TWENTY-THIRD ANNUAL REPORT

OF THE

NAL ADVISORY COMMITTEENATI(FOR AERONAUTICS

1937

INCLUDING TECHNICAL REPORTS

NOS. 577 to 611

UNITEDSTATES

GOVERNMENTPRINTINGOPFICEWASHINGTON:1838

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TECHNICAL REPORTS

JNO.577. Prwhamber Comprwion-Ignition Engine Per-formance. By CharleaS. Moore and John H.Cdl@ Jr-------------------------------

No. 678. Flight Measurement of the Dynamic hngi-tndinal Stability of Several Airplanm and acorrelation of the MemmrementaWith Pilots’Observationsof HandlingCharaotiristies. ByHartley A. WU16-------------------------

No. 679. A Study of the Tw#lntrol Operation of anAirplane. By Robert T. Jon~-------------

No. 580. Hent Tranafer to Fuel Sprays Injected IntoHeated Gaaee. By Robert F. Selden andRobert C. S@ncer ------------------------

No. 5S1. Measurementsof Intensity and Scale of Wind-Tunnel Turbulenceand Their Relation to theCrMeal Roynolde Number of Spheres. ByHugh L. Dryden, G. B. Schubauer, TV. C.Mock, Jr., and H. K. Skrarnstad-----------

No. 682. A Theory for Primary Failure of Straight Cen-trally Loaded Columns. By Eugene E.Lundquietand Claude M. Fligg------------

No. 683. The Rolling Friction of SeveralAirplaneWheelsand Tiresand the Effect of Rolling FriotiononTake-Off. By J. W. Wetrnoro-------------

No. 684. Strength of Welded Alromft Joints. By W. C.Bme~eun -----------------------------

No. 585. Span Laad Distribution for Tapered WingeWith Partii+pan Flaps. By H. A. Pearson-

No. 586. Airfoil Secticm Cbaracteristim aa Affeoted byVariations of the Reynolds Number. ByE&man N. Jacobs and Albert Sherman----

No. 587. Blower Cooling of Finned Cylinders. ByOscar W. Schey and Herman H. Eller-broak, Jr--------------------------------

No. 688. Fuel Spray and Flame Formation in A Com-premion-IgnitionEngineEmploying Air Flow.By A. M. Rothrock and C. D. Waldron-----

No. 589. An Analysis of Lateral Stability In Power-OffFlight With Charts For Use In Design. ByCharlesH. Ztiermn-------------------

No. 590. Presaun+llistribution Meammements of AnO-2H AirplaneIn Flight. By H. A. Pearson-

No. 691. An Analytical and Experimental Study of theEffect of PeriodiaBlade Tw@t on the Thrust,Torque, and Flapping Motion of an AutogiroRotor. By John B. Wlieatley----------___

No. 592. Full-scale Te@a of N. A. C. A. Cowlings. ByTheodore Theodorsen, M. J. Brevoort, andGeorge W. StioMe------------------------

No. S93. Cooling of AirplaneEnginesAt hw Air Spexis.By Theodore Theodormn, M. J.Brevoort, andGeorge W. StioMe------------------------

No. 594. Characterieticaof Six Propellers Including theHigh-SpeedRange. By TheodoreTheodorwn,George W. Stickle, and M. J. Brevoort-----

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49

69

76

91

109

141

169

177

209

227

269

281

297

319

353

361

391

401

Yo. 595. Full-Scale Tats of A New Type N. A. C. A.Nose-Slot Cowling. By Theodore Theodor-sen, M. J. Brevoort, George W. Stickl~ andM. N. Gouge----------------------------

No. 596. Cooling Twt of A Single-Row Radial EngineWith Several N. A. C. A. Cowlings. By M.J. Brevoort, George W. Stickle, and HermanH. Ellerbrock, Jr-------------------------

No. 597. Air PropellersIn Yaw. By E. P. Lealey, GeorgeF. Worley, and Stanley Moy---------------

No. 598. Alternating-CurrentEquipment For the Meas-urementof Fluctuations of Air Speed In Tur-bulent Flow. By W. C. Mock, Jr----------

No. 599. Flight Tests of the Drag and Torque of the Pro-@ler in Terminal-Velocity Dives. By Rich-ard V. Rhode and Henry A. Peareon-_------

No. 600. An Analyaieof the Factors That Determine thePeriodio Twiet of an Autogiro Rotor Blad~With A Comparison of Predicted and Meas-ured R.emlta. By John B. Wheatley-------

No. 601. Toreion Tests of Tubes. By Ambrose H. Stang,Walter Ramberg, and Goldie Back---------

No. 602. Wind-Tunnel and Flight Tests of Slo&LipAilermw By Joseph A. Shortal-----------

No. 603. Wind-Tunnel Invwkigationof Wmge With Ordi-nary Ailerons and Full-Span External-AirfoilFlaps. By Robert C. Platt and Joseph A.Shorti ---------------------------------

No. 604. Premure-Distribution Measurements At LargeAngles of Pitch On Fins of DiEerent Span-Chord Ratio on A l/40-Scale Model of theU. S. Airehip “Akron”. By Janw G.McHu@--------------------------------

No. 606. R&mrn6and Analyeie of N. A. C. A. LateralControl Ikearoh. By Fred E. Weiok andRobert T. Jon---------------------------

No. 606. Electrical Thermometer For Aircrdt. By JohnB. Peterson and S. H. J. Womack-_--------

No. 607. Spinning Characteristic of the XN2Y-1 &-plane Obtained From the Spinning Balanceand Compamd With RemdtaFrom the Spin-ning Tunnel and From Flight Teds. By M.J. Bamber and R. O. House---------------

No. 608. Strew Analysis of Beams With Shear Deforma-tion of the Flanges. By Paul Kuhn------_-

No. 609. llxperimental Investigation of Wind-Tunnel In-terference On the DowmvaahBehind an Air-foil. By Abe Silvemteinand S. Katzoff-----

No. 610. Teatsof Related Forward-CamberAirfoils in theVariableDensity Wind TunneL By EastmanN. Jacobs, Robert M. Pinkerton, and HarryG-&~ -------------------------------

No. 611. Wind-Tunnel Investigation of Tapered WiigsWith Ordinary Ailerons and Partial-SpanSplit Flaps. By Carl J. Wenzinger---------

111

Pma

439

449

459

475

493

503

516

537

563

586

605

633

649

669

689

697

733

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LEIYl?ER OF TRANSMITTAL

To THE CONGRESS OF THE UNITED STATES:In compliance with the provisions of the act of March 3,1915, establishing the Nationsl Advisory Committee

for Aeronautics, I transmit herewith the Twenty-third Annual Report of the Committee covering the ficnl yearended June 30, 1937.

l?RANKLIN D. ROOSEVELT.

The TVHITE HOUSE,January 7,1998.

v

LETTER OF SUBMITTAL

NATIONAL ADVISORY COmmEE FOR AERONAUTICS,

Wmhington, D. C., Novender 29,1937.Mr. PRESIDENT:

In compliance with the provisions of the act of Congress approved March 3,1915 (U.S. C., title 50, sec. 153),I hove the honor to submit herewith the Twenty-third Annual Report of the National Advisory Committee forAeronautics covm@ the ilscal year 1!337’. .

During the past year the United States has maintained its position in the forefront of progressive nations inthe technical development of aircraft for both military and commercial purposes. This has been due chiefly tosound organization and liberal support of scientific laboratory research in aeronautics in this country.

The War, Navy, and Commerce Departmem%, having equal representation on the Gmunh%e, cooperate inevery way in its work, and each receives the results of the scientific investigations conducted. Thus the researchneeds of all branches of aviation are met without overlapping or duplication of effort. The C!ommittee’s activi-ties, however, are limited to research. They do not include experimental engineeringin the application of researchresults to the development of military, naval, or commercial aircraft.

The greatly increased interest of the major powers in fostering aeronautical research and their determinedefforts to excel in this rapidly advancing engineering science constitute a scientific challenge to America’s presentleadership. It is the responsibility of the National Advisory Committee for Aeronautics to see to it that theUnited States will not become dependent upon any foreign nation for fundamental scientific data on which to basethe design of American aircraft. To do this effectively it will be necessary that this Committee continue to havethe liberal and far-sighted support of the President and of the Congress.

Respectfully submitted.JOSEPH S. bm, Chairman.

THm PRESIDENT,The White Howe, Wmhington, D. (?

VII

NATIONAL ADVISORY COMMJTI’EE FOR AERONAUTICS

HEADQUARTERS,NAVY BUILDING,IVASHINGTON.D. C.LABORATORIES,LANGLEYPI13LD.VA.

Created by act of congress approved March 8, 1915, for the supervision qnd direction of the scientificstudy of the problems of fight (U. S. Code, Title 50, Se~ 151). Its membership was increased to 15 byact approved March 2, 1929. The members are appointed by the President, and serve as such withoutcompensation.

JOSRPHS. AMES, Ph. D., CtiirmanjBaltimo~ Md.

DAVIDW. TAYLOR D. Eng., Vice ChairnwqWashington, D. C.

WILLIS RAY GREGG,Sc. D., Chairmaq Executive Committee,Chief, United Statea Weather Bureau.

WILLIAMP. MCCRACKEN, J. D., Vice Chairmq ExecutiveCommitt4e,

Washington, D. C.CHARLESG. &BOT, Sc. D.,

Secretary, Smithsonian Institution.LYMAN J. BRIGGS,Ph. D.,

Director, National Bureau of Standards.ARTHUR B. COOK, Rear Admiral, United StR~ Navy,

Chief, Bureau of Aeronautics, Navy DepartmentFREDD. FAGO,JR., J. D.,

Director of Air Conuner- Department of Commerce.

HARRY F. Gu(lmmmmr, M. A.,Port Washington, Long Island, N. Y.

SYDNRYM. KRAUS,Captain, United States Navy,Bureau of Aeronautics, Navy Department.

CHARLESA. LINDBRRQH,LL. D.,New York Ci@.

AUGUSTINEW. ROBINS,Brigadier General, United StatesArmy,

Chief Mat&riel Division, Air Corps, Wright Fiel&Dayton, Ohio.

EDWARDP. WARNER,M. S.,Greenwich, Corm.

OSCARWBSTO~ Major General, United States Army,Chief of Air Corps, War Departnwk

OR~ WRIGHT,Sc. D.,Dayton, Ohio.

GEOROEW. LEWIS,Direakw of Aeronautical Research

JOHN F. VICTORY,SecretaW

HENRYJ. E. REID,EngineeAn-Churge, Langley Menwria 1 Aeronautical Laboratory, Langlq Fie@ Vu.

JOEN J. IDE, Technicul A8eistunt in Euwoe, Pati, France

TECHNICAL COMMITTEESAERODYNAMICS AIBCRAFTSTRUCTURESPOWERPLANT%FORAIBCRAPT AIRCRAFTACCHmNTSAIRCRAPrMATERIAIS INVENTIONSANDDESIGNS

Coordinatwn of Research Nee& of Militmy andCM Aviation

Preparation of Research Programa

LANGLEY MEMORIAL AERONAUTICALLANGLEYPH3LD.VA.

Allocation of Problems

Prevention of Dupliccutwn

Consideration of Invent&ma

LABORATORY OFFICE

Unified conduct, for all agencies, ofscientific research on the %damentalproblems of flight.

OF AERONAUTICAL INTELLIGENCElvASHINGTON,IL C.

Collection, classiikation, compilation,and dissemination of scientific and tech-nical information on aeronautics.

Ix

THE NEW N. A. C. A. FREE FLIGHT WIND TUNNEL IN WHICH INVEST1GATIONS OF AIRPLANE STABILITY AND CONTROL CHARACTERISTICS CAN BE MADE ON ANAIRFIANE MODEL m FREE FLIGHT.

TVVENTY-THIRDANNUAL REPORT.

OF THE

NATIONAL ADVISORY COMMITTEEFOR

AERONAUTICS -WA-GTQN, D. C., ~OVW&’?’ 10,19$7.

To tb Oongre-88of tlt.e Um’ted iNa&28:In accordance with the act of Congress approved

March 8, 1915 (U. S. C., title 50, section Ml), whichestablished the National Adviwry Committee forAeronauticsj this Committee submits herewith itstwenty-third annual repo& covering the fiscal year193’7.

Responsibilitiesof this organization.-The prescribedfunctions of this organization are to “supervise anddirect the scientific study of the problems of flight,with a view to their practical solution,” and to Wirectand conduct research and experiment in aeronautics-”In the discharge of its functions under the law theprimary responsibilities of the National AdvisoryCommittee for Aeronautics are: (1) To recqpize inadvance the tiend of aeronautical development, civiland military; (2) to anticiprtte the research problemsthat will arise; and (3) to design and provide researchequipment to meat the needs of this rapidly advancingenbtieering science, and then to conduct the necessaryscientific investigations.

Created by law in 1915 as on independent Govern-ment establishment,the Committee, with the consistentand liberal support of the President and of the Con-gress, has gradutiy developed a large and vrell-equipped aeronautical research laboratory at LangleyField, Vir=tia. In this laboratory it has conduqtedfundamental scientfic research in aeronautics with thesincere and indispensable cooperation and assistanceofthe Wm., Navy, and Commerce Departments. As aresult, the scientific basis for aircraft design in theUnited Stales for both military and civil uses is notexcelled in any other country. Long adherence tosound policy has won for the United States generalrecoatition as a leader among the probave nationsin improving the performance, efficiency, md mfetyof aircraft.

The continued improvement in the performanm ofboth military and commercial aircraft has confrontedthis Committee with a variety of problems that are

pressing for immediate solution. Among examplw ofsuch problems may be mentioned the need for devisinga method. for studying the stalling characterisb ofhighly tapered wings; the determination of the nems-sary load factors and their variation with size andspeed; the problem of reducing or eliminating if pos-sible the formation of ice on winag, propellers, andcontrol surfaces, and of providing effectively for theautomatic removal of ice when it does form; problemsinvolved in the design of wings, control surfaces, andflaps, as well as other devices to secure better controlat low speeds incident to tnking off and landing; prob-lems of suppressing vibration and flutter, improving .engine and propeller efficiency, capacimj and clepemla-bility, extending the range, enlarging the capac&,and at the same time constantly increasing the speedand safeQ of aircraft.

In addition to meeting urgent needs of the present,the Committee tries to look into the future and toanticipate some of the problems that may arise. Forexample, what are the maximum requirements for mili-tmy and commercial aircraft going to be ? Will speedsin excess of 400 miles per hour be required ! .How muchwill the size of commercial aircraft exceed 60 tonswithin the next few years? What are the problemsthat will require scientific analysis before such craftcm be successfully designed and constructed? Willairships be further developed for naval use or fortransoceanic transportation and, if so, whnt are funda-mental problems this Committee should investi=@e ?

The organizationof researah.-To analyze the presentand probable research needs of aviation, civil and mili-tary, the N. A. C. A has set up standing technicalsubcommittee on aerodynamics, power plants for air-craft, aircraft mwterials,and aircraft structures. Thesubcommittee are oqgmized along lines similar to themain Ckmunitteeand include specially qualified repre-sentatives of all the governmental agencies concernedwith aeronautical development, as vmll as experts fromprivate life. The members of the subcommittees, likethe members of the main Committee, se’rve as such

1

2 REPORT NATIONAL ADVISORY COMMITL’EE FOR AERONAUTICS

without compensation. The subcommittees prepareand recommend research programs. The more funda-mental problems are usually assigned for investigationat the Committee’s laboratory at Langley Field, Vir-ginia, primarily because of its special equipment foraeronautical research. Problems am also assigned tothe National Bureau of Standardsj so as to make thebest use of available Government facilitkx and at thesame time to avoid duplication in the field of aero-nautical research. In the same manner problems areassigned and funds transferred to universities andtechnical schools. In this way aeronautical reseamhis stimulated and coordinated.

Advances in the science of aeronautics have givenrise to various trends, as the possibilities of aircraftincrease. At the present time the tmmd of design ofaircraft in all nations is definitely toward higher speedsand larger structures, with greater range and carry-ing capacity. This is true in both the military andcommercial fields. Scientific and technical problems donot diminish but on the contrary incm in numberand in d.iilicuky with each advance in speed or size.It is the duty of this Committee to supply the funda-mental data on which the dwign of new aircraft isbased. If the Committee does not meet this responsi-bility adequately, the United States will quickly fallbehind, because of the great emphasisnow being placedon aeronautical resenrch and development by otherprogressive nations.

Research facilities.-Up to 1932 the Committee hadconstructed at its laboratories at Langley Field, Vir-ginia, known as the Langley Memorial AeronauticalLaboratory, special equipment such as the variable-density tunnel, the propeller-research tunnel, the full-scde tunnel, and the hydrodynamic laboratory-a ma-plane towing basin. They were at the time of con-struction the only such piecm of equipment in theworld. The possession of such equipment was one ofthe chief factors in enabling the United States to be-come the recognized leader in the technical develop-ment of aircrafi Since 1932 this research equipmenthas been reproduced by foreiag countries and in somecases special resnrch equipment for the study ofproblems in aeronautics has been developed and con-structed abroad which is more modern than and su-perior to the equipment existing at Langley Field

Since 1932 the importance of scientific research inaeronautics has been more generally appreciated byEuropean nations and several of the larger powers have~mtly augmented their research facilities and actiti-tiw The competition in the development of researchequipment and facilities between the progressive na-tions is just as intenseas the competition in the produc-tion of airmaft of superior perfornmnca This condi-tion has impressed the Committee with the advisability

of providing additional facilities promptly as neededfor the study of problems that are newssary to besolved, in order that American aircraft development,both mil$ary and commercial, will not fall behind,

In answering this soientitlc challenge the Cmnmitteehas under construction at its Moratories at LangleyField a new-wind tunnel having a diameter of 19 feetthat can be operated under a pressure of three or moreatmospheres at an air speed of mom than 200 miles perhour. This tunnel will permit the investigation of thecharacteristk.s of large models of aircraft at muchhigher values of Reynolds Number than can be obtainedin any of the Committee’s existing wind tunnels, TheCommittw also has under construction a refrigeratedwind tunnel for the investigation of the problems ofice formation on aircraft. This tunnel has throat di-mensions of 7~2 by 3 feet and will embody featuresand principles which, it is believed, will make it meffective instrument for the purpose intended.

The Committee during the past year developed anentirely riew type of wind tunnel. The experience ofthe CQmmittee in the operation of the free-spinningwind tunnel indicated the advantage of being ~ble toreproduce and observe aircraft motion under controlled ~conditions in a wind tunnal. Methods of studying stn-bility, control, and motion of an aircrwft in previoustypes of wind tunnels, where the model is fixed on abalance, are long and laborious, and leave much to bedesired in accuracy. Realizing the need for studyingstability, control, and motion of a model of an aircmftwhen flying unrestrained, the Committee developed inthe past year a new form of wind tunnel known as a%?rwMight wind tunnel.”

The & tunnel of this type constructed was 5 feetin diametm, rmd was so arranged that by tilting thetunnel ita longitudinal axis could be set parallel tothe glide path of the model under test. To do this thetunnel was suspended from above at a single point sothat the axis of the wind tunnel could be varied througha wide range of anglw, making this tunnel what mightbe called a %ilting wind tunnel.”

The results obtained with this small tunnel were soencouraging that the Committee proceeded with theconstruction of a free-flight wind tunnel having adiameter of 20 feet.

With the establishment of commercial service acrossthe Pacific Oman by seaplane transports and the enrlyprospect of such wvice acro~ the Atlantic, operatorsand designers are focusing their attention on aircraftof larger sizes having improved eEciency and carlyingmore paswngers and a hemier mail and express load.The design of the seaplane hull is a most importantfactor affecting the eficiency of transowmic transports.Anticipating the need for extensive investigation ofseaplane hull models in comection with the develop-

RHI?ORT NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS 3

ment of larger seaplanes, the COmmi@ d~ing thepmt year modernized its hydrodynamic laboratory.The towing basin was lengthened from 2,000 feet to2,900 feet. The towing carrkge was enlarged and theoperfiting speed increased so that investi~gtions cannow be made at speeds corresponding to the highertake-off and landing speeds of seaplams.

The Cohunitteds laboratories are on a portion ofLangley Field assi=~ed to this organization by theSecretary of War and are under the direct cantrol ofthe Committee. The Committee’believes that iti lab-oratories, despite the recent great eq?enfit~ on I’S-search organizations abroad, are as yet unexcelled bythose of any other single nation. In addition to thenew research equipment under construction as notednbove, the Committed laboratories include: An 8-footi500-mile-per-hourwind tund; a 60- by f10-foot full-scale wind tunnel; a 20-foot propeller-research tunnel;a &foot variable-density wind tunnel; a 7- by 10-footwind tunnel; a &foot vertical wind tunnel; a M-footfree-spinning wind tunnel; two high-velocity jet-typewind tunnels of 11- and 24inch throat diameters, re-spectively; a hydrodynamic laboratory; an engine re-search laboratory; a fight research laboratory; and aninstrument research laboratory.

Relation of Committee’swork to national defense.-Therelationship of the work of this oratiation to nationaldefense has long been recognized and appreciated by theWar and Navy Departments. The Army and Navy, airoqymizations rdy upon the N. A. C. A. to anticipabnnd to meet their research needs and thus to enablethem to achieve and maintain leadership in the highlycompetitive field of military aircraft development.The snfety and security of our countxy in time of warmay depend upon a decision in the air. The com%eofa war will mrtairdy be influenced in favor of that sidewhich can gain supremacy in the air. Sound tacticalorganization, large numbers of aircraft, sutlicienttrained personnel, and ample productive capacity inthe industry are not in themselves suftlcienti The air-craft that engage the enemy in action must, if possible,be superior in perfomnanca The hope of retaining ourpresent superiority in technic.d development, in theface of the increaskg emphasis being placed upon aero-nautiwd research and development abroad, will dependhugely upon the ability of this organization to solvepromptly and effectively the fundamental problems at-tendant upon rapid progn=s in this branch of engi-neering science.

In this connection, the economic value of the workof this organization is worthy of referenca The pro-curement programs of the Army and Navy call for theexpenditure of lar=- sums ta carry into effect thenational defense policy approved by the Congrw. Un-les the aircraft procured are at least equal in perform-

anm to thow possessedby other nations, their net valueto the Army and Navy in time of war would be almostat the vanishing point. A national investment in in-ferior military aircraft would not only invite the risk ofloss of the aircraft in time of war, but also the trainedflying personnd. It would be as disappointing ~ddisastrous as it usually is to try to win on the second-best hand in a poker game. Without up-to-date, re-liable results of scientific laboratory resaarch, ourArmy and Navy would not be able, even with the mostsincere cooperation of the industry, to design and pro-cure aircraft with any assurance that they would notbe “second best” in time of war.

Commercialaviation.-The continued search for trendsof development, and the effort to meet these trendsby the provision of adequate research facilities andinvestigation of the right problems, ako have a veryimportant bearing upon the development of commer-cial aviation. Researches initiated primarily to meetmilitary needs are in many cases broadened in scopeto meet the needs of commercial aviation. Researchproblems peculiar to commercial aviation alone arealso investigated. The Committee is materially as-sisted in this respect by suggestions from the Bureauof Air Commerce and from the air transport lines.Aircraft manufacturers also offer reseaich SugaWtionsand are alert to incorporate changes which the Com-mittee’s researches indicate will improve the safety oreficiency of aircraft. That the United States leadsthe world in the development and operation of com-mercial aircraft is due not alone to this healthy condi-tion, but also in large measure to the national policy ofair mail payment and to the indispensable asistanceof the Bureau of Air Commercein providing unexcelledair navigation facilities and otherwisa helping in everypracticable way to promote the safe~ and efficiency ofair navigation. We cannot in this connection under-estimatethe importance of the meteorological servim ofthe Weather Bureau in aid of safety, nor the numerousand valuable contributions to commercial aviation thathave resulted from the experiments and developmentson aircraft, engine9, “instruments, and acceswries bythe Army and Navy.

Our growing air transport business iinds a healthyreflection in an aircraft production industry betterequipped to respond to the needs of national defense intime of emergency. A healthy nucleus of an aircraftindustry capable of rapid expansion in time of need isessential to our national defense. If it were not forthe stimulation and support given the manufacturersby the growth of commercial air transportation in theUnited States.,the aircraft industry would be so muchwaker that, in view of disturbed world conditions atthis time, there would be need for some form of arti-ficial stimulation and development of productive W-

4 REPORT NATIONAL ADVISORY

pacity. That we are not confronted with such aproblem at this time is due partly to the fact that theresults of the Committee’s researches have made pos-sible the development of commercial air transports inthe United States superior to those of any other coun-try. This has not only facilitated a rapid growth ofcommercial air transportation in this country, but hasgiven to the American aircraft industry an advantagein world markets, evidenced by orders received fromforei=~ countries for commercial airplanm of Amer-ican manufactum.

The improved eficiency and safeQy of Americanair transports have permitted economies h operation,which in turn have resulted in materiaJless8ning of thecost of carrying air mail and of passenger fares.

Economiovalue of reseamh.-No money estimati canbe placed upon the economic value of greater nationalsecuri~ through development of the means of produc-ing superior military aircti Nor can a money esti-mate be placed upon the economic value of lives andproperty saved through improvements in the safe~ ofaircraft. Nor can the educational advantages offeredby air travel, the time saved, and the pleasure affordedto passengers be evaluated, nor $0 value to the nationof extending its national influence through world traderoutes of the &ir. The researches of this Committee,however, do have a tremendous economic value thatcan be measuredin dollars and cm%. Improvements inaircraft that have resulted from the Committee’s inves-tigations and that have a definite economic value arenumerous. Careful computations have been made ofthe economic value of a few of the more important con-tributions of this. organization. These indicate thatthe annual savings in money made possible by the Com-mittee’s researches exceed the total appropriations forthis organization since its establishment in 1915.

&mnnary.-WNh the rapid expansion. of aviation innational defm, it is more than ever necessary thatfacilities be available for the prompt and adequatestudyof thow fundamental problems in aeronautics that in-fluence the speed, range, capacity, and cmtrol ofaircraft.

COMiUI!LTEE FOR AERONAUTICS

The Committee believes that the future development sof American aeronautics is largely dependent upon thesupport and effort given to the orderly and sustainedprosecution of fundamental scientific research. It isthe cordident hope of the CommitW that the UnitedStates will never be in a position where fundamentalinformation necessary for the design of aircraft ofmaximum performance, efficiency, and safety will haveto be impotid from any foreign nation.

In commercial aviation the major problem is one ofimproving safety without penalizing those factors thatare necessary to increase the speed, efficiency,operatingrange, and comfort of aircraft. When this Committeewas establishedover twenty-two years ago there was butlittle appreciation of the value of aeronauticsto natiomddefense and practically no appreciation of the possibfi-tie9 of aircraft in commerce.

Aviation has now become such an important factorin national defense, in the promotion of transportationin the United States, and in the extension of inter-national commerce and good will that the organizationand conduct of aeronautical research have attained thegreatest si.g.gc.ante and importance.

Forei=gn nations me making determined efforts todesign and produce superior research facilities and todevelop superior aircraft, both civil and military. TheCommittee in order fully to meet its responsibilities isendeavoring to modernize, improve, and augment its re-search facilities so as to maintain the present advantageof the United States.

To assure effective functioning on the urgent prob-lems of the Army ahd Navy in time of war means forstabilizing the personnel of this organization must befound. From a study of the problem thus far it wp-pears that enactment of legislation for this purposemay be necessary.

The Committee believes that the results achieved inthe past and the problems to be faced justify a con-tinuation of the liberal support of its work, and it fur-ther believes that in order to secure the best resultsthere should be no change in its functions or in itsstatus as an independent Go-rerhmentestablishment.

PART I

REPORTS OF TECHNICAL COMMITTEES

Ill order tO carry out effectively ib principal f UUC-Ction of the supervision, conduct, and coordination ofthe scientillc study of the problem of aeronautics, theNational Advisory Committee for Aeronautics has es-tablished a group of technical committees and subcom-mittees These technical committees prepare and rec-ommend to the main Committee programs of researchto be conducted in their respective fields, and as a remitof the nature of their organization, which includes

representation of the various agencies concerned withaeronautics, they act as coordinathg agencies, provid-ing effectively for the interchange of information andideas and the prevention of duplication.

In addition to its standing committees and subcom-mittees, it is the policy of the hTationd Advisory Com-mittees for Aeronautics to establish from time to timespecial technical subcommittees for the study of par-ticular problems m they arise.

During the past year there has been a major changein the orewnization of the Committee’s standing tech-nical committees. The Committee on Aircraft Struc-tures and Materials, which was one of the threeprincipal technical committees, its Subcommittee onStructural Loads and Methods of Structural halysisand the latter’s Subcommittee on Research Proa~amon Monocoque Design have been replaced by two co-ordinate cornmittem,both reporting direct to the mainCommittee, namely, the Committee on Aircraft Mate-rials and the committee on A~craft s~ct-. ~change wcs made in recognition of the greatly in-creased importance of the problems of structural designin the field of aeronautics, and of the need for greaterconcentration of effort on these problems.

With this change in organization, the Committeehas four principal technical committ~the Commit-tee on Aerod~amics, the Committee on Power Plantsfor Aircraft, the Committee on Aircraft Material% andthe Committee on Aircraft Structures Under thesecommittees there are six standing subcommittees.The membership of these technical committees andsubcommittees is listed in Part II.

The Committees on Aerodynamics and Power Plantsfor Aircraft have direct control of the aerodynamicand aircraft-engine research, respectively, conductedat the Committee’s laboratory at Langley Field, andof special investia@ions conducted at the National Bu-

reau of Standards. Most of the research under thesupervision of the Committee on Aircraft MateriaJs isconducted by the National Bureau of Standards. Thegreater part of the research under the cognizance ofthe Committee on Aircraft Structures is carried on bythe National Bureau of Standards, but a number ofstructural investigations, especially those of a theoreti-cal nature, are conducted at educational institutionsand at the Committee’s laboratory at Langley Field.The four technical committees recommend to the mainCommittee the investigations in their respective fieldsto be undertaken by educational institutions under con-tract with the National Advisory Committee for Aero-nautics, and keep in touch with the progress of thework and the results obtained, The experimental in-vestigations in aerodynamics, aircraft power plants,aircraft materials, and aircraft structures undertakenby the Army Air Corps, the Bureau of Aeronauticsof the Navy, the National Bureau of Standards, andother Govenmmnt aggncies are reported to these fourcommittees.

REPORT OF COMMITTEE ON AERODYNAMICS

LANGLEY MRMORL4L AERONAUTICAL LABORATORY

L.4NDmGSPEEDANDSPEEDRANGE

F1.aps.-Tbe use of TV@ flaps on high-performanceairplanes is no-iv almost universal. The research thathas been conducted by the Committee during the pastseveral years on the most promising forms of flaps hasresulted in establishing their relative merits and hasmade possible the selection of the most satisfactorytype for a given design. During the past year, attm-tion has been directed mainly toward obtaining morespecific design data for flap application.

In the variable-density wind tunnel, tests of ordi-nary and split flaps of 20-percent wing chord on theN. A. C. A. 23012 airfoil have been made with a largerange of flap settings at a value of the effective Reyn-olds Number of about 8,000,000, for the purpose ofproviding designers with mom reliable data as to theairfoil section characteristics for these combinationsat lar=g values of the Reynolds Number. While theresults have not been completely analyzed, they cor-roborate, in general, the conclusions drawn from pre-vious tests at lower values of the Reynolds hTumber.

5

6 REPORT NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS

The split flap is somewhat more favorable to speedrange and landing speed than is the ordinary flap.

In the 7- by 10-foot wind tunnel a study of slottedflaps is under way in which tests of flaps of variousshapes with slots of various forms are being con-ducted on an N. A. C. A. %3012vving of 3-foot chord.With this installation, airfoil characteristics corre-sponding to a Reynolds Number of about 2,500,000am being determined. The resuh% to date indicatethat with a properly desi.aed slotted flap, ~USU~Yhigh maximum lift coeilicients may be obtained. Iiaddition, very low profle drag coeilicienti at high liftcoefficients may be obtained with the flap deflected,which should result in improved take-off and climbcharacteristics. For controlling the glide-path angle,the slotted flap may be deflected beyond the angle formaximum lift without appreciably ehangjng the liftcoefficients. With this @e of operation, the flap issimilar to the glide-control flap previously dewibedin Technical Note No. 552.

The results of the investigation in tight and in thefull-scale wind tunnel, of a Zap flap mounted on aFairchild 22 airplane, previously mentioned, have beenpublished in Technical Note No. 596. Results of asimilar invwtigation on the external-airfoil flap arepresanted in Technical Note No. 6(!4.

Tests have also bem made in the ‘7- by lo-foot windtunnel for private companies and for the Bureau ofAeronauti= of the hTavy Department of the aerody-namic characteristics of saveral models equipped withflaps.

Maxwell slot.-The results of tests of another devicefor the improvement of speed range, the Maxwell lead-fig-~an ~ot,, mentioned ~ ]s.%year’s repor$ have beenpublished in Technical Note No. 698.

Measurementof miui.mumspeed.-Opportunity was af-forded during the year, in connection vviththe investi-~gdion of the maximum lift coefficient of a 21L12 vvingon a Fairchild 22 airplane, to obtain a comparison be-tween the flow conditions in flight and in the full-scalewind tunnel and thus study the effect of various testprocedures and conditions on the measured minimumspeed of an airplane. The main fight program coveredthe effect of wing loading and altitude on minimumsped By extension of the prcgmm the effects of pro-peller position, throttle setting, wing-surface roughnes,and the rate at which the angle of attack was increasedviere investigate+ It vm.sfound that for a constantweight the minimum speed might vary by 5 percent,depending on the fictom. The masimum lift coefficientobtained with one loading cannot k directly appliedto the computation of the minimum speed with anotherloading, because of the variation of the lift coefEcientwith speed.

CONTROLANDCONTROLLABILITY

For a number of years the Committee has been en-gaged in a systematic wind-tunnel investigation of lat-eral control with special reference to the improvementof control at low air speeds and at high angles of at-tack. Many different ailerons and other lateral-controldevices have been subjected to the same systematicinvestigation in the 7’- by 10-foot wind tunnel and the

; devices that seemed most promising have been testedin fight. As has been stated in previous reports, tilewind-tunnel and fight resultswere not always in ngree-ment and indicated tha$ in determiningg actual controleffectiveness from wind-tunnel results, it was necessaryto include what had been previously considered sec-ondary factors. A mathematical method of analysiswas consequently developed to include those secondnryfactors and this method of analysis has been in use forabout two years.

The experience gained has resulted in a revised bnsisof comparison of lateral-control devices and on this re-vised basis a critical rtitl and analysis of the Com-mittee’s research to date on lateral control has beenmade and has been published in Technical Report No.605. The analysis indicates that for normal-flight con-ditions, ordinary ailerons with the gap between theaileron and the wing sealed”arethe most generally sat-isfactory. An added advantage of these ailerons is thatithey appear to be practically free from icing hazds.

Slot-1ipailerons,-l%e complete results of the wind-tunnel and tlight investigation of slot-slip ailerons hnvebeen published in Technical Report No. 602. It wnsstated in the last annual report that slot-lip aileronsinstalled on a Fairchild 22 airplane produced unsntis-f actmily sluggish control, although such sluggishnesswas not detected by the pilots when thew ailerons wereinstalled on the W1–A airplane. An analysis mndeduring the year has shown that the di.ilerencebetweenthe response of the two airplanes is esplai.mble by thedi%’erencein their lateral-stability characteristics. Al-though some reduction in the drag of the slot-lip niler-ons over thnt previously reported was obtained with amodMed slot shape, the drag of this type of aileron isstill considered excessive for modern high-perform-ance airplanes.

The wind-tunnel investigation mentioned last yenrof the special form of slot-lip aileron, consisting of aplain aileron forming the trailing edge of an airfoil&quipped with an extend-airfoil flap, has been com-pleted. The characteristicsof these ailerons on an N. A.C. A. .%O12wing equipped with 20 and 30 percent chordfull-span external-airfoil flaps of the same section weremeasured and are reported in Technical Report No. 603.TIwse ailerons were found to be capable of developinglarge rolling moments but the hinge moments hnd cer-

REPORT NATIONAL ADVISORY COMhDTTEIil FOR AERONAUTICS 7

.

tain undesirable characteristics and should receivefurther study.

Ailerons on tapered wings,-At the request of theArmy Air Corps an investigation of the efkctiven~of conventional ailerons on a tapered wing vm.smadefor direct comparison with a straight wing havingnilerons of the same size. A 2:1 tapered wing withconventional flap-type aileron was mounted on a l?air-child 22 airplane and investigated in flight and in thefull-scale wind tunnel. Conventional ailerons on thiswing were found to be slightly more effective thanailerons of the same dimensions on a straight wing.The improvement was of the order of only 5 percentat low speed, and was so slight that it was not ap-parent to the pilots in the handling of the airplane.The results are being prepared for publication.

An investigation of ordinary sealed ailerons on twowings having medium and high taper ratios and par-tial-span split flaps has been described in TechnicalReport No. 611. The report presents aerodynamic in-formation nec=ary for aileron design, including roll-ing, yawing, and hinge moments, as well as the aero-dynamic characteristics of the wings.

Floating wing-tip ailerons.-Comparative tests meremade in the full-scale wind tunnel and in flight to de-termine the relative effectiveness of floating-tip aile-rons and conventional trailing-edge ailerons. Thetests were made on a Fairchild 22 airplane equippedwith a 2:1 tapered -ivingthe wing tips of which couldbe removed and replaced by floating-tip ailerons. Thefloating-tip ailerons were made as large as seemedreasonable from considerations of structi weight.These ailerons were found to be approximately one-half as effective in producing rolling moment as con-ventional ailerons on the same wing. The floating-tipailerons produced small favorable yawing momentswhile the trailing-edge ailerons produced appreciableunfavorable yawing moments

Combinationsof spoilers.-At the request of the Bu-reau of Aeronautics of the Navy Department, the late-ral-control possibilities of combinations of spoilersarranged in tandem were investigated in the 7- by 10-foot wind tunnel. Since the time of response withsuch an arrangement was questionable, the investiga-tion consisted primarily of measuring the responsecharacteristics by means of a motion-picture study ofthe motion of a wing model restrained by springs butfree to move when the control device was operated.The rolling moments produced by the control deviceswere measured with the same installation. It wasfound that while a combination of front and rearspoilers without lag was possible, no improvement incontrol was obtained over that with the rear spoileror retractable aileron alone when the wing vmsequipped with a full-span flap.

Reduotionof aileron control forces,-With the increasein size and speed of airplanes, increased interest hasbeen shown in means of reducing the forces requiredto operata ailerom On a large percentage of airplanesaerodpmmic balances of the Frise or slotted types areused, with an accompanying loss in control effective-ness. In addition, such balances, with their projectingsurfaces, are subject to icing Wliculties.

The use of trailing-edge tabs in the conventionalmanner to balanm the control forces of ailerons is ac-companied by a sacrifice of some control effectiveness.A less conventional but apparently more succesfulmethod of applying tabs to ailerons is to use a verynarrow-chord full-span tab to increase the up-floatingangle of the ailerons by deiiecting the tabs downwardon both ailerons in conjunction with a proper d.itler-ential movement of the ailerons. A study of aileronhinge moments as aflected by dillerential linkages hasbeen made and the results published in Technical NoteNo. 586. The value of a tab and ditlerential linkagesystem has been investigated with a large wing in the7- by 10-foot wind tunnel and on a Fairchild 22 air-plane in fight. The abili@ of the arrangement to re-duce the control forces to any desirable value was veri-fied in both installations.

The flight investigation, in addition to verifying, ingeneral, the principles involved in the theoreticalanal-ysis, has indicated certain practical details requiringfurther study. The effect of the tabs on the aileronfloating angle appears to be critically dependent on thetab shape. Tabs consisting of flat plates extendingback of the aileron trailing edge were found to havevery little effect on the aileron floating angle and con-sequently little effect on the control forces, whereastabs inset within the aileron contour me satisfactory.

Wind-tunnel tests have shown thnt the effectivenessof a given aileron may be increased considerably bysealing the gap between the aileron leading edge andthe wing to prevent leakage of air at this point. Theeffectiveness of the sml is greatest for narrow-chordailerons, the increase being of the order of 50 percentwhen the aileron chord is about 10 percent of the chord.The increase in effectivenessmaybe utilized to improve”the controllability or, if the controllability is satisfac-tory, to redum the control forces by the substitutionof a smaller sealed aileron for one having a gap at thehinge.

The actual application of this system of improvinglateral contrcd or reducing aileron stick forces de-pends on how much leakage occurs at the hinge in anormal aileron installation. In order to study thisproblem, measurements -weremade of the lateral con-trol of the Fairchild 22 airplane, which has aileronshaving a chord of 18 percent of the wing chord, withthe original aileron hstallation and with a fabric seal

8 REPORT NATIONAL ADVISORY COMiUITTEa FOR AERONAUTICS

over the gap at the hinge. A 30-percent improvementin the control effectivenesswas obtained. On the basisof thesa findings, sealed ailerons of half the chord ofthe ori.fial ailerons, or 9 permnt of the wing chord,were installed on the airplane. These ailerons areabout as effective ns the original unsealed ailerons butrequire less than half the operating effort.

Two-control operation of an airplane.-Control of anairplane by means of two controls instead of the threenormally used has appeared to offer promise of simpli-fying the operntion of an airplane. Flights have beenmade with airplanes in which both aileron-elevator andelevator-rudder combinations were utilized for two-con-tiol operation, but considerable uncertaiu~ remains asto which of these modes of operation is likely to provethe better and also whether either of them is capableof affording the controllability required for safety inflight.

In order to obtain additional information on thesubject, an analytical study was made of two-controloperation of a conventional airplane by the method ofthe theory of disturbed motion nnd is presented inTechnical Report No. 579. Control maneuvers werecomputed for various combinations of rolling and yaw-ing moments with an rtirplane for which the lateral-stability derivatives were varied. It was conchdedthat, while the most dwirable control characteristicswould depend somewhat on the lateral-stability chm-acteriaticsand on the rate of application of the controldevice, the two-control operation of an airplane -wouldlie most generaUy satisfactory with controIs which gaveprimarily a rolling moment with a slight amount offavornble yawing moment.

l?lying qualitiesof huge airplanes.-b was mentionedin the last annual report, a research is in progress todetermine how much is known quantitatively regard-ing the actual stability, controllability, and maneuver-ability of large airplanes, and also -whatthe procedureshould be in any investigation to determine these char-mteristk in quantitativeform. During the past yeara progrnm of investigation in flight covering the meas-urement of all the quantities believed to be of impor-“tanca with respect to flying qualities, hns been formu-lated, the instrumentation developed, and the programsuwxdully tried with a single-engine five-plain high--wing cabin monoplane. Some mod.iikations in theoriginal progyun regarding the measurement of thegeneral stabili~ and the effectiveness of the ruddercontrol mere indicated to be desirable. The modiiiedprogram and certain items referring to asymmetricpower conditions that could not be invwtiggted witha single-engine airplane are being studied with a twin-enbtie bombardment monoplane, and the measurementshave been initiated on modern transport airplanes.

Flight with unsymmetricalyower.-The problem offlight with only the propellem on one side operathg

was investigated as part of the investigation of thepower-on characteristics of large multi-engine modelsin the full-scale tunnel.

Flight with zero yaw, accomplished by banking theairplane slightly to balanm the side forces due to tlmpropellers and rudder, was found preferable to balanc-ing the side forces by yawing without banking, both nsregards the maximum cdi.ng and the rudder deflectionrequired. For unqmmetrical power conditions, the10S.SCSin performance, aside from the reduction of thethrust, are due to the drag of the inoperative propellersand the deflected rudder. The propeller drng is themajor item urdessthe propeIler is feathered or alIowedto free-wheel.

mANEuvlmABnITY

At the request of the Bureau of Aeronautics, NavyDepartment, the Committee is undertaking an investi-gation of the maneuverability of several Navy airplanesprimarily for the purpose of determiningg the maximumangular accderntions in pitch and roll to which themachines may be subjected. The tests have been com-pleted on two airplanes. The investigation includesmeasurements of the angular accelerations in rollingproduced by abrupt use of the ailerons alone rmd alsoby combined use of the ailerons and other controls.Pitching accelerations are investigated in abrupt pull-ups from level flight and in recoveries from verticaldives. In a.Ucases the angular accderations me cor-related with the linear accelerations of the center ofgravity. In addition to the memurements of angularacceleration, information is being obtained on the pres-sure inside the wings during vertical dives and data areobtained to compam the lo= of aItitude in recoveriesfrom dives with that predicted by means of charts de-veloped as a result of previous investigations.

In connection with the study of the vertical-divemaneuver, the velocity-altitude relations for airplaneshave been studied. Charts have been prepared (Tech-nical Note No. 599) that present in a readily usableform the solution of the relation betwwm time, veloci~,and altitude for airplanes having various terminalvelocities. The variation of density with nltitude istaken into account on these charts.

ST.mIIJm!

A review of all available previous and contemporarywork on stabili~, which wns mentioned in the lnstannual report, has been completed and an estensive pro-gram outlined for systematic research in the variousfacilities available to the Committee. Work is now inprogress upon several of the projects deemed to be themost urgent.

The investigation of new equipment for the study ofstability is being continued. An experimental 5-footfree-fight wind tunnel has been developed to a point

REPORT NATIONAL ADVISORY COMbJ3TCEEl FOR AERONAU!TXX3 9

of satisfactory operation. This tunnel can be used tostudy the free-flight behavior of models up to 22 inchesin span, With a tunnel of this type it is possible toinvestigate inherent and controlled stability, motion ingusty air, stalling ch&acteristics, the power of controls,and many other factors directly related to the actualfree-flight behavior of the airplane. Even at the verylow scale of tests possible in the present i5-foot tunnel,observation of model behavior has led to very inter-esting conclusions regarding the effect9 of such factorsas the adverse yawing moments of ailerons, the effectof the position of the wing wake on the damping oflongitudinal oscillations, the behavior of an aircraftwhen the tail is in the violent wake behind deflectedsplit flaps, etc. The free-flight tunnel, of which thepresent 5-foot experimental version is the ~ and onlyone of the type, gives promise of greatly facilitatingthe entire study of aircraft motion. .

Iaferal Stability.-Most existing work on stabilitydeals with the inherent stability of the craft itself withthe controls either tied or free. Actually, the mostusual condition of flight is that in which the aircraftis held to a detlnite course by either a human pilot ora compass-controlled automatic pilot. The pilot en-deavors to bring the craft back to the course after adisturbance and in so doing alters the stability char-acteristics. A study of the stability of controlled mo-tion along a definite course is now in progress andshould show the effects of various ways of using thecontrols. It may also lead to a mod.iikation of presentideas regarding the importance and proper values ofcertain factors which affect the motion, since the pres-ent ideas are based on requirements for inherentstability.

In any study of stability with referenm to a certaincourse, it is of ~-t practical importance to know howthe factors that govern the stability iniiuence the mag-nitude and violence of the motion when an atmosphericdisturbance is encountered. A mathematical study ofmotion in gusty air is being carried out and is ap-proaching completion for the case of lateral motion.

A report on latwal stability in power-off flight hasbeen published as Technical Report No. 589. Thisreport parallels Technical Report No. 521, which dealswith longitudinal stability. It includes discussions ofthe problem and of the individual factors involved. Anumber of charts are presented from which the lateralstability of a new desiamcan be quickly and easily esti-mated

One of the factom that most critically affects thelateral-stability characteristics is the rate of change ofyawing moment with change in sideslip. There hasbeen considerable uncertain~ as to what allowanca tomake for the effect of the fusela=mwhen this factor isestimated. During the past year, the Committee has

undertaken a study of all readily available data on thisfactor with a view to developing suitable empirical re-lationships for its estimation. A technical note is beingprepared giving the results of this investigation.

The investigation of the effect of tip shape and di-hedral of rectangular monoplane wings on the lateral-stability characteristics, reported last year, has yieldedbasic information on the subject. For practical appli-cation to complete airplanes,however, the wing-fusdageinterference would eeem to be an important factor indetermining the stability characteristics. Quantiixkiveinformation on this effect will be obtained from aninvestibmtionthat has been started in the 7- by 10-footwind tunnel with fuselages of various cross sections andwith tapered, swept-back, swept-forward, and rectangu-lar wings.

Longitudinal staMlity.-Work is now in progress ona general study of longitudinal stability with poweron. An attempt is being made to prepare charts simi-lar to those in Technical Reports 521 and 589 to enablethe designer to estimate quickly the effect of power onthe stability.

The investigation of wing-fuselage interference inprogress in the variable-densi~ wind tunnel has beenextended to include the study of the effects of addingtail surfaces to typical combinations. Conventional tailsurfams and horizontal tail surfaces with end plates amboth being investigated with a view toward exploringthe parameters of combination as ailecting the aerody-namic interference, particularly as regards longitudi-nal stability. The effect on the moment of the tail sur-faces entering the wing wake is noticeable but small,particularly when compared with the effect of the wingstal.L

The analysis, reported last year, of the htmizontaltailsurface required for airplanes equipped with wing flaps,has been completed. A rational system for computingthe horizontal tail area was evolved and has been pre-sented in Technical Note No. 597.

A comprehensive investigation has been undertbin the Committee’s full-scale wind tunnel to determinethe effect of propeller operation on the importaut char-acteristk of airplan~ such as the lift, stabili~, con-trol, balance, etc. Full-scale data have been obtainedfor five airplane9 havingdiffersnt geometrical arrangwments, and a report presenting an analysis of thesa re-sults is in preparation. Th* tests include measure-ments of the air-stream velocitim and downwash anglesin the region of the tail. plane, and a study is beingmade to determine the variation qf thw quantitieswith the propeller thrust. -,

Stalling.-The problem of avoid@ excessive dangerfrom the stall has been a recurrent one. Most airplanemanufacturers dealt with the problixn rather satisfac-torily several years ago, either empirically or through a

10 lU3J?ORT NATIONAL ADVISORY COMMITTED FOR AERONAUTICS

reasonably smmd understanding uf the phenomenon,gained as the result of research work both here andabroad

In general, the .s&tions embodied the use of increasedstatic longitudinal stabili@, thus provi~u a definitewarning of the approaching stall thro~oh the backwardmovement, position, and forces on the control column,togw%erwith a gradually developing stall securedeitherby allowing the upper or lower wing of a biplane tostall first or by the use of monoplanes with little or notaper and with “poor” wing-fuselage juncturcq whichfurther tended to bring about a gradually developingstall, be=tiing at mid-span. These nbasures assuredthat the stalled condition would develop progressivelyafter a reasonably definite vmrning; furthermore, lat-eral control was often maintained up to or beyond thestall (wing maximum lift), owing to the fact that theessentially effective parts of the wing system remainedunstalled even after the angle of attack had exceededthat of maximum lift. lhsmuch as the pilot has littlaincentive to ~g beyond this point, such a solution wasand still is considered satisfactory.

With such satisfactory solutions in common use, atitention has for the past few years been diverted fromthe problem of minimihg stall@ dangers. Recentlyhowever, modern design trends are bringtig theproblem back again in an acute form. These tiendsare toward higher wing loadings and landing speeds;the substitution of efficient high-speed sections havingmore sudden and hence less desirable stdli.ug charac-teristic; the ahnost exclusive usaof tapered-wing mono-planes; the use of increased taper; the low-wing posi-tion which contributes to reduced longitudinal stabilitywith increasing lift; the use of ‘good” wing-fuselaamjunctures; and, flmd.ly, high-lift devices. The high-Iift devices may further add to the dangers of tip stall-ing, add to balance and stability Wliculties, and usuallycause a vicious section stall corresponding to a sudden,large, and usually unsymmetrical 10s of lift.

These trends have already gone so far. that it nowappenrs that many airplanes in common use cannotbe considered reasonably safe, even for experiencedpilots. The worst offenders may give no indication ofan approaching stall which, when it occurs, is mani-fested by a vicious uncontrolled rolling dive, that re-sults from a sudden loss of lift on the right or leftwing and a simultaneous loss of lateral control.

During the year practical methods of avoiding theseconditions in modern @es of airplanw have beensought.. The investigations have proceeded mainly onthe theory that the vicious stall may best be avoidedin monoplanes by causing the wing to stall progressivelyfrom the center toward the tips Not only are the sud-den 10S of lift and violent roll thus avoided, but lat-eral control is maintained through the first Sta=m of

the stall and the tendency toward an upwash on thetail surfaces asociated with the loss of lift near thecenter of the wing may be umd to bring about amarked increase in longitudinal stability as the stallis approached.

In the flr-stinvestigation. conducted in flight, sharpleading-edge strips extending out along the wing fromeither side of the fuselage were employed to bring aboutthe desired symmetrical center-stalling characteristic,Wiid-tumml experiments with airfoils having sharpleading-edge sections over a small portion near theirmidspan had indicated how the flight investigationshould proceed. The flight investigations for the power-off condition showed that an airplane having viciousstalling characteristics could be improved as expectedby thus bringing about a gradually and symmetricallydeveloping center stall. The extreme maximum liftcoe5cient was, of course, slightly reduced, but the prnc-tical gliding or approach speed was not increased; infact, it was actually reduced. This phase of the flightinvestigation is, however, only preliminary in that theairplane tested had no flaps or other high-lift devices,whereas the problem is of most practical interest andis probably more dii3icult when high-lift devices nreemployed. The investigations are being extended.

The method employed to start canter stalling may beobjectionable on the grounds that the sharp leadingedges will always tend to reduce the maximum lift.An irmstigation in the variable-density tunnel of meth-ods of accomplishing the same result without loss ofmaximum lift led to the development of a new cle-vice known as the %tdl-contrel flap.” The flap tendsto produce a well-rounded lift curve similar to thatproduced by the sharp leading edge but, together witha split flap or other conventional high-lift device, highmaximum lift coefficientsmay be obtained. A specialwing incorporating a stall-control flap has been con-structed and installed on an F–22 airplane converted toa low-wing type. Flight tests are now being started onthis airplane and from preliminary results it appearsthat, besides bringing about the desired center stall,several attendant advantages, such as favorable inducedyawing moments from the ailerons, may be realizedthrough its use.

sPnmmG

The 15-foot free-spinning wind tunnel has been keptbusy with routine testing of scale models of specificairplanes The ?&d4riel Division of the Army AirCorps, and the Bureau of Aeronautics of the NavyDepartment, are requiring spinning tests of modelsof new designs that are expected to be spun extensivelyin service. Four such models have been tested duringthe past year and three more are being prepared fortesting in the immediate future. The work carried on

REPORT NATIONAL ADVISORY COMM.H?J!DEIFOR AERONAUTICS 11

in this connection includes not only tests of the par-ticular design, but also investigation of changes neces-sary to improve the spinning characteristics where suchchanges appear to be necessary.

The free-spinning tunnel is available for the testingof models for commercial concerns, and two such modelshave been tested during the year.

A certain amount of general information is beinggleaned from the test results with speciiic designs.Conclusions stated in the last annual report regardingthe importance of the tail unit in spinning have beenconfirmed and amplified during the past year. & aresult of tests of a number of models of modern low-wing monoplanes, it now appears possible to draw cm-tain conclusions about the effect of changes in mass dis-tribution on such designs. In most cases the spinningcharacteristics of low-wing types have been improved,ancl in no casa have they been impaired, by movingweight from the fuselage to the win~ This fact isof special significance in view of the present trend to-ward multi-engine airplanes with the engines in thewinaw.

During the past year a method has been developedfor measuring, on free-spinning model% the hinge mo-ment required to reverse completely the rudder duringthe spin. Such measurementshave been made on threemodels. Indications are that the requirements of rapidrecovery from the spin and reawnably low rudder mo-ments me in c8rtain cases very difficult to meet witha rudder that is also satisfactory in normal ilighti

In nddition to the spinning of models of specific air-l)lnlles, a ~stematic investigation is being carried outin the free-spinning tunnel to determine the effects ofchanges in wing arrangement, in tail arrangement andmnss distribution. This investigation is about 20 per-cent completed. It is designed to reveal the relativeimportance of the various factors which affect spinningnnd to show which of these factors is most deservingof more detailed study. The results to date tand to con-firm the conclusion that the tail arrangement is the mostimportnnt single item. The effects of wing plan formnnd tip shape are, however, of considerably greater im-portance than has hitherto bean thought to be the cam.The effect of wing section appears to be relatively slight.

Tests of a model of the Fleet airplane on the spinningbalnnce, reported last year, have been published asTechnical Report No. 607. h investigation on thespitig balance of effect of wing plan form on th~spinning characteristics has also been completed andthe results published in Technical Note No. 612. Thetests included a rectangular wing with square tips andwith rounded tips and a tapered wing with roundedtips. An investi5@ion in progress will show the effec~of nirfoil section on the spinning characteristics ofmonoplanes with rounded tips.

An investigation on the spinning balance of the effectof stagger of rectangular biplane cd.lules has beencompleted and will be the subject of a repoti Therange of stagger investigated was from negykive25 per-cent stagger to positive 25 percent stagger. While nogeneral conclusions can be drawn regarding the effectof stagger, the resultscan be nsad in studying the stendyspinning characteristics of particular airplanes.

Tests for the purpose of making a direct mmparisonbetween the actual spinning behavior of a low-w@monoplane and the behavior of a model of the same nir-plane in the spinning tunnel have been started Someditliculty and delay have been encountered in obtaininga suitable airplane for the tests. Two have been triedin tligh~ With one, the oscillat@ nature of the spinmade measumments impossible. With the second air-plane, the rudder forces built up to such a magnitudeon the entry into the spin as to make it extremely un-certain that the pilot could supply the form newsnryto assurethat the airplane would recover from the pro-longed spins required for the measurements. The me-chanical advantage available to the pilot in operatingthe rudder of this airplane was increased and the forcesthat the pilot had to apply were reduced to the extentthat it was possible to continue the tests.

TAEX-OFF

The results of the investiagtion of the rolling frictionof airplnne wheels,mentioned in last year’s report, havebeen published in Technical Report No. 583.

h the calculated prediction of the take-off perform-ance of airplanes, common practice has been either toneglect the transition period between the end of theground run and the be@ming of the steady climb orto take it into account by assuming a simple motion,since the actual motion is too complex for simple mathe-matical treatment. This lack of knowledge re=guiiingthe motion of the airplane in the transition introduces,of cours~ a deegreeof uncertainty into the results. &mentioned last year, an investigation of this phase ofthe take-off was fi”dertaken in an tiort to eliminate thisuncertain@. The study is now completed and the re-sults are being prepared for publication. It was foundthat the calculated value of the air-borne distance re-quired in taking off over a 50-foot obstacle might besubject to an error of about 10 percent if the transitionis neglected.

The investigation served also to emphasize the dit3i-culties which are encountered in attempting to obtainrepresentative comparisons directly from take-off tests ‘and which arise from the fact that it is practicallyimpossible for a pilot to conform exactly to a pre-scribed procedure throughout a series of complete take-offs, particularly if the air conditions are not abso-lutely steady. At present an attempt is being made to

12 REPORTN~TIO~ALAD~SORY COU!lTIJll EORAERONAIXIXCS

deveIop a method whereby the true take-off capabilitiesof an airplane may be evaluated vvithout considerationof the personal element or the air conditions. Onesolution that appeam promising is to determine fromindividwd tests the relation between ground run, dis-tance, and speed, and the relation between angle ofclimb and speed, the latter to be measured at some alti-tude where smooth-air conditions prevail. These quan-tities should not be appreciably affected by pilotingand when properly combined, together with a suitableallowance for the transition, should provide an accu-rate measureof the take-off perfomnance of an airplane.An investigation has been made to determine the feasi-bility of this system and the results are being analyzed.

The characteristics of the propeller producing thethrust are an important inlluence on the take-off.Available propeller data have to a great extent beanrendered inadequate bec.ausaof the chmq+s in designnecessitated by higher engine power and airplaneSPeedS,requiring lmbg= propellers of higher pitch andwith three or more blades For the purpose of estab-lishing the desiag factor for propellers in this category,an extensive investi5@ion on full-scale propellers hasrecently been made in the propeller-research wind tun-nel. The investi=ntion is more completely covered ina later section of this report.

The above-mentioned investigation that -was madein the variable-density wind tunnel of ordinary andsplit flaps of 20 percent of the wing chord on N. A.C. A. 23012 airfoils indicates that neither of these flapscan be considered a satiefactory high-lift device forw in take-off because of the high profle drag causedby these flaps at high values of the lift coe5cienk Inthis respect the ordinary flap is inferior to the splitflap. At any value of the lift coefficient where theflaps are useful, a lower value of the pro~e drag coeffi-cient can be obtained with the split flap than with theordinary flap.

The stall-control flap previously mentioned, espe-cially when combined with a low-drag trailing-edgehigh-lift device, appears to offer improvements in thetake-off characteristics of flying boats and airplanesequipped with three-wheel landing gears, because thisflap permits high lift coefficients to be obtained withthe airplane in a level attitud~

LANDmG

Landing loads.-At the request of the Bureau of AirCommerce and the Army Air Corps, the Cam-nittee isundertaking the accumulation of statistical informa-tion on the loads sustained by the landing gear in land-ings. Investi=@ions have been made with fourairplanes and one autoatio. Measurement9 of the atti-tude and vertical velocities immediately prior to con-toct and simultaneous measurements of the linear

accderations of the center of gravity and the angularaccelerations in pitch are made in order to correlatethe magnitude and direction of the resultant groundreaction and the approximate distribution of forcebetween the main and tail wheels with the motion andattitude of the airplane at contact. The investigationwill be continued as more aircraft become available.A preliminary analysis is being made of the data ob-tained thus far.

Stable landing gears.-The tricycle landing gear hasrecently been receiving considerable attention becauseof its possibilities for greatly improving the stabilityand handling characteristics of the airplane on theground and for increasing the ease with which land-ings may be made. A study of the various factorsatkcting the geometrical arrangement of the landinggear has been made.

With the use of tricycle landing gems, the shimmyof the castering now wheel has presented a problem,The Committee has made an analytical investigation ofthe stabili~ of castering wheels as a result of whichinformation was obtained as to the muse of wheelshimmy and several means of overcoming it were sug-gested. The allowance of a certain amount of lateralfreedom of the wheel on i+ axle was indicated as aremedy. Model tests, and full-scale tests with theWI–A airplane, verfied the indimtions of the analyti-cal investigation and have shown that the shimmy ofthe castering wheel may be overcome by allowing orelatively small amount of lateral freedom of thewhed. To center the wheel, clamping of the sidewisemotion shodd be provided, which in the investigationdescribed was done by curving the axle slightly.

The accelerations in landing of an mirplane with ntricycle landing gear have been studied to ascertainwhether the passengers might eqerience relativelysevere accelerations in an emergency landing. Thestudy revealed that the predominant acceleration wasdue to braking forces applied to the main wheels andthat the vertical acceleration due to nosing over onthe nose wheel should not be serious from the standp-oint of passenger comfort.

~FOIL9

The vvork on airfoils carried on by the Committeeduring the past year has been contlned mainly to tkeconsolidation of the lar=g amount of data obtained inrecent years and to the estension of its usefulness byproviding more divefied and accurate methods of itsapplication to practical problems.

Section characteristics.-Airfoil data obtained in thevariable-density wind tunnel since 1930 have been coJo-rected by the empirical method mentioned last yen]-,to give more accurate section characteristics than ithas been possible to obtain previously from tests of

REPORT NATIONAL ADVISORY COMM.ITTIMI FOR AERONAUTICS 13

rectangular airfoils in the variable-deti~ wind tun-nel. These corrected data are to be presmted in tworeports. The & of these (TechnicsJ Report 610)presents the complete results obtained from the investi-gation of related forward-camber airfoils, of which theN. A. C. A. 23012 airfoil is representative. The secondrepor$ now in preparation, will contain the completeresults for a large number of miscellaneous airfoilsinvestigated since 1980 and will also include a tablegiving the improved section characteristics for the air-foils on which data are presented in Technical ReportNo. 460. These results are reasonably complete at onevalue of the Reynolds Number. Since airfoil datamust be employed in practice at widely diilerent valuesof the Reynolds Number, scale effect must also be takeninto account.

The results of an investigation of airfoil wale effectwhich have been avaihtble only in condensed form as aconfidential report have been publiehed in full in Tech-nical Report hTo.586. These data give the most reliablebasis available for the prediction of airfoil-section dataat values of the Reynolds Number o@er than that atwhich the section data published in the reports men-tioned in the preceding paragraph were obtained.However, uncartaintics in the prewnt knowledge mustbe admitted, and it appears that entirely satisfactory re-sults must await future research at full scale in a non-turbulent air stream. The dilliculty is the lack ofknowledge about the transition from kuninar to turbu-lent flow in the boundary layer of the airfoil.

Many of the effects of scale, turbulence, and surfacecondition are intimately connected with the transitionfrom laminar to turbulent flow in the boundary layer.The importance of these effects may be realized froman analysis of the effects of transition on the drag ofairfoil sectiom If it is assumed that the boundarylayer over the surface of an airfoil is entirely huninar,remarkably low drag coefficients are found for thehigher values of Reynolds Number. The drag coe5-cient for a flat plate with laminar boundary layer is0.0008 at a Reynolds Number of 10,000,000. If theboundary layer is assumed to be turbdent from thelending edge onward, the drag coefficient is more thanseven times as large as the huninar’ value at the samevalue of Reynolds “Number, actually amounting to0.005’7.

It is known, however, that it is not possible to have alaminm boundary layer over the entire airfoil sur-face. Calculations made by the method given in Tech-nicnl Report No. 504 show that at zero lift on theN. A. C. A. 0012 airfoil section separation would beexpected if the boundary layer were laminar at about55 percent of the chord back of the leading edge, be-cause of the adverse pressure gradient existing over therearward portion of the airfoil. If transition occurs at

this point, the drag will be intermediate between thevalues given for the completely laminar and the com-pletely turbulent flows, but will still be markedly lessthan that for the completely turbulent layer.

Some experimental results, including data from re-cent tests in the 8-foot high-speed wind tunnel andsome theoretical considerations as well, indicate that.with very smooth m-ingsin an air stream having zeroturbulenw the transition may tend to remain near thelaminar separation point. If such is the case, savingsof approximately 40 percent of the wing proiile dragat a Reynolds Number of 10,000,000are indicated, ascompared with that predicted from a normal extrapola-tion of data from tie variable-density wind tunnel.

In this connection some direct evidence on the natureof transition has been obtained from an investigationcarried out in the nonturbulent N. A. C. A. smoke tun-nel. Boundary-layer surveys were made throughout thetransition region on a smooth flat plate having an ad-verse pressuregradient. The investigation showed thatwhile the extent of the transition region decreased con-siderably with an increase in Reynolds Number, thepoint at -whichmarked changes in the laminar bound-ary-layer flow first occurred vm.s independent of theReynolds Number throughout the range included inthe investigation. The transition region was close tothe position at which separation of the laminar bound-ary layer was to be expected unl= premature transi-tion was brought about by slight roughness near theleading edge of the plate. The tests were carried to aReynolds Number of 150,000 based on the distancafrom the leading edge to the calculated point of separa-tion. Visual observation of the flow over the plate in-dicates that similar conditions may exist over the rane~of Raynolds Number up to 500,000. A technical noteis being prepared presenting the results of this instig-ation.

Wing dmracteristics.-’lle calculation of the char-acteristics of tapered wings from airfoil section datahas been continued with several wings of varying as-pect ratio and taper ratio. The basic section data andthe data on scale effect, if applied by the method de-scribed in Technical Report No. 572, will enable thquser to reduce the wind-tunnel data and to estimatethe best wing for a given airplane. The calculatedcharacteristics of 20 tapered wings will be comparedwith the experimental results for the same wings.

Measurementof profile drag in flight-It has beenfeasible to investigate the protlle drag of an airfoil sec-tion in flight by means of the pitot traverse method.This method has been used in an investigation of thecomparison of air-flow conditions in flight and in thefull-scale wind tunnel, the data obtained being evaluat-ed to determine the profile drag from the momentum10S in the wake of an airfoil. The airfoil was an N–22

,

section and was iirst investigated with a smooth sur-face that was later modiiied by the addition of a threadhaving a diameter of 0.01inch and located on the uppersurface about 5 percent of the chord back of the lead-~g edbw. me ~~ ~d,im~d t~t the addition ofthe small thread increased the profile drag of thesmooth airfoil by about 18 percent. The addition ofanother small thread to the under surface of the air-.foil at the same chordwi.se location further increasedthe profile drag, the total increase due to the twothreads being about 32 percent.

EFFECI’OF~ ANDOTEERSURFACE~llG~ ON~G DRAG

Past investigations in the full-scale and variable-density wind tunnels have shown that rivet heads andother surfme irreagylaritiwincrease the drag of wingsappreciably. As aircraft have been made otherwisemore efficient, the importance of the increases in dragdue to smaIl surface irregularities has become moreapparent and a need has arisen for more completeinformation on the maguitude of such chx=gincreases.

An investigation has been made in the 8-foot high-speed wind tunnel to provide data on the effect on vvingdrag, over a comprehensive range, of rivet size, type,and arrana%ment,lap type and arrangement, and sur-face roughn~. This investigation was made with amodel of an N. A. C. A. 23012 airfoil of 5-foot chordat air speeds from 80 to 500 miles per hour at values ofthe Reynolds Number up to 18,500,000.

Rivets,-D@m the investigation tasts were made of&- and +inch brazier-head rivets, &-inch thinbrazier-head rivets, and &inch countersunk rivets invarious chordwise and spanwise arrangements. The~~-inch brazier-head rivets in a typical arranegunentincreassd the drag of the smooth airfoil 27 percent at225 mik per hour. The dnqg increasesdue to the otherprotruding rivet heads were approximately propor-tional to the height of the heads, indicating that rivetswith the thinnest practical heads should be used. Thecountemmk rivets increased the drag 6 percent underthe same conditions. Increasing the spanvrkwpitch ofthe ri~ets had little effect unless it was made more than2.5 percent of the wing chord. The investigationshowed that more than ’70 percent of the rivet dragwas due to the rivets on the forward 80 percent of thewing. About. 66 percemtof the rivet dmg was due tothe rirets on the upper surface of the airfol

Lapped joint&-A typical arrangement of conven-tional plain laps facing aft increased the drag over thatfor the smooth airfoil by 8 percent. Joggled laps in-creased the drag only half as much. Plain laps facingforward were found to be slightly inferior to plain lapsfacing aft, but if they were faired by rounding the edgesof the sheets, the increase in drag -wasless than thatwith conventional laps facing aft. Rivets and laps

employed together increasedthe drag only slightly morethan rivets alone.

Surface roughness.—The effect of five ditl!erent de-grees of surface roughns on airfoil drag was investi-gated. At 225 miles per hour the drag of the smoothairfoil was increased 44 percent by covering the surfacewith 0.0013-inch Carborundum grains. Even the rou@-nes due to spray ptit@ increased the drag 14 percentat this speed. sandpapering the painted surface -withNo. 400 sandpaper made the drag as low as that of thehighly polished airfoil. The investigation showed thatthere is considerable scale effect on the drag due toroughness.

121Tecton drag of wing due to manufaotaring disorep-ancies.-In order to determine the effect on the drag ofa ~ due to manufacturing discrepancies, such rLswaves in the metal covering sheets and inaccuracies inthe profle, tests were made on a model wing constructedto represent avera=g present-day tolerances and work-manship. The drag of this “swvice wind was 11 per-cent greater than that of the truer wind-tunnel modelwhen both had the samearrangement of rivets and laps,and was 42 percent greater than the drag of the smooth-surface wind-tunnel model without rivets or laps. Thisexcess in drag of 42 percmt is equivalent to 273 extrahorsepower on airplanes of the size and speed of thoseused on presant air lines.

AERODYNAMICINTERFERENCE

Wing-fuselage interference.-A report is now beingprepared on the interference investigation recently com-pleted in the full-scale wind tunnel with an Air CorpsYO-31A observation monophme. The airplane wasfirst @ted with the original gull wing and then withparasol wing arraqggwuentsin which the wing wasplaced at various heights above the fuselage. Whenthe parasol tests were made the gull-wing roots werereplaced by a straight center section. For the purposeof detmmhing the interference effects the principwlcomponent parts of the airplane were tested Separately.in addition to the testsof the complete machine for eachwing arrangpnen~

An investigation of the effects of triangular and ellip-tical cross-sectional fuselage shapes on the aerodynamicinterference between wing and fudage has been com-pleted in the variabledensity wind tunnel, togetherwith tests of a special shape of juncture. During thecow of the tests it was shown that ordinary criticalcombinations could be sometimes benefited, as regardsthe occurrence of the interference burble, by verysmoothly hished surfaces at the wing junctures. Inthis respect one special shape of juncture showed a verypowerful effect, its use resulting in the suppression ofthe premature interference burble entirely, with noincima.sein the minimum drag.

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REPORT NATIONAL ADVISORY COMMI’JW13DFOR AERONAUTICS 15

An investiawtionhas also been made to obtain a com-parison between a combination including the airfoil-tgpe fuselage, and an efficient conventional wing-b-lags combination. Tail surfaces have been added totypical combinations in an investigation comprising anextension of the program of wing-fuselage interference.An interesting development of this phase thus far is thesurprisingly low drag found possible for such acomplete model combination.

FOIICEDVIBRATIONSAND AIR DAMP~G OF A wING SYSTEM

A theoretical study has been made of the vibrationresponse and air damping of a wing-aileron systemin auniform air stream to impressed alternating forces andmomemk. The mathematical treatment is a direct ccm-tinuation of that presented in Technical Report No. 496to analyze the flutter problem. The response character-istics of the vibrating wing-aileron systemin a completerange of velocities and frequencies up to the criticalflutter conditions can be determined in any speciiic casewithout extensive calculations. Thus not only are thecritical flutter velocity and frequency readily deter-mined, but also the vibration response and the air damp-ing at intermediateconditions. The study thus presentsa more completi picture of the phenomenon of flutterthan has prwiously been available in aerodynamic lit-erature. In particular, it is shown that in the case offorced vibrations large responsesmay often be expectedwhen flutter conditions are approached, even whenactual flutter cannot occur. The results of this work arebeing prepared for publication.

%PROPELLERS

Investigation of full-scale propellers.-The remdts ofthe investigation of six full-scale propellers in conjunc-tion with a standard nacdte unit equipped with sixdifferent N. A. C. A. cowlings have been published inTechnical Report No. 594. The inv%igation cmeredthe complete range of flight conditions, includingground operation, take-off, climbing, and high-speedflight. The range of the advanca-diameter ratio wasextended far beyond that of earlier full-scale experi-ments, blade angles of 45° at ’75 percent radius beingincluded, which are equivalent to air speeds of morethan 300 miles per hour for propellers of normal sizeand diameter.

An extensive investigation of full-scale propellers,which was planned last year and which will provideconsiderable data in addition to those just mentioned,has been proceeding for saveral months in the 20-footpropeller-research tunnel. A large number of tests ofpropellers of 10-foot diameter driven by a 600-horz-e-power engine have been made in conjunction with acowled nacelle such as would house a radial air-cooledengine. A number of testx have been made also inconjunction with a nacelle for liquid-cooled engines.

The propellers on which this investigation is beingmade are of modern type, with the blade graduallyfairing into the hub section, in contrast to the older@pe with airfoil sections carried in very close to thehub. Comparative tests indicate a small aerodynamicadvantage for the latter type, but their use is precludedby the characteristics of existing engines

In this investigation blade-angle settings up to 45°at 7’5-percentradius were also used and in several casesblade-angle settings up to 60°. A maximum efficiencywas obtained under the conditions of this investigationat a rotting of about 30° and there was little failing offeven at 60°. This investigation gives further evidenmthat the old practice of designing propellers with a lowbasic pitch and then setting the blades at much higherangles should be modified for high-pitch propellers. Itappears that high-pitch propellers should be designedto have a constant pitch when the blades are set at 20°to 30° at the 76-percent radius. This method v-ill re-sult in a der washout of pitch toward the hub at thehigher blade-angle settings, which is of some ad-mn-tage in obtaining the best thrust distribution forminimum energy loss.

During this investigation particular attention hasbeen paid to the effect of tip speed on the eficiency inthe take-off and climbing range of propeIler operation.A small progressive loss in ticiency begins to appearwheri the tip speed reaches approximately 700 feet persecond. There seemsto be some variation with the air-foil section of the propeller, the Clark Y section hold-ing its eficiency under these conditions to higher tipspeeds than does the R. A. F. 6 section. Calculationsfrom the data obtain~d show, however, that when ap-plied to the controllable propeller the change in powercoefficient is such that the propeller must be set at alower blade angle than would be required if no tip-sped effect were present, with the result that the tip-speed effect is practically eliminated.

Analysis of the data obtained with propellers differ-ing in airfoil sections,but otherwk similar, shows thatthe difference in characteristics am very small, as vrasexpected. The analysis is not yet complete and otherdeductions may be possible after further esamimtion.

A definite improvement is noted with a spinner onthe propeller of a liquid-cooled engine, in contrnst toradial-engine Wations, where it was found that theuse of a spinner over the hub had a negligible effecLAn improvement of about 4 percent in the net efficien~of the liquid-cooled installation was caused by the spin-ner. In thk connection a spinner just covering thehub and having the nacelle lines faired into it wasfound to be as good as a larger spinner.

A number of tests have been made in the negativetorque (windmilling) region covering the conditionsfrom mm thrust to propeller locked at blade-anglemttings from 0° to 90°. The data from these tests will

16 REPORT NATIONAL ADVISORY COLOll~El FOR AI.ORONAUTICS

provide information on the drag of idling and stoppedpropellers and on the braking effect of the propellerin the diving of military types of aircraft. It appearsthat the stopped propeller feathered to a blade-anglesetting of 90° causes the least drag, but an idling pro-peller set at 50° and operating against normal enginefriction has nearly as low a drag.

A series of five reports, each covering a eection ofthis propeller investigation+ is now being prepared.The many factors involved in a study of this scope re-quire a ditiion of the subject for the sake of clarityof presmtation, as well as facility in use. Other re-ports may be required to premnt analyses of minorphases and data yet to h obtained.

Investigationof oppositelyrotatingtandempropellers.—Tlm ccmtinuol increaea in the power ratings of air-plane enginw and the large propellers required, as wellas the effect of torque reaction when large gearedengines are used in small high-performance airplanes:have turned attention to the possibilities of oppositelyrotating tandem propellers. The &my Air Corps re-quested an investigation of the problem, and StanfordUnivemiQ, which is a pioneer in propeller twting inthe United %at~ a=greedto make the investigationunder contract with the Committee as a part of theCommittee’s prcqqam of cooperation with universities.

The investigation -wasmade with model propellersof 3-foot diameter, and the results indicate that a4blade propeller is slightly inferior in performsmca totwo 2-blade propellers of the same diameter and bladedimensions rotating in opposite directions. Both are,of course, inferior to normal 2-blade propellers. Thespacing of the tandem propelle~ was varied from 8to 30 percmt of the propeller diameter, and practicallyno effect of spacing was noted except that the clowrspacings produced more noise. At the lower bladwangle settings the rear propeller had to be sxt at asmaller angle than the fint one in order to absorb thesame power, but, as the blade-angle settings of thepropeller were increased to give higher pitches, therear propeller gradually required a setting higher thanthe front propeller. Increasing the propeller spacingof the tandem propellers when the blade-angle settingswere in the low range also required an incrww in thesetting of the rear propeller. It is proposed to extmdthis investigation to compare a 6-blade propeller withtwo oppositely rotating 3-blade propellers

Investigationof modelpropellemin yaw.-The charac-teristics of propellers whose axes are at an angle tothe air stream are of considerable importance in thestudy of airplane stability with power on, and to someextent in the calculation of airplane performance. Awries of tests of model propellers of 3-foot diameterin yaw has been made at Stanford Univemity undercontract with the Committea to provide data of this

nature, and the results have been published in Techni-cal Report No. 597.

I’rediction of propellerperformamoefrom airfoil sectiondati-The analysis of airfoil section data as applied tothe selection of sections for propeller blades has beencontinued during the past year. In addition methodsfor predicting the performance of propellers fromthe section data are being devised and further analysismade of the distribution of energy losses for conven-tional propellers. The characteristics of three pro-pellers having different blade sections have been mm-lytically determined from the section data obtainedin the variable-density wind tunnel and the smrdlerhigh-speed wind tunnels, and three full-scale propellersof the same design will be tested in the 20-foot windtunneL The experimental data obtained should pro-vide an excdlent check on the method of predictingthe performance analytically.

Propellerviiration.-’lle model method of cletermina-tion of the dangerous vibration frequencies of pro-pcdlers mentioned in the twenty-first anual report ofthe Committee has been verified and superseded by amethod applicable directly to any propeller in ques-tiom The method consists in the um of a carbon-resistanm strain gage attached to the propeller and ameans for producing artidcially forced vibrations ofany mode, the propeller being electrically driven atfull speed in a partial vacuum.

Propeller noise.-Experimental -work on the soundemision from propellem has been continued, particu-larly with a view to obtaining grentm absolute ac-curacy in the measurements. The intensity of thesound emitted from the propeller in various directionshas been measured for the five lowest harmonics forthe purpose of obtaining data for use M a basis fortheoretical work The measurements have been com-pleted for the range of propeller tip speeds below thespeed of sound in air and will be continued into thesupersonic speed range.

A paper has been published (Technical Note No.605) indicating the effect of blade thickness on pro-peller noise. The theoretical relations given in thepaper permit calculation of sound intensity of longwave lengths from a propeller with symmetrical sec-tions at zero blade angle. With the aid of experimentaldata, an empirical factor was introduced into thetheoretical relations to make possible the calcul~tio~of higher harmonics of the rotation noisn.

THZOREI’KML AZRODYNAMIC9

Compressibleflow,-!l?he study of compressible flowabout symmetrical Joukowi@ profiles has been con-tinued, and expressions have been developed for deter-mination of the velocity and therefore the prewure dis-tribution over the airfoils. Ii particular, lift nnd

REPORT NATIONAL ADVISORY COMMlTT13E FOR AERONAUTICS 17

pitching-moment formulas have been obtained for thinprotlles at large angles of attack It has been foundthat the expression for lift is analogous to that for in-compressible flow, but that the expression for pitchingmoment, in addition to being analogous to that for in-compressible flow, contains a term which amounts to ashift in the center of presmre toward the leading edge.In addition to developing the expressions for lift and

‘pitching momen$ the limiting value of the ratio of theair-stream velocity to the velocity of sound in an undis-turbed stream has been calculated for several Joukow-sky proiiles, and the effect of angle of attack and thick-nessupon this ratio has been determined

l?ressnredistributionon flappedairfoila.-A method hasbeen devised for calculating the chordwise pressure dis-tribution over airfoils with ordinary flaps. The distri-bution has been determined by altering the theoreticaldistribution and may be applied to airfoil sections ha,v-ing more than one flap. Technical Reports Nos. 360and 568 show a disagreementbetween experimental andtheoretical forces and pres.sure distribution. In tlmmore recent analysis the empiricil correction to thetheory was determined through lmowledge of the lift,pitching moment, and flap deflection. Work is con-tinuing on this method of analysis to develop an exprw-sion for airfoils with split flaps.

~TUNNEL CORRECTIONS

The interference of the wind-tunnel boundaries onthe dowmvash behind an airfoil has been experimen-tally investigated, and the results have been mmparedwith the available theoretical results for open-throatwind tunnels. This investigation has yielded resultsthat are particularly valuable in correcting the down-wash angle in the region of the tail plane. The experi-mental results show that the theoretical assumption ofan irdinitefree jet at the test section of the wind tunnelmay lead to erroneous conclusions if applied to thedovrmvashin the region behind an airfoil where the tailsurfaces would normally be located. The results of atheory based on the more accurate concept of an open-jet wind tunnel as a finite length of frm jet providedwith a closed exit passage gave good qualitative agreem-ent with the experimental results. The results of thisinvestigation have been presented in Technical ReportNo, 609.

The investigation to determine the scale effect on themaximum lift of an airfoil has been extended by addi-tional tests in flight and in the full-scale wind tunnel.The investigation was made -with a 2R,12 airfoilmounted on a Fairchild 22 airplane, and the variationsof Reynolds Number in fight were obtained chiefly byvarying the wing loading of the airplane and by vary-ing the altitude at which the tests were made. Themaximum lift as obtained in flight and in the full-scale

wind tunnel agreed within 2 percent, the results thusfurther substantiating the agreement obtained withsphere tests, which indicated a low percentage of tur-bulence in the full-scale wind tunnel.

The investigation of the factors leading to discrepan-cies between the power-on performance of an airplaneas predicted from wind-tunnel data and as measured inflight is being continued. In order to avoid the dMi-culties usually experienced in obtaining precise meas-urements of climbing performance, the exaxa horse-power available for climb is being determined in levelflight.

This determination is accomplished by the towing ofparachutes of various sizes to absorb the excess horse-power at various speeds. The horsepower is computedfrom the tmsion in the towing line and the velocity ofthe airplane. This method avoids, in particular, theerrors usually experienced in climb owing to variationsin the wind velocity with altitude. A second airplaneis being equipped to study quantitatively the effect onclimbing performance.of variations in the wind velocitywith height by correlating the excess horsepower meas-ured in level flight with the rates of climb actuallyexperienced in several climb tests. The results will bechecked by tests of the same airplanw in the full-scalewind tunnel under power+n conditions.

CO~EESSIBILITYEFFECI’SDUETOHIGESPEED

Aerodynamic phenomena encountered at high speedshave heretofore been considered of importance mainlyin relation to the adverse effects on propellers operat-ing at high tip speeds It has no-iv been establishedthat marked adverm effects due to compmssibili~ mayoccur on other parts of airplanes when the forwardspeed of the airplane is approximately one-half thespeed of sound. Investigations conducted in both the24inch and the 8-foot h&h-speed tunnels have shownthat the compressibility burble results in a large enereq10S. A large increasa in” drag may therefore occurwhen the flow about any part of the airplane producesa local veloci~ equal to the speed of sound. A bltibody and one having a high curvature produce highinduced velocities, and therefore the critical speed ofsuch bodies is low.

The results from an investigation in the 11-iuch high-speed tunnel on the drag of circular and elliptical cyl-inders and prisms of triangular and square cross sec-tions show that the critical velocities or, in other words,the forward spmd at which compri%ibility effects be-come noticeable, may be as low as 0.4 the velocity ofsound.

Similar resultshave been obtained in the 8-foot high-speed tunnel on a wing-nacalle combination. One-fifth-scale models of a family of radial-engine cowlingswere tested on a nacelle with a -wing of 2-foot choriL

18 REPORT NATIONAL ADVISORY COAIAII’JH’EEFOR AERONAUTICS ,

Five of the cowling shapes had previously been testedin the propeller—msear& tunnel, and at the lower speedpossible in the propeller-research tunnel these cowlingswere considered satisfactory. One cowling shape wasfound to have a critical speed between 280 and 350milesper hour, depending upon the attitude of the cowlingand nacelle. When the compressibili~ burble, or shockwave, occurred at the critical speed the drag of thecombination was increased from 50 to 200 percent, withonly a slight increase in the tunnel spud.

Dur@ the investigation it had been found that if theP~ distribution over the cowling was known, thecritical speed could be accurately predicted. Therefore,two cowlings viere desi=~ed with the nose curvaturesproportioned to reduca the peak negative pressure andobtain a uniform negative presmre distributiono~er the now By so changing the nose shape thecritical speed of tlmcowling was increased to more than500 miles per hour and approached the critical speedof the N. A. C. A, 23012 wing, which was used for theinvestigation. It was found that when the critical speedof the cowlings was increased other advantaa- wereobtained. The cowling with the highest critical speedalso had the lowest drag throughout the entire speedrange, and the drag remained substantially constantover a larger range of angle of attack

In order to determine at a large scale the possiblevariation in pitching moment with speed, four wingsof ~-foot chord were tested in the 8-foot high-speedwind tunnel through a ran=%of speeds up to that atwhich’ the compatibility burble was experienced. Thefour wings tested had the following N. A. C. A. sec-tions: 0012,23012, %03.2-64, and 44X2. The N. A. C. A.~so~ ~d ~fj~ afifoi~ ~ere chosen as ~tions oflow pitching moment and the N. A. C. A. 4412 as asection of high pitching moment- All the sectionstestedshowed an increasa in pitching-moment coefficient withincreased spee~ the increase amounting to as much as46 percent at 500 miles per hour. This change inpitching moment has little practical significsmcain thecase of an airplane on which a wing section having lowpitching moments is ueed, because the *ting abso-lute change in pitching moment at high speeds wouldbe of little importance in the design of the wing or tailsurfaces. In the case of an airplane with a wing see-tion of high pitching moment the change may be veryimportant in high-speed dive-s.

BOUNDARY-IAYERCONTROL

The investigation of boundary-layer control has beencontinued iR the propeller—reswrch tunnel, and testshave been completed on a tapered wing of N. A. C. A.8318 section with upper-surface suction slots to controlthe boundary layer. Tapering the slot vvasfound to bevery effective in producing an even distribution of con-

trol over the span, and the suction power required wasintermediatebetween the low power required for a thickwing and the high power required for a thin wing.Measurements of boundary-layer thiclmees were macleboth with and without the control in operation.

ICR PRBVRNTION

In view of the fact that mveral accidents duringthe last year may be directly attributed to ice forma-tion on the airplanes, a survey has been made of the ice-prevention investigations that have been conducted bythe various Clovemment and commercial organizations.A compilation of these data is being made so as to makeavailable to al-1concerned information that maybe vrLlu-able in preventing accidents due to ice formation.

In order to detetie the effect of rubber de-icers onthe aerodynamic characteristicsof a wing, a model of a5-tube de-icar was tested on an N. & C. A. 23012 wingof ti-foot chord in the 8-foot high-speed tunnel. Theresults show that for both the inflated and deflated con-ditions the de-icers did not appreciably affect the lift orpitching moment for high-speed or cruising conditions,but with either two or three tubes of the de-icer inflatedthe drag of the wing was increased in the order of 80percent. The conventional de-icer equipment cleflntcdincreased the drag of the wing 16 percent at 200 milesper hour. At air speedsgreater than 200 miles per hourthe de-icer lifted from the wing and in some casesbreaksin the rubber -wereproduced. In order to reduce thedrag of the de-icer in the deflated condition a flushbhzllation was made by the use of a metal attachment ,strip, which on the full-scale airplane would be l/32-inch thick. With this installation the drag incrementwas reduced from 16 to 9 percent, but the same difficultywas experienced in the lifting of the de-icer from thewing at speeds greater than 200 miles per hour.

ROTATINGWINGAIRCRAFT

The development of the direct-control type of auto-giro has been delayed to some extent by the introductionof certain secondary difficultiesconnected with the pro-vision of a satisfactory variation of control forces withair speed and with the elimination of vibration. Astudy of the effect on certain rotor characteristics of aperiodic variation in blade-pitch angle has been mnde,and the resultshave been published in Technical ReportNo. 591. The predicted value of the flapping motion ofthe rotor blade was radically altered when the periodicpitch variation was inserted in the rotor analysis, andan appreciable iniluence of the periodic pitch on therotor thrust coefficient was indicated. An analysis hasbeen made of the factors involved and a method devel-oped of predicting tie periodic variation of the pitchangle. The results have been published in TechnicnlR8port NO. 600.

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REPORT NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS . 19

An imwtigation has recently been conducted both inflight and in the full-scale wind tunnel on a direct-control autogiro to determine the lift, drtig, controlforces, flapping motion of the rotor blade, and periodicvariation in pitch angle. The testsin the full-scale windtunnel were made on the complete autogiroj on the rotoralone, and on the machine without the rotor to deter-mine the interfenmce effectsbetweenvmious par& Theclatwobtained from these tests are being analyzed forueain the study of any desired variation of the locationof the center of pressure on the rotor.

An investigation has been started in the propeller-resenrch tunnel on a series of model autogiro rotorshaving airfoil sections of d.Memntthickness and differ-ent mean camber lines, and will include two rotors thatdiffer only in plan form of the rotor blades. This workis an extension of an investigation previously made inwhich the effect of airfoil section and plan form on thelift-drag ratio of an autogiro rotor was studied.

The analysis of the results obtained during the auto-giro jump take-off tests has -been completed and pub-lished in Technical Note No. 582. The report covers atheoretical study of the jump take-off without forwardspeed and includes an experimental verification.

An analytical study of the rotor-blade oscillations inthe plane of the rotor disk has been made, and the resultshave been published in Technical Nob No. 581.

A study of the autogiro rotor-torque equation hasbeen made, and a report is in preparation which willinclude rLsolution of the problem in chart form.

~llSCELMOUS‘l?Ml%OFCO~LETEB1ODEU OF AIRPL.4NES

The improved aerodynamic e%iciencyof the modernairplane has made it increasingly important to maketestson a complete model of a projected airplane beforeit is constructed. Consequently a large number of com-plete models have bun tested in the 7- by 10-foot, the20-foot, and the full-scale wind tunnels. Most of thesatests have been conducted at the request of the Armyand Navy, but eaveral models have been tested formanufacturers at their expense.

The models tested in the full-scale tunnel have been1/2and 1Atie, and the testshave included considerabledevelopment work that could be conveniently carriedout on thesa lnrge-scale models at considerably less costthan would be involved in doing the same work on theactual airplane after it has been constructed. Althoughthis development work has restricted to some extent thelwarch programs in the tunnels, it is felt that the testshave resulted in a large saving of money to the Govern-ment. It might also be pointed out that the develop-ment work in the wind tunnel will save much of thetime required to take an airplane throughmental stages and place it in production.

the experi-

NA’ITONAL BUREAUOF STANDARDS--TUNNEL INVESTIGATIONS

The aerodynamic activities of the National Bureau ofStandards have been conducted in cooperation with theNational Advisory Committee for Aeronautics.

Wind-tannel turb&nce.-Within the last few yearsthe equipment used in the study of wind-tunnel tur-bulence has been redesigned for use with an alternating-current power supply instead of storaambatteries. Adescription of the new equipment and of its perfomn-ance has been published in Technical Report No. 598.

As mentioned in last year’s repor$ the investigationof turbulence has been extended to include the measure-ment of the scale or eddy size of the turbulence as wellas the intensi~. The most satisfactory method of in-troducing turbulenm into the wind-tunnel stream wasfound to be by means of screens placed acres thestream, the scale behg controlled by the size of thescreen and the intensity by the distance downstreamfrom the screen. The measurements of scale and in-tensi~ have been made and the aerodynamic effect ofthesa two factors has been determined. The results ofthis work have been published as Technical Report No.581. The screens described in this report are now re-garded. as st~dard equipment in the Bureau’s 4+&footwind tunnel and are used to introduca turbulence of tl~edesired scale and intensity within the limits obtainable.

Preparations are being made to continue the studyof turbulence by measuring the distribution of energyin turbulent motion with the wave length of the turlm-Ience. According to recent theories the spectral distri-bution of energy is a characteristic property of tur-bulence related to the intensity and scale.

Boundarylayer near an elliptio cylinder.-Durimg thepast year boundary-layer investigations have been inprogress with an elliptic cylinder of l%inch major axisand 4inch minor axis, placed with the major axisparallel to the wind. The laminar boundary layerformed about the cylinder was previously studied andthe resultswere published as Technical Report No. 527.. The rewnt work has consisted of the measurementofveloci~ distributions in the boundary layer with theair speed in the tunnel high enough to produce transi-tion from huninar to turbulent flow in the layer beforeseparation occurred. .Two cases were investigated: thefirst with the low turbtienca normally prevailing in thewind tunnel and the second with the stream turbulenceraised to about 4 percent by means of the l-inch screenplaced 18 inches ahead of the cylinder.

Marked differences were found between the types oftransition occurring in the two cases. Transition withthe low stream turbulenm was the result of a laminarseparation, and occurred tithin a very short length ofthe surface, about nn inch ahead of the point of separa-

20 REPORT NATIONAL ADVISORY COMM.I- FOR AERONAUTICS

tion of the turbulent layer. Work with the higherstream turbulenm gave no evidence of a laminar sepa-ration, but showed a gradual transition extending overabout a third of the distance from the leading to thetrailing edge of the cylinder (i e., over about 4 inches).This latter @pe of transition was very dMicult to detectby any single means and was found only by carefulstudy of the velocity distributions in the layer. Inorder to throw more light on the transition phenomenaat the higher stream turbulence measurements weremade of the fluctuations in veloci~ throughout thelayer at various points about the surface. Thesa meas-urements also showed the gradual nature of thetransition.

Studies of transition.-The two different typeg oftransition found on the elliptic cylinder suggested anextension of ,the work to cover the general effects ofturbulence and Reynolds Number on transition, thepurpose of the extension being to learn under whatconditions each @e of transition exists and how theregion of transition shifts with chane= in ReynoldsNumber and changw in scale and intensi~ of thestream turbulence-

s ma pointed out previously, the location of thetransition reggon could be determined with the avail-able equipment only by extensive measurements ofthe distribution of mean veloci~ or fluctuation ofvelocity across the boundary layer. In order to f acili-tate the investigation, a new device for quickly andeasily detecting transition vras sought. Previous workhas shown that transition occurs in the neighborhoodof the point where the intensi~ of skin friction is aminimum. This immediately suggested the w of somedevice, such as the Stanton surfam tube developed inEngland, by which the surface friction may be meas-ured. However, the adaptation of the surface tubewas not considered feasible on the elliptic cylinder.Instead a sliding steel band 6 inches tide and 0.002inch in thicknes was fitted about the cylinder so thatthe heated element of a hot-wire anemometer, fixed atthe center of the band, could be moved around the con-.tour of the ellipse at a small iixed distance from theSUrfam.

While an actual measurement of the velocity by thismeans is not readily possible, the wire can be used todetect where the speed is a minimum as the band isslipped around the surface. In the t%s already madea platinum wire 0.016 millimeter in diameter and 18millimeters long was mounted 0.21millimeter from thesurface of the band. The device has proved quite sat-isfactory and.shows suillciemtpromise to justify furtherdevelopment. It maybe possible to use a device of thissort for locating transition on an airplane wing infright.

Investigation of boundary layer by diffusion of heatt—The method of thermal dMusion described in TechnicalReport No. 524 h~ been applied to the study of ve-locity fluctuations in wthick turbulent boundary lwyerformed on the surface of a flat plate 10 feet wide and24 feet long. The procedure consists of measuringwith a thermocouple the sprend of the heated wakedownstream from a line but long heated wire placedtransverse to the flow in the boundary layer. Thesprend of the wake is caused by the components ofturbulent motion normal to the meaq direction of “flow,and the purpose of the work is to compute the mngni-tude of the components from the measured spread.By this means the magnitude of the velocity fluchm-tions normal to the surface has been determined. Ina similar manner it is planned to determine the magni-tude of the component parallel to the surface. By theusual hot-wire equipment the component in the direc-tion of the mean flow will be measured so that finallya comparison between all three components of thefluctuations will be po=ble.

AEEONAIJTIGINSTkZUMENT lNVESTIGATIONS

fie work on aeronautic instruments has been con-ducted in cooperation with the National AdvismyCommittee for Aeronautics and the Bureau of Aero-nautics of the Navy Department.

Reports on airmail instrtunents,-A report on thepressure drop in tubing used to connect tircrwft in-struments to vacuum pumps and pitot-static tubes hasbeen published as Technical Note No. 593, and a re-port on electrical thermometers is being published MTechnical Report No. 606.

An experimental investigation of the performancecharacteristics of venturi tubes used in aircraft foroperating air-driven gyroscopic instruments has beencompleted and a report prepared.

Progress has been made on reports on the effect ofvibration on service aircraft instruments and on gyro-scopic instruments for aircraft.

Testsand test methods.-It was originally planned tomeasure humidity in the aerograph test apparatus bythe dew-point method. A simpler method has beendeveloped in which advantage is taken of the fact thatcompletely saturated salt solutions have a characteristicvapor pressure so that a particular salt solution pro-duces a practically constant relative humidity whenplaced in a closed chamber. Corrections can be ap.plied for the relatively small variation of the relativehnmidi~ with temperature.

Altitude mercurial barometers for field use shouldwithstand shipment without breakage and should bedesigned so that the accumulation of gas above the mer-cury column is easily removable. Principally for thesemasons it is advisable to iill the barometei tube in the

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REPORT NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS 21

field. Experiments with the Barnes type, which meetsthese requirements, indicata that the procedure to befollowed is too complicated. In cooperation with aninstrument manufacturer, the common-typ altitudebarometer has been modified to make it po~ble for thetube to be fled in the field by following a relativelysimple procedure. The barometer must be designed wthat the end of the tube is always well cmered -ivithmercury while the barometer is tipped from the normalto the upside-down position. The usual capillary re-striction in the end of the tube must be of such size thatthe p-of gas is not impeded by mercury stic@ngin the capillary. ‘

Laboratory test methods have been developed, and●

data on the performamm obtained, on fuel-air-ratio in-dicators of the thermal conductivity type. In thasatestsknown mixtures of nitrogen and hydrogen and ofnitrogen and carbon dioxide were passed through theinstrument subject to various conditions, such as tem-perature, pressure,and Volta=m.

New instruments.-Instruments designed and con-structed for the Bureau of Aeronautics include: ahelium purity meter utilizing a porous plug of a typerecently developed commercially; a superheat meter ofthe electrical-resistance @pe for a K airship; an ex-perimental pitot-static tube for installation on the wingtip of monopkmes. Development of a fuel flowmeter ofthe oritice type is in progress.

SUBCOMMMTEE ON AIRSHIPS

The Subcommittee on Airships formulates and rec-ommends programs of airship investigations to be un-dertaken at the Langley MemoriaJAeronautical Labora-tory and maintains C1O= contact with the work inprogress.

The Committee recently published as Technical Re-port No. 604 the results of the investigation conductedby the laboratory at the request of the Bureau of Aero-nautics of the Navy to determine the pressure distribu-tion at large angles of pitch on iins of different span-chord ratios on a large model of the airship AkromThis investigation was requested by the Bureau to pro-vide information particularly desired by the SpecialCommittm on Airships of the Science Advisory Board,of which Dr. W. F. Durand, of Stanford University,is chairman. Mention is made here of the publicationof the technical reports of this committee, which covercertain phases of airship technical problem

Models and apparatus are being prepared for theinvestigation in the Cmmnittee’s20-foot wind tunnel ofboundary-layer control on airship forms. This investi-gation will include a form with blower in the nose, andalso a form with propeller in the rear with control ofthe boundary layer by both suction and discharge jets.

At a meeting of the Subcmmnittee on Airships held

in January 1937,plans were discussed for the extensionof the invwtigation of the forcOs acting on an airshipduring ground handling, as published in Technical Re-port No. 566, to include a study of the effect of windgradient and also of the effect of fin angle. Considera-tion was also given to the desirability of conducting aninvestigation at the Committee’s laboratory on the loadson the tail surfaces of an air-shipin tight, and also aninvestigation of the forces on a large airship model withtail surfaces of the form used on the Bindenhrg.

SUBCOMMITTEE ON MEI’EOROLOGICAL PROBLEMS

The Subcommittee on Meteorological Problems keepsin contact with the pro=~ of investigations being con-ducted by the various aggncies on problems relatingto the atmospheric conditions which are of particularimportance in connection w-iti aircraft design andoperation.

Atmospheric diaturbanoes in relation to airplane acoeler-ations.-Extensive measurements of =- have beenmade by the Langley Memorial Aeronautical Labora-tory by means of flights to altitudes of 19,000 feet witha large military-type airplane and flights with a smalllight airplane. From partial analysis of the data ob-tained, it appears fiat it may be possible to correlatethe gust strength and gradient with the energy avail-able for turbulence in the atmosphere. The new re-sults do not invalidate the conclusions previouslyreached tentatively that, in stable atmospheric condi-tions, with large wind gradients, vertical gust veloci-ties of the order of 30 feet per second are reached in ahorizontal distance of about 100 feet, and fiat the gustgradient increases with decreasing gust intensi~.

Surveys of clouds of cumulus type indicate, in gen-eral, stronew downward-acting than upward-actinggusts. On one occasion a downward gust of 53 feetper secon~ which reached maximum intensity in a dis-tance of 53 feet, was experienced.

The development of a special acceleration-altituderecorder for installation at various Weather Bureaustations throughout the country is nearing completion.When available, these instrumem%will be used in con-junction with air-speed recorders to obtain data on therelation between gust intensity and altitude.

The accumulation and analysis of records of accelera-tions on transport airplanw in reggar operation is be-ing continued with tie cooperation of a number of theair transport operators The records obtained repre-sent conditions encountered in operation over practi-cally eveg part of the United States, in transpaciilcopration, and in operation over the Andes Mountainsin South America. Records from flying boats in thetrampacfic service indicate effective ~fystvelocities asgreat as 33 feet per second, which is substantially equalto the maximum recorded on flying boats in service

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22 REPORT NA’IXONAL ADVISORY

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COMMITTEE FOR AERONAUTICS

between Florida and the West Indiw and South Amer-ica and on land transports.

Investigation of wind gustiness.-The study of windgustiness, including both atmospheric turbulence underordinary conditions and the fluctuations of wind ve-locity during the passage of cold fronts, conducted bythe Daniel Guggenheim Airship Institute at Akron,Ohio, in cooperation with the Weather Bureau and theBureau of Aeronautics of the Navy, has kn mn-tinued. Additional measurements are being made bymeans of instruments installed on the radio tower atAkron and on movable towers placed at various posi-tions in relation to the radio tower and to each other,with supplementary records obtained by the use ofballoons and theodolites.

Ice formation.-The problem of ice formation is re-ceiving considerable attention at the Langley MemorialAeronautical Laboratory, and a report hm m~ntly beenissued to American manufacturers giving the resultsof a study of the prevention of ice formation on pro-pellers. In this report information is given as to theconditions under which ice forms on propellers, and aninvestia~tion conducted by the Cmnmittea on the pro-peller de-icer developed under the sponsorship of theBureau of Air Commerce in cooperation with the B. F.Goodrich Company and Transcontinental and WesternAir, Incorporated, is describad.

The problem of ice formation on wings and aileronsis also being studied, and a report is hing prepmedp=nt~g au the information at present available. IIIaddition, a pro=gam is being f ornmlated for the studyof the effect on the aerodynamic characteristics of a~g, of ice parti~~ that adhere after the de-icer hasacted. Data on the shape and location of such par-ticles for use in the preparation of this program havebeen supplied through the @-operation of the AirTransport Association of America.

Electrical phenomew-The question of the po=ibleeffect of electrical phenomena on airplanes has beenbrought to the Comniittee’s attention and will be dis-cus-sedat a meeting of the Subcommittee on Meteoro-logical Problems to be held in the near future. Observa-tions of pilots on the subject have ken obtained froma number of sources, and the question will be thor-oughly studied by the subcommittee.

SUBCOMMITTEE ON SE.4F’LANES

World-wide interest in seaplanes has grown at anaccelerated rate and ahuost every month has broughtword of the launching of new craft of greater size andspeed. Designem are discussing with confidence theconstruction of flying boats of magnitudes that wouldhave been considered impracticable a few years ago andare looking forward to the construction of even largerand faster flying boats within a relatively short time.

With the increases in size and range have come in-creased get-away speeds and heavier loads on the hulls.The power required for the take-off of such large flyingboats is sometimes 100 percent greater than that ordi-narily used in fight, and in such cases the designer isconfronted with the necessity of choosing between thew of larger engines involving a serious increaw inmight and the possibility of shortened engine life as8 result of running at excessive power during take-off.

The cost of these large flying boats makes it essentialthat the form of hull sel;cted shall be the best possiblecompromise between the requirements of low drag inflight and good performance on the water. Resemchin the N. A. C. A. tank has therefore been directed ,toward the improvement of the over-all performance offlying boats and seaplanes by the reduction of the re-sistance on the water and the general improvement ofthe form of the hull. In contrast to previous work, theaerodynamic improvement is being given considerationat the same time.

Improvementsto N. A, C, A. tank-In anticipation ofthe demand for testsof models of larger hulls at highertake-off speeds, the Committee is enlarging theX. A. C. A. tank and increasing the speed of the towingcarriage. When the work now under may is completedthe tank will have 2,880 feet of water at a depth of 12fee~ which is m increase of 900 feet. The extensionhas been specially constructed to permit the generationand propagation of waves for use in testing models inwaves and the simulation of operation in rough water.

The increase in length has been matched by an in-crease in the speed of the towing carriage. It isexpected that when the aerations are completed thecarriage will have a mtium speed of about 80 milesper hour. The carriage will also be able to tow muchlarger models.

At lower speeds, with models of the same size, it willbe possible to increase the amount of testing per daybecause the ratio of the distance that can be used intesting and obtaining readings to the distanm requiredfor stopping and starting the carriage will be consider-ably increased.

A two-story office building has been built at thesouthern end of the tank and the shop spaces have been’cmtended..100feet.

EfEectof variation in-dimensions and form of hull ontake-off.-The result of incorporating longitudinalsteps on the forebody of a V-bottom hull was deter-mined by an investigation of a sariesof models in whichthe form and number of stepswere systematically varied.h generrd, the longitutifl steps were fo~d tO de-creaswresistance at high speeds by reducing the area incontact with the water> but to ~cre~e ~t~ce atlow-speeds where the bottom is wetted out to the chines.One longitudinal step on each side of the keel was

REPORT NATIONAL ADVISORY 00MMI!J?IYCE FOR AERONAUTICS 23

superior to two longitudinal steps,except at high speedsand very light loads. Spray strips fitted along thestepsreduced both the resistanceand spray if they wereset at the proper angle. This investigation is describedin Technical Note No. 574.

Various methods of artificial ventilation of the stepwere investigated on two typical hull forms, one havingstraight V sections and one having chine flare on bothforebody and afterbody. In both casx+the chines aftof the step were clear of the water at the hump speedand above. When the chines were clear the step wasventilated by air flowing in from the sides and the in-troduction of additional air through ducts or slotsproduced no further change in resistance or trim. Inthe case of the form with chine flare, nati ventilationwas delayed at speeds below the hump speed and arti-ficial ventilation through ducts aft of the step resultedin an appreciable reduction in resistance and trim.The results of this investigation have been publishedin Technical NToteNo. 594.

Testsof modelsof representativeflying-boathulls.-Thebull of the U. S. Navy PB-1 flying boat, which wasbuilt by the Boeing Aircraft, Company in 1925, hadtwo transverm steps very close together and a long ex-tension carrying the tail surfaces. The forebody wasmuch like that of the NC hull, from which it wasapparently derived. Comparisons of its watir per-formance as obtained in the N. A. C. A. tank with thatof the NC hull and the Sikorslq S40 hull are pre-sented in Technical Note No. 676.

A model of the hull of the British Singapore It-cflying boat was investigated in the N. A. C. A. tankin response to sqg+stion of the Director of Research,British Air Minktry. This investigation made it pos-sible to determine the hydrodynamic characteristi~ ofa typical British hull form over an extensive range ofloadings and speeds. It -wasfound that the Singaporehull had higher resistanceat the hump spead and lowerresistance at higher planing speeds than the Americanhull with which it was compared. The results of thisinvestigation, toa%therwith a comparison with similarwsults obtained in the British R. A. E. tank with thesame model, me presented in Technical Noti No. 580.

A large model of the hull of the British Short Cal-cuttmflying boat was made from lines supplied by theBritish manufacturers and investigated in the N. A.C, A. tank. The form is the immediate predecessor ofthe Sin=yqyme hull, and is representative of Britishflying-boat design in 1928. The results of these task,together with calculated comparisons of its take-off per-formmce with that of typical America forms, arepublished in Technical Note No. 590.

Trim-angle indioator.-The importance of holding aseaplane at the trim angles that would give least resist-ance during the process of take-off was described in

w~

Technical Note No. 486, issued in 1934. In that publi-cation there is described and illustrated a trim indicatorfor showing the pilot of a seaplane the trim angle atwhich the craft is traveling. Several versions of thistype of trim-angle indicator have since been constructedand tested in servk. It has been found that if a pilothas a trim-angle indicator and the information obtainedfrom tank tests of the hull as to the trim angles thatgive least resistanceduring the take-off, it is po~ble forhim regularly to take off in much shorter time than herequires when no such instrument and data are avail-able. The pilot of a heavily loaded amphibian operat-ing in the tropics reported that he attributed the uni-formly successful operation of his craft, especially theeasa with which it took off in smooth water, to the useof a trim-angle indicator that had been supplied by theCommittee. In another case the use of a trim-angleindicator by a test pilot is credited with so greatlyimproving the take-off characteristics “that a seaplanewhich at first appeamii very unsatisfactory gave verygood performance.

REPORT OF COMMITTEE ON POWER PLANTSFOR AIRCRAFT

LANGLEY MEMORIALAERONAUTICAL LABORATORY

ENGINEPowml

The recent demand of aircraft d~igners for enginesof increased power output has been fuliilled by the sup-plying of radial air-cooled engines developing 1,500horsepower during take-off. This large increase inpower has been obtained by increasing the number ofengine cylindem and by dwigning the engines to takethe greatest possible advantage of the antidetonatingquali~ of the improved fuels now available for aircraftengines. These large engines will be u~d in aircraft.designed to transport greater loads at increased speedsover prwwnt airways. The several investigations of theCommittee on the cooling of air-cooled engines haveindicated that it will be posible to cool satisfactorilyenghm of even greater power.

Engine performance with high ootane fnels.-Thegreater percentage of the recent increase in power ofaircraft engines is due to the use of fuels having in-creased antidetonating quality. An investigation todetermine the maximum engine performance with fuelshaving a range of octane numbers from 87 to somewhatgreater than 100has been in progress at the Committee’slaboratory during the past year, under the cognizanceof the Subcommittee on Aircraft Fuels and Lubricants,and will be described in the report of that subcommittee.

Valve overlap.—Thepower of aircraft engines maybeincreased by removing the exhaust gases from the cylin-der clearance volume. An efficientmethod of removingthe exhaust gas is to operate with a large valve overlap

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24 REPORTXATIOIUL+VISOR~ COi~TTEE FOR AERONAUTICS

and 10Wboost p~ At the request of the Bureauof Aeronautic of the hTavyDepartment, the Committeeis determining on a single-cylinder test engine the per-formance and optimum valve overlap to give efficientscavenging of a radial air-cooled fuel-injection engineoperating at a maximum speed of 2$00 r. p. m.

The results indicate that satisfactory scavenging can.be obtained with a -ivilve overlap of 180°. From thetests on the single-cylinder engine it was found that asthe boost pressure was increased the gain in power withthe two-valve cylinder was slightly less tham that ob-tained in previous tests with a cylinder having fourvalves The results showed that an engine operatingwith valve overlap would develop 25 percent morepower at the same cyIinder temperature than an engineoperating with normal valve timing. The tmdency todetonate was reduced so that the engine with valveoverlap, for the one fuel tested, showed ~ ~CreWWi.nbrake mean effective pressure of 25 percent withoutdetonation as compamd with the normal valve timing.

The 2-stroke-cycle engina-bcreased power outputcan be obtained from a given engine displacement byoperation on the 2-stroke cycle instead of on the 4strokecycla The availability of improved fuels having in-creased antiknock values has renewed the interest in the2-stroke-cycle spark-ignition fuel-injection engine- Aninvestigation has bem conducted to determine the opti-mum location of the fuel-injection valve and the bestarrangement of fuel-valve orifices for injecting the fuelinto the en~ginecylinder. Favorable results have beenobtained in a limited series of tests, and the rmti.program is being continued to obtain information onthe operating characteristics of this type of engine as

resmres, and inductionaffected by spea~ scavenatig pand exhaust conditions. With fuel of 100 octane num-

. her, scavenging pressure of 3 pounds per square incl+and a speed of 1,650r. p. m., the single-cylinder enginedeveloped an indicated mean effective pressure of 166pounds per square inch, the corresponding fuel con-sumption being 0.37 pound per horsepower-hour. Amaximum indicated mean effective pressure of 198pounds per square inch has bean developed with a fuelconsumption of 0.44 pound per horsepower-hour. Apositive valve-operating mechanism for this engine isbeing developed that will permit the masirnum enginespeed to be increasad from 1,800to 2,500r. p. m.

Air intercoolers,-An analysis has been made of datafrom laboratory tests for the purpow of selecting themost desirable intercooler for various opmating condi-tiom+the cooling, drag, presure drop through cooler,and weight of core being consider@. On the basis ofthis analy-* a program of tests for intacmders hasbeen prepared that includes both full-scale tests in awind tunnel and tests of promising cores in the enginelaboratory.

COMBUSTIONRZ9EARCR

A study of combustion both in spark-ignition and incompression-ignition engines has been undertaken withthe object of obtaining new knowledge concerning thecombustion phenomena. The problem of detonation ininternal-combustion engi.ncsis being attacked with theaid of high-speed schlieren photo=~aphs to indicate thetemperature variations in the front and rear of thecombustion zone following ignition.

Ignition lag in compression-ignitionengines,-The in-vestigation of the effect of air temperature and densityon the auto-ignition and combustion of Diesel fuel witha constant-volume bomb has bwm extended. Vely littlereduction in ignition lag is posible for the particularfuel under test by the use of temperatures and pres-sures in excessof thos8 attained in compression-ignitionengines. The combustion process, however, is more sat-isfactory at densities corresponding to considerablehost. A concentration of combustion products severaltimes greater than that corresponding to tlm resid-uals in a compression-ignition engine is capable ofdefinitely increasing the ignition lag. Technical Re-port No. 580 has been published giving the results ofthis investigation.

compression-ignitionengine with air flow.-Tl~e in-vestigation of the fuel-spray and flame formation oc-curring in a compression-ignition engine having airflow that was set up by a displacm on the piston crownhas been described in Technical Report No. 588.

Detonationin engines.-With a schlieren set-up and ahigh-intensity electric spark m the light source, bymeans of which 10 photographs are taken at rates upto 2,000 pictures w second with an exposure intervalfor each picture of approximately one-millionth sec-ond, photographs have been obtained thnt show clearlythe depth of the combustion zone and also the burningof the end gases in normal combustion. No evidencehas bcxm obtained of any sonic wave precediig thecombustion front. Such waves were arti6cidly pro-duced in the chamber and, although their effect on thecombustion front was visible, t@ey dicl not cause thecharge to detonate. Even with very severe detonation,the combustion reaches all, or nearly all, the way acrossthe combustion chamber before the detonation occurs.The resdts of this investigation are being preparedfor publication.

An apparatus has been constructed and is beiig usedfor preliminary tests of the detonation of gasoline-airmixtures. The combustible mixture is prepared in nreservoir heated to a temperature below the auto-ignition point but sufficiently high to vaporize till thefuel. A portion of this mixture is then admitted bymeans of a poppet-valve mechanism to an evacuatedtubular bomb heated to a temperature such thot nuto-ignition of the charge will occur after wrelatively long

REPORT NATIONAL ADVISORY COJ1311!CTEEFOR AERONAUTICS 25

time. If this mixture is spark-i=gited at one end in.such a way that the normal flame can traverse the tubewithin this lag period, no detonation occurs. On theother hand, when the spmk is so applied to the mix-ture that the flame travels only a large portion of thetube length, then severe vibrations, presumably due todetonation, are set up in the optical pressure indicatorattrtchedto the tube at the end opposite the sparkingend.

Analysis of engine oycle.-The calculated ideal. enginecycle does not include consideration of the actual com-bustion process, so that the results depart considerablyfrom those obtained from engine tests. In order to ob-tain better corrslntion between theoretical and experi-mental results, a study of the spark-ignition enginecycle was made and n thermodynamic cycle set upclosely approximating the actual operating cycle.I?rom a consideration of this cycle, equations for thecycle characteristics, such as indicated horsepower andfuel consumption, mtium cylinder pressure, andpoint at which the maximum cylinder pressure occursin the cycle, were written as functions of three com-bustion parameters that specify the rate, the complete-ness, and the position in the cycle at which combustionoccum. The variation of the combustion parameterswith engine operating conditions was obtained fromindicator cards. The cycle characteristics calculatedfrom the combustion parameters agree closely withthose obtained in the engine tests.

Air flow in oylinde.m.-An investigation has beenstarted to determine the effect of air fiow on combwtion in spark-ignition engines. The air flow is set upby shrouds plnced on the inlet valves. Preliminarytests have shown tlmt with an orderly swirl in thecombustion chamber the entire combustion front is ro-tated, but that there is little apparent effect on thecombustion velocity.

FUEL CONS~ION

Any reduction in the fuel consumption of enatiesused in long-rrmge or transport aircraft can be utilizedto increase the usefid load or the range of the aircraft.Large savings in fuel have resulted from the use ofmixture indicators by commercial operators. The im-provement in cylinder cooling has progressed to sucha point that aircraft engines me capable of operatingat mixtures leaner than are accurately indicated bycommercial mixture indicators. The use of fuels ofhigh octane number has also resulted in an appreciablereduction -in fuel consumption.

Mixture distribution.-’l%e results obtained born aninvestigation of the distribution of fuel to each cylin-der of a single-row radial air-cooled engine by chem-ically analyzing the exhaust gases have been publishedas Technical Note No. 583.

IMel distribution-The use of a fuel-injection s@eminstead of the conventional carburetor requires that ad-ditional air flow be setup within the cylinder to assistin mixing tie fuel and air. A study has been started todeterminethe effect of air movement on the distributionof the fuel spray during the suction and compressionstrokes. The apparatus consists of a glass cylinderckunped between the jacket and the cylinder head of anN. A. C. A. single-cylinder test engine. The piston sidethrust is taken on the steel liner, and a dummy pistonscrewed in the main piston moves in the glass cylinderwith very small clearance. The air flow is made visibleby goose down introduced with the inlet air and is re-corded by high-speed motion pictures taken at a rateof 2,400frames per second. Tests have been completedwith a pent-roof cylinder head in which the inlet valveswere shrouded to give different degrees of air move-ment. V?ith the shrouds arranged to give a tan=mntialswirl, the photographs show that the tangential swirlpersists throughout the compression stroke. With theshrouds arranged to direct the air parallel to the cyl-inder diameter, a decided vertical swirl is produced.With the shrouds radially arranged, a general indis-criminate air movement similar to that obtained with-out shrouds is obtained. The data are being preparedfor publication.

Decreaaedfuel consumptioIL-A study of the fuel-con-sumption characteristics of modern air-cooled en=tiecylinders at various values of engine speed and torquehas been complete& The determination of these char-acteristics was made on two single-cylinder air-cooledtest engines having compression ratios of 5.6 and 6.9,respectively. The resultsshowed that to securebest fueleconomy an engine should be operated at high torqueand at 65 percent of rated speed. Increasing the com-pre&on ratio from 5.6 to 6.9 decreased the fuel con-sumption but did not change the air-fuel ratio thatproduced maximum power or minimum fuel consump-tion. A report is being prepared giving the results ofthi9 investigation.

.M&tare-ratio indicatom.-With transport aircraftmaximum range is obtained by operating the engines atthe air-fuel ratio giving minimum speciiic fuel con-sumption. The Committee is investigating the morepro+g typSS Of~ -ratio indicatom suitable foraircrafi The w of these instruments is limited, how-ever, to air-fuel ratios from 15 to 9. Since aircraft en--ties under cruising conditions are already operatingat air-fuel ratios of approximately 18, there is needfor an improved instrument that will include the full-range of mixture ratios. An investigation has beenstarted to determine potible methods of operating suchan instrument.

Exhaust-gas amdysis.-As most commercial *u-ment.sfor indicating air-fuel ratio depend upon one or

26 REPORT NATIONAL ADVISORY COMMm!mm E’OR AERONAUTICS

more constituents of the exhaust gases, it is importantin connection with the development of such an instru-ment to know the correlation of these constituents withair-fuel ratio. The most reliable method of determin-ing this correlation is by chemical analysis of the ex-haust.~ b investigkion to determine the correla-tion for a number of engines and a rangg of engine-operating conditions has been complete~ and the resultsare in proce.sa of publication as Technical ReportNo. 616.

xNGrNEcowLmGs

The N. A. C. A. cowling.-The results of the compre-hensive investigation carried out with full-scale modelsof the N. A. C. A. cowlingg in the N. A. C. A. 20-footwind tunnel have been published in Technical ReportsNos. 592, 593, and 594. The effect of cowlings on thecooling characteristics of a Pratt & Whitney WaspSIH1-G en5@neis reported in TechnicsllReport No. 596.

Nose-slotcowling.-The preliminary results obtainedwith the nose-slot cowling in the wind tunnel have beendescribed in Technical &port No. 595. This cowling ischaracterized by the fact that the exit opening dis-charbtig the cooling air is not, as usual, located behindthe er++nebut at the foremost extremity or nose of thecowling. This nosa-slot cowling is inherently capableof producing two to three times the pressure head ob-tainable with the normal type of cowling, because theexit opening is located in a low-pressure field. Thusidentical conditions of cooling can be obtained at corre-spondingly lower air speeds. In general, the efficiencyis found to be h&~ owing to the fact that highervelocities may be used in the esit opening.

Investibgtion of the nose-slot cowling has been ex-tended to include flight tests on the XBFC-I airplane.A two-slot design with an adjustable no% section con-trollable from the cockpit has given very good results.This cowling compares very favorably with the originalinstallation of the conventional N. A. C. A. cowling.Greater pressure is available for cooling on the ~ground,while the top speed of the airplane is increased 8 milesper hour. This investigqkion is being continued toimprove the”ground cooling further and to eliminatesome conditions of local heating caused by the changein direction of the air flow. In the second design of thenose-slot cowling tightly fitting baftleswere used. Th-balk were much superior to the service-type bafk,lowering the temperature of the cylinder heads 40° andrequiring the expenditure of only one-iifth the power.

The in-line air-cooled engine--With increase in thepow-er output of the air-cooled in-line engine the dd3i-culties of obtaining satisfactory cooling and low draghave increased. The Committee is investigating theproblems connected with the cowling and cooling of a6-cylinder in-line air-cooled engine. In the in-line en-

ginethe opening available for the entrance of the cool-ing air is quite small, so that the air must enter at rela-tively high speed. The air must be turned through 90°in order to flow over the engine cylinders. Owing tothe relatively high velocity, it was found that 80 per-cent of the available pressure was lost in turning the airbefore it entered the cylinder ba5es. The energy re-quired for cooling was therefore high compared to theenergy required in the radial engine. “

A new cowling has been constructed that will insurea smooth flow of air over the cowling. Enlarged open-ings and pa.ssagx on the air-entrmm side of the cylin-ders will be used to reduce the turning loss of the air,From the results obtained in the tests on this cowling asupplementary investigation will be planned.

ENGINE COOIJNG

Aircraft engines must be operated at approximatelyone-half the rated power and with lean mixtures toobti maximum range. by improvement made inthe cooling of air-cooled erq$nescan be utilized in oper-ating the engine at higher power output during take-offand in cruising with leaner mixtures.

Fin dimensions.-An analysis has been made to de-termine the best proportions for metal lins for givenrates of heat flow, consideration being given to the mini-mum pressure drop acro~ the fins, the minimum powerrequired for cooling, and the minimum weight ofthe iins.

This investigation has shown that:” A considerableimprovement in the heat transfer of conventional alu-minum iins is possible by the use of correctly propor-tioned fins; correctly proportioned aluminum fins willtransfer more than 2.25 times as much heat as steel finsfor the sameweight and pressure drop; the best iin pro-portions for maximum heat transfer for a given finweight and pressure drop are also best for obtaining ahigh heat transfer for a given power expenditure incooling.

As a result of the invwtigation of ~ dimensions’itwas found that, for a given width of fln and velocity,there was an optimum spacing below which the heattransfer rapidly decreased. In order to determine thecause of this decrease,an investigation has been startedin which the type of flow of air around large-scale modelcylinders is determinedby meansof smoke-flow pictures.A hot-wire anemometer is also used to dekmnine thechange from laminar to turbulent flow. The effect ofcylinder diameter, h space, and fin width on the typeof flow is being detetied.

Heat-transfercoefEcients.-The calculation of the heatflow from air-cooled finned surfaces depends upon theexperimentally detmmined heat-transfer coefficients.An investigation to determine the surface heat-transfer

REPORT NATIONAL ADVISORY COMMITTEE HOR AERONAUTICS 27

coefficientsof closely spaced fins from wind-tunnel testswith and without bailles and with blower cooling hasbeen described in Technical Note 602.

An investigation has been made to determine theheat-transfer coefficients of clowly spaced aluminum-tdloy iins having a width of 1.22 inches and copper finshaving a width of 3 inches. The primary object ofthese tests was to determine whether the heat transferas calculated from a theoretical equation checked theexperimental values for finned surfaces constructed ofmetalshav@ diflerent thermal conductivities. The opti-mum fin spacing with wide fins was also investigated.

Cylinderbailles,-A study has been completed of theaerodynamics of cooling air-cooled engine cylinderswith baffles. The air passage was recognized to be aventuri and was studied from this point of view. Theuse of a baffle approximating the best venturi posibleunder the conditions impowd by a radial air-cooledengine resuked in an improvement of 20 percent incooling on a model cylinder. When the results of thisstudy were applied in the bailling of a modern %rowradial engine the cooling on the head was improved28 percent.

Further work is in progress on the problem of im-proving the cooling by changing the cylinder contour.An attempt is being made to overcome some of theditlicultiw in constructing a good venturi in the con-ventional circular engine cylinder. Although the studyis being made for convenience on a model sim~atingthe barrel of the cylinder, the results are applicable tothe head of the cylinder. Since 80 percent of the heatis dissipated through the head, and simm contourchanges are more easily made on the head than on thebarrel, the results will be applied to the head of thecylinder.

Blower cooling.-The results of an investigation on acylinder with fins 1.22 inches in width and with spac-ings varying from 0.022 to 0.21 inch have been pub-lished in Technical Report 6S7. The cylinders -wereenclosed in jackets and cooled with air supplied by ablower. The results showed that maximum coolingwas obtained with a fin spacing of 13 & per inch andthat the heat-transfer coefficient was not sensitive to thefin spacing for values near the maximum, whether moreor less. With M. or 16 iins per inch the heat transferwas 95 percent of that obtained with a iin spacing of 13ti per inch.

The results of the investQation to determine theeffect of h width, fin spacing, entrance and exit areasof the jacket around the cylinder, separator plates, andfillets on the pressure drop and power required to forceair around tied cylinders at air speeds from 15 to230 miles per hour have been prepared for publicationand will be released as Technical Note 621. An analy-

sis has been made of the losses occurring around thecylinder. As a supplement to this work, some miscel-laneous tests are being made to determine the effect ofcertain special jacket and baille designs on the heattransfer and pressure drop of finned cylinders.

Cylinder-temperaturecorrection factor%-The results ofan investigation to determine the effect of engine power,weight velocity of the cooling air, and atmospherictem~rature on the cylinder temperatures of a Pratt &Whitney 1535 engine under fight conditions have beenpublished in Technical Note 584.

The study of the factors for correcting cylindertemperaturesof air-cooled engines to a standard atmos-pheric temperature has been extended to include thecorrection factors for various flight and test conditions,such as level flight, climb, take-off, airplane stationaryon ground, and conditions of constant mass flow ofcooling air and of constimt veloci~ of cooling air.The correction factors range from approximately achange in cylinder temperature of 0.6° to 1.1° perdegree change in atmospheric temperature, the value ofthe factor depending on the fight or test condition. Areport covering this work is being prepared.

Heat trsmsfer.-The study of the cooling of air-cooledengines has been continued. A report has been pre-pared and will be published as Technical Report 612,presenting an analysis in which equations for the rataof heat transfer from the engine gases to the cylinderand from the cylinder to the cooling air, as -well asequations for the averagm head and barrel temperatures,as functions of the important engine and cooling vari-ables, are obtained. Data obtained in tests of single-cylinder engines of cylinders from Pratt & Whitney1535 and 134-O-Hengines for checking the analysis andfor providing the empirical constants in the equationsfor thw cylinde= are presented in the report. hillustration of the application of the equations to the ‘correlation of cooling data obtained in fight tests of aGrumman Smut (XSF–2) airplane is also given in thereport.

An investigation of the effect of turbulence in thecooling air stream on the cooling of the Pratt & Whit-ney 163s cylinder showed that in some cases the turbu-lence caused an increase of as much as 30 percent in theheat-transfer coefficient of the fins for the samepressuredrop acrow the cylinder. These data are included in thereport.

Further cooling tests have bean made on a cylinderfrom a Wright 1$X)-G engine for obtaining the con-stants of the heat-transfer equations for this engine.

R.adiatms.-A study of radiatm design has been un-dertaken. The entrance and exit conditions are beingstudied with a view to improving their aerodynamic.performance. The study has revealed that 50 percent of

28 REPORT NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS

the power required to cool a radiator is lost in the exit

of the air from the radiator tubes in the conventionalhoneycomb tube radiator. The results show that an

important part of this loss can be avoided: Furtherj the

diameter and lenb@h of tubes for the minimum power to

cool is beiig determined. The results will give the

optimum dimensions for several operating conditions

. and installations

COBIE’RESSION-IGNITIONEN~

The compl~on-ignition engine is of particular in-terest as a power plant for transport aircraft becauseof its inherently low fuel consumption. The criticismprwiously made of the compmion-ignition enbtie wasthat it could not produce the necessary high power out-puts for take-off and that the weight of the enbtiewould be excessive because of the high maximum cylin-der presures. The results obtained by the Committeein tests of siugle-cylinder engjn= with the ~. A. C. A.displacer-type combustion chamber showed that theboosted performance of this compression-ignition en-gine was equal to that obtained from the latest type ofair-cooled enaties operating with fuel of 100 octanenumber. Under take-off conditions the maximum cylin-der pressurw developed in conventional air-cooled en-gines have been found to equal thoee in the compres-sion-i=tition engine. The two types of engines shouldtherefore weigh approximately the sanm

Prechamlmr type of combustion chmaber.-The resultsof the investibgtion of the prechamber type of combus-tion chamber for compression-ignition enaties havebeen published in Technical Report 67’7.

Integral type of combustion chamber.-The investiga-tion of engjne performance at 2,500 r. p. m. with a dis-placer piston and a vertical-disk form of combustion

. chamber has been continued. Ii order to accommodatethe increase in the engine rotative speed from 2,000 to2,500 r. p. m. the air induction and exhaust systems werealtered and development work conducted to determinethe proper air-flow passages and the arrangement offuel sprays in the combustion chamber. Test resultsshowed that with existing fuel-injection equipment theinjection period was too long, as evidenwd by late burn-ing and a smo~ exhaust. Even without the mrrectrate of fuel injection an indicated mean effective pres-sure of 260 pounds per square inch was developed at2,500 r. p. m. for a boost pressure of 10 pounds persquare inch. The corresponding speciilc fuel consump-tion was 0.42 pound per indicated horsepower-hour.

Altitude performance.-k investigation of the per-formance of a compression-i=tition engine under alti-tude conditions has bwn completed, and the resultsshowed the Diesal engine to be under no handicap whencompared with the carburetor engine. Tests were mn-

ducted at presure altitudes up to 80,000 feet and attemperature and pressure conditions up to 14,000 feet.Boosted performance was also determined at conshmtinlet-air temperature from boost pressures of O to 10pounds per square inch over a range of exhaust pres-sures corresponding to altitudes from O to 19,000 feet.The scope of the research was expanded to include the -investigation of the effect of single variables of tem-perature and pIWSul13of the inlet air and exhaust backprmure. A report presenting the results of the workis in process of publication.

Si.ngle@inder and multhylinder engines.-An air-cooled compression-ignition cylinder having a push-rod-valve mechanism suitable for use on n radiol en-gine has been designed by the Committee nnd is beingsupplied by the Bureau of Aeronautics, Navy Depart-ment, for investigation. The cylinder has the displacerform of combustion chamber developed by the Com-mittee nnd will be used to investigate its adaptation toair-cooled cylinders. Information will also be obtninedon the factors of multicylinder compression-ignitionenatie performarw and the problem of air-cooling ncompression-ignition engine cylinder.

The %troke-oyele engine,-The investigation of the2-stroke-cycle compression-ignition engine has beencontinued, and tests have been made to determine theeffect of the shape of the inlet ports on engine per-formance. A cylinder liner providing 62 inlet ports,each. of 11~2-inch diameter arranged in three stag-gered rows and drilled at an angle of 56° from theradial, has been tested for ssveral lenbdh-diameterratios of the ports. Best performance was obtainedwhen the length-diameter ratio was 0.’7 and was ap-proximately equal to that with the eight huge rec-tangular ports previously used. work is in progressto determine the effect of varying the timing and dura-tion of exhaust on engine performance.

I?uel-injection rates,-The results obtained from theinvestigation of the rates of discharge from Q single.cylinder fuel-injection pump comected to two injec-tion valves have been published in Technical Note 600.

The increase in rotative speeds of the compression-iguition engines has resulted in inferior perfonrmnceof the fuel-injection equipment. Special apparntus hasbeen constructed whereby accurate and convenient de-termination of injection rates has been made for agroup of available fuel pumps, plungem, and cams invarious combinations The tests included variations ofengine speed and quantity of fuel injected for the sev-eral injection-qstem combinations. Results indicatedthe unsuitabili~ of any available injection equipmentto give satisfactory introduction of the fuel charge intothe cylinder at engine speeds in excess of 2,000 r. p. m,and the urgent need for further injection-system testsand de-reloprnent.

REPORT NMJXONAL ADVISORY COMMI!M!FJEFOR AERONAUTICS 29

I?uel-injeotion pumps,-h improvement in the per-formanm of several cornpresion-ignition engines hasresulted from changvx in the rate of fuel injectiom Aknowledge of the rate of injection of the various fuel-injection systems has been obtained only after investi-gation of their characteristics. A unit type of injectionsystem was investigated to obtain a direct control overthe injection rate by variation in the cam outline. Acam-operated injection pump was closely coupled tothe injection valve, and the effect of chan=w in ori6cadiameter, injection-tubO length, throttle W5bg, pUmpspeed, type of injection valve, and WID outline W=studied.

The cam outline directly controlled the injection rateduring the tit five pump degrees of injection for alarge ori&e diameter and n differential-area valve.After this time interval, leakage at the pump affectedthe control. An open nozzle in combination with aball-check valve reduced the initial rate of dischargeto about half that of the differential-mew valve. Thisrate increased with fuel quanti~ to a mmcinmmat cut-off. With the diii!erential-area valve, the rate of in-jection reached a maximum a few degrew after thebeginning of injection and an increase in fuel quantiQdid not increase this rate. An increase in pump speeddecreased the maximum rate and increased the periodin degrees Increase in injection-tube length had lesseffect on the open-nozzle valve. Secondary dischargeswere not obtained under any operating conditions withshort kjection tubes, but were obtained with increasein tube length under operating conditions in which ahigh initial pressure wave was obtained. The odcediameter materially affected the injection rate, owingprimarily to the high leakage rate at th6 injectionpump. The maximum rate decreased with decrease inorifice diametar. With a suitable pressure seal at thepump nnd w relatively large orifice diameter in a dif-ferential area wdve, the rate of discharge should becontrollable by the cam outline for the unit-typeinjector.

Fuel and comlmstion ameleratms.-The efficiency of thecompression-ignition engine at increasing loads is re-duced by late burning during the power stroke. Someevidence has been presented that the problem of elimi-nating the late burning may not be entirely the me-chanical process of fuel and air mixing but one alsoof overcoming chemical retardants. The use of chemi-cal combustion accelerators in the fuel has been sug-gested as a possible means of overcoming this handicap.A tetranitromethane Diesel oil dope has been obtainedrmd tested in various percmdages in the standard labo-ratory fuel. The small improvement in performance(2 to 8 percmt) was considered economically undesir-able. A sample of a second combustion accelerator has

been ordered for test. A program is also under wayto determine the relative merits of combinations of fueloil and alcohol in various percentages,particularly withrespect to more complete utilization of the air charge.

Fuel investigation-The correlation of engine-per-formance data requires a lmowledge of the heat of com-bustion of the fuel used. The determination of thisfactor and the distillation characteristics of the fuelmake possible the recognition of changes in fuels due toaging or replacement. The heating values of five sam-ples of Diesel fuel used by the Committee for enginetesting have been determined. The values found varyfrom 19,’790B. t. u. to 19,930B. t. u. per poud

The smoky exhaust obtained with compression-igg-tion en=ties operating at air-fuel ratios richer than thetheoretical (15 pounds of air to one pound of fuel)indicatw that considerable fuel is wasted in unburnedcarbon. An investigation is being made to deterrohethe amount of this carbon and its variation with air-fuel ratio. The method used is to determine the actualhydrogen-carbon ratio of the fuel from complete com-bustion tests and the apparent hydrogen-carbon ratiofrom exhaust-gas analysis, the dMerence in the twovalues being the carbon in the exhaust. The actualhydrogen-carbon ratio of five samples of Diesel fuel oilrepresentative of the fuels used during the past twoyears by the Committee has been determined. Thevalues found varied from 0.160to 0.161.

INsmcmmrrs.

l?nel flovnneter.-Flight testing of the electrical typeof indicating fuel flowmeter which has been developedby the Committee has been conducted by the MaterielDitilon of the Army Air Corps. The fuel flowmeteris being altered to incorporate desirable changes indi-cated as a result of the flight tests.

High-speedcareen-The design of a high-speed mo-tion-picture camera to photograph combustion at ratesup to 40,000frames per sacond has been completed, andconstruction of the camera baa been started. The oper-ating principle of the cmnerahas been checked by meansof a mock-up of the canmm

Fuel-injectionpressureindioator.-A piezo-electric pick-up unit has been adapted to a fuel-injection valve toobtain instantaneous values of the fuel pressure at thedischarge oriiice- The presures are shown on acathode-ray tube. Photoe-phic records are made ofthese instantaneous pressure trace9. The rate9 of fueldischarge calculated from the pressure records show avery close agreement with the rates measured on therate-of-ihcharge apparatus. This unit allows a rapiddetermination of rates of fuel discharge and of anycyclic variations in the discharge.

30 REPORT NATIONAZ ADVISORY COM?LHIEJ711EFOR AERONAUTICS

NATIONAL BUREAU OF STANDARDS

Phenomena of combustion.-A spherical explosion ves-sel with centmd ignition and auxiliary apparatus forobtaining simultaneous records of flame travel and pres-sure development has been constructed. The bomb con-sists of two flanged hemispheres, about 10 inches indiameter, clamped together on a short ring of glasswhich atlords a view of the flame in a narrow, verticalcenter-wtion of the bomb.

The proe~ of the flame as it spreads from the cen-tral spark gap is photographed on a ti -which is car-ried on a drum rotating at a known speed on a verticalaxis The movement of the tlhn under the lengtheningimaaw of the narrow flame section produces a time-displacement record of the flame fronk

Six diaphragm prwmre indicators, desi=~ed with aview to securing high accuracy throughout the prwmrerange of the esplosio~ are mounted on the bomb.Each indicator is set to ilose an electric contact theinstant some predeter~ed pressure is reached in thebomb. men the contact is closed a neon lamp of highintensity is lighted, which photographs on the rotatingiihn as a line beside the flame trace. In addition to thesix lamps corresponding to the six indicators, there isa lamp which flashes 1,000 times a second under thecontrol of a tuning fork and a laIup which burns cm-tinuously to provide a reference line for the measure-ment of flame displacements. The flhn thus umtainsall the information necessary for plotting time-dis-placement and time—p~ curves for the explosion.

Formulas have been developed for calculat~g fromthese curves (1) the transformation velocity” or fun-damental speed at which the flame front advances intoand transforms the unburned charge; and (2) the ‘ex-pansion ratio” or ratio of the volume of burned gas tothe volume of the same mass of gas before explosionat constant prwsure~ Experiments will be conductedwith this apparatus to investigate the separate effect9of char=% composition, temperature, and presmre ontransformation velocity and expansion ratio.

Some experiments were made in which a cylindricalglas bomb was used with no pressure indicator todetermine the effect of water vapor on the period ofsubnormal flame velocity just after the ocmrrence ofthe spark. In equivalent mixtmes of carbon monoxideand oxygen saturated with moisture at atmosphericpressure this delay period is very short and high-filmspeeds must be used to detect it- Constant flame ve-loci@ is attained much more slowly when the moisturecontent is reduced below about one percent by volume.The causa of the delay is not known and it is hopedthat new information concerning it will be obtainedwith the spherical bomb.

A brief mimeographed circular outlining the com-bustion experiments which have been conducted at the

Bureau in en=fies, soap bubbles, and bombs, and con-taining a list of published reports on these experimentshas been prepared for distribution to visitors and toothers interested. A mimeographed bibliography con-taining 162 references on high-speed pressure indi-cators, clasified according,to type, is also available.

Investigationof piston cooling.-As the output of air-craft engines is raised the problem of heat di~ipationfrom the piston head becomes increasingly serious. Aprogram has been outlined for determining the heatflow in suitable test specimens under conditions Similarto those encountered in service by aircraft-engine pis-tons. Prelimm“ ary static experiments showed greatlyimproved heat transfer for a hollow steel specimenwith internal moling over a solid aluminum specimenof approximately equal strength, size, and weight.

SUBCOBIMHTEEON AIRCRAFI!FUELSANDLUBRICANTS

Engine performance with iso-ootane fnelso-As men-tioned in the report of the Langley Memorial Aero-nautical Laboratory above, an investigation is beingconducted at that laboratory to determine the maximumengine perfornww with fuels having octane numbersranging from 87 to somewhat greater than 100, Inthis investigation the engine performance has been de-termined with the N. A. C. A. high-speed single-cylinder test engine having a cylinder bore of 5 inchesand a stroke of 5.75 inches. The tests have been madeat an engine speed of 2,500 r. p. m. and a coolant tem-perature of 250” F. The desired octane number of thefuel has been obtained by using commercial iso-octrmeblended with a gasoline having an octane number of 18.For octane numbe= greater than 100, tetraethyl lendhas been added to the iscyoctane.

Tests have been completad with fuels of 87, 91, %,and 100 octane number as detemnined by the C. F. R,method. IiI addition, tests are almost completed onthe iso-octane with 1 cubic centimeter of tetraethyllead. The limiting performance of these fuels has beendetermined at maximum power and at best fuel econ-omy for both incipient and audible knock. The resultsshow that as the inlet-air temperature is increased forany one compression ratio the effectiveness of the fuelsof higher octane number appreciably decreases. Onlyat the lower inkk-air temperatures are the greatest in-creases in performance realized for the fuels of higheroctane number. The tests have shown that the powerof the engine does not vary as the inverw square rootof the inlet-air temperature, but as an approximatelylineal function.

8tability of aviation oils.-The investigation of theAbility of aircraft-engine lubricating oil, conducted bythe National Bureau of Standards in cooperation withthe Bureau of Aeronautics of the Navy, has been ex-tanded to include laboratory tests of the stability of oils

RIDPORT NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS 31

in an apparatus in which the oil flows in a thin illmdown the walls of a heated cylinder and thus simulatesengine conditions. The investigation of this method isnot yet completed, but the data obtained thus far indi-cate a correlation betwean the results of these tests andthe resultsof testswhich have been made in a Pratt andWhitney Hornet engine.

An investigation of the stabili~ of compounded oilshas been initiated in cooperation with the Subcommitteeon Aircraft Fuels and Lubricants, and the effect of anumber of compounding materials on the stability ofthe base oil has been studiecl The results of this inves-tigation will serve as a basis for the choice of com-pounded oils to be used in comection with the study ofwear and oiliness chmacteristix of aviation enginelubricating oils.

Oil aoidi~ and bearing oorrosion.-The investigation,conducted by the National Bureau of Standards incooperation with the Bureau of Aeronautics of theNavy, of the effect of increase in oil acidi~ during serv-ice on the corrosion of master-rod bearings has beencontinued. Study of oils in the apparatus for formingacids in oils has indicated that this apparatus can beused to produce changes in the acidity of oils similar tochanges which occur during service in aviation engines.It has been found desirable to construct additional ap-paratus for use in this investigation and this apparatusis being designed.

Aviation engine wear,-l%e investigation of the rel-ative wear with different oils in actual aircraft engines,carried out at the National Bureau of Standards incooperation with the Bureau of Aeronautics and certainpetroleum organizations, has been continued through-out the fiscal year. The assembly of the operatingequipment for engine control and absorption of poweris essentiallycompleted. Considerable precautions havebeen taken to insure reproducibility of operating con-ditions Special fixtures for use with the precisioninstrumentsrequired for measuring the engine parts areunder construction.

Wear and oiliness characteristics of aviation enginelubricating oils.-The investigation of the oiliness andwear characteristic of mineral and compounded lubri-cating oils, conducted by the National BWWU of S~d-rwds in cooperation with the Army Air Corps and theBureau of Aeronautics, was continued throughout thefiscal year. An apparatus for determiningg the dMer-ences in piston-ring and cylinder-wall ivear with vari-ous oils and compounding aggnts under conditionsapproximating those of actual engine operation hasbeen completed, and preliminary tests are in progress.Construction of a second wear apparatus of differenttype has been begun. The design and construction of amachine for the study of oilims as related to frictionin master-rod bearings is under way.

REPORT OF COMMPI”I’EE ON AIRCRAFTMATERIALS

SUBCOMMITTEE ON M13TALS USED IN AIRCRAFT

Weathering of aimraft struotaral sheet metals-lightalloys.-The series of atmospheric exposure tests ofaluminum-alloy sheet materials was completed duringthe spring of 1937 after four years’ duration at threetest sites, typical of conditions prevail@ at a tropicalmarine, a temperate marine, and an inland location.The results amply cordirm the tentative conclusionsannounced in last year’s report concerning the most cor-rosion-resistant types of alloys and satisfactory coatingtreatments for all alloys of this general kind. A reportintended for publication summarizing the essentials ofthe test and the important facts established is inprogress.

Preparations are approaching completion for a newseries of tIX& This series, which is on a somewhatsmaller scale than the two previous ones, will be con-ducted at only one location, a marine one. HamptonRoads Naval Air Station is the site selected. Bothaluminum and magnesium alloys are included in theprogram of tests scheduled, which are intended pri-marily for investigating the effects of rivet@, vveld-ing, and contact betmwn unlike metals, as well as themeriti of newly developed protective surface treat-ments. The rnanufactumm of thesa materials are co-operating actively in the preparations, and this willinsure that the industrial aspects of the problem willremive the careful consideration they deserve.

Corrosion-re&tant steeL-The trend toward the use inaircraft of corrosion-resistant steel in thin sheet formhas led to the inauguration of a similar prcgram onthis type of materiaL Deterioration of this material,if it occurs, takes place in a different manner fromthat of the light alloys, and the inspection and testingprocedure must be correspondingly diilerent. In bothprob&wms the effect of continuous exposure to themarine atmosphere as well as intermittent exposure tosea-water (the so-called %ide-water” twts) is to bedetermined.

Surface treahnent for improving the durability of mag-ne3ium.-The ultimate aim in this investigation is toproduce a tightly adherent surfaca flhn, highly im-pervious to corrosive agents, particularly chlorides, towhich paint and other applied coatings will adhereover long periods of time without peeling or flaking.Anodic treatment in a bichromate-phosphate bath bythe method developed in cooperation with the Bureauof Aeronautics, according to repeated laboratog testsat the National Bureau of Standards, continues to bethe preferred method for the surface treatment ofmagnwhun and its alloys. Studies on the improvementof the anodic treatment have been continued, and the

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32 REPORT NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS

results have indicated certain modilimtions by whichfurther improvement appears possible. “Sealing” ofthe pores in the anodic film after it has been formedis important to produce a highly impervious fi.This may be accomplished either by chemical meansor by immersion in a hot oil or resin bath. Tests alongthis line are continuing. Initial cleaning before anodictreabnent is also important in obtaining a film on thetreated specimen of superior resistance. Tests on paintadherence as affected by the sealing treatment andother surf ace characteristics are in proayxs in thelaboratory and on the outdoor exposure rack.

Sub-zero temperature and aircraft metals,-’l%e originalprogram, undertaken in cooperation with the Bureauof Aeronautics, has been completed and a report ren-dered, copies of which are available to all interestedGovernment agencies. The only important adverseeffect of low temperatum, down to —60° C., is the de-creased impact resistance of ferritic steels, which is inmarked contrast to the aluminum alloys and the aus-tenitic steels. Study of the factors responsible for thislowered impact resistance of ferritic steels is beingcontinued -with the aim of reducing and posibly elimi-nating the effect by suitable initial heat treatment ofthe steel. The investigation has been extended to in-clude a study of the impact resistance at low tempera-tures of welded joints in steel members.

Elastio properties of high-strength aircmft metals.-Theelastic properties of metals which owe their high-strength properties to strengthening by cold workingare only nominal and vary greatly with the precisionof the method used for their det8nnination. An out-standing example is austenitic steel, such as 16-6 stain-less steel, which because of its high corrosion resistanceis favored for many important uses in aircraft. Themethod used in this work is essentially an “over-load”or ‘>roof-stress” method, consisting in the determina-tion of yield strength after various degrees of coldworking by stretching immediately prior to testing.A rim in proof stress with increase in prior cold workis indicative of an impro~ement in the material, andvice versa for a decrease in proof stress. A reportsummarizing this phase of the work will be forthcom-ing shortly. Hysteresis m easurements, such ns thosevrhich may be obtained in the ordinary tensile-testingmachin~ are now in prcqyess.

Strnotural changes in aircmft met.aIsoccurring as a re-sult of service stxessing.-The principal aim in this in-vesti5@ion is expressed in the question, Does continuedfatigue-stressing below the endurance limit adverselyaffect aircraft metals ? The widely used aluminum pro-peller alloy, 2$S, is the material used in this study. Avariety of approaches to the problem have been made,some of which were abandoned at early stages for morepromising ones. The project is still in the stage of at-

tempts to detect siqnifiwtt changes (other thnn crnckformation and propagation) in physical properti~microstructure, and X-ray diffraction pattern as resultsof continued repeated strewing in the range of maxi-mum fibre stressfrom 5,000to 26,000pounds per squmninch. Up to the present no nondestructive method ofinspection has been found w~ch shows a signiflcuntditferencn between the metal not stressed and the snmemetal after it has been subjected to fatigue stressing.Special mention may be made of the fnilure to detect alowering of impact resistancewhich could be attributedto prior fati=guestrcsiug.

Eopeller materials,-’l%e possible deleterious effect offabrication defects on the endurance properties of steelused in hollow steel propellers merits serious study.Also, the influence on the endurance of propellers ofsurface coatings, such as chromium plnting ns a finish,should not be overlooked.

The fatigue limit of such steel is approximately one-half of the tensile strength, which is considered to benormal for this material. Determinations of the fatiguelimit of sound weld metal showed this to be about 60percent of that of the parent metal. Scaling and sur-face decarbuiizing, such ns maybe present accidentallyon the inside of the welded structure and cannot beremoved, reduced the fati=we limit to one-half that ofthe polished steel, i. e., not much below that of the weldmetal. The effect of accidental defects in the weld isvariable; such defects may cause a very sharp reductionin the fatigue limit of the weld metnl.

The effect of chromium plating vnries with the con-dition of the steel and thiclmess of the plating. Speci-mens of normalized steel (previously polished) bearingrelatively thick coatings showed no significant reduc-tion in fatigue limit and a tier coating had only wslightiy greater effect. On specimens of the same steslin quenched-and-tempered condition, however, a reduct-ion in fatib~e limit was noted, which appeared to be ofmore significance and was greater for a very thin coat-ing than for a coating ten times as thick, the plating ineach caw being applied directly to the previouslypolished steel. The use of a nickel %nder coat;’ inaccordance with commercial usage, prior to plating thequenched-and-tempered steel,gave similar results. Thesubject is receiving further study.

Further study of the unusual structured fenturespreviously reported for aluminum-alloy propellerblades has failed to show that any practical signifi-cance can be attached to them.

Miacellaneoua.-The fact is well established that thecorrosion resistance of many of the aluminum alloyswhich are strengthened by heat treatment is dependentin large measure upon the control of the conditions ofheat treatment. A simple rapid test to determine inadvance of service whether structural mnterials of this

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REPORT NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS 33

kind have been suitably heat-treated so as to developmaximum corrosion resistance should serve a very use-ful purposa A study is being made of a proposedmethod, the essential feature of which is a determina-tion of the solution potential of the material underconsideration.

A relatively inexpensive method of preparing smalifittings of unusual shape is to use transve~e sections ofan extruded shape of the proper size and contour. Astudy of extruded aluminum fittings made in this man-ner is under way, with a two-fold purpose, namely, (a)the improvement of such fittings with respect to certainfeatures which have not proved entirely satisfactoryunder all service conditions, and (b) the determimtionof the practical si=mificanceof certain suspected struc-turedfeatures.

The need for a certain degree of ductili~ in a struc-tural member, as in an aircraft assembly, is well recog-nized. The amount and the manner in which it is speci-fied are, however, matters on which d.iilerenceof opin-ion exists. Determinations of the ductili~ of variousstructural steels under various conditions of stress ap-plication have been continued, in cooperation with theBureau of Aeronautics of the Navy. Interpretationsas to the practical significance of dMerence9 in thisproperty observed under various conditions areyet to bemade.

SUBCON~lIITEEONhlL’3CELLANEOUSMATERIALSA.NDACCESSORIES

The problems under the cognizance of this subcom-mittee during the past year which are being investigatednt the National Bureau of Standards include the de-velopment of a flexible substitute for gla= and thedevelopment of substitutes for linen webbing and silkshroud lines for parachutw. Consideration has alsobeen given to the possibilities of plastics as a materialfor aircraft structures and to the adequacy of thermaland acoustical insulation.

Developmentof flexible substitutefor glass.-Commer-cial nnd experimental transparent plastics which havebeen investigated to determine their suitability for air-craft windshields and windows includo cellulose ace-tate, acrylate resins, cellulose nitrate, ethylcellulosejvinyl chloride-acdate, vinyl metal, glyceryl-phthalate,styrene, phenol-formaldehyde, and cellulose acetobuty-rate.

The tests included light transmission, hazines, dis-tortion, resistance to weathering, scratch and indenta-tion harnesses, impact strength, dimensional stability,resistance to water and various cleaning fluids, burst-ing strength nt normnl and low temperatures, and flam-mability.

The two types of tn-msparentplastics which are nowin use on aircrnft, namely, cellulose ncetateand ncrylate

resin, were found to have certain defects which, it isbelieved, can be overcome in part by suitable modifica-tion of the composition and processing of the material.

Cellulose-acetate plastic wns found to have excellentimpact strength, bursting strength, and flexibility, butthe commercial products tested varied considerably inresistance to vwathering and were all subject to markedshrinkage in one year’s time. The shrbkage pro-duces warping and sets up strains in the plastic sheets,which cause them to craze and crack. These strainsare believed to be the cause of the spontaneous crnck-ing of cellulose-acetate windshields after they havebeen in service for six months or longer. This is par-ticularly true of windshields which are exposed to lowtemperatures, as by ascent to high altitudes, as addi-tional strains are thereby introduced in the windshieldbecause of thermal contraction. Considerable variationm-is observed in the weathering resistance between cellu-loee-acetate sheets received from different manufac-turers and also between Merent lots of the materialfrom the same manufactm+r.

The acrylate-resin ,plastic was found to be remark-ably transparent, more stable to light and weathering,and more re9istant to scratching than celhdose acetate,but i~ impact strength and flexibility are much poorer.Surface crazing of the acrylate resins was noted afterone par’s exposure on the roof and also after storagefor a similar period. It is claimed, however, that amethod of processing has been developed vrhich elimi-nates this tendency to craze. Further tests on modiiiedsamples of both celluloti acetate and acrylate resins arein progress to determine whether more uniformly du-rable products than have been on the market to date canbe made available to the aircraft industry.

Certain of the other materials, which are not nowcommercially available, appear very promis@

Tests for impact resistancewere developed on a scalecommensurate with service conditions. Soft rubberballs, five inches in diameter, loaded to weigh threepounds, were fired from guns at the Naval ProvingGrounds. The muzzle velocity was approximately 300feet per second. No material, whether plastic or kuni-nated glass, was found able to withstand a direct hitwith such a projectile. The experimental pieces were,of course, limited as to weight and thickness by prac-tical considerations of airplane design. It was there-fore concluded that the windshield alone cannot be re-~gymdedas a protection against ducks.

substitutefor linen webbing.-h all-cotton webbingwhich meets the requirements for breaking strength,weight, width, and thickmxx contained in U. S. ArmySpecification No. 15-11-D for linen webbing has beenproduced commercially. While the construction is notidentical with that of the Type-G webbing, the cottonwebbing appears to be a satisfactory substitute.

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34 REPORT NATIONAL ADVISORY COMMITTEE FOE AERONAUTICS

Substitute for silk shroud lines.-Attempts to makeshroud lines from some material other than silk havenot been sumessful to date Whether cotton or rayonwas used, the Strw@h-weight ratio of the line has notequalled that obtainable vvith silk. Experiments arebeing continued to obtain information on the effect ofvariations ~ tile co~uction of fie ~~

Developmentof plastiomaterialfor aircraft strnc.tares,—A survey of the literature on this subject was com-pleted and a report presented to the Committee. Thereport contains data on density, tensile and compressivestrengths, modulus of elasticity, fatigue, energy ab-sorption, corrosion, and methods of fabrication. The&mmrittee is now studying this report with a view todeciding whether or not to go further into the matter.

Materialsfor acousticaland thermalinsulatioIL-A re-port bringing together some of the information avail-able on this subject has been presented to the Com-mittee. Plans have been made to ascertainthe practicalimportance of this subject, and upon the answer to thisquestion will depend future developments.

REPORT OF COMMITTEE’ ON AIRCRAFTSTRUCTURES

IANGLEYBDIMORL4L AERONAUTICAL LABORATORY

Applied loads on airplane stmdm.r~ loads.-Co-ordinated measummenlk of acceleration and air speedon transport airplanes have been continued during the

. PA ym, and tie total flying time represented on therecords has been extended to over 30,000 hours, Themaximum accelerations previously recorded have not,however, been exceeded and the maximum effective gustvelocitiw for normal transport operations remain at*35 feet per second.

Gust resesroh.-l%e measurements of gust intmsitiwand gradients on light airplan~ begun last year, havebeen continued and the data greatly extended. Thenew results do not invalidate the pretious tentative ccm-clusions, that in stable atmospheric conditions withlarge wind ~mdients, vertical gust velocitiw of theorder of 30 feet per second are reached in a horizontaldistance of about 100 feet and that the gust gradientincreases with decreasing gust intensi~.

Surveys of cumulus @pes of clouds indicat13, in gen-eral, stronger downward-acting than upward-actinggusts. On one occasion a downward gust of 53 feet persecond, which reached maximum intensi~ in a distanmof 63 feet, was experienced.

hat tunneL-During the past year an apparatus forcatapulting dynamically scaled models through artifi-cial ~gustshas been developed to the point of satisfac-tory operation. In this apparatus the model islaunched into a condition of steady glide, following-whichit flies through an air jet whose angle relative to

the flight path can be controlled. ‘l!he model cnrriesa small optically recording accelerometer, and m itflies through the gust the acceleration is recorded andsynchronized with external photographic measurementsof the speed, path angle, and attitude angle.

Although this equipment is not ideally suited to theinvestigation of some of the important fundamentalproblems of unsteady flow, it can be used and was de-signed for the direct determination of the effects ofchanges in the several airplane and gust variables onthe airplane motion and wing loads. This function isjustification for the equipment in view of the rapidtrend toward larger transport airplanes, to which thestatistical data obtained on past and presant types ofairplanes do not apply.

Gust-reliefdevices.-A preliminary analytical studyof the merit of two devices for reducing accderationedue to gusts has been made. The more effective ar-rangement appears to be a trailing-edge flap operatedby a small vane located somewhat ahead of the wing.This arrangement responds more quickly and reducesthe acceleration further than the other device studied,which was simply a mass-overbalanced flap.

Load distribution.-’lle results of a previously re-ported investigation of the span-load distribution onwings with partial-span flaps have been published asTechnical Report No. 585. This report includes asimple set of computing forms for determining thedistribution by the L&z method with sui%cienthar-monics retained for good precision. The work onwings with partial-span flaps has been extended toinclude the calculation of the angle of zero lift, thepitching moment, and the induced drag. Wing modelsare now being constructed for investigation to providedata for comparison with the calculations.

several presure- distribution tests have been made inthe 7-by 10-foot wind tunnel of wings with various flaparrangements, including Fowler flaps with chords 30and 40 per cent of the -ivingchord.

Several reporiw describing investigations conductedprior to this year have been imued and include a reporton pressure-distribution measurementson an O-2H ob-servation airplane in tight (Technical Report No. 690),a report presenting an empirical method for determin-ing tip corrections to the theoretical span-load distribu-tion (Technical Note No. 606), and a report on thetheoretical span loading and moments of tapered wingsproduced by aileron deflection (Technical Note No.589).

II’@ tank vents.-During a dive from high altitudesthe presure changes rapidly on the outside of an air-plane. Unless the venting tubes to the fuel tanks andplugs are of the correct size, a pressure difference maybe built up that will be au5cient to collapse the fueltanlmor plugs.

REPORT NATIONAL ADVISORY COMIWP’TEE FOR AERONAUTICS 35

The Committee has been requested by the Bureau ofAeronautics, Navy Department, to investigate thesepressure diffemmces for a range of diameters and lengthsof vent tubes. Apparatus has been assembled in thelaboratory that makes possible the rapid determinationof the prwmre diilerenm between a tank of given vol-ume and the atmosphere during a dive. The laboratorytests have been made at constant ternpemti, as calcu-lations show that this does not introduca an appreciableerror.

Tests have been made for terminal velocities of 300,400, and 500 miles per hour for dives starting at 10,000to 40,000 feet altitude with float and tank volumes from10 to 60 cubic feet. Several lengths of vent tubes 1.5inches in diameter and 0.76 inch in diameter have beeninvestigated. Presure differenms of 10.5 pounds persquare inch have been recorded with a tube 0.5 inch indiameter and 12&t long.

Stressed-Skin Design-stress analysis of lwx& with sheardeformation of the tlamges.-The rapidly increasing sizeof aircraft structures is forcing designers to rely in-creasingly, for economic reasons, on mathematical *IWSSanalysis rather than on static tests. It is well lmownthat the classic methods of analysis are not always suf-ficiently accurab and efforts are being made to correctthese metho+.

& a step in this direction, the bending action of boxbeams such as airplane wings has been extied. Ithas been realized for some time that the flanges of suchbeams deform sutliciently under shear stress to alter thestress distribution materially. The mathematical theoryof this action has been developed to the point of practi-cal applicability and has been partially verified by tests.lhrther tests are under way to determine under whatconditions the theory can be used without modificationand, for cases in which modiktions are necessary, tolead over into the range of the classic engineering theoryof bending.

Strength of stifeners,-A theory for primary failureof straight centrally loaded columns has been publishedas Technical Report No. 682. In the report the theoryfor twisting failure of open-section stiffeners, as pre-sented by Herbert W~5gner (Technical MemorandumsNos, 807 and 784), has been elaborated to include thetwisting failure of open+ection stiileners attached to askin, with streses carried above the elastic range. Anillustrative computation of the column curve for thetwisting failure of an I-section skin-stiffener combina-tion is also included.

Work is being continued on the twisting failure ofother types of stiffener sections, notably the Z sectionand the U section, with and without flanged edges. Ckm-sideration is being given to the manner of shift of theaxis of rotation in twisting failure, both in and above

the elastic range, in order to establish the extent ofrefinement necessary for practical application.

Besides the study of twisting failure, which is aprimary failure, the local failure of various types ofstiilener sections is being investigated, and the theo-retical strength curves are being compared with suchexperimental data as become available from time totime.

Stabili@ of structural systems,-A report has been pre-pared and published as Technical Nob No. 617 dealingwith the stibility criterion for structural systems.The Hardy Cross method of moment distribution isemployed. In order to simpli& the application of thestability criterion, detailed tables are given for theready evaluation of the stiifnws and carry-over factors.Sample problems me also included to illustrate the wof the method.

NATIONAL BUREAU OF STANDARDS

Tubes under loads other than tmsion.-Considerabletime has been spent during the year in revising andbrin.tig into conformi~ with latest Navy Departmentspeciik.ations a report which has been vvritten on the&cation of struts; that is, the column strena@hof tub-ing elastically redxam“ ed at the ends. This report isnow completed and will be published by the NationalAdvisory Committee for Aeronautics as a technicalreport. It gives the column strength of chromium-molybdenum steel, 17ST aluminum alloy, stainlesssteel, and heat-treated chromium-molybdenum-steeltubing, and suggests a method by which planar trussesthat are continuous at the joints may be analyzed anddesigned for stability. Two numerical examples aregiven.

In order to determine the minimum ratio of slender-ness below which thin tubes fail by crinkhg ratherthan as columns, and to determine the crinklingstrengkh,tests of short tubes must be made under axialload. The crinkling strength under axial load of rela-tively short specimens of round 17ST a$uninum-alloytubing has been determined for values of the diameter-thicknem ratio approximately from 15 to 100. Workis in pro- and has been almost completed to deter-mine the crinkling strength of chromium-molybdenum-steel tubing.

The modulus of rupture of round 17ST ahuninum-alloy tubing has been determined for values of thediameter-thiclmes9ratio approximately from 15 to 100.This has been done under third-point loading with theload applied (1) in such a way that failure occurredin the free length between loads, and (2) in such away that failure occurred under a lend. The lattermethod of loading simulates practical conditions oc-casionally encountered under vvhich the load is applied

36 REPORT NATIONAL ADVISORY COMMHM’EE FOR AERONAU!MCS

through a compression member tending to dent thetube. Two empirkal formulas involving the tensileyield stren=@h of the tube material and the dimensionsof the tube were derived to describe the modidus ofrupture for the two serie9 of tests.

The moduhs of rupture obtained with the firstmethod of loading does not depend to any marked ex-tent on the position of the loadirg points, and the em-pirical formula for this method of loading may beused with safety whenever the maximum bending mo-ment occurs in the free len=@h of tube between loadingpoints (including Suppofi). The results are conserva-tive for all other cases exmpt in thos8 relatively fewinstances in which the load is applied through a com-pression member tending to dent the tube. Underthese conditions the empirical formula obtained fromthe tests with the second method of load should beused. The results of the second series of tests can beextended rationally to apply to other than third-pointloading.

work is in progress and has almost been completedto determine the modulus of rupture of round chro-mium-molybdenum-steel tubing under the same condi-tions of test as obtained for the 17ST aluminum-rdloytubing.

Determination of elastiu constants on stainless-steel sheetmatetial.-~ study vms made of the elastic propertiesof stainless-steel sheet of three thiclmesse9 (0.007,0.016, and 0.022 inch) in order to determine effectivevalues of Young% modulus and of Po&cm’s ratiowhich could later be used in calculating stresses fromthe deformation under load of a model structure ofthis material.

The variation of Poison’s &tio and of Young’smodulus with stres, sheet thickness, direction of roll-ing, and prestre&ng was measured by cutting tensilespecimens in the direction of rolling and at right anglesto that direction and measnrin g the ratio of transverwstrain to axial strain with a set of four pairs of Tucker-man optical strain gages suitably placed to eliminatethe effects of nonuniformity of stress distribution.

The values of Poisson’s ratio were found to rangefrom about 0.2 to 0.3. On the 0.007-inch specimen thePoisson’s ratio in the direction of rolling was about0.27, while at right angles to that direction it was onlyabout 0.21. In some cases a considerable difference invalues was found for the second run as compared to thefirst, showing the effect of prdmssing on the elasticproperties of the material.

Large, variations in the value of Young’s moduluswith direction of rolliryg, sheet thiclmmj and stresswere also fouucl In the c.asaof the 0.007-inch speci-mens tested in the direction of rolling the Young’smodulus dropped from around 28.5 I& pounds persquare inch at a stress of around 5,000 pounds per

square inch to a value less than 26.0 10° poundsper square inch at a stress of mound 30,000 poundsper square inch.

The test results indicated the anisotropy of thestainless-steel sheet material. Stresses determinedfrom strain measure ments on a model constructedfrom such material would be subject to a probableerror of several percent due to the variations in elasticproperties alone.

Flat plates under normal pressure,-Experimental workwas cordlned to tests of circular plates under normnlpressure. The stres-strain curve of the materifd inthe center of the plate was derived from the measuredstrains and the measured contoum under load for twoof the plates. In both cases the stress-strain curve ob-tained was found to differ from the tensile strew-straincurve of a coupon cut from the plate in that the stresscontinued to rise after passing the knee of the stress-strain curve; the mechanism of yielding in bilateraltension seemed to be different from that in straighttension.

The experimental work was paralleled by an exten-sion of Stewart Way’s analysis of clamped circularplates of medium thickness under normal pressure togreater deflections than the deflections of 1.2 times thethickness of the plate to which Way carried his tables.The deflections in the present plates amounted to nboutfour times the plate thiclmess before yielding becameappreciable. With the derivation of the curves ofmaximum stress and of deflection at the center of thisorder it will be possible to make an instructive com-parison between the obswved and the calculated clefor-mation of circular flat plates, which it is hoped willlead to an understanding of the yielding in the rectan-gular platm also.

Jhelasth behavior of dnralumin and’ alloy steels in ten-sion and compression-The investigation of stress-straincurves of sheet matmial in tension and compression hasbeen continued. A large number of tensile and ‘~pack’~compressive tests have been made on specimens cutwith and across the direction of rolling from sheetranging in thickness from 0.082 to 0.081 inch. Strw-strain curves have been obtained for aluminum alloys1’X5T, 24ST, 24SRT, Alclad 17’ST, and Alclnd 24 ST.The difference in yield strength in compression M com-pared to tension was found to be of the order of 10 to15 percent. The data suggest that the compressiveyield strength of sheet material in the direction ofrolling can, in general, be approximated roughly by thetensile yield strength at right angles to that direction,and vita versa.

The accuracy of the pack compression test was in-vestigated by comparing the stress-strain curves ob-tained on solid specimens of cold-rolled steel, aluminumalloy, and brass 0.7 by 0.7 inch in section, with streas-

REPORT NATIONAL ADVISORY COhEM.ITTEEFOR AERONAUTICS 37

strain curves from pack compression tests on packsbuilt up from leaves cut from the same bar stock. Thetwo sets of stress-strain curves were found to agreewithin A 2 percent.

The pack compression tests on 24SRT aluminumalloy had shown a value of Young’s modulus which wasconsistently higher by about 3 percmt than the Young’smodulus in tension. This differenm could not beascribed to errors in the compression tests. Prelimirmqtests indicated it to be due to a continuous increase inthe slope of the stress-straincurve in passing from smalltensile stresses through zero to small compressivestresses.

Tubeswith torsionalloads.-The report on torsion testsof 61 chromium-molybdenum-steel tubes and of 10217ST aluminum-alloy tubes was completed and will bepublished as Technical Report No. 601 of the NationalAdvisory CommitteQfor Aeronautics.

A comparison of the empirical formulas proposed inthis report with the torsionaI strength of tubes of 17STand &l.SW aluminum alloy as tested at the AluminumResearch Laboratories showed close agreement, al-though the tubestestedby the Aluminum Research Lab-oratories were considerably shorter and in the case ofthe 51SW material had considerably diflerent mechani-CW1properties than the tubes tested at this Bureau. Theagreement muy be ascribed to the use in the empiricalformulas of ratios involving the tensile properties ofthe tube material.

Beams and stressed-skinresearch.-The proaam onwing beams has been continued with the completion oftests under asial load, transverse load, combined axialrmd transverse loa& of eight wing-beam specimens ofnhuninum alloy with an I-type section having tiltedflanges. Failure in these beams occurred by local insta-bility of one of the flan~ The measured strains anddeflections are being analyzed with the help of com-pressive stres-strain curves for the flange materialwhich were obtained by the pack method. Failure ofthe combined-load specimens occurred at a flange stresscalculated from the loads which ranged from 3~700 to36,400pounds per square inch.

The analysis of the data obtained on the two sheet-stringer panels testedin end compassion at the NationalBureau of Standards has been completed. Comparisonwith the results of similar tests at the Navy ModelBasin on paneIs of the same design showed good agree-ment for the load carried by the sheet at failure. Theload carried by stringers at failure was found to beabout 10 to 20 percent lower for two of the specimenstested at the Model Basin. This relative loss in strengthis probably due to the diilerenca in end restraint, theflat end condition used at the Model Basin providing1ss.srestraint against buckling than the casting of the

ends in wood’s metal wd at the National Bureau ofStandards.

The measured strain distribution in the sheet of thetwo panels tested at the National Bureau of Standardsand the measured buckle shape were compared with thedeformation calculated from approximate theories de-veloped by S. Tirnoshenko, by J. M. Frankland, and byK Marguerre. None of the approximate theories wasfound to agree accurately with observed deformations.,The deflections of the buckled sheet were best describedby Timoshenko’s theory, the axial strains were aboutequally well described by all tlmm theorkx+ the trans-verse strains were best described by Frankland’s theory,and the sheet load was best described by Marguerre’stheory.

The analysis of the deformation of the stringers inthe sheet-stringer panels was confined to a series of plotsof def ormation against deformation overload in accbrd- .ante with Southmdl’s method. If the deformationplotted leads to an inetabili~ of the type to whichSouthvell’s relation applies, all points will lie on astraight line with a slope equal to the elastic bucklingload. Excellent straight lines could be obtained forsome of the stringer twists as measured by the rotationof pointers mounted on the stringer, the slope of thelines being in C1OWagreement with the obwwed buck-ling load The agreement was 1S satisfactory for plotsof other deformations. The lack of general agreementis not surprising, sinca a proof for the validity of South-well’s method has been given so far only for the columnfailure of beams under eccentric axial load and undercertain combinations of axial and txansveme loads.

Eighteen sheet-stringer panels are being fabricated atthe Naval Aircraft Factory for the investigation of theeffect on the compressive strength of such panels ofrivet spacing and spot-spacing. The panels will be l$!and 18 inches long and will con&t of three Z-typestringers fastened to the sheet by rivets or spots spacedan amount ranging from ~2 to 4 inches. The spacingbetween stringers, the sheet thickness, and the spacingbetween rivets or spots will be varied to explore theeffect of rivet spacing on both the buckling of the sheetbetween rivets and on the effective width of the sheetbetween stringers

Airplane vihation.-Close cooperation was main-tained with the Bureau of Aeronautics of the Navy.’- ‘Department in its program on airplane vibration. ThaNational Bureau of Standards participated actively ina number of conferences at which methods were dis-cussed for recording the readingg of vibration pick-upsand of strain pick-ups mounted on various portions ofan airplane in fl.ighti

An important part of the program is the developmentof dynamic-strain pick-ups suitable for attachinent to

●

38 REPORT NATIONAL ADVISORY

the structural parts of an airphum In connection withthis work a number of special strain pick-ups have beenbuilt by the Sperry Gyroscope Company which em-bodied a principle of inertia compensation Sug=-d byTiGlliam M. Blealmey, of the Engineering MechanicsSection of this Bureau. A description of this principlehas appeared in the Journal of Research of the NationalBureau of Standards for June 1937 under the title“Compensation of Strain Clagw of Vibration and Im-pac~” by TIG1l.iamM. Ble.dmey. Thea of the experi-mental pick-ups built by the Sperry C@wcope Com-pany were tested for compensation and for ruggednessof construction on a device subjecting them to accdera-tions up to 50 times .avity with negligible strain.Compensation for inertia forces adequate for pres&tapplications was obtained on one of these. after a num-ber of small adjustments had been made. The cali-brations also mggested a number of changes in thedesi=gp of the gage which would probably improve itsoperation.

A second type of strain pick-up on which consider-able work was done at the Bureau is the strain pick-upof the carbon-resistance type developed by A. V. de-Forest. Static and dynamic calibrations were made on20 carbon resistance strips, 5 of them of the “granular”type used at the Hmnilton Standard Propeller Cem-pany, and the remaining 15 of the m-called ‘k-strip”typa A report describing the results of thes bsts indetail has been forwarded to the Bureau of Aeronauticsof the Navy Department The report gives quantita-tive resultsfor the effect of frequeng, strain amplitude,time under load, and temperature on the calibration ofa number of these strain pick-up%

The best dynamic characteristics viere found for thega=w of the Klk-strip” type. These gages showed aresistance amplitude that was nearly proportional tothe strain amplitude up to strains of 0.001 (correspond-ing to stresEs of about 10,000pounds per square inch inaluminum alloy). The calibration factor calculated bydividing the constant of proportionality by the direct-current resistance of the gab~ was independent of fre-quency between 30 and 100 cycles per second within&10 percent, independent of temperature lwtween–10° C. and 40° C. within *10 percent, independent oftime for one day within 55 percent and for 40 dayswithin *9 percent.

The static calibration tests, -which were coniined togages of the ‘l&s-strip” typ~ gave calibration fac-tors ranging from 40 percent below to 35 percent abovethe dynamic calibration factors. The effect of tempera-ture variations and of time under load were found to bedlicient to render this type of strain gage very muchinferior to accepted gages such as the Tuckernmn opti-cal strain gage or the Huggenhrger extensbmeter in

COMMITTEE FOR AEI{ONAUTICS

those cases where static strainsto be measured.

on a large structure are

The dynamic calibrations of “Ess-strips~’ which weremade by attaching the gage to a propeller blade andthen vibrating this blade in resonance, had indicakdthe need for a calibrator that would subject the stripsto uniform sinusoidal strains of suilicientamplitude rmdof a frequency that co~d be varied over a wider rangethan the restricted number of resonance frequencies (30to 100 cycles per second) that could be sat up in thepropeller blades. A devim was accordingly designedfor calibrating dynamic-strain gages up to 8 inches inlength by subjecting them to uniform sinusoidal strainsup to 0.001at frequencies ranging from 10 to 200 cycle9per second. This device is now being constructed.

Strengthof riveted joints in aluminumalloy.-The in-vestigation described in Technical Note 585 of the Na-tional Advisory Ckmunittcefor Aeronautics has beenextmded to joints in which combinations of the follow-ing alloys were used: rivets, A17ST, WYiV, MST, and24ST; and sheet, 24ST, 24SRT, and Aklad 24ST.

In accordance with the suggestions of manufacturers, ‘tests have been made to determine whether the results .previously obtained on 0.25-inch rivets are applicableto riveb of other sizes. Single shear and double sheartests made so far on rivets ranging from %2 to 6~0inch in diameter indicate that for practical purposesthere is no diilerence between the results obtained onthe various sizes. The driving stress required to forma flat head of a given size was found to increaseslightlywith the diameter of the rivet, but this tendency -wasnot observed for button heads.

Tests to determinethe effect of aging upon the drivingstressrequired to form the head, the shearing strengthof rivets of the various alloys, and the mechanical prop-erties of rivet wire are being carried out.

To supply information needed by the industry on“rivetedjoints of the flush type, specifications for jointsto be made by manufacturers have been prepared anddistributed. Several sets of specimens have been re-ceive~ and these are now being &d. Other flushriveted specimens are being made at this Bureau.

A sat of ihtures has been constructed for drivingrivets by means of a pneumatic hammer in n mannerwhich minimks the personal element in the hendingprocess

Investigation of fatigue resistanceof fabricated struc-tural elementiof airmaft-l%e fatigue test on the remupper wing beam of a BF2C-1 airplane was followedby a similar test on the front beam of the same wingcell. The test was carried to failure at a nominal stressamplitude of about 5,700 pounds per square inch, ascompmyii to a nominal stress amplitude of about 8,tiO0pounds per square inch for the first test. Aftm about

REPORT NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS 39.

2,900,000cycles one flange parted with a. sharp reportat w section where a rib attachment had been rivetedto the flange. Several other cracks were found in thesame flangg, and a large crack was found in the webjust outside one terminal attachmen& Comparison ofthe stres history with the endurance curve of similarmaterial indicated a stressconcentration factor of about3.7. This is considmably higher than the stress con-centration factor of about 3 derived for the fit test,and indicates that the fatigue limit of the fabricatedstructure may be well below one-third the fatigue limitof the material, perhaps as low as a nominal stress of4,000pounds per square inch.

Two complete mtEof BF2C-1 wings have been sup-plied by the Navy Department for the fatigue tests.The wing beams have been removed from these wings,and a method of cutting them has been devised whichwill give eight wing-beam specimens of sufficientlyuni-form section for the tests It is planned to test thesespecimens at diilerent amplitudes of nominal stress inorder to obtain a sullicient number of values of stressagainst cycles to failure to draw a S-N curve for thefabricated wing beam, which may then be comparedwith the S-N curve of the wing-beam material. Thefirst of these eight specimens is being set up for testin the fatigue machine.

PART II

ORGANIZATION AND GENERAL ACTMTIES

ORGANIZATION

The National Advisory Committee for Aeronauticswas established by act of Clmgress approved March 8,1915 (U’. S. Codej title 50, sec. 151). The Committeeis composed of fifteen members appointed by the Presid-ent and mrving as such without compensation. Thelaw provides that the members shall include two repre-sakatives each from the mar and Navy Departmentsand one each from. the Smithsonian Institution, theTVeather Bureau, and the National Bureau of Stand-ards, together with not more than eight additional per-sons %ho shall be acquainted with the needs of aero-nautical scienca, either civil or military, or skilled inaeronautical en~tieering or it9 allied sciences.” Oneof these eight is a reprewntative of the Bureau of AirCkxnmerca of the Department of Commerce. Underthe rules and- regulations governing the work of the@nmittee as approved by the President the Chairmanand Vita Chairman of the Committee are elected an-nually. At the meeting held on October 21, 1937, Dr.Jowph S. bes was reelected Chairman for the ensu-ing year and Dr. David TV. Taylor was reelected ViceChauunan.

Dr. Joseph S. Ames resigned as Clmirman of theExecutive Committee in April 1937, a position he hadfilled continuously since October 9, 1919. At the meet-ing held on April 22,1937, Dr. lVillis Ray Gregg, Chiefof the TVeather Bureau, vw elected to fill out Dr.Ames’ unexpired term as Chairman of the ExecutiveCommittee. At the meeting held on October 21, 1937,Dr. Gregg was elected Chairman of the Executive com-mittee for the ensuing year and Dr. Wfiam P. McC-racken Vim Chairman of the Executive Committee.Dr. David W. Taylor had served as T%e Chairman ofthe Executive Committee since that position was cre-ated in 1927. He remains Vice Chairman of the maincommittee.

During the past year there was one change in themembership of the main Committee. Dr. Fred D.Fagg, Jr., vrho had succeeded Honorable Eugene L.Vidal as Director of Air #mmerca of the Departmentof Commerca, w% on April 23, 1937, appointed by the

40

President to succeed Mr. Vidal as a member of theNational Advisory Canmittee for Aeronautics.

The executive officasof the Committee, including itsoffices of aeronautical intelligence and aeronautical in-ventions, are located in the Navy Building, Washing-ton, D. C., in close proximity to the air organizationsof the Army and Navy.

The office of aeronautical intelligent was establishedin the early part of 1918 as an integral branch of theCommittm’s activities. Scientific and technical dataon aeronauti~ secured from all parts of the world amclassified, cataloged, and disseminatedby this office.

To assist in the collection of current scientific andtechnical information and data, the Committee main-tains a technical assistant in Europe with headquartersat the American Embassy in Park

CONSIDERATIONOFAERONAUTICALINTENTIONS

By act of Congress approved July 2, 1926, an Aero-nautical Patents and Design Board was establishedcon-sisting of Assistant Secretaries of the Departments ofWar, Navy, and Commerce. In accordance with &atact as amended by the act approved March 3, 192’7,theNational Advisory Cmumitt%efor Aeronautic+ passesupon the merits of aeronautical inventions and designssubmitted to any aeronautical division of the Govern-ment and submits reports thereon to the AeronauticalPatents and Dwign Board. That board is authorized,upon the favorable recommendation of the Chnmittee,to “determine whether the use of the design by theGoverrmmnt is desirable or necmsmy and evaluate thedesign and flx its worth to the United Stabs in anamount not to exceed $75,000.”

During the past year the inventions section receivedfor consideration 1,475 new submissions. It conductedthe necessary correspondence and granted interviews wrequested by the inventors. Approximately & per-cent of the new submissions -wereremived through theAeronautical Patents and Design Board. In thosecases reports on the merits of the submissions weremade to that board, and in all other roses replies weresubmitted directly to the inventors.

REPORT NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS 41

AERONAUTICAL RESEARCH IN EDUCATIONALINSTITUTIONS

In continuation of the plan initiated as a result ofrecommendation of the I?ederal Aviation Co &ion,a special allotment of $25,000 was made available fromthe Committee’s funds during the fiscal year 1937 foraeronautical research in educational itiitutions. Un-der this allotment eleven contracts were made dur~~the year with five universities and technical schools, forspecial investigations and reports on the basis of theprobable usefulness and value of the information toneronautic9.

Sweral of the pwpers propamd under contracts madethe preceding year have been published by the com-mittee, while others have supplied information of valuens rLbasis for further research either at the Committee’slaboratory or elsewhere. The papers received undercontracts which have been published by the Committeeinclude one technical report and three technical notes.In addition, one paper has been issued in advance con-fidential form to Americam manufacturers.

COOPERATION WITH THE AVIATION INDUSTRY

The Committee, in the preparation of its program ofrescmch, makes provision for the requirements ofthe aviation industry as to problems to be investi-gated, both in connection with design and opera-tion. The drcraft manufacturers” and operators bringtheir problems to the Cknnmitteds attention as theyarise, either by correspondence or by personal contactsand informal conferences. Advantage is taken by theCommittee of every opportunity to obtain suggestionsand recommendations from representatives of the in-dustry m to investigations which are of particular im-portance to them. TVhen the need arises in comectionwith any particular problem of the industry it is thepolicy of the Committee to call a special umference, or,as previously stated, to establish a special subcommittee,including in either case representation from theindustry.

Realizing that frequently the value of information isgreatly enhanced by its prompt availability, every effortis made to place in the hands of the industry at theearliest possible date the results of researchw that areof particular interest to commercial aeronautics. Itsometimesappears, in the course of an extensive inves-tigation being conducted by the Committee, that the~e.suitsso far obtained will be of special interest andvalue to the aircraft industry if made availableimmediately. In such cases the Committee issues theinformation in advance confidential form to Americanmunufactiers and the Government services.

Some of the subjects on which tits have been re-leased in this manner during the past year are the pre-

vention of ice formation on propellers; the characteris-tic of related forward camber airfoils, from tests inthe variable-density wind tunnel; the characteristics oftapered tinge having N. A. C. A. mean lines; the char-acteristics of tandem air propellers, as instigated byStanford University under contract with the Commit-tee; wing-fuselage interference, including in the firstreport a comparison of conventional and airfoil-typefuselage combinations, and in the second report thecharacteristics of thirty combinations, from tests in thevariable-density wind tunnel; transparent plastics foruse on aircraft, as investigated by the National Bureauof Standards for the Committee; tricycle-type landinggwm, including three phases of the subject-fi~ accel-erations in landing, second, factors affecting the geo-metrical arrangement; and third, the stability of cas-tering wheels; and the characteristics of tapered wingswith ordinary ailerons and partial-span split flaps, asdetemninedin wind-tunnel investigation.

Annual reseamhconference.-As an important aid inkeeping in close contact -with the problems and needsof the aviation industry, the Committee holds each Mayfit its laboratories at L~ley Field an aircraft engi-neering research conference with representatives ofaircraft manufacturers and operators. This conferencewas initiated in 1926, and has two principal purposes,as follows: First, to enable representatives of the in-dustry to obtain &t-hand information on the Com-mittee’s research facilities and the results obtained inits investigations; and, second, to afford them an op-portunity to present to the Committee their sugf+stionsfor investigations to be included in the Committee’sresearch program.

Owing to the large number of those who desired toattend, the conference ‘for the past two years has beenheld on two days, the same program of discussions anddemonstrations being followed both days. The datesof the 1987 couferenca were MLy 18 nnd 20.

Acting under authorization of Dr. Joseph S. &nes,Chairman of the National Advisory Committee forAeronautics, who was prevented by illn~ from beingpresent, Honorable Edward P. Warner, n member ofthe Committee and Chairman of the Cmnmittm onAerodynamics, served as (lhairmrm of the conferenceon May 18; and on May 20 Dr. Willis Ray Gregg,Chairman of the Executive Committee of the NationalAdvisory Cmnmittee for Aeronautics, was chairman.The Committeewas represmted on both days by officersand members, and on May 18 also by its CommitteesonAerodynamics and Power Plants for Aircraft, and onthe 20th by its Committee on Aircraft Structures andMaterials and Subcommittee on Structural Loads nndMethods of Structural halysis.

At the morning session each day the principal in-vestigations under way at the laboratory, both in aero-

—.. A.——t . . . . . L _G_A— –.—

42 REPORT NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS

dynamics and power plants, were explained by theengineem in charge of the work and charts were ex-hibited showing some of the results obtained. Theguests were then conducted on a tour of inspection ofthe laboratory and the research equipment was shownin operation.

In the afternoon six simultaneous conferences wereheld for the discussion of six different subjecl%,namely,airplane performance and design characteristics, aero-dynamic efficiency and interference, cowling and cool-ing research, aircraft-engine research, seaplanes, androtorplanw. At these conferences the tits of thecommittee’s resarches were presented in further de-tail, and sug=~ons were submitted by the represent-ativesof the industry for problems to be added to thecommittee’s program. Each of these suggw-tions, ac-cording to its natur~ was referred to the Committeaon Aerodynamics, the Committee on Power Plants forAircraf$ or the Subcommittee on Structural Loadsand Methods of S&uctnral Analysis and was con-sidered by that committee in the preparation of theresearch program being carried on under its cogni-zance.

SuBcobmmmlms

The Adviso~ Cmnmittea has organized four mainstanding technical committees, with subcommittees, forthe purpose of supervising its work in their respectivefields. The four main tedrnical Committem on Aero-dynamics, Power Plants for Aircraft, Aircraft Mate-rials, and Aircraft Stzmcturesand their subcommitteessupervisa and direct the aeronautical research con-ducted by the Advisory Camn.ittea and coordinate theinvestigations conducted by other agenciw.

& previously stated, during the past year there hasbeen a major change in the organization of the Com-mittee’s standing technical committees. The Ccmunit-tee on Aircraft Structures and Materia@ which wasone of the three principal technical committees, andtwo of its subcommittees, the Subcommittee on Shxm-tural Loads and Methods of Structural Analysis andthe Subcommittee on Research Program on MonocoqueDesign, were dischar=d, and two new standing com-mitt+ the Commiti%eon Aircraft Materials and theCommittee on Aircraft Stmmhmes, were established,each with a status coordinate with that of the COmmit-tee on Aerodynamics and the Canmittee on PowerPlants for Aircraft. The Subcommittee on MetalsUsed in Aircraft and the Subcommittee on Miscellane-ous Materials and Accessories were retained as subcom-mittees of the new Committee on Aircraft Materials.

The work of the standing technical committws andsubcmnmittws has been described in part I.

The or~gmization of the committees and of thestanding subcommittees is as follows:

COMMITTEE ON AERODYNAMICS

Hon. Edward P. Warner, Ohairman.Dr. George W. Lewis, Nattonal Advisory Committee for

Aeronautics, Vice Chatrman.Maj. H. Z. Boge~ Air CWW United Statea Army’, Mat&ld

Division, Wright Field.Dr. L. J. Brim National Bureau of Standards.Theophfle depo~ Mat6riel D1viston, Army Air Corps,

Wright Field.LL Comdr. W. S. DieW United StateE Nmy.Dr. H. L Dryden, National Bureau of Stnndards.LL CeL O. P. Echols, Air Corps, United States Army,

Mat4r1elDIvtsio~ Wright meld,Richard 0. (Mzley, Bureau of Air Commeree, Department

of commerce.Lt Comdr.L. ALGran&United States Navy.Dr. WiMs Ray Gregg, Untted States Weather Bureau.Lawrence V. Kerber, Bureau of Air Commerm Department

of commerce.Delbert M. Littl% United States Weather Bureau.Elton W. Miller, National Advtsory Committee

nanttcs.Comdr. F. W. Pennoyer, Jrm United States Navy.H. J. El. Rekl, National Advisory Ckmnntttee

nautks.Dr. David 1%’.Taylor.

for Aero-

for Aero-

Dr. & l?. “Zahm, Dlviaion of Aeronanti@ Library of Cen-gress.

SIJRCOMMITIZE ON AIRSBPS

Hon. Edward P. Warner, Chairman.S&m Trusco& National Advisory Committee for Aero-

nauti~ Vice Chairman.Dr. Karl Arnstein, Goodyear-ZeppeUn Corpomtion.Maj. H. Z. Bo~ Air Caps, Untted Statea Army, Mat&iel

Division, Wright Field.co mmander Garland Fulton, United States Navy.Dr. Qeorge W. Lwv@ National Advisory Ckmunittee for

Aeronautics (~ ollido member).Ralph H. UpsorL h Arbor, Mkh.

SUBCOMMI’M’REON ?kIEIEOROLOGICALPROBLEMS

Dr. Willis Ray &egg, United States Weather Bureau,Ohakoan.

Dr. TV. J. Humphrey& United States Weather Bureau.Dr. J. C. Hummker, Masaaehusetta Institute of Technology,Dr. George W. Ikv@ National Advisory Committee for

Aeroxmutica (ex ofiido member).Delbert M. LMt@ United States Weather Bureau.Dr. Charles F. Marvin.Lt Comdr. F. W’. Reichelderfer, United States Navy, NrLval

Air Station, Lakehurst.Dr. C. G. .Rossby, Maesachusette Instttute of Technology.Maj. B. J. Sherry, United States Army, Signal Corps, War

DepartmentEugene Sibley, Bureau of Air Commerce, Department of

Commer=SUBCOMMI’ITBEON SEAPLANES

Capt E C. Richardson, Untted States Navy, Chairman.Maj. E Z. Boge~ Air Oorp& United $taka Army, Mat6rlel

Division, Wright Field.Theophtle dePorti MrIb5riQlDivision, ArmY Air OcmPst Wrl~ht

Field.LL Comdr.W. S. Diehl, Untted States Navy.

REPORT NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS 43

Richard (3. Clazley, Bureau of Air Commerce, Department ofCommerce.

Jack T. WIy, Bureau of Air Clommerce, Department ofCommerce.

Dr. George W. I&wIs, National Advisory Committee forAeronautics (ex otlicio member).

Lt. Comdr. A. O. Rule United States Navy.Starr Truscoi+ National Advisory Committee for Aero-

nautics.

COMMI’ITEE ON POWER PLANTS FOR AIM&WI!

Dr. WiiMam P. hfaccrncken, Ohairman.Dr. George W. Lewis, National Advisory Committee for

Aeronanti~ Vice Chairman.LL Comdr. Rico Bet@ United States Navy.Dr. ,H. C. Dickinson, National Bureau of Stnndards.Joim H. Geissq Bureau of Air Commer~ Department of

Commerce,Cnrlton Kemper, Nntionni Advisory Committee for Aero-

nnutimCinylord TV. Newton, Bureau of Air Commerce, Department

of Commerce.Maj. El, R Page, Air Corps, United States Army, Matdriel

Division, Wright Field.Prof. O. I?nyette Taylor, Afnssnclmsetta Institute of Tech-

nology.

SUBCOMMITTEE ON AIRCRAFT FUEI.S AND LUBRICANTS

Dr. H. O. Dickinson, National Bureau of Standards, Chair-mnn.

Lt. Comdr. Rico Bottn, United States Navy.Dr. O. 0. Bridgeman, National Bnreau of StnndarhLL Comdr. James V. Carney, United States Navy.H. K. Cummings, National Bureau of Standards.L. S. Hobbs, The Pmtt and Whitney Aircraft Company.Robert V. Kerley, hIat&iel DivisiorL Arroy Air Corps, Wright

l?ield. GDr. George W. Lew@ National Advisory Committee for

Aeronautics (ex odicio member).Qaylord W. Newton, Bureau of Air Commerce, Department

of Commerce.Arthur NutC Wright Aeronautical Corporation.Maj. D. R Page, Air Corps, United Statex Army, Afat&iel

Division, Wright Field.Addison M. Rothrociq Nationai Advisory Oommittee for

Aeronauthm

COMMITTEE ON AIRCRAFT MATERIALS

Dr. L J. 13rigg&Nationai Bureau of Standards, Chairman.Prof. EL L Whitjemorq National Bureau of Standar&$ Vice

Ohnirman. ,I@. H. 22 130ger4 Air Corps, United States ArmY, Mat6riel

Division, Wright Field.S. K. Colby, Aluminum Co. of America.LL Comdr. 0. E’. Ootton, United States Navy.Edgar H. Dix, Jr., American Magnesium Corporation.Wnrren D. Ehnley, Nationni Bureau of StandardaComdr. Garland Fulton, United States Navy.Richard Cl. Chuzley,Bureau of Air Commercq Department of

Clommerce.Jack T. Grny, Bureau of Air Commereq Department of

Commerce.O. K Heirns, Nattonai Advisory Committee for AeronauticsJ. B. Johnson, Matdriei Division, Army Air Corps, Wright

Field.

Dr. George W. Lewis, National Advisory Committee for Aero-nautics (ex oflicio member).

H. S. Rawdon, National Burenu of Standards.E. C. Smith, Republic Steel CorporationPaul F. Voi~ Jr.l Carnegklllinois Steel Corporation.Hon. Edward P. Warner.

SUBCOMMITTEE ON METAM USED IN AIRCRAF1’

H. S. Rawdon, National Bureau of Standar@ Chnirman.HI.H. Dix, Jr., American Mngnesium Corporation.Oomdr. Garland Fnlton, United Stat= Navy.J. B. Johnson, hIat6riei Division, Army Air Corp% Wright

Field,Dr. George W. Lewis, National Advisory Committee for Aero-

nautics (CZXorncio member).El. O. Smith, Repubiic Steel Corporation.John Vitol, Bureau of Air Commer~ Department of Com-

merce.ProL H, L. Whittemorq National Bureau of Standards.

SUECOMMITTEEON MISCELLANEOUSMATERIAM ANDAGGW801UB5

Warren E. Emley, National Bureau of Standnrdt&CIMrrnan.C. J. Cleary, hIat&riel Division, Army Air CorLW ‘A’right

Field.John Easton, Bureau of Air Commer~ Department of Com-

merce.C. H. Hem Natiomd Advisory Committee for Aeronautics.El. F. Hickson, National Bureau of Standards.Dr. George W. Lew@ Nationni Advisory Committee for Aer&

nantics (ax ofticio member).J. El. Suiiivan, Bureau of Aeronautb, A’avy Deparhnent.G. W. Trwer, Forest Servi~ Department of Agriculture.

COMMITTEE ON AIRCRAFT STRUCTURES

Dr. L, J. Briggs, National Bureau of Standards, Ohairman.Richard O. Gazley, Bureau of Air Oommer@ Department of

Commerce.Lt. Comdr. L IL Grant, United States Navy.Maj. C. F. (lreen~ Air CorW United States Army, Mnt&iel

Division, Wright Fieid.CapL Paul 1% Kemmer, Air Corps, United Statw Army, Mn-

t&riel Division, Wright Field.Dr. George W’. Le~ Nationai Advisory committee for Aero-

nautic (ex officio member).ElngeneEl.Lundquist, Nationai Advisory Committee for Aero-

nautics.Lt. @mdr. R. D. MacCarb United States Navy.Prof. Joseph S. New~ Massachusetts Institute of Technology.Dr. Waiter Rwnberg, Xationrd Bureau of Standards.Richard V. Rhode National Advisory Committee for Aero-

nautics.Edward L Ryder, Bureau of Air Commer~ Department of

Commerce.R L. Templin, Aluminum Oompany of America.Dr. L. B. Tuckerman, Nationai Bureau of Standards.Hon. Eldward P. Warner.

COMMITPEE ON AIR~ ACCIDENTS

Hon. Edward P. Warner, Chairman.LL J. I?. @eensiad~ United States Navy.Maj. El. V. Harbe& Jr., Air Corps, United States Army.J. W. Lankford, Bureau of Air Commerc% Department of

commerceDr. George W. LewhL National Advisory Committee for

Aeronautics.

44 REPORT NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS

Lt. Comdr. A O. Rul& United States Navy.J. T. Shumat% Bureau of Air Commer~ Deparhnent of

Commerce.Maj. LmveR H. Smith, Atr COrP&United StateS *Y.

COMMITTEE ON AERONAUTICAL INTENTIONS ANDDESIGNS .

Dr. IL J. Brim Natioml Bureau of Staudards, Ohairman.Dr. WilUs Ray &egg, United States Weather Bureau.Capt. S. M- Kmw United States Navy.Brig. Gea. & W. Robins, Air Corps United States Army.

Mat6rIelDivisioII,Wright Field.Dr. David W. Taylor.John F. Victory, Secretary.

CONMITI’EE ON PUBLICATIONS AND INTELLIGENCE

Dr. Jcaeph S. Ames, Chairman.Dr. WiRis Ray @egg, United States Weather Bureau, Vice

Chairman.Miss M. M. MuRer, Secl!btary.

COMMITTEE ON PERSONNEI+ lKJILDINGSy ANDEQUIPMENT

Dr. Joseph S. Ames, Chairman.Dr. David W. Taylor, vice Chairman.Dr. Willis Ray Gregg, United States Weather Bureau.John F. Victory, Secretary.

TECHNICAL PUBLICATIONS OF THE COMMI1l’EE

The Committee has four series of publications,namely technical reports, technical notes, technical mem-orandums, and aircraft circulars.

The technical reports present the results of funda-mental research in aeronautics. The technical notes aremimeo=mphed and present the results of short researchinvestigations and the results of studies of speciiic de-tail problems which form parts of long investigations.The technical memorandums are mimeographed andcontain translationsand reproductions of important for-ei=m aeronautical articles. The aircraft circulars aremimeographed and contain descriptions of new types offoreia= aircraft.

The following are lists of the publications issued:

LIST OF TECHNICALREPORTSISSURD DUR~G THEPASTYEAR

N’o.S77.PreclmmberComprwsion-I@tion Engine Performance.

By @arles S.MooreandJohnH- Collhu+Jr+N A. C.A.6iS. l?lightAleasurementsof the DynamicIangitndinal Sta-

bility of Several Airplanes and a Correlation of theWmmrernents with Pilots’ Observations of HandlingOharacteristica. BY Hartley A- Soul& N. A. C. L

579. A Study of the Two-Contiol Operation of an Airplane.By Robert T. Jones, N. A- C. L

6S0. Heat Transfer to Fuel Sprays Injected into Heated@es. By Robert F. Selden and Robert C. Spencer,N. A. O.A.

5SL Memmrements of Intensity and Scale of Wind-Tunnel!l?arbulence and Thdr Relation to the Oriticd ReynoldsNumber of Spheres. By Hugh L. Drydem G. B. Schu-bauer, W. O. Mock, Jr., and E K. Skramstad, NationalBureau of Strmdards.

5S2. A Theory for Primary Failure of Strnight OentmllyLoaded COlarnUS. By Eugene E. Lundquist nnd ClnudoAL Fligg, N. A. C. A.

5S3. The Rolling Friction of Se~eral Atrplrme Wheels midTires and the Effect of Rolling Frlctlon on Trike-Off.By J. W. Wetroore, N. & C. A.

W. Strength of Welded Aircraft Joints. BY W. O. Bruegge-man, National Bureau of Stnnclnrds.

5Ei5.Span Load, Distribution for Tnpered Wings with W rtial-Span Flnps. By H. A. Pearson, N. A. O. A.

5S6. Airfoil Section Clmmcterietics as Mected by Varlntionsof the Reynolds Number. By Eastman N. Jncobs nndAlbert Shennnn, N. A. C. A.

5S7. Blower Cooling of Firmed Cylinders. By Oscar W. SclIeyand Herman H. Ellerbrock, Jr., N. A. O. A.

5SS. Fuel Spray and Flame Formation in n Comprcsslon-Ignitton Dngine Employing Air Flow. By A. hf. Rotb-rock and O. D. Wnldron, N. A. C. A.

5-S9.An Annl@s of Lateral Stability in Power-OIT Flight withCharts for Use in Design. By Ohnrles H. Zhnmermnn,N. A. O.A.

6S0. PressnwDlstributioti hIeasarements on nn O-2H Airpkumin Flight. By EL & Pearson, N. A. O. A.

691. An Analytical and Experimental Study of the EtTect ofPeriodic Blnde Twist on the Tim@ Torque, nnd Flnp-ping Motion of an Autoa@o Rotor. By John B. TVhent-Iey, N. & C. A.

692 Full-scale TMs of N. A. O. A. Cowlings. By TheodoreTheodorsen, M. J. Brevoort, and George W. Stickle,N. A. O.A.

59S. Cooling of Air@nne Engines nt Low Ah Speeds. ByTheodore Theodorsen, M J. Brevoorti and George W.SticklCAN. A. O. A.

604. Chamcteristlcs of Sis Propellers Includlng the High-Speed Range. BY Theodore Theodorsen, George W.Stiekl% and AL J. Brevoor4 N. A. O. A.

595. Frill-Scale Teds of a New Type N. A. O. A. Nose-SlotCowling. BY Tlm@ore Theodorsen, M J. Brew@rGUeorge W. Stickl% and M. N. Gough, N. A. O. A.

596. Cooling Tests of n Single-Row Radinl Engine vdth Sev-eral N. A. C. A. Cowlings. By M. J. BrevoorG GeorgeW. Sticklq and Herman H. Mlerbrwk, Jr., N. A O. A.

697. Air Propellers in Yaw. By E. P. Lesley, Cleorg’eF. Wor-Iey, and Stmdey Moy, Stanford Universlti.

59S. Alternating-Onrrent Eqrdpment for the Measurement ofFluctuations of Air Speed in Turbulent Flow. BYW. C. MoclG Jr., Nntional Bnrenu of Stamlnrds.

699. FUght Tests of the Drag nnd Torque of the Propeller inTerminal-Velodty Diwn. By Richnrd V. Rhode nmlHenry A, Pearson, N. A. O. A.

600. An Analysis of the Factors That Determine the PeriodicTwist of an Autogiro Rotor Blndq with n Oompnrlsonof Predicted and Measured Results. By John B.Whentley, N. L C. A.

601 Torsion Tests of Tabes. By Ambrose H. Stang, WnlterRamberg, and Goldie Bnc& Nntional Bureau ofStandnrd&

602 Wind-Tunnel and Flight Tests of Slot-Lip Ailerons. ByJoseph A. shOItfd, N. A. O. A.

603. TViqd-Tnnnel Investigation of Wings with Ordinary Ailer-ons and Full-Span EMernal+iirfoil Flnps. By RobertC. Plntt and Joseph A. Shortnl, N. A. O. A.

604 Prwmme-Distribution Measurements nt Large A@es ofPitch on Fins of Different Spnn-Ohord Rntio on n l/43-Scale Model of the U. S. Airship “Akron.” By Jnmes G.McHugh, N. A. O. A.

REPORT NATIONAL ADVISORY

605. R&mm@ and Analyeis of N. A. C. L Lateral Ccmtrol Re-search. By Fred E. Welck and Robert T. Jones, N. A.o. A.

@)13.Electrical Thermometers for Aim&L By John B. Peter-son and S. H. J. TVomac~ lfntionrd Bureau of Standards.

607. Sphm[ng Chamcterlstics of the XN2Y-1 Airplane Obtatnedfrom the Sptnning Balanc@ and Compared with ReEuItsfrom the Spinning Tunnel and from Flight Twtz, ByIL J. Bamber and R O. HOUSSN. A. O. A.

60S. Stress Analysis of Beams with Shear Deformation of theFlanges. By Paul Kuhn, N. A. O. A.

600. Experimental Investigation of Wind-Tunnel Interferenceon the Dowmvash behind an AirfoiL By Abe Silwrsteinand S. KrItzoff, N. A. O. L

610. Tests of Related Ii’orward-Cam&r Alrfolls in the Variable-Density Wind Tunnel. By Eastman N. Jacobs, RobertM. Pinkerton, and Harry Greenberg, N. A. O. A.

611. Wind-Tunnel Investigation of Tapered Wings with Or-dinary AUerons and Partial-Span Split Flaps. By CarlJ. Wenztnger, N. A. 0. A.

LIST OF TECHNICAL NOTES ISSUED DURING THEPAST YEAR

No,L%?.Analysis and Model Tests of Autogiro Jump Take-Off. By

John B. Wheatley and Carlton Bioletti, N. A. 0. A.GS3,Mixture Dlstribntion in a Single-Row Radial IEnglm By

Harold 0. Gerrish and Eked Voss, N. A. C. A.W4. Effect of Several Factors on Cooling of a Radial Engine

in Fllghk By Oscar W. Schey and Benjamin Pink@N. A. 0. A.

COMMITTEE FOR AERONAUTICS 45

56& Wind-Tunnel Tests of a Olark Y Wing with “Maxwell”Leading-Ildge Slots. By William Ill. Gauvain, N. A. C. A,

699. Charts Exprwsing the TM% Velocity, and Altitude Rela-tions for an Airplane Diving in a Standard Atmosphere.By H. A. Pearson, N. A. C. &

600. Discharge Characteristics of a Double Injection-Valve Sin-gle-Pnmp Injection System. By Dana TV. Lee and IL T.Marsh, N. A. 0. A.

60L The Lateral Instability of Deep Rectangular Beams. ByO. Dnmont and H. N. Hill, Aluminum Oompany ofAmerica.

602. Heat Transfer from Oylinders Having Olosely Spaced l?imBy Arnold D. Bierm~ N. A, C. A

303. A preliminary Study of Flame Propagation in a Spark-.Ignition Engina By A. M. Rothrock and IL 0. Spencer,N. LO. A.

604. Full-scale Wind-Tunnel and Flight Tests of a Fairchild22 Airplane Equfpped with Elxternal-AWoil Flap& ByWarren D. Reed and William C. Clay, N. A. C &

60& Noise from Propellers with Symmetrical Sections at ZeroBlade Angle By A. F. Deming, N. A. C. A.

606. Empirical Corrections to the Span Load DSstibution atthe Tip. By EL A. Pearso~ N. A. O. A.

607. The Behavior of Thin-JVaR Monocoque Oylinders UnderTorsional Vibration. By Robert E. Pekelsm& Universityof Michigan.

W& Free-Spinning W’ind-Tnnnel Tests of a l%v-lVing Mono-plane with Systematic Ohanges in Wings and Tails.I—Baeic Leading Condition. By Oscar Seidman and.LLNeiho~N. LO. L

U%. Mechanical Properties of Aluroirmm-AUoy Rivets. By Wm. . 609. Considerations Affecting the Additional Weight Required

0, Brneggeman, National ~nreau of Standards.in Mass Balance of AUerons. By W. S. Diehl, Bureau

5S0. The Reduction of Aileron O~mting Force by Differentialof Aeronautic Navy Department.

Linkage. By Robert T. Jones and Albert L Nerken, 610. EfPect of Air-Entry Angle on Performance of a 2-Strok&

N. A. C.A. Clycle Compression-Ignition Engin& By Sherod L. Earle

GS7.The Forces and Moments on Airplane Elngine Mounts. ByPhilip Donely, N. & O. A.

GM. Strain Measurements on Small Duralumin Box Beams inBendtng. By Paul Kuhn, N. A. C. A.

EM. Theoretical Span Loading and Moments of Tapered WingsProduced by Aileron Deflection. By H. A P~n,N. A, C. A.

G60. Hydrodynamic Tests in the N. A. C. A. Tank of a Model ofthe Hull of the Short Calcuttn Flying BoaL By Ken-neth El Ward, N. A. (Y.A.

1111.Full-Scale Span Lead Distribution on a Tapered Wingwith Split Flapa of Various Spans. By John B. Parsonsand Abe Silverstein, A’. A. C. L

092. A Study of the Factors AfWcting the Range of Ah@nes.By David Biermanq N. A. O. L

593. Pressure Drop in Tubing in Aircraft Instrument Installa-tions. By W. A. TVildhack, National Bureau ofStandards.

Gill. Tank Tests of Two Models of Flying-Boat Hulls to Deter-mine the Elffect of Ventilating the Step. By John 1%Dawson, N. A. 0. A.

5fJ&Bending Tests of Clircular Oylinders of Corrugated Alumi-nurn-tklloy Sheet. By Alfred S. NileE, John C Buck-vralter, and Warren D. Reed, Stanford University.

606. Full-Scale Wind-Tnnnel and Flight T&x8 of a Fairchild 22Airplane Equipped with a Zap Flap and Zap Ailerons.By O. H. Dearborn and H. A. Soul& N. A. C. A.

507, Notes on the Calculation of the Minimum Horizontal TailSurface for Mrplanes Equipped with Wing Flaps ByHartley A. Soul&, N. A. C. A.

and Francis J. Dub N. A. O. A.OIL The Sonic Althneter for AtrcrafL By 0. S. Draper, Mas-

sachusetts Institute of Technology.612. Spinning Characteristics of Wings. HI-A Rectangular

and a Tapered Olark Y Monoplane Wing with RoandedTiF& By M. J. Bamber aud R- O. HOW N. A. C. A.

613. The EM&t of Onrvatnre on the Transition from Laminarto Turbulent Boundary Layer. By, Milton Clauser andFrancis Olauaer, California Institute of Technology.

614. Fuselage-Drag Te&a in the Variable-DensMy Wind Tunnel:Streamline Bodies of Revolution, Fineness Ratio of &By Ira E Abbot& N. A C. A.

615. Motion of the Two-Control Airplane in Rectiilnenr Flightafter Initial Disturbances with Introduction of ControlsFollowlng an Exponential Law. By Alemmder Klemln,New York University.

LIST OF TECHNICAL MEMORANDUMS ISSUED DURINGTHE PAST YEAR

No.S05. General Considerations on the Flow of Compressible Flaids.

By L. Prandtl. Paper presented at Volta meeting inItaly, September 30 to October 6, 1935.

S00. The Que&ion of Spontaneous Wing Oscillations (Deter-mination of Critical Velocity through Fllght-Oscilla-tion Tests). By B. v. Schlippe. From Luftfahrtfom-chung, February 20, 1936.

S07. Torsion and Buckling of Open Sections By Herbert Wag-ner. From the 26th anniversary number of the Tech-nische Hocbschulq Danzig 1904-1929.

46 REPORT NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS

S03. High-Speed Wind Tunnebi. By J. Ackeret. Paper pr+sented at the dfth convention of the Volta Congr~Italy, September 30 to October 6, 1935.

S09. Testa for the Determhmtion of the Stress Condition inTension Fields. By R Lahde and H- ‘iVagUer. FromLuftfahrtforschung, August 20, 1936.

S1O.Impact of a V&Type Seaplane on Water with Refer-ence to Imlsticity. By I!’. Weinfg. From Luftfahrt-forschung, May 20, 1936.

Ml. The Impact on FloatE or Hulls During Landing as Af-fected by Bottom Width, BY El. Mewes. From Luft-fahrffomchung, May 20, 1936.

SW. The Horsepower of Aimraft -es and Their ~umFrontal Area, By Michel PrecouL From L’A&onau-tiquc No. 207, Augnst 1936.

SL3. The Cetene Scale and the Induction Period Prweding theSpontmwme Ignition of Diesel Fuels in Bombs. By M-N. Michailova and hf. B. Nemnann— From ComptesReudus (Doklady) de l’Academie d= S&mea de1’URSS, VOLII (=), No. 4 (W), 1~.

SM. Experimental Studies of the Effective Width of BuckledSheet& By R. Lahde and EL Wagner. From Lmftfahrt-forschtmg, Jdy 20, 1936.

S15. Automatic Stabilization- By Fr. Ham. From L’A&ronau-tiqu% March 1936.

616. The Gyroplan&Ita Principles and Its Posdbilitiea. BYIAN& BregneL From Jonrnees Techniques Internation-als de l’A4ronautiqu~ November 23-27, 1936.

S17. The Sb-ew Distribution in Shell Bcdiea and Wings as anINmillbrium Problem Bv H. Waemr. From LnfKahrt-

S29. Metlml of Oarved Models and Its Application to the Studyof OurvlMnear F&M of Airship Part I. By G. A.Gourjienko. From Central Aero-HYdrodYuamical In-stitute Moscow, Report No. I.&2,1934.

S30. Method of Chrved Models and Ha Application to the Studyof Curvilinear Flight of Airships. Part H. BY G. A.Gourjienko. From Central Aero-Hydrodynamical Insti-tut% Moscow, Report No. #2, 1934.

WI.. Contributions to the Theory of Incomplete Tension Bny.By El. Schapitz. From Ltitfarhrtforwlmng, hfm’eh 20,1937.

&E?.The Critical Velocity of a Body Towed by a Unble from anme. BY C. Koning and T. P. DeHans. FromRijka-Studiedienst voor de Luchtvaa~ Amsterdam, Re-port A 367.

633. The Apparent Width of the Plate in Compression. ByKarl Margnerre. From Lnftfahrtfomchung, March 20,1937.

S34 The Stability of Orthotropic 13111pticOylindera in PureBending By O. S. Heck. From Lnftfahrtfor%chung,March 20, 1937.

S36. Prwmre Distribution on a Wing Section with SlottedFlap in Free Flight Tests. By Georg KM. From Luft-fahrtiorachung, February 20, 1937.

836. The Ground EITect on Lifting Propellers. By A. Bet?&From Zeitschrlft fiir angewandte Mathematik undWchaui& April 1937.

=7. Oharts for Checking the Stability of Plane Systems ofm. By K. Borkmann. From Lnftfarhrtforschung,Febmary 20, 1937..__ ——.— .—– .—

fol%clmng,September 20; lsw - . 83S.The Strengthof SheUBodies-TheorY and Practice. By H.t31&Valv=Pring Snr@. By WLUyMarti. Federal l?olytech- Etmer. From Luftfahrtforschnng, March 20, 1937.

nic Institute of Zurich. 1935.SL9. Experimental Apparatus for the Study of Propellem. BY

M. PanettL From Experimental reporta by the Aero-’nautical L@oratory of the Royal Engineering Instituteof Turin, serie5 1.

S20. Some I!lxperhnents on the Slipstream Effect. By CLFer-rari. From IMperhnental reports by the AeronauticalLaboratory of the Royal Iilngineering Institute of Turin,Sedes !2.

S2L. On the Actual Loads on Airplane Landing Genrs. By S.Shiakin. From Report No. 269, of the C-entral Aero-Hydrodynamical Institute Moscow, 1936.

622. Turbulent Bouudwy LaYer of an Airfotl. BY K. Fedfaev-sky. From Report No. ~ of the Central Aero-Hydro-dynnmical ImkM@ Moscow, 1936.

623. Experimental Investigation of the Problem of SurfaceRoughnes+. By H. Schlfchting. From Ingenienr-Ar-chlv, Febmary 1936.

S24 The Photoelastic Investigation of Three-Dimensional Shessand StraLn Conditions. By G. OpE& From Forschnngauf dem Qebiete da Ingenlenrw_ Septembe&October1$36.

S25. The Source of Propeller NoisrABy W’. Ernsthausen. FromLuftfaMforschun& December 20, lfB&

S26. The Scale Effect in Towing Tests with Airplan&Fioat Sys-tems. By Rudolph SchmidL From Luftfahrtforsdnmg,July 20, 193&

S27. Helicopter Problems. By H. G. Kihxmer. From Luftfahrt-forsclmng, January 20, 1.937.

t3%i Ground EtMt-!llwory and PractiQ BY II. piStO1eSL

From Pnbblicaziord dells IL Scnola d’Ingegneria di P=series Q July 1.935

LIST OF AIRCRAFT CIRCULARS ISSUED DURING THEPAST TEAR

No.%-. The Hafner A.R.111 C&roplane (BrlWh). E’rom I’Ught,

Febmary M, 1937.206. Armstrong WMtworth 27 ‘%nsign” Commercial Airplane

(British). An All-Metal High-W@ Monoplane. ~rOIUFligh~ January 7, and April 1,1937.

207. Baynes Bee Light AIr@me (British). A Two-Seat High-Wing Monoplane. From The Aeroplane, March 1’7,1937;and I?ligh& March It, and March 1S, 1937.

20s. The ~ “Oxford” Trairdng Airplane (British). ATwo-Engine Cantilever Monoplane. From The Aero.plane, June 23, and July 26, 1937; tmd l?ligh~ April 29.and July 1, 1~.

FINANCIAL REPORT

The gene~ appropriation for the National Advi-

sory @n.rnMee for Aeronautics for the &cal year1937, as contained in the Independent Offices Appro-priation Act approved March 19, 1936, was $1,168,860.

A supplemental appropriation of $1,36’7,000 was madeavailable in the First Deficiency Appropriation Act!&al year 1936, approved June 22, 1936, for the samepurposes spec~ed in the Committee’s regular nppro-pritttion act for 1936, to continue available until June30, 1937, and providing for expenditure of not toexceed $1,100,000 for the construction and equip-ment of an additional *d tunnel (19-foot pressure

REPORT NATIONAL ADVISORY CO~PM!EEI FOR AERONAUTICS 47

tunnel), and not to exceed $267,000 for increasing thelength of the seaplane model testing tank and foradditional equipment therefor. The total amountavailable for general expenditure during the iisc.alyenr 1937, therefore, was $2,525,850. The nmountexpended and obligated was $2,337,638, itemized asfollows :

Personal services _—_.-—— ------------Sapplies and materials-- __ -—-------Communication service—--—--——--— --------------Tmvel expenses ——-—--- ——---——-——Transportation of things _———— —----Fnrnfsldng of electricity _____ — - —- . ---—----—Repairs and altemtions-- _ —--. ——_--—Special investigations and reports_—-____————__——EquipmenL_— _____———- —- —— —--Sbuctia————----————-——--

$92s, 33771,7898,053

144642,742

36, 25S4, S39

80,744m, 510s14, 0a4

DxP@nded and obligated- —---— 2237, e3sUnobligated Wanes _—-_-——--———————— 1ss, m

Tow general appropriation_— ------- 2,625, S60

The appropriation for printing and binding for1937 was $18,’700, of which $18,679 was expended.

The sum of $19,689 was received during the &c.al

yam 1937 as special deposits to cover the estimated

cost of scientitlc services to be furnished privateparties. The total cost of investigations completed

for privnte parties du~~ the flscnl year, tunounting

to $12)072, was deposited in the Treasury to the creditof Miscelltmeous Receipts.

The amount of the regular appropriation for the fi-

cal year 1938 is $1/259,850, as provided in the Inde-pendent Offices Appropriation Act approved June 28,

1937. A supplemental appropriation of $453,000 wasmade available in the Second Deficiency Appropria-tion Act, fiscal year 198’7, approved May 28, 1937, forthe same purposes specified in the Committw+s’ regular

appropriation act for 193’7, to continue avafiable until

June 30, 1938, and providing that $~53,000 shall beavailable only for the construction and equipment offacilities nnd for the purch= of an *lane of the

light metal private type; and provifing further, thatthe unexpended balance of the supplemental appropria-tion of $1)67,000 for 1937 be continued available un-

til June 30,1938. That unexpended balance was $186,-968. The total. amount available for general expendi-ture during the fiscal year 1938,therefore, is $1,899,818.In addition, the.amouqt of $21,000was appropriated forprinting and binding for the fiscal year 1938.

An allotment of $7,35o was received from the StabDepartment for payments during the fiscal year 1937to employees stationed abroad, on account of exchange10SRSdue to appreciation of foreign currencies, andof this amount $2,866was paid during the fiscal year toemployees of the Committee stationed in the Paris05ce, leaving a balanca of $4,484 turned back into the~.

Of the allotient of $2,000 for participation in theGreater Texas and Pan American Exposition, whichopened at Dallas, Texns, June 12, 1937, the amount of$4o4 was expended and obligated as at June 30, 1937.

CONCLUDING STATEMENT

The greatly extended use of aircraft for both mili-tary and civil purposes has been reflected in an in-creased activilq on the part of progressive nations inextending their aeronautical research facilities. Thedemands made upon the Committee by the War, Navy,and Commerce Departments for new information areincreasing in number and in &.tEcul@with the increasein the speed and size of aircraft. The Committee fullyrecog&es its enlarged responsibility to make provisionnot only to take care of researoh needs arising fromcurrent problems, but also to look well into the futureand to anticipate the neds that will arise as a resultof the trend toward the construction of much largerlandplanes and saaplane~

The Committee is grateful to the President and tothe Congress for the earnest consideration and suppxtthat have been given to its needs, and urges the con-tinued support of this most fundamental activity of theFederal Govemmmnt in connection with aeronautics

&pSC~y submitted,NATIO~fi ADVISORYCoammmm

FORAERO~A~~,JOSEPHS. Aras, OAu&vmzn+