A.R.C. RLViEW1949-1954

MINISTRY OF SUPPLY

AERONAUTICAL RESEARCHCOUNCIL

Review for the Years 1949-1954

LONDON: HER MAJESTY'S STATIONERY OFFICE

J955

HVE SHU L I N O S NET

MINISTRY OF SUPPLY

AERONAUTICAL RESEARCHCOUNCIL

Review for the Years 1949-1954

Crown Copyright Reserved

LONDON: HER MAJESTY'S STATIONERY OFFICE1955

CONTENTSPage

I . INTRODUCTION . . . . . . . . . . 1

I I . AERODYNAMICS . . . . . . . . . . 4

III. PROPULSION . . . . . . . . . . 1 1

I V . MECHANICS . . . . . . . . . . . 1 6

V . MISCELLANEOUS . . . . . . . . . . 2 0

APPENDICESI. Membership of the Council during the period under review . . . 2 7

I I . Terms of Reference of t he Council . . . . . . . 28

III. Membership of all Committees and Panels at December 31st, 1954 . . 28

IV. List of Monographs and Books published between 1949 and 1954 . . 31

V. Numerical Lists of Reports and Memoranda and of Current Papers pub-lished between January 1st, 1949 and December 31st, 1954 . . . 3 1

ii

/. INTRODUCTIONThe last review of the work of the Aeronautical

Research Council dealt with the period 1939-1948.Since that date the Council has reported confidentiallyto the Minister of Supply but no attempt has beenmade to review for publication the progress of areo-nautical research on which the Council advises theMinister. We have welcomed the Minister of Supplyat several of our Council meetings during these years.

We pointed out in our last review how the basis ofaeronautical research had started again to expand.Throughout the long history of the AeronauticalResearch Committee the chief subject of study hasbeen that of Aerodynamics, and this continues to bethe case within the ever broadening front of aeronauticalengineering. The Power Plant and the Aircraft Struc-ture come next in importance and all three are dealtwith in separate sections of this review. We haveexpanded our interests in research matters dealing withmilitary aircraft but cannot do more than refer generallyto them on account of their confidential nature exceptin those cases where the information has already beenpublished. We have, for instance, continued ourinterest in naval and civil aircraft problems, includingoperational research ones, for which we have SpecialCommittees and we have kept alive an interest in heli-copters and seaplanes. The Guided Weapons AdvisoryBoard reports both to the Scientific Advisory Counciland to us and we have instructed our technical com-mittees to take an increasing interest in matters dis-cussed by this Board.

In addition to the above, we have maintained aninterest in Materials and keep in touch with the Inter-Service Metallurgical Research Council. We havewelcomed the formation of a Joint Services Materials(Non-Metallic) Advisory Board. Meteorology is dealtwith by the Meteorological Research Committee andour Gust Research Committee reports to that com-mittee as well as to our own Aerodynamics Committee.We have appointed a new committee to deal with com-putation, a subject of increasing importance since bothdigital and analogue computers are a valuable aid insolving some of the new problems whose great com-plexity would otherwise defy solution. On the otherhand, we have regarded electronics as a tool for researchpurposes and becoming so universal in its applicationthat it did not need a special committee, and this viewhas proved satisfactory.

One major change in the operation of aircraft hastaken place in the last few years which is influencingour discussions to an increasing extent. Althoughaerodynamics is still perhaps the most important singlesubject dealt with by the Council, the stability andcontrol of aircraft are now determined not by theaerodynamic qualities alone, but by these in combina-tion with factors which depend on the radio guidanceand the mechanical properties of the automatic control.

In dealing with the guidance and control of militaryaircraft and the navigation of both military and civilaircraft, the Council has therefore begun to call uponthe assistance of radio and control mechanism expertsso that all the factors affecting control and guidance,not only of piloted aircraft but also of guided weapons,can be fully taken into account. The responsibilityfor advising the Minister of Supply on radio and radarproblems rests, as a matter of history, with the Radarand Signals Board of the Scientific Advisory Council.The application of the techniques to aircraft is, how-ever, our responsibility. This division of responsibility,although not ideal, has so far proved a practicalarrangement, and may well continue to do so. Linksbetween the two bodies are already effected by commonmembership between the Radar and Signals Board andthe Committees of the A.R.C. which deal with problemsof guidance and control and similar links in other sub-jects are naturally growing.

The scope of the Council's discussions increasedearly in the period under review to a somewhat widerfield in other subjects, especially as regards jet engines,rockets and certain engineering problems of aircraft.Work in the last field was not previously co-ordinatedby any of the Council's committees and includes suchsubjects as de-icing, fire prevention, pressurization,improvement of plastic materials, etc. For our dis-cussions on these matters the Council has been greatlyhelped by a panel of experts nominated by the Industryupon whom the Sub-Committee can call for specialdiscussions in the subjects on which they are experts.The Council's outlook also expanded during 1949 to1950 to the inclusion of many of those problems ofguided weapons which naturally arise in the subjectsalready covered by the Council's Committees. Duringthe intervening years our Committees have becomethoroughly familiar with guided weapon work andbetter able to contribute to its advancement; we antici-pate problems needing advice on a choice between themanned aircraft and the guided weapon and on the useof the guided weapon by the manned aircraft. The lastthree years have been a period during which an influxof new technologies has entered aeronautical engineer-ing, needing forums for their discussion and a feedingof the results into existing technologies as far as possi-ble ; for example, the rapid development of servo-mechanisms is influencing both the control of aircraftand power-plants and our appropriate Committees aredealing with these matters.

A closer contact with the Aircraft Industry notedin our previous review has been maintained by pairsof members selected from nominees put forward by theSociety of British Aircraft Constructors and appointedto most of the technical Committees and Sub-Com-mittees ; in a few cases additional members have beenappointed. With their specialized knowledge they have

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been most helpful both in discussions at meetings andin the communication of papers.

Liaison has been well maintained with theDominions of Canada, Australia and New Zealandand with the Union of South Africa. The Chairmanand two members of the Council were Delegates bothat the Second Meeting 'of the Commonwealth AdvisoryAeronautical Research Council in Ottawa in September,1950 and the Chairman and three members at theThird Meeting held in London in September, 1953.Reference to these matters will be found later in thisreview.

Policy of the CouncilThe Council has continued to act solely in an

advisory capacity, sending their recommendations onresearch problems to the Principal Director of ScientificResearch (Air) at the Ministry of Supply, who is theCouncil's executive officer. Our strength lies in com-mittees whose memberships are nearly equally dividedbetween independents and officers chosen from govern-ment departments. The latter have assisted greatlyin day-to-day problems and our contacts in this waywith the people responsible for, and those undertakingresearches, have been very good, partly by the attend-ance of the research workers at meetings and partlyby the visits of committees and independent membersto the various government establishments. This appliesnot only to the Ministry of Supply but also to theAdmiralty whose representatives have helped us formany years. Similar contacts have been maintainedsince the formation of the Council with the Air Ministryand the Ministry of Transport and Civil Aviation and,to a lesser extent, with the War Office, on variousmatters, affecting aeronautical research and aircraftoperation.

Because the officers responsible for research areoften members of our committees that discuss theirwork, this has made it unnecessary in many cases tomake formal recommendations, because action is takenby the officer concerned following the discussions atthe respective meetings.

We expressed concern in May, 1951 at the swing todevelopment at the expense of research by which mostgovernment scientists in the aeronautical field hadbeen switched to work having an early or immediateapplication, and suggested that there should be morepersons directing their attention to the principles under-lying progress. We have been pleased to observechanges in the desired direction and the Council itselfhopes alway to devote a good part of its time to theconsideration of investigations not directly related toany immediate end product.

Equipment for ResearchAs long ago as 1944, the requirements for aero-

nautical research and development were reviewed .andset out in a special Report to the Minister, and follow-

ing the adoption of this Report by the Government,preliminary plans for the National Aeronautical Estab-lishment were made in the ensuing year. Work startedat Bedford in June, 1946 and, although progress wasslow for some years, we are now able to express oursatisfaction with what has been done in the last fewyears and what is immediately planned. The presentposition of new equipment at that Establishment isgiven elsewhere in this review, but we wish to recordhere the adoption of our recommendation for the con-struction of a specially long runway at the N.A.E.During the past two years we have been consulted bythe Minister about the future of the N.A.E. and theCouncil has visited both_Jhese establishments duringthe past year.

We have reviewed the existing facilities for gasturbine research and development at the National GasTurbine Establishment and we have emphasized theurgent need for more research equipment for propul-sive investigations, as only in this way can the UnitedKingdom maintain its present pre-eminence in thisfield. Much has been done in the past about provisionfor the testing of components but the immediate needis for the erection of a high-altitude test bed. We havelaid down what we consider to be the chief require-ments for the proposed test plant catering for highthrust engines and we were glad to learn early in 1954that the project had been approved by the Treasury.It is appreciated that the speeds of both civil andmilitary aircraft will be rapidly increasing during thenext two decades, but remembering that a major de-velopment in a power plant takes about ten years todesign, develop and use to the stage at which it be-comes obsolete, it is considered likely that the enginesin use ten years hence will be similar to those whichare in the minds of designers to-day. We contemplatethat the requirements should be such as to meet a speedwith Mach number equal to 3 at 70,000 ft. within thistime.

Equipment at firmsThe Council has been pleased to note the steady

increase of useful equipment at firms and at universitiesfor undertaking aeronautical research and considersthat this can still, with advantage, be further increased.Our liaison with the universities is a close one, mainlybecause so many university men interested in our sub-jects are members of our committees. We learnt withpleasure of the setting up of the Aircraft ResearchAssociation by the Aircraft Industry, and understandthat their plans to erect a large wind tunnel are nowwell forward. Occasional research reports are receivedfrom individual aircraft firms, and we would welcomemore. The Society of British Aircraft Constructorsmakes us acquainted with much of the research under-taken at firms. Such contacts are valuable to us, andwe endeavour to foster the excellent, and naturallymore continuous relations, between official researchstaff and those at aircraft firms.

Research StaffIn several Reports to the Minister of Supply we have

drawn attention to the importance of adequate staff forofficial Research Establishments and have emphasizedthat some of this staff must be of the highest quality.Whereas in production work, even to some extent indesign and equipment work, scientific and engineeringstaff of average ability can, because of the nature ofthe work, be efficiently employed, particularly if wellled, the use of too large a proportion of similar staffin the research field may easily lead to no useful resultsat all, or to the production of mediocre results byunnecessarily expensive methods, or even to the cloud-ing of issues that would otherwise have been maderapidly clear. Research depends essentially on the bestmen in the field.

The Council welcomed the steps taken in 1950 tointroduce certain higher posts in the Scientific CivilService to be held by scientists on account of the highvalue of their individual work and without administra-tive responsibilities. Various questions about the staffto be employed at the N.A.E., Bedford and theiramenities have been discussed and the Council hasdrawn attention to some of the factors which help inproviding those conditions under which research staffsdo their best work. Salaries for scientific grades andthe wages for industrialists should be adequate to pre-vent many of them from being tempted away to thehigher wages offered in industry.

The question of the supply of more good scientistsis a national one. The Council has on its part pointedout the tendency for the best men to take Arts degreesin some of the universities so that the relative positionof Engineering and Science compared with the Artsis decreasing, possibly due to the fact that the qualityof scientific teaching in the schools is depreciating andthe best boys tend to gravitate to the best teachers.Headmasters have also an important influence on thedirection taken by a boy's studies. The Council drewattention to these matters in 1952, emphasizing thattechnology was an essential culture of a modern kind.Aerodynamics—Supersonic Research

We drew attention, in *>ur last review, to the fact thatexperimental aircraft had flown .at a speed as high asM = 1'4. During the intervening years, experimentalresearch aircraft have increased this speed to at leastM=2-5. The speeds of some operational aircraft arealready supersonic and a host of new problems needsolution as their speeds increase still further. Muchcan be done by work in supersonic wind tunnels—otherresults are obtainable from experiments on modelsflown at these speeds, but the ultimate test is on theaircraft itself. For this reason the Council has empha-sized the importance of having available, at an earlydate, aircraft flying at supersonic speeds, so thatresearch and experiments at these speeds can go onhand-in-hand in flight and in the laboratory. We arealso encouraging other experimental work at still

higher Mach numbers in order to acquire fundamentalknowledge for a future date. We recommended earlyin 1949 that supersonic research aircraft should be de-signed and constructed to be followed up by opera-tional types as soon as possible.

High Speed Flight ResearchThe aim of most wind-tunnel research is to provide

either fundamental knowledge on aerodynamics or dataof use to the aircraft designer. Its value depends onchecks which can best be obtained in flight. Thereis a danger that flight research at high speeds and highaltitudes will be seriously curtailed for lack of facilitiesowing to rival demands on the few suitable aircraftavailable for such work. The newest types are required,and, consequently, there is a serious risk that the smallnumber of prototypes which are ordered will be insuffi-cient to meet the claims both of development and re-search. The Council has accordingly recommendedthat there should be an adequate supply of aircraft,material and personnel for flight research to proceedat a reasonably rapid rate. As an example, it wasdesired to get a direct comparison between swept-backand non-swept-back wings on otherwise similar air-craft. This was possible on one type at the beginningof 1950 and some preliminary measurements weremade. The first reports received from both the Aero-plane and Armament Experimental Establishment andthe Royal Aircraft Establishment on the stability andhandling characteristics of this aircraft as a result oftests on several prototypes show that in both casesperformance and handling characteristics were excellentup to M = 0-9, but very large changes of trim andstability were encountered above this speed. The flighttests on these prototypes have yielded valuable informa-tion about the various stability and stalling boundariesin the high subsonic Mach number region. Thestandard of this work was ranked so highly by theCouncil that letters of congratulation were sent in 1950through P.D.S.R.(Air) to the pilots at the two Establish-ments.Handling Problems of High-speed Aircraft

The Stability and Control Sub-Committee hasdevoted several special meetings to discussions withpilots on the handling qualities at both high and lowspeeds of modern high-speed aircraft. Many test pilotsattended by invitation from the Experimental Estab-lishments, from Central Fighter Establishment and fromaircraft firms. There was a substantial body of opinionamong pilots that, at the present stage, tailless aircraftwere less satisfactory for high-speed research workthan the more conventional tailed designs. The twochief objections brought against tailless aircraft were:(i) a tendency to instability at high speeds due to areduction of the damping in pitch which has not yetbeen explained, and (ii) the fact that trailing-edge con-trol surfaces tend to become ineffective at high Machnumbers, so that the aircraft cannot be kept under fullcontrol.

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Much consideration has recently been given to thestalling problems of thin wings in view of the tendencyshown by some high-speed fighter aircraft to suddenand sometimes catastrophic wing dropping. Flightexperiments carried out on one aircraft have shownthat very small modifications to the wing section nearthe leading edge can have a profound effect on thecharacter of the stalling of the wing. Work will beundertaken in wind tunnels with the aim of understand-ing this phenomenon but the difficulties of representingthe modifications to the wing in tunnel experiments atan adequate Reynolds number are many. A methodused at the R.A.E. for observing the development ofthe stall by coating the surface of the wing with a fairlythick oil and photographing the flow pattern revealedon this surface is promising.

American experience on transonic aircraft has re-inforced the view of the Council that a manned super-sonic aircraft is a most desirable tool for exploringcertain aspects of the transonic field. We are gladto learn that a supersonic aircraft has recently becomeavailable for experiment as it will be a great aid insolving certain problems of performance and of stabilityand control which cannot be undertaken readily by anyother means.Structural Fatigue

The accidents to the de Havilland Comet have drawnpublic attention to problems dealing with the fatigueof aircraft structures. We draw attention in theMechanics Section of this Review to the importanceattached during the last few years to research investiga-tions on this subject.

//. AERODYNAMICS1. TRENDS IN AERODYNAMIC RESEARCHIn 1951, the Aerodynamics Committee carried out

a general review of the important trends in aero-dynamic research, in order to advise on the mostimportant fields in which effort in this country shouldbe concentrated. The views of the Royal AircraftEstablishment, of the Aerodynamics Division, NationalPhysical Laboratory, and of the Aircraft Industrythrough the Society of British Aircraft Constructors,were obtained and a study of the papers submitted bythese bodies revealed a remarkable unanimity of viewbetween the Government Establishments and theIndustry.

It was recognized that the total resources in thiscountry available for work in aerodynamics wouldhave to provide not only the requirements for normalaircraft, but also those for supersonic aircraft andguided weapons, not to mention helicopters. In theaircraft field the most pressing problems were con-nected with aircraft with operational speeds near thespeed of sound but the problems of supersonic aircraftwere also imminent. The problems of guided weaponswith their much higher supersonic speeds and theirunorthodox shapes, differ largely from those of mannedaircraft.

The Committee was impressed by the unanimousview of the Industry that the greatest contributionwhich the Government Establishments could make-towards the solution of the problems facing the designerwas to improve the understanding of fundamentalproblems. It was therefore recommended that at leasthalf the total effort in the Establishments should bedevoted to research of a systematic nature. At thesame time, the indisputable need for investigationsrelated to specific designs was recognized. In certainfields the accumulation of general knowledge can per-haps best be effected by beginning with a particulardesign and generalizing the experiments by progressive

modifications. In others, the requisite fundamentalknowledge can only be obtained by systematic experi-ments not immediately related to specific designs.

Some of the problems which have exercised theAerodynamics Committee and its Sub-Committeesduring the period under review are discussed underseparate headings below. Before proceeding to thisdetailed review, however, something should be saidabout the general methods of investigation and theprogress that has been made in providing experimentalequipment in this country. Fundamental to systematicadvances in aeronautical knowledge is the theoreticalwork whose aim is to systematize the existing empiricalknowledge, fill in the gaps where experimental evidenceis lacking, and by extrapolation, to guide experimentalinvestigators in the choice of problems to be explored.Turning to experimental work, the principal tool forfundamental research remains the wind tunnel andmuch progress has been made during the past five yearsin the provision of tunnels, particularly for supersonicand transonic testing. There are, however, severelimitations on the size of model which can be testedin wind tunnels at transonic speeds and this type ofwork must be supplemented by other methods ofexperiment. The technique of ground-launched rocket-propelled models is one which has already proved itsvalue in tests covering the whole transonic range. Thewing flow method by means of which models aretested by mounting them on the wings of aircraft inflight, has been used to a limited extent. Finally,many problems, particularly in relation to the handlingof aircraft in the transonic region, must rely for theirsolution largely on tests of actual aircraft in flight.In this connection, the Aerodynamics Committee wel-comed a suggestion made by the S.B.A.C. that thefacilities for flight research at the firms should be morefully employed, and it is satisfactory to note that therehas recently been a marked increase in the research

activities of the firms. Mention should also be madeof a new and powerful technique for the study ofaerodynamic problems, particularly in the fields ofstability, control and oscillation: viz., the use of elec-tronic analogue machines and digital computers.

2. EXPERIMENTAL TECHNIQUES ANDFACILITIES

(a) Transonic tunnels. During the period underreview, intensive effort has been devoted to the designof transonic wind tunnels, i.e., tunnels in which it ispossible to test models in a wind stream flowing atspeeds equal or near to the speed of sound. This hasbeen made possible by an idea which was developedfirst in America, although it was mooted by SirGeoffrey Taylor in this country before the war. If amodel is tested in an ordinary wind tunnel with con-tinuous solid walls in the working section at increas-ingly high subsonic speeds, a point is reached whenchoking occurs and no higher speed is possible. Itis also possible to design supersonic tunnels in which,by suitable tunnel geometry, the air stream is accele-rated through the speed of sound in front of the work-ing section to enable models to be tested therein atsupersonic speeds. Hitherto, however, there has beenno means of covering the range in the immediateneighbourhood of the speed of sound. The new prin-ciple makes use of slotted or perforated walls in theworking section through which the stream expandsinto a chamber surrounding the working section itself,thus avoiding choking and permitting continuous varia-tion of wind speed through the speed of sound with-out any change in the geometry of the working section.Much research, particularly at the N.P.L. and R.A.E.,has gone into the study of different shapes of slot andperforation with a view to obtaining the most nearlyuniform distribution of pressure or velocity in theworking section and to minimize the shocks reflectedfrom the walls. The largest tunnel in this countrywhich has so far been fitted with a transonic workingsection is the 3 ft. x 3 ft. tunnel at the National Aero-nautical Establishment, Bedford. It is also plannedto convert the 10 ft. x 7 ft. High Speed Tunnel atthe R.A.E. for transonic running.

(b) Supersonic tunnels. The first large supersonictunnel at the R.A.E. was built primarily for guidedweapons work and has a working section 18 in. x 18 in.This has now been running for some years and hasbeen used for general aerodynamic testing as well asfor guided weapons work. At the N.A.E., Bedford,in addition to the 3 ft. x 3 ft. tunnel mentioned above,which will run supersonic up to a Mach number of 2,a much larger tunnel primarily for supersonic workwith a working section of 8 ft. x 8 ft. is now in courseof construction. At the N.P.L. the largest supersonictunnel so far in operation has a working section of18 in. x 14 in. but two larger tunnels are nearing com-pletion. Besides those mentioned there are manysmaller supersonic tunnels at the three Establishments

and at various universities and firms. Most of thesesupersonic tunnels cover a range of speed up to aboutM = 1-8 or 2, although some cover a higher Machnumber range and the Bedford 8 ft. x 8 ft. tunnel isdesigned to run up to M = 2'5. Plans have beenapproved for the construction of a new medium sizedtunnel to cover a higher speed range. This tunnelis intended to yield experimental data at a reasonablyhigh Reynolds number on missiles or aircraft, usingthe words in their most general sense, which may beexpected in the future to fly at Mach numbers as greatas, or greater than, M = 3'5.

(c) Hypersonic tunnels. During 1952, the Aero-dynamics Committee discussed at some length theproblems of flow at very high Mach numbers (hyper-sonic flow), and at very low density (superaerodynamicflow), corresponding to conditions of flight at altitudesmuch higher than those of current manned aircraft,and recommended that work in this field should beundertaken in this country with a view to the extensionof fundamental knowledge. Proposals were put for-ward at that time for hypersonic tunnels to be con-structed at the R.A.E. and the N.P.L. Both receivedthe strong support of the Council.

Three regimes of hypersonic or superaerodynamicflow have been defined, namely, (i) continuum flow inwhich the usual equations of gas dynamics apply, (ii)slip flow, in which there is discontinuity of velocityand of temperature at the boundary, and (iii) free-molecule flow, which can be treated only on the linesof the kinetic theory of gases. These three regimesoverlap but can be approximately defined by theoreticalcriteria based on the ratio of the molecular mean freepath to the thickness of the boundary layer aroundthe body. Continuum flow is by far the most impor-tant of the three regimes from the point of view ofpractical application and the proposed tunnels at theR.A.E. and N.P.L. are designed for the study of thistype of flow, with a maximum Mach number of about8 or 10. At the same time, universities have beenencouraged to give consideration to problems involvingslip flow or free molecular flow, particularly flow atvery low densities and also at very high temperatures.The apparatus required for work of this kind is notvery expensive and might consist of (a) a small low-pressure tunnel, (b) a shock tube, or (c) an " ionic"wind tunnel in which electro-magnetic means are em-ployed to produce a very high-speed flow of the ionizedgas.

(d) Rocket model research. A valuable tool, inuse for some years, for the investigation of the aero-dynamic characteristics of specific aircraft or missileconfigurations, is the ground-launched rocket modelmethod. The models are propelled from a launchingsite on the ground with the aid of rockets whicheventually detach themselves from the model whenthe required speed has been reached. The subsequentfree flight of the model is recorded by electronic, photo-graphic and other means. This method has yielded

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a large quantity of useful information on stability andcontrol characteristics in the transonic region wheredata from other sources are often meagre. It has thedisadvantage that it is not possible to vary the con-ditions of the experiments continuously, or to covera large range of values of different parameters, as canbe done in wind tunnels. On the other hand there isno problem of interference from the tunnel walls which,in the case of wind-tunnel experiments, requireelaborate corrections to be made to the results.

(e) Flight research. There are many vital problemsof high-speed flight which can only be investigatedon full-scale aircraft in flight and even when labora-tory experiments on the ground can conveniently bemade, full-scale confirmation from flight tests is oftennecessary. In the past, flight research has been severelyhampered because of the shortage of advanced air-craft available for research purposes. Experience hasshown that even when a particular aircraft is originallydesigned for research use it has not in fact alwaysbecome available for this purpose if it has proved tobe of interest as a military aircraft. Cases exist oftwo prominent aircraft both originally ordered asresearch aircraft, of each of which only two prototypeswere built in the first instance. When these aircraftproved to be of military interest urgent problemsarose in connection with their possible developmentas military aircraft, with the result that they werenot in fact available for full-scale flight research exceptfor short periods.

To overcome this difficulty, the Council recom-mended to the Ministry of Supply that orders shouldbe placed for a sufficient number of certain advancedtypes of aircraft at an early stage in the design, sothat when built, at least one of the early prototype orpre-production aircraft could be allocated for full-timeresearch work.

(£) Other experimental techniques. The Council haspressed for a more extensive development of instru-ments, including the further application of telemeteringtechniques to flight experiments on piloted aircraft, aswell as to ground-launched rocket tests and guidedmissiles, on both of which they have been used withsuccess. An important problem is the rapid analysisof flight data, so that results may be quickly availableas a guide to the next experiment or as an indicationof the desirability of a repeat. Efforts have beenapplied to the problem of recording the readings ofaircraft instruments in a form which can immediatelybe fed into a calculating machine. This process couldequally well be applied to wind-tunnel observations andcould do much to increase the effectiveness of ourtunnels.

Elsewhere in this Review reference is made to theactivities of the Computation Sub-Committee whichconcerns itself with various types of computationalequipment including both digital and analogue com-puters for the solution of problems in the aeronauticalfield. Special mention is, however, made here of

TRIDAC, the three-dimensional analogue computerconstructed at the R.A.E. for the study and solutionof problems in the design and control of guidedweapons. Experience in the use of this machine hasshown that the operator may, with its aid, gain aninsight into the problems he is investigating whichgoes far beyond the mere numerical results obtainedwith the aid of the machine. It is felt that this is atechnique which might well have far-reaching applica-tions to the design of manned aircraft as well as guidedweapons, enabling the designer to investigate the effectof varying the parameters of the aircraft before the firstprototype is constructed.

3. AERODYNAMIC THEORYIn the Council's Review covering the years 1939-48

some account was given of the advances in supersonicflow theory arising from solutions of the linearizedflow equation which is based on the supposition thatthe disturbances introduced by a body travelling at asupersonic speed are small in comparison with thespeed of the foody itself. Since that review therehas been further development of detailed linear super-sonic theory on this basis and experimental evidencehas shown that this theory, although only an approxi-mation to the flow of an ideal fluid, is of great valuewhen the flow over a body is virtually supersonicthroughout.

A much more difficult problem is presented intransonic aerodynamics where the flow over a bodyis partly subsonic and partly supersonic and whereshock waves and their interaction with the boundarylayer play an important part. The main progress intransonic theory has been made with the aid of small-perturbation theory, which is limited in its applicabilityto wings and bodies which are thin, to small incidencesand to inviscid flow, and which neglects the vorticitygenerated by shock waves. Some wings designed forsupersonic flight will be sufficiently thin to meet theneeds of the theory. The limitation to small incidencesis a serious one and that to inviscid flow ignores theimportant effects of shock-wave and boundary-layerinteraction. Despite these limitations, it is believed thatthis theory, even in its present form, is of assistance inthe understanding of transonic flow and that solutionsof limited problems may be of assistance in appreciat-ing other problems, the solutions of which are notyet known.

In 1938 the Clarendon Press published for theCouncil two volumes entitled Modern Developments inFluid Dynamics, the material for which had been com-posed under the aegis of the Fluid Motion Panel, asit was then called, and edited by Sydney Goldstein.These volumes dealt only with incompressible flow and,although notable advances have been made in thisfield since that date, these volumes still give anauthoritative account of the main scope of knowledgein that field. With the increasing emphasis on highersubsonic, transonic and supersonic speeds, where thecompressibility of the atmosphere cannot be neglected,

the need was felt for a companion publication dealingwith high-speed flow problems. Once more the taskof overseeing the contributions was allotted to the FluidMotion Sub-Committee, many of whose members con-tributed to the new publication, which was edited byProf. L. Howarth. The two volumes, entitled ModernDevelopments in Fluid Dynamics—High Speed Flow,were published for the Council by the Clarendon Pressin 1953 and have been recognized as the most com-prehensive and authoritative review of the subjectwhich has so far appeared.

During the same period a special Panel wasappointed, under the Chairmanship of Prof. L.Rosenhead, to prepare a volume of tables for use incompressible flow calculations and a companion volumeof graphs. These two volumes were published by theClarendon Press in 1952 and 1954, respectively, andconstitute essential working tools for calculations basedon the theoretical methods discussed in the Howarthvolumes.

4. SUBSONIC FLOW PROBLEMSDespite the increased emphasis on problems of

transonic and supersonic flow, there remain importantand pressing problems associated with flight at sub-sonic speeds. Two fields in which research has been,and remains, very active are (a) drag reduction, witha view to increasing the efficiency of aircraft, par-ticularly long-range civil and military aircraft, and (b)the low-speed problems of aircraft designed primarilyfor high-speed flight.

(a) Drag Reduction. Researches of Goldstein andothers during the war led the way to the design oflaminar-flow wings, i.e., wings designed to secure themaximum area of laminar flow over their surfaces.The drag caused by laminar flow in the boundary layeris only a fraction of that caused by turbulent flow,and the position on the surface of the wing of thetransition point where laminar flow changes to turbu-lent has a large effect on the drag of the aircraft.Theoretically, it is now possible to design wings onwhich laminar flow is maintained over more than halfthe surface without the aid of any form of boundary-layer control. In practice, however, such results canonly be achieved if the wing surface remains smoothand free from deposits of dirt, flies, etc., since anyprotuberance or irregularity of the surface is apt toinitiate turbulence in the boundary layer. Increasinglyrefined techniques have been developed for studying inwind-tunnel and flight tests the conditions in the bound-ary layer. The evidence concerning the amount ofroughness and waviness that can be tolerated withoutcausing transition has been satisfactorily analyzed.Much has been done towards reducing surface rough-ness but it must be admitted that the operationalproblem of dealing with flies which may impinge onthe wing of an aircraft especially at the lower altitudeshas not yet been completely solved.

In addition to the technique of obtaining laminarflow through the use of specially designed wing sections,

great progress has been made in the application ofsuction and other means of boundary-layer control towings. Drag reduction is only one of several purposesfor which the principle of boundary-layer control maybe used, but it is probably the one which offers thegreatest economic gains in the long run. The earlywork on the use of slot suction to reduce the drag onthick wings was brought to a halt during the periodunder review : this application is only feasible on air-craft with cruising speeds not higher than, say, 300 or350 m.p.h., since at higher speeds compressibility effectswould be too severe on thick wings. Owing to the factthat even for passenger aircraft the recent trend hasbeen towards higher cruising speeds, the main emphasison boundary-layer control for low drag has shifted towings of normal thickness. Work on boundary-layersuction has included both suction through slots andthrough porous surfaces. Flight tests have been carriedout on gloves fitted over portions of Vampire wingsusing two methods of boundary-layer suction. It willprobably be necessary to suck away the whole turbu-lent boundary layer to obtain laminar flow when fliesare deposited on a leading edge. Whether such a pro-cedure is economical depends on how close to theleading edge the suction slot can be sited and on thedevelopment of an efficient ducting system.

Flight tests have shown that the difficulty in obtain-ing laminar flow on full-scale wings is greatly increasedwhen the wing is swept-back. Visual observations oftransition have been made on a number of wing andfin surfaces in flight which suggest that the nose radiusof the wing section may be a dominant factor affectingthe destabilizing of the laminar boundary layer near thenose of the swept-back wing. It has also been shownin wind-tunnel tests that closely spaced vortices aregenerated within the laminar boundary layer with theiraxes along the wind direction associated with unstablecross flow over the wing ; as the wind speed is increasedthese vortices break down and cause transition to turbu-lent flow near the leading edge. Limited success hasbeen achieved in maintaining laminar flow under theseconditions by the application of boundary-layer suctionat the nose; the tunnel results have subsequently beenconfirmed in flight but the suction quantities required atzero incidence to maintain laminar flow to the positionof minimum pressure are of the same order as thoserequired to maintain laminar flow over the whole chordof an unswept wing. Unfortunately there is a con-siderable decrease in the stability of the flow over thelower surface with increase of incidence, which makesthe practical use of suction on swept wings somewhatdoubtful.

(b) Low Speed Problems. As the top speeds of air-craft have increased, so the problem of obtaining asufficiently low speed for landing has become increas-ingly severe. This is essentially a matter of increasingthe range of usable lift coefficient before the wing stalls.Recently both theoretical and experimental work havethrown light on the nature of the stall on thin wings.Low-speed wind-tunnel tests have shown that when a

laminar boundary layer separates from the leading edgeof a thin aerofoil at incidence the flow often becomesattached to the surface again some distance downstream.The region of separated flow is called a bubble and itschordwise dimension may vary from a minute fractionof the wing chord to a length comparable with thechord, depending on incidence, Reynolds number andtype of aerofoil section. An analysis of tests made inthis country and America indicates that the length ofthe bubble depends primarily on the Reynolds numberbased on the displacement thickness of the boundarylayer at the separation point. If this Reynolds numberis less than 410, a long bubble is obtained and as theincidence of the aerofoil is increased, the reattachmentpoint moves gradually back to the trailing edge and thestall is gradual. If, on the other hand, the Reynoldsnumber has a higher value than the above, the separatedflow is unstable, quickly (becomes turbulent, and theflow reattaches at a very short distance behind theseparation point. With increase of incidence of anaerofoil with a short bubble of this type there is littlechange in the separated length until the bubble bursts,when the flow ceases to reattach itself to the surface andthe stall is abrupt. Further work is in progress whichshows promise of throwing light on the mechanism ofthe bursting of the bubble.

Much of the recent work on boundary-layer controlhas been directed towards increasing maximum lift. Onemethod of doing this is to suck away the boundarylayer at the nose, but there are several alternativetechniques, such as the use of suction or blowing overtrailing edge flaps. It may well be that this applicationof boundary-layer control will be the first to proveacceptable on operational aircraft. On both civil andmilitary aircraft there is an urgent need to increase therange of usable lift coefficient at low speeds in orderto keep the required runway length within bounds andto improve the handling characteristics of the aircraftin approach, landing and take-off.

Statistics of civil aircraft accidents show that a sub-stantial proportion of fatal accidents is still associatedwith stalling, although in many cases the accident mayprimarily have been due to some other cause. Theneed for some kind of a stall warning device is recog-nized by the Air Registration Board and the view ofmany pilots is that, on aircraft where there is no naturalstall warning, an artificial warning, preferably in theform of a stick-shaker, should be provided. On manymodern aircraft, particularly jet aircraft with power-operated controls, there is no natural stall warning.Furthermore, on some recent aircraft very high rates ofdescent may be built up very quickly before the pilotis aware of the fact, a consequence of the much greaterinduced drag of wings which are thin and of smallaspect ratio; it would therefore be an advantage ifsome form of angle-of-attack indicator were providedas well as a specific warning of the approach of the stall.

(c) Spinning. The main experimental tool for theinvestigation of spin and recovery characteristics of air-craft is the vertical spinning tunnel in which models

built to dynamic similarity with the full-scale aircraft(apart from Reynolds number effects) are tested. Aftermaking an allowance for the difference in Reynoldsnumber between the model and full-scale aircraft, full-scale characteristics of the spin are predicted from themodel tests. A new spinning tunnel is nearing com-pletion at the N.A.E., Bedford. In this tunnel, which hasa working section of 16 ft. diameter and can bepressurized to 4 atmospheres, it is estimated thatReynolds numbers up to about one-eighth of full-scalevalues will be obtainable in free spinning model tests;in rolling balance tests Reynolds numbers up to abouthalf the full-scale values will be obtainable. TheseReynolds numbers represent an advance by a factorof about 15 on those obtainable in the existing R.A.E.spinning tunnel.

A new technique which may prove valuable forbridging the gap between wind-tunnel tests and fullscale, consisting of free-flight tests with large radio-controlled models, has received the support of theAreodynamics Committee. Until recently this methodwas impracticable owing to the fact that there was nomulti-channel proportional control radio set of suit-able size, weight and cost which would satisfy theconditions of the required experiments. A suitableradio control system of this type has now beendeveloped by the Low Speed Aerodynamics ResearchAssociation at Farnborough and the AerodynamicsCommittee has recommended that official supportshould be given to the further development of themethod.

Spinning tunnel tests on new aircraft cannot be madeuntil the design of the aircraft is almost settled andit is important that the designer should have someguide to the probable spin and recovery characteristicsof the aircraft in the early stages of design. Variousattempts have been made in the past to producecriteria based on the geometry of the aircraft for pre-dicting recovery characteristics and a new criterionhas recently been proposed at the R.A.E. The prin-cipal advantage which it has over its predecessors isthat it includes the important parameter B/A, the ratioof the pitching and rolling moments of inertia of theaircraft, and indicates that the recovery standards willimprove as this ratio increases. This is in agreementwith recent full-scale experience The new criteriondoes not apply to twin-boom aircraft such as theVampire and Venom and it has other limitations, e.g.,it considers only the effect of the rudder as a recoverycontrol and sideslip does not appear explicitly in thecriterion. Nevertheless, it has proved to be remark-ably successful in separating both straight wing andswept-back wing aircraft into " pass ", " borderline "and " fail" classes from the point of view of recoveryfrom the spin.

When an aircraft enters a spin from straight andlevel flight the path of the e.g. changes from a hori-zontal path to a spiral about a vertical axis. Duringthis changeover period oscillation in the angular velo-cities about the body axes of the aircraft are bound to

occur. In some spins these oscillations are dampedout between the second and fourth turns and thenthe aircraft spins smoothly with the angular velocitiesabout the body axes remaining almost constant. Thisis the familiar steady spin. On many present-dayaircraft, however, the oscillations do not damp out butgradually increase in amplitude up to the fourth turnand in some cases the amplitude continues to increaseup to at least the eighth turn. When the oscillationsare of a mild type the pilot experiences no very violentchanges but is aware of a continuously changing angleof wing tilt, the outer wing appearing to move fromwell above the horizon down to the horizon and backagain, once in each turn : this type of oscillation hasbeen called a wallowing spin. In a fully-developedoscillatory spin the oscillations in the angular velo-cities about the aircraft axes are quite violent, therate of roll, for example, changing from zero to asmuch as 3'5 radians per second and back again ineach cycle.

The oscillatory spin is not a new phenomenon butit is becoming increasingly important. To the pilotit can be an unpleasant experience in which the noseof the aircraft oscillates up and down in relation tothe horizon, accompanied by marked variations inacceleration in roll and pitch. At the same timepronounced aileron snatching is apt to occur. Ingeneral, an oscillatory spin is apt to occur on aircraftwith good recovery standards. It is an essential featureof the phenomenon that the wing should unstall itselfat one point of each cycle and very little action isrequired on the part of the pilot to effect recovery.The recommended drill is for the pilot to centralizethe stick and if the aircraft does not come out of thespin by the time an altitude of 7,000 to 10,000 ft. isreached, he should bale out. As regards scale effect,flight experience shows that the oscillatory spin ismore likely to occur on full scale than on model scaleeven though the proper scale effect allowance, basedon recovery standards from the model spin, has beenapplied to the model results.

5. PROBLEMS OF TRANSONIC FLIGHIAs has been pointed out above, the most difficult

aerodynamic problems are associated with speeds inthe neighbourhood of the speed of sound, i.e., at andnear M = 1. The transonic region in the broadestsense, however, may be taken to include, not merelythe immediate neighbourhood of M = 1, but the wholeregion within which there is a mixed regime of sub-sonic and supersonic flow over a body. In otherwords, the transonic region begins where small areasof supersonic flow appear on the surface of the air-craft or missile, accompanied by shock waves mark-ing the transition between subsonic and supersonicflow. As the speed of flow is increased, the shockwaves become more pronounced and the areas ofsupersonic flow more extensive. Finally, the upper

limit of the transonic region is reached when theflow over the whole body is entirely supersonic. Wind-tunnel observations and theoretical considerationshave distinguished a number of different regimes withinthe transonic region as a whole, defined by the posi-tion and nature of the shock waves on the body andnear its leading and trailing edges.

Shock waves have the effect of greatly increasing thedrag on the body, and through their interaction on theboundary layer, they may also have adverse effectson lift, on stability and on control effectiveness. It istherefore of the greatest importance to the designer oftransonic aircraft that their effects should be mini-mized as far as possible. One of the principal methodsof doing this is to make wings as thin, and bodies asslender, as is practicable. Another is to delay theeffects of compressibility, including the formation ofsevere shock waves, to as high a Mach number aspossible by sweeping back the wings. From swept-backwings of conventional aspect ratio to delta wings ofsmall aspect ratio is a logical step which further alle-viates the effects of compressibility, and one whichhas been adopted by a few manufacturers in thiscountry with considerable success.

(a) Shock-Wave Boundary-layer Interaction. It isconsidered that some of the major difficulties andobscurities of transonic flow are associated with effectsof the interaction of shock waves with the boundarylayer, particularly when separation of the boundarylayer results from the interaction. The conditions underwhich separation occurs are now known with reason-able accuracy and many of the effects in flight areat least partially understood. On a wing or aerofoil,separation occurs at or upstream of the foot of ashock wave when the pressure rise across the shock,i.e., the shock strength, exceeds a certain value. Thisvalue is lower for a laminar boundary layer than fora turbulent boundary layer, at the Reynolds numbersobtainable in wind-tunnel tests. Separation on onesurface, by arresting the rearward movement of theshock wave on that surface and reducing the rate ofrecovery between the shock and the trailing edge,causes the trailing edge pressure to fall rapidly andhence to diverge from the smooth and gradual variationwith free-stream Mach number which would occurif separation were absent. This disturbs the equality,or near equality, of pressure on the two sides of thewake at the trailing edge, which must be satisfied forsteady flow, and, to compensate for this disturbanceof the trailing edge pressure, the shock waves on thetwo surfaces move towards the trailing-edge at differentrates, with consequent changes in the pressure dis-tribution on the aerofoil. Adverse effects which maybe associated with these phenomena include loss of liftand control effectiveness, changes in trim and stability,and wing dropping, whilst it appears likely that buffet-ing arises from the formation of large-scale disturb-ances as a result of instability of the vortex sheetsformed at separation.

To avoid separation, the local Mach numbers mustbe kept low; thin wing sections, sweep and low aspectratio all help to do this at low incidences, but highlocal Mach numbers are always likely to occur forhigh wing incidences or control deflections. The deflec-tion of trailing edge controls when the flow over thewing is locally supersonic leads to an abrupt increasein Mach number on the convex side of the hinge andhence an increased tendency to separation. For thisreason, all-moving wing tips for tailplanes may bemore satisfactory than conventional trailing edge con-trols for transonic flight, and other unconventionalmethods of control are also under consideration.Although separation effects are frequently minimizedby careful choice of section shape and plan form, it ispossible that application of boundary-layer control maysometimes be needed to prevent separation. Workis in progress on the application of vortex generators,fences and various forms of boundary-layer control inthis connection.

(b) Drag. In the design of transonic and super-sonic aircraft, one of the prime considerations is toreduce to a minimum the wave drag, i.e., the dragassociated with shock waves. Something has been saidabout the adoption of thin and swept-back wings forthis purpose but there remains a serious problemassociated with the increased wave drag due to themutual interference of the wing and the body at theirjunction. The design of air intakes for jet engines isan integral part of this problem.

(c) Limitations on Lift at Transonic Speeds. Air-craft designed for military operation at transonic speedsmust be able to manoeuvre and this implies that theaircraft should have a reasonable range of usable liftbefore stalling occurs.

Apart from the stall itself, limitations on maximumlift at high Mach numbers are frequently imposed bybuffeting and loss of longitudinal stability. There isneed for much more fundamental understanding ofthese problems. Progress towards this end has come,not only from the study of shock-wave and boundary-layer interaction, but also from recent work, boththeoretical and experimental, on the stalling of thinand swept-back wings. In particular, much effort hasbeen devoted to means of countering the tendency topremature tip-stalling on swept-back wings.

(d) Stability. There remains an urgent need formore accurate knowledge of stability derivatives.Whilst the subsonic and supersonic value of stabilityderivatives can be predicted with reasonable accuracy,there is as yet very scanty knowledge of values inthe transonic region. Continued effort, utilizing free-flight models and wing-flow techniques as well as wind-tunnel experiments, is required to extend knowledgein this field. As regards longitudinal stability, the mostimportant problem is probably that of the variationsin the damping of the short-period longitudinal oscilla-tion, particularly in the region between M = 0-9 andM = 1, which on some aircraft amounts to a significant

loss of damping. In addition, large negative staticand manoeuvre margins are reported to occur on someswept-wing aircraft at lift coefficients above 0-7 in theregion from M = 0-85 to M = 1-0. There is at presentvery little knowledge on lateral stability derivativesbut it is possible that only their order of magnitudeneed be known.

(e) Control Effectiveness. Data on control effective-ness in the transonic region are being accumulated,particularly through free-flight model experiments, andthe designer now has some basis on which to choosehis controls. In particular, a systematized body ofknowledge exists on the effects of sweepback andtrailing-edge angle on the characteristics of conven-tional trailing-edge controls.

Certain alternative forms of control have possibleadvantages over the normal trailing-edge type attransonic speeds in particular respects, for example,in being less likely to cause shock-induced boundary-layer separation, but the choice of control is often acompromise between these particular advantages anddisadvantages in other respects or at other speeds.

It is considered that, at any rate for some timeto come, power operation of controls will be essentialfor transonic aircraft and that the right policy is toconcentrate on making power controls reliable andnot to think in terms of manual reversion. This willmake the difficult problem of aerodynamic balance ofcontrols much less severe, but it is important to ensurethat deformation in the control unit is reduced to theabsolute minimum iby ensuring that all the effectivestiffnesses are as high as possible.

6. PROBLEMS OF SUPERSONIC FLIGHTIn the supersonic field a main aim of fundamental

research is to evolve a body of experimental resultswhich will provide a basis for testing and improvingthe aerodynamic theories which have already beendeveloped. Of great importance here is the bringingin to full and effective use of the large-scale supersonictunnels referred to in an earlier paragraph, althoughmuch useful information is being obtained from testswith ground-launched rocket models.

Aircraft designed to fly at speeds up to twice thespeed of sound may not have sweptback wings sincethe advantage of sweepback is mainly to postpone thedifficulties associated with transonic flow to a higherspeed of flight, and not to avoid them altogether. Thefirst aircraft to fly at supersonic speeds in level flight,namely, the American Bell X.I, had straight wings,and so have the majority of guided weapon configura-tions. Many of the problems confronting the designerof a supersonic aircraft are similar to those met in thedesign of an aircraft required to operate at high sub-sonic and transonic speeds, but with increased emphasison the body and body-wing interference contributionsand on the air intake problems. It should beemphasized that, although an aircraft may be designedto have a top speed of, say, twice that of sound, it

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may have to fly fairly steadily and to manoeuvre closeto the speed of sound; there also remains the problemof achieving satisfactory low-speed characteristics onaircraft designed primarily to fly at transonic and super-sonic speeds.

(a) Aerodynamic Heating. The aerodynamic heatingof the surface of the aircraft at supersonic speeds, andthe consequent effect on the structure, may be a limitingfactor affecting the speed of flight of the fastest aircraftin the future. The problem is difficult to treat satisfac-torily owing to the complicated effects of fine structuraldetail but it appears that the maximum thermal stresseson wings are likely to occur at the leading edge and atmid-chord. When the duration of flight is short, therate at which the temperature builds up is importantand this is affected by the rate of heat transfer and bythe heat capacity of the material. At M = 2 it isassumed that it takes about half a minute for thetemperature to build up and in some cases the durationof flight at this Mach number might be less than this.The acceleration at which the aircraft attains this flightspeed in turn affects the initial heat transfer rates andthus the magnitude of the thermal stresses. Insulationmay help to delay the effects of the build-up of tempera-ture. An aspect of this subject which is thought to beof special importance is the effect of heat transfer onboundary-layer transition. It would seem to be estab-lished that transition is delayed when the heat flow isfrom the fluid to the body, so that it may be easier to

maintain laminar flow over bodies at high altitude if theheat lost by radiation is high. At very high altitudes theReynolds numbers may be relatively low and thechances of extensive laminar boundary layers arecorrespondingly enhanced.

(b) Guided Missiles. The advent of guided missileshas laid emphasis on certain aerodynamic problemswhich are not important in relation to manned aircraft,associated with such factors as (i) relatively large bodies,(ii) much higher incidences, (iii) frequent use of cruci-form wing arrangements, with pitch and yaw of equalimportance, and (iv) a more complex downwashproblem than on most aircraft since the wings and tail-planes constitute two sets of surfaces of comparablespan. A very large amount of data is required to definethe aerodynamics of a missile, particularly with cruci-form wings and the associated problem of mutual inter-ference between the two sets of wings. There exists nosatisfactory theory which can be applied to the problemsof missiles at supersonic speeds and high incidences ;the existing linear supersonic theories are of no help inthis connection. Furthermore the problems of stabilityin flight where acceleration cannot be neglected is onewhich does not yield to the classical treatment in termsof linear differential equations with constant co-efficients. A beginning has been made on a theory ofstability in accelerated motion and valuable informationon guidance and control problems is being obtainedfrom TRIDAC, the three-dimensional simulator forguided weapons at the R.A.E., mentioned above.

///. PROPULSION1. TEST FACILITIES FOR AIRCRAFT ENGINES

In 1951 the Council submitted, on the recommenda-tion of its Propulsion Committee, certain proposals forequipment and facilities for propulsion research to theMinistry of Supply. This included plant for the full-scale altitude testing of engine components and an alti-tude test cell for complete engines, both of which wereconsidered highly desirable. Since that time additionalequipment has been provided at N.G.T.E. for testingcomponents and a great deal has been done in theaircraft engine industry fpr the testing of large unitcomponents. During 1954 the matter has again beenreviewed in the light of probable engine developmentsduring the next 10 to 15 years. No fundamental changesin the aircraft engine are foreseen at present and ithas also to be borne in mind that it takes about tenyears to design, develop and use an engine to the stageat which it becomes obsolete. The Propulsion Com-mittee has expressed the opinion that an altitude testplant for complete engines should be constructed with-out delay in order that this country shall maintain thelead which it now holds in engine research and develop-ment.

The Committee has recommended that a test plantin the form of an altitude chamber should be capable

of accepting an engine of high mass flow and repro-ducing conditions of temperature and pressure equiva-lent to flight at M = 3-0 at 70,000 feet. The desirabilityof testing engines at high speed at sea levels shouldalso be borne in mind, and provision should be madewithin the above limits of mass flow, for simulating air-flow around small engines. A satisfactory range ofoperation would be that given by the maintenance ofconstant indicated airspeed over the recommendedrange of altitude, but it is felt that consideration of suchdetails is unnecessary at this stage. The approval ofthe plant in principle has been agreed by H.M.Treasury; the details of the final design have not yetbeen decided.

2. ENGINES FOR JET LIFTThe development of engines of low specific weight

has made possible the achievement of vertical take-offand landing using jet thrust. The further developmentwill be materially assisted by the advent of small jetengines of lighter weight. In America attention is beingdirected to the take-off of the aircraft from a verticalattitude from supports under a cruciform tail. In thiscountry experiments have been made on a 'FlyingBedstead' in which both direct lift and controlled flight

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have been achieved, based solely on the jet thrust givenby Nene engines. The Council has been in touch withthese developments from their commencement and hasgiven its strongest support. It may well prove that thefuture of the most powerful aircraft will lie in directlift types which do not need large areas for their take-off and landing.

3. HELICOPTER POWER PLANTSProposals have been put forward for the powering of

large helicopters by turbo-jet engines mounted at therotor tips. It has been estimated that a machine ofbetween 20,000 Ib and 50,000 Ib all-up weight, poweredby three engines of 7,500 Ib thrust, would be capableof travelling at 100 m.p.h. for a distance of 500 mileswith a load of 24 tons, or for 100 miles with a 54 tonload. The scaling-up to this size of the conventionalshaft-driven machine appears to be impracticable dueto the rapid increase in the proportionate weight of thetransmission and the excessive blade weight which isrequired to maintain a reasonable coning angle. Thislatter problem is partially solved if the engines areused as blade tip weights, and it is felt that althoughthe use of turbine engines in this way would give riseto many problems such as high bearing loading andthe effect of high centrifugal force on the operationof the fuel system, such problems would not beinsuperable and would be matters for developmentrather than research. If the construction of suchengines be contemplated, they should be designed speci-fically for this purpose and not adapted from existingengines.

Other possible forms of helicopter power plant aretip mounted ram jets or pulse-jets, tip jets suppliedby a gas-turbine driven compressor and conventionalshaft-driven rotors powered by gas turbines in placeof piston engines. Promising results have been obtainedin America on experimental machines using the twoformer methods, and there would appear to be anapplication for ram jets and pulse-jets for use in verysmall helicopters. No decision can, however, be reachedon the optimum power plant for helicopters or onthe desirability of undertaking research on specializedturbine engines, gas generators, ram jets or pulse-jets,until definite helicopter requirements are drawn up.

4. INTAKESAircraft intakes have, in the past three years, been

a special subject for consideration, including the per-formance of twin ducts at the roots of swept-backwings. This form of intake gives minimum wing flowdisturbance but has the disadvantage that a part ofthe fuselage boundary layer is taken into the ductand the efficiency of the intake is found to be largelydetermined by this boundary layer air. Use of a by-pass slot to remove the boundary layer increases theefficiency but it is difficult to obtain a reduction inoverall drag coefficient by this method as the drag ofthe bypass offsets the gain in the duct. Interest has

more recently been directed to supersonic intakes,consideration having been given to the problems ofdrag loss of centre body intakes, flow instability, theeffect of intake volumetric capacity on flow oscilla-tion, and the performance of an intake in the presenceof a boundary ' layer. More information is requiredand is being obtained on the effects of variable intakesand, in fact, on the whole problem of intake arrange-ment.

5. COMPRESSORS(a) General. At the N.G.T.E., emphasis is being

placed on the transonic or low supersonic range ofcompressor, as this appears to offer something of thebest of both subsonic and supersonic regimes. Thetransonic compressor will probably be smaller, lighterand cheaper than the conventional compressor, whileits mechanical problems will be less than those of thesupersonic compressor, and provided that combustiontechniques follow the aerodynamic advances thereappears to be a promising future for the transoniccompressor engine. It is intended at N.G.T.E. todevelop the transonic compressor up to a Mach num-ber of 1-2, and a temperature rise of 50°C per stagewith an acceptable efficiency. *

The Propulsion Committee has agreed that thepresent approach to the supersonic compressor by wayof development via the transonic type, and by detailedanalysis of all available experimental results, is themost profitable method of attack. Direct approachto the true supersonic compressor should not howeverbe entirely abandoned, as the ultimate developmentof a single-stage compressor with a pressure ratio ofabout 5 : 1 and a low diameter ratio is a most im-portant aim. It should also be remembered that boththe transonic and supersonic compressor are merelysteps towards the attainment of an inexpensive light-weight engine.

Interest was taken in American work on supersonicaxial compressors at the beginning of the period underreview and the American results were so encouragingthat work was put in hand. However, based on massflow per unit frontal area, the supersonic unit com-pares unfavourably with the orthodox axial-flow com-pressor, a conclusion supported by some work on asupersonic compressor tested at the N.G.T.E.

(b) Aerodynamic Research. At Cambridge Univer-sity, an investigation has been made into the flowabout a cascade when the inlet velocity varies alongthe span. Good agreement has been obtained betweencalculated and experimental determinations of thespan wise variation of lift and circulation. The flowangles downstream from the cascade have been foundto depend not only on the secondary flow in the bladepassages but also on the stream displacement in thespanwise direction needed to establish radialequilibrium.

The actuator disc theory of flow in closely spacedrows of compressor blades has been developed and

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compared with the results of tests on a two-stage com-pressor at Cambridge. Theory compares satisfactorilywith experiment even in the stalled region and enablesthe effect of hub-tip ratio and axial spacing betweenthe blade rows to be determined.

This compressor has recently been used to investi-gate the phenomenon of rotating stall, a conditionwhich can arise when the compressor as a whole iseither surged or unsurged. The rotating stall takes theform of a reduced flow through one or two bladepassages, the region of stall rotating relative to theblade row in the same sense as the compressor rota-tion. An axial compressor may have from one toas many as seven stall cells rotating at about halfcompressor speed in any blade row. This phenomenonmay be a cause of blade failure by vibration.

Experiments on compressor cascades of differentdesigns have been reported from Metropolitan-VickersCompany and from the National Gas Turbine Estab-lishment, the former including photographic studiesand covering a range of Mach number and incidence,which shows the growth of shock formations in theblade passages and their interaction with and effectupon the boundary layer.

Valuable information on the growth of shock for-mations on turbine and compressor cascades has beengiven in several papers including evidence fromsehlieren photographs which provides some explana-tion of the form of the loss curve at high speeds. Onepaper of special interest, R. & M.2728, shows the resultsobtained from a series of conventional turbine cas-cades, indicating a rise in loss coefficient with increasein speed above the critical value, due to a X shockformation, until a single shock downstream has aneffect on the pressure distribution and therefore on theboundary layer, reducing the adverse pressure gradientand therefore reducing the rate of increase of losscoefficient. This effect continues until the loss reachesa maximum and thereafter in some cases considerablydecreases.

6. COMBUSTION(a) The Process of Carbon Formation. The Com-

bustion and Fuels Sub-Committee has devoted con-siderable attention to the^ subject of carbon forma-tion, on which a number "of papers have been com-municated from the Royal Aircraft Establishment, fromthe Thornton Aero Engine Research Laboratory andfrom the Joseph Lucas Research Laboratories andsome have been published externally.

Much recent experimental evidence has been accumu-lated by extensive studies of diffusion flames and bythe application of a newly developed and promisingmethod for the spectroscopic examination of flames.Fundamental investigations of the chemistry of theprocesses involved have also been undertaken. Yet,in spite of the technical importance of the subject, thefundamental processes leading to carbon formation inhydrocarbon flames are not fully understood.

There are three main theories to explain themechanism of carbon formation. First, the polymeriza-tion theory which assumes that the hydrocarbon isfirst dehydrogenated and this is followed by successiveprocesses of polymerization leading eventually tocarbon particles in mist form. Second, the C2 poly-merization theory which suggests that the C2 radicalsare polymerized to form carbon complexes. The thirdtheory, called the oxidation theory, assumes that thehydrocarbon is first dehydrogenated and that this isfollowed by oxygen attack, leading to peroxidizedradicals which break down to form a number ofsimple chemical products and atomic carbon, the latterpolymerizing to form carbon complexes. The observedexperimental effects have been compared with thetheories. The first is favoured as it agrees with the factthat the onset of carbon formation is critical to pressure.The C2 polymerization theory has been found to beuntenable. The main difficulty of the third, the oxida-tion theory, is that the time available for the finalpolymerization is very short. Some colour is lent tothe significance of hydrogen atoms in the initiation ofthe reactions which lead to carbon formation andfurther experimental and theoretical work are requiredfor its confirmation.

Much new work has been done on the fundamentalsof the process of carbon formation and related subjects,and suggestions regarding the most likely mechanismhave been presented. Due to the complexity of theprocess the exact details are not yet fully understoodand further conclusions can only be presented whenmore experimental evidence has been obtained.

Although carbon formation is an ever-presentproblem during development work, there is with con-temporary fully-developed designs of combustionchamber little or no practical difficulty. In certaincases there has been, however, some emphasis on theproblem of carbon deposition on burners. The desir-ability of being able to control carbon formation in thefuture design of combustion chambers emphasizes theneed for further fundamental investigations into theproblem.

(b) Effect of Linear Scale. A theoretical investiga-tion of the problem of the effect of linear scale wasinitiated at the N.G.T.E. at the request of the Pro-pulsion Committee, the request originating from theCommittee's discussions of the equipment and facilitiesavailable for propulsion research and development.The expense and difficulty of supplying air for the full-sale testing of combustion systems over a wide rangeof operating conditions makes it very desirable toconsider how far useful results can be obtained fromtests on a small scale. Fundamental knowledge ofscale effect would also be of general assistance indeveloping combustion chambers of various sizes.

In the early stages of the study, a list of componentprocesses was drawn up, comprising fifteen differentrelevant processes under the general headings of aero-dynamics, heat transfer and combustion. Sufficient

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information is now available to enable the relativeimportance of most of these to be assessed, althoughit is agreed that there is no clear-cut answer to thequestion of which of the variables will be the mostimportant in any particular combustion chamber, andthat the gaps in present knowledge are bound to throwdoubt on any generalizations. It was found possiblehowever to reduce the fifteen basic parameters to eightwhich were considered to be of probable primaryimportance, and having done this the next step wasto consider how many of these could be satisfied ina model test. The conclusion was that a large numberof them would be correctly simulated by a half-scalemodel running at the same air velocity and fuelpressure as the full-scale design, but at twice thepressure and half the mass flow.

It is felt that the N.G.T.E. study probably marksthe limit to which dimensionless analysis can contributeto the solution of the problem at this stage and a con-siderable amount of experimental work now remainsto be done. The variables are so numerous and sointer-connected that there is no simple solution to theproblem of deciding on the most important para-meters. Even if these can be resolved experimentallyand exactly satisfied on a model scale, there stillremains the question of rig power, since according tothe conditions required, it is not impossible that asmall-scale rig may need more power than the full-scale rig.

It is of interest to note that although the theoreticalinvestigation at the N.G.T.E. did not cover the use ofsegmental models of annular chambers, the Establish-ment has had considerable success in the testing of ahalf or " D " section of a ram-jet combustion chamber.

(c) Combustion Chamber Cooling. Considerableattention has been paid by the Combustion and FuelsSub-Committee to (the subject of combustion chamberwall cooling, including external circulation of thecooling air using if necessary fins or secondary surfacesto increase the heat transfer rates, effusion cooling usingporous walls, cooling by localized injection of air, anda combination of the methods of internal circulationand localized injection.

Work at the N.G.T.E., R.A.E. and elsewhere hasemphasized the superior cooling efficiency of theporous wall effusion cooling method. A practicalpoint to be considered is the blockage of the pores,but it was noted that the blockage experienced so farcould be cleared by blowing air through the wall inthe reverse direction. There is scope for research tofind new materials of sufficient mechanical strength foruse as porous walls.

Boundary-layer cooling is only directly effectiveagainst convective heat transfer, and in some casesabout 50 per cent of the total heat transfer is byradiation. It is evident, therefore, that the radiationproblem is of some importance, and more informationis needed on the distribution of total radiation betweenluminous and non-luminous types, and on methods of

predicting the luminous emissivity at any point of theflame with different kinds of fuel.

The general conclusion of the work to date is thatthe most efficient method yet considered is effusioncooling through a porous wall, although it is realizedthat the full advantages of this method will depend onthe development of suitable porous materials. Acompromise between the louvred and the porous walltypes of cooling might be to use some form of gauze.

(d) Combustion at High Mach Numbers. Anysignificant advance in engine aerodynamics towards theachievement of low weight and low cost will have tobe accompanied by an equivalent advance in com-bustion technique in fast air streams, considering firstlythe chamber as an aerodynamic system and secondlythe chemical process of combustion. The controllingfactors from an aerodynamic viewpoint are length/diameter ratio, velocity and temperature ratio, whilechemically the best parameters are probably residencetime and the time required for ignition. Greatlyimproved performance could be obtained, andchambers of a much higher rating constructed, if itwere possible to dispense with the requirement ofidling and relighting at high altitude, and it is feltthat the heavy penalty paid as a result of this require-ment may not be fully realized. There does not seemto be a great deal of room for further developmentof combustion chambers operating at medium pressures,as efficiencies are already high. The losses associatedwith reheat systems for instance, considerably out-balance any possible gains in the engine combustionchamber. There will however be new problems to faceif and when the supersonic compressor comes intogeneral use.

7. TURBINES(a) Axial-Turbines. In order to predict the perform-

ance of a turbine or to design it to a given^specification,it is necessary to know the behaviour of various bladeforms not only in cascade but in the turbine itself. Ifthe performance of a sufficient number of turbines isanalyzed, then rules and coefficients may be evolved tomake future design more certain, and such an analysisfor conventional sharp-nosed blading is attempted ina paper prepared by the N.G.T.E. This survey coversthe eifects of the various aerodynamic and geometricvariables on loss coefficient and gas angles at both highand low Mach numbers, and also considers the effectsof those losses which are in general independent ofblade form. Having established the design angles andcoefficients, the paper also gives data for predicting theoff-design performance in terms of stalling incidence,and variation of both profile and secondary loss withincidence. A further paper gives a method of stage-by-stage performance calculation using the detailedblade performance figures previously established,together with corrections for such variables as tipclearance, blade curvature and annulus flare. Withthe design rules given in these papers the efficiency of

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a conventional turbine can be predicted within about2 per cent which is within the usual limits of testaccuracy. •

The Sub-Committee has discussed these papers fullyand considers that they form a valuable addition to theinformation available to the turbine designer. Nodefinite rules are however provided for the effect ofboundary-layer thickness on secondary loss, and it isfelt that this gap in our knowledge could be filled bywork on blades in cascade, followed up by work inrotating rigs. Such work could be done by a Universityor the N.G.T.E., which has equipment ideally suitedto the problem, and the Sub-Committee has suggestedthat University research students might use N.G.T.E.rigs for this purpose.

Considerable gains are possible if turbine efficienciescan be improved but insistence by designers on lowweight and high work capacity makes this achievementdifficult. N.G.T.E. has put forward a method of pre-dicting performance of an axial-flow turbine (C.P.30).Research has been initiated to clear up the remainingdifferences between theory and experiment, in particu-lar, the high loss coefficients of certain turbine bladecascades, where the losses measured are greatly inexcess of those which would be predicted.

(b) Radial Turbines. Radial turbines have for sometime been considered for particular applications, andare in fact already in use in aircraft auxiliary powerunits. Their rotor form is robust and they appear tobe particularly suited to small-scale engine application,and both the Gas Turbine and Engine AerodynamicsSub-Committees have discussed a number of paperswhich together summarize most of the available per-formance data. Most of the tests have been carried outon centrifugal compressors of about 8 inches diameterrunning backwards, a condition which approximatesvery closely to the optimum design for a radial-flowturbine, and peak efficiencies of 85 to 86 per cent havebeen measured. This is slightly inferior to the 50 percent reaction axial turbine but is better than the lowreaction axial. An efficiency of 80 per cent has alsobeen claimed for a 4-inch diameter turbine. The torqueratio of the radial turbine is less than that of theaxial machine, and its operating range is narrower, thusmaking the matching problem rather more difficult, butthis latter problem is offset by the ease with whichvariable inlet nozzles can be incorporated.Mechanically, the maintenance of running seal clear-ances presents a considerable problem, and it is con-sidered that stress limitations will put an upper limiton power output of about 500 h.p. In general there is

a feeling that the chief merits of the radial turbine lienot so much in its promise of high efficiency, but insecondary advantages such as low runway speed andthe ease with which rotor cooling and adjustable nozzlescan be incorporated.

(c) Turbine Cooling. It has been accepted for sometime that cooling is advantageous for all types of tur-bine engine except possibly the unreheated subsonicturbojet, and it is generally agreed that the majoreffort should be concentrated on air cooling, althoughwork on liquid cooling should continue as this mightprove to be essential for high-supersonic flight andmight be usefully employed in the turbo-propellerengine and the high-temperature expendable engine.Interest has so far been centred on the turbine blades,research being directed towards the most efficient useof the cooling air supply. To this end work is neededon full-scale engine tests of blade cooling systems, ontests of complete blades on stationary and rotating rigsand on fundamental heat-transfer coefficients for thevarious systems.

The possibility of the use of high temperatures is ofcourse not the only asset of the cooled turbine. Anequally important advantage is the possibility of usinglow-alloy steels in place of expensive heat-resistantmaterials, the most promising arrangement of fabricatedblade being that formed by a central core with machinedgrooves in the surface and a thin sheetmetal sectionwelded to it. Mechanically, this construction is notentirely satisfactory but it is considered that strategic-ally the blade is good since only the outer skin needbe in oxidation resistant material. The most generalobjection to fabricated blades is that they frequentlymake use of brazing, a process which is as yet notentirely reliable, and for which a satisfactory non-destructive method of inspection has yet to be found.

Both the hollow fabricated and the solid blade withspanwise holes are cooled by the turbulent flow of airthrough passages in the body of the blade. With theeffusion-cooled blade, the position of the transitionfrom laminar to turbulent flow on the blade surface isparticularly important because of the considerableincrease in heat transfer in the turbulent region. Theeffusion flow required to maintain a uniform surfacetemperature is great near the leading edge, which isprobably the most difficult position at which to main-tain a high value of permeability. Experimental workon effusion cooling is in progress in this country at theN.G.T.E. and at the engine firms, and the results ofthis work are awaited with interest.

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IV. MECHANICS1. STRUCTURES

The comparatively slow straight-wing aircraft of thepast have been designed mainly on a static strengthbasis and the stiffnesses necessary for flutter preventionand control effectiveness have been provided at littleextra cost. Aircraft are now reaching speeds and flyingat altitudes where it is essential that the structure shouldbe designed with due consideration of speed and Machnumber as well as normal acceleration. In aircraft ofthe highest speeds with very thin wings, a main problemis to provide adequate stiffness for prevention of flutterand loss of control. Two other factors assume import-ance : one the problem of fatigue and the other thatof adequate strength to meet intense gusts which arerelatively more severe for high-speed aircraft because thechanges of velocity are passed through more quickly.

(a) Structural Fatigue. On account of gustiness inthe atmosphere aircraft are subjected to varying loadsin flight leading to fatigue of the structure. It is clearthat for certain types of aircraft, particularly civil trans-port aircraft, the matter is one which must be givenvery serious attention in design, but it is also one forwhich the necessary fundamental data are lacking. Thematter of gravest concern is that fatigue cracks mayspread undetected till catastrophic failure results. Inaddition there is abundant evidence of maintenancetroubles resulting from repeated loads : the cracking ofplating and the loosening and fretting of rivets arecommon examples. These defects add to the runningcost of aircraft and are of great concern to bothoperators and manufacturers.

At the beginning of the period under review we drewattention to this problem of repeated loading of aircraftstructures, and pointed out that research was needed intwo directions. First, accurate data were needed on themagnitudes and relative frequencies of occurrence ofapplied loads. The accumulation of the necessary datarequired the development of suitable instruments, suchas the counting strain gauge and the counting accelero-meter. It is now possible to record that a countingaccelerometer has been produced. Secondly, much moreinformation was needed on the way typical aircraftstructures, structural elements and materials behavedunder repeated loads. There was at this stage experi-mental evidence that for many types of loading, loadsgreater than about 50 per cent of the ultimate staticstrength occur very infrequently in normal service. Thispermitted the concentration of effort on obtaining dataon the magnitudes and frequencies of the lower loadsand on the life of structures tested in the laboratoryunder similar conditions.

In 1953 we drew the attention of the Ministry ofSupply to the fatigue of aircraft structures following thereceipt of a valuable report on this subject from ourStructure Sub-Committee. This report describes manyof the factors affecting fatigue strength, and also reviewsbriefly the present situation for civil aircraft. The

outstanding impression is that progress has been madeand a number of different aspects of the problem arenow being explored and experimental data accumulatedsteadily. Even so, the problem remains most serious,and research work needs to be energetically pursued.Since no adequate theory of fatigue has yet been pro-duced, the experimental work has an empirical basis.From the lengthy nature of the experiments required, itfollows that rapid accumulation of data cannot beexpected.

It is necessary to accept the principle that the structureof an aircraft wears out just as many other parts do.Subject to economic limitations, the first objective fora new design should be to provide a sufficiently longfatigue life solely by attention to the initial design.Knowledge already obtained by research and experi-ment should enable the life of new designs to be ex-tended appreciably beyond that now being achieved andat no additional cost in structure weight.

A scheme has been produced by the R.A.E. to assistin the prevention of fatigue accidents to civil aircraft,which may be envisaged as proceeding in three stages.At the first stage a safe short "life" is allotted ongeneral theoretical grounds and from past experienceof other aircraft types. This arrangement enablesfatigue testing of specimens to proceed while the air-craft is operating normally. The next stage producesa revised estimate based on, these laboratory tests andnormally gives an extension of life. This extensionmakes use of specific test data, but is related only togeneralized knowledge of gust effects. A third stagemakes use of gust measurements on the particular typeand may give a further extension of life. The averagelife of existing types of civil aircraft is assessed in thisscheme at roughly 10,000 hours (for standard Europeanconditions of operation), and it has been suggested thatfor new designs this should be increased to about 30,000hours by attention to ab initio design.

On this question of fatigue due to repeated loads, wehave been kept acquainted with the important investiga-tions that have been conducted at the R.A.E. during1954 in connection with the accidents to the deHavilland Comet I.

(b) Strength of Structures. Despite the almost uni-versal adoption of swept-back wings, there is still aserious lack of theoretical knowledge on the methodsof stress analysis applicable to real structures. Severaltheoretical treatments of this subject exist but eachhas its practical limitations and both experimental andtheoretical work are required for their elucidation. Theanalytical difficulties emphasize the importance of theexperimental approach and existing experimental re-search programmes should accordingly be extended asrapidly as possible. It is essential that the testspecimens used for this purpose should be built of thecorrect materials and to as large a scale as possible in

16

order to reproduce with adequate accuracy thecharacteristics of larger structures.

The aircraft designer has frequently to cope withthe problem of load diffusion in his structure. Possiblythe most common example is in the region of the under-carriage cut-out in a wing; other examples are aroundfuselage doors and any points of application of a con-centrated load, e.g., from a fin post. In the past theseproblems have been solved largely by ad hoc methodsand the value of each solution has been uncertain.With the development of new types of aircraft, structuralefficiency has become even more important than in thepast, and a better understanding of load diffusionproblems is essential. Theory has yet to be extended tocover the effects of the end loads produced in the ribbooms and the shear transmitted down the rib web,particularly as regards the rib at the edge of a cut-out.The end loads in the rib booms cause lateral bendingof the spar boom and give some relief to the sheet.These further developments of theory should give acloser estimation of the loads in the subsidiarystructure.

2. FLUTTER OF AIRCRAFTThe Society of British Aircraft Constructors, in a

letter to the Controller of Aircraft, has expressed con-cern at the number of flutter incidents affecting air-craft during their development stage. A recent reviewof the situation has shown that most prototype aero-planes have experienced flutter or allied vibrationtroubles. These troubles specially concern fast aero-planes and the control surfaces of aeroplanes in general.Early in 1952 the Mechanics Committee made a num-ber of detailed recommendations because action toremedy this situation was urgently needed. Since thattime additional effort has been directed to the prob-lem. There are three principal requirements :

(a) Increased knowledge of those aerodynamic derivativeswhich are essential data for calculations on flutter.

(&) Improved techniques and facilities for testing aeroplanes,both on the ground and in flight, in relation to theirsusceptibility to flutter.

(c) Greater effort on flutter calculation during the designstage, fully assisted by all helpful computing equipment.

The knowledge of derivatives, which is gravely lack-ing and most urgently required, is concerned especiallywith high-speed flight and with control surfaces. Suchknowledge can only be provided reliably by experi-ments in wind tunnels and the provision of wind-tunnel facilities, especially in high-speed tunnels, forthe measurement of derivatives is a matter of thegreatest importance and urgency. However, thetheoretical study of derivatives is also of great impor-tance and must be prosecuted with vigour.

It must not be overlooked that, if a truly irrever-sible control surface were available, flutter problemsinvolving controls would disappear and mass balancecould be dispensed with. The small amount of pro-

82697

gress that has been made in the application of irrever-sibility to manual or aerodynamic servo controls hasnot been due to a lack of suggestions for irreversiblesystems, but rather to certain features of the deviceswhich are undesirable from aspects other than flutter,and which appear to be inherent to the nature ofirreversibility. For instance, plain irreversibility of adirect control system is flatly contradictory to the pilot'srequirement for "feel".

An attraction of powered controls is that in prin-ciple they can be made irreversible, and irreversibilityhas already become a reality for a few large aircraft-fitted with this type of control. However, it must beemphasisized that the application of powered controlsdoes not necessarily eliminate the possibility of flutter.In practice the " irreversibility " may not be absolutebecause the unit is too remote from the control sur-face ; backlash and local flexibility at the connectionscan, in particular, be very significant. Furthermore,the actuator is itself a source of energy and mightexcite oscillatory responses from the control systemto which it is connected.

At the present time, an aircraft with power-operatedcontrols which are mass-balanced is given flutter clear-ance, provided tests show that the mass balancing iseffective and that the complete control installation isstable on the ground; in addition it must, however,pass a full flutter analysis. If the controls are notfully mass-balanced, then an investigation is made usinga method based on impedance matching; this involvesthe measurement of the impedance of the control systemand the carrying out of a normal type of flutter cal-culation. From the testimony of various specialistsit appears that the actuator unit may go wrong inways which are difficult to anticipate. The conclusionreached is that straightforward malfunctioning of theunit may be as great a hazard as flutter itself.

With this in mind, the Mechanics Committee hasendorsed the work the R.A.E. is doing on the develop-ment of power-operated control units: special atten-tion should be given to producing units which havea consistent performance. The Mechanics Committeehas also emphasized the importance of developingreliable techniques for the vibration testing on theground and in flight of aircraft fitted with poweredconrols.

New Forms of Flutter. The Mechanics Committeehas also recommended that some effort should be givento the study of possible new forms of flutter. In thepast, flutter incidents have opened up new fields ofresearch which, in their turn, have produced new know-ledge. The main argument is that workers in the flutterfield should, through their own efforts, have somewarning of possible new kinds of trouble and themeasures necessary for their prevention The outcomeof this work now recommended cannot be foretold ;there may be no result, but the effort is judged worthwhile and should include both theory and experiment.

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3. NOISEThe noise of aircraft is becoming a problem of con-

cern to all. The Council took notice of this matterin their Report in 1950 after the present position ofknowledge on the source of noise and its suppressionhad been reviewed by some of its Sub-Committees.

Two types of noise generation of increasing interestin modern aircraft are the noise produced by thepassage of the aircraft through the air, which maybe thought of as chiefly originating in the boundarylayer, and the noise produced by aerodynamic effectsin the jet stream of the engine.

With the boundary layer noise, preliminary workindicates that the rate of emission of energy increasesvery approximately as the sixth power of speed. Flightmeasurements have shown that in a large part of thecabin the noise originates almost entirely in the aero-dynamic turbulance of the boundary layer. Little isyet known of the fundamentals of this problem.

Jet Noise. The steady increase in power now beingdeveloped in jet engines is rapidly leading to theposition where the aircraft powered by such enginesmay prove to be too noisy to be operated from aero-dromes near populated areas. The biggest annoyanceis caused by the ground running-up of engines,especially at night, but the noise created during take-offand landing is almost as great a nuisance. Thedevelopment of external devices such as acousticscreens and portable ground muffs to alleviate the noisewhen running-up on the ground is proceeding andshould be encouraged, but a more fundamental solutionis required if the noise from aircraft in flight is to bereduced.

The overriding parameter of importance in noisereduction is the velocity of the jet. At jet speedsbelow about 1,000 ft. per second the aerodynamicnoise of the jet is unimportant compared with com-bustion noise and with noise generated by the com-pressor blading. At higher speeds, for a given turbu-lence level and size, the noise energy of the jetincreases approximately as the eighth power of thevelocity; with overchoked conditions a power as highas the twenty-ninth has been observed. The presenttrend of development of jet-engine design is thereforeproceeding at enormous cost in noise and it is ofprimary importance to reduce the jet velocity, evenat the expense of some weight penalty. For thisreason, the by-pass and ducted-fan types of engines arelikely to be considerably less noisy than conventionaljet engines. Measurements taken on the Conwayengines by Messrs. Rolls-Royce have, in fact, shownthat it is about 8 to 12 decibels quieter than the Avon.

There is a growing understanding of the mechanismof noise production in jets. The theoretical work ofProf. Lighthill, followed by experiments at theUniversity of Southampton and the College ofAeronautics, has produced results which form a solidbasis for further investigations on actual jet engines.Ad hoc noise suppression devices include notches and

teeth projecting into the jet and sleeves, diffusers andaugmenters covering the jet. Some of these deviceshave, in small-scale experiments, been found to reducenoise levels by up to 5 decibels in subsonic jets andby up to 20 decibels in supersonic jets. Some con-firmation of the results of these model tests has alreadycome from full-scale work by the engine firms.

The subject of noise reduction is so important andthe field for research so wide that encouragement shouldbe given to all efforts directed to a better understandingof the, problem and offering possible solutions.

4. MATERIALS(a) Transparent Materials. Considerable difficulties

are being experienced with windscreens and canopiesand these are likely to get worse as the operationalconditions at higher speeds and greater heights becomemore severe. Much trouble has been encountered dueto misting and frosting after rapid descent from aprolonged high-altitude flight. In addition, consider-able trouble has been experienced due to a structuralfailure of fighter canopies and failure of the jettisoningmechanism.

It is expected that existing transparent materials willbe inadequate to withstand the high temperaturesreached in flight at the very high speeds which newaircraft are likely to achieve. Furthermore, at thesevery high speeds the shape of the canopy will becomeaerodynamically critical and the whole problem ofvision will have to be treated in a somewhat differentmanner. It is expected that considerable difficulty willbe expecienced in giving an adequate field of view tothe pilot of a supersonic fighter even by an orthodoxcanopy. Moreover, its drag may represent a very largeproportion of the total aircraft drag and may thusbe a critical factor in the design of such an aircraft.An investigation is needed into the fundamentals ofpilot's view, covering the use of indirect vision, theeffect of shock waves on the accuracy of vision, andmany physiological problems.

The use of transparent canopies for the cockpitraises special problems. It has been abundantly shownby experience at the increased altitude to which post-war aircraft can reach that all known transparentmaterials are so unsatisfactory as to be actuallydangerous. The mechanical properties of glass andglass substitutes are far from ideal for the windowsand cockpit hoods of present-day aircraft. Glass isheavy and its strength often unreliable. "Perspex",the most generally used substitute, has strength andelastic properties that vary rapidly with temperature,a large coefficient of expansion, low notch sensitivity,and crazes if exposed to a solvent vapour while undertension. These difficulties are overcome at present bydesign ingenuity in using and mounting the transparentpanels. Even so, .the replacement rate of "Perspex"windows is embarrassingly high, and the replacement ofdefective canopies in war time would be a serious

18

drain upon industrial and transport facilities. The needfor improving transparencies is, therefore, a problemof immediate importance for aircraft now in use. Butits importance is greatly increased for aircraft of thefuture. The speeds and heights at which aircraft arenow being designed to fly make more exacting theconditions which hoods and windows have to meet, andstill further impair the strength properties of existingplastic materials.

(b) Light Alloys. In addition to the above mattersaffecting transparencies there is also a problem affectinglight alloys. Work on the shatter of high-strengthlight alloys is going ahead well on a co-operative basisbetween firms, the R.A.E. and the Inter-Service Metal-lurgical Research Council. The tests include the effectsof ball and high-explosive ammunition on stressed andunstressed plate at normal and low temperatures.Under certain conditions the material shows a markedtendency to shatter or split and tests are in hand toinvestigate the influence on this of varying the chemicalcomposition of the material within the specificationlimits. The danger of shattering may possibly beavoided by reducing the alloy content without neces-sarily reducing the mechanical properties below thoseof the current specifications, but the present evidencein this sense is meagre. The tests also include theeffects of different heat treatments and varying degreesof cold working. Similar trials have been made onpanels of sandwich construction where the extent ofthe damage is greatest for those panels in whichadhesion between the skin and the filling is low.

(c) Temperature Effects on Materials. It is becomingincreasingly important to know how variations intemperature affect the strength of aircraft structures.The introduction of thermal methods of de-icing theflying surfaces and the use of gas-turbine engine installa-tions in which the jet pipe passes through a cut-out inthe wing spar are examples of design trends whichexpose major structural components to temperatures of150°C or above. On the other hand, at the very greatoperating heights for which they are being designed,many new aircraft will be exposed to temperaturesmuch lower than has hitherto been considered in design.

The behaviour of materials and structures at lowtemperatures is also important. It is significant thatcertain ferritic alloys most affected by low temperatureshave the same crystal structure; a close watch shouldtherefore be kept on the development of new alloyswith the same structure. It appears that notch effectsare very important at low temperatures and good detaildesign may offset some of the bad effects of suchtemperatures.,

The Council has recommended that, in view of theserious effect of high temperature on the strength oflight alloys, available data on the temperatures reachedby parts of the aircraft structure exposed to great heatshould be collected and published.

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5. AERODYNAMIC HEATING IN HIGH SPEEDFLIGHT

High thermal stresses can arise in aircraft structuresdue to the rapid changes of temperature in flight. Twomain conditions have to be considered. One is thatof the unpiloted aircraft or missile with a flight dura-tion in which steady conditions of temperature are neverreached, so that thermal stresses in the structure mayarise due to the temperature gradient in the materials ;the other condition is that of the piloted aircraft witha relatively long flight duration in which steadytemperature conditions are attained, and where the mainproblem will be that of obtaining materials which canfunction satisfactorily at as high a temperature aspossible.

Between these two main conditions is the pilotedaircraft with high acceleration rates accounting forboundary layer temperature increases of the order of20 °C per minute. Estimates of stabilised temperaturesare reasonably accurate for long flights where thetemperature has had time to become steady. For un-steady conditions, however, it has not so far beenpossible to check the estimated values owing to thedifficulty of doing full-scale tests.

The R.A.E. is setting up a laboratory and theoreticalsection to investigate the effects of transient temperaturegradients (thermal shock). The first indication is thatthere might be a strong case for the use of insulationcombined with refrigeration. A small thickness (e.g.| in.) of insulation has a very great effect in relievingtemperature gradients due to accelerated flight. Forflight at steady speeds of relatively short duration, how-ever, an appreciable thickness (e.g. 1 in.), is needed toslow down the flow of heat and the temperature rise.But it is clear that eventually refrigeration will beneeded, because if the structure is allowed to get hot,the situation will be intolerable; at M = 1-5 theproblem is not too difficult, at M = 2-0 it is difficult,but at M = 3-0 something drastic will need to be done.

6. VULNERABILITY AND ESCAPEThere is a variety of other problems associated with

structures. Some of these are vulnerability of aircraftand damage to the structure by fire, and these have beensubject to experimental research. Structural problemsof guided weapons have been discussed in relation tothe work of the Guided Weapons Advisory Board,since the problems differ appreciably from thoserelevant to aircraft.

Another problem is that of escape from aircraft andsome progress has been made in devising means forincreasing the safety of crew who wish to escape athigh speeds and at great heights but much remains tobe done. Parachute problems have also been beforea committee of the Council, in view of the variety oftheir uses, including:

(1) For escape in an emergency or in troop dropping.(2) For supply dropping.

B 3

(3) For stabilising objects dropped from aircraft.(4) For anti-spin and landing devices.(5) In the guided weapon field, for the recovery of expensive

test missiles.

7. COMPUTATIONThe Council appointed a Computation Panel (now

a Sub-Committee) in 1952 to consider the problems ofmechanical aids in the form of digital and analoguemachines to assist in the solution of complicatedproblems. A great deal has already been done bothin Government Establishments and in aircraft firms toimprove existing methods and provide better digitaland analogue machines to aid in the solution of themany complicated arithmetical problems that needsolution. It is increasingly appreciated that numericalanalysis is a very powerful and indeed necessary aidto the aircraft designer.

Great assistance to the Aircraft Industry has alreadybeen provided by the large digital computing machines,such as the ACE at the National Physical Laboratoryand it is expected that the new AMOS machine atFort Halstead will also render good service.

The main fields in which analogue machines areuseful is judged to be those in which exploratory workhas to be done. Analogue machines are suitable forflutter investigations and some machines have alreadybeen developed and used for this purpose, includingthe R.A.E. flutter simulator, which was the first ofthis type to be constructed. In general, digital andanalogue machines are considered to be complementaryto each other in their applications in the field of aero-nautical science and engineering; for example, ananalogue machine can often be used to make a pre-liminary survey of the whole field so that the problemcan be narrowed down to a form suitable for solutionby a digital machine.

V. MISCELLANEOUS1. CIVIL AIRCRAFT

The Civil Aircraft Research Committee has recentlyreviewed the research needed in connection with thedesign of future civil aircraft, that is to say, the genera-tion which will succeed the Comet and its contem-poraries. The Committee has also discussed topicsbearing on the more strictly operational aspects of civilaviation including safety, air traffic control, meteorologicalforecasting and human factors, as well as such othersubjects as gusts, helicopters and noise which are dis-cussed elsewhere in this review.

(a) Approach and Landing. The increases of per-formance of civil aircraft in terms of cruising speedand range have been achieved largely at the expenseof the low-speed end of the range. Operators haveconstantly stressed the need for higher lift coefficientsto reduce landing speeds and give greater manoeuvra-bility in the approach. The air traffic control problemat busy airports would be eased by a reduction in thepresent variation in approach speeds which are oftendictated by the characteristics of the aeroplane. Lowerapproach and landing speeds and improved aircrafthandling characteristics would reduce the number ofoccasions when diversion was necessary from the air-port of intended landing because of bad weather.Strong support is therefore given for work on leading-edge suction and other devices designed to improvethe low-speed and landing characteristics of the air-craft. In order that designers may appreciate thecontrol and handling qualities that should be built intoaircraft to ensure a high degree of approach and land-ing success, the Civil Aircraft Research Committee hasrecommended that a theoretical and experimental studyshould'be undertaken to determine standards for thehandling and control characteristics necessary for suc-

cessful approach and landing, especially in bad weatherconditions.

(b) Landing Aids. During the period under reviewthe Civil Aircraft Research Committee has taken agreat interest in landing aids ; in particular they haveencouraged the Calvert approach lighting systemdeveloped first at the R.A.E., and later adopted byICAO.

The Committee has twice visited the Armament andInstrument Experimental Unit (A.I.E.U.) which wasformerly known as the Blind Landing ExperimentalUnit, and having discussed its work and programme ofresearch, is of the opinion that considerable time andeffort will be necessary before fully automatic methodsof landing can be introduced into civil aviation. Buta very useful first step would be to find out how toget the most out of the existing system whereby theaircraft is fed accurately and automatically into andalong the line of approach and in such an attitudethat, by the aid of the lighting system, a visual landingcan be made manually.

In view of the contribution that FIDO is capableof making to successful landing in difficult conditionsof visibility, the Committee has recommended that anexperimental installation should be made for tests ofrecent developments in this method of fog dispersal.

(c) Air Traffic Control. On several occasions duringthe past few years discussions have taken place on AirTraffic Control. In order to gain first hand knowledgeof some of the problems the Committee has visitedthe Air Traffic Control Centre at Uxbridge which con-trols aircraft flying in the London Control Zone, andhas watched the procedures that are in use at LondonAirport. There has been a considerable increase in

the volume of air traffic and a significant change inits composition caused through the introduction ofgas turbine aircraft.

The U.K. airways system of agreed traffic lanes cover-ing the most important routes has been a big stepforward towards the desired goal of a completely co-ordinated system, and the continuing work of a high-level Inter-departmental Committee, advised by aDevelopment Staff, was welcomed by the Committee inthe hope that further progress would be made in thedevelopment and production of a fully integrated AirTraffic Control (A.T.C.) plan for the U.K. and pos-sibly overseas. Trials were also recommended toassess the extent of any special procedures necessaryto deal with the mixing of turbo-jet, turbo-prop andpiston-engined aircraft, especially in the Airport Ter-minal Area. These trials were made and have con-tributed to the successful methods at present in use.

Other aspects of A.T.C. that have been consideredhave included the radio navigation aids to be used,and the contribution to safety and to expediting theflow of traffic that radar can offer. Great importanceis attached to the development of suitable radar equip-ments and to the techniques of displaying and applyinginformation derived from such equipment.

(d) Engines for Civil Aircraft. It has often beenargued that civil aircraft should have engines speciallydesigned for civil use rather than engines primarilydesigned for military aircraft, and this argument islikely to carry more weight in the future. What formof engine will be best suited for airliners on differentroutes is, however, a question still under discussion.For the longer routes, the by-pass type of engine givesadvantages in decreased fuel consumption and thedevelopment of this type of engine may lead to powerplants with a lower noise level than the pure jet.

The possibility of using titanium in civil engines isone which offers a prospect of considerable economicgains. It has been estimated that, on an Avon engine,a total saving in installed engine weight of about 600 Ibper engine might ultimately be achieved by this means.The Committee has recommended that adequate sup-plies of titanium should be made available so thatthe best methods of fabrication can be determined.

(e) Meteorological Forecasting. The MeteorologicalOffice has made good progress with the evaluation andforecasting of winds and temperatures at high altitudes,a matter for which the Committee pressed some yearsago. Observations of wind at the 200 mb. level are,however, sparse compared with observations of theother meteorological elements. Over the Atlantic, theeffect on weather forecasting of a proposed withdrawalof the Ocean Station Vessels was carefully consideredand strong recommendations were made to the appro-priate authorities that the Atlantic Weather Ship net-work should be retained. The Committee were gladto learn that this' had been done.

The airline operator finds a most serious deficiencyin the accurate forecasting of the terminal conditions.

8269721

To reduce fuel reserves he must be certain that theterminal will be open when the aircraft arrives. TheCivil Aircraft Research Committee has emphasized thecurrent difficulties and uneconomic consequences ofoperating in bad terminal conditions. Particularelements of the general problem are being consideredbut the Committee are not satisfied that these separateefforts are sufficient or adequately co-ordinated, northat aircraft designers are paying enough attention tothe need to reduce approach and landing speeds and toimproving handling characteristics at these approachconditions. It is the Committee's considered view thatthe whole problem of civil aircraft in the terminalarea and of their safe, regular and successfulapproach and landing should be studied, both intheory and in practice, by a single team of workers.Following a recommendation along these lines, aWorking Party has been set up to study the problem.

(f) Human Factors. Particular attention has beenpaid to the problems of the efficiency of pilots andAir Traffic Control operators. Experiments have beenconducted on the ability of human beings to listen totwo messages simultaneously, on simultaneous visualand aural perception, and on the question of the rightloading of a human being to produce efficiency.Progress has also been reported towards an internationallanguage for civil aviation.

2. NAVAL AIRCRAFTDuring the period under review the Naval Aircraft

Research Committee has fostered two importantdevelopments in aircraft carriers; one, a flexible deckupon which aircraft can land without an under carriageand the second the so-called " angled deck". Theincentive for the former arose from the improved per-formance, the smaller weight and less complication inconstruction if an aircraft was designed without anundercarriage. Means were therefore sought for land-ing such an aircraft on the suitably strengthenedundersurface of its fuselage. The idea was firstdeveloped by model and then by full-scale experimentsat the R.A.E., to be followed by the fitting of a trialdeck to H.M.S. Warrior; with the aid of this deck andan arrester gear, undercarriageless aircraft made manysuccessful landings on the carrier.

The angled deck was originally proposed and theidea tried experimentally on a British carrier to seewhether it worked. It was first fitted for operationaluse on the American ship U.S.S. Antietam, and lateron H.M.S. Albion. On these ships aircraft land on apath inclined to the axis of the carrier. This does awaywith the need for a barrier to prevent the landing air-craft from overrunning into aircraft parked on theforward part of the deck, and allows pilots to landfurther up the deck or to take off again immediately ifthe pilots so wish. Other carriers are being similarlyfitted with angled decks. Associated with the angleddeck is the development of a mirror sight which enablespilots to approach and land along a predetermined

B 4

path without the aid of a batsman; this aid is becom-ing necessary because the increasing speeds of approachare too fast for the successful co-operation of batsmanand pilot.

Ship Motion. A valuable paper has been preparedby the Director of Naval Construction on ship motionat the request of and for the information of the NavalAircraft Research Committee. It gives a very com-plete analysis of the motion of an aircraft carrier undera great variety of conditions of waves and wind. Thepaper has drawn attention to a number of interestingpoints: a close relationship exists between the periodof pitch of a ship and the period of encounter of theship with the waves ; the null point of the flight deckis about two-thirds from the bow when the sea is deadahead; the loss of speed in waves is an importantfactor for a carrier and the longer the ship the lessis this effect.

From an operational point of view, the maximumwave height has been defined in the above paper as onewhich just broke over the bow and an interval can bechosen between maximum waves when it is possible tocatapult an aircraft between them. It is much easierto judge the correct moment to launch an aircraft thanto judge the cut point at the right moment whenlanding on. An aircraft can in fact be catapultedfrom a ship when it could not be expected to land safelyon the deck.

To further our knowledge of the subject, a numberof experiments have been made on H.M.S. Implacableto measure the ship motion and it is proposed to carryout additional experiments to study the effects on theaircraft of the motion of the ship. What are neededare some rough-water trials, but the desired conditionsare not necessarily to be found during a given cruise.

A paper on the above subject has been read byMr. J. L. Harriett to the Institution of Naval Architects.

3. HELICOPTERSWe drew the attention of the Minister of Supply

in 1952 to the need for pressing on with helicopterresearch since this type of aircraft is able to undertakecertain duties which other faster aircraft cannot. Thesteadily increasing importance of the helicopter fromboth the military and the civil points of view and thegreater number now flying in this country, has calledfor an increase in the effort allocated to helicopterresearch to meet the needs of the aircraft designer.We have therefore pressed during the past three yearsfor an increase in the amount of effort which has nowbeen allotted by the Ministry.

Special attention has been drawn to the followingitems in the helicopter research programme as beingof first urgency :

(a) Automatic stabilization (including maintenance of fixedposition during hovering),

(b) Flight experiments on blind flying and navigation,

(c) Wind-tunnel experiments on rotor and wing combina-tions,

(d) Vibration experiments on ground resonance effects.The above items are only a part of the research

effort, which should be increased over the whole field.

4. SEAPLANESDuring the last five years there has been a great

change in the design of flying-boat hulls. As a resultof tank research and full-scale experiments, mainly inthe U.S.A., the advantages of hulls of much smallerfineness ratio than was adopted in the past havebecome apparent. The fineness ratio, which may bedefined as the ratio of hull length to beam, was about5 : 1 for the very successful series of flying boatsdesigned in this country between the two wars. Thisratio was increased to 7 :1 for the Saunders-RoePrincess. Much higher values, possibly as high as15 : 1 might very well be adopted in a future design.

The result of this revolutionary change is to placeparticular emphasis on research, both on tank modelsand large flying models, which are necessary to investi-gate water behaviour. In the past the large experienceof previous hulls, all of similar shape, or at any ratemodified only in details, was adequate to ensure asuccessful design. The main difficulty was in theincrease in scale as flying boats became larger andlarger. Today, the design of a large flying boat wouldintroduce a number of new problems in water perform-ance and handling, and would need a considerablebackground of knowledge, built up on model research,if it is to be a success.

Valuable work on the new hull shapes has been doneby a small staff at M.A.E.E. during the period underreview and a large number of reports on tank testshave been published. The research work has beenhandicapped by the absence of a flying model, onwhich alone experiments on water behaviour can bemade. Attempts to obtain such a model have un-fortunately not been successful.

Another important new development is the use ofwater skis for landing aircraft both on water and onrafts. Such aircraft would generally be launched bycatapult. Here again most of the work has beendone in the U.S.A., but one firm in this country,Messrs. Saunders-Roe, has done some important workin their tank.

5. GUSTSDuring the period under review, the Council

appointed a Gust Research Committee to considerwhat could best be done to accumulate information onthe gusts that occur in the atmosphere. This Com-mittee reports to the Aerodynamics Committee of theCouncil and also to the Meteorological ResearchCommittee.

Gust Records. Experiments on the determinationof atmospheric gusts have been continuing with some

22

interruptions for a great number of years. A greatdeal is now known of their frequency and magnitudeat the lower heights but more data needs to be collectedfor heights above 30,000 ft. The use of V-g recordersin aircraft to measure simultaneously the speed andacceleration of the aircraft has given results whichhave covered reasonably well heights up to abeut15,000 ft. and this has been supplemented by informa-tion from recording accelerometers and other instru-ments. However, aircraft are now being producedwhich will operate in the future at heights of 40,000ft. and higher and as they are designed to utilisematerials of greater ultimate strength at high unitpressures structural fatigue will require closer atten-tion than in the past. There is a need to emphasizethe investigations of those gusts which can occur with-out warning in clear air. Other severe gusts met incumulus or cumulo-nimbus clouds can usually beavoided by the experienced pilot and in any case willnot be unexpected. A little information has beenobtained at high altitudes but there does not appear tobe either staff or facilities available to obtain informa-tion on gusts up to, say, 55,000 ft. within a reasonabletime.

Records for many thousands of hours have beenobtained at relatively low altitudes on five types ofaircraft at medium altitudes from 10,000 ft. to 16,000ft. No startling differences between the results fromfive types of aircraft were found. The main purposewas to check the adequacy of the present gust designspecifications, and these are broadly confirmed.

The larger gusts were observed at the slower speedsand the reason for this was that the pilots slowed downwhen they encountered turbulence; in fact, for manyyears it has been a practice to reduce speed greatlyon entering thundery weather. There is, however, aminimum speed now known as the " safe speed"below which it is dangerous to fly because the aircraftis liable to stall on meeting a large gust. The safespeed has been deduced from the results of theAmerican Thunderstorm Project.

The Airworthiness Authority in this country basesits strength requirements on the accelerations which itexpects aircraft will meet in flight. The estimatedfigures supported in .the main by results given by theN.A.C.A. V-g recorder have given aircraft of adequatestrength since they rarely fail in flight, but there remainsa need to obtain additional information applicable tofatigue problems. This is being collected by two typesof counting accelerometer: the mechanical typecounts the number of times a certain acceleration isexceeded, and the electrical gives a virtually con-tinuous curve. Work on the collection of this informa-tion continues, but the emphasis is now laid on recordsfrom flights at greater altitudes, say, above 30,000 ft.

Interpretation of Accelerometer Records. The con-cept of an " Equivalent sharp-edged gust" is used inthe interpretation of accelerometer records obtainedfrom one type of aircraft so that results may be applied

82697

to other types. In this it is assumed that the verticalgust velocity increases from zero to U ft./sec. in a dis-tance of 100 ft. and then remains constant at U ft./sec.(the flat-topped gust). The equivalent sharp-edged gustis then obtained by multiplying U by an alleviationfactor K. At present K is assumed to depend solelyon the wing loading of the aircraft. The accelerationimparted to an aircraft by such a gust is then propor-tional to KUV and other simple parameters of theaircraft size and weight, where V is the forward speedof the aircraft. The alleviation factor K is intendedto allow for the relieving action of the aircraft'sresponse to the gust, and for the fact that lift changesdo not follow air flow changes instantaneously but takea finite time to grow.

Two papers communicated by the Ministry of Supplyhave drawn attention to the inadequacy of the presentmethod of deriving results from accelerometer recordsmade on particular types of aircraft for use in thedesign of new aircraft or in application to other types.The alleviation factor, it is shown, really depends onthree parameters: the mass parameter, the gust shapemeasured relative to the aircraft's size, and the wingaspect ratio. The mass parameter takes into accountwing loading, altitude of flight, and size of aircraft.Gusts are of many shapes and sizes, but a single flat-topped gust gives the largest acceleration to an aircraftand therefore this concept may usefully be retained.

The Committee has therefore recommended that thealleviation factors now in use for calculating gust speedsfor design purposes should be superseded by valuesassuming that the shape of the gust is flat-topped. Useof these new values of alleviation factor will resultin a given acceleration to a modern aircraft at highaltitude (say, above 40,000 ft.) being associated witha calculated gust velocity, which is considerably highernumerically than the gust velocity calculated from thepresent formula in A.P. 970. The Committee con-siders, however, that there is no reason to suspect thatthe present maximum gust speeds used for designpurposes are too small at high altitude when translatedinto acceleration of the aircraft. If the new formulafor gust speed is used the design gust speeds will haveto be altered so that there is no change in the associateddesign acceleration.

A third paper communicated by the Ministry ofSupply, which will be published, extends to swept-backwings the theory of gusts as developed for straightwings. For an aircraft with high wing loading andsmall aspect ratio the overall effect of wing sweep ongust loads is small. The Committee has recommendedthat the methods described in this paper should beused for the estimation of gust loads on swept-wingaircraft.

Thunderstorms. The most severe gusts are found incumulus and cumulo-nimbus clouds. The relationbetween the radar echos from cumulus and cumulo-nimbus clouds and the turbulence within those cloudsis dealt with in a Meteorological Office Paper. The

23B 5

turbulence encountered in flying through a cumulo-nimbus cloud is shown to be associated with the exis-tence within the cloud of neighbouring up and downcurrents of comparable magnitude. Measurements ofthe speed and extent of these vertical currents havebeen reported. These currents, sometimes calleddraughts, may have speeds exceeding 50 ft./sec. andare of the order of three-quarters of a mile acrossthus having dimensions many times greater than thoseof the gusts which cause bumps to aircraft. Up anddown draughts of comparable speed are often in closeproximity, being separated by a turbulent zone of theorder of 300 yards across in which large up and downgusts occur. Existence of these turbulent zones canbe inferred from the radar echo as seen in a verticalcross section. Turbulence was usually found near theedges of the vertical currents which are associated withthe edges of the radar echoes as seen in vertical crosssection. Accelerations of 0 • 5 g. or greater were foundonly in those portions of the cloud which gave an echoon a ground radar. The greatest acceleration expe-rienced in these trials which were carried out by theRoyal Aircraft Establishment and the MeteorologicalOffice jointly, was 1 -5 g. corresponding to an equivalentgust velocity of 54 ft./sec.

It is probable that in an active cloud the greatestturbulence is likely to be encountered within the echobut if this turbulence is severe there may be some sub-stantial gusts in that part of a cloud which fails to givean echo. From the point of view of flying aircraft itis important to know at what distance from a cloudsevere turbulence will not be found. As the worstturbulence may be on the edge of the radar echo it islikely that severe turbulence may occasionally be foundsome distance outside the echo and occasionally up tothree miles distant from it; it is therefore preferableto avoid the neighbourhood of cumulo-nimbus clouds.A case has been reported of a pilot being guidedthrough the holes between the clouds with apparatusused by an observer: this apparatus has now passedthe development stage and will shortly be put onvarious aircraft.

Avoidance of Gusts. A final report of the trialsof an improved cloud and collision warning radar hasbeen received from the Air Ministry. Cumulo-nimbusclouds in Malaya were detected up to 40 miles and, inall, some 110 cloud penetrations were made. A lot ofvaluable data was accumulated and the maximummeasured acceleration of 1 g. corresponded with agust velocity of about 50 ft. per second.

In response to an enquiry as to how useful radarcan be in the avoidance of gusts the Gust ResearchCommittee has replied that the incidence of severeturbulence and icing conditions in flight can be sub-stantially reduced by the proper use of airborne radar,which is better than the eye for detecting the moreturbulent types of cloud. This is substantiated by aconclusion from some Singapore trials regarding tur-bulence associated with convective cloud that prac-

tically all turbulent areas can be avoided if the radarresponse areas are passed at a distance of about onemile.

Convective Storm. The Committee has discussed thetype of convective storm which occurs in Bengal inspring and early summer (the Bengal Nor-Wester) andalso in other parts of the world notably West Africa.These storms derive part of their energy from thefalling of masses of air previously very dry but cooledrelative to their environment by the evaporation ofrain; most other convective storms derive their energyfrom the rising of bubbles of air warmer than theirenvironment. These Bengal and West African stormsare well known to aviators as being exceptionallyturbulent; they would show up on a radar scope.

In an analysis by the Meteorological Office of alarge number of cases of severe turbulence above20,000 ft., a high percentage were associated with jetstreams which are comparatively narrow bands of highvelocity winds in the upper troposphere and lowerstratosphere. Most of the observations of turbulencelay on the low pressure side of the jet stream. Severeturbulence over the British Isles is usually at heightsnot greater than 35,000 ft. but more recently informa-tion has been received about severe turbulence over thiscountry at the unusually great height of 54,000 ft.; inthe tropics turbulence has several times been observedat 45,000 ft. Some of these results have been publishedin the Meteorological Magazine.

In 1951 the Gust Research Committee asked theRoyal Air Force and the Royal Aircraft Establishmentto arrange high-altitude flights to explore specialweather features for turbulence. The results of thesespecial flights over a period of 18 months confirmprevious tentative conclusions regarding the associationof turbulence with particular weather features, the mostimportant being that with jet streams (see above).

The Committee was satisfied with these conclusionsand suggested that further analyses of observations ofturbulence in a search for associations with variousweather types would be unprofitable except for alti-tudes of 45.000 ft. or above. The Committee recom-mended that further flights to investigate the regionabove 45.000 ft. for gusts were unnecessary as it con-sidered that observations would probably accumulatefrom flights for other purposes. The Committee hasexpressed its thanks and appreciation for the resultsachieved by the R.A.F. and R.A.E. in these specialflights.

A further paper submitted by the MeteorologicalOffice (15,785) has described measurements of turbu-lence in the high atmosphere (up to 100,000 ft.) derivedfrom the behaviour of radiosonde balloons. The methodso far used could only detect eddies of sizes greaterthan about 1,000 ft. in depth. New equipment will soonbe in use which will permit measurements of eddies ofsmaller sizes and comparable with some of the eddieswhich cause bumps to aircraft.

24

6. COMMONWEALTH ADVISORY AERO-NAUTICAL RESEARCH COUNCIL

The Ministry of Supply has submitted to the Aero-nautical Research Council for its opinion the Reportsof the Second and Third Meetings of the Common-wealth Advisory Aeronautical Research Council, andthe A.R.C. has recommended that the Reports shouldbe accepted by the United Kingdom as a membercountry of the Commonwealth Council. The Chairmanand some members of the A.R.C. represented theUnited Kingdom either as delegates or non-membersattending at both the Second Meeting in Canada in1950 and the Third Meeting in London in 1953. Thoseof us who attended these meetings welcomed andenjoyed the opportunities it gave for free discussionswith the delegates from the participating countrieswithin the Commonwealth ; we appreciated both therange and depth of these discussions.

The Commonwealth Council has a scheme wherebyco-ordinators are nominated by each member countryin a number of subjects. Reports of each co-ordinatorare sent to a chief co-ordinator in a selected countrywho reports yearly on the whole subject to a CentralSecretariat and to the Council before each of itsmeetings. The A.R.C. has strongly endorsed the recom-mendation that the Co-ordination Scheme started in1948 after the First Meeting in Australia should becontinued and extended, and that the responsibleauthorities in each country should provide opportunitiesfor meetings between members of each co-ordinatingteam. The Council are glad to learn that arrangementsare made for such meetings.

The A.R.C. enthusiastically supported a recom-mendation from the Second Meeting that visits and inter-changes of staff between member countries should beencouraged as much as possible and are glad to statethat a good deal of co-operation has been possible inthis respect between Canada, Australia and the UnitedKingdom.

One recommendation made at the Canadian meetingwas for the continuation of flight research into boun-dary layer control in Australia. This flight researchinitiated at an earlier meeting and carried out inAustralia was on a thick suction wing and led to adeeper understanding of boundary layer control andto the solution of -many engineering problems, asso-ciated with the application of suction to practical air-craft. Reference is also made in the report of thatmeeting to flight work on distributed suction on a con-ventional aerofoil fitted with a porous surface testedat low Reynolds numbers at Cambridge University.The results of these investigations indicated that largereductions in the drag of conventional aerofoils canbe obtained if the practical difficulties of installationand maintenance can be overcome and these investiga-tions have been the beginning of a large developmentof research into boundary layer control both for dragdecrease and for lift increase, the latter being alsomentioned as a promising application at the Canadianmeeting.

The Aeronautical Research Council appreciates thework that has been and is being done in Canada onthe investigations on low temperature operation andon the protection against icing of airframes and engineswhich was the subject of the ninth recommendationin the Second Report.

Special attention is here drawn to three other matterscontained in the Report of the Third Meeting. Thefirst is the need felt by the Commonwealth Council fora closer co-ordination of researches concerning newmaterials, particularly outside this country. We havedrawn the attention of the I.S.M.R.C. to this matter andhave asked them to inform the other participatingcountries of what has been done to meet this needin the United Kingdom. The next subject relates tothe human factors that are becoming of increasing im-portance in aeronautical engineering. We agree withthe Commonwealth Council that the importance ofthe study of these human factors should be furtherstressed and that there should be closer co-operationbetween physiologists, psychologists and engineersdirected towards the problems of conditioning aircraftto human occupation and control; we have madecertain alterations to the membership of some of ourown committees with a view to advancing this matterin our own work. The third subject is that of flightresearch, where we have endorsed the first recommenda-tion of the Council's Report: " That it is of great im-portance for the progress of aeronautical science thatsuitable aircraft should be made available for flightresearch in all the member countries where suchresearch can be undertaken and, with this end in view,aircraft might be lent by the United Kingdom ".

We have noted from the Report of the Third Meetingthe valuable contributions to aeronautical research thatare being made by Canada and Australia, and hopeand expect that in the near future New Zealand, SouthAfrica and India will gradually be able to add con-tributions of their own.

This last Report makes special reference to therecommendations of the Documentation Committee ofAGARD of NATO. This Committee has recommendedthat aeronautical documents should conform to an inter-national standard size (A.4) which is wider than foolscapand a good deal shorter. The stowage of internationalpapers would be greatly facilitated by adopting thisstandard size, but a large amount of equipment wouldneed to be altered if the standard size were adopted foraeronautical work in this country. We, as a Council,have expressed our general agreement with the proposedchange if it be found practicable by the Ministry ofSupply and H.M. Stationery Office.

7. PUBLICATIONThe Council has reviewed its methods of publication

of scientific papers. The number of papers issued inits original Reports and Memoranda Series has beenreduced and is now restricted to papers of lasting valuerecording a definite advance or containing some

25

novelty. The decision to include a paper in this Seriesdepends on its probable utility in five years' time.Papers of more current interest but not regarded asreaching an inferior standard are now published in asecond series of papers called " Current Papers ", thefirst of which was put on sale by H.M. StationeryOffice on 19th May, 1950. Current Papers are type-script documents of foolscap size with a distinctivegreen cover bearing the title, author's name and serialnumber; by the end of 1954 nearly 200 had beenissued in this Series of publications. They will notbe collected together and issued in annual technicalvolumes like the Reports and Memoranda Series. Inthe main, the contents of a Current Paper areidentical with that originally discussed by a committeeof the Council plus an attached Addendum andCorrigendum sheet. A list of the serial numbers ofboth R. & M.s and Current Papers published duringthe period under review is given in Appendix V.

The Oxford University Press has published, duringthe past two years, four volumes, for which the FluidMotion Sub-Committee of the Council has been respon-sible. Two volumes entitled " High Speed Flow"

edited by Prof. L. Howarth and published in 1953provide a sequel to Modern Developments in FluidDynamics edited by Prof. S. Goldstein and publishedin 1948.

The Compressible Flow Tables Panel, under theChairmanship of Prof. L. Rosenhead, has been respon-sible for " A Selection of Tables for use in calculationsof Compressible Airflow" which were published inNovember, 1952. A companion book of Graphs waspublished in September, 1954.

The Fluid Motion Sub-Committee are also arrangingfor a great deal of the matter in the original Goldsteinvolumes to be brought up to date. They will also bepublished by the Clarendon Press.

Mr. W. G. A. PerringThe Council wish to record the very serious loss to

aeronautical science by the death of Mr. W. G. A.Perring, the Director of the R.A.E. He not only madevaluable contributions himself, but was a constantsource of inspiration to the staff who worked withand under him at the R.A.E. Mr. Perring was likewisea great source of strength to the Council.

GLOSSARY OF ABBREVIATIONS

A.G.A.R.D. .. .. .. .. .. .. .. Advisory Group for Aeronautical Research and Development.A.I.E.U. .. .. . • • • • • • • • • • • Armament and Instrument Experimental Unit.

A.P. . . . . • • •• •• •• • • • • Air Publication.A.R.C. .. .. . • • • • • • • • • • • Aeronautical Research Council.A.T.C. .- .. .. .. • • .. .. .. Air Traffic Control.C.P. . - . - .. . - - - . . .. .. Current Paper.

I.C.A.O. .. .. .. .. .. .. .. .. International Civil Aviation Organization.

I.S.M.R.C. .. .. .. .. .. .. .. Inter-Service Metallurgical Research Council.M.A.E.E. .. .. .. .. .. .. .. Marine Aircraft Experimental Establishment.

N.A.C.A. . - . • .. • . . • • • - • National Advisory Committee for Aeronautics.N.A.E. .. .. .. .. .. .. .. - . National Aeronautical Establishment.N.A.T.O. .. . - .. .. - . .. .. North Atlantic Treaty Organization.

N.G.T.E. .. .. .. .. .. .. .. National Gas Turbine Establishment.N.P.L. .. .. .. .. .. .. .. .. National Physical Laboratory.R.A.E. .. .. .. .. .. .. .. .. Royal Aircraft Establishment.

R. & M. .. .. .. .. .. .. .. .. Reports and Memoranda.S.B.A.C... .. .. .. .. .. .. .. Society of British Aircraft Constructors, Ltd.

26

APPENDIX I

Membership of the Council. December, 1954

Prof. A. G. Pugsley, O.B.E., D.Sc., M.I.C.E., M.I.Struct.E.,F.R.S., F.R.Ae.S., A.M.Am.Soc.C.E. (Chairman).

Prof. Sir Leonard Bairstow, C.B.E., D.Sc., F.R.S., Hon.F.R.Ae.S. (Vice-Chairman).

Sir Edward Bullard, M.A., Sc.D., Ph.D., F.R.S.*Mr. W. R. J. Cook, C.B., M.Sc.jProf. W. J. Duncan, C.B.E., D.Sc., M.I.Mech.E., F.R.S.,

F.R.Ae.S.Sir Harry Garner, K.B.E., C.B., M.A., F.R.Ae.S.Dr. A. A. Griffith, C.B.E., D.Eng., F.R.S.Sir Arnold Hall, M.A., F.R.S., F.R.Ae.S. JProf. W. R. Hawthorne, M.A., Sc.D.Mr. E. T. Jones, C.B., O.B.E., M.Eng., F.R.Ae.S.J

Sir Melvill Jones, C.B.E., A.F.C., M.A., F.R.S., Hon.F.R.Ae.S., H.F.I.Ae.S.

Dr. W. P. Jones, M.A., D.Sc., F.R.Ae.S., A.F.I.Ae.S.§Prof. E. J. Richards, M.A., B.Sc., F.R.Ae.S.Mr. W. J. Richards, C.B.E., B.Sc.}Prof. O. A. Saunders, M.A., D.Sc.(Eng.), M.I.Mech.E.,

F.InstP.Sir Geoffrey Taylor, M.A., F.R.S., Hon. F.R.Ae.S.Dr. O. H. Wansbrough-Jones, C.B., O.B.E., M.A., Ph.D. J

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

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

* Representing the Department of Scientific and Industrial Research.J Representing the Ministry of Supply.

t Representing the Admiralty.§ Representing the National Physical Laboratory.

Membership of the Council, 1949-54

The following were Chairmen of the Council during the period:—Dr. S. Goldstein.. .. .. .. .. .. January, 1949-March, 1949Prof. Sir Leonard Bairstow .. .. .. .. April, 1949-March, 1952Prof. A. G. Pugsley .. .. .. .. .. April, 1952

The following have been members during the period:—(Independent)(Admiralty)(D.S.I.R.)(Independent)(M.o.S.) ..(Admiralty)(D.S.I.R.)(Independent)

(N.P.L.) ..(M.o.S.) ..(Independent)(Independent)(Independent)(Independent)

(Independent)

(M.o.S.) ..(Independent)(M.o.S.) ..(Independent)

(N.P.L.) ..(M.o.S.) ..(M.o.S.) ..(Independent)(Independent)(Independent)(Independent)(M.o.S.) ..

27

Prof. Sir Leonard BairstowSir Frederick Brundrett..Sir Edward BullardProf. A. R. CollarMr. H. ConstantMr. W. R. J. CookSir Charles DarwinProf. W. J. Duncan

Mr. A. PageSir Harry Garner

Prof. E. GiffenDr. S. Goldstein..Dr. A. A. Griffith

Sir Arnold Hall ..

Prof. W. R. Hawthorne.Mr. E. T. Jones ..Sir Melvill Jones

Dr. W. P. Jones ..Sir Ben LockspeiserMr. W. G. A. Perring .Prof. A. G. PugsleyMr.E.F.Relf ..Sir Harry RicardoProf. E. J. RichardsMr. W. J. Richards

January, 1949January, 1949-July, 1950February, 1950 ..April, 1949-March, 1952January, 1949-March, 1954July, 1950January, 1949-August, 1949April, 1949-March, 1951April, 1952January, 1949-June, 1953October, 1949-February, 1953April, 1953April, 1951-March, 1954January, 1949-October, 1949April, 1950-March, 1953April, 1954January, 1949-March, 1949April, 1950-July, 1951August, 1951September, 1951October, 1949 ..April, 1949-March, 1952April, 1954April, 1954January, 1949-April, 1949January, 1949-April, 1951April, 1950January, 1949-March, 1949January, 1949-March, 1949April, 1942April, 1954

Prof. O. A. Saunders .. .. (Independent)

Sir Geoffrey Taylor .. .. (Independent)

Prof. G. Temple.. .. .. (Independent)

Dr. O. H. Wansbrough-Jones .. (M.o.S.) ..

January, 1949-March, 1950April, 1953January, 1949-March, 1951April, 1952January, 1949-March, 1950April, 1951-March, 1954February, 1953 ..

In the above list, leaders after a date indicate that the individual was a serving member atDecember, 1954, when the list was compiled.

APPENDIX IITerms of Reference of the Council

1. To advise the Minister responsible on scientific problemsrelating to aeronautics.

2. To keep under review the progress of aeronautical re-search and to advise the Minister on the programme and theplanning of aeronautical research carried out for the Govern-ment of the United Kingdom.

3. From time to time, to make recommendations to theMinister on research which the Council considers it desirableto initiate.

4. When requested to do so, to tender advice upon any re-

search carried out by or on behalf of the aeronautical industry.5. Subject to the needs of security, to make the results of

British research generally available, by the publication of re-search 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 institutions inthe Dominions and foreign countries.

8. To make an annual report to the Minister.

APPENDIX IIIMembership of Committees, Sub-Committees and Panels. December, 1954

Aerodynamics Committee,—Prof. Sir Leonard Bairstow(Chairman); Prof. E. J. Richards (Vice-Chairman); Mr. F. S.Burt (Ad.); Mr. A. N. Clifton (S.B.A.C.); Prof. A. R. Collar;Mr. H. Davies (M.o.S.); Prof. W. J. Duncan; Mr. A. Page;Sir William Farren (S.B.A.C.); Sir Arnold Hall (M.o.S.); Prof.L. Howarth; Sir Melvill Jones; Dr. W. P. Jones (N.P.L.); Prof.M. J. Lighthill; Dr. J. W. Maccoll (M.o.S.); Mr. M. B. Morgan(M.o.S.); Mr. L. F. Nicholson (M.o.S.); Dr. J. H. Preston;Prof. A. G. Pugsley (ex officio); Mr. E. F. Relf; Mr. R. A.Shaw (M.o.S.); Prof. G. Temple; Prof. A. Thorn; Prof. A. D.Young.

Secretary: Mr. R. W. G. Gandy (N.P.L.).Fluid Motion Sub-Committee.—Prof. M. J. Lighthill (Chair-

man); Prof. A. Thorn (Vice-Chairman); Prof. Sir LeonardBairstow (ex officio); Dr. G. K. Batchelor; Prof. W. G.Bickley; Mr. M. J. Brennan (S.B.A.C.); Mr. I. J. Campbell(Ad.); Mr. W.F. Cope (N.P.L.); Mr. I. M.Davidson (M.o.S.);Prof. W. J. Duncan; Mr. A. Page; Mr. A. Grimes (M.o.S.);Dr. D. W. Holder (N.P.L.); Prof. L. Howarth; Mr. P. A.Hufton (M.o.S.); Dr. W. P. Jones (N.P.L.); Dr. J. W. Maccoll(M.o.S.); Prof. W. A. Mair; Mr. P. R. Owen; Dr. AlanPowell;Prof. L. Rosenhead; Prof. H. B. Squire; Sir Geoffrey Taylor;Prof. G. Temple; Mr. C. K. Thornhill (M.o.S.); Dr. B.Thwaites; Mr. G. W. Trevelyan (S.B.A.C.); Mr. C. H. E.Warren (M.o.S.); Prof. A. D. Young.

Secretary: Mr. N. Gregory (N.P.L.).

Performance Sub-Committee.—Prof. E. J. Richards (Chair-man); Prof. W. A. Mair (Vice-Chairman); Prof. Sir LeonardBairstow (ex officio); Mr. D. W. Bottle (M.o.S.); Mr. F. S.Burt (Ad.); Mr. K. W. Clark (M.o.S.); Prof. A. R. Collar;

Prof. W. J. Duncan; Mr. S. B. Gates (M.o.S.); Mr. G. T. R.Hill; Dr. D. W. Holder (N.P.L.); Mr. P. A. Hufton (M.o.S.);Sir Melvill Jones; Mr. G. H. Lee (S.B.A.C.); Dr. R. C. Pank-hurst (N.P.L.); Dr. J. H. Preston; Mr. E. F. Relf; Prof. O. A.Saunders; Mr. R. A. Shaw (M.o.S.); Mr. T. V. Somerville(M.o.S.); Mr. L. H. G. Sterne (M.o.S.); Mr. J. C. Stevenson(S.B.A.C.); Prof. A. Thorn.

Secretary: Mr. E. W. E. Rogers (N.P.L.).Stability and Control Sub-Committee.—Prof. A. D. Young

(Chairman); Dr. J. H. Preston (Vice-Chairman); Prof. SirLeonard Bairstow (ex officio); Mr. F. S. Burt (Ad.); Prof. A. R.Collar; Mr. R. F. Creasey (S.B.A.C.); Mr. R. P. Dickinson(M.o.S.); Dr. K. Doetsch (M.o.S.); Prof. W. J. Duncan; Mr.S. B. Gates (M.o.S.); Mr. G. T. R. Hill; Mr. D. I. Husk(S.B.A.C.); Mr. H. B. Irving; Sir Melvill Jones; Dr. W. P.Jones (N.P.L.); Mr. R. H. Macmillan; Mr. D. E. Morris(M.o.S.); Dr. R. C. Pankhurst (N.P.L.); Sq. Ldr. W. J. Potocki(M.o.S.); Mr. E. F. Relf; Prof. E. J. Richards; Group Capt.S. L. Ring (M.o.S.); Mr. M. O. Robins (M.o.S.); Dr. A. M.Uttley (M.o.S.); Mr. H. F. Vessey (M.o.S.); Mr. C. A. A. Wass(M.o.S.); Dr. J. H. Westcott.

Secretary: Mr. R. W. G. Gandy (N.P.L.1).Aerofoil Theory Panel.—Dr. B. Thwaites (Chairman); Prof.

W. A. Mair; Mr. P. R. Owen; Dr. R. C. Pankhurst (N.P.L.);Prof. L. Rosenhead; Prof. A. D. Young.

Secretary: Mr. N. Gregory (N.P.L.).Laminar Boundary Layer Panel.—Prof. L. Rosenhead (Chair-

man); Dr. G. K. Batchslor; Mr. N. Gregory (N.P.L.); Dr.C. W. Jones; Prof. M. J. Lighthill; Dr. B. Thwaites.

Secretary: Mr. H. H. Pearcey (N.P.L.).

28

Propeller Panel—Mr, A. Page (Chairman); Mr. P. Brett(S.B.A.C.); Mr. H. G. Ewing (M.o.S.); Mr. C. H. Griffiths(M.o.S.); Mr. A. B. Haines (M.o.S.); Dr. R. C. Pankhurst(N.P.L.); Prof. E. J. Richards (ex officio); Mr. A. C. Walker(S.B.A.C.).

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

Mechanics Committee.—Prof. W. J. Duncan (Chairman);Prof. A. J. SuttonPippard (Vice-Chairman); Prof. A. R. Collar;Sir Harold Roxbee Cox; Mr. F. J. W. Digby (S.B.A.C.); Mr.R. Graham (M.o.S.); Mr. H. Grinsted; Prof. C. Gurney; SirArnold Hall (M.o.S.); Prof. W. S. Hemp; Mr. H. B. Howard(M.o.S.); Mr. B. P. Laight (S.B.A.C.); Mr. M. B. Morgan(M.o.S.); Prof. A. J. Murphy; Prof. A. G. Pugsley (ex officio);Prof. S. C. Redshaw; Mr. J. E. Serby (M.o.S.); Dr. D. G.Sopwith (D.S.I.R.); Sir Richard Southwell; Prof. G. Temple;Dr. P. B. Walker (M.o.S.).

Secretary: Mr. E. H. Mansfield (M.o.S.).

Computation Sub-Committee.—Prof. S. C. Redshaw (Chair-man); Brig. G. H. Hinds (Vice-Chairman) (M.o.S.); Mr.D. N. de G. Alien; Mr. K. V. Diprose (M.o.S.); Prof. W. J.Duncan (ex officio); Dr. E. T. Goodwin (N.P.L.); Dr. S. H.Hollingdale (M.o.S.); Mr. B. A. Hunn (S.B.A.C.); Dr. W. P.Jones (N.P.L.); Dr. T. Kilburn; Dr. J. W. Maccoll (M.o.S.);Mr. I. T. Minhinnick (M.o.S.); Mr. N. P. Shevloff (S.B.A.C.);Prof. G. Temple; Dr. M. V. Wilkes.

Secretary: Mr. M. Woodger (N.P.L.).

Engineering Physics Sub-Committee.—Prof. C. Gurney(Chairman); Mr. R. Graham (Vice-Chairman) (M.o.S.); Dr. L.Aitchison; Dr. E. H. Bateman (M.o.S.); Mr. F. H. Beer(M.o.S.); Prof. W. J. Duncan (ex officio); Prof. E. Giffen; Mr.A. Grimes (M.o.S.); Prof. K. A. Hayes; Mr. H. B. Irving;Prof. A. J. Sutton Pippard; Mr. E. A. Poulton (M.o.S.); Mr.D. G. A. Rendel (M.o.S.); Group Capt. W. K. Stewart (A.M.);Prof. G. Temple; Mr. H. C. B. Thomas (M.o.S.).

Secretary: Dr. M. H. L. Waters (M.o.S.).

Oscillation Sub-Committee.—Prof. W. S. Hemp (Chairman);Prof. W. J. Duncan (Vice-Chairman); Prof. Sir LeonardBairstow; Mr. J. B. Bratt (N.P.L.); Mr. E. G. Broadbent(M.o.S.); Prof. A. R. Collar; Mr. J. R. Forshaw (M.o.S.); Mr.H. Grinsted; Mr. H. P. Y. Hitch (S.B.A.C.); Mr. H. B. Howard(M.o.S.); Dr. W. P. Jones (N.P.L.); Prof. A. G. Pugsley; Prof.S. C. Redshaw; Mr. C. Scruton (N.P.L.); Mr. F. Smith(M.o.S.); Mr. L. H. G. Sterne (M.o.S.); Mr. H. Templeton(M.o.S.); Mr. J. C. Wimpenny (S.B.A.C.); Mr. M. O. W.Wolfe (M.o.S.); Prof. A. D. Young.

Secretary: Mr. N. C-Lambourne (N.P.L.).Structure Sub-Committee.—Prof. S. C. Redshaw (Chair-

man); Prof. C. Gurney (Vice-Chairman); Dr. J. H. Argyris;Mr. J. C. Bissett (S.B.A.C.); Mr. H. L. Cox (N.P.L.); Prof.W. J. Duncan (ex officio); Prof. W. S. Hemp; Mr. H. B.Howard (M.o.S.); Mr. E. D. Keen (S.B.A.C.); Mr. D. J. Lyons(M.o.S.); Prof. A. J. Murphy; Mr. C. E. Phillips (D.S.I.R.);Prof. A. J. Sutton Pippard; Prof. A. G. Pugsley; Sir RichardSouthwell; Mr. J. Taylor (M.o.S.); Mr. W. Tye; Dr. D.Williams (M.o.S.).

Secretary: Mr. L. S. D. Morley (M.o.S.).Propulsion Committee,—Prof. O. A. Saunders (Chairman);

Dr. A. A. Griffith (Vice-Chairman); Prof. A. D. Baxter; Mr.F. S. Burt (Ad.); Mr. H. Constant (M.o.S.); Dr. J. W. Drink-water (M.o.S.); Mr. G. B. R. Feilden; Sir Harry Garner; Prof.

E. Giffen; Mr. F. M. Green; Sir Arnold Hall (M.o.S.); Prof.W. R. Hawthorne; Dr. S. G. Hooker (S.B.A.C.); Mr. E. T.Jones (M.o.S.); Mr. W. H. Lindsey (S.B.A.C.); Mr. P. Lloyd(M.o.S.); Prof. A. J. Murphy; Prof. A. G. Pugsley (ex officio);Dr. D. M. Smith; Mr. T. V. Somerville (M.o.S.); Mr. R. G.Voysey; Mr. R. H. Weir (M.o.S.).

Secretary: Mr. R. P. Bonham (M.o.S.).

Combustion and Fuels Sub-Committee.—Prof. E. Giffen(Chairman); Prof. A. D. Baxter (Vice-Chairman); Dr. J. Barr;Mr. S. L. Bragg (S.B.A.C.); Dr. J. S. Clarke (S.B.A.C.); Dr.J. W. Drinkwater (M.o.S.); Sir Alfred Egerton; Dr. A. G.Gaydon; Mr. G. A. E. Godsave (M.o.S.); Dr. J. W. Linnett;Mr. I. Lubbock; Miss E. J. Macnair (Ad.); Mr. N. P. W.Moore; Dr. B. P. Mullins (M.o.S.); Dr. W. G. Parker (M.o.S.);Prof. O. A. Saunders (ex officio); Dr. D. B. Spalding; Prof.M. W. Thring; Dr. H. G. Wolf hard (M.o.S.).

Secretary: Mr. P. W. H. Howe (M.o.S.).

Engine Aerodynamics Sub-Committee.—Dr. A. A. Griffith(Chairman); Mr. A. G. Smith (Vice-Chairman); Mr. D. G.Ainley (M.o.S.); Dr. J. Black; Dr. D. M. Cockburn (S.B.A.C.);Mr. W. F. Cope (N.P.L.); Mr. G. B. R. Feilden; Mr. S. Gray(M.o.S.); Prof. W. R. Hawthorne; Mr. A. R. Howell(M.o.S.);Mr. W. Merchant; Mr. H. Pearson (S.B.A.C.); Mr. A. C. Reid(Ad.); Prof. O. A. Saunders (ex officio); Dr. J. Seddon (M.o.S.);Mr. R. G. Voysey.

Secretary: Dr. B. S. Stratford (M.o.S.).

Gas Turbine Sub-Committee.—Prof. W. R. Hawthorne(Chairman); Dr. A. A. Griffith (Vice-Chairman); Prof. G.Wesley Austin; Mr. B. D. Blackwell (S.B.A.C.); Dr. H. Cohen;Mr. J. R. Collingbourne (M.o.S.); Mr. J. E. P. Dunning(M.o.S.); Mr. G. B. R. Feilden; Prof. E. Giffen; Mr. A. R.Howell (M.o.S.); Mr. P. Lloyd (M.o.S.); Mr. R. H. Macmillan;Mr. J. Marlow (S.B.A.C.); Dr. A. W. Morley (S.B.A.C.); Dr.J. Remfry (M.o.S.); Mr. C. P. Rigby (Ad.); Mr. G. F. C.Rogers; Prof. O. A. Saunders (ex officio); Mr. R. H. Schlotel(M.o.S.); Dr. J. F. Shannon.

Secretary: Mr. P. F. Ashwood (M.o.S.).

Rockets Sub-Committee.—Prof. A. D. Baxter (Chairman);Dr. T. P. Hughes (Vice-Chairman) (M.o.S.); Dr. L. AitchisonMr. J. F. Alcock; Mr. S. Alien (S.B.A.C.); Prof. C. E. H.Bawn; Mr. A. V. Cleaver (S.B.A.C.); Mr. P. J. Duncton(S.B.A.C.); Mr. J. E. P. Dunning (M.o.S.); Dr. K. D. Errington(M.o.S.); Sir Harry Garner; Dr. C. H. Johnson (M.o.S.); Mr.I. Lubbock; Miss E. J. Macnair (Ad.); Dr. W. R. Maxwell(M.o.S.); Dr. W. G. Parker (M.o.S.); Dr. H. J. Poole (M.o.S.);Prof. O. A. Saunders (ex officio).

Secretary: Mr. N. J. Morris (M.o.S.).

SPECIAL COMMITTEESAir Navigation Committee.—Prof. C. Holt Smith (Chairman);

Dr. H. J. J. Braddick; Dr. A. W. Brewer; Mr. C. S. Durst(A.M.); Mr. S. F. Follett (M.o.S.); Mr. A. Grimes (M.o.S.);Mr. R. F. Hansford; Capt. V. A. M. Hunt (M.T.C.A.); SirHarold Spencer Jones; Prof. A. C. B. Lovell; Group Capt.D. C. McKinley (A.M.); Prof. A. G. Pugsley (ex officio); Dr.W. F. Rawlinson (Ad.); Mr. F. H. Scrimshaw (M.o.S.); Mr,S. B. Smith; Mr. H. L. Stevens; Mr. J. Stewart; Mr. C. E.Strong; Dr. A. G. Touch (M.o.S.); Mr. E. V. Truefltt (A.M.);Dr. A. M. Uttley (M.o.S.).

Member-Secretary: Mr. J. A. Preiss (M.o.S.).

29

Air Reconnaissance Committee.—Sir John Carroll (Chair-man); Dr. W. J. Bates; Mr. G. C. Brock (M.o.S.); Wing Cdr.M. W. Coombes (A.M.); Dr. J. W. Findlay (M.o.S.); Mr.R. W. Fish (M.o.S.); Mr. J. Guild (N.P.L.); Capt. H. R. B.Janvrin (Ad.); Mr. C. A. Jarman (M.o.S.); Col. R. C. N.Jenney (W.O.); Dr. J. W. Mitchell; Prof. A. G. Pugsley (exofficio); Dr. L. A. Sayce (N.P.L.); Mr. T. Brian Smith (M.o.S.);Mr. A. Stephenson; Mr. H. L. Stevens; Group Capt. L. J.Stickley (A.M.); Mr. H. B. Stringer; Dr. H. Hamshaw Thomas;Prof. E. H. Thompson.

Secretary: Dr. P. M. Barham (M.o.S.).Air Warfare Committee.—Sir Melvill Jones (Chairman);

Prof. E. J. Richards (Vice-Chairman); Mr. N. Coles (M.o.S.);Mr. S. W. Coppock (W.O.); Mr. R. P. Dickinson (M.o.S.);Air Cdre. D. R. Evans (A.M.); Sir William Farren (S.B.A.C.);Air Cdre. H. Ford (M.o.S.); Sir Harry Garner; Dr. A. A.Griffith; Prof. W. R. Hawthorne; Mr. W. H. Hill (M.o.S.);Prof. A. C. B. Lovell; Sq. Ldr. L. T. Miedzybrodzki (M.o.S.);Prof. J. L. M. Morrison; Mr. L. F. Nicholson (M.o.S.); Mr.A. E. Woodward Nutt (M.o.S.); Prof. A. G. Pugsley (exofficio); Mr. W. J. Richards (M.o.S.); Capt. A. J. T. Roe (Ad.);Dr. A. E. Russell (S.B.A.C.); Mr. W. H. Stephens (M.o.S.);Mr. G. A. Whitfield (M.o.S.).

Member-Secretary: Mr. J. W. Frame (M.o.S.).Civil Aircraft Research Committee.—Sir Harold Roxbee

Cox (Chairman); Prof. G. Temple (Vice-Chairman); Mr. F. S.Barton (M.o.S.); Dr. G. E. Bell (M.T.C.A.); Mr. J. M. Gray(M.o.S); Mr. F. M. Green; Mr. A. Grimes (M.o.S.); SirArnold Hall (M.o.S.); Mr. C. H. Jackson (B.O.A.C.); SirMelvill Jones; Air Cdre. W. E. G. Mann (M.T.C.A.); Mr. C.Moore (M.o.S.); Mr. M. B. Morgan (M.o.S.); Mr. R. C.Morgan (B.E.A.); Mr. A. E. Woodward Nutt (M.o.S.); Mr.A. C. Campbell Orde (B.O.A.C.); Prof. A. G. Pugsley (exofficio); Prof. E. J. Richards; Mr. N. E. Rowe; Mr. B. S.Shenstone (B.E.A.); Prof. P. A. Sheppard; Prof. H. B. Squire;Mr. W. Tye; Mr. R. H. Walmsley (M.T.C.A.).

Joint Secretaries: Mr. R. W. G. Gandy (N.P.L.).Mr. R. A. Pearson (M.T.C.A.).

Gust Research Committee.—Sir Geoffrey Taylor (Chairman);Prof. P. A. Sheppard (Vice-Chairman)*; Mr. H. W. L. Absalom(A.M.)*; Mr. A. Page; Mr. A. Grimes (M.o.S.); Mr. H. B.Howard (M.o.S.); Prof. A. G. Pugsley (ex officio); Mr. R. W.Symmons (M.o.S.); Sq. Ldr. A. W. Tarry (A.M.)*; Mr. J. K.Zbrozek (M.o.S.).

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

Helicopter Committee.—Mr. H. Grinsted (Chairman); Capt.R. N. Liptrot (Vice-Chairman); Prof. Sir Leonard Bairstow;Mr. M. J. Brennan (S.B.A.C.); Mr. F. S. Burt (Ad.); Mr. S. W.Coppock (W.O.); Mr. O. L. L. Fitzwilliams (S.B.A.C.); Dr.A. A. Griffith; Mr. R. Hafner (S.B.A.C.); Dr. G. S. Hislop(S.B.A.C.); Mr. W. G. Jennings (M.o.S.); Mr. A. McClements(M.o.S.); Prof. J. B. B. Owen; Mr. E. A. Poulton (M.o.S.);

Prof. A. G. Pugsley (ex officio); Mr. N, E. Rowe; Mr. F. Smith(M.o.S.); Prof. H. B. Squire; Mr. H. F. Vessey (M.o.S.); Mr.R. H. Whitby.

Member-Secretary: Dr. R. C. Pankhurst (N.P.L.).

Naval Aircraft Research Committee.—Sir Melvill Jones(Chairman); Prof. Sir Leonard Bairstow (Vice-Chairman); Mr.L. Boddington (M.o.S.); Mr. R. Hanbury Brown; Mr. G.Bryant(Ad.); Mr. F. S. Burt (Ad.); Mr. H. Constant (M.o.S.);Mr. R. R. Duddy (M.o.S.); Mr. S. B. Gates (M.o.S.); Mr.F. M. Green; Dr. A. A. Griffith; Sir Arnold Hall (M.o.S.);Mr. R. Hills; Mr. A. W. Hotson (M.o.S.); Vice-AdmiralCaspar John (M.o.S.); Col. A. V. Kerrison (Ad.); Air Cdre.H. J. Kirkpatrick (A.M.); Dr. E. Lee (Ad.) Capt.; E. D. G.Lewin (Ad.); Prof. W. A. Mair; Mr. M. B. Morgan (M.o.S.);Lt. W. Noble (M.o.S.); Mr. A. E. Woodward Nutt (M.o.S.);Cdr. S. G. Orr (M.o.S.); Prof. A. G. Pugsley (ex officio); Mr.J. E. Serby (M.o.S.); Mr. L. H. G. Sterne (M.o.S.); Sir GeoffreyTaylor.

Joint Secretaries: Mr. J. L. Nayler (N.P.L.).Mr. B. D. Clark (Ad.).

Seaplane Committee.—Sir Harry Garner (Chairman); Prof.Sir Leonard Bairstow (Vice-Chairman); Mr. P. Ward Brown(S.B.A.C.); Mr. F. S. Burt (Ad.); Prof. A. R. Collar; Mr. H. G.Jones (M.o.S.); Mr. H. Knowler (S.B.A.C.); Mr. R. F. Lofft(Ad.); Air Cdre. D. F. Lucking; Group Capt. A. J. Miley;Prof. A. G. Pugsley (ex officio); Mr. J. R. Shearer (N.P.L.);Mr. A. G. Smith; Mr. W. F. Spurr (M.o.S.); Dr. D. Williams(M.o.S.).

Secretary: Mr. D. M. Ridland (M.o.S.).

Wind Tunnel Design Committee.—Sir Geoffrey Taylor(Chairman); Mr. E. F. Relf ( Vice-Chairman); Prof. Sir LeonardBairstow; Major G. P. Bulman (M.o.S.); Prof. A. R. Collar;Mr. R. Hills; Dr. W. F. Hilton (S.B.A.C.); Dr. D. W. Holder(N.P.L.); Mr. L. E. Leavy (S.B.A.C.); Dr. J. W. Maccoll(M.o.S.); Prof. W.'A. Mair; Mr. L. F. Nicholson (M.O.S.);Mr. P. R. Owen; Prof. A. G. Pugsley (ex officio); Mr. L. H. G.Sterne (M.o.S.); Prof. A. Thorn; Mr. J. S. Thompson (M.o.S.)

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

Guided Weapons Advisory Board.—Sir Harry Garner (Chair-man); Mr. F. S. Barton (M.o.S.); Mr. L. H. Bedford; Sir JohnCarroll (Ad.); Dr. W. Cawood (M.o.S.); Dr. R. Cockburn(M.o.S.); Mr. W. R. J. Cook (Ad.); Prof. W. J. Duncan; Mr.G. W. H. Gardner (M.o.S.); Dr. A. A. Griffith; Sir ArnoldHall (M.o.S.); Prof. W. R. Hawthorne; Mr. E. T. Jones(M.o.S.); Dr. F. E. Jones (M.o.S.); Sir Melvill Jones; Prof.J. L. M. Morrison; Dr. H. J. Poole (M.o.S.); Prof. A. G.Pugsley (ex officio); Mr. W. J. Richards (M.o.S.); Prof. SirEricRideal (ex officio); Mr. H. A. Sargeaunt (W.O.); Mr. J. E.Serby (M.o.S.); Prof. C. Holt Smith; Mr. W. H. Stephens(M.o.S.); Dr. O. H. Wansbrough-Jones (M.o.S.); Dr. W. H.Wheeler (M.o.S.).

Acting Secretary: Mrs. M. Garrard (M.o.S.).

' Representing the Meteorological Research Committee, Air Ministry.

Ad.A.M.D.S.I.R. .

M.T.C.A.M.O.S. .

Representation of various departments, etc., has been indicated above as follows:—Admiralty. N.P.L.Air Ministry. W.O.Department of Scientific and Industrial B.E. A.

Research. B.O.A.C.Ministry of Transport and Civil Aviation. S.B.A.C.Ministry of Supply.

30

National Physical Laboratory.War Office.British European Airways.British Overseas Airways Corporation.Society of British Aircraft Constructors.

APPENDIX IVList of Monographs and Books published between 1949 and 1954

Monographs

R. & M. 2222 .. Research on high-speed aerodynamics atthe Royal Aircraft Establishment from1942 to 1945. Staffs of the High SpeedTunnel and High Speed Flight Sections,R.A.E. Edited by W. A. Mair. (Septem-ber, 1946.)Published 25th July, 1950.

R. & M. 2300 .. Investigation of aircraft accidents involvingairframe failures. J. B. B. Owen andF. Grinsted. (July, 1947.)Published 17th October, 1949.

R. & M. 2323 .. Experiments on tail flutter. C. Scruton.(May, 1948.)Published 21st February, 1950.

R. & M. 2492 .. Aircraft flutter. J. Williams. (August, 1948.)Published 1st August, 1951.

R. & M. 2522 .. Combined stress monograph. Parts I and II.Some experiments on the resistance ofmetals to fatigue under combined stresses.H. J. Gough, H. Pollard and W. J.Clenshaw. (28th June, 1949.)Published 19th March, 1952.

R. & M. 2560 .. The High Speed Laboratory of the Aero-dynamics Division, N.P.L. D. W. Holder.(1946.)Published 28th August, 1954.

R. & M. 2627 .. Electronics applied to the measurement ofphysical quantities. G. E. Bennett, G. R.Richards and E. C. Voss. (September,1947.)Published 25th March, 1953.

R. & M. 2638 .. Heat transference and pressure loss for airflowing in passages of small dimensions.J. Remfry. (June, 1947.)Published 29th April, 1954.

R. & M. 2704 .. Four studies in the theory of stress concen-tration.Part I. The effect of holes on the strength

of materials under complex stresssystems.

Part II. Stress concentration due to holesand grooves other than elliptical inform.

Part III. The effect of surface irregulari-ties on fatigue strength.

Part IV. Stress concentration in twistedshafts. H. L. Cox. (January, 1950.)

Published 10th December, 1953.

Books

(Published by Oxford University Press)

A selection of Tables for use in calculations of CompressibleAirflow. Prepared on behalf of the Aeronautical ResearchCouncil by the Compressible Flow Tables Panel. Published1952.

Modem Developments in Fluid Dynamics. High Speed Flow.

Volumes I and II. Edited by L. Howarth. Published 1953.A selection of Graphs for use in calculations of Compressible

Airflow. Prepared on behalf of the Aeronautical ResearchCouncil by the Compressible Flow Tables Panel. Published1954.

APPENDIX VNumerical List of Reports and Memoranda and Current Papers published between January, 1949 and December, 1954

R.&.M.NOS.1900, 1913, 2074, 2165, 2197, 2200, 2222, 2230, 2232, 2233, 2242, 2246, 2249, 2252, 2253, 2255, 2256, 2262-2266, 2272, 2273,2275-2278, 2281, 2286, 2287, 2289, 2292-2295, 2297-2300, 2303-2379, 2381-2461, 2463-2549, 2551-2580, 2582-2682, 2684-2729,2731-2742, 2744-2746, 2748-2753, 2755-2762, 2764-2778, 2780-2782, 2784, 2787-2793, 2796-2803, 2805, 2807, 2808, 2810-2812,2814, 2816-2821, 2823, 2824, 2827, 2830, 2834-2837, 2839, 2840, 2852, 2853, 2857-2860, 2862, 2868, 2875, 2896, 2904, 2909, 2914.Current Paper Nos.1-179,181 and 182.

31

AERODYNAMIC SYMBOLS

1. GENERALm Masst TimeV Resultant linear velocityQ Resultant angular velocityp Density, a relative densityv Kinematic coefficient of viscosityR Reynolds number, R — IV jv (where Us a suitable linear dimension).

Normal temperature and pressure for aeronautical work are 15° C.and 760 mm.For air under these//) =-- 0-002378 slug/cu. ft.

conditions\ v = 1-56 X 10~4 ft.2/sec.The slug is taken to be 32-2 Ib.-mass.

a Angle of incidencee Angle of downwashS Areab Spanc ChordA Aspect ratio, A = bz/SL Lift, with coefficient CL = L/%PV*SD Drag, with coefficient CD = D/^pVzSy Gliding angle, tan y = DjLL Rolling moment, with coefficient C, = L/^pV*bSM Pitching moment, with coefficient Cm = Mj\pV*cSN Yawing moment, with coefficient Cn = N/^pV*bS

2. AIRSCREWS» Revolutions per secondD Diameter/ VjnDP PowerT Thrust, with coefficient kT =Q Torque, with coefficient kQ —rj Efficiency, r\ = TV/P — JkT/2nkQ

32

SYSTEM OF AXES

Axes

Force

Moment

Angle ofRotation

Velocity

SymbolDesignation

Positivedirection

Symbol

SymbolDesignation

Symbol

LinearAngular

Moment of Inertia

Xlongitudinal

forward

X

Lrolling

<£

uP

A

ylateral

starboard

Y

Mpitching

6

V

q

B

znormal

downward

Z

Nyawing

V

wr

c

Components of linear velocity and force are positive in the positive directionof the corresponding axis.

Components of angular velocity and moment are positive in the cyclic ordery to 2 about the axis of x, z to x about the axis of y, and x to y about the axis of z.

The angular movement of a control surface (elevator or rudder) is governedby the same convention, the elevator angle being positive downwards and the rudderangle positive to port. The aileron angle is positive when the starboard aileron isdown and the port aileron is up. A positive control angle normally gives rise to anegative moment about the corresponding axis.

The symbols for the control angles are :—f aileron angler\ elevator angler\T tail setting angle£ rudder angle

33(82697) Wt. 3112— K8 11/55 D.L. PRINTED IN GREAT BRITAIN

A.R.C. REVIEW1949-1954

Publications of theAeronautical Research Council

ANNUAL TECHNICAL REPORTS OF THE AERONAUTICALRESEARCH COUNCIL (BOUND VOLUMES)

1936 Vol 1. Aerodynamic* General, Performance, Airscrew:*, Flutter and Spinning. 40:. (+is i J )Vol II Stability and Control, Structures, Seaplanes, Engines, etc. 50*. (51* i</.)

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Annual Reports of the Aeronautical Research Council—'933-34 »• M (:/- 8^.) 1937 2s. (21 z/)'934-35 ls- M. (it. %J.) 1938 u. 6J. (it. $<t.)

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December i, 1936 — June 30, 1939 R. & M. No. 1850. n. id. (i/.July i, 19^9 — June 30, 194.5 R. & M. No. 1950. n.(is.i\J)July i, 1945 — June 30, 1946 R & M No. 2050. is. (is. i\J)July i, 1946 — December 31, 1946 R. & M No. 2150 is. 3</ (isJanuary i, 1947 — June 30, 1947 R. & M No. 2250. w. 3 .̂ ( i f .July, 1951 R S. M No. 23^0 ij- 9</ (n ioj</.)January, 1954 R. & M No. 2450 is. (2.1. i|</.)July, 1954. R. & M. No. 2550 as. 6d. (is. 7j</.)

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