteorological Office.Department of Scientific and

Research.Ministry of Civil Aviation

Industrial

M.o.S. .. .. Ministry of Supply.N.P.L. .. .. National Physical Laboratory.W.O. .. .. War Office.B.E.A. .. .. British European Airways.B.O.A.C. .. British Overseas Airways Corporation.B.S.A.A. .. .. British South American Airways.S.B.A.C. .. .. Society of British Aircraft Constructors.

APPENDIX IVNumerical list of Reports and Memoranda published between 1939-1948.

1847-1860, 1862-1899, 1901-1912, 1914-1999, 2000-2085, 2087-2093, 2096-2099, 2100-2121, 2123-2159, 2161-2164,2166-2187, 2189-2199, 2200-2231, 2233-2241, 2243-2248, 2250-2253, 2255-2264, 2266-2270, 2272-2274, 2279-2280,2282^2286, 2290-2291, 2300-2302, 2312-2313, 2319, 2327.

31