DOCUMENT RESUME

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AUTHOR Anderton, David A.TITLE Aeronautics. Anterioa in Space: The First Decade.INSTITUTION National Aeronautics and Space Administration,

Washington, D.C.REPORT NO EP-61PUB DATE 70

NOTE 30p.AVAILABLE FROM Superintendent of Documents, Government Printing

Office, Washington, D.C. 20402 ($0.45)

EDRS PRICE MF-$0.65 HC-$3.29DESCRIPTORS *Aerospace Education; *Aerospace Technology;

*Aviation Technology; Instructional Materials;Reading Materials; Research; Resource Materials;Science History; Technological Advancement

IDENTIFIERS NASA

ABSTRACTThe major research and developments in aeronautics

during the late 1950's and 1960's are reviewed descriptively with aminimum of technical content. Ttlpics covered include aeronauticalresearch, aeronautics in NASA, The National Advisory Committee forAeronautics, the X-15 Research Airplane, variable-sweep wing design,the Supersonic Transport (SST) , hypersonic flight, today's aircraft,helicopters and V/STOL aircraft, research for spacecraft,air-breathing power plants, and reduction of engine noise. Manyphotographs and illustrations are utilized. (PR)

U S DEPARTMENT OF HEALTH,EDUCATION & WELFAREOFFICE OF EDUCATION

THIS DOCUMENT HAS BEEH REPRODUCED EXACTLY AS RECEIVED FROMTHE PERSON OR ORGANIZATION ORIGINATING IT POINTS OF VIEW OR OPINIONS STATED DO NOT NECESSARILYREFRESENT OFFICIAL OFFICE OF EDUCATION POSITION OR POLICY

National Aeronautics and Space Administration

AmericaInSpace:TheFirstDecade

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by David A. Anderton

National Aeronautics and Space Administration, Washington, D.C. 20546

Introduction

In 1958 the National Aeronautics and SpaceAdministration was brought into being to explorecertain broad areas of research and development whichincluded not only the exploration of space but alsothe continued responsibility in aeronautics which hadbeen the primary function of its predecessor agency,the National Advisory Committee for Aeronautics.It is seldom recognized by the generai public thatNASA has a vital and necessary role in the advance-ment of military and commercial aviation in theUnited States, and that the level of effort whilea small fraction of the agency's total programis very substantial. Roughly 2500 NASA employeessupported by funding of about $160,000,000 per yearare directly engaged in conducting the researchdescribea in "Aeronautics."

Thc frontiers of light have not all bcen exploredand the applications of NASA's advanced researchin aeronautics will continue to keep the United Statesin first place in commercial and military aviation inthe years ahead until someday we will ix, able to travel

as casually from New York to Australia at 6000 mphas millions do now from New York to Pahis at nearly600 mph.

Nep, A. ArmstrongDeputy Associate Administrator/AeronauticsOffice of Advanced Research and Technology

TableOfContents

Aeronautical Research 1Aeronautics in NASA 2The National Advisory Committee for Aeronautics 3

The X-15 Research Airplane 5Variable-sweep Wings 8The Supersonic Transport (SST) 10

Hypersonic Flight 14Today's Aircraft 15

Helicopters and V/STOL Aircraft 16Research for Spacecraft 19Air-breathing Power Plants 20Reduction of Engine Noise 21Problem Solving 22

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AeronauticsAeronauticalResearch

Up at the rim of the atmosphere, the rocket-poweredX-15 research airplane accelerated to hypersonicspeed in one of NASA's aeronautical programs toprobe the performance envelopeF of tomorrow's airtransportation.

At another cenier, poised a few yards above theconcrete apron in dont of its lr-mgar, the hovering X 14measures the stability of vertical takeoff and landingaircraft in a different NAS k aeronautical program.

Across the continent, wind-tunnel fans blast air past anintricate model of one of the ,Lzwest military aircraft tocheck its predicted perk/mance against actral flight-test data.

In other wind tunnels and test facilities of theNational Aeronautics and Space Administration there

1 Interior of a wind tunnel at the Langley Research Center.

are other models, ranging from a conceptual designfor a hypersonic transport to a light twin-enginedairplane flown at hundreds of airports throughout theworld by thousands of private pilots.

These aircraft and models span the performancecapabilities of modern airplanes from the ground tothe edge of space, and from zero speeds to velocitiesof several thousand mile5; per hour.

They are some of the tangible signs of the manyprograms in aeronautics underway at any one timewithin NASA. But they .ire more than just evidenceof work now being done. They point the way toimproved and safer airplanes for tomorrow's privatepilot, and to more economical and speedier transportsfor the air traveler of the 1970s.

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These aircraft, operating at the extremes of today'sflight performance, emphasize the wide range ofaeronautics and the depth of the research programs withwhich they are associated.

And they build on NASA's continuing expertise inaeronautics, that NASA and its predecessororganization, tl.e National Advisory Committee forAeronautics, have pioneered consistently for morethan fifty years.

Aeronauticsin NASA

Aeronauticsthe scientific and engineering disciplinesthat deal with the design, construction and operationof aircraftaccounts for a fascinating portion of thecurrent work of the National Aeronautics and SpaceAdministration.

The basic aeronautical research program, carried outon a broad front at NASA research centers, servestwo vital functions.

First; it provides the needed technical support foraircraft programs in the national interest through theNASA staff of experienced aeronautical scientists andengineers, and the unequaled test and experimentalfacilities available to them and to industry.

Second, it encourages the exploration of new conceptsand new probiem areas, and the development of newfacilities to aid that exploration.

The latter function has provided, through the years,the strong foundation of aeronautical technology onwhich the aerospace industry and the military serviceshave built their requirements.

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Hundreds of NASA personnel and about one-quarterof a billion dollars worth of test facilities are groupedin the four centers where aeronautical programscurrently are in progress: Langley Research Center,Hampton, Va.; Ames Research Center, MoffettField, Calif.; Flight Research Center, Edwards, Calif.;and the Lewis Research Center, Cleveland, Ohio.

In addition to its own research projects for these peopleand facilities, the total NASA aeronautical programincludes a large number of contracts placed withindustry, research institutions and universities allover this country and in some foreign lands.

An intangible, but important, factor in the aeronauticalresearch program is a continuity of effort that hasmarked every step of the way from the early daysof the National Advisory Committee for Aeronauticsand its first methodical approach to the solutions of theproblems of strut- and wire-braced biplanes.

Time and time again, the history of a specific researchproject shows that influence. An older engineerremembers previous work done that can be adaptedor extrapolated. An obsolescing wind tunnel isgiven a new lease on life by a modification to makeit serve an entirely new task. A simulator that onceproduced insight into the behavior of a research aircraftnow singles out the problems facing astronauts infuture lunar landings.

And beyond these specifics, there is the overallapproach to problem-solving that has characterizedNASA's aeronautical research. A problem is aproblem, whether it was raised in 1918 or 1968.The approach to the solution of that problem does notchange with time. First, understand the problem byexamining it, defining it, trying to measure it withmeaningful parameters. Then go after the solution.That was NACA's earliest approach, and it workstoday.

The progress of the last ten years in aeronautics hasbeen marked by a series of major developments thatserve as milestones along the road of aeronautics.Those milestones have been placed on the solidfootings of the aeronautical technology conceived,researched and developed by the National Aeronauticsand Space Administration.

To look back at 1958, the calendar year that sawthe birth of the National Aeronautics and SpaceAdministration, is to look back at a year when theairlines of the world were plying their routes withaircraft whose lineage traced back to the Second WorldWar. The largest airliners carried about 70 passengers.Their straight wings mounted a quartet of pistonengines, driving three- and four-bladed propellers.Compared to today's swift jet transports, they trundledtheir way along at a speed under 300 mph.

In October 1958, the month of NASA's birth, thefirst scheduled transatlantic air service flown by jettransports was started, first by British Overseas AirwaysCorp., and later by Pan American World Airways, Inc.Six years before, BOAC had pioneered jet serviceson other routes with the first de Havilland Comets,but structural fatigue problems with the airframeforced the withdrawal of that service about twoyears later.

In the low-speed flight regime, the helicopter was theonly vehicle that promised much. Developed too latefor extensive use during World War II, it was temperedin the Korean action and showed a performance thatits proponents saw as pointing the way toward afuture solution of short-haul transportation problems.There were some strange hybrid vehicles, which weresupposed to bridge the gap between the helicopterand the fixed-wing airplane by performing thefunctions of both. These V/STOL aircrafttheirdesignation was shorthand for Vertical or ShortTakeoff and Landingwere experimental models, withessentially unproven performance, and uncertaincharacteristics. They were a long way from beingpractical.

Supersonic flight was the rare privilege of a fewmilitary and civilian test pilots, and the worldwidetotal was measured more accurately in dimensionsof minutes rather than in hours.

But in a single decade all this changed. Today's airtraveler rides in a sweptwing jet aircraft that may carryas many as 350 people to the edge of the stratosphere,at a speed that was, in 1958, the exclusive province ofthe military. He roads about progress on a supersonictransport, an even larger aircraft that will whisk him

across continents at more than two and one-half timesthe speed of sound. He talks with his fellow passengersabout the next generation of giant jets that will carrymore than 300 passengers or about the huge airbusesthat will fly the short runs between such cities as NewYork and Washington, or Los Angeles and SanFrancisco.

He may have heard some of the ideas for an even fasterairliner, the hypersonic transport, that will slicethrough the thin upper reaches of the atmosphere atspeeds seven times that of sound.

But in one respect, there is little change between theair traveler of 1958 and the passenger of 1970: Hestill has the short-haul transportation problem to faceat one or both ends of his journey. The helicopter hasnot yet been developed to the fine point where it canbe operated economically as an inter- or intra-citytransport, and the promise of the V/STOL generationremains just a promise.

The NationalAdvisory Committeefor Aeronautics

The foundations for today's subsonic jet transport andtomorrow's supersonic transport were laid in large partby NASA and its parent organization, the NationalAdvisory Committee for Aeronautics. Founded by anAct of Codgress in 1915, NACA's work for thefuture was defined by these words from a jointresolution of the Congress:

". . . it shall be the duty of the Advisory Committee forAeronautics to supervise and direct the scientificstudy of the problems of flight, with a view to theirpractical solution, and to determine the problemswhich should be experimentally attacked, and todiscuss their snlution and their application to practicalquestions. In the event of a laboratory or laboratories,either in whole or in part, being placed under thedirection of the committee, the committee may directand conduct research and experiment in aeronauticsin such laboratory or laboratories."

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As NACA grew through the years after its founding,it contributed to the rapid growth of the art ofaeronautics, and was one of the instrumental bodiesin transforming that art into science.

Five times the NACA and its scientists and engineerswere honored by the award of the Robert J. Collier.Trophy, given each year for the greatest achievementin aviation in America, and presented by thePresident of the United States.

In 1929 NACA won the Collier Trophy for itsdevelopment of the NACA cowling, a systematicallydeveloped housing for radial air-cooled piston enginesto minimize their drag and improve the cooling airflow.

In 1946, the Collier Trophy was awarded for NACA'sdevelopment of a thermal ice-prevention system thatled the way to safer flight.

In 1947, NACA shared the award with the UnitedStates Air Force and Bell Aircraft Corp. for thesuccessful demonstration of sustained supersonicflight in the rocket-powered Bell X-1 research aircraft.

In 1951, NACA's work on the transonic wind tunnelreceived another Collier Trophy. That awardrecognized the theoretical and empirical work thatdeveloped a technique of testing models close to,and in the transonic region of flight, that previouslymysterious area where conventional testing techniquesfailed and where theory was still largely unproven byexperimental results.

In 1954, the Collier Trophy went again to NACA forthe concept and experimental verification of the arearule, an aerodynamic design approach that madeit possible for a given airplane to go faster andfarther with the same engine thrust.

These awards highlighted the contributions of NACAto aeronautics during the years of its existence. Thelast three of them further emphasized one of the biggestproblem areas that was occupying more and more ofthe time and energy of the research organization:fligh-speed flight. The demonstration of the ability tofly safely at supersonic speeds, the development of atesting technique to corroborate flight performanceand to predict it for unflown designs, and the

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application of an advanced aerodynamic techniqueto the design of a high-speed aircraft, all showed thedirection of the future at NACA.

And then came 1958 and the creation of NASA toabsorb NACA and other research and developmentalagencies into one group, similarly dedicated to advanc-ing the frontiers of flight in and above the Earth'satmosphere and into space.

Quite naturally, NASA inherited the aeronauticalproblems of NACA; it also acquired a new set ofproblems as a result of its expanded role in thedeveloping theater of space flight. The experimentaltechniques that had been painstakingly developed overthe years of NACA's life were to be turned to newproblems posed by the thrust of aeronautics outwardand upward into new areas for exploration.

By the time that NASA was formed, the technology forsustained supersonic flight had been developed to thepoint where a supersonic transport seemed feasible. Anew approach to a tactical fighter configuration hadevolved from NACA studies, a concept which dependedon changing the shape of the airplane in flight byaltering the wing sweepback angle radically.

Wind tunnel and flight tests, by NACA, industry andthe military services, had selected and rejectedcandidate configurations for V/STOL aircraft, and theresults of those tests pointed toward the next steps inthe development of those specialized aircraft.

Finally, NACA's traditional role in support of a widerange of military aircraft projects was transferred toNASA along with other basic aeronautical researchproblems and programs.

Over the years, a coordinated 'approach to problem-solving had evolved. It utilized theory, developed orextrapolated by NACA scientists. To verify theoreticalstudies, wind-tunnel tests were made in a sophisticatedarray of specialized facilities. General and specificmodels, ranging in measurement from fractionalinches to the full size of the actual aircraft, wererun thwugh extensive tests to verify or expand thetheoretical approach.

Carefully instrumented flight tests of the full-sizeaircraft made valuable contributions to understandingthe problem. The flight tests served to give finalverification of the other theoretical and experimentalapproaches and, at the same time, to increase the

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general understanding of the inherent errors and ofthe corrections that needed to be applied to theoryand scaled-down experiment to produce usefulanswers.

This three-way approachtheory, model test and full-scale flight testwas a foundation of NACA'stechnology, and it became a foundation of the work ofthe National Aeronautics and Space Administrationafter 1958.

A major contribution to aeronautical research had beenmade by the joint NACA/USAF/USN series of "X"aircraft, from the X-1's through the X-5, which weredesigned and flown specifically to advance thetechnology of piloted aircraft. These aircraft stemmedfrom the original Bell XS-1, a bullet-shaped, stubbyand thin-winged rocket-powered plane that wasconceived in 1943 as a vehicle to fly through the"sonic barrier," a theoretically formidable regionwhere the airplane speed was approximately that of thespeed of sound, and where aerodynamic disturbanceswere expected to cause disruption of normal flightparameters.

The XS-1, later designated the X-1, led to a wholeseries of research aircraft, flown to explore the farreaches of airplane performance by engineering testpilots from NACA, the U.S. Air Force, the Navyand Marine Corps.

The X-15Research Airplane

The last of the series, North American Aviation'sX-15, powered by a 59,000-pound-thrust rocket engine,was first rolled out of the factory two weeks afterNASA's first day of business. Less than one year later,it made its first powered flight, and continuedto extend the boundaries of manned flight to the edge

of space. Five U.S. Air Force pilots have qualified forastronauts' wings as a result of their flights in the X-15above a 50-mile altitude; three NASA research pilotsalso have flown the X-15 to altitudes above the 50-milelevel. Two X-15 pilots have become NASA astronauts.And one, Neil A. Armstrong, went on to be the firstman to land on the Moon.

In 1962, the Collier Trophy was awarded to four X-15pilots for ". . . invaluable technological contributionsto the advancement of flight and for great skill andcourage as test pilots of the X-15."

The X-15 program was completed with a final flighton October 24, 1968. In the ten years of its activelife, it proved the feasibility of manned space flight,extended the borders of manned flight into the edgeof space and the hypersonic speed range, and carriedresearch experiments to sustained heights and speedsthat had never before been attained by mannedaircraft.

The origins of the X-15 program are obscure. It wasconceived after several years of advance thinking aboutsome of the problems of manned flight at very highspeeds and altitudes. Industry and the militaryservices, particularly Bell Aircraft Corp. and theAir Force, were influential in establishing the need,the early feasibility and the concept that led to theconstruction of the X-15.

Its original purpose was twofold. First, it was toverify its theoretical design and its flight envelope,the boundaries of speed and altitude performanceestablished by its own aerodynamic and physicalcharacteristics.

Second, it was to explore methodically the flightenvelope, looking at such problems as stability and

2 One of the X-15 aircraft was given a white ablative coatingfor tests in high-speed and high-temperature flights.

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3 A small scale model of the X-15 in the four by four-footsupersonic pressure tunnel at the Langley Research Center.Lines flowing away from the model are shock waves.

4 X-15 model in the supersonic tunnel at Laliy.

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control, aerodynamic heating from the rush of air atthe high speeds envisioned, and the relationship of manto the machine

Later, a third purpose was added: it was to Serve asa carrier vehicle for tests and experiments at sustainedaltitudes and speeds that could not be reached withany other type of aircraft or rocket.

Like other research aircraft before it, the X-15 was tobridge the gap between the theory and experimentsin the laboratory, and the actual free-flight performanceof the aircraft. That gap had been the subject ofconsiderable debate during the early thinking that ledto the entire "X" series of aircraft, and it continues toexcite interest today.

The original goals of the X-15 program were to reach6,600 feet per second (more than six times the speedof sound) and an altitude of 250,000 ft. The speedwas reached and exceeded; so was the altitude goal.The current altitude mark for the X-15 is 354,200 feet,or 67 miles, and at that level, the X-15 was above99.999% of the Earth's atmosphere. The X-15 reached4,520 mph. in its fastest flight, just exceeding its speedgoal.

An enormous amount of detailed engineering data hascome from the test flights of the X-15. The predictedhypersonic aerodynamic characteristics were verified,proving that the gap between theory and experimentwas not so wide as had been feared in this particularcase. The heating rates of the structure, caused byits rush through the air during reentry into the bulkof the Earth's atmosphere, also were verified by X-15flights.

In that environment of high heating and the high loadsimposed by reentry and maneuvering flight, the X-15structureinstrumented to determine its characteristicsproduced valuable data about the way to buildhypersonic aircraft and spacecraft. There were somesuperficial failures of structure due to the heating, butno primary structure ever failed, or gave any indicationof failing.

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Such localized phenomena as skin buckling, althoughit did not materially affect the X-15 or its performance,did underline the importance to designers of futurehypersonic aircraft to investigate the problem carefully.Skin panel flutter, where a section of the aircraftcovering would vibrate under aerodynamic loadingthat triggered a resonant response, was evaluated andcured on the X-15. Windshield crazing or crackingon seve,a1 flights taught another lesson in the designand construction of transparent surfaces for hypersonicflight.

When the X-15 was flying above most of theatmosphere, there was quite literally not enough air forits conventional airplane-type control surfaces to"bite" into. The X-15 had to be stabilized andcontrolled during the flight at those extreme altitudesto avoid a reentry at some unusual attitude that coulddestroy the aircraft. The problems of such stabilityand control needs were probed and solved by theX-15.

One of the largest contributions made by the X-15program was in the area of the importance of manto the machine, or the pilot-aircraft relationthip.Studied in a simulator, the basic flight profiles of theX-15 produced no extraordinary problems for thechosen pilots. But a flight simulator on the groundis a totally different environment from the real aircraftin the air. There is a new dimension of anxiety addedby the real thing which never can be simulated.

Consequently, early flights of the X-15 measured pilotphysiological responses, and helped to determineperform'ance and the importance of the man in theairplane.

Other flights proved that the pilot served as anextremely important sensor and recording instrument.There were many occasions when the pilot was theonly factor that made completion of the researchmission possible. Automatic equipment had failedor was malfunctioning. There were also occasionswhen the airplane would have been lost had there notbeen a-pilot aboard to analyze the problem, applyjudgment, and take action.

Part of the man-machine relationship was thepressure suit developed for the X-15 programspecifically. It began as just another component of the

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overall X-15 system that required development, andevolved through continuous updating. Its design hasmade contributions to the manned space flightprograms, and an adaptation of the pressure suit hasbecome the standard for U.S. Air Force pilots in theAir Defense Command.

As the X-15 went from success to success in its initialresearch programs, some scientists began consideringits use as a vehicle to carry aloft experiments thatcould not get to high altitudes or speeds by any otheravailable vehicle. As a prelude to the space program,it seemed very desirable to make tests with data-gathering packages that could remain out of the Earth'satmosphere for a fairly lengthy test period, and thenbe returned intact to the ground for subsequent studyand evaluation.

The X-15 offered a method of doing this, and during itstest program it carried packages that photographedthe Earth, the upper atmosphere and the stars; evaluatedstructural components and coatings for sustained high-speed and high-temperature flight; measuredmicro-meteorite density in some regions of the flightenvelope; and determined the exhaust characteristicsof infrared and ultraviolet radiation in the exhaustplume of its own rock:t engine.

In its last test role, covered with a white protectivecoating, X-15 No. 2 carried out ar. assaulton Mach 8 speeds, using additional fuel in auxiliarydrop tanks, in order to evaluate a hydrogen-burningsupersonic combustion ramjet engine mounted in placeof the aircraft's ventral fin.

The X-15 has made major contributions to theunderstanding of the problems of manned flight, bothin the atmosphere and in space. It has exploredthe phenomenon of weightlessness, aided thedevelopment of protective clothing for the crews ofsupersonic fighters and manned spacecraft,demonstrated man's ability to control a flight vehiclein the high-speed and high-altitude environment, andpointed the way to efficient structural design ofcomponents to withstand the high temperatures ofreentry from space. It has been called the mostsuccessful of the research aircraft, and there are fewwho would quarrel with that accolade.

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Variable-SweepWings

In the excitement following the rollout of the X-15from North American's factory in 1958, it was easy tooverlook another major development in the evolutionof manned flight, made in a NASA wind tunnel.Continuing along a line of development they hadstarted at NACA, scientists solved the problems ofstability for a wing whose sweepback angle couldbe changed in flight. In doing so, they opened anentirely new range of aircraft designs.

The concept of changing the wing sweep in flight isnot a new one. It had been conceived, tested in modelform, tried on a handful of full-sized aircraft anddiscarded for several reasons long before NASA wasborn. But in at least one of its applications, to theBell X-5, one of the research aircraft, it stirred enoughinterest to stimulate a low level of continuing studywithin NACA.

The reason for using sweepback is to reduce the dragof the airplane for economical operation at high speed.This is the primary reason that talay's militaryfighters and bombers, and commercial jet transports,mount sweptback wings. But using sweepback doesintroduce some complications, among them beinghigher landing and takeoff speeds, and occasionalstability and control problems. At some point in time,many engineers must have visualized that the best wayto solve those problems was to make the wing sweepvariable. Start (and complete) the missim with thewings spread to a nearly straight position, theythought, and take advantage of the simplifiedcharacteristics of an essentially straight wing. Thenincrease the sweep angle to increase the speed of theairplane, and take full advantage of sweepback that way.

The Bell X-5, which first flew in June 1951, was thefirst full-scale airplane to be developed whose wingsweep angle could be changed in flight. Its test program,conducted at NACA's High-Speed Flight Station atEdwards kir Force Base, California, proved itscapabilities in :fort takeoffs and landings. Withits wings fully swept, the Bell X-5 showed an extraflight dividend: It demonstrated that it would respond

less to gusts and other turbulence at extremely .lowaltitudes and high speeds than would the moreconventional airplanes of the day.

But the X-5 required an intricate and heavy mechanismto move the wing fore and aft along the fuselage asthe sweep angle was changed. It had to be done thatway to keep the airplane within acceptable limits ofstability and controllability.

For various reasons, variable sweep as a designapproach lay dormant for several years. But about1957, military and engineering thinking began tocoalesce around the concept of a multi-mission aircraftthat could perform more than one job effectively. Ithad previously been the policy to design interceptorsfor high-altitude work and ground attack aircraftto work at the lower levels. The performance ofeach type had suffered when it was pressed, as hadhappened historically with high frequency, into a rolein the environment for which it was not designed.

Interest in variable sweep was revived because it seemedto be an answer to several problems which were beingraised. First, it appeared to make possible the designof a multi-mission aircraft that could perform at highor low altitudes and at high or low speedr by reshapingitself in right to the most efficient aeronynamic formfor the mission.

Second, it seemed to offer the possibility of developmentinto a configuration that would include the capability

5 A wino tunnel model of the F-111 varlable-sweep fichter.

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to cruise at supersonic speeds over long rangesinstead of over short dashes.

Third, it offered a way to fly very close to the groundat very high speeds to avoid detection by any enemyradar until the last possible seconds before the strike.

The breakthrough occurred in November 1958.Scientists. working in the NASA wind tunnels ondevelopments of variable-sweep concepts discovereda way to beat the old tendency toward instabilityand uncontrollability. By moving the pivot pointsoutboard on the wings, so that there remained a fixedcenter section and only the outboard panels swung inthe fore-and-aft direction, the configuration remainedstable at both extremes of the sweep position. It variedonly slightly from the extremes during the swingcycle.

This development was the real beginning of thevariable-sweep aircraft configuration that laterdeveloped into the Boeing 2707 and the GeneralDynamics F-111 in this country.

Within a year, the Air Force and Navy had studied theidea and asked NASA for further information andstudies of the application of variable sweep to multi-mission military aircraft.

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The Navy first considered the idea, applying it to anairplane being developed for combat air patrol, tomake the plane theoretically able to perform high-altitude attack and low-level strike missions equallywell. It was a "paper" airplane, based on limited dataand a "paper" engine, but it showed so much potentialthat it completely outclassed any weapon system thenin the conceptual stages.

The military requirements, the work done by NASA,and the paralleling studies conducted by industry, andmilitary research and development agencies finallywere merged in February 1961. Secretary of DefenseRobert S. McNamara ordered that the several require-ments of the military be combined into a single fighterunder the project designation of TFX.

The TFX design competition was won by GeneralDynamics Corp., and work began on the F-111 series ofaircraft, tactical fighters planned around the variable-sweep concept and intended to serve the Air Force andNavy in a number of roles.

With the competition settled, NASA's role in the F-111program reverted to its traditionalone of post-researchsupport. Refined design data and evaluations ofproposed changes were areas where NASA lent ahelping hand. Specific proulems were subjected to

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theoretical analysis and wind-tuanel experiments toproduce solutions, even after the prototype aircraft hadbeen built and were flying. :le NASA work in supportof the F-111 program was accomplished by analysis,experiment and flight-test work on an F-111 assignedto NASA.

The SupersonicTransport (SST)

There was a parallel between the military requirementsfor a multi-mission fighter and the commercialrequirements for a supersonic jet transport. Nocommercial SST would be bought by the airlinesof the world unless it were to prove capable ofcruising efficientlyand therefore economicallyatsupersonic speeds over intercontinental distances.No supersonic transport would be acceptable to anyairline unless its stability and control at the low-speedend of the scale guaranteed safe operations duringtakeoffs, approaches and landings.

Commercial jet service around the world started in1959. By the end of that year, NASA scientists wereready to present their case for a supersonic transport

6 A NASA test of a supersonic configuration at LangleyResearch Center wind tunnel.

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that would be efficient and economical. They had justfinished a round of briefings to the military andindustry on the advantages of variable-sweep for themulti-missimi fighter and were, in effect, lookingtoward a new technical world to conquer.

Sustained supersonic cruise was to be demonstrated bythe flight performance of the North American XB-70,an aircraft in which NASA-developed technologyplayed an important part. But the XB-70, which firstflew in September 1964, was a military aircraft andcould tolerate something well outside the economicguidelines that airlines had established for transportoperations. Further, there was less concern for thelow-speed end of the XB-70 performance because ofthe higher landing and takeoff speeds acceptable by theexigencief of military operations.

NASA proposed that the variable-sweep concept beapplied to the design of a supersonic transport, incombination with a new and advanced propulsionsystem. This combination, NASA reasoned, wouldsolve the problems associated with the required wideperformance range of a commercially effectiveSST. And, said NASA in 1959, "The present researchposition is that no fundamental problem appears withregard to these off-design conditions that cannot besolved by concentrated research effort."

NASA made its formal presentation to theAdministrator of the Federal Aviation Agency, thenLt. Gen. E. R. Quesada. Published later as aTechnical Note, the NASA briefing discussedperformance, noise, structures and materials, loads,flying qualities, runway and braking requirements,traffic control and operat:ons, variable-geometry designconcepts and possible areas for performanceimprovements.

That briefing was the beginning of serious effort onthe commercial SST program. Within weeks, a jointNASA-FAA program was well along.

NASA work on the SST program centered on thedevelopment of basic configurations that would meetthe requirements of airline customers. In spite of itsearly espousal of the variable-sweep concept, NASAprepared to make configuration studies on a variety ofaircraft layouts. Called by the acronym of SCAT, forSupersonic Commercial Air Transport, a series ofconfiguration studies was started in 1962. The over-riding general requirement, of course, was to make acommercially feasible aircraft configuration. Some of

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the specific points were to better the XB-70's lift-dragratio in cruise, and to make possible aerodynamicallyefficient flight at the off-design points in the aircraft'smission.

Less than one year later, the NASA approach hadselected four candidate conggurations for theSST: SCATS 4, 15, 16 and 17. SCAT 4 was a fixed-wing airplane that carefully integrated wings, fuselage,tail surfaces and powerplants into a highly swept,twisted and cambered configuration. SCAT 15 and 16were based on variable-sweep wings, using two differentapproaches. SCAT 17 had a fixed delta-wingedplanform with forward canard control surfaces, similarto the basic concept of the XB-70.

At this point, NASA went to industry and invitedevaluation of the four concepts. Two were chosen,the SCAT 16, eventually to be a foundtlion for theBoeing 2707, and the SCAT 17, to leaa toward thecompeting SST configuration developed y LockheedAircraft Corp.

The enormous and detailed amount of thewetical andexperimental work that accompanied the SST programand the development of the SCAT configurationspaid a handsome dividend. As test results led towardmodification of theories, so did the theories becomethat much more able to predict the real conditions.This narrowing of the gap between theory and practiceled to the ability to predict, by computer techniques,the aerodynamic characteristics of aircraft. Theprincipal characteristics that determined airplaneperformance could be spotted within 3 percent ofactual test data, time after time. This meant that anairplane could be designed or changed on paper,transformed into a computer program, and analyzedfor performance within a matter of hours, instead of theweeks it formerly took to complete the design andanalysis cycle.

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41 I

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7 rour candidate configurations of supersonic transportsvere developed at Langley: (A) SCAT 4; (B) SCAT 15; (C)SCAT 16; fO) SCAT 17.

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NASA has extended that technique into two otherareas. One of them is the prediction of the performanceof an airplane under severe structural loads whichcause it to become deformed from its idealconfiguration. Since the loads and response of anaircraft during maneuvering are of great importanceto both military and commercial operators, this stepforward in analysis will prove very valuable.

In the other approach, the computer program whichdescribed the airplane's aerodynamic characteristicscan be modified to produce the airplane's geometriccharacteristics as well. The geometric output of thecomputer can be fed through a numerical tape controlinto a machine tool to produce a wind tunnel modelof the design within a matter of hours.

The supersonic transport as an operational airplanehas accounted for several major programs of researchby NASA. In one of them, tiny models of the proposedSST were tested in supersonic wind tunnels todetermine the characteristics of the sonic boom, thatnatural phenomenon that threatens widespreadcommercial employment of the &ST. Parallelingthe tests were extensive theoretical investigations andflight tests made with available supersonic aircraft, to

13

try to determine the magnitude of the seine boomproblem and to isolate, define and perhaps modifysome of its parameters.

On the flight testing side, a special modification wasmade to Boeing's original prototype jet transport,the 707-80, so that it would simulate the handlingcharacteristics of the SST in flight. NASA test pilotsflew the 707-80 through a series of approaches andlandings, in carefully instrumented tests, to simulatethe behavior of the SST in this critical flight regime.

Other simulation of the SST's operations, this timein the approach area to the John F. KennedyInternational Airport, was the subject of a jointprogram with NASA and the FAA. Two simulatorsone of the SST itself at Langley Research Center,and the other of the air traffic control situation,operated by the FAA at the National Aviation FacilityExperimental Center, Atlantic r) .y, N.J.wereintegrated to study the problem c: handling the SST inthe existing patterns of arrivals and departures ofother aircraft. Experienced, professional airlinepilot crews from United Air Lines and Trans WorldAirlines flew the simulated flights, and defined, earlyip the game, some of the immediate and long-termproblems that would be faced with the entry of anSST into commercial flight operations.

The structure of the SST was influenced by earlystudies made by NASA on concepts, and by ascreening process to find suitable materials for thestructure. Fatigue of the metals and changes in theirphysical properties, as they were run through heatingcycles for durations up to 30,000 hours, were evaluatedin NASA tests.

14

HypersonicFlight

The research on supersonic transports, bombers andtactical fighters that has occupied a major share ofNASA's aeronautical work during its life has led toserious looks at studies of hypersonic flight, the nextstage in the evolution of aircraft. The X-15 researchaircraft has demonstrated hypersonic flight, eventhough it was only able to sustain such flight overrelatively short periods of time.

A now cancelled program, the Dyna-Soar, which wasconducted by the Air Force with NASA support, wasaimed at extending the flight range from the hypersonicspeeds of the X-15 right up to the orbital speeds ofEarth satellites. Dyna-Soar was basically a spaceglider, to be launched by a multi-stage rocket boostervehicle and to reenter the Earth's atmosphere usingthe flight principle of dynamic soaringfromwhich term came the name Dyna-Soar.

Before the program was cancelled, Dyna-Soar hadprovided a lot of the basic insights and some of thefundamental data that directed NASA thinkingtoward sustained hypersonic flight. At the operationalspeeds of Mach 7 now under consideration, a typicalhypersonic aircraft would develop temperatures above2,000°F on its nose and above 1,600°F on the leadingedge of the wing.

The coilfiguration of such an aircraft has been understudy in NASA wind tunnels for several years. Aseries of proposed shapes has been developed andtested, using such ingenious techniques as buildingtiny models out of quartz to enable them to withstandthe heat of the tunnel test.

That heat on the full-scale counterpart imposesthe major restraints on the design of a hypersonicaircraft. Completely new approaches to structuraldesign have been investigated by NASA, using suchideas as the thermos bottle, where an outer shelltakes the heat, houses the insulation and holds aninner shell which houses fuel and passengers. Otherstructural ideas, developed as part of the Dyna-Soarprogram by NASA and industry, have been evaluated.

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Selection of materials for the structure reaches intothe superalloy field, and NASA is studying andscreening, much as it did for the supersonic transport,the range of candidate materials for hypersonicaircraft.

A few years ago a new NASA wind tunnel becameavailable at the Langley Research Center, adding aunique capability to the agency's testing facilities. Theonly one of its kind in the world, the new tunnel has aneight-foot diameter test section which can be run atsustained high temperatures characteristic of hypersonicflight. The size of the test section, and theperformance capability of the tunnel, make it possibleto study large models, and in some cases, full-sizecomponents, of proposed hypersonic craft undersimulated flight conditions, including full temperaturesimulation.

Today'sAircraft

But these are tomorrow's aircraft. There are stilltoday's aircraft that have problems, or that show somepotential for further improvement. NASA studies areaimed at these types, also.

8 Model test for the heavy logistic transport C-5A.

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The current subsonic jet transport, for example, isone of these. Its basic design dates back to thetechnology available in the early 1950 time period.Now, nearly 20 years later, those basic designs havebeen honed and polished, but basically they haven'tchanged much.

Today's jet transports, for example, cruise at subsonicMach numbers, generally somewhere between 0.72 and0.80. These speeds cover the normal long-range andhigh-speed cruise conditions. If those cruise speedscould be raised, the working potential of each transportcould be increased. By getting from point to point inless time, it could make more round trips in a givenperiod of time, thus increasing its productivity.

The NASA Supercritical Wing holds a promise for thatkind of a cruising speed. It uses a trailing-edge slot tomix high energy air from the under surface of the wingwith the lower energy air off the top surface and keepthe boundary layer attached to the wing. This results indecreased drag, and a higher cruise speed. It istheoretically possible, NASA studies show, to reachcruise speeds above Mach 0.90 with the NASASupercritical Wing.

15

Air transports could also be made to fly, more slowly,NASA believes. Takeoff, approach and landing speedscould be reduced substantially by resorting to a formof boundary layer control, such as the blown flapsystems installed on the Boeing 707-80 or the LockheedBLC-130. NASA pilots evaluated both aircraft todetermine what the handling qualities of such anairplane, so equipped, would be.

The comfort of air travel is related to the aircraft'sresponse to air turbulence. More than 20 years ago,NACA scientists were ihvestigating a method of gustalleviation, in which the airplane is instrumented tosense oncoming turbulence and to anticipate and correctfor it by appropriate control motion. The controls areapplied automatically to compensate for the turbulence,and the result is a smoother ride, or one whichstresses the airplane less.

Recently, the basic principle of gust alleviation wasbuilt into a test Boeing B-52 airframe under a programfunded by the Air Force, and the data from thoseflight tests provided valuable insight into prolongingthe life of large, flexible aircraft, and easing the ridefor its passengers.

Operations of today's aircraft have occupied a largeshare of program time at the various NASA researchcenters. The dangerous phenomenon of tirehydroplaning, in which the airplaneor automobiletire rides clear of the ground on a slick wave ofwater, was first analyzed and evaluated by NASA.The inherent dangers of hydroplaning, which has been

responsible for several known aircraft accidents andprobably for countless automobile accidents, werefirst described to the aircraft and automobile industryby NASA.

Related to hydroplaning is the problem caused by slushon the runway. One-half inch of slush is the currentlimit for permissible legal aircraft operations, and itwas NASA studies of the problem and their systematictests that established that particular criterion.

Helicoptersand

V/STOL Aircraft

Far down in the low-speed flight regime are thehelicopters and V/STOL aircraft that the militaryservices and NASA have sparked and tested duringrecent years. Here again the work has followed thetraditional patterns of problem-solving, integratingtheory and experiment in test facilities with flighttests of full-scale aircraft. And beyond problem-solvingthere has been the conceptual development of a classof VTOL aircraft that now appears to offer efficientshort-haul transportation.

In this latter category is the tilt-wing configuration,which evolved from wind tunnel and dynamic modelflight tests by NASA scientists through concepts,

9 The Lockheed XH-51A In studies of hingeless rotorhelicopters.

16

detailed designs and analysis, and tests of advanced .configurations in model form. One of the results of thatprogram was the tri-service XC-142A, a four-engine,four-propeller, tilt-wing cargo transport developed forthe military by a group of companies including Ling-Temco-Vought, Ryan and Hiller.

Early NASA tests of the tilt-wing concept demonstratedthat it could hover, and could make the difficulttransition in flight between vertical hovering andhorizontal flight. Subsequent tests extended the

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configuration studies through the use of small windtunnel models and evaluated the final choice ofdesign with a large-scale model of the XC-142A inthe full-scale tunnel at the Ames Research Center.

A similar type of aircraft, the Vertol 76, was used asa flying test bed by NASA to evaluate many of theflying quality parameters that were later applied to thedesign of the XC-142A. Specifically, the approachand hover phases of flight received detailed scrutiny byNASA test pilots.

After the XC-142A became a tri-service militarytransport, NASA continued to back up the programwith research. A remarkable one-ninth scale modelwas built to exacting detail and flown under conditionsdynamically similar to those of full-scale flight in thefull-scale wind tunnel at Langley. The model and thetest technique used permitted making complete

transitions from hovering to forward flight in the windtunnel. The results predicted the characteristics ofthe real aircraft when it entered flight testing at alater date. Still later, an XC-142A was assigned toLangley Research Center for flight research.

Other concepts have been evaluated by NASA. Oneof the first VTOL vehicles available anywhere, the Belldeflected-jet X-14, has been extensively flown by

10 Tri-service VI STOL transport, the XC-142A, was testedwith dynamic models.

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NASA pilots, and has been used to develop generalizeddata as well as to train pilots to fly on other laterVTOL craft.

The tilt-duct idea, first seen on the Doak VZ-4 andlater on the Bell X-22A, was tested in its early stagesat NASA facilities. The fan-in-wing types of VTOLcraft, typified by the General Electric-Ryan XV-5A,were evaluated in model and full-scale form by NASA.So was Britain's Hawker P.1127, a fighter prototypethat used deflected thrust from the swiveling nozzlesof its jet engine to provide the vertical lifting thrust.In model form, the Hawker P.1127 was extensivelytested by NASA in one of the most detailed VTOLtest programs ever conducted.

These were largely experimental or research vehicles.But production helicopters also have been evaluatedby NASA test pilots. One of them, a Vertol YHC-1A,

23 17

11 The Verto/ 76 tilt-wing VTOL aircraft was evaluated atLangley using (A) a free-flight model and (B) the actualairplane.

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has been modified to serve as a variable-stabilityhelicopter. It can simulate the flying qualities of a widerange of helicopters and VTOL aircraft, and is one ofthe most useful research tools in the flight testing work.

Somewhere beyond both the rotary wing of thehelicopter and the fixed wing of the airplane is theflexible wing, a new concept pioneered at NASA andNACA. The name describes it; it is made from clothand generally has no rigid structure to hold its shapeinto a wing form. Instead, a combination ofaerodynamic forces on the wing and reactions from

18

the load suspension system serve to shape and maintainthe form of the flexible wing.

Some stiffening has been used to match requiredcharacteristics in specific applications, but the mostinteresting variations are those which have no stiffeningand therefore can be packed like parachutes.

24

More than 20 years of NACA/NASA testing haveevolved a spectrum of flexible wing configurations.At one end are the completely unstiffened clothsurfaces, which can be usedand have been testedfor precision aerial delivery of cargo or personnel.Proposals have been made and studied to use this typeof stowable wing for landing spacecraft or recoveringlaunch vehicles.

At the other end of the spectrum are stiffened wingsfor towed or powered aircraft, where it is important toobtain higher speed performance at the expense ofstowability.

Research

forSpacecraft

When President Dwight D. Eisenhower signed theNational Aeronautics and Space Act July 29, 1958,his statement on the signing said, in part: "The presentNational Advisory Committee for Aeronautics(NACA) with its large and competent staff andwell-equipped laboratories will provide the nucleus forNASA. . . . The coordination of space explorationresponsibilities with NACA's traditional aeronauticalresearch functions is a natural evolution . . ."

At first glance, it seems a far cry from the technologyof a fixed-wing airplane to the engineering design ofa manned spacecraft that will never fly in an atmospherewhere wings or control surfaces would be of any use.But there are many similarities and analogies, andthe comforting thought is that a problem is a problem,and subject to standard methods of problem-solving.

12 British Hawker P.1127 V STOL tactical fighterdevelopment aircraft, was flown in free-flight tunnel in modelform and in tests.

Theodore von Karman, the late elder statesman ofaeronautical engineering, put it this way: ". . . thosewho say that all that men teach and all that meninvestigate, under the name aeronautical engineering,is obsolete, seem to assume that by some miracle thedesigners of space vehicles will not encounter problemsinvolving such classical sciences as fluid mechanics,structures, materials and vibrations. I am sure that thiswill not be the case."

He was right; it was not the case. Those problems wereencountered, and they were solved, in many cases bythe applications of aeronautical technology developedover the years. This is not to say that there were nonew approaches to the problems. The environment ofa spacecraft launch, for example, superimposes somany new problems that it is impossible to treat themin any classical manner. The strange new shapes oflaunch vehicles plus spacecraft, with weight and inertiacharacteristics different from those of any airplaneever built, pose a different kind of problem. Theclassical disciplines can be adapted to the solution, butnot in the classical way.

13 Full-scale prototype of XV-8A "Fleep," a Flex-wingaircraft built by Ryan, was "flown" In a full-scale NASA windtunnel.

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19

There are a few areas where the problems are aboutthe same, and are being solved in the same way. Oneof these is in the concept of a lifting body glider orpowered vehicle, for returning astronauts from space.

The basic idea of the lifting body is to give the astronautcrew the flexibility to select a landing site, and tomaneuver to it, instead of being committed to a limitedoceanic recovery area, and being further constrainedby the necessity to make a parachute deceleration andletdown into that area.

The lifting body flies on the aerodynamic forcegenerated by the shape of its body. It has no wings, butit does have control surfaces and fins to provide stabilityand control.

One of the earliest of the NASA programs was thedevelopment of two different types of lifting-bodyconfigurations, tested earlier by NACA in wind-tunnelevaluations. Development continued to the point wherethe logical next step was to build and fly some kindof a test vehicle. This was done by constructing asimple vnd inexpensive test glider, designated theM2-F1, from plywood and tubular steel in a reversionto the aircraft construction techniques of the 1920'sand 1930's.

The success of the first tests with the lightweight M2-F1encouraged NASA to advance the program. Twoheavier fifth ; bodies were designed, and built, differingin detail geometry and in the system of control.

The M2-F2 was designed with a flattened uppersurface, a rounded belly, two vertical fins, and a bubblecanopy projecting outside the lines of the body shape.

The HL-10 in contrast was rounded on top, had a flatbelly, three fins, and a canopy constructed within theprofile of the body shape.

Both of these aircraft were built for NASA byNorthrop's Norair division, and both made glidingflights after being carried to altitude under the wing ofa Boeing B-52 mother ship. The M2-F2 was severelydamaged in a landing accident after 15 missions andwas taken out of flight status.

An X-24 was built for the Air Force and incorporatedinto the NASA-managed flight program. It was of adifferent design from the M2-F2 and HL-10, with moresophisticated controls.

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20 f,

Air-breathingPowerplants

The lifting-body concepts represent one of thefarther-out applications of aeronautical technology.Another area, that of air-breathing power plants, alsoseems far removed from aeronautical technology, butis currently considered as part of the NASA programin aeronautics.

One of the reasons for this is that air-breathing engineshave increasingly become creatures of aerodynamiccomplexity. As the early turbojet designs evolved intoengines with higher and higher performance, theydemanded more and more refinements in compressorand turbine blade aerodynamic design, inlets, diffusersection geometry and fan blade designs. And as theengines got more powerful, they also got bigger andnoisier. To tackle the noise problem requires aknowledge of the behavior of the hot exhaust gases,which again drew on the background of aeronauticalknowledge developed by NASA, and before it, bythe NACA.

NACA's work with aircraft engines began shortly afterthe formation of NACA in 1915. There was a waron, and there was obviously a significant militaryadvantage to be gained by having an aircraft enginethat would perform well at hiei altitudes.

At that time, there were no test stands which could beused to simulate altitude operation. The only way wasto truck the engine up to the top of a convenientmountain, and run it in the rarefied air at the peak.NACA had commissioned the Bureau of Standards todevelop and build a high-altitude test stand, and itoperated for the first time late in 1917. But the teststand didn't have all the bugs worked out. At the endof 1917, an NACA technical staff member was sent tosupervise altitude tests of a Liberty engine, conductedat the top of Pike's Peak, Colorado.

Systematic propulsion research started at an enginelaboratory built in 1920 at the Langley laboratory ofthe NACA. Propulsion research programs later weretransferred to what is now the Lewis Research Center,in Cleveland, Ohio. Lewis was opened in 1941, usinga nucleus of personnel drawn from Langley, butadding and expanding both staff and facilities.

Current programs in aircraft engines include NASAwork on the development of advanced air-breathingengines. The turbojet and turbofan engines whichpower today's jet transports are highly developed as a:lass of power plants. But there is room forimprovement: Fuel consumption might be reduced;thrust might be increased without increasing engineweight or volume; noise might be lessened.

Such broad problem areas are under study by NASAscientists, as are such specific problem areas as theefficient operation of an engine air inlet.

Because an engine needs different amounts of air tobreathe in order to generate different thrust levels, themost efficient kind of an inlet is one whose area can bechanged to match the requirements. The engine itselfhas a fixed inlet area, determined by the dimensions ofthe engine and its rigid construction. The only areathat can vary is upstream of the engine inlet face, atthe entrance to the engine air intake dusting.

To change this area is relatively simple, mechanically;but the problem is complicated because a change atthe inlet changes everything downstream, including theexhaust area. So NASA investigated the effects ofinlet and exhaust nozzle areas on the performancecharacteristics of air-breathing engines to evaluate theparameters of the problem, and to discover ways ofcontrolling the matching of those areas for optimumperformance of the engine.

Another work area was in weight reduction ofturbojet engines. Most of the weight of a turbojet isconcentrated in the rotating compressor. Thecompressor is made of several compressor stages,which are necessary to get the overall compressionneeded to make the engine efficient.

If each stage could, be designed to do more work thanit currenny does, then the total number of stages wouldbe reduced, and the total engine weight would drop.To get more work out of a stage,:the blades must becurved more; the greater the curvature, the more workdone by each blade, up to the point at which theairflow breaks away from the blade and the workoutput drops drastically.

Detailed study ol blade shapes and ways to get morework out of a single stage of compression have beena continuing program at Lewis for some years. OtherLewis work has studied increased turbine operating

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temperatures, because with higher turbine temperaturesgo higher thrusts.

Two approaches have been pursued. The first hasbeen the development and evaluation of new materialswith increased resistance to heat, and greater strengthat the higher temperatures. The second has been thedevelopment of cooled blades, generally using air ledfrom a cooler location in the engine, and fed into thebase of the turbine blade. Centrifugal force pushes theair through the blade and out through a series of tinyholes, slots or even pores in certain materials. Thecirculation ot the air cools the blade and allows it tooperate at a higher than usual temperature.

Similar work continues to be done by industry, andexperimentaland productionengines have been runwith cooled turbine blades.

ReductionofEngine Noise

As engines produce more thrust, they almost invariablyproduce more noise. Bigger engines and more ofthem, as air traffic increases, have aggravated the noiseproblem until it looms as a major obstacle to thefurther expansion of air transportation.

NASA, and others, are trying to reduce engine noise.With so many noisy engines in service, the obviousfirst thing is to develop a temporary fix to reduce noiselevels as much as possible consistent with safety andeconomy of operation. The use of sound-absorbingmaterials in engine inlets has proven effective, forexample, and is expected to become a widespreadsolution for the near-term problem.

On a long-term basis, the second obvious thing is todesign an engine which is inherently quieter thancurrent types.

NASA has combined both these approaches into athree-step assault on the noisy engine. The first step isan expanded basic research program on the mechanismsof noise generation. The second step consists ofstudies and the development of means of reducing theradiation of fan-compressor noise from nacelles bymeans of acoustic treatment of inlet and dischargeducts. The third is development of quiet enginetechnology to minimize the noise produced by therotating machinery and the jet exhaust.

21

NASA is working on component studies and tests, andhas placed contracts with engine and aircraftmanufacturers for additional work on the quiet engine,and on quiet installations.

ProblemSolving

With an increasing amount of technology available onsuch possible major improvements as the quiet engineand the super critical airfoil, one can visualize anothergeneration of jet transports, or military aircrpft,utilizing some of the unique solutions explored in theresearch centers of NASA. But in addition to thesemajor areas, there are other important subjects directlyrelated to aeronautical progress under study at NASA.

In aircraft operations, study and experiments haveadvanCed the knowledge of how to fly more safely.Periodic conferences on the problems of aircraftoperations, attended by industry, airline and militaryrepresentatives, have provided invaluable exchangesof ideas, and suggestions for new experimentalprograms. Aircraft instruments and standards ofmeasurement have been criticized, studied, evaluatedand improved as another result of these conferences.New piloting techniques have been tried, new types ofpresentations of data to the pilot have evolved, andso have new ideas to lessen the pilot's workload duringthe more-severe demands on his abilities caused bybad weather or aircraft malfunctions.

These are natural tasks for NASA, growing out of itsyears of experience in contributing to the solution ofthe problems of flight. But there is a difference. Inearlier days, much of the NACA work was confined todefining problems, and later, to solving problems.

The wartime years were almost entirely spent indevising "quick fixes" to solve an urgent problem inmilitary aircraft performance. Postwar, the work of theNACA took on renewed strength in the direction ofaircraft research.

22

In the early years of national reaction to the RussianSputnik, and the subsequent formation of NASA, basicaeronautical technology seemed almost to have beenignored in favor of the quick and necessary developmentof some capability in space. But the forced transitionof NACA into NASA, a space-oriented group, providedbenefits, as well as some possible drawbacks,aeronautically speaking.

In NASA there has been more emphasis on systemswork, the study of all the factors which bear on theproblem. This was caused partly by evolution, becauseairplanes, missiles and spacecraft were getting morecomplex and demanded a systems approach as the onlyadequate road to accurate and informed analysis.

But there was also some revolution, as the people andfacilities which had been developed to solveaeronautical problems were put to work on the differentproblems of space flight. The nature of the peopleand facilities changed under this exposure to newdisciplines, and NASA itself changed.

Today, NASA's aeronautical efforts are geared to theneeds of compkte-aircraft systems, includingpowerplants, instrumentation, navigation andcommunications aids, pilot's comfort and capabilities,structures, and operations.

NASA has built on more than fifty years of aeronauticaltechnology that started with fragile biplanes built ofwood, covered with linen and braced with wire.Today's progress traces its roots back to that firstsystematic approach to the problems of aeronautics.Tomorrow's progress will be based on the work beingdone today at the research centers of the NationalAeronautics and Space Administration.

28 U. S. GOVERNMENT PMINTING OFFICE : 1970 0 197-141

AdditionalRadingFor titles of books and teaching aids related to thesubjects discussed in this booklet, see NASA's educa-tional publication EP-48, Aerospace Bibliography,Fifth Edition.

Inforination concerning other educational publicationsof the Nalional Aeronautics and Space Administrationmay be obtained from the Educational ProgramsDivision, Code FE, Office of Public Affairs, NASA,Washington, D. C. 20546

?sr ale lq ths Superbeisket of Daum*U.S. erarmisM Poo* OMee, Wulss, 0.0. 201102Met 411 es* .

Aeronautics

National Aeronautics and Space Administration

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