NASA Aeronautics

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NationalAeronautics andSpaceAdministration

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NationalAeronautics andSpaceAdministrationFor sale by the Superintendentof Documents,U.S.Government Printing Office, Wash., D.C. 20402


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Contents

In t roduc t ion t o a Mys te ry 1NASA: What and Ho w 2Driven by Ai r Movements 4Four W ays to Research 4Th e Tools of Research 6Energy-Eff ic ient Aircraf t 7Shorter Takeoffs , Lower Noise 9Revolu t ionary Lift 11Real -Wor ld Env i ronments 13Study in C ont ras ts 1 5Fast, Faster, Fastest 17Single Pivot for a Win g 19T h e Science of Shapes 21Genera l Avia t ion Programs 23Bui ld ing I t S t ronger 26

~~T he Fu tu re o f Aeronau t ics 27


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IntroductiontoaMY-Y

T h e r e i s a g rand mystery toflight, a mystery tha t still de-fies analysis and c om pleteunderstanding.T h e erratic flapping of abutterfly, th e swift swoop of afalcon, the soaring silence of asailplane share that mysteryand partially reveal only th reeof its many faces.Now, we are almost twocenturies into th e experi-ences of flight, almost 200years from the time th eMontgolfier bro thers firstharnessed hot air to hoisttheir demonstration ballooninto t he skies of France. Th eyears between then and nowhave added imm easurably toou r store of aeronauticalknowledge. T he refinementof theory and the gathe ring opractical data by en gineersand scientists have increasedour understanding of whyflight is possible. B ut, as lateas these latter decades of the

view.Realize, for example, that

Twentieth C entury, muchstill remains hidden from ou

the re is still no way to predicaccurately the am ount of turbulen ce in airflow, and its e

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1for an advanced super-is shown before40- by 80-foot windighter model is in -to have vertical or shortand landing capability,

and uses thrus t vectoring t oachieve tha t goal. T he exhaustfrom win GeneralElectricJ-79turbojets is directed over thewing flaps t o increase their I@increment for short-field per-formance. Later, a thrust aug-

mentation system will be addedt o increase the available thrus tand achieve vertical tak eo ff .T h is particular model i s three-quarters full-scale, and wasmounted for low-speed tests inthe Ames tunnel facility.

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Conceptual design studies are amajorportiono f the workloadinNASA test facilities. Here, aliftt-fanpowered aircraft, in-tended for vertical takeoff, i sbeing inspected before beingfect on flight. In th e con-trolled environment of to-days wind tu nnels , turbu -lence affects test results to adegre e still to be exactly de-termined. Turb ulence is animportant component offlight mechanics, and a verycomplex one. It is so com-plex, in fact, that it can noteven b e analyzed totally bythe fastest and m ost capablecontemporary computers.

tested i n the Ames ResearchCenters40- by 80-foot ind versions. Note the lifting fannear the nose of this aircrab,tunnel. This huge facility is ca-pable of handling many full-scale aircrab, or models ap-proaching the size of full-scaleBut it can be app roximated,

and quite closely, in som ecases. So can some of th e les-ser m ysteries of flight: Th osethat cause an airplane to turnand climb and dive; those thatmake it possible to build alight and simple structure th atcan withstand the wind s ofsuper-hurricane force hurtl-ing across a wing; those thatextend th e range of an airplaneso that it can cross oceans.

and the two vertical jetexhausts, one f w n each nacelle,aft of the model suspensionsystem.Aeronautical research,

then , is often a science of ap-proximations. It attem pts tounderstand t he why, notjust the how of flight. I tdoe s this, because under-standing how a thing works isthe main path toward makingit work better. So aeronauticalresearch also becomes th escience of the approximationsof improvement.

NASA:Whatand How

T h e National Aeronauticand Space Administrationwas chartered officially toconduct aeronautical re-search, amon g its other dfined tasks. That was th e task for NASAs predecesthe National Advisory Cmittee fo r Aeronautics,founded in 1915.T h e Ntional Aeronautics and SAct of 1958, the legislatthat established NASA , sthat th e general welfare security of the United Strequire a dequ ate provisiobe m ade for aeronauticativities, and that these activities should be so conducted as to contribute mrially to on e or more of tobjectives:0 Th e expansion of knoedge of phenomena in thatmosphere.

Th e improvement o f tusefulness, performancespe ed, safety, and efficieof aeronautical vehicles.0 T he preservation of throle of the U nited Stateleader in aeronautical scand technology.

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Th e m ost effective utiliza-e scientific and en -ng resources of th eStates in ord er tod unnecessary duplica-effort, facilities and

A research scientists,includesmen t organizations,

to-road objectives.Specifically, NA SA aims itsch tow ard the ad-t of both civil andof, seekin g new ap-to solve the ever-

transportation,olving new ideas toe the design ers of

NAS As broad field ofmary subjects the vehi-and powerplants th at useEarths atmosph ere for. It also is conc ernedaeronautical aspects

A joi nt NASA-N auy programuses this Gw m m an F-14Afighter as a flight research uehi-cle to investigate a new controlsystem concept originating a t theLangley Research Center. Thevew system features a n aile-ron-rudder interconnect (AH)for mproved handling qualitiesa t high angles of atta ck. ThisF-14A has been modified t o in -clude a spin-recwery parachutean d two-position deployablecanard sudaces. Thecanards,shown extended rom thefuse-lage sides ju s t forward of thepilots position, are par t of thespin-recweiy system on this re-search aircraft.

of space vehicles that de partfrom, or land on, the Earth.Th e major share of thiswork is done at four NASAcenters: Langley Resear chCente r, Hamp ton, Virginia;Ames Research Center,M offett Field, California;Dryd en Flight ResearchCe nter , Edwards, California;and the Lewis Research Cen-ter, Cleveland, Ohio.Additional studies are don eat other NASA labs, or at thelaboratories and facilities ofothe r government agencies.Private industry m akes majorcontributions, from self-supported research and de-velopmen t programs, and

from NA SA-funded pro-gram s. Universities have auniqu e contribution to maketha t reflects-their long tradi-tion of academically oriente dresearch studies. Th e militaryservices become partne rswith N ASA on specific pro-grams o r projects, o r long-term participants in one o rm ore fields of investigation.to supp ort the needs ofoperatin g agencies, such asthe Dep artment of Defenseand the Department ofTransportation, and of theaerosp ace industry, with itsmyriad of ideas for futu re de-signs and developm ent.

NAS A research is planned

To solve theproblem of engineinlet airf low separation,h iResearch Center and Gru mm aAircraft Corpora tion conductea joint test project using thistypica l nacelle ins tallationwhich houses the engine of aVISTOLpowerplant. A n an-nu lar je t of ai r was blown ovethe internalsudace of theengininlet t o delay the separation ofair flo w from tha t region. Theuseful nacelle angle -ofattac krange was essentially doubled busing the blown jet. This irstsuccessful demonstration of theprinciple could lead to substantiall y lig hter and more compacinlet designs for VISTOLaircraft.

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Drivenby AirMovements

An advanced turbofan enginethat powers US. ir Force andNavy supersonic fighters isshown in the test section of ahigh-altitude facility atNASA's h i s Research Center.The test section door has been

swung up and openfor access tothe engine. Almost all of the ex-temalvisible mass ofpiping andcabling is test instrumentation,installed onIyfor the researchprogram in the Lewis facility.For a typical test program, both

T h e driving force behindNA SA research is the simplefact of the overwh elming im-portance of air transporta-tion, whether it be themovements of people,freight, or weapons. In adynamic world that is be-coming m ore international bythe day, and where develop-ing co untries are spawningmajo r industrial complexesthat generate passenger andfreight traffic, air transporta-tion is probably the single

most important supportingservice.Today, tou rists and busi-ness travelers a re flying acrossseas and co ntinen ts for vaca-tions or comm erce. Expand-ing industries reach o ut tonew sources of raw materialsor labor, generating a newtraffic pattern for th e flow ofgoods. Oil, the comm on de-nominator of movement, hasalone remodeled the air travelpatterns of the globe.Projections for the future

of air transportation almoststagger the im agination. Amajor problem is how to han-dle the dem ands for growth,particularly in a world of ap-parently decreasing oilsupplies and escalating prices.M ore efficient aircraft de-signs are needed, and that re-quirement dem ands newkinds of powerplants, newapproaches to lightweight andefficient structures, and newways to increase rang e by de-creasing drag. Mo re aircraftmovem ents carry the poten-tial for increased neighbor-hood noise near major air-ports around the world, andalready have crowded thetraffic lanes of the air to thepoint of near-saturation.NA SA looks aheadjworkingon problems that will obvious-ly require solutions beforeth e nex t ten years have passed.Bu t a large portion of NA SAwork also is directe d to th eimmediate problems oftoday, whether they be someaerodynamic quirks of a

Four WaystoResearch

the engine and the altitude in-side the test chamber are con-trolled t o verifr engine per-formance ouer a wide range ofambient conditions of speed andaltitude.

NA SA aeronautical reseis categorized in aqu artetheadings: Proof of concepttension of the art, future nan d problem solving.Proof o f concept is an apprthat ofte n, but not alwayquires th e building and ting of a special aeronautivehicle. Th e best-knownexamples are the famedseries of research aircrafveloped by N AC A and dustry in the late 1940ssubsequently. A more reexample is th e joint NavArmy-NASA-Bell XV- 1unique rotorcraft with atential for both military civil use. Te chno logy is aable for proof of concepneeds to be transformeda tangible flying machinthe ultimate test.Extension of the art takesbasis the contemporary of that art, and builds onfoundation. Today's subtransport aircraft are, foexamp le, well und erstoofighter just ente ring operation, But continuing researchor th e strains o n a production aerodynamics, propulsioengine being boosted to new structures, materials andlimits of perform ance . ionics indicates that tom

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horizontalplaneus hown here.TheXV-15 its militaty desig-nation) can I$t OfluerticaIIyand then, by a progressiuefor-ward tilting o f the rotor as-semblies, can translate the uer-tical lifting force into forwardthrust. Thisproject i s a jointprogram shared by theArmyand NASA. The basic purposei s to conduct a thorough inues-tigation and evaluation of thetilt-rotor systemfor advancedvertical and short takeoflandbnding aircraft.

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ranspo rts could be im-ideas. Th e art has been

to in -as foundation stones

aircraft.call for th est research goals,mes the e nd point ofto havee practical curren t ap pli-on. An example: T h e in-

ive ma-s for use in some futur eerplant. A t todays prices,st of using the materialscally, th e costs o f new

as h eber o f applications in-es. And the re n ever willre applicationss research is do ne nowlead toward them.

is obvious re-h. Th e best of designs,ng analysis,wind-tun nel testingev en after

for som e years, in the case ofcivil aircraft-may dev elop aproblem that could not havebeen predicted earlier, aproblem related perhaps tolong-time exposure to someexternal force. That kind ofproblem-solving is typical ofthe work that NASA hasdone.These four categoriesfurthe r subdivide themselvesinto two broad areas. Th e firstis disciplinary researc h, de al-ing with a branch of theaeronautical art.

Aerodynam ics, propulsion,structures and m aterials aretypical areas where discipli-nary research is conducted.T he second is researchapplied to specific classes ofaircraft, for example, sub -sonic transports or fighters.In either of thes e classes ofresearch , flight vehicles maybe used to prove a concept,test a refinement, or t o carrysom e particular research ex-periment in to an environ-ment not so efficientlyreached o n the ground.

Thesecondof the twoTilt-RotoResearch Aircrafi (TRRA),built by Bell Helicopterfor ajoint NASA-Army program, ishown i n horizontal flight.Fixed wing surfaces cawy therotor assemblies and powerplannacelles, and generate liJt forhorizontal flight.

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The ToolsofResearch

T h e general pop ular impres-sion of N ASA s aeronauticalresearch visualizes a hu gewind-tunnel section contain-ing a full-sized airplanemou nted on struts, dwarfingthe researcher standing nearto give scale. Wind tunnelswere, and are, a most impor-tant component of NASAfacilities, and a very lon g-standing method of tonduct-ing research experiments.They provide a means totest accurate scale models, orev en full-size actual aircraft,over som e of the normalspeed range enco untered inflight. The se a re carefullycon trolle d tests, with a calib-rated a irstream rushin g pastthe mounted model. Accu-rate balances measure theforces, and comp uters trans-late those measurem ents ofpou nds of tension and com-pression in to coefficients oflift, drag and pitching m o-ments.But before wind-tunneltesting o ccurs, analyticalmeth ods traditionally areused to predict the behaviorof an aircraft in flight. On celaboriously d on e with pencil,

sl ide rule and perhaps a deskcalculator, such analyses noware th e special provinces ofhigh-speed com puters. Theyprocess c odes fashioned toforecast flow patterns andforces aroun d a fuselage orwing, or their juncture.T he simulator offers a thirdapproach to research. Drivenby many computational cir-cuits that calculate th e be-havior of an aircraft and pre -sen t it in a display, th esimulator offers a way o fflying an aircraft be fore it isbuilt. Th e characteristics ofthe vehicle, determ ined fromdrawings, analysis and mo deltests, are programm ed intothe com puter. Played back to

A dynamically similar scaledmodel of the Grumman P-14Afighter aircraft isshown duringa test program in the LangleyResearch Centerfull-scale tun-

nel. The tethered model canflown from pilot stations i ntunnel to simulate behaviorthe low-speed end of the F-14flight envelope. Studies of th

engineers o r pilots flyingthe new design, they revealthe good and bad qualit ies.A simulator can be used toduplicate an existing aircraftsflying qualities,,and to pre-sent them in a realm that mightendanger a crew o n a realflight. It can refine an airplanedesign befo re final produc-tion drawings are released tothe shops. I t can study theeffects of minor o r majorchanges in th e aircrafts com-ponents, powerplants, orother systems.simulation all contribute tothe u nderstanding of theperform ance of a fl ight vehi-cle. On e step remains: Flight

Analysis, mod el testing and

of th e vehicle i tself. N ASresearch pilots, who also engineers, cond uct a metious program that gradualprobe s th e flight envelopedging toward the s peed,titude and load limit tha t define the final performaof t he aircraft itself. This fscale research fu rnishes aswers that will corroboraextend and perhaps correthe inputs from analysis,wind-tunnel tests, andsimulation.These a re the four majtools of NA SA researcheThey have be en used singor in concert , to explore plem areas in the safety, efciency, o r comfort of airc

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nd controlt high angles of attack, such asnstrated here, may lead tofor improvements inor handling, or both.

v---Energy -EfficientAircraft?' * . . -

Co mm ercia l t ransports burnabou t ten billion gallons ofaviation fuel each year. A fivepercen t improvemen t in theiroverall efficiency would savethe U nited States 500 milliongallons of fuel annually. Andfive percent is well within thepotential for improvem entsin aerodynam ics, propulsion,and o ther active systems ofcomm ercial transports.NA SA's Aircraft Energy

Efficiency (A CEE ) prog rama ten-year planne d effort thlooks simultaneously atnear-term a nd far-termproblems. It attempts to develop solutions that can beapplied to existing transportto th eir derivatives expectewithin a few years, and to neclasses of aircraft de signe d scifically t o be, fuel-efficientT he broad goal of theACEE program is the de-The exceptional aerodynamiccleanliness of th is prototypegeneral aviation aircra ft re-d te d in outstanding high-;peed performance, achieved ajarently by attaining a highdegree of natural laminar floN A S A evaluated the aircra fta flight-test program a tLangley, t o determine i t s dracharacteristics and to ascertatheextent of the laminarflowcharacteristics. Results are aplicable not onIy t o thedesign1 future light,general-aviatio

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Spin ning characteristics of atypical ligh t single-enginedaircraft were studied i n a pro-gressive program at the LangleyResearch Center. The test seriesbegan by observing the behaviorof small dynamically similarmodels in the Langley spin tun-nel. Later, radio-controlledmodels were flown in small-scale, free-fligh t tes tsfo r com-parison wit h spin-tunnel re-sults. The n thefull-scale air-craft began i ts flight researchprogram to investigate the basic

qualities and q uantities of thespin, and to relate them to theresults obtained from model tests.ASpart of the aircraft researchprogram, a number of differentvertical and horizontal tailconfigurations were evaluatedfor their effect on aircrafi spincharacteristics.Modifications othe standard airplane also in -cluded wingtip booms for in-strumentation and a spin-recovery chute mounted on anexternal bracket below and be-hind the base of the rudder.

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velopm ent of an inventory oftechnology, available to themanufacturers of transportsand powerplants in theUnited States. Mo st of the re-search and technology proj-ects grouped un der this pro-gram are being done by in -dustry, the con structors ofairframes and engines. Theirexisting facilities and te st air-craft can d o the work effi-ciently. Additional efforts arebeing made by the commer-cial airlines, who fu rnish the irspecial inpu ts to the seekersof ope rational solutions.ACEE is a continuation ofan earlier progra m thatNA SA had insti tuted beforethere was a fuel crisis. Duringthe early 1970s, the agencybegan studies of AdvancedTransp ort Technology(A"), with th e goal of ex -amining new concepts andtheir effect on prod uctivity.Many of t he ideas that origi-nated then-supercriticalaerodynamics, compositestructural materials, and ac-tivec ontr ol systems-becamefoundation stones for currentACEE work, because theyalso reduce fuel consum ption.

The Energy-EfficientTransport (EET) studies, oneof six technology program sthat comprise the overallACEE work, serve to illus-trate th e interdisciplinary ap-proach to new solutions.Com mercial airlines are con-cerned with three operationalfactors: Th e direct operatingcost (DOC ), the range, andthe weight of the aircraft.More than half of the cu rrentD O C is charged to fuel; obvi-ously, any reduction in fu elconsumption would mean amajor improvem ent in DOC .Reductions in drag, and oth erattainable impr ovem ents inthe ratio of lift to drag, willimprov e the range capabili-ties. Ne w materials andstructural conce pts, com-bined with the use of activecontrols, can produ ce lighterand smaller airframes.Th e NA SA supercriticalwing design and its sub-sequent development is onemethod for improving thelift-drag ratio. Th is unusu alairfoil section c ontrols t heflow over the wing; it avoidsthe sudden increase in dragthat would occur with con-

Four of the empennage geome-tries evaluated on N A S A 501,the spin-research aircraft typi-cal of light single-enginedplanes, demonstrate different

,C.Tail 2-Iai l 3Tail 6ventional airfoils ope rating inhigh-speed airflow. Further,i t shows this lower drag fea-tur e in spite of an increased

aerodynam ic approaches t o tproblem of spin recovery. Tafeatures a small endplate onof the rudder. T ai l 4 has alow-set horizontal surface, bTa i l6 has thehorizontal taihigher, on the lower portionthevertical in.N A S A 5 0 1 , the spin researaircrafi typical of light sin-gle-engined designs, i s showfli gh t above the test area adcent to the WallopsPlight Cter, W allops Island, Vir ginNumber 2 on vertical tail incates th at theplane i s f lyingwith the second of several empennage configurations de-veloped for improved spin reery. Note the instrumentatibooms extending orward froeach wingtip , and the spin-recovery parachute mountedthe af t fuselage behind andbelow th e horizo ntal tail .thickness of th e wing sectConsequently, a properly signed supercritical wing three direct benefits that prov e aircraft efficiency:First, it reduce s wing dragsecond , it increases internvolume f or fuel storage; thit increases the structural eciency of th e wing and leato lower weight.T h e total benefit of a wdesigned supercritical wincould be a reduction of 115 percent in the amountfuel burned for a specifietrip.Oth er aerodynamic improv em ents with fuel-savpotential include wingletssmall surfaces mo unte d atabove the wingtips; high-devices used during climbdescen t; active controls, treduce the size-and therefore th e drag anw ei gh t-o f horizontal anvertical tail surfaces ; andcareful integration of thepropulsion system into thaerodynam ic flow con tourth e aircraft.O ne method wi th greapotential for d rag reductiolaminar flow con trol (LFC


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ShorterTakeoffs,Lower Noise

sing suction throu gh m ulti-slots in th e wing surface toirflow over th e wing.interdisciplinary ap-n a l ight-g and rigidtructure combined with auction system that couldake practical LFC systems aeality.Improve ments in propul-ion include the developm entf engine components-urbine-that have high erciencies. B e-ond that work, there is po-ential for developmen t of aasically new p owerp lant

e a way station o njourney from piston en-to jetes. Bu t now, th e fuel ef-ency of such an eng ine,h develop mentstechnology, havea new look at this old

T he big difference is in theance o f the propel ler .ead of the th ree Or fours commonly seen o n

propellers used with pistonengines, the new propellerhas multiple blades, curvedand shaped for m aximum ef-ficiency a t high rotationalspeeds. The se scimitar shapeshave been tested in wind tun-nels and will evolve throughsmall-scale mo dels to a full-size developm ent, if the pre-liminary studies point in thatdirection.Th e example of the ACEEprogram show s how NASAfunctions. It involves a teameffort by government agencyand industry. It crosses thebound aries of aeronauticaldisciplinary area s, and inte-grates them into a plannedand phased program. I t usesthe fou r basic classes of re-search too ls available toNASA: Computers, thatanalyze flow, performa nceand d esign characteristics;wind tunnels, that test scalemodels of components, or ofcomp lete aircraft; simulators,that verify th e effects of smallchanges in existing airplanes;an d flight vehicles, such as thedrones that will carry theexamples of advanced wingdesigns into the air.

T h e broad aims of the ACEEprogram apply best to long-range tran sports that carry ahundred or more passengersacross continents an d oceans.In such long-distance, high-capacity flights, increas ed air-craft efficiency really pays interm s of fuel saved. Fuelcosts, on ce a relatively smallpart of the direct operatingcosts of an airline, have be-com e instead a major portionof thos e charges. That fact istrue equally for the smallerthird-level air carriers as wellas for the major trunk andinternational airlines.change the pattern of airtravel, and as the sho rterrou te segmen ts once flown byth e major carriers are takenove r by the sm aller ones, newdem and s may arise forcategories of aircraft no t yetdevelope d. In som e cases, therequirem ents of an air car-riers route structure may bestbe served by the introductionof a large-capacity shorttakeoff and landing (STOL)airplane.Th e technology of STOLhas long been a subject of

As fue l availability and cost

great interest at NASA cen-ters. Tied closely to it hasbeen the investigation ofnoise, because one use ofSTOLand vertical takeoff anlanding (VTOL) aircraft isplanned around the conceptof close-in airports. Such lo-cations demand aircraft with low noise level. This is not toimply tha t noise reduction isnot necessary at major termi-nals; it is.Several factors have alterethe noise environmentaround airports since jets firsappeared on the scene in thelate 1950s.Ther e has been atremendous constructionboom, and undeveloped laneveryw here was used for suburban homes. Much of theundeveloped land aroundmajor cities was also aroundthe major a irports that servedthose cities. Consequ ently,houses we re built right up toth e borders of th e field, insome cases. There was also rapid expansion of travel,which mean t mor e flights antherefore m ore airplanes togenerate more noise aroundth e a irport. Finally, the firstgeneration turbojet engines

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The Quiet Short- haul ResearchAircraft (QSRA) s a proofioficoncept vehicle to investigate thetechnology of a Propulsive liftsystem that uses wing upper-surface blowing. I t utilizes a de

Havilland C-8A Buffalolight military transport loanedby the Amy for the program,and modified by The BoeingCompany t o incorporate thepropulsive lift system in an en-

tirelynewwing design. Here thQSRA is being checked out byBoeing company pilots beforedelivery to NASAs Ames Re-search Centerfor the major potion o f its research flying.

in th e transpo rts gave way tolater and mo re efficient tur-bofan engines; but the se laterpow erplants had a differentnoise pattern which changedth e perceived sound levels.The se factors, although theydid not initiate NA SA pro-grams in noise research, cer-tainly were additional spurs toaccomplishment.NA SA has developedmethods fo r lowering thenoise level of large jet trans-ports by an acoustic treatme ntof th e engine nacelles. T hequ iet nacelle found wideacceptance am ong airline op-erators. B ut that was, obvi-ously, an interim so lution.T h e better way was to de-velop a qu iet engine, andNASA-in a joint pro gram

with industry-de velopedsuch an experim ental pow-erplant that produce d a sig-nificant reduction in g ener-ated noise.Tha t work also led toanother developmental pow-erplant designated QCSEE,for Qu iet, Clean, Short-haulExperimental Engine. Itbegan test run s at the LewisResearch C enter in the late1970s. Th e goal of the pro-gram was to produce a pow-erplant for a four-engined,150-passenger STO L trans-po rt with a small and rela-tively low noise footprint.Th e STOL technologyaround which the Q CSEE wasdevelope d utilized the eng ineexhaust to produce in-creme ntal lift. In o ne case, the

exhaust was blown directlyove r external flaps to producethe added l ift for STOL. Inthe o ther, part o f the bypassair was du cted to blow overthe u pper surface of the wingto gen erate additional lift.Both these types of engineswe re b uilt and successfullytested.velopment of the QSR A(Qu iet Short-haul ResearchAircraft), which originated asa proof-o f-concep t vehicleand a resea rch tool. I t was in-tended to validate thetechnology of apro pulsive l iftsystem that used upper-sur-face blowing. Add itionally, itsoperations would developcriteria for certification offuture trans ports that used

A parallel step was the de-

propulsive l ift. T he geometof th e QSR A is typical of ashort-haul transport , and thlow-speed flight regime is tarea of particular interest.Noise levels, flying qualitistability and co ntrol, and oerational constraints are iteon the QSRA test programTh e wing of the QSRA,which incorporates the propulsive lift system, was de-signed and buil t by Th e Boing Com pany, and installeda m odification to a de Havland of Canada C-8A Buffalo,aU.S. Army light STtransport. Flight evaluationbeing done at the Am es Rsearch Center, designatedlead NASAs VTOL andSTO L programs.

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tary- win g aircraft are in af both STOL and VTOL

r unusual aerial maneuv-pose p rob-gued re-hers at NAS A and else-. Th ethe na-of their lift generation.eir wings are rotatingwhirled at high speed sa horizontal plane, and ad-

a com-in orde r toaxes.Tw o differe nt flight vehi-are the keystones ofs rotary-wing researchs. First of the se is theesearch A ircraftA), built by BellTextron und er afort tha t originally wasy the A mes Researchter and the Armys Airy Research a nd D e-nt Laboratory. TheXV-15 its m ilitarytwin roto rss mou nted atof a high wing. Th e

d

Th e Ar my IN AS A Rotor SystemsResearch Aircraft (R SR A) ,de-veloped by Sikorsky Aircr aft, i sshown in level fli gh t near theAmes Research Cen ter. Tw o ofthese unusual craft were builtfor the joint program, one wi th

the ability t o beflown as a com-pound helicopter w it h fixedwings and a orwardpropulsionsystem as add-on features. Th esecond, shown here, was de-signed t o ly as a pu re helicoptert o furnish baseline test data,

and to investigaterotor systemand other helicopter features oit s own. One notable ide ntification feature of the RSRAhelicopters is the ta ll verticalT- tai l tha t carries the anti-torque rotor.

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One of two Rotor Systems Re-search Aircraft (R SRA) de-veloped or a joint N ASA -Ar myprogram by Sikorsky Airc raft,thisparticular RSR A i s shownin i ts compound helicopter orm.The ixed wings carry some ofthe lift in horizontalflight, and

help to unload the rotor system.A standard Sikorsky S-61 rotorhead is used i n the design. Theturbofan engines mountedon thefuselage la nks arefor orwardpropulsion; the lifting rotor i sdriven by t w in turboshaft en-gines mounted above the fuse-

lage. A unique crew escape sytem was developed fo r this research aircraft , wh ich ejects tthree-man crew in split-seconsequencing following ejectionthe rotor blades.

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r

rotors can be tilted from hori-zontal, permitting verticalflight, to vertical, permittinghorizontal flight.T w o XV- 5 aircraft werebuilt. Th e first, after a fewhours of check flights, wasmoun ted in th e Ames full-scale tunnel and testedexhaustively. Th e secon d,which first flew in the hovermode in early 1979, ecamethe primary flight-researchsubject. B oth aircraft now arebeing flown in a detailed re-

search program which is con-tinuing.Ro tor Systems Research Air-craft (RSRA), built bySikorsky Aircraft Division ofUnited Technologies Corp.for NASA and the Army. Thetwo aircraft built und er theprogram use Sikorsky S-61helicopter rotor head s as thebasic lifting system , but a redesigned to be able to test awide variety of roto r systems.Th e RSRA can be flown as a

Th e second type is the

r

conve ntional helicopter, or asa compo und helicopter, withfixed wings installed to un-load the roto r by assumingsome o f the l if t.Th e RSRA br ings newflexibility and vers atility toNA SAs rotary-wing fl ightresearch program. It operatesover a wide speed range, sothat th e l ikely fl ight enve lopeof any near-future helicopterdesign could be ex plored ex-tensively. B oth aircraft havebeen delivered and are flying

at the Ames Research CenTh e RSRA and the XV-also can perform additionflight research, onc e theirbasic program s have beencompleted. T h e RSRA aicraft will be used for studynoise, the dynamics of rocraft, and rotor modificatiBo th aircraft will be usedthe developm ent of avionsystems for improvedhelicopter operations in bclear and bad w eather.

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era t ion a l and safe ty prob-traditionalSA aeronauticalngs on w ets, an d airport ap-

flow havestudied and improvedA programs.ntinuingon the Terminal-Con-re-earch airplane with uniqu eapabili ties. T he T C V wasodified f rom a standardBoeing 737 twin-engined jettransport by adding a secondcockp it, with adv anced digitalvionics systems, in th en of the 737.w o sets of crews may f ly theC V; up front , in the usual

ositions, is the safety crew.Back in the second cockpitare the pi lots w ho fly the TC Vin its research toward im-proving terminal a rea capac-ity and efficiency, and towardimproving approach andlanding capabilities in badweather conditions.In the late 1970s, delayscost the airl ines ab out a half-

O ne of th e most productive

cc?A

The internalawangement of theNASA Terminal-ConfiguredVehicle (TCV) s shown in thiscutaway model of the modifiedBoeing 7 37 aircraft. The testprogram isflownfrom the re-

billion do llars annually. Con -cerned organizations such asNA SA , the Federal AviationAdministration, th e A ir LinePilots Association, and in-dustry, have be en studyingways to increase the handlingcapacity and capab ility of thenations high-density air ter-minal areas. Th ey believesuch increases are excellentways to increase the p ro-ductivity of th e air traffic con-trol system and the airports.O ne suggested partial so-lution is the use of a time-controlled descent to the air-port. FAA air traffic control-lers at three major U.S. ir-ports have b een w orking withthat method to simplify thecontrol of traffic in the ap-proach. A comp uter sorts outand sequen ces arriving air-craft in a time-based trafficcontrol sy stem, matching the

search cockpit, located in theforward fuselage of the TCV.Safetypilots in the conventionalcockpit sewe as backup to the re-search pilots, and can f l y theairplane as required. Seating

airport demand to its capac-ity. Addin g a smart airplanewith a dvan ced avionics sys-tems permits th e controller toprogres s from active meter-in g of traffic to passive me-tering. Th e TCV program isinvestigating the techniqu esneeded to achieve th eassigned-time objectives ac-curately and effectively.Research with the TC V air-craft has show n a consistentability to place the airplane ata po int in space-for exam-ple, at the start of the descentto the airport-within a fewseconds. If ther e a re unfavor-able winds, that time may beincreased to as much as tenseconds. But that compareswith perhaps two minutes ac-curacy with c urren t conven-tional meth ods of air trafficcontrol.Th e desc ent itself, handled

behind the research cockpit isfoflight test engineers whomonitor and interpret the videdisplay system.

by th e smart avionics in thTC V, is don e along a fl ightpath that uses minimum fueso that there is apotential fuesaving by using the systemsand techniques developed bthe TCV programs. Oth erpotential payoff areas includroutine op erations in badweathe r, pilot participation ith e traffic control system looby using a coc kpit display otraffic, reduc ed lateral sep-aration and spacing, and re-duc ed runway occupancytime. All of these factors tento increase th e capacity of aairport in bo th clear and baweather.Bad weathe r can affect acraft far from their term inaareas. Boiling up off th e midwestern plains in the hea t osummer, violent thun-ders torm s could wrack an acraft and d o serious damag

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ing-root extensions haveadded to a typical agricul-in thewind tunnel athas been investigating

t o improue the per-nce capabilities, handlingd safety o f theselized airplanes andpters. The subject of thisstudy was the airflowin the region of the

its structure and systems.rather than sought, there is little detailed,their characteristics.bad qualities aree turbulence,ng strikes, torrential

t quantifying thosestics has not bee nN A S A hasatestof a lightning-hard-General Dynamics F-eptor aircraft, tothe unknowns of thun-by flying throughy se ekinglightning strikes andto assessaircraft.e aspect of this researchl be th e investigation ofto protec t on-board avi-s against a directning strike o n the aircraft.Th e violent turbulence of adersto rm has a parallel ininiature tornado gener-

of a larg e and h eavyide-orts now

Because thunderstorm s are

6 I !

Their wingtips genera te avortex flow, a rotating andexpanding cone of high-energy air, strong enough totumble a smaller and lighteraircraft passing in to its field ofinfluence. Much study hasgone into und erstanding andattempting to defeat thetrailing vortex b ecause, insome cases, th e strengths ofthese vortices determine th esafe spacing betw een landingsat an airport.O ne promising solution isthe use of an aerodynamic

spoiler to break up the vor-tex. Flight resear ch of spoilerson a modified Boeing 74 7 isbeing do ne, first, as an ap-proach to reducing th estrength of th e vor tex gener-ated by th e airplanes passage,and second, to understand th egeneral mechanism of thatgeneration. Th e methodshows promise for reducingthe p resent separation dis-tance from six miles to three,with a corresponding improve-me nt in airpo rt capacity.As a side light, all vortices

are not potentially da ngero r harmful. Generation ofwingtip vortex by agricultsprayer and duste r aircrafhelps lay do wn a swath ofsecticide or fertilizer. B ut all operators agree thatgenerating a vortex is th e bmethod to distribute matethrough th e wake of the acraft, and on e of NASAsmany unusual research prgram s is investigating wayspread m aterials from lowflying planes.

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AH

StudyinContrasts

T h e r e could hardly be moredifference between t he shapeand func tion of an angular ag-ricultural aircraft and tho se ofa sleekly contoured super-sonic fighter. Yet un der-standing how b oth of themwork finds common groundin unde rstanding the basicflow fields around the m, andthe effects their shapes haveon that field.Th e traditional way to de-termin e flow fields aroundaircraft has bee n by calcula-tion, later verified or cor-rected by wind-tunnel andflight tests. In earlier times,

this routine was do ne withslide rules and de sk cal-culators. Those techniqu esresulted in approximationsthat were accurate enough forthe unsophisticated airplanesof the time. But in more re-cent years, the increasingcomp lexity of aircraft hasbeen matched by th e availa-bility of th e compu ter tohandle the real chores ofairflow com putatio ns veryrapidly and efficiently. Bu teven the advanced capabili-ties of contempo rary com-puters are not sufficient tosolve th e highly co mplex flow

equations that result from atrue three-dimensional situation in the presence of a turbulent boundary-layer flowFor two-dimensional flowth e situation is different. In1970, it took th e most ad-vanced com puter of its day shours to compute a two-dimension al flow field,excluding th e effects of th eboundary layer, a thin,slow-moving s hee t of air neto th e surface. By 1 980, compu ter capabilities had in-creased so that th e same caculation could be p erformein five to ten m inutes, in--erodynamic evaluation of anagricAturaI aircraft in t iefull-scale wind tunnel at theLangley Research Center re-vealed some potential im-provements i n this specializedtype of aircraft.Tuftswere fas-tened to the external surfaces ofthe entire aiplanefo r a visualstudy of airflowpatterns. Dark-ened sectors behind tuft attach-ment points vividly showregions o f airflow instability.

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plitting a model on a verticalisone method devised by Langleyesearch Center scientists to re-uce t o a minimum the inter-ejfects of wind-tunnelounting arms. In this Uni-

model of a super-design concept is beingd. The dividing plane canseen splitting the model intoand right halves. Thengtip suspension systemholdsmodel.mic forces on the ldt

by the methodsuspension.

e boundary-layerReynolds Num ber (RN ) sa dimensionless parameterused as one basis for compari-son of th e results of wind-tunnel tests with those offull-scale flight. Th e clo serthe Reynolds num bers corre-spond, th e closer the test re-

sults agree. To attain full-scale R N values in a small-scale wind tu nnel is very dif-icult, and the story of ent haseen told largely in term s ofer R N values. High-els have beento obtain an in-

ty. High-spee d tun-so increase the R N. Us e of th e largestdel size possible raises theue further. T he only placefor improvem ent nowto be a lowering of they of th e w orkin g fluid.ther prob-to the developmentthe N TF tunnel.It is a cryogenic tunn el; its

nitrogen gas. It is also apressure tunn el working atnearly nine times th e outsideatmospheric pressure. Its testsection is about 2. 5 meterssqua re, and a typical mo delwill have a one- mete rwingspan. T he predictedvalues of R N will correspondmo re nearly to those attainedin a much larger wind tunn el,say in a test section on th eord er of eight meters square.NASA sees a future needfor fu rther increases incapacity and capability of itscom putational facilities. Toput this future need intoperspective, considerNASA s most powerful com-puter on-line in 1980. It han-dles between 20 an d 140mil-lion operations per seco nd,and can sto re a millionwords.To compute some of

the flow patterns around to-days and tomorrow s aircraft,scientists foresee a nee d toprocess on e billion ope ra-tions each second, and tostore 40 million words.Th e development and pro-curem ent costs for such anadvanced com puter a re high,and the time required forputting it in place is long, so itmay well be several years be-fore new computationalfacilities will go on line.T h e wind-tunnel facilitypicture is brighter. Eventhough this revolutionarycomputational capability isneeded to understand fullythe complex flow patterns,the theories still need to beselectively verified by ex-perim ent. Assisting in thisverification of theory are ad-vanced resea rch tools such as

the National T ransonic Fity (NTF) tunnel, scheduto start calibration runs i198 3. When it is fully optional, it will increase greNA SAs ability to obtain curate wind-tunnel pre-dictions o f full-scalephenomena. T he key is tattainability of largeReynolds numbers. Wintunnels have oth er problesince they are no t perfecsearch tools. For exam plepresence of th e test sectiwall is an artificial constraon any testing. N o realairplane flies around sur-rounded by a solid surfacthat does not match th estreamlines of flow. But pos e a wind-tunnel wall cobe made to conform to thshap es? Some early reseaand tests reflect optimism

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22/32

The HiMAT vehicle used inNASA's program to studyHighly Maneuverable AircraftTechnology is a scaled-down re-motely piloted research aircraft.This experimental techniquewas developed by NASA severalyears ago and is useful to studyhigh-risk technologies. Further,tests with small-scale, unmanned

models are more economical.The HIMAT vehicle is carriedaloft by a modified Boeing 8 - 5 2mother ship and launched ataltitude, typically 45,000feet.I t can f l y for approximately 20t o 25 minutes after release,landing on the dty lake bed at theDtyden Flight Research Center,Edwards, California.

an aerod ynam ic instability ofsome sort that may cause theairplane to whip ou t ofcontrol.Th e studies of the interre-lations of all these factors,don e by NASA , the militaryservices' laboratories, and in-dustry, have coalescedaround a single programcalled HiM AT (Highly Ma-neuverable A ircraft Technol-ogy). It is ano ther example ofNASA 's approach to re -search, because HiM ATbegan as a serie s of analyticaland com puterized studies,progressed to tests of scalemodels in a n umb er of windtunnels, and now is in theflight-research stage, usingunm anned , remotely pilotedvehicles appro ximately halfthe size of a typical fighterdesign.HiMA T has two basictasks. First& is used to studythe interrelated prob lems ofall aspects of t he flight of atypical advanced fighter con-figuration. Seco nd, it is con-tributing to th e design of fu-ture fighter types by furnish-ing fun dam ental aerodynamicand s tructural loads data that

will assist design ers inindustry.HiM AT is a joint NASAIUSAF program, with the de-sign and construction of itstest vehicles being th e re-sponsibility of Rockwell In-ternational's L o s AngelesAircraft Division. The basicconcept of HiM AT is that of aclose-coupled canard layout,with advanced airfoil designand aeroelastic tailoring. I t isa subscale mod el of an ad-vanced fighter, synthesizedby Rockwell designers astypical of the year 1990.Th e detailed designspecified a core vehicle with abasic engine, airframe andsystems. Th e remaining com-ponents were designed asmod ules that could easily beattached to the core vehicle,and just as easily replaced bydifferent or developed unitsas the program progressed.Com posite materials ac-count for nearly one-third ofthe airframe structural weightof the H iMA T vehicles and,for the first time, these newmaterials are being used tocapitalize on t he ability togive them unidirectional

shock of landing and tofurnthe braking required t o stopvehicle. The remotely pilotedhicle can sustain, typically,twice the rate o f turn of conteporary fighters because of th

The HiMAT vehicle makes itsfina l approach for landing onthe lake bedat the Dryden FlightResearch Center, Edwards,California. t uses landing skiisrather than wheels to absorb thestiffness. Th e com posite wingand canard surfaces are de-signed so that th e naturalbending of both surfacesund er maneuvering loads willcontrol the changing of theaerodynamic shape of theH i M A T to maintain optimu mlift and drag con ditions.Flights of H iM AT beginwith an air launch from'amodified Boeing B-52D air-craft. T h e research pilot sits ina cockpit on he ground a tNASA'S Dry den Flight Re-

search Ce nter, and he fl iesvehicle from there, m oniting its performance on aserie s of displays typical ofighter cockpit. A backupcontroller, aloft in a Lockheed TF-l04G , can assumcommaqd of HiMA T ifground control is lost . Anshould both fail, the vehicautomatically goes into cotinuous tu rning flight and wstay in that mane uver u ntcontrol is regained byeither pilot.

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of itsion. HiMATa joint project of NASA ande US. ir Force. Thispicturecom-o f its third test flight.T he basic technique of re-flight was de-ped by NAS A at thecenter, and has beenearlier test programs,amp le, stall and sp in re-e model of theP-1 SA .Th e advantages of such a

as H i M A Treadily apparent. Its m od-it relativelyma jor com -as an engineto evalu-

~

Single Pivotforawing

a te it und er test conditions infre e flight. Its smaller scaleserves to reduce costs, bothinitially and opera tionally. It ssize also allows it to be testedin large wind tunnels, for di-rect com parison ofaerody nam ic data with free-flight results. And with apilotless vehicle, the ex-trem es of the flight and ma-neuverability enve lope can beexplored without the need topu t a pilots life at risk.

Th er e s an old saying in avia-tion that if an airplane looksright, it will fl y right. Th ere isalso an old maxim that eve ryrule has an exception. Com -bine these, and you have animpression of the NA SAoblique-w ing aircraft, a con-cept that looks as wrong aspossible. On one side, a winglunges forward to meet theoncoming air; on the oth erside, it sweeps back.And it flies right.This radical dep arture fromthe conventional geometry ofaircraft layouts was dev isedby NASAs Robert T. Jones,and first advanced by himseveral decad es ago. Grea tskepticism gree ted th e idea,even though i t had be entested in a wind tun nel andseemed to be wo rkable. Butat that stage of the art, it mayhave be en impractical toprovide the structure re-quired to perform the uniquetask of sw eeping one-half ofthe wing forward and th eoth er half back.

rection, the ob lique wingconcept called for a secondlook. ones had never aban-doned the idea and, in fact,had continue d to develop it iscale-model testing. He usesmall radio-controlled mod-els which flew well and con -t inued to dumfound thecasual observer.Ob lique wing studies hadbeen extended earlier to therequirements of supersonicflight and had sh own , sur-prisingly to som e, that theodd shape offered am ajor advantage in the design of asupersonic transport. Analysis and wind -tunnel workdon e at Ames ResearchCenter pointed to a fuelecono my twice as good as haof the first genera tion of operational supersonic trans-ports. The re was a bonus: Thconcept seemed to producesubstantially weaker sonicboom, on e of the banes ofsupersonic flight.NASA funded the designand construction of a small,With the adven t of com pos- piloted research aircraft witite materials, and their unique a pivoting wing. This proof-ability to b e tailored to carry of-conc ept vehicle was builloads along any desired di- by the Am es Industrial Corp

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N Y , and th e air-is flying in an ex-t the subsonic flightof th e unusuale researchdesignated th e AD-1,nd fiberglass.t wingspan and

1,800 pounds.t is a pair of

For ow-speed flight, thee fuselage centerline, andexcellentstics of a straight-

winged airplane. In that con-figuration, it has goo dstability and con trol qualities,no need for ornate high-liftsystems, and reduced enginethrust for takeoff. For high-speed flight, th e wing pivotsto angles up to 60 degreeswith respect to the aircraftcenterline. Th e drag is de-creased substantially.Once again, the progres-sion from an idea throughanalysis, wind-tunn el testsand into flight research un-derscores NASA's systematicapproach to a new and uniqueconcept for the improvementof aeronautics.

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The ScienceofShapes

I

The Ames- Dryden-1 (AD- )photographed during a testflight from NASAs DrydenFlight Research Center, i s beingflown to study the concept of theob lipe wing. Invented by AmesResearch Center scientist RobertT . ones, the oblique wing ispivoted at a centralpoint span-wise. Rotated by actuators, onew i n g tip movesforward and theotheraft o sweep angles up to 60degrees with the fuselage cen-terline. This aircraft,flown bypilots of the Dtyden Plight Re-search Center, is an example ofthe NASA r$v-oof-of-conceptresearch.~ approach i n aeronautical

O n e f t he h is to ric ta sk s a tNASA has been the de-velopment of new shapes offlight. Th e years have seenthe biplane, with its struts andwires, give way to the canti le-vered monoplane. Straightwings made way fo r sweep-back, the n for variable sweep ,with the special case of theoblique wing mentione dabove. Th e search for m orespeed and mo re efficient air-craft has recently led to afamily of sh ape s in which th ewing and the fuselage areblended into an integratedwhole of sweeping and CUN-ing surfaces.Part of this work has beenaimed at the supercruiseclass of airplan es, designs thatare intended to fly econo mi-cally and efficiently at sup er-sonic speeds. At first, NAS Aprograms in this area con-centrated o n the specificneeds of the U.S. supersonictransport. But now the workis aimed primarily at th e de-velopm ent of new shapes forfighter aircraft, shapes thatwill permit unusual ma-neuverability c oupled withdazzling speed and the ability

to accelerate to supersonicflight rapidly and efficiently.On e of the things learnedin these studies has been th eimportan ce of the strake, afairing that stretches from theleading edge of th e wing topoint forward o n th e fuselageO n a very high speed aircrafthat strake may becom e amajor portion of the liftingsurface. It can be used tocreate a vortex that generatelift, and to apply that lift to-ward maneuv erability. T h econcep t is an exciting on e,and it is finding applicationsin the new generation offighter aircraft.Aircraft efficiency is mea-sured simply; it is the ratio olift to drag. Th e higher thatratio, the mor e efficient theairplane. Th e major problemin su personic flight is that thlift-drag ratio inhe rently hasno t been high, and it has nobeen easy to raise the m odesvalues that ar e routinelyattained.Consequently, NA SA habee n analyzing ways to in -crease lift and reduce drag owings, shaping the m to th eneeds of supersonic flight. A

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Experiments with plastic coat-ings to reduceskin friction dragon wing and tail surfaces arebeing done on a Boeing 727 op-erated by Air Micronesia in atropical environment. Two dg-ferent types of coatings-Chemglaze M3 13 andCAAPCO B-2 74-ure beingevaluatedfor drag reductionand resistance to the particularenvironmental factors of the airoperations in Micronesia. Po-tential fuel savings from smalldrag reductions are substantial,and increase with the increasingcost ofjetfuel. Thissketchshowsthe location and extent of theplastic coatings.

a further refinement, thesewings then are fitted with avariety of h igh-lift devices, toimprov e their characteristicsin the takeoff and landing re-gimes of flight. Some of theseideas are finding applicationsin the A CEE program as wellas on th e futuristic shapesbeing developed for tomor-rows fighting aircraft.Chasing down drag is anendless task. N o sooner doesone comp onent seem to havebeen brought to the irreduci-ble minimum of drag produc-tion than an othe r shows as acontributor of sizable drag in-crement to th e aircraft. A jetengine installation on a con-tempo rary transp ort is a typi-cal example. The re is a flowinterference in the regionbetween the wing and the en-gine nac elle, and it adds a sub-stantial sum to the total dragof th e aircraft. And becausether e are, typically, either twoor four of thes e intersectionsbetwee n wing and nacelle ontodays transpo rts, its a re-gion worth exploring with theaim of red ucing its contribu-tion to aircraft drag.NASA investigators are

,hemgIaze -+M313

\3-274CAAPCO

concentrating on prope rshaping of th e pylon thatholds the en gine nacelle tothe w ing, looking to smooththe flow und er th e wing andto reduce any tendencies for acrossflow to develop.Wind-tunnel tests of pylonredesigns and oth er m odifi-cations have show n ways toreduce their drag contri-bution.Aircraft control surfacesare sized to me et th e stabilityand control requirementsspelled out in Federal Avia-tion Administration or othercognizant agency regulationsand handbo oks. The surfaces$e large, because they arede-signed to static stability re -quirem ents. Th e tail surfacesact like a weathervanes tail;t hey keep the a i rp l ane -orthe weathervane-pointedinto the relative wind. Theyare passive controls; they

react to a d isturbance.Active controls are a sub-ject under m ajor study atNASA . Th e approach is onth e basis of wh at are calledrelaxed stability require-men ts, in which an instabilityis anticipated by se nsors andtransformed into signals tothe control surfaces to correctfo r that instability even as it isoccurring. By do ing that, thecontrol surfaces can be madesmaller, and there fore lighter,than normally. Any thing thatsaves weight and size also re-duces the drag and th eamoun t of power required tofly. An d that, in turn, reduc esthe amount of fuel burned. Soth e active control programsund er investigation at NA SAhave been aimed at the broadgoals of the ACEE efforts,and in related studies for ap-plications outs ide th e trans-port field.

An obvious way to reduairplane drag is to wax itssurface. O n a small personaircraft thats feasible; on aBoeing 747 its not ve ry pratical. But coating th e airplawith s om e sort of a synthesurface might achieve thesame results as hours andhours sp ent waxing th e ex-terior. NA SA has funded astudy of airplane coatingswith Air Micronesia, whysBoeing 727s work in theSou th Pacific islands, in anenvirohm ent of sand andcoral abrasion, torrentialrains, torrid Sun , and saltspray. Th e leading edges othe wings and rail of on e oth e airlines 727s have beecoated, and are being studiover a long t ime period tosess the effects of the coatinon performance, and the efects of the environment oth e coatings.

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Aviation

e n e r a l aviation is a catch-allto describe a very im-ent oft includes all ofll of co rpor atetive transportation,of ag ricultural flying, mu chnewly em erging com-ter air transportation mar-and a m iscellany of an -pieces, homebuilt

e list is long, andve of th e variety andmpo rtance of gen-l aviation.NASAs interest in this al-ield g oes backthe early 1920s, and theNACA.n, th e agency was in-to make per-mo re reliable,

Currently, N A S A focusesn several basiclem areas in general avi-on. Th e first, and mos t im-second is impro ving the

and eng ines,noise levelsof exhaust

Leading-edge slats, extendingwellfirward of the outer wingpanels of this typical lighttwin-engined general aviationaircrafi, were evaluated inLangley Research Centersfull-scale wind tunnel. Wingand engine nacellesudaces carryproducts. A third is improv -ing th e en ergy efficiency byimproving the performanceof major components andsystems. NAS A also has em-phasized increase d utility inits studies.O ne way to improve safetyis to study how airplanescrash, in the h ope of findingsom e basic structural or otherdesign ch anges that will in-crease the survivability ofcrew an d passen gers in an ac-cident. For several years,N A S A has been deliberatelycrashing a number of single-and twin-eng ined lightplanes

hundreds of tufts, used as visualindicators of the direction andtype of locala irflw. This par-ticular test was part of a con-tinuing series at NASA tostudy, evaluate, and deriveaerodynamic improvements fortypical general aviation air-in a carefully controlled, in-strumen ted and documentedseries of spectacular impacts.A s the result of a flood a fewyears ago, which inun datedth e final assembly lines of amajor m anufacturer of gen-eral aviation aircraft, NAS Aacquired a num ber of nearlycompleted airframes. Thesehad been co ndemned as un-airworthy because of waterdamage, but they becameuseful research tools.Th e crash tests at theLangley center have pro-gressed from the early few,which w ere essentially guided

craf . These full-scale tunneltests can later be correlated witactualflight tests of the aircrat o determine the degree of agrement between the twosetsof results.

free-falls on to con cretepavement. M ore recently,small rocket m otors havebeen installed in the eng inenacelles to boost the impacvelocity in a simulation ofcrashes at higher speed s.Extensiv e instrumentatioin the aircraft as well as outside, high-speed p hotogra -phy, and other m eans areused to acquire data and todocument the crashes. An-thropomorphic dum mies arharnessed in crew andpassen ger positions, in-st rumented and photo-graphed to assess their

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This spectacular photographshows a light twin-enginedgeneral aviation aircrafi mo-ments before its impact with arunway sudace i n the seuen-teenth o f a series of crash tests atthe Langley Research Center.Flame streaks are the exhaust offour olid-propellant rocketswhich thrust the plane to ahigher impact speed than ispossible i n a simple grauity-accelerated drop. The impactoccurs i n front of a griddedbackdrop which allows mea-surements of aircraft accelera-tions and decelerations.

chances of surviving th e de-liberate crash.this test environment is astudy of energy-absorbingaircraft seat design. N ew con-cepts in passenger s eats, eval-uated in high-speed rocketsled tests by the FAAs CivilAir A eromedical Institute,later were installed in testairframes for th e crashes.absorbing struc tural designtechniques were used tomodify the fuselages ofcrash-test airframes. Po st-crash examination of th efuselages and th e insttumen-tation results was used to as-sess the applicability of thenew designs for futurelight aircraft.T he best way to survive anaccident is no t to have one, ofcourse. On e of the majorlong-term areas of NASA sactivity in ge neral aviation isin th e investigation of stallsand the spins that sometimefollow. A leading cause ofcivil air accidents, th e stall/spin is a phen om enon that in-creasingly is being unde r-stood , analyzed, and cou n-

O n e investigation th at uses

In a related effort, energy-

tered. Typically, researchstarts with a small dynamicallysimilar mo del of an airplanewhich is tested in the spintunnel at Langley. Recently,these tests have been fol-lowed by free-flights of ra-dio-controlled scale models,and finally by flight researchwith the real aircraft. Severalgene ral aviation aircraft serveNA SA as vehicles for stall/

spin flight research. O n e wasmodified so that a number ofvertical tail designs could beinstalled f or investigation oftheir effect on t he stall/spinrecovery. O th er design mod-ifications have included t headditio n of strakes (fin-likesurfaces) and, m ost im portanto f all, changes towing leadingedge configurations. Thewing leading edg e configura-

tion has been discoveredhave apowerful effect onresistance.A m ajor program to donstrate the technology Quiet, Clean General Ation Turbofan (QCGA Tgine was established by Lewis Research Cen ter, funded contract work plwith industry. T he goal wshow that the technology

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e suspension system th at as-the correct angle of impacttheconrete sudace i n thesecrash tests is beinghere before hoisting thetwin-engined aircraft torelease point . This test, sev-nth i n a series of controlledto investigate aircraftral behavior followingact, used fo ur solid-propel-rockets mounted i n the rearthe engine nacelles t o acceler-the airframe t o a higherd th an possible wi th a grav-in t schemeofaircraft, so th at high-speedion of airframe reaction

emission reduction,to large turbofane transferredthe design and develop-t of turbofan engines incategories useful for. Garre tt's AiResearchCo. and Avcoeach m odified anng engine in their com-to meet th e re-major effort was directed

t was achiev ed inengines. A second goals to reduce the carbonunburned hy-ides of nit-itted; that, too , waseved. O ne constraint wassh these redu c-t any increases in

significantly.A series of four study pro-lso with indu stry,d at the feasibility of de-mall turb opro p en-ral aviation ine 300 to 700 shafthorse-pete with highly

Aircraft structure behavior onimpact wi th theground i s beingstudied i n a n on-going programat theLangley Research Center.UsingpIanes ypical of the lightsingle- and twin-engined air-craft in general aviation use,NASA engineers deliberatelyrelease theplanes along a con-trolled flight pa th onto a con-crete apron. Highspeed camerasand other instrumentation re-cord the loads, decelerations anddistortions of the aircraft. ln -strumented anthropomorphicdummies, which accuratelysimulate the human frame, maybe included i n the test t o studythesurv ivability aspects of aparticular type of impact. Thissequence reads from top t obottom, to show thestages fromini tia l impact through sub-sequent deceleration to a stop.Both NASA and theFAA sup-port this testprogramas one wayof helping t o increase occapantsurvivability in general avia-tion accidents.

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Building It Stronger

One of two competing quiet,clean general aviation turbofanengines (QCGAT), developedunder contracts funded byNASAs h i s esearch Center,shows the general configurationof thepowerplant.Purpose of theprogram was to demonstratetransfer of technology from com-mercially available, large tur-bofan engines to smaller enginesin a lowerpower class. Garretts

A iResearch ManufacturingCompany-their engine isshown here-nd Avco Lycom-ing both developed an existingengine to the requirements ofgeneral aviation. Both man-ufacturers achieved major re-ductions in noise level, and inthe emission levelsfor carbonmonoxide-and unburnedhydrocarbons.

developed internal combus-tion engines. Th e aim of thestudies was to see if such en-gines appe ared feasible in th elight of fuel consump tion,weight and co st constraints.T h e studies indicate that thisshould b e possible with ad-vanced technology enginecom ponents and manufac-turing techniques. Advancedtechnology programs arebeing proposed to achievethese objectives.Additionally, propeller de-sign, frozen in th e past withfew exce ptions, has been longoverdue for a transfusion ofmodern technology. NASAhas been looking at ways to

increase propeller efficiency,through such possiblechanges as the use of m odernairfoils instead o f th e o lderconventional airfoils nor-mally used. N ew designs in-clude NASAs supercriticalairfoil technology f or ap pro-priate flow regimes. Th ecomp osite materials also offerprom ise, because the indica-tians are tha t propellers couldbe built with less weight andwith better structuralcharac teristics and fatigue lifeusing modern compositestructural design technology.Further, their aerodynamicperformance would show amajor improvement.

T h e dynamics of th e aircraftcrashes at Langley have led tothe deve lopment of new seatdesign concepts and seat re-straint systems. B ut they alsohave led to a careful analysisof th e way an airframe is dam-aged in a crash, how th e pro-gressive destruction of th eairframe moves from thepoint of impact throughou tthe structure. It may be thatsom e simple changes will befound to increase thecrashw orthiness of aircraft.The se studies have b een ex-trapolated to large transports,and all three m ajor manufac-turers of airliners have NAS Acontracts to investigate th eproblem of crashworthinessin airplanes of the size theydesign and build.something fails is th e key toefficient design of that piece.Know ing that, the design cantake into account som e spe-cial fea ture tha t will delay oreven p revent a specific modeof failure. O ne example is theuse of small extru ded trips ofmetal on a pressurized fuse-lage skin panel to act as rip-stoppers. An other examp le isthe tailoring of a compositestructure to absorb th e load

Understan ding how

along an axis of particularstrength.Composites seem to bevery useful materials for acraft structures. Made frofibers of carbon or otherhigh-strength substances ibed ded in a matrix, these nmaterials can be formed instructures replacing manycomp onents of modern aicraft. N AS A has a long-teprogram in which controlsurfaces , stabilizers, andfuselage fairings have beedesigned and built usingcomp osites. The se parts, istalled as replacem ent un ion comm ercial transports,in long-term airline use toevaluate their durability inthe real world of routineoperations.Thes e composite struc-tures a re very light and vestrong; they can be made vstiff, also. Or, the st rengthand deflection can be applalong a specific pa th, or aba specific axis. Oth er N AScomposite structures arefound in the H iMA T reseavehicles, and in a series ofsub-scale test wings beingflown on dron es into a higspeed aerodynam ic regimwhere flutter is studied.

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The FutureofAeronautics

I n 1980,the cost of every-thing was of major concern,and the price of NA SA re-search was no exception. Co stconsiderations have been themajor reason behind thesometimes slow pace ofaeronautical research. But,because ind ustry finds itselffacing the same problem s, ithas bee n turning increasinglyto NASA for the funding ofresearch program s that mighthave been regarded as prop-rietary sub jects a few yearsago. A str ong case can bemade for d oing the kind of re-search that industry wants andneeds, based on the N ASAcharter defined by the 1958National Aeronautics andSpace Act.NASAs record has shownthat its research and technol-ogy programs have advancedth e progress of aviation. Itspresent programs are makingvaluable an d timely contribu-tions to th e design of ad-vanced fighters, to the safetyof general aviation, to the im-provement of air transportopera tions in areas of high-density traffic. NASA s fu-ture plans fo r modernization,such as those for th e NationalTran sonic Facility, were con-

ceived in th e best tradition ofaeronautical research. Tha ttradition, which began in191 with the establishmentof the N ational AdvisoryCommittee for Aeronautics,is agrea t intangible advantagethat pervades t he staff andlaboratories of todaysNASA. T ogether, they con-stitute a national asset of greatworth, of past proven per-formances, and of enormo usfutu re potential.

The HiMAT vehicle used inNASAs program to studyHigh& Maneuverable AircraftTechnology is a scaled-down re-mote& piloted research aircraft.

t

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