COPY FOR OFFICIAL USE

AERONAUTICS

TECHNICAL REPORTOF THE

AERONAUTICAL RESEARCHCOMMITTEE

FOR THE YEAR 1932-1933(With APPENDICES)

VOL.1Aerodynamics, Buffeting and Flutter, Meteorology

Crown Copyright Reserved

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Ill

CONTENTS

VOLUME IPAGE

FRONTISPIECE. Sir Richard Tetley Glazebrook, K.C.B., F.R.S. -Members o f t h e Committee - - - - - - - - xReport f o r t h e year 1932-33 - - - - - - - - 1

APPENDICES TO THE REPORTAERODYNAMICS :

(a) General:—(i) The distribution of turbulence over the central region of

a pipe.—A. Fage, A.R.C.Sc., and H. C. H. Townend,B.Sc. ( R , & M. 1474) - - - - - - 9 5

(ii) Induced flow through a partially choked pipe.—H.Glauert, F.R.S., D. JI. Hirst, M.A., and A. S. Harts-horn, B.Sc. Communicated by D.S.R., Air Ministry.( R . & M . 1469) - - - - - - - 1 0 1

(iii) Turbulence in the wake of a bodv.—A. Fage, A.R.C.Sc.(R. & M. 1510) - - -* - - - - 116

(iv) Effect of turbulence on drag of airship models.—Hilda M.Lyon, M.A., A.F.R.Ae.S. (R. & M. 1511) - - 123

(v) Air torque on a C5'linder rotating in an air stream.—A. Thorn, D.Sc., Ph.D., and S. R. Sengupta. Com-municated by Professor ]. D. Cormack. {R. & M.1520) - - - - - - - - - 1 4 9

(vi) Velocity distribution in the neighbourhood of a corrugatedsheet.—R. Houghton, M.A. (R, & M. 1466) - - 156

(vii) Graphical solutions for inviscid flow.—H. F. Winny,Ph.D. Communicated by Dr. N. A. V. Piercy.( R . & M . 1473) - - - - - - - 1 6 1

(viii) Arithmetical solution of problems in steady viscous flow.—A. Thorn, D.Sc., Ph.D. Communicated by ProfessorJ. D. Cormack. (R. & M. 1475) - - - - 177

(ix) Vortex system behind a sphere moving through viscousfluid.—H. F. Winny, Ph.D. Communicated by DrN. A. V. Piercy. (R. & M. 1531) - - - - 183

(b) Wind Tunnels :—(i) High speed induced wind tunnel.—A. Bailey, M.Sc.,

A.M.lnst.C.E., and S. A. Wood, M.Sc. (R. & M. 1468) 197(ii) Wind tunnel interference on aerofoils.—H. Glauert,

F.R.S. Communicated by D.S.R., Air Ministry.( R . & M . 1470) - - - - - - - 2 1 8

(iii) The interference on the characteristics of an aerofoil ina wind tunnel of circular section.—H. Glauert, F.R.S.Communicated by D.S.R., Air Ministry. (R. & M.1453) - - - - - - - - - 2 2 9

(17790-1) A 2

IV

AERODYNAMICS—oont.(b) Wind Tunnels—cont. PAGE

(iv) Interference on characteristics of aerofoil in wind tunnelof rectangular section.—H. Glauert, F.R.S. Com-municated by D.S.R., Air Ministry. (R. & M. 1459) - 241

(v) Wind tunnel interference on streamline bodies.—C. N. H. Lock, M.A., and F. C. Johansen, M.Sc.,A.M.I.Mech.E. (R. & M. 1451) - - - - 248

(c) Aerofoils:—(i) Applications to aeronautics of Ackeret's theory of aero-

foils moving at speeds greater than that of sound.—Professor G. I. Taylor, F.R.S. (R. & M. 1467) - - 269

(ii) Lift and drag measured in a velocity gradient.—F. B.Bradfleld, Math. & Nat. Sci. Triposes, and J. Cohen,B.A. Communicated by D.S.R., Air Ministry.( R . & M . 1489) - - - - - - - 2 7 6

(d) Performance:—(i) Determination of the best basis of aircraft performance

reduction from flight tests. Part I. Superchargedengines. Part II. Unsupercharged engines.—J. L.Hutchinson, B.A., and E. Finn, B.Sc. (R. & M. 1532) 280

(ii) Sideslip and performance of multi-engined aircraft.—E. T. Jones, M.Eng. Communicated by D.S.R., AirMinistry. ( R . & M . 1455) - - - - - 2 9 8

(iii) A flight path recorder suitable for performance testing.—R. P. Alston, B.A., D. A. Jones, A.M.I.Ae.E., andE. T. Jones, M.Eng. Communicated by D.S.R., AirMinistry. (R. & M. 1471) - - - - - 304

(iv) Aircraft turning performance. Part I.—S. B. Gates,M.A. Communicated by D.S.R., Air Ministry.( R . & M . 1502) - - - - - - - 3 1 2

(v) Measurement of take-off and landing runs.—D. Rolinson,M.Eng. Communicated by D.S.R., Air Ministry.( R . & M . 1458) - - - - - - - 3 2 0

(vi) Possible increase in level speed of high speed aircraftcaused by a diving start.—H. M. Garner, M.A., andR. K. Gushing. Communicated by D.S.R., AirMinistry. ( R . & M . 1530) - - - - - 3 2 3

(vii) Measurement of position error on high speed aircraft.—R. K. Cushing. Communicated by D.S.R., AirMinistry. ( R . & M . 1472) - - - - - 3 2 7

(e) Interference:—(i) Drag and pressure-distribution experiments on two

pairs of streamline bodies.—C. N. H. Lock, M.A., andF. C. Johansen, M.Sc., A.M.I.Mech.E. (R. & M. 1452) 332

(ii) The effect of a tractor airscrew on body-wing interference.—E. Ower, B.Sc., A.C.G.I., R. Warden, Ph.D.,M.Eng., and L. J. Jones. (R. & M. 1512) - - 351

AERODYNAMICS—cont,(e) Interference—cont. PAGE

(iii) Improvement of airscrew-body performance by radialvanes.—F. C. Johansen, M.Sc., A.M.I.Mech.E.( R . & M . 1495) - - . - - , - 3 8 5

(iv) Tests on a Bristol Bulldog fitted with a thin Townendring,—W. G. A. Perring, R.N.C. Communicated byD.S.R., Air Ministry. (R. & M. 1504) - - - 412

(v) Wheels, fairings and mudguards.—F. B. Bradfleld,Math. & Nat. Sci. Triposes, and G. F. Midwood.Communicated by D.S.R., Air Ministry. (R. & M.1479) - - - - - - - - - 4 3 0

(/) Airscrews:—(i) Present position of investigation of airscrew flutter.—

W. J. Duncan, D.Sc., A.M.I.Mech.E., and A. R.Collar, B.A., B.Sc. (R. & M. 1518) - - - 444

(ii) Periodic flow behind an airscrew.—C. N. H. Lock, M.A.,and D. M. Yeatman. (R. & M. 1483) - - - 488

(iii) Some possible advantages of a variable pitch airscrew.—W. G. Jennings, B.Sc. Communicated by D.S.R.,Air Ministry. (R. & M. 1516) - - - - 503

BUFFETING AND FLUTTER :(i) Two reports on tail buffeting. By the Aerodynamics

Staff of the National Physical Laboratory. (R. & M.1457) - - - - - - - - - 5 2 8

(ii) Resistance derivatives of flutter theory. Part I.—W. J. Duncan, D.Sc., A.M.I.Mech.E., and A. R.Collar, B.A., B.Sc. (R. & M. 1500) - 563

(iii) Wind tunnel tests of recommendations for prevention ofwing flutter.—B. Lockspeiser, M.A., and C. Callen.Communicated by D.S.R., Air Ministry. (R. & M.1464) - - - - - - - - - 5 7 7

(iv) The influence of wing density upon wing flutter.—A. G.Pugsley, M.Sc. Communicated by D.S.R., AirMinistry. ( R . & M . 1497) - - - - - 6 0 9

(v) Statistical method of investigating relations betweenelastic stiffnesses of aeroplane wings and wing-aileronflutter.—H. Roxbee Cox, Ph.D., D.I.C., B.Sc. Com-municated by D.S.R., Air Ministry. (R. & M. 1505) - 626

(vi) A theory of binary servo rudder flutter with applicationsto a particular aircraft.—W. J. Duncan, D.Sc.,A.M.I.Mech.E., and A. R. Collar, B.A., B.Sc.( R . & M . 1527) - - - - - - - 6 5 6

METEOROLOGY:(i) Relation between ground contours, atmospheric turbu-

lence, wind speed and direction.—W. R. Morgans,M.Sc. Communicated by The Director, MeteorologicalOffice. ( R . & M . 1456) - - - - - - 6 7 9

VI

METEOROLOGY—cont. PAGE(ii) Acceleration of aeroplanes in vertical air currents. Parti.

—H. R. Fisher, B.A. Communicated by D.S.R., AirMinistry. ( R . & M . 1463) - - - - - 7 1 8

(iii) Acceleration of an aeroplane upon entering a verticalgust.—L. W. Bryant, B.Sc., A.R.C.Sc,, and I. M. W.Jones. ( R . & M . 1496) - - - - - - 7 3 4

VOLUME IISTABILITY AND CONTROL :

(i) Experiments on the Hawker Hornbill biplane. Part I.—S. B. Gates, M.A., A. Ormerod, B.Sc., and R. A.Fairthorne, B.Sc. Part II.—A. V. Stephens, B.A.Part III.—H. B. Irving, B.Sc., and A. S. Batson, B.Sc.Communicated by D.S.R., Air Ministry. (R. & M. 1422) 751

(ii) Lateral stability of an aeroplane beyond the stall.—L. W.Bryant, B.Sc., A.R.C.Sc., I. M. W. Jones, and G. L.Pawsey. ( R . & M . 1519) - - - - - 7 7 0

{iii) Experiments on swept back and swept forward aerofoils.—D. H. Williams, B.Sc., and A. S. Halliday, B.Sc.,Ph.D., D.I.C., with an Appendix by H. B. Irving, B.Sc.( R . & M . 1491) - - - - - - - 7 8 8

(iv) Aerodynamic characteristics of a semi-rigid wing.—A. G.Pugsley, M.Sc. Communicated by D.S.R., AirMinistry. (R. & M. 1490) - - - - - 810

(v) Reversal of aileron control due to wing twist.—W. J.Duncan, D.Sc., A.M.LMech.E., and G. A. McMillan,M.Eng. (R. & M. 1499) - - - - - 821

(vi) Theory of loss of lateral control due to wing twisting.—H. RoxbeeCox, Ph.D., D.I.C., B.Sc., and A. G. Pugsley,M.Sc. Communicated by D.S.R., Air Ministry.( R . & M . 1506) - - - - - - - 8 4 3

(vii) Tests of floating ailerons on a Bristol Fighter aeroplane.Part I.—Rolling balance tests.—F. B. Bradfleld,Math. & Nat. Sci. Triposes, and G. F. Midwood.Part II.—Full scale tests.—A. V. Stephens, B.A.Communicated by D.S.R., Air Ministry. (R. &M. 1501) 854

(viii) Slotted R.A.F.34 Bristol Fighter. Forces on slat in flight.—A. Ormerod, B.Sc. Communicated by D.S.R., AirMinistry. (R. & M. 1477) - . . . 879

(ix) Efficiency of tail plane behind wing of R.A.F.34 section.—D. M. Hirst, M.A., and A. S. Hartshorn, B.Sc. Com-municated by D.S.R., Air Ministry. (R. & M. 1478) - 885

(x) Slipstream effect on the downwash and velocity at thetailplane.—F. B. Bradfield, Math. & Nat. Sci. Triposes.Communicated by D.S.R., Air Ministry. (R. & M. 1488) 889

(xi) Full scale experiments with servo rudders.—J. E. Serby,B.A. Communicated by D.S.R., Air Ministry.(R. & M. 1514) . . . . . . . 896

Vll

SPINNING : PAGE(i) Spinning calculations on some typical cases.—H. B.

Irving, B.Sc,, and A. S. Batson, B.Sc. (R. & M. 1498) 904(ii) Simplified presentation of the subject of spinning of

aeroplanes.—H. B. Irving, B.Sc. (R. & M. 1535) - 930(iii) A comparison of the spinning properties of a high and

low monoplane as obtained from autorotation experi-ments (with yaw).—H. B. Irving, B.Sc., A. S. Batson,B.Sc., and A. G. Gadd. (R. & M. 1534) - - - 962

(iv) Spinning of a Bristol Fighter.—A. V. Stephens, B.A.Communicated by D.S.R., Air Ministry. (R. & M.1515) - - - - - - - - - 9 6 7

(v) Airflow about aeroplanes shown by Wooltufts.—B.Melville Jones, A.F.C., M.A., and J, A. G. Haslam, M.C.,D.F.C., B.A. ( R . & M . 1494) - - - - - 9 8 9

ENGINES :(i) Radial engine tested at reduced mixture strength and

with variable ignition timing.—J. Swan, B.Sc., andA. W. Morley, M.Sc., Whit. Sch. Communicated byD.S.R., Air Ministry. (R. & M. 1485) - - - 1001

(ii) Experiments with a supercharged single-cylinder unit.—G. F. Mucklow, D.Sc. Communicated by ProfessorA. H. Gibson, D.Sc. (R. & M. 1460) - - - 1013

(iii) Lubrication in oxidising conditions.—R. O. King, andC. Jakeman. Communicated by D.S.R., Air Ministry.( R . & M . 1517) - - - - - - - 1069

(iv) Oil cooling for aircraft.—B. C. Carter, F.R.Ae.S.,M.I.Mech.E. Communicated by D.S.R., Air Ministry.( R . & M . 1486) - - - - - - - 1083

(v) Heats of formation of nitrous oxide and carbon dioxide.Part I.—J. H. Awbery, B.A., B.Sc,, and Ezer Griffiths,D.Sc., F.R.S. Part II.—R. W. Penning, M.B.E.,B.Sc., D.I.C., and F. T. Cotton, B.Sc. Work donefor the Department of Scientific and IndustrialResearch. ( R . & M 1513) - - - - - 1141

(vi) Abstract. The oxidation of fuel vapours in air.—E.Mardles, D.Sc., F.I.C. (R. & M. 1524) - - 1183

(vii) Abstract. Detonation, Spark-plug position and enginespeed.—R. O. King, M.A.Sc., and H. Moss, D.Sc.( R . &M. 1525) - - - - - - - H85

(viii) Reduction of fire risk by induction pipe flame traps.—Andrew Swan, B.Sc., A.M.Inst.C.E., Squadron LeaderW. Helmore, M.Sc., A.F.R.Ae.S., and W. C. Clothier,M.Sc., Wh. Sch. Communicated by D.S.R., AirMinistry. (R. & M. 1484) - -1187

(ix) Surging in centrifugal superchargers.—G. V. Brooke,B.Sc., Tech. Communicated by D.S.R., Air Ministry.( R . & M . 1503) - - - - - - - 1203

(x) Design and test data for aircraft radiators.—C. AndertonBrown, A.M.I.Mech.E. Communicated by D.S.R., AirMinistry. ( R . & M . 1461) - - - - - 1246

vmENGINES—cont. PAGE

(xi) Estimation of wing surface area for evaporative cooling.—C. Anderton Brown, A.M.I.Mech.E., and A. W.Morley, M.Sc. Communicated by D.S.R., Air Ministry.(R. & M. 1481) . . . . . . . 1302

STRUCTURES:(i) Method of testing strength and stiffness of large wing.—

I. J. Gerard, M.Sc., Assoc. M.Inst.C.E., A.F.R.Ae.S.Communicated by D.S.R., Air Ministry. (R. & M. 1462) 1323

(ii) Distortions of stripped aeroplane wings under torsionalloading.—D. Williams, B.Sc., A.M.I.Mech.E. Com-municated by D.S.R., Air Ministry. (R. & M. 1507) - 1328

(iii) Critical reversal speed for an elastic wing.—A. G. Pugsley,M.Sc., and G. R. Brooke, Nat. Dipl. Communicatedby D.S.R., Air Ministry. (R. & M. 1508) - - - 1351

(iv) Stability of static equilibrium of elastic and aerodynamicactions on a wing.—H. Roxbee Cox, Ph.D., D.I.C.,B.Sc., and A. G. Pugsley, M.Sc. Communicated byD.S.R., Air Ministry. (R. & M. 1509) - - -1361

(v) Loads in a fuselage under combined bending and torsion.—G. W. Mullett, D.I.C., Wh. Sch. Communicatedby Professor L. Bairstow. (R. & M. 1533) - - 1381

(vi) Distortion of thin tubes under flexure.—A. H. SuttoiiPippard, M.B.E., D.Sc., M.Inst.C.E. (R. & M. 1465) - 1411

(vii) Abstract. Calculation of stresses in braced frameworks.—R. V. Southwell, F.R.S. (R. & M. 1526) - - - 1416

(viii) Application of a method for determining the stresses inbraced frameworks.—L. Chitty, A.F.R.Ae.S. (R. & M.1528) - - - - - - - - - 1417

(ix) Abstract. Flexural centre and centre of twist of anelastic cylinder.—W. J. Duncan, D.Sc., A.M.I.Mech.E.,D. L. Ellis, B.Sc., A.R.T.C., and C. Scruton, B.Sc.( R . & M . 1529) - - - - - - - 1453

MATERIALS :(i) Relative temperatures of brass when subjected to

reversed direct stresses in vacuo and in air.—H. J.Gough, M.B.E., D.Sc., and D. G. Sopwith, B.Sc., Tech.(R. & M. 1482) - - . - - - - - 1457

(ii) Stressless corrosion followed by fatigue test to destructionon aluminium crvstal.—H, J. Gough, M.B.E., D.Sc.,and G. Forrest, B.Sc. (R. & M. 1476) - - - 1461

(iii) Abstract. Intercrystalline corrosion of duralumin.—A. J. Sidery, Assoc. Met. (Sheff.), K. G. Lewis, M.Sc.,and H. Sutton, M.Sc. (R. & M. 1523) - - - 1472

SEAPLANES AND FLYING BOATS :(i) Porpoising tests on a model of a flying boat hull.—H. M.

Garner, M.A. Communicated by D.S.R., Air Ministry.( R . & M . 1492) - - - - - - - 1475

(ii) Effect of float setting on take-off and top speed of theIIIF.—J. L. Hutchinson, B.A. Communicated byD.S.R., Air Ministry. (R. & M. 1487) - - - 1487

(iii) Stability on the water of a seaplane in the planingcondition.—W. G. A. Perring, R.N.C., and H. Glauert,F.R.S. Communicated by D.S.R., Air Ministry.( R . & M . 1493) - - - - - - - 1489

Index

E. & M. No. 1422„ 1451„ 1452„ 1453„ 1455„ 1456„ 1457„ 1458„ 1459„ 1460„ 1461„ 1462„ 1463„ 1464„ 1465„ 1466„ 1467„ 1468„ 1469„ 1470„ 1471„ 1472„ 1473„ 1474„ 1475„ 1476„ 1477„ 1478„ 1479„ 1481„ 1482„ 1483„ H84„ 1485„ I486„ 1487„ 1488„ 1489„ 1490„ 1491„ 1492

IX

to Serial Numbers ofPAGE

- 751- 248- 332- 229- 298- 679- 528- 320- 241- 1013- 1246- 1323- 718- 577- 1411- 156- 269- 197- 101- 218- 304- 327- 161- 95- 177- 1461- 879- 885- 430- 1302- 1457- 488- 1187- 1001- 1083- 1487- 889- 276- 810- 788- 1475

the Technical

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Volume II commences at page 751.

PAGE- 1489- 989- 385- 734- 609- 904- 821- 563- 854- 312- 1203- 412- 626- 843- 1328- 1351- 1361- 116- 123- 351- 1141- 896- 967- 503- 1069- 444- 770- 149- 1472- 1183- 1185- 1416- 656- 1417- 1453- 323- 183- 280- 1381- 962- 930

Reports and Memoranda Nos. 1304, 1454, 1521 and 1522 were not receivedin time for inclusion in this report.

Report and Memorandum No. 1480 is a monograph and will not be includedin this report.

* These Reports and Memoranda are abstracts of papers published indetail in outside journals.

MEMBERS OF THE COMMITTEE

March, 1933

Sir RICHARD T. GLAZEBROOK, K.C.B., F.R.S. (Chairman).Sir JOSEPH E. PETAVEL, K.B.E., F.R.S. (Vice-Chairman).*Professor L. BAIRSTOW, C.B.E., F.R.S.Dr. C. V. DRYSDALE, C.B., O.B.E.fMr. W. S. FARREN, M.B.E., M.A.Dr. R. H. GREAVES, M.B.E., D.Sc., F.I.C.|Mr. A. H. HALL, C.B.E., M.I.C.E., M.I.M.E.Professor B. M. JONES, M.A., A.F.C.Dr. G. C. SIMPSON, C.B., C.B.E., F.R.S.Sir FRANK E. SMITH, K.C.B., C.B.E., F.R.S.*Professor R. V. SOUTHWELL, F.R.S.Professor G. I. TAYLOR, F.R.S.Mr. H. T. TIZARD, C.B., F.R.S.Mr. H. E. WIMPERIS, C.B.E., M.A., F.R.Ae.S., M.I.E.E.

Secretary : Mr. J. L. NAYLER.Assistant Secretary : Mr. E. OWER.

National Physical Laboratory,Teddington, Middlesex.

*Representing the Department of Scientific and Industrial Research,f Representing the Admiralty.J Representing the War Office.

1

AERONAUTICAL RESEARCHCOMMITTEE

Report for the year 1938-33

The Most Hon. the Marquess of Londonderry, K.G., M.V.O.,Secretary of State for Air.

June, 1933.My Lord Marquess,

We, the Aeronautical Research Committee, beg leave to submitour report for the year 1932-33.

In April last Sir Richard Glazebrook retired from the Chairmanshipof the Committee which he had held since its establishment in 1920.Previously he had been Chairman of the Advisory Committee forAeronautics since its formation in 1909, under the Presidency ofthe late Lord Rayleigh. Sir Richard has thus been responsible foradvising the Government on aeronautical research for a continuousperiod of 24 years, during which aeronautics has grown from primitivebeginnings into an important world industry. That we can justlyclaim in this country to be in the forefront of this advance is duein no small measure to Sir Richard Glazebrook. He had the visionto see the scientific organisation that was needed; the power topersuade others; and the energy and ability to get things done.As a result we now have an organisation in this country second tonone in the strength of its links from the Laboratory to the finishedproduct. There is no need for us to dwell upon his great services toscience and the state in this and other directions ; it is enough to saythat we part with the greatest regret from one who has presided overus with such distinction and who has helped and encouraged us inso many ways. The good wishes of all his colleagues, past andpresent, go with him in his retirement.

Last year we referred to the attainment of the world's speed record,which was established by the S.6.B. seaplane after winning the finalcontest for the Schneider Trophy. The past year has been no lessnotable in that two other important world records have come toGreat Britain—the height record won by the flight of CaptainC. Uwins to 43,975 ft. on a Vickers Vespa fitted with a Bristol air-cooled engine, and the long distance non-stop record attained by theFairey Long-Range Monoplane (see Illustration No. 1) whenSquadron Leader O. R. Gayford and Flight Lieut. G. E. Nicholettsne\v a distance of 5,309 miles from England to Walvis Bay, SouthAfrica.

i L L U s f U A U O N No. 1.

The l-'airey I.on<j K;nif{c M < > i i

For the attainment of high speeds and long distances it isessential that every effort should be made to reduce air resistanceas far as possible ; Jong distance flying demands in addition thegreatest economy in fuel consumption. The preparation for theserecord flights has consequently entailed much research, the resultsof which are of direct application to the design and operation of civilaircraft. Height records, on the other hand, are not so dependenton minimum resistance or fuel consumption, but introduce a numberof other special problems. We consider it unlikely that presentheight records wUl be substantially increased without considerableadvances in the design of aircraft, a matter which we consideredlast year and on which we are glad to say a number of investigationsare in progress.

Equipment.—We note with pleasure the progress which has beenmade this year in the provision of further equipment for aerodynamicresearch. The main structural members of the new 24 ft. open-jetwind tunnel, which is needed for experiments on full scale enginesand fuselages, have been erected at the Royal Aircraft Establishment,and the tunnel is likely to be completed by April, 1934. A newhigh speed wind tunnel has been built at the National PhysicalLaboratory (see Illustration No. 2) to replace an obsolete tunnel,and approval has been given for a second tunnel of this type to beerected in the same building. These tunnels will provide jets ofair 9 ft. X 7 ft, in cross section which will flow at speeds up to140 m.p.h. Modifications have also been made to the R.A.E.5 ft. open-jet tunnel so as to reach a speed of 210 m.p.h.

A number of technical problems have been overcome in theoperations of the Compressed Air Tunnel at the N.P.L. Thebalance, which has been designed on novel lines by Mr. E, F. Relf,is working satisfactorily. It consists essentially of a complete ringsurrounding the tunnel jet, and shielded from air currents by suitableguard plates. The model is attached rigidly to the ring by wires.The wind force on the model is thus transferred to the ring, and itsmoment about three separate parallel axes can be measured. Fromthese measurements, lift, drag and pitching moment are readilycalculable. The change from one axis to another can be made bymeans of three phase induction motors, an indicator showing at aglance which axis is in use at any time. The moment about anyaxis is balanced by the electro-magnetic attraction between coils ofwire placed at the top of the balance frame, the system being ineffect a Kelvin current balance. Equilibrium of the balance isindicated electrically on the control table. Electro-magnetic devicesare employed to vary the sensitivity of the balance in accordancewith the size of the force under measurement; while a step-by-stepmotor of special design enables the angle of incidence of a wing or acomplete model to be varied progressively. The whole apparatusis easily operated by one observer outside the tunnel, while thecontrol of the speed of the wind and the recording of the pressure

I I I US I k AT I O N No. 2

N I ' I. l) It • 7 It Op M I J i t \\ m i l I min i I

and temperature inside the tunnel at intervals are done by a secondobserver. The accuracy of the balance is such that aerodynamicforces of -J Ib. to 1,000 Ib. can be measured to 1 per cent.

The R.A.E. Seaplane Testing Tank (see Illustration No. 3) hasbeen completed, and preliminary experiments on models to ascertainthe effect of the walls and the depth of the tank are in hand. Oneof the first problems to be thoroughly investigated will be porpoising—a particular form of instability when taking off from or alighting onthe water—which is found with many seaplanes that have beenconstructed in this country and abroad. The apparatus and modelfor this work are ready for experiment. Another tank of largedimensions but slower speed, built at the N.P.L. for commercialpurposes, will, it is hoped, be available for some comparative testson larger models.

AERODYNAMICSFlutter and Buffeting of Aeroplanes.—Researches on the nutter

of the wings and tail units of aeroplanes have been in progressthroughout the year, and have provided information which we hopewill be of considerable practicable value to designers. The generalcauses of this phenomenon are now well understood, but manydifficulties arise in practice in the strict application of preventivemeasures to particular designs. As the general level of speed ofaeroplanes rises it becomes more important to overcome thesedifficulties and therefore a good deal of further detailed work willbe necessary. There can be no doubt that this is one of the mostimportant factors affecting the safety of flight. The results ofinvestigations have already enabled us to lay down definite rulesfor the mass balancing of ailerons and rudders.

One particular flutter problem has arisen during the year inconnection with the servo rudder of a certain aeroplane. It hasbeen shown that correct balancing of the servo flap will overcomethe difficulty in this particular instance. Some more complicatedaspects of the servo problem are being examined with the objectof introducing improved types of servo control.

Theoretical and experimental work has also been undertakenat the N.P.L. on the flutter of airscrews, and a further programme ofwork on this subject, in co-operation with the R.A.E., has beenagreed. We expect that the type of flutter involving combinedtorsion and bending has been successfully covered by the investi-gations already made. There is, however, need for further researchon other aspects of the subject.

Buffeting, as is now well known, is a term given to a violentmovement of the tail structure of a machine caused by eddies fromthe wing. Its importance was first realised during the enquiryinto the accident at Meopham, and experimental investigations

lU.l'sl U \ \ ION No 3

R.A.E. Sf.ipl.mr Testing ' I , i n k .Tank C 'a i i i , i j ; c s l iounif i Crc.ir,

Towed ^^<)( l (• l , i n < l < ) l ) s e r \ ; i t i i>M I ' l . i t lorni

were put in hand. Dtiring the year the disturbed flow in the wakesof different wing sections has been examined and the results havebeen compared with earlier work. It has been shown that smallexcrescences on the wing, especially on the upper surface, may inducesevere buffeting. We have been much helped in these investigationsby information from a number of sources, including the FaireyAviation Company Ltd.

Spinning of Aeroplanes.—Knowledge of the spinning of aeroplanesis considerably more definite than it was a few years ago, and hasbeen helped by experiments in the vertical wind tunnel at theR.A.E. and by the analytical and wind tunnel work at the N.P.L.New dangers have arisen and we have accordingly had to reconsidercertain aspects of the spinning problem.

The Society of British Aircraft Constructors have asked whetherit would be possible to prepare simple design rules for the use ofaeroplane designers to guide them in making their machines safefrom spinning. At our request Mr. H. B. Irving has written amemorandum on our present knowledge, which contains a simplifiedstatement of interim recommendations regarding those featureswhich should, or should not, be incorporated in aeroplanes from thepoint of view of safety in spinning. This memorandum has beendiscussed and approved, and will shortly be published (R.& M.1535).

During the year full use has been made of the vertical windtunnel at the R.A.E. An outcome of this line of enquiry is the dis-covery that the slots of slotted wings may cause difficulties in aflat spin. A " family " of model aircraft has been chosen for testsin this tunnel, in which the effect of varying one property at a timewill be investigated. In the first series of experiments the wingposition and arrangement will be varied for monoplanes and biplanes,using a standard body and tail. Concurrently with this investi-gation a systematic research on the effect of different shapes ofbody and tail will be begun in the horizontal tunnels at the N.P.L.Some of these body-fin combinations will afterwards form the basisof tests in the vertical spinning tunnel, using standard wings anddifferent tail arrangements.

Stability and Control at and above Stall.—It is reported by pilotsthat some unslotted aeroplanes are more satisfactory than othersin respect of stability and control at angles in the neighbourhood ofthe stall. The reasons for the reported differences are not altogetherclear, and we consider that there is still need for both full scale andmodel experiments, to determine on the one hand the nature of thedifferences in behaviour which give rise to these diverse reports,and on the other hand the particular features of the aeroplanesto which the differences are due. Research on these matters isproceeding, but has not yet advanced far enough for a general reportto be issued.

Performance.—The development of means for visualising the airflow past models erected in wind tunnels and past the surfaces ofaeroplanes in flight will be of considerable interest to designers ofaircraft. We have therefore encouraged experiments in thisdirection. In 1928, Flight-Lieut. J. A. G. Haslam, working underProfessor B. M. Jones at Cambridge University, successfullydeveloped a method (see R, & M. 1209) whereby wool tufts wereattached to the surface of an aeroplane's wing and their behaviourwas watched during flight. When the air flow is steady the tuftslie along the wing surface, but when it is turbulent they either waveviolently about or even point forwards, thus showing the regionswhere the flow near the wing surface is reversed. Professor Jonesand Flight-Lieut, Haslam have continued the work and havepublished during the past year a further report (R. & M. 1494)describing a study of air flow over the •wings and tail during stalledflight and spinning. These and other methods of rendering airflow visible in a wind tunnel have been the subject of experimentsat the R.A.E. and N.P.L., and a recent report by the R.A.E.suggests that tufts provide most information and are simplestand quickest to use. We wish to take the opportunity of directingthe attention of designers to these simple methods. This investi-gation is being further developed both by the R.A.E. and by ProfessorJones, with whom Cambridge University Air Squadron at DuxfordAerodrome are co-operating.

The resistance and mutual interference of various parts of anaeroplane has been studied on models at the N.P.L. for a numberof years. A monograph on this work, R. & M. 1480, by Mr. E. Ower,has now been published, which includes a discussion of resultsobtained in this country and abroad. Many of the interferencephenomena are shown to fall into line with general principles whichare indicated by data from models chosen to exaggerate the effectsof interference. As a result of a joint meeting between represen-tatives of the Aircraft Industry and the Interference Panel, aseries of new tests will shortly be begun on models of more practicalinterest to aircraft designers.

Airscrews.—A great deal of research on airscrews having high tipspeeds has been carried out in recent years at the R.A.E. When thetip speed approaches the velocity of sound the efficiency usuallydecreases, and we consider that sufficient evidence has now beenaccumulated regarding the magnitude of this effect for an account:>f the whole subject to be prepared. Owing to the limitationsimposed by tunnel speed, tests have hitherto been made only withine pitch airscrews, but now that the high speed tunnel at theR A.E. is available the work is to be extended by tests on higherpitch airscrews. A report will shortly be published summarisingthe work so far carried out. Attention has been drawn to the

desirability of limiting the thickness of the blade section at thetip, but it would appear that an important objection to the thinsection is its small maximum lift coefficient.

With improved performance airscrews are now being used withhigher pitch/diameter ratios, especially on racing aeroplanes andhigh speed aircraft for the Royal Air Force. A research on thissubject has been commenced at the N.P.L., in order to obtaindata on airscrews whose pitch/diameter ratio extends up to a valueof 2-5.

Landing and Take-off Characteristics of Aircraft.—We have beeninterested in a question raised by the Society of British AircraftConstructors as to why some aircraft appear to float a considerabledistance just clear of the ground before touching, while others seemto alight in a very much shorter distance after flattening out.After a discussion the conclusion was reached that there is nothingin these differences of behaviour which cannot be explained byexisting theory and from a knowledge of the aerodynamic character-istics of the machine. The whole question of safe and easy landingrequires, however, further attention, and we are considering pro-posals for a comprehensive investigation.

The Director of Scientific Research, Air Ministry, has communi-cated a report by an Air Force Officer on his experiences during theR.A.F. South African Flight 1931, which indicated that, in certaincircumstances, a heavily loaded aeroplane, although able to takeoff, experienced difficulty in climbing from a few feet above theground to a height of 200-300 ft. Above this height the rate ofclimb became normal again. In discussion Dr. Simpson referred tothe very rapid fall of temperature with height in Ismailia, and theCommittee have asked for a number of experimental flights to bemade through this unstable atmosphere to determine whetherit has any marked effect on performance.

Autogiws.—We welcomed an opportunity last year to see atFarnborough an early flight trial of the new experimental winglessautogiro developed by Sefior de la Cierva. This machine is a greatadvance on previous designs ; the control is now independent offorward speed, with the result that both the vertical descent andtake-off are greatly improved and a more powerful control on theground is provided. The longitudinal and lateral control are effectedentirely by operating the axis of the rotor, which is tilted fore andaft or sideways. Recently the Committee have had an opportunityto discuss developments with Sefior de la Cierva.

We are keeping in touch with the progress of the new autogiro(of the wingless type) that is being built to Air Ministry order, andare examining certain problems of its stability and control.

Fluid Motion.—The projected memoir on problems of fluid motion(mentioned in last year's report) has not made the progress which wasexpected, on account of the illness of its general editor. To our

great regret, Sir Horace Lamb has felt obliged to relinquish thistask, but we are glad to report that Dr. Goldstein has consented toserve in his place, and work on the memoir has now been resumed.

Examination of the details of turbulent flow—by the ultramicro-scope, by smoke (titanium tetrachloride) and by photographing theshadows thrown by heated air—has been continued at the N.P.L.during the year, and light has been thrown on several questions whichhad formerly been in doubt. These matters hardly permit of briefdescription, and details are accordingly reserved for the Supplementto this Report.

Many theoretical papers have been received during the year,both from official and from independent sources. The problemsconsidered have included the transmission of heat from hot bodiesto fluid streaming past them, the flow of viscous and inviscid fluidspast obstacles of various shapes, the stability of certain types offluid motion, and the flow past aerofoils at speeds above that ofsound. Full mention of all these papers will be found in theSupplement on Fluid Motion.

ENGINESWe gave last year a general survey of the chief problems in aircraft

engine research. It was pointed out that the production of stilllighter petrol engines now depended mainly on improvements indetail, but that much remained to be done in promoting fuel economy,especially under cruising conditions. Following the developmentat the R.A.E. of a device for the automatic control of fuel-airmixtures, recent investigations have provided results of outstandinginterest. It has been shown that it is possible to reduce fuel con-sumption at the reduced power required for cruising to a figure verysubstantially below anything attained in flight hitherto. Thiswork is being actively pursued with a view to the reproduction inflight of results obtained on the test bed. Successful developmentalong these lines should be of considerable interest to civil airtransport.

Research on heavily supercharged single cylinder units has beencontinued. In the case of petrol engines it has been shown that theindicated power increases practically proportionally to the degreeof supercharge up to initial pressures as high as three times the normalpressure. It has been found, however, that whereas at ordinarypressures it is possible to get satisfactory combustion of weak mixturesof petrol and air, the effect of supercharging is to narrow the practicalrange of mixture strength. Apart, therefore, from the loss ofeconomy to be expected in a supercharged engine by reason of thenecessary lowering of compression ratio, and from having to drive itsown supercharger, it appears that definite limitations to the degreeof supercharging in practice may be imposed by difficulties of com-bustion rather than by mechanical considerations.

(17790—1) B

8

When compression ignition engines are supercharged the indicatedpower does not increase in proportion with the initial pressure.Theoretical investigations indicate that this difficulty is not likelyto be overcome by improvements in design, and therefore that theproduction of light compression ignition engines will not be facilitatedby heavy supercharging. A moderate degree of supercharging has,however, many advantages. As we stated in last year's report, weconsider that the development of the two-stroke compression ignitionengine holds out the greatest promise of success in the production ofa satisfactory power unit sufficiently light to compete with the petrolengine. (Illustration No. 4.)

At present, research is proceeding at the works of Messrs. Ricardo& Co. upon a sleeve-valve unit, and we are informed that there is alikelihood of the construction in this country of an alternative typeof 2-stroke engine in which two pistons are employed per cylinder.At the same time development is proceeding normally on varioustypes of 4-stroke engine, and with these valuable practical experienceis being accumulated.

Lubrication.—In our last report we referred to the setting up of aPanel of the Engine Sub-Committee to study problems of lubricationof aircraft engines. This Panel have now made a general survey ofthe present position, and have issued a preliminary report. Anextensive series of investigations has been started, including a studyof the oxidation of lubricating oils and of the methods by whichoxidation can be retarded ; experiments on these lines are being madeboth in the laboratory and in the engine. A search for suitable gumsolvents is in progress with a view to the early removal of the gummydeposits from the pistons if their formation cannot be prevented.

The stability of oils tends to decrease with increase of viscosity,and the extent to which it is possible in practice to use low viscosityoils is being determined by engine tests. Lowering the viscositytends to increase the oil consumption, i.e., the passage of oil past thepiston, and the Panel are putting in hand experiments to determinethe nature of the action of the piston rings in promoting the passageof oil past the piston.

The problem before the Panel is complicated, and some time islikely to elapse before their final report is issued.

Engine Power at Heights.—The problem of the variation of enginepower with height has been under investigation for many years.So far as the unsupercharged engine is concerned, the reductionfactor proposed has varied from one dependent solely on densityto one dependent solely on pressure.

The early Martlesham Heath experiments on the power law for thesupercharged engine appeared to indicate a density basis for fullysupercharged engines and a pressure basis for moderately super-charged engines. A recent re-investigation has not confirmed the

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ILLUSTRATION No. 4.Condor III B Compression Ignition Engine.

9previous results for supercharged engines nor the disparity betweenmoderately and fully supercharged types, but the results agreewith the conclusion adopted some years ago" by the N.A.C.A. fornormally aspirated engines, namely, that the'power varies as thesquare root of the product of pressure and density. It must beremembered that this is an approximate rule and does not necessarilyapply to a particular engine,

Fuels.—During the year we have reviewed the present positionof the supply of volatile fuels for aircraft engines. Clearly themost suitable fuel is that which has the highest possible contentof available energy per unit weight, and which can be used with thehighest thermal efficiency that mechanical considerations allow;but practice demands the use of fuels which are readily availableall over the world at a reasonable cost. The idea still seems prevalentin some quarters that there may some day be brought into use aliquid fuel with a substantially higher content of available energyof combustion per unit weight than the hydrocarbon fuels nowavailable. This we may say definitely is unlikely. On the otherhand available hydrocarbon fuels are not at present used with theefficiency that should be possible ; it is the fuel that sets a limit tothe achievements of designers of petrol engines. The use of dopes,such a tetra-ethyl lead, goes far to remove this difficulty but intro-duces other difficulties in practice : these are gradually yielding tocontinuous investigation in this and other countries. It is not,however, out of the question that a synthetic fuel may be producedwhich, though it may have no greater or even less available energyper unit weight than petrol, may yet have properties which permitof a higher thermal efficiency in practice. We shall explore any suchpossibility.

Flame Traps.—During recent years a satisfactory form of flametrap has been developed at the R.A.E. to prevent back-fires from theengine sending flames down the induction pipes. These flame trapsare made of thin sheet metal which divides the pipe into a largenumber of passages sufficiently small to cool and damp out anyflame travelling along the pipe. The traps have stood up to longperiods of artificial back-firing under test bench conditions, and havealso been flown for a number of hours in the air without any sign offailure. In view of these successful tests the Accidents Sub-Com-mittee have amended their recommendation, made some years ago,that, on account of the risk of fire, air intakes should preferably beplaced outside the fuselage of an aeroplane ; they now suggest thatwith a satisfactory flame trap the intakes may safely be placed insidethe fuselage. There are clearly other advantages resulting from theadoption of internal air intakes, for example, the absence of chokingin snow or sand storms, and it has been noted that general car-buration is improved, with the result of smoother running of theengine, when a flame trap is fitted.

:"30)—I B2

10STRUCTURES

Thin Sheet Metal.—In view of the use of thin metal sheet forconstruction work on aircraft, the types of failure of panels of sheetmetal are being investigated. The Bristol Aeroplane Company,Ltd., have collaborated in the work of designing and testing alarge cylindrical test specimen. Special specimens have also beenprepared and tested at the R. A.E, to supplement and extend the workof this Company.

The main object of the work .at the N.P.L. is the developmentof reliable theoretical methods for the determination of the strengthof structures built up from thin sheet metal. In the first instance,some experiments are being made on the collapse (as distinct fromthe buckling) of rectangular thin sheets, of which all four edges areclamped, under compression parallel to one pair of opposite edges.Similar tests on rectangular thin sheets of which all four edges aresimply supported have been carried out in America : the purpose ofthe N.P.L. tests is to determine whether the approximate theoreticalanalysis that has been applied with some success to the results ofthe American work can be adapted to the more practicable caseof the panel with all four edges clamped. As a result of these testsit is hoped to determine the critical strain that such panels willsupport without collapse, and it is considered that if the stiffenersare then designed to support the same critical strain withoutbuckling, the behaviour of the stiffened construction will be deter-minable.

Torsion of Metal Tubes.—The strength of steel tubes in torsionhas been investigated by Professor Andrew Robertson andMr. Newport of Bristol University. Tests were carried outon drawn mild steel tubes and on solid drawn tubes.

By their mode of failure the tubes can be divided into three classes,namely, thick tubes that first yield and then fail by shearing; thintubes that fail by elastic instability, their strength depending uponthe elastic properties and not upon the strength properties of thematerial; and tubes of intermediate thickness that first sustainthe shear yield stress of the material, and afterwards collapse bythe formation of wrinkles in the walls of the tube at stresses whichvary with the ratio of the thickness to the diameter. It was foundthat the stress at which yielding occurred was not independent ofthis ratio. This work has produced results of considerable interestto aircraft constructors.

Up to the present time no satisfactory theoretical analysis of thestability of thin walled tubes in torsion has been published. Theproblem has been considered by Japanese and German workers ;but since their analyses are based on the theory of thin shells, whichis open to objection as applied to the problem of a tube in torsion,the results must be regarded as inconclusive. This view is supported

11by the fact that the results of the two analyses do not agree eitherwith each other or with the results of the tests carried out byProfessor Robertson and Mr, Newport. The development of asatisfactory theory is therefore thought to be a matter of considerableimportance.

Reversal of Aileron Control.—A theory of the loss of lateral controldue to wing twisting has been produced at the R.A.E., based onthe behaviour of " semi-rigid " wings, together with a method offinding, by a process of successive approximation, the reversal ofcontrol speed for an elastic wing. The applicability of the semi-rigid theory to elastic wings was tested by comparing its predic-tions with the results of wind tunnel tests done at the N.P.L. on thelight aeroplane wing used originally for flutter experiments, and withthe results of the successive approximation method mentioned.It was concluded that the semi-rigid theory could be successfullyapplied to practical problems on loss of lateral control for wingsof normal design.

The N.P.L. tests on the light aeroplane wing showed that minorfactors which theoretically affect the problem, such as aileron gap,aileron hinge position, and aileron control lever position, are unim-portant in practice.

We are of opinion that satisfactory methods are now available forthe calculation of the critical " aileron reversal" speed of anyaircraft of normal type, provided that the necessary elastic and aero-dynamic data are available. We believe also that these methodscan be extended without much difficulty to aircraft of special types,such as those having multi-spar wings, or wings with stiff covering.

Stiffness of Wings.—Methods for calculating wing stiffness havebeen developed at the R.A.E., and in particular the effect of thewing ribs on wing stiffness and spar stresses has been studied. Forwings of normal design these methods appear to be accurate andconvenient in use.

Aeroplane Spars.—Considerable progress has been made with alengthy series of tests on seven aeroplane spars kindly supplied byaircraft firms, to discover whether existing methods of test forstrength and stiffness are satisfactory, and how they can be corre-lated with tests on the strip material from which the spars areconstructed, and for which various new types of tests are beingdevised and tried out. It has been proposed that the presenttests be replaced by tests (a) on a short length of spar under aslightly eccentric end load, (b) on a longer length of specimen todetermine the variation of the elastic constants, and (c) to destructionon the test piece used in (b). These proposals are being borne inmind, but the Structure Sub-Committee are not at the present timein a position to recommend any change.

12Professor Southwell has communicated a paper, since published

by the Royal Society, which shows that the problem of stresscalculation for a tubular framework, generally representative of arigid airship hull, can be solved exactly for any specified conditionsof loading. His method involves no appeal to consideration ofstrain energy, but obtains the required solution by a synthesis oftype solutions of simple form. It seems likely to have applicationsin problems concerned with fuselages of monocoque construction,and a paper has been written by Miss L. Chitty describing thepractical application of the method for the benefit of any who maywish to use it. The latter paper has been published as R. & M. 1528 ;further papers on similar lines are hi contemplation, dealing withother specific problems.

ACCIDENTSThe Accidents Investigation Sub-Committee are investigating a

series of accidents involving structural failures in the air of the Puss-Moth. They are not yet in a position to issue a report.

MATERIALSFatigue.—The influence of the atmosphere upon the fatigue

strength of metals has been investigated at the N.P.L. Com-parative tests on the fatigue of representative aircraft materialswere made in air, with and without a coating of lanoline grease, andin vacuo. As a further investigation of this effect, tests under alter-nating direct stresses were carried out on more uniform researchmaterials ; these showed that, when tested under very low pressuresin the absence of air, the fatigue strength of a mild steel was increasedby 5 per cent., of annealed brass by 26 per cent., and of annealedcopper by 13 per cent. Similar tests made in air on specimenscoated with lanoline showed that the effect of the coating was notprotective, the fatigue strengths being slightly lower in tests onuncoated specimens. The very considerable increase in resistanceto fatigue exhibited in the tests in vacuo make it apparent that,in normal tests in air, atmospheric corrosion may play an importantpart; but it is not yet decided whether this corrosion is to beattributed entirely to the oxygen or whether water vapour, actingeither independently or as a catalytic agent, is essential to theprocess.

A summary of the present state of knowledge regarding corrosionfatigue was given by Dr. Gough and presented last year as theAutumn Lecture to the Institute of Metals. Experimental evidenceshows that the effect of a protective film must be important; but itmay not be possible to attribute all corrosion fatigue phenomena tothe effect of such films : the stress or strain in the metal itself may bea direct factor in the process. Several suggestions have been made

13for experiments designed to determine whether corrosion fatiguedepends entirely on the behaviour of the film, but there seems to beno simple experiment that is likely to lead to a direct answer.

Welded Joints.—We have considered some problems of weldingbrought to our attention by the Society of British Aircraft Construc-tors and makers of aluminium alloys. Although sound welds inheat-treated alloys can now be made without difficulty, the materialin the immediate neighbourhood of the weld necessarily loses theproperties due to heat-treatment, and to restore its full strengthsubsequent heat treatment and cold work, or, in some cases, coldwork alone, would be required. In the case of aircraft structures,neither of these operations would as a rule be practicable afterwelding, and therefore the use of welding commonly involvesconsiderable reduction of the strength of high tensile alloys.

We are taking steps to collect available information on this subjectfrom aircraft constructors and elsewhere in order to decide whetherany scientific investigations would be helpful.

Magnesium Alloys.—Several papers have been received from theR.A.E. on methods of protection of magnesium alloys against corro-sion. A more detailed account of this work will be found in theSupplement.

SEAPLANESThe important subject of the porpoising of seaplanes has been

dealt with in several papers communicated during the year. Thefirst paper (R. & M. 1492, by Mr. Garner), describes a series oftests on a scale model to investigate the effects of changing thethrust line and centre of gravity, fitting wings and tail, applyingpitching moments, and preventing the vertical movement of themodel. The model was found to be unstable for certain positions ofthe thrust line and centre of gravity, and for certain applied moments;the effect of the wing and tail was to stabilise the model considerably.1*Yhen vertical movement of the model was prevented no instabilitywas found.

A theoretical analysis of the motion of a towed model (outlinedin the above paper) showed that instability is most likely to ariseon account of the effect of certain factors associated with the verticalmotion; the theory has been examined in some detail in a paperV R. & M. 1493), by Mr. Perring and Mr. Glauert, and approximateexpressions have been deduced for the derivatives.

These calculations of stability are based on very crude data, butthey suggest that, provided the ratio of the mass to the momentof inertia about the lateral axis is kept correct, the porpoisingcharacteristics of the seaplane hull will be predicted correctly. Itis hoped that the systematic experiments now being undertaken atthe X.P.L. will provide data from which more complete computa-tions can be made of some of the quantities involved in the analysis.

14The R.A.E. Seaplane Testing Tank will also be used for tests ondynamically correct models, complete with wings and control surfaces,free to porpoise during their run, and apparatus is being designedfor the measurement of the derivatives required for the calculationof stability.

A visit was paid by the Seaplane Sub-Committee to the R.A.E.to view the Seaplane Testing Tank which was running satisfactorilyat the beginning of the year 1933. An early series of experimentsto be carried out in this tank will consist of measurements of resistanceon two similar models of lengths 4 ft. 6 in. and 9 ft., and on a pair ofthe 4 ft. 6 in. models tested simultaneously. A comparison of theresults will show whether the wall effect on models of these sizesis small, or, if large, whether it is capable of accurate estimation.Further experiments will test the effect of the depth of water on theresistance and other characteristics.

In our report last year we referred to the work in hand at Felix-stowe hi which the water resistance of a large scale model of theSingapore II hull was being measured by attaching it to a MothSeaplane. We have now recommended that a second hull of themodified Singapore II type should be constructed for test in the sameway. It is hoped that occasions will be found when the waterconditions are sufficiently smooth for some results to be obtained onthe first hull while it remains serviceable. The second huh1, whichwill be of the same design as the model tested recently in the WilliamFroude Tank at the N.P.L., might be used both for resistance andpressure plotting measurements.

The first part of the N.P.L. programme of seaplane research hasbeen completed and a report of the model tests on the Singapore IIhuh1 is in preparation. The other experiments in the WilliamFroude Tank will be on a pair of surfaces in tandem ; in thisconnection two similar models with the same angle of V but adifferent beam have been chosen, in order to obtain experimentalresults from which some of the stability derivatives necessaryfor the calculation of porpoising characteristics can be deduced.

ATMOSPHERIC TURBULENCEIn order to record the intensity of the accelerations to which

aircraft are exposed when flying in bumpy weather, a number ofnights have been made from Farnborough of aeroplanes fitted withrecording accelerometers. Flights have been made on four typesof aircraft whenever gusty weather was expected; the resultsobtained are of considerable interest and value, and we wish torecord our appreciation of the work carried out by the pilots, forthe records show that the conditions must frequently have beenextremely unpleasant. The maximum accelerometer readingsrecorded normal to the flight path were 2-Sg. and — 0-6g. respec-tively. Although flights were made on every occasion of high winds,

15the year was unusually free from really bad weather, and it is feltthat further observations should be made during gales. Flights will,therefore, continue to be made at Farnborough when it is anticipatedthat the gradient wind will exceed 30 m.p.h., unless the conditionsare such as to render flying dangerous, e.g., in the near neighbourhoodof thunderclouds and line squalls.

We think it important to collect statistical information by fittingaccelerometers to aircraft, both service and civil, which are carryingout routine flights, in order to obtain records over long periods oftime. It is considered that from such records valuable informationwill be obtained regarding the stresses likely to be imposed onaircraft structures by gusts.

NOISEA paper (R. & M. 1542) on the silencing of aircraft has been

written by Dr. A. H. Davis in a form intended to be suitable for theuse of aircraft designers. It gives figures for the loudness levels ofvarious noises that occur in houses, in streets, and in differentvehicles, and for the noise levels of airscrews, of exhausts and ofengine clatter. Reference is made to the insulating value of varioustypes of cabin wall, and to the importance of locating the power plantin some favourable position. Results of noise measurements madein various types of commercial air liner are presented and analysed.A tentative table is given from which it is possible to assess the orderof loudness of the noise in the cabin of a machine, provided thesituation of the engine, of the exhaust and of the airscrew are known,in addition to data concerning the tip speed of the airscrew and thestructure of the cabin walls. The analysis proves to be in generalaccord with the results of experiments which have been carried outon testing plant. This paper has been circulated to members ofthe aircraft industry.

Interesting results have been obtained from experiments on ex-haust silencers manufactured by Messrs. Rolls Royce, Ltd. Onthe test bench the silencer was shown to be capable of reducingexhaust noise by a very large amount, but on the aeroplane the totalnoise level is not reduced by this amount, because after a certainreduction the airscrew noise predominates. Different types of enginecowling had no effect on the noise levels, so that engine clatter was not:n this instance of importance. The conclusion reached is that unlessairscrew noise can be substantially reduced, it is not of importanceto proceed to extreme limits in silencing the engine exhaust.

We wish to record the valuable co-operation and assistance givento the Aircraft Noise Sub-Committee by Dr. W. S. Tucker and theWar Office staff at Biggin Hill.

RELATIONS WITH OTHER BODIESAs in previous years, we have held meetings with representatives

of the Society of British Aircraft Constructors.

16We have been in touch with the Aeronautical Departments of the

Governments of Canada and Australia on various matters of commoninterest.

We are obliged to the Australian Branch of the Royal AeronauticalSociety for information communicated to us in connection withcertain aircraft accidents in that country.

We had the pleasure of welcoming Dr. J. S. Ames, the Chairmanof the National Advisory Committee for Aeronautics, U.S.A., inSeptember, 1932. We are indebted to him for much useful informa-tion, and to the N.A.C.A. for help and co-operation in several mattersthat have been the subject of correspondence. In addition weshould like to acknowledge the courtesy shown to Professor R. V.Southwell on the occasion of his visit to the United States of Americaduring the past year.

(Signed)H. T. TIZARD,

Chairman.