Fifty Years of Aeronautical Research

8/7/2019 Fifty Years of Aeronautical Research

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Introduction

It is fifty years since the first symbolic shovels full of earth were liftedabove the soil of Langley Field to signal the start of construction ofthe first research laboratory for the National Advisory Committee forAeronautics.Those shovels of Virginia ground symbolized more than the construc-tion of a research laboratory. They were tangible proof that this coun-try was determined to build an aeronautical research establishmentsecond to none in the world, aimed at regaining and then maintain-ing the lead in aeronautics which had been given to America byOrville and Wilbur Wright less than 14 years before.In mid-1917, America had been at war for three months, in a conflictwhich was to see the airplane grow from a scientific curiosity and asportsmans plaything to an effective weapon of war.But when the war broke out in 1914, the United States was last onthe list of world powers equipped with military aircraft, running apoor fifth behind France, Germany, Russia and Great Britain.Not only the tangible evidence of aeronautical progress was lacking.The other powers had seen the value of aeronautical research labora-tories and facilities as early as 1866. In that year, the AeronauticalSociety of Great Britain was formed to stimulate research and ex-periment, and to interchange the information gained. Herbert Wenhamand Horatio Phillips, members of that Society, invented wind tunnelssoon after 1870.France had major installations: Gustave Eiffels privately owned windtunnels at the foot of the Eiffel Tower and at Auteuil; the Armysaeronautical laboratory at Chalais-Meudon; and the Institut Aero-technique de St.-Cyr. Germany had laboratories at Gottingen Uni-versity and at the technical colleges of Aachen and Berlin; the govern-ment operated a laboratory a t Adlershof. and industry was well-equippedwith research facilities. Italy and Russia had aeronautical laboratorieslong before the United States took the step.National concern mounted as more and more scientifically prominentAmericans discovered the woeful position of this country in aeronaut-tical research. In 1911, it was suggested that the Smithsonian Insti-tution, earlier the supporter of Samuel Pierpont Langleys pioneeringwork, be given responsibility for an aeronautical laboratory. Objec-tions by both the War and Navy Departments were influential inkilling the idea for the time being.But the Smithsonian pressed its case, and by the following year appearedto have met initial success. President William Howard Taft appointeda 19-man commission to consider the organization, scope and costsof such a laboratory, and to report its findings, along with itsrecommendations, to the Congress.An administrative oversight killed this approach; the appointmentshad been made solely by Presidential action, without the traditionaladvice and consent from the Senate. The legislation which wasproposed to authorize the laboratory failed to get unanimous consent.The Smithsonian decided to try it alone, and reopened Langleyslaboratory. One of the first tasks was a survey of major research andexperimental facilities abroad.The report which came out of that survey showed clearly the dangerousgap between the state of aeronautical technology in Europe andin the United States. Once again, the Smithsonian decided,to approachthe Congress, and on February 1, 1915, delivered to the Speakerof the House of Representatives a statement which said, in part:


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A National Advisory Committee for Aeronautics cannot fail to beof inestimable service in the development of the art of aviation inAmerica . . .The aeronautical committee should advise in relatiopto the work of the government in aeronautics and the coordinatlon ofthe activities of governmental and private laboratories, in which ques-tions concerned with the study of the problems of aeronautics canbe experimentally investigated.That statement became a joint resolution of Congress and was added

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as a rider to the Naval Appropriations Act approved March 3, 1915.The Act established an Advisory Committee for Aeronautics (Theword National was to be added later a t the first Committee meeting),detailed its organization, apportioned its membership, and describedits general task in words which need no improvement today:. . . it shall be the duty of the Advisory Committee for Aeronauticsto supervise and direct the scientific study of the problems of flight,with a view to their practical solution, and to determine the problemswhich should be experimentally attacked, and to discuss their soh-tion and their application to practical questions. In the event of alaboratory or laboratories, either in whole or in part, being placedunder the direction of the committee, the committee may direct andconduct research and experiment in aeronautics in such laboratory orlaboratories.The first Committee appointments were made by President WoodrowWilson on April 2, 1915, and the first full Committee meeting washeld April 23 .Among the early projects completed by the Executive Committee ofNACA was a facilities survey of industry, government and universi-ties. Ou t of that work, NACA concluded that it would require both alaboratory and a flight-test facility, the former for model work andexperiment, and the latter to work with full-scale problems. Withforesight the Committee recognized that building and equipping thesefacilities ought to be a gradual and continuing process, so that thelaboratory could stay abreast of developments in technology.During 1916, NACA called a meeting of aircraft and engine manu-facturers to discuss the problems and progress in airplane engine designand development. That meeting was the first of many to come, andit initiated the close working relationships between the governmentlaboratory and private industry which have existed ever since.Meantime, the Secretary of War has been told by Congress to surveyavailable military reservations to find one suitable for an aeronauticalexperimental station, or to recommend a new site, if no existingsite were suitable. The Army appointed an officer board which selecteda site a few miles north of Hampton, Virginia.I t fulfilled the requirements of the search: I t was flat land, frontingon water so that test flights could be made over both land and water.I t was east of the Mississippi and south of the Mason-Dixon line,where weather was generally good for flying. I t was no farther than12 hours by train from Washington, D. C. I t was not so close to anunprotected coastal area as to be subject to attack or possible cap turein the event of war.A special NACA subcommittee went through a similar search for itsown experimental station site, and concluded that the Armys choicewas a wise one. The subcommittee recommended that the Armybuy the site north of Hampton as a test area for joint Army, Navyand NACA experiments.That site was to become Langley Field, named after Samuel PierpontLangley. NACA (which in 1958 became the nucleus of the NationalAeronautics and Space Administration) would build its first testcenter there, but neither the Army nor the Navy would use it forexperimental work. The Army would establish its test area at McCookField, near Dayton, Ohio; the Navy, oriented toward tests of seaplanes,would move its experimental work across the water to Norfolk, Virginia.


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1917-1927Langle y Research Center, born during the fir stWorld War, saw the shaping o f the framew orko f decades to come during its first ten years o flife.The war had introduced day and night bombing.It had spurred the development o f bomb sights,automatic pilo ts, radio communication and navi-gation aids, self-sealing f uel tanks and pilotlessaircraft.Wi th in three months after the Armistice, com-mercial aviation started in Germany whenDeutsche Luftreederei began its passenger-carrying service. Th at year also had seen the

first daily commercial air service started, withflight s between London and Paris. Th efirstinternational passenger Jigh ts fr om the U. S.followed in 1920; by 1925 , regular air freig htservice had been established between Chicagoand Detroit. The new transport industry becamesubject to its first regulatory legislation, the AirCommerce Act, signed into law in 1926 byPresident Calvin Coolidge.Recordflights by the score showed the way towardthe f uture routine accomplishments o f civil andmilitary aviation. Th e A tlantic was crossed firstby a U . S. Navy Curtiss NC-a Jying boat,and then, non-stop, by Britains Capt. JohnAlcock and Lt. Arthur W. Brown in 1919.Four ye ar s late r, the first non-stop transcontinen-tal crossing o f the United States by air wasmade by Lts. 0 . G . Kelly and 3.A. Macready.In 1924, two o f four Army Douglas amphibiousb$lanes completed a round-the-worldflight,another first in aviation history. Durin g the26,350-mileJight, theyJew the j r s t trans-Pacijk crossing and the firs t westbound N orthAtlantic crossing.But the most-remembered achievement o f thepost-war years w as the solo crossing o f theAtlantic by Charles A. Lindbergh. Hishistocy-making Jigh t drew world-wide attentionto the potential o f the airplane, and gave animpetus to aviation that no other single fe atsince the W rig ht brothers jr st Ji gh t ever hasmatched.Other developments during that j r s t decade pointedthe way toward the futur e o f aviation. A Curtiss3jV -4 wa s remotely controlled in the air fr omanother 3N - 4; the Sperry gyro-stabilized auto-pilo t was successfully tested. Inaccessible part so f Alaska were mapped fr om the air; a Haw aiianfore st was planted fr om the air; cloud-seedingexperiments began.

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Target battleships were sunk by bombing; pzjied,midair refueling was demonstrated. A n all-metal,smooth-surfaced wing was built in Germany byRohrbach, the progenitor o f the stressed-skinstructures which are standard today.And in wide& separated parts o f the world, Dr.Robert H . Goddard successfully developed andfired liquid-fuelled rocket motors, the GermaaSociety fo r Space Travel (Vereinfuer Raum-schifahrt) was organized, and the Russiangovernment established a Central Committeef o rthe Study o f Rocket Propulsion.The problemsfacing the airplane designer in theearly post-w ar years were daficult. Th e struttedand wire-braced biplane had h&h drag, and alow lift-drag ratio. i t had poor propeller per-formance, and an engine-or e n gi n e so f lowhorsepower and doubtful reliability.Added to this were the complete lack o f anymeans to control the landing speed and the approachangle, the lack of knowledge o f gusts and maneu-vering loads, and stability and handling charac-teristics that varied fr om acceptable to dangerous.It is remarkable that any av iation progresswas made.But it was. The list of technological innovationso f this decade i s impressive.I t includes the development o f a reliable, air-cooled engine; cantilevered design; the use o fmetal in structures; the concept o f tri-motoredaircraft; the experimental use o f superchargers;the trend to the monoplane; and the developmento f limited blindflying equzjiment.This was the for m o f the first decade at Langle y.It was a ten-year period o f startling growth f o rthe aiqlane, out o f its role as a winged weapono f war and into new jo bs fo r the military anda wide range o f commercial services.But the growth had been more accidental thanplanned. Deskners worked with a paucity o fdata andjlled the gaps with their own experi-ence or the experience o f others. i t was a decadeo f empirical development, of l u c k F a n d , toooften, unlucky-solutions to the manifo ldproblems o f airplane design.It would be the aim o f NA CA s new aeronauti-cal research laboratory at Langley Field toreduce the element o f luck in airplane design, toreplace it with a body o f carefully developedscientajk data , and to point the way to improvedairplane design concepts.


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1. One of two CurtisJN-4H Jenny trainersbefore speed tests, 1919.

2. Sperry M-1 Messengerwas evaluated in flightand in the propeller

research tunnel.

In the heat of July 1917, excavation beganat Langley Field for the first researchlaboratory to be built for the NationalAdvisory Committee for Aeronautics.Langley had been authorized as the site forNACAs experimental air station just themonth before, and a contract had beenlet for construction to the J. G. WhiteEngineering Corp., of New York City.Estimated cost of the laboratory was$80,900.By November 1917 , after surveys of exist-ing industry and airfields to determine thestate of aviation in the United States,NACA authorized the preparation of plansand specifications for its first wind tunnel.It was to be like the pioneering wind tunneldeveloped by Gustave Eiffel, with a testsection about five feet in diameter and aninsert which could be used to reduce theworking area to a cross-section with a two-and-one-half foot diameter.Work began on the tunnel in the spring of1919, and it was ready for operation oneyear later.By then, NACA had proposed a nationalaviation policy, and among its recornmen--dations was one that research be expandedat the Langley laboratory. NACA alsooffered the use of its experienced personneland its new facilities to universities andindustry in order to foster aeronauticalresearch and experimental work outside ofgovernment laboratories.The new wind tunnel was operated for thefirst time a t the formal dedication of theLangley Memorial Aeronautical Labora-tory, now the Langley Research Center,on June 11, 1920. Visitors to the lab saw asmall brick-and-concrete building, fromwhich sprouted two bell-shaped surfacesopen at the ends. This was the wind tunneland the test building.The test building was about ten by fourteenfeet in floor dimensions, and it stood about23 feet high. Through the center of thebuilding ran the cylindrical test section inwhich test models were suspended on wires.Below the test section were chairs whereengineers sat and read the balance arms ofordinary weigh scales which had beenmodified to measure the loads on the modelduring the test.The tunnel could produce a test sectionspeed as high as 120 mph., believed to bethe fastest useful test speed then attainablein the world. Further, it apparently hadexcellent flow characteristics, compared toits contemporaries, and what were termedsatisfactory means for measuring the forceson models at the highest velocities.


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' Within six months or so, the Committee*authorizedconstruction of a second windtunnel, a compressed-air unit designed tocorrect for the scale effect which produceddifferences between model and full-scaledata. Plans were approved one year laterand construction was authorized.The tunnel was designed to run at pres-sures as high as 20 atmospheres (about 300psi.), and the test section was to have afive-foot diameter.The compressed-air tunnel, later to bedesignated the variable-density tunnel, wasoperated first at the annual meeting of thefull NACA Committee on October 19,1922. Incidentally, there was not enoughelectrical power available at Langley to runboth it and Tunnel No. 1 concurrently.The Committee must have been impressedwith the growth and stature of the LangleyLaboratory at the time of the 1922 meet-ing. It now was made up of s i x units:The research laboratory building, whichincluded administrative and drafting offices,machine and woodworking shops, andphotographic and instrumentation labs;two aerodynamic laboratories, each con-taining a wind tunnel; two engine dyna-mometer laboratories, one of which was ina permanent building while the other wasin a converted hangar; and an airplanehangar on the flying field.Test equipment included an automaticbalance and a high-pressure manometerfor the variable-density tunnel, and a spe-cial wire balance, for the first wind tunnel,

I suitable for making tests of biplane andtriplane models.These test techniques and facilities wereaimed at measurements of the aerodynamiccharacteristics of existing aircraft andtheir components, to devise concepts toimprove those characteristics.But wind tunnels weren't the only testtechniques available to the Langley engi-neers. Within the second year of Langley'sexistence, work had started on the develop-ment of instruments for flight-test work)so that measurements could be made onfull-scale airplanes and correlated withdata obtained from models in wind tunnels.That first instrumentation program calledfor ways to measure engine torque andrpm., propeller thrust, airplane speed andangle of attack. Knowledge of these param-eters of a full-scale airplane would bothsupplement and complement data takenduring wind tunnel tests.This two-pronged approach to the problemsof aeronautics-by model tests and by full-scale flight tests-established the interde-pendence of these two test disciplines earlyat Langley. Emphasis on that dual ap-proach has been strong ever since, and isone of the foundation stones of Langleyresearch policy today.By mid-1919, with construction of the firstwind tunnel underway a t Langley, re-search was authorized for the first NACAflight tests with full-scale airplanes. Thepurpose of the tests was to compare in-flight data with wind tunnel d ata for the

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6 same aircraft to show the degree of cor-relation, and to determine, if it could bedone, a way to extrapolate wind tunneltests to full-scale results.The first program used two CurtissJN-4HJenny trainer biplanes in a detailed in-vestigation of airplane Kit and drag. I twas the forerunner of a myriad of detailedinvestigations that would later lead to thedevelopment of a series of research aircraftto explore the unknowns of subsonic andsupersonic flight.There was a second important result ofthat first program with the Jennies. Th eNACA Technical Report which describedthe tests also noted that there was a needto develop a special type of research pilot.This was perhaps the first time tha t therole of the engineering test pilot had beenrecognized and described.Th e faithful Jennies served in a variety oftests during the years. They pioneered in-flight investigations of pressure distributionso tha t designers could calculate the airloads acting on the wings and tail of theaircraft. In the first program, begun in1920, NACA technicians installed 110pressure orifices in the horizontal tail ofthe wood-and-fabric Jenny, hooked to abattery of liquid-in-glass manometers whichcould be photographed in flight.Early in January 192 1,research was begunto compare the characteristics of wings inmodel tests and in full-scale flight tests, sothat designers could be furnished with com-plete and accurate data on which to basetheir performance estimates.

During that same year, new instrumentswere developed and tested in flight ,to ameasure control position and stick forcesexerted by the pilot. This was done tounderstand and improve handling charac-teristics, and thus increase flight safety. Re-fined and miniaturized instruments usedfor the same basic purposes find continuedemployment today in the tests of high-speed jet aircraft or rocket-propelledresearch vehicles.Pressure distribution investigations becamea major portion of the flight-test work atLangley. From the measurements of loadsin steady-state flight, the work was ex-panded to study the effects of acceleratedflight or maneuvers, because at tha t time,there was virtually no data available todesigners on the distribution of the loadon the wing of the airplane in acceleratedflight.Later work extended the pressure-distribu-tion measurements to the nose of a non-rigid airship, first under steady flight con-ditions, and then during maneuvers overa range of airspeeds and atmosphericconditions.Five airplanes shouldered the load of flighttest work during 1921. Three of them werethe Jennies, CurtissJN-4H types. Theyshared the flying field with the Lewis&Vought VE-7 and a Thomas-Morse MB-3.Together, the Jennies logged 110 hr. offlight time in 260 flights during 1921.More than half of the flight time was spentin da ta collection.Other pacemaking research began in 1922,


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when the first systematic series of takeoffand landing performance measurementswas made at Langley. During that year,the Navy Bureau of Aeronautics askedNACA to undertake a comparative studyof the stability, controllability and maneu-verability of four airplanes: Th e VE-7, theMB-3, a British SE-5A, one of the mostwidely used pursuit aircraft in WorldWar 1, and the famous Fokker D-VII, themainstay of the German Imperial AirService during the same conflict.The SE-5 and a De Havilland DH-4 hadjoined the Langley flight test fleet in 1922,to raise the number to seven aircraft. Inaddition, four more aircraft were beingrefitted for test programs or support work:The Fokker D-VII, a Nieuport 23, aS.P.A.D. VII, and a De Havilland 9.

1. Flight research, 1924:JNslH, Fokker D-VII,MB-3, DH-4 and Sperry2. Thomas-MorseMB-3joined the Langley testfleet in 1921.

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Again the Jenny was used as a test vehiclein 1922 in an extensive investigation ofmaneuverability. The aim was to find asatisfactory definition of the word, in anaerodynamic sense, and to establish waysof measuring it. Before this time, maneu-verability was a subjective judgment by apilot, full of personal likes and dislikes.The same airplane could be judged lighton the controls and maneuverable by amuscular pilot, and heavy on the controlsand sluggish by a lesser man.What was needed was some way of reduc-ing subjectivity to objectivity, and NACApilots and engineers at Langley set aboutfinding that way.They instrumented the Jenny to measureits angular velocity following a motion ofits controls, as a first approach to definingwhat maneuverability was.Like so much of Langleys pioneering work,this early study of maneuverability grewinto the extensive flight research workdone today on the handling qualities ofaircraft. The basic approach laid downthen is valid now.Th e calibre of the flight-test work beingdone at Langley began to attract attentionfrom the military services. In 1923, theNavys Bureau of Aeronautics came toLangley with a request that the Laboratoryrun a series of flight tests in the low-speedregime on its TS aircraft, a scout aircraftdeveloped by Curtiss. The Navy was par-ticularly interested in accurate determina-tion of the stalling speed, and the takeoffand landing speeds.The Army Air Service also was concernedwith similar questions. Th e service askedNACA in 1924 to study the acceleration,control position, angle of attack, groundrun and airspeed during the takeoff andlanding of most of the airplanes then in

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8 service with the AAS. The list included theCurtiss JN-6H; the Lewis & Vought VE-7;the De Havilland DH-4B; the FokkerXCO-4, the prototype of the C.IV two-place biplanes then in service with severalcountries; the SE-5A; the S.P.A.D. VI I;the MB-3; the Martin MB-2, a biplanebomber; and the Sperry Messenger.By then, Langleys flight line sported 11test aircraft; during 1924 they logged 918flights for a total of 297 hr. of flight time.The same year, the Army requested a flightresearch investigation of the pressure dis-tribution over the wing of a Lewis &Vought VE-7 tandem trainer. The servicetransferred one of the aircraft to Langleyfor the program.The VE-7 soldiered on through other workafter that test was completed, including alandmark program using seven differentpropeller designs, aimed at determiningthe effects of different propeller design onperformance.Those tests, along with tests with a seriesof six interchangeable wings, each with adifferent airfoil section, on a Sperry Mes-senger biplane, became the first of manyNACA comparative tests where a system-atic approach was used to develop a betterinstallation or to design a better component.Sophistication had come both to flight test-ing and wind-tunnel testing. By mid-I 924,NACA was able to make complete pres-sure distribution surveys, either in thewind tunnel or in flight, in one day ofwork. Formerly, such tests had required aseries of runs over a time period as long astwo months.

Later the same year, NACA reported afurther refinement in flight testing tech-niques. Recording instruments had beendeveloped, the Committee said, to make acontinuous record of pressure distribution,accelerations, and other parameters duringflight tests of aircraft.During 1925, the flight-test program con-tinued to grow, and there were 19 aircraftin various phases of test work a t Langley.They made a total of 626 flights during theAn engine research laboratory had beenstarted and a dynamometer, to measureoutput and other performance data on air-craft engines, had been installed in 1919.Since then, a second had been added.Both were kept busy, and so were thepowerplant engineers. Early work on super-chargers, investigated at Langley in 1924,led to consideration of supercharging toboost engine power for high-altitudebombers, and to obtain a good rate ofclimb for interceptors. This engine researchlaboratory later became the nucleus of theLewis Research Center.One specific study was made to determinethe adaptability of supercharging to anair-cooled engine and its effect on theflight performance of the engine.Two more pioneering programs were be-gun a t Langley in 1925. The first of thesewas an attempt to standardize wind-tunnelresults, a necessary preliminary to com-parison of data taken from two differentwind-tunnel installations. NACA engineersdeveloped a series of circular discs whichwere tested in the Langley tunnel, and then

year, and logged 245 hr. of flight time.


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sent to otherwind tunnels for testing underthe same conditions. Th e results, whencompared, offered a way of checking theresults of one wind tunnel against another.Second of these early programs which ledthe way was the beginning of the measure-ment of landing loads, even today a majoreffort at Langley laboratory. But a t thattime, the loads were to be measured onseaplane floats, so that the specificationsfor the design of float bracing could beimproved.On May 24, 1926, NACA held its firstjoint conference with representatives of theaircraft manufacturers and operators atLangley. I t was the first of what was tobecome a recurring event and a greatNACA tradition: the inspection tour. Butit went further; it provided the guests withan opportunity to criticize current researchand to suggest new avenues they believedpromising.The second of these conferences, held thefollowing year, was expanded to includerepresentatives of educational institutionsthat taught aeronautical engineering, apdof trade journals that played such animportant part in the dissemination ofaeronautical information.This interchange of information betweenindustry and NACA, always one of themajor factors in directing the course of theCommittees research, has been maintainedover the years since the first formal jointconference in 1926.By that time, the outstanding work of theLangley Laboratory had also been recog-nized by foreign institutions. Typical ofthat recognition was a request from theAeronautical Research Committee of GreatBritain, which asked Langley to run aseries of wind-tunnel tests on three airfoilsections, incorporated in wing designs onthree different aircraft models. The resultswere to be used for comparison with wind-tunnel and full-scale flight results previouslyobtained in England.One of the more significant developmentsin aeronautical research to grow outof the Langley laboratories had its begin-ning in a letter sent from the Navys Bureauof Aeronautics in 1926. The Navy hadbeen convinced that the air-cooled enginewas a more practical solution to its power-plant problems than the liquid-cooledpowerplants favored by the Army. ButNavy engineers were well aware that air-cooled installations had more drag andwasted more power in cooling the enginethan seemed necessary. Th e engineers be-lieved there was some way to put a stream-lined cowling around the engine to reduce

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1. Ford truck,Huckstarter, and Lewis &Vought VE-7, around1924.2. War booty, thisGerman Fokker D-VI1was tested at Langleyin 1922.


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The second decade o f work at the LangleyMemorial Aeronautical Laboratory began onthe upsurge of a new wave o f popular interestin aviation. Lindberghs historical crossing ofthe Atlantic had touched the imagination o f theworl d, and had converted skeptics into believers.T h i s decade would produce a revolutionarychange in the appearance and performance o fairplanes, jr m l y establishing their position inthe growing transportation networks o f the worldand guaranteeing their fu tu re predominance inthat je ld .I n commercial aviation, Transcontinental G?Western Ai r inaugurated the j r s t coast-to-coastthrough air service in 1930, between N e w Torkand Los Angeles. Th e Boeing 247 and theDouglas DC-1, progenitors of long lines o ftransports to come and o f years o f commercialrivalry between the companies, made their j r s tflights during 1933. T h efollowing year, Douglasstarted work on the DC-3, the plane that wasto revolutionize air transport. It j r s t f l ew in 1934.Th at same year, Pan American started surveyJights withflying boats across the Pacijic and

followed with the start o f air mail service fromSa n Francisco t o Manila . In 1936, the airlinecarried th e jr st passengers on its new trans-Pacijic route. In 1937, Pan A m and the Britishcarrier, Imperial Airwa ys, made survey flig htsacross the Atlantic , and Pan A m started th ej rs tair mail service between the United States andNew zealand.During the decade, Boeings Model 299, theprototype o f it s B-17 Flying Fortress series,made it sj r s t flight (1935). In Britain , the proto-type Hawker HurricamJ7ew for thejrst time,and t he jr st report on radio detection and rang-ing (radar) was presented to the British AirDefence Research Committee.Three wars, which led to an increased appre-ciation o f airpower, erupted during this period.Japan began it s operations against Ch ina in1931; Italy declared war on Abyssinia in 1935;the Spanish Civil W ar began in 1936.The tragic Spanish conflict drew other nationsto the jg ht in g within Spains borders, and gavethem the opportunity to test and develop newweapons and concepts. Guernica, the seat o f theBasque government, was bombed and devastatedby German aircraft in a demonstration o f thingsto come.

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1928-1937Th e decade saw the death o f the dirigible fo l-lowing a series o f tragic accidents to the BritishR-101, the U . S. Navys Akron and Macon,and the German Hindenburg.Some o f the most radical developments o f the tenyears took place i n jet propulsion. Th eyear 1928saw the j r s t rocket-powered glider fli gh t made inGermany, and the publication o f a fundamentalpaper on jet propulsion by Frank Whi ttle. Nineyears later, hi sj rs t engine was run. Th e Rus-sians published thej r s t volume o f a nine-volumeencyclopedia on interplanetary fli gh t that year .I n 1929, thejrst known use ofjet-assisted take-off was successfully demonstrated in Germany.T hefollowing year, the German VereinfuerRaumschayahrt established a test site in Berlin,and the German Army Ordnance Corps organizedits rocket weapon program and moved it into atest station at Kummersdorf.Static tests o f a Heinkel He-112, converted tobe fl ow n w ith an auxiliary rocket engine, weremade in m id-1935, and the airplane made it sj r s t successful testflight early in 1937. It wasthe forerunner o f later German developments inrocket-poweredjghters.In 1937, German Army Ordnance opened itsrocket development station at Peenemunde. InRussia, three rocket test centers were establishednear Moscow, Leningrad, and Kazan.The biplane was the standard design whenNACAs Langley Memorial Aeronautical Lab-oratory started its second decade o f life. TheArmy Air Corps newest bomber was the CurtissCondor, a twin-engined biplane wit h jx e dlanding gear, strut bracing, open cockpit and abiplane tail assembly. It s hottestjghter wasanother Curtiss product, the P-1 series, progeni-tor o f a long line of Curtiss Hawks. It toowas a biplane, with strut bracing, j x e d landinggear, and a liquid-cooled engine.T h e commercial airwa ys were served by the tri-motored monoplane Fords, an all-metal high-winged design, the Boeing 80 biplanes, also tri-motored, and various single-engined designs suchas the Fokker Universal.In most o f the commercial and m ilitar y designs,the basic airplane was a strut-braced and wire-braced biplane, built o f wood or steel tubing, andcovered with fabric . I ts landing gear wa sj xe d;it s engine, if aircooled, wa s uncowled. Th e pro-peller w as a jxed-p itch type. Th e monoplane


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1. Army Curtiss AT-5Awas first airplane fitted

with NACA cowling:2. Langley metal work-

ers fabricated NACAcowlings for early testinstallations.

1928.

design had been established, but in most in-stances as a strut-braced layout. I ts designerswere unsure o f the problems o fj ut te r and aero-elasticity.By the end of this second decade, the biplane wasalmost as dead as the dodo. Military and com-mercial craft were internally braced, unstruttedmonoplanes, with sleekly cowled engines, retrac-tible landing gear, and wing$aps. Th e designrevolution of the early 1930s had been sparked bydevelopments at Langley.The propeller research tunnel, which beganoperating in 1927 at the end of Langleysfirst decade, began to pay off its investmentin the earliest years of the second decade.For the first time, an aeronautical labora-tory had a research wind tunnel big enough,and versatile enough, to test full-size air-craft components. There was an additionalbenefit; the scale of testing was physicallylarge enough so that tiny components,which would have been nearly invisible onthe small wind tunnel models previouslyused, could be evaluated. This was to makepossible a whole new world of test studiesthat would result in detailed refinement ofmany aircraft to come.Th e first program in the propeller researchtunnel was directed toward the problemsstated by the Navy and industry earlier:Th e reduction in drag and improvement incooling efficiency of an air-cooled engine.The result, after systematic wind tunneltesting, was the construction and installa-tion of an NACA-designed cowling on aCurtiss AT-5A advance trainer of the ArmyAir Corps. Th e NACA Annual Report for1928 said that . . .the maximum speedwas increased from 118 to 137 mph. Thisis equivalent to providing approximately83 additional horsepower without addi-

tional weight o r cost of engine, fuel con-sumption, or weight of structure. This*single contribution will repay the cost ofthe Propeller Research Tunnel manytimes.The Wright R790-1 air-cooled engine whichpowered the AT3A was rated at only 220hp. The additional equivalent of 83 hp.power, or an equally staggering reductionin engine drag, depending on the viewpointof the designer.NACA received the 1929 Collier Trophyaward for the development of the cowling,Th e Trophy, an annual award for thegreatest achievement in aviation in theUnited States, was presented in 1930 toDr. Joseph S. Ames, then NACA Chairman,by President Herbert Hoover.The design revolution had begun. TheNACA cowling was to become the standardenclosure for air-cooled radials, and wasto be continually revised and improved inthe future. Th e dramatic reduction in cool-ing drag produced by the cowling leddesigners to ask for, and NACA to lookfor, other areas where drag could be reducedsubstantially.One obvious source of drag was the fixedlanding gear, long recognized as a primeproducer of built-in headwinds. The SperryMessenger was tested in the propeller re-search tunnel, and its fixed landing gearwas found to account for nearly 40 percentof the total airplane drag. These measure-ments were the first to pinpoint the exactamount of drag caused by the landing gear,and the first to show the performancepenalty incurred by not retracting thegear.Still working in the interests of drag re-duction, NACA engineers looked at a tri-

s

was a staggering boost in available engine


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motored Fokker transport powered bying these engines, they reasoned, shouldmake a substantial improvement in theperformance of the airplane. But it didnt,and they began to wonder why.The wondering led to the belief that maybethe awkward powerplant installation hadsomething to do with it. The standarddesign of the period was to support theengines above or below the wing on astrutted structure, whose dimensions weredetermined by eye rather than by anyaerodynamic considerations.Studies in the propeller research tunnelsoon showed there was an optimum posi-tion for engine nacelles, and it wasntabove or below the wing. The optimumwas for the nacelle to be faired into theleading edge of the wing; the improvementagain was marked.Meantime, NACA had been conductingsystematic investigations of propellers, ofairfoil sections, of high-lift devices, of inter-ference drag between fuselage and wing,or fuselage and tail. Wing fillets were de-veloped, and reported in a 1928 TechnicalNote. Even the drag of small fittings, suchas a protruding gasoline tank filler cap,could be measured and its effect onperformance assessed.The quiet revolution was well underway.For the first time, designers could build aclean airplane, could estimate its drag

Wright.5-5 Whirlwind powerplants. Cowl- and performance more accurately, andcould understand the possibility of a smallchange causing a major increment inperformance.The availability of the NACA cowling,propellers of increased efficiency, moreefficient airfoils, wing fillets, and knowledgeof the mechanism of drag led directly tothe change in design from the struttedbiplane to the sleek monoplane.No longer could a designer argue that itwasnt worth the weight and complexityto retract the landing gear for those fewmiles per hour. The aerodynamicists couldtell him that those miles per hour werentfew, and that retracting the gear couldmean the difference between winning andlosing a contract.Even before the NACA cowling had beencompletely developed in the propeller re-search tunnel, NACA realized that a full-scale tunnel would be a necessity. Airplaneswould be bigger than the 20-ft. throat testsection of the PRT, and the work load offull-scale airplane testing was bound toincrease as soon as industry and the mili-tary realized the advantages of such testwork.The need for the full-scale tunnel was firstoutlined in a letter from Dr. Ames to theDirector of the Bureau of the Budget.Construction began in January, 1930, andthe tunnel was officially dedicated a t thesixth annual conference in May, 1931.

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16

1. Langleys variable-density tunnel, damaged

by fire in 1927, wasphotographed in March,

1929, when tests beganagain.2. Military aircraft of thedecade, shown during

tests in the full-scaletunnel at Langley:

Boeing PW-9 of 1925.3. Vought 03U-1,

in 1931 the first com-plete airplane to be

tested in the full-scaletunnel.4. Dough XO-31 Of

1930.4

I


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Other research facilities at Langley grewbut of specific needs. Some research workhad been done in 1927 on the preventionof aircraft icing by thermal systems, butthe study had been completed withoutfurther action. Early in 1928, the AssistarSecretary of Commerce for Aeronauticscalled a conference of military and govern-ment agencies, including NACA, to studythe causes and prevention of ice formationon aircraft. A few days earlier, the NavysBureau of Aeronautics, frequently a pioneerin defining a problem area, had askedNACA to determine the conditions underwhich ice forms on an aircraft, and todevelop some means of prevention.Th e result was NACAs first refrigeratedwind tunnel, which began operations dur-ing 1928. Its aim was to study ice forma-tion and prevention on wings and propel-lers of aircraft, and its tests pointed theway toward the successful developmentof schemes to prevent, or remove, iceaccretions.These studies grew into a major effort thatlater won another Collier Trophy for anNACA scientist. Lewis A. Rodert, who

began his NACA career at Langley, wonthe 1946 trophy for his pioneering re-search and guidance in the developmentand practical application of a thermalice-prevention system for aircraft.Rodert conducted most of his basic researcfrom 1936 to 1940, during which time hewas in the Flight Research Division ofLangley. He transferred to the Ames labor-atory in 1940, and was Chief of FlightResearch a t the Lewis laboratory when hewon the Collier Trophy.In 1928, the Armys experimental flight-test facility at Wright Field had begun aseries of tests to determine the spin charac-teristics of aircraft. Two years later, Langleyhad started to operate a free-spin windtunnel, in which models could be spun ina manner simulating the dynamics of full-scale, free flight.This led to the construction of a largerspin tunnel, with a 15-foot throat and ad-justable airflow velocity so that the modelcould be held at one position in the throatand observed visually from outside thetunnel.The success of this type of wind tunnel ledNACA directly to the more complex free-flight tunnel, a major research tool whichhas given birth to a range of test techniquesused with models of todays aircraft.The first of Langleys hydrodynamics testtanks was completed in 1931, to serve theresearch needs of the seaplane and am-phibious airplane designers. The windtunnels would provide aerodynamic be-havior of the aircraft; the test tanks wouldanalyze the behavior of models on thewater in an analogous manner.The tank was 2,000 ft. long, although laterextended to 2,900 ft., and was used pri-marily to determine the performance char-acteristics of hull shapes. By towing themodel hull through the water from a stand-ing start to a simulated takeoff speed,Langley scientists could determine thehydrodynamic performance of the hull andsuggest changes or improvements in thebasic design.Th e tow tank was used also for systematicdevelopment of families of hull shapes. Inlater years, a second tank, 1,800 ft. long,was built. In that tank, simulated forcedlandings on water would be done withlandplane models, and still later the Mer-cury, Gemini and Apollo water-landingtechniques would be checked out usingthe same tank.At the time when airplanes were routinelylogging speeds of less than 200 mph., NACAwas looking ahead to the future where

17


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18 speeds up to 500 mph. might be possible.Late in 1933, NACA outlined its needs fora 500-mph. wind tunnel, called then thefull-speed tunnel, and estimated its costat under a half million dollars in a letterto the Federal Emergency Administrationof Public Works. Construction of the tun-nel was completed in March, 1936, and i tbegan operations in September that year.Its test section had an eight-foot diameter,enough to investigate large models of air-craft and some full-scale components.The eight-foot tunnel was to become apioneering tunnel in high-speed aero-dynamic research in this country, and wasto be the foundation of the future structureof Langleys brilliant work in the highsubsonic speed range and on into themysteries of the transonic region.Other pioneering facilities were designedand started during this second decade.The 19-foot pressure tunnel constructioncontract was awarded early in 1937, andlate that year the first low-turbulence windtunnel entered construction.The 19-ft. tunnel was a leader in propellerresearch, because it could test a full-scalepropeller in a close approximation of itsoperating range.The low-turbulence tunnel was to becomethe source of the NACA low-drag (laminarflow) airfoil.Still closely coordinated with the aero-dynamic work at Langley was the job offlight research. A new kind of aircraftcalled an autogyro had been flown in theUnited States for the first time in 1928.This was the first departure from the fixedwings of the basic Wright brothers design,a radical approach providing lift by usingrotating wings.During 1931, Langley bought a PitcairnPCA-2 autogyro and started its work onrotary-wing aircraft. The PCA-2 was in-strumented and test-flown. Its rotor wastested in the full-scale wind tunnel forcorrelation between tunnel and flight tests,

and a model of its rotor was tested in thepropeller research tunnel to determige.scale effects. A camera was mounted on thehub of the rotor to photograph the bladebehavior during flight.Th e flight tests of the PCA-2 included somemeasurements during severe maneuvers,with results still applicable to the fast-moving helicopters of today. Th at particu-lar autogyro had a fixed wing surface tocarry some of the weight of the aircraft innormal forward flight. The flight testsmade at Langley included some work inwhich the incidence of the wing was varied,so that it carried a different proportion ofthe.aircraft weight in each of a series oftests. These experiments indicated some ofthe problems faced today by designers ofhigh-speed helicopters, who want to unloadthe rotor by using a fixed or variable wingsurface to generate additional lift.This was the first major project accom-plished by the rotary-wing research group,a small unit which has been maintainedthroughout the years to specialize in theproblems of rotary-wing systems.Flight research was maturing rapidly. Dur-ing 1931, a landmark report was published.NACA Technical Report 369, titled,Maneuverability Investigation of theF6C-3 Airplane with Special Flight Instru-ments, was the first published reportwhich dealt with the handling qualities ofaircraft, a task that has occupied manyof the Langley and other NACA/NASApersonnel to this day.In 1932, the flight research laboratory wasofficially opened. It was a separate area,with hangar space for aircraft, its ownrepair shop, and office space for the staff.During 1933, the forerunners of two greatfamilies of airliners first flew: The Boeing247 and the Douglas DC-I .Both wereradical departures from their predecessors;both were all-metal, low-winged craft,with cowled, air-cooled engines and re-tractable landing gear. They had two

-

Boeing XBFB-1 of 1934,last of the fixed landing-

gear military aircraft.


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20

engines instead of the more-common tri-motored arrangement. With both enginesoperating, performance was outstanding.But if one engine failed, the available powerwas halved, instead of being reduced onlyby a third.The engine-out situation became a primaryconcern of industry, and Langley was askedin mid-1935-six months before the DouglasDC-3 first flew-to evaluate the handlingand control characteristics of a twin-en-gined airplane with one engine inoperable.The program had been suggested by theDouglas Aircraft Co.Other research paralleled the aerodynamicsand flight work. A new engine lab hadbeen opened in 1934, and began to play animportant part in powerplant development.Part of the workload was directed towardsolution of existing problems, generallyassociated with the cooling of air-cooledengines.But some of the research was aimed at find-ing out the fundamentals of the internalcombustion engine, a type of powerplantthat had been operating for years withoutany real understanding of what went oninside its cylinders.NACA wanted to find out, and initiated aseries of research programs on the funda-mentals of fuel ignition and burning. Goosedown was used to show the air flow patternsof air and mixed gases inside a cylinder,and the motions were stopped by high-speed cameras developed at Langley.Research on aircraft structures was theprovince of a handful of engineers at Lang-ley. Yet out of the very early years grew aprogram that is still active today, and abasic research instrument that is installedon fleets of military and civilian aircraftflying at this moment. It started as a V-Grecorder, to measure the vertical accelera-tions experienced by an airplane flying inrough air. The aim was a simple one: Togather statistical data about air turbulence,

Boeing P-26of 1935during flap development

work.


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21

its frequency and intensity, and from thatdata, to evolve criteria for design of aircraft.Today, a sophisticated form of recorder isinstalled in aircraft of all types and sizesand performance capabilities, from single-engined private planes to the eight-enginedjet bombers of Strategic Air Command.The wealth of data is analyzed by com-puter techniques, and continues to expandthe range of mans understanding of thephenomena of flight.By the end of the second decade, the designof aircraft had changed for all time. Theall-metal, low-winged transport ruled theairlanes, and its sister ships made up thebulk of the military air fleets.One of the newest military craft was theBoeing Model 299, prototype of the B-17Flying Fortress series, which had flownin mid-1935. In its early flights it surpassedpredictions and expectations, and Boeingwent on record with a letter to NACAwhich said, in part:You may recall sending us, some timeago, the data which you had obtained onthe so-called balanced flap. It appearedto give such promising results that wedecided to use it on our model 299 bomber.We were also much gratified to find thatthe NACA symmetrical airfoil lived up toour expectations. It appears that in addi-tion to the effectiveness of the flap, theailerons are more effective, for a given area,than with the conventional airfoil.So, with the use of the NACA cowl inaddition, it appears your organization canclaim a considerable share in the success ofthis particular design. And we hope thatyou will continue to send us your hotdope from time to time. We lean ratherheavily on the Committee for help inimproving our work.But in spite of the enthusiasm of such en-dorsements of the work and contributionsof NACA, a nagging feeling had persistedthat more could be done. The possibility

existed that other countries were makingmore positive contributions to their aero-nautical industries than NACA was makingto the industry of the United States.The scientific challenge to the aeronauticalresearch supremacy of the United Stateshad been recognized and was voicedstrongly in the 1937 Annual Report of theCommittee to the Congress and the Presi-dent of the United States. The report ex-plained that, up until 1932, the laboratoriesat Langley were unique in the world, andwere one of the chief reasons that thiscountry was the technical leader in aviation.But since then, much of that equipmenthad been duplicated abroad and, in somecases, had been bettered so that Langleysequipment was no longer the best.The report went on: This condition hasimpressed the Committee with the advisa-bility of providing additional facilitiespromptly as needed for the study of prob-lems that are necessary to be solved, inorder that American aircraft development,both military and commercial, will not fallbehind.For some time, the warning went unheeded;Langley and NACA continued to workunder pressure, making do with facilitiesand equipment that were beginning to showtheir age. There was no particular reasonto improve the laboratories, no overwhelm-ing problem that couldnt be handled inthe ordinary routine of NACAs workingday. In a way, the attitude reflected thegeneral American view toward all worldproblems, not just the specific problem ofmaintaining aeronautical leadership.The war in Europe was far away; thiscountry was beginning to pull out of thecrushing depression of the early part of thedecade. Things looked reasonably good,and who really cared if foreign scientistswere testing rocket motors or developingdive bombers? What difference did asupersonic wind tunnel in Italy make?


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1938-1947World War 11dominated the third decade o fLangleys work. It broke out in September 1939,and before it was concluded ojicially in Septem-ber, 1945,the shape o f aircraft had beenchanged again.A handful o f technical developments caused thissecond revolution in aircraft design. Sweepback,an aerodynamic innovation discovered almostsimultaneously by several investigators, was ex-ploited in advancedjghter and bomber projectsby German engineers.Jet propulsion, another example o f parallel dis-covery and development, made great strides dur-ing the war. Thejrst aircraft powered by aturbojet wasflown in Germany on August 27,1939; both Germany and Britain had operationaljet-propelled jg ht er s before the war ended.Rocket development was paced by the demands o fwar. Th ej rs t German V-2 (A4) ballistic mis-sile w as jr ed unsuccessfully twice in 1942 beforeit sj rs t successful launching i n October that yea r,It was to become operational as a j e l d weaponless than tw o year s later, only a f e w monthsafter the pulse-jet powered V- Ifl yi ng bomb wasused to bomb London.Guided missile warfare started in August 1943with the German use o f radio-controlled rocket-powered glide bombs against sh;Ps.Nuclear weapons were conceived, developed, testedand used operationally during Wo rld W a r 11,culminating in the bombs dropped on Hiroshimaand .Nagasaki.Mis sile s as defense weapons received their j r s timpetus when Project Nike was originated inFebruary 1945,to strike at high-altitude, high-speed bombers that would be coming into service.The destruction of war gave way to the pursuito f more peaceful aim s in aviation after the sur-renders in 1945.Landplane speed records wereshattered, j r s t by the British who moved themark over the 600-mph. point with GlosterMeteors basically the same as those used opera-tionally by the Royal Air Force near the end o fthe war.Passenger service across the Atlantic had begunin 1939 by Pan American. A little more thanseven years later, the British D e Ha villand Air-craft Co. received an order to build two proto-gpes o f a four-je t passenger-carrying aircraftwhich would become the Comet, the worldsjrstjet transport to enter scheduled service.

23

T h ej r s t o f the research aircraft, Bells rocket-propelled X - I , had been conceived and designedduring the war. It made its jr st poweredflightin December, 1946,and in October, 1947,AirForce C a p . Charles E. Teaserf lew it throughthe speed o f sound fo r th ej rs t time and pioneeredthe way into the age o f supersonic f lig ht .The month before, a serious research report issuedby the Ran d Corporation stated that man-madesatellites o f the earth were completelyfeasible.Others had said essentially the same thing before,but they had been regarded as visionaries at best,and as crackpots at worst. Th e Rand Corpora-tion w as operating under fu n ds allocated by theU. S. government, and had made the s t u 4specajicalhfor the new Department o f Defense.Th e pronouncement had to be taken seriously, andit was, after the initial speculation by enthusiastswho saw supermarkets in the sky, giant lenses toburn the enemy, launching sites f o r atomic bombs,and a host o f horrible possibilities in what wasessentially a simple statement that certain tech-nology now appeared to be available.The earth satellite was not to be for this decade,but the Rand report was a benchmark in mansmeasured tread to the stars. N o w there wa s hopethat the technology o f war could be turned to thepeaceful development o f space.


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24

Grumman XF4F-3prototype was tested in

the Langley full-scaletunnel late in 1939;production models,

modified by Langleytests, were F4F-4 Wild-

cats, fighter mainstayof the U. S. Navy early

in World War 2.An experimental Navy fighter airplane, theBrewster XFZA-1,was delivered to Langleyin April, 1938, for tests in the full-scalewind tunnel. Systematically, Langley engi-neers measured the drag of the airplaneand of individual parts: Exhaust stacks,landing gear, machine-gun installation andthe external gun sight. When they reportedthe results of the tests, they concluded thatthe top speed of the airplane could be inrcreased by 31 mph., more than a tenpercent improvement in performance.This landmark test was the first in a longseries of clean-up programs performed orthe Army Air Corps and the Navy Bureauof Aeronautics. The success of the test pro-gram established the technique as standardfor both the Army and Navy, and produceduseful design data applied to future airplaneprojects.By October 1940, 11 different airplanes hadbeen tested in the full-scale tunnel, in aclean-up program of unprecedented pro-portion. A summary of the tests waspublished that month as an NACA Ad-vanced Confidential Report, to be circulatedonly to industry and the military. The con-clusion stated that . . .the drag of manyof the airplanes was decreased 30 to 40percent by removal or refairing of ineffi-ciently designed components. In one casethe drag was halved by this process. Em-phasis on correct detail design appears atpresent to provide greater immediate possi-

bilities for increased high speeds thanimproved design of the basic elements.The implication of the report was clear.Insufficient attention to detail design wascausing major performance losses. It did nogood to build a clean wing, with low dragcharacteristics, if the wing was dirtied by amachine-gun installation that protruded ata critical juncture. The machine-gun in-stallation was necessary; but so was maxi-mum performance of the airplane. As aby-product of these tests, designers beganto realize that airplane design had to be acompromise between the theoretical idealsof the aerodynamicists dream and thepractical values of operational requirements.As the clean-up program grew, so did otherprograms at Langley. The pressure was on,higher than ever, and in 1938 the AnnualReport again cited the need for additionalfacilities. Structural research, the Committeewarned in a letter to the Congress, pro-duced the greatest single need for newadditional equipment because of increasesin size and speed of aircraft. Further, saidthe Committee, the interests of safety andof progress in aeronautics demanded thatthe structures facilities be added at theearliest possible date.In October, 1938, a Special Committee ofNACA was appointed to study the needfor facilities and to make recommendations.Th e Committees December report urgedthe immediate establishment of another


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research laboratory at Sunnyvale, Califor-t nia, p?rs the augmentation of the Langley

facilities by a structures research laboratoryand a stability wind tunnel.Congress finally authorized the Sunnyvalestation in August, 1939, just days beforewar broke out. With Europe starting toburn, ground was broken for the newlaboratory at Moffett Field, Sunnyvale.A second Special Committee, headed byCharles A. Lindbergh, was appointed fol-lowing the outbreak of war, and within afew weeks turned in a report stronglyrecommending a third research center forpowerplant work. The report said thatthere was a serious lack of engine researchfacilities in the United States. At thepresent time, American facilities for re-search on aircraft powerplants are inade-quate and cannot be compared with thefacilities for research in other fields ofaviation.By mid-1940, Congress had authorized anew powerplant research facility. Earlierin 1939, money had been requested for anextension of the facilities at Langley aspart of a supplemental budgetary requestwhich included funds for the Sunnyvalelab. In November, Langley was authorizedto take over additional acreage at LangleyField as the site for a new 16-foot high-speed wind tunnel, the stability tunnel, thestructures laboratory, and supportingfacilities.The structures laboratory was completed inOctober, 1940, and the stability wind tun-nel in January, 1942, along with a secondtowing tank for seaplane development, andan impact basin where hull loads could bemeasured during simulated water landings.During 1941, both the low-turbulence pres-sure tunnel and the 16-foot high-speedtunnel became operational in wartime ex-pansion. Langley capabilities had to increaseat the same time that it was losing staffmembers to help organize and operate thenew station at Sunnyvale, now named theAmes Research Center after Joseph S.Ames, NACA Chairman for 20 years.With this exodus hardly out of the way, asecond began. Congress had authorized theconstruction of the engine research labora-tory in mid-1940, at a site near the Cleve-land, Ohio, municipal airport. Th e newlaboratory was to be geared solely to theproblems of power generation and propul-sion, from the fundamental physics of com-bustion to the flight-testing, in instrumentedaircraft, of complete powerplant installations.Personnel for the new center at Clevelandalso were drawn from Langley laboratory

staffs. Some idea of the magnitude of thestaffing problem can be gained by com-paring employment figures at Langleybefore and a t the end of the war. In 1939,before the expansion moves, Langley had524 people on its rolls, of which 204 wereprofessional people. At the end of the war,more than 3,200 were employed at Langley.During this third decade, the primary jobat Langley was to refine the basic airplanethat its earlier researches had made pos-sible. The propeller-driven, all-metal air-plane with a low wing, cowled engines,retractable landing gear, and flaps neededrefinement. Engine power was on the rise,and corresponding improvements in air-plane performance were possible. But theairplane had to be designed carefully,especially in detail, if maximum advantagewas to be gained.The drag tests on the Brewster XF2A-1pointed the way. At first in routine pro-grams, and later under the pressures ofwartime demands, airplane after airplanewent through the Langley tunnels, throughthe flight research department laboratory,into the spin tunnel, in model and full-sizeform, until all that could be known aboutthe airplane was measured and reported.At one time in July 1944, 78 differentmodels of airplanes were being investigatedby NACA, most of them at Langley.Spin tests were made in the Langley free-spinning tunnel on 120 different airplanemodels. The atmospheric wind tunnel crewstested 36 Army and Navy aircraft in de-tailed studies of stability, control, andperformance.From these tests came a wealth of data,first for the correction of existing problems,and second for the designers handbooks.These tests were backed by theoreticalinvestigations and experimental programsthat developed airplane components to thehighest degree attainable at the time. Asone example, in June 1938, Langleys low-turbulence tunnel began tests of an airfoilwhose contours differed from earlier de-signs. The point of maximum thicknesswas farther aft, and the trailing portion of.the airfoil showed an odd reflexed form.Th e measured drag was about half of thelowest ever recorded for an airfoil of thesame percentage thickness, and the investi-gation became the start ing point of Langleysdevelopment of a series of low-drag airfoils.Less than two years later, the British wereto give North American Aviation 120 daysto come up with a fighter prototype thatmet their requirements. The fighter becamethe famed P-51 Mustang, after consider-

25


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0

26 able development. It was one of the firstfighters to use an NACA low-drag airfoil,developed at Langley as part of the overallfamily of laminar-flow airfoils.Flight research work on a variety of air-planes began to build a backlog of corre-lated experiences on the flying and handlingqualities of airplanes. Early pioneeringwork at Langley had given pilots a newappreciation of flying qualities, and thewartime tests sharpened that appreciation.As performances increased, so did some ofthe flight problems. Again using the sys-tematic approach, Langley pilots and engi-neers developed measurable handling andflying qualities for aircraft, and furtherdefined them in terms of wind-tunnelmeasurements.After 19 airplanes had been systematicallytested in flight, Langley engineers prepareda summary report on the group. The reportincluded suggestions for minimum criteriato define a good aircraft from the view-point of its handling characteristics.That report became the foundation of theextensive work to be done later by NACA,the military services and industry. Also, itwas a spur to the writing of a militaryspecification on handling qualities, the firstsuch to be written in this country.Other work at Langley during the wartimeperiod included an extensive study of wingplanform shapes and their effects on thestalling characteristicsof an airplane.Variations in taper and thickness ratio,sweepback and twist, were investigated inwind tunnels.Aircraft loads in maneuvering flight, stillsomewhat of a mystery, were studied inflight, in the wind tunnels, and by theory.Changes in stability and control due toengine power, another misunderstood flightphenomenon, were delineated in flight testand in the Langley tunnels.The NACA cowling was refined furtherfor a higher speed range. A special flush-riveting technique was developed to reducethe parasite drag of airplanes.One pursuit plane was plagued by a seriesof in-flight tail failures. Langley engineersisolated the problem, helped suggest asolution. The plane went on to be one ofthe fondly remembered fighters of WorldWar 2.Another Army pursuit developed a tuck,a tendency to steepen its dive until ittucked past the vertical into a partiallyinverted attitude, and trouble began. Windtunnel tests at Langley in the eight-foothigh-speed tunnel, and by the manufac-turer, unearthed the problem. Langleysuggested the dive-recovery flap, based

partly on that experience and partly onsome earlier test work authorized to, *develop a dive brake for airplanes.Over-the-water combat flights, and thenumbers of crews lost in ditching on thewater, quickened interest in a way ofgetting an airplane safely onto the waterssurface. Langleys hydrodynamics testfacilities were turned to a high-priorityprogram of testing scale models in simu-lated water landings and recording theirbehavior in motion pictures.Some of the aircraft couldnt have beenmore poorly designed for landings on water.Belly intakes, bomb-bay doors, or wheelwells scooped up water and served tosomersault the airplane. They sank,inverted.The answer was to develop some kind ofa ditching flap that would counter theeffect of the scoops and bays and wells.Langley work produced such a flap, but itwas never used on any aircraft. The pro-duction changes were regarded as tooextensive.An experimental model of an Army pursuitplane had weak ailerons, a design defectthat could prove dangerous in combatmaneuvering. Langley pilots flew the plane,measured its performance; on the ground,engineers pondered the problems and sug-gested a dual approach. First, they doubledthe deflection angles of the aileron, whichincreased its effectiveness. Then theybalanced the ailerons aerodynamically, sothat the response was light and quick.The result was an airplane with doubledroll performance, and one that set newstandards by which later fighters werejudged.These were typical problems faced a t Langleyduring the war years. It was the urgencyof war that predetermined the direction ofso many of the NACA programs. Most ofthem were aimed at the quick fix thatwould get an airplane out of its currenttroubles.But most of the air war was fought withairplanes that had been designed before orearly in the war, and many of these haddrawn on basic NACA data for their de-signs. Secretary of the Navy Frank Knoxsaid in 1943: The Navys famous fighters-the Corsair, Wildcat and Hellcat-arepossible only because they are based onfundamentals developed by the NACA. Allof them use NACA wing sections, NACAcooling methods, NACA high-lift devices.The great sea victories that have brokenJapans expanding grip in the Pacificwould not have been possible without thecontributions of the NACA.


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As the war progressed, speeds kept edging. up. The pursuit airplanes that experienced

need for understanding this new charac-teristic of high-speed flight. It was onething to fix a problem of high-speed flighttemporarily; it could be done empirically,through tests in the Langley tunnels, orby carefully controlled and instrumentedtest flights.But to avoid this problem from the startmeant that the designers had to have abacklog of information, the very kind ofdata that NACA and the industry hadbeen too pre-occupied to collect during thewar years.In spite of the wartime work load, Langleystaff members had been thinking aboutsome of the problems of high-speed flight.In 1939, for example, the Airflow Researchstaff had another look at the basic con-cepts of jet propulsion, a long-known prin-ciple that had briefly come to light in a1923 Technical Report published by NACAIn this respect, NACA scientists were notalone. In other countries, their counter-parts were looking at and working on theproblems of jet propulsion. The Germanswere close to flying an experimental jet-propelled airplane. The British had writtena specification for their first. The Italianswere flying a rudimentary jet-propulsionscheme in a test-bed aircraft.

. compressibility troubles emphasized theBut jet propulsion, in 1939, seemed l i e theanswer only to the interception problem.Th at was not the major concern of theU. S. military services, who were strugglingto get every bit of range out of their air-craft for strategic reasons. Back into thefiles went the jet propulsion reports.Another example of high-speed researchwas started in 1941, when a group beganto test in the eight-foot high-speed tunnel,working on propeller designs that could beused to drive an airplane at the then-unheard-of speed of 500 mph. Langley per-sonnel in this group were the nucleus oflater work on high-speed flow that was towin the agency two more Collier Trophies.Working in the high-speed wind tunnel wasa guaranteed way to unearth the problemsof attaining high speeds. But it was onlyone of the methods that NACA tradition-ally had used to obtain design data. Flighttests had to supplement the wind tunnel,and a variety of other kinds of tests inspecial facilities, such as the free-flighttunnel, had to be integrated into a testprogram before the engineers believed thedata was good enough to provide a designbase.At 500 rnph., designers would be workingnear the fringe of the transonic region andthe speed of sound. That speed had beendefined as a problem some years before,when a British scientist had said that sonic

Early Curtiss P-40fighter in drag clean-uptests at Langley during1940.

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1. North AmericanP-51B, one of the most

effective air weapons ofWorld War 2, went

through drag clean-uptests in the Langley

full-scale tunnel late in1943.2. Bell YP-59A undertest in the Langley full-scale tunnel. Plane was

service test modificationof XP-59, first United

States jet-propelledairplane, which first

flew October 1, 1942.I.


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speed . . . looms like a barrie r. . . against. the fuSther development of flight. Thewords, sonic barrier, passed quickly intothe literature and folklore of flight.Was it a barrier, or only a smokescreen?There was no availawle way to find out.Some flow experiments had been made atLangley by dropping instrumented andhighly streamlined shapes from high alti-tudes, measuring forces and speeds andcorrelating the two to determine the changein drag and lift at the transonic region.But these results were not too conclusive.The re was one acknowledged way to getaccurate transonic design data, and thatwas from flight tests of a full-scale airplane,built specifically to fly into and through thetransonic region.In 1943, such an airplane was conceivedat Langley. More o r less simultaneously,others in industry and the military labshad been thinking along the same lines.The Langley study expanded and, in March1944, was presented at a seminar attendedby personnel from the Army Air Force,the Navy and NACA. NACA put its weightbehind the study, and proposed that ajet-propelled airplane be built specificallyfor the purpose of flight research in thetransonic region.This was a pioneering step in aviationhistory. I t marked the beginning of a sys-tematic exploration of the transonic regionin flight tests tha t would win world-widerespect and reknown. It led also to the laterstable of research aircraft operated byNACA and the military in unique pro-grams that supplied fundamental designdata for years to come.Today, research aircraft like the X-15 arebeing flown near the borders of the un-known, in tests which are producing designdata for the aircraft of tomorrow.This first research airplane was designatedXS-1, and was to be built by Bell AircraftCorp., where much of the original designthinking had taken form in 1943. The con-tract was let by the Air Materiel Commandearly in 1945, and design and constructionproceeded.At Langley, scientists were still trying othermethods. It was not so much a case ofhedging bets as it was trying to developtest techniques that would supplementthose of full-scale flight, and which mightindicate a way to go that was cheaperthan constructing a complete airplane eachtime.One of the unique approaches to obtaininghigh-speed flow was conceived at Langleyin mid-1944. It was based on the existence

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of transonic flow in a small region over theupper surface of the wing of a high-speedsubsonic airplane. A small, half-span modelof a wing shape was built and mounted,perpendicular to the upper surface of thewing and aligned with the airflow, near thepoint of maximum thickness. The airplanewas flown into a high-speed dive, andtransonic flow developed over the wing.Instrumentation in the mount of the modelwing recorded the forces and airflow anglesfor reduction into design data after theflight.Revisions in instrumentation, and specif-ically the development of radio telemeteringtechniques a t Langley in 1944, prompted asecond series of bomb-drop tests. With a ninstalled telemetering package, forces couldbe measured in flight and transmitted to aground station for recording and futuredata reduction.The problem was basically that the avail-able operational altitudes didnt permitenough velocity buildup before impact ofthe bombs. Consequently, the data pointsnever got very much over the sonic mark,and didnt prove too useful.Of these techniques, the most productiveresults were to come from the wing-flowmethod tests. They determined that a thinwing didnt behave at all like a thick wing,and that its characteristics were far superiorfor high-speed flight.Near the close of World War 11, a Langleyscientist conceived the idea of wing sweep-back as one method of obtaining higherflight speeds. In effect, sweepback fools theair into thinking that it is flowing over avery thin wing, and it delays the suddendrag rise associated with the transonicregion. In the supersonic speed range, asweptback wing can be designed so that itlies entirely within the shock wave cone.This avoids the problems of mixed flowthat would otherwise occur.Wing sweepback was not a Langley inven-tion, because other scientists were workingon the idea a t about the same time. Thefirst intelligence reports that filtered backto industry and the NACA laboratories inthe closing months of the war showed tha tthe Germans had taken aggressive advan-tage of the concepts of sweepback, in designsof jet-propelled aircraft that-on paper-were superior to anything under develop-ment either in this country o r in GreatBritain.Those designs set the pattern for the post-war years of aviation development. Thedemand was for more speed, higher altitudesof operation, more thrust from turbojet androcket engines. But the XS-I had yet to

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fly. Operational German aircraft withadvanced features were so few, and thereally advanced types so experimental,that there was no way of obtaining muchsolid data from flight tests of full-scaleairplanes.Langley had done some experimentationwith rocket-propelled models, launchingthem from the ground in attempts to getmeaningful free-flight data. This lookedlike a valid test technique, and the workexpanded to a point where a separate testfacility was established at Wallops Island,Virginia, up the Atlantic coast from Lang-ley. The Pilotless Aircraft Research Division(PARD) moved into the area late in June,1945, and on October 18 launched its firstsuccessful drag research vehicle.This was a rocket-propelled model aircraft,designed to evaluate wing and fuselageshapes to provide basic design informationat transonic and supersonic speeds.Th e test vehicles became more elaborate.The following June, PARD launched acontrol-surface research vehicle whichevaluated controllability in roll by deflect-ing the ailerons in a programmed maneuver.Wallops Station has long outgrown thatoriginal test site and now is sprawled overportions of the former Naval air station atChincoteague. In recent years, Wallopswork has provided major contributions tothe Mercury, Gemini and Apollo mannedspace flight programs, in tests of escapesystems and other rocket-launched vehicles.The first flight of the XS-I was approach-ing, and the test work flights were scheduledto take place at the Army Air Force flighttest area on Muroc Dry Lake, Calif. Pro-gram personnel were moving to the areafor support of the tests, and Langley trans-ferred 13 engineers, instrument specialistsand technical observers to Muroc. The unitwas designated the NACA Muroc Flight

1. Boeing B-29 long-rangebomber model was testedfor ditching character-istics in the Langley tankNo. 2 early in 1946.2. Navy swept-wingmodificationof Bell P-63was tested by Langleylate in 1947 to deter-mine low-speed stabilityand stalling character-istics.


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32 Test Unit; it was the origin of todaysNASA Flight Research Center at EdwardsAFB, which grew out of the site of theMuroc operations.The Bell XS-1 was a conservative design.Its rugged structure was planned to take amaximum load of 18 times its normal flightloads, where most fighters were designedfor only nine times the normal load. Itspowerplant was a proven unit. The designprinciples were simply stated: Avoid allidentifiable uncertainties.One of the uncertainties was the way tofeed the fuel to the rocket engines. Thelightest weight unit would have been aturbine-driven fuel pump, but it wasntready when the XS-1 needed it. The deci-sion was made to go with a pressurized fuelsystem, in which bottled nitrogen gas,stored in 12 spherical containers at 2,000psi., was used to force the fuel and oxidizerfrom their tanks to the engine.Th e pressurized system was heavier, anddisplaced precious fuel so that only enoughwas left for two and one-half minutes ofpowered flight. To make the most of theavailable fuel supply, Bell suggested thatthe XS-1 be carried aloft under a speciallymodified Boeing B-29 bomber, and air-dropped for launch.This would accomplish a couple of things,they said. First, it would enable the air-plane to be flown without power in a seriesof glide flights which would establishwhether or not the basic airplane designwas right, aerodynamically, at lower speeds.Second, it would conserve fuel so that itcould be almost all earmarked for the dashthrough the transonic region, for which theairplane was built in the first place.Glide flights were made early in 1946, overPinecastle, Florida, and the first poweredflight following air-launch was made earlyin December that year.Back at Langley, work still was continuingon methods to reach the same speed rangein wind tunnels, or in free-flight with models.One of the major accomplishments during1946 was the development of a rocket-powered research vehicle that flew fasterthan 1,100 mph. I t was par t of the workdone at Wallops Island, and it was launchedto test a series of wing planforms of dif-ferent sweepback angles and proportions.The wing-flow method of transonic speedstudies was adapted for wind-tunnel use byinstalling a hump in the test section of theseven- by ten-foot wind tunnel at Langley.Mach numbers of about 1.2 times the speedof sound could be reached before the tunnelchoked with the shock waves of super-sonic flight and the results became uncertain.

I t was, and is, the presence of shock wavesin the tunnel test section that makes i! sodifficult to obtain meaningful results aroundthe speed of sound. But Langley researcherspostulated that the shock waves could becancelled or absorbed instead of being re-flected. If absorbed, then the test sectionwould be free of the reflected shocks thatdisturb the flow and the measurements.Two Langley researchers, one working withflow theory and the other with experimentsin a small 15-inch tunnel attached to the16-ft. high-speed tunnel, were able to estab-lish transonic flow in a test section whichhad been slotted with longitudinal open-ings. The slotted throat absorbed the shockwaves and kept the test section clear formeasurements.This was a breakthrough in wind-tunneltechnique. I t led directly to the developmentof the slotted-throat tunnel for transonicflow studies, and later, in 1951 after thestory could be told, won a Collier Trophyfor John Stack and his associates at Langley.In April 1947, PARD (Pilotless AircraftResearch Division) launched its first scaled-down airplane in a test for performanceevaluation. I t was a model of the RepublicXF-91, a radical fighter design which com-bined turbojet and rocket engines forperformance at extreme altitudes.Th e success of this test program was fol-lowed by model flight tests of most of theAir Force and Navy supersonic and subsonicaircraft designs.


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Then, on October 14, 1947, the sonic bar-rier*no longer was a mystery. The BellXS-1; piloted by Air Force Capt. CharlesE. Yeager, reached Mach 1.06 on its ninthpowered flight, in a clear demonstration ofcontrollable flight through the transonicregion.I t was the first of many supersonic flightsto come for the XS-1 (later to be designatedthe X-1 and to be joined by sister ships inthe same series with improved performance)and, later, for other experimental andproduction aircraft.But it was the pioneering achievement ofthe XS-1 program and the people associatedwith it that was recognized by the awardof the Collier Trophy for 1947 to LangleysJohn Stack, Lawrence D. Bell of Bell Air-craft, and Capt. Charles E. Yeager of theUnited States Air Force.Supersonic flight now is no longer unique.Within a few years, airline passengers willbe traveling at speeds nearly three timesthat reached during the first piercing of thesonic range.But in 1947, the attainment of supersonicspeed was a history-making culmination ofa long research effort that had begun earlyin the war at Langley Memorial Aeronauti-cal Laboratory (now, Langley ResearchCenter). It was also the first step into thefuture of a new and pioneering age inaviation-the age of supersonic flight.

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Sixteen aircraft arewaiting for flight testsat Langley during atypical day in WorldWar 11.

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1948-1957Thefour th decade o f research at Langley wascharacterized by rapid and drastic changes inaircraft types and performance, often shaped bythe application o f new technologies draw n fr omN A C A experience.In the ten years between 1948 and 1957, thespeed o f servicejghters in the U. S. Air Forceand Navy virtually doubled. In September 1948,the world speed record was raised to 670.981mph. by a standard North American F-86Ajighter. At the end o f the decade, a McDonnellF-101 A Voodoo blasted its wa y to 1,207.6mph, beating by a handsome margin the previousrecord set by a British research aircraft, theFairty Delta 2.Trans portat ion speeds increased also. I n 1948,the Britishjew the worldsjrst turboprop air-liner, the Vickers Viscount, and followe d it wit hthe jrs t j i ght , in the fo llowing year, o f theDe Havilland Comet, a turbojet-propelled transport.The Comet entered scheduled airline service withBritish Overseas Airways Corp. in May, 1952.T w o years later, the bright dreams were dulledby tragedy and the Comet was wit hdraw n fr omservice.Th e remarkable series o f Xaircraft, whichhad been born during the previous decade withthe Bell XS-1, grew into a stable o f diverseopes to probe and analyze new problem areas.From the barely supersonic performance o f theoriginal X- 1, the research series blasted j r s t pastMach 2 and then Mach 3 speeds.Th e j r s t tentative steps toward vertical takeofand landing ( V T O L ) aircraft were taken, anddevelopment later was spurred partly by the out-standing success o f the helicopter in the Koreanaction, and a knowledge o f its shortcomings.The Century Series ofji ghte rs, so-called be-cause o f their numerical designations whic hstarted with F-100, were developed andjownduring this decade, and set new performancestandards. They also posed new stability andcontrol problems, such as roll coupling and pitch -up, which were to plague their designers andN A C A for solutions.Andjinally, in the closing months o f the decade,North American Aviation was awarded the con-tract fo r the X B- 70 bomber, an awesome aircraftintended toJ y at three time s the speed o f sound.Th e airplane had come fa st and f a r in the decade

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between 1948 and 1957. The Be rlin Airli ft,which began in June 1948, w as jo wn with thepiston-engined transports left over from WorldW a r 2, and designed before then.The Consolidated Vultee B-36 was the standardbomber o f the Air Force, and jet-propelledjighterswere ju st getting t o squadrons. There was achange in the o&g, marked by t h e j r s t j i g h t o fBoeings XB-47, a sixjet sweptwing bomber,which took to the air for t h j r s t time February 8,1949.But the U . S. went to war in Korea with left-over Boeing B-29 bombers, and thejirst kill wasmade by a North American F-82 Twin Mustang,a piston-engined jgh ter .I n November 1950, the j r s t dogjght between je taircraft seared the sky over Korea and set thepattern fo r future combat.In June 1951, the Bell X-Sjefletufor thejrs t t ime.One o f the research aircraft, it was characterizedby its ability to change the sweep angle o f it swing in jig ht. It was the precursor o f the GeneralDynamics F - 1I lA jghte r and the Boeing supersonictransport.Air transportation made a tremendous impact onthe public during the Berlin Airl ift. Three yearslater, air passenger mi les overtook Pullm an pas-senger miles traveled fo r th ej rs t time. The trendhas never reversed.The Boeing 707prototype, j r s t o f a long line o fjet transports, made its jr st ji g ht July 15, 1954.Later, the French made a unique contributionwith the Sud Aviation Caravelle, whose rear-mounted turbojets set a sole trend. The Caravellejirst Jew M ay 27, 1955.In October that year, Pan American World Air -ways ordered 45jet transports, 25 DC-8s fromDouglas and 20 Boeing 707s. T he jr st round o fj e t orders was sparked by th is move, and the j e trace was on.In January 1951, the At las intercontinentalballistic missile program w

Fifty Years of Aeronautical Research

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