nasa aeronautics research and technology

8/8/2019 NASA Aeronautics Research and Technology

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Foreword

Aviation in the United States occupies aunique position with its contribution totrade, its coupling with national securityand its symbolism of American tech-nological might. Since the beginningof manned flight, the United Stateshas been the world leader in aviation.This world leadership is founded ona strong national research and techno-logy base and the innovative applicationof advanced technologies to new con-cepts and missions.

NASA contributions over the past 70years have been a major factor in estab-lishing and maintaining United Statespreeminence in aviation. The Agency iscommitted to continuing an assertive,leadership role in developing the know-ledge base in emerging areas from whichimportant new advances and break-throughs in U.S. aircraft capabilitycan flow.

The recently established NationalAeronautical R&D Goals outline oppor-tunities for significant advances intechnology that will reshape civil andmilitary aviation by the turn of thecentury. The sequel report National

Aeronautical R&D Goals: Agenda forAchievement, released by the President'sScience Advisor in February 1987,presents a national strategy and eightconcrete actions for preserving America'sleadership and achieving the NationalGoals. They provide a sound roadmapfor addressing the exciting future possi-bilities in aeronautics which are as greatnow, if not greater, than at any time inthe history of aviation.

The 1986 Annual Report on theNASA Aeronautics Research and Tech-nology Program features the technicalaccomplishments and research high-lights of the past year and offers aglimpse of the exciting possibilitiesfor future research as we focus ourprogram in new directions.

Office ofAeronautics andSpace Technology

Pathfinder model in the National TransonicFacility


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ContentsForeword 1Introduction 5Vehicle Technology 11

Hypersonic 11Supersonic 14High Performance 15Subsonic 21Rotorcraft 27

Discipline Research 31Aerodynamics 31Propulsion 34Materials and Structures 39Information Sciences and

Human Factors 41Flight Systems/Safety 44

Organization and InstallationsSupportive Resources 54

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F-111 Mission AdaptiveWing


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Windunnelestofadvancedurboprop

Introduction

For the greater part of this century,NASA and its predecessor, NACA,have pioneered advanced technologyfor superior U.S. aircraft. This techno-logical superiority in aeronautics hasbeen attained through independent,far-term, fundamental research. Theproducts of this research have signifi-cantly benefitted the nation. In addi-tion to making a positive contributionto the trade balance and a secure na-tional defense, American aeronauticsis a symbol of this country's techno-logical strength.While U.S. aircraft still maintain abroad technology advantage, the mar-gin of that advantage has narroweddramatically in recent years. In agrowing number of aircraft related ar-eas, foreign technical capabilities arenow comparable, if not superior, tothose of the U.S. The implications ofthis change are important to thenation.

For the U.S. to retain world leader-ship in aviation into the next century,the nation must aggressively pursuethose technological opportunitieswhich will enable dramatic advancesin aircraft performance and capability.NASA, with the technical expertise ofits cadre of internationally acclaimedresearchers and its unique aeronauti-cal facilities, will have a pivotal rolein developing these emergingtechnologies.In recognition of the serious chal-lenge to America's world leadershipin aviation, NASA has maintained astrong commitment to aeronautics re-search and technology. The goal ofthe NASA program is to conduct ef-fective and productive aeronautics re-search and technology developmentwhich contributes materially to theenduring preeminence of U.S. civiland military aviation. This goal is

supported by comprehensive programobjectives which acknowledge andstrengthen NASA's central role inaeronautics research and technologydevelopment, and focus the researchefforts on emerging technologicalopportunities.

The first objective of the program isto maintain the excellence of NASA'sAeronautical Research Centers by re-pairing and replacing aging facilities,as well as developing additions andimprovements; advancing scientificand engineering computational ca-pabilities; and enhancing staff compe-tence through the selection of highlyqualified personnel and providingthem with challenging careeropportunities.

The second objective is to identifyand concentrate on those emergingtechnologies with potential for order-of-magnitude advances in aircraft ca-pability and performance. Theserevolutionary advances require abroad program of fundamental re-search that focuses on critical technol-ogies and accelerates technologyreadiness for future vehicles.

The third objective is to ensuretimely and efficient transition of re-search results to the U.S. aerospacecommunity through reports, confer-ences, workshops and active partici-pation of industry in contractual andcooperative programs.The fourth objective is to providetechnical expertise and facility supportto the Department of Defense, othergovernment agencies and U.S. indus-try for major aeronautical programs.

The fifth objective is to ensurestrong university involvement inNASA's program to broaden the baseof technical expertise and innovation.

A number of comprehensive stud-ies in recent years have endorsed the


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need for a dynamic and positivethrust in Aeronautics, and identifiedconceptual vehicles which serve to fo-cus technology development. The Of-fice of Science and Technology Policy(OSTP) chaired a multi-agency studygroup in 1982 whose detailed reviewof U.S. aeronautical R&T policies reit-erated the importance of aeronauticsto the nation, strongly emphasizedthe necessity for a research and tech-nology base to support the develop-ment of superior U.S. aircraft, and re-confirmed the roles of governmentagencies in aeronautics.

The Aeronautics and Space Engi-neering Board of the National Re-search Council conducted a workshopin 1984 that projected the state ofknowledge and capability in aeronau-tical technology areas through theyear 2000. This activity also providedvehicle concepts and applications intothe next century based on technologyand system advances.In 1985, OSTP established the Na-tional Aeronautical R&T Goals whichoutlined numerous opportunities fordramatic advances in technology thatcould reshape civil and military avia-tion by the beginning of the next cen-tury. The U.S. Air Force's Forecast IIStudy, released in 1986, reiterated theimportance of a strong commitmentto pursue technologies that could en-able a leapfrog of current military air-craft capability.

These recent studies have provideda vision of new generations of ad-

vanced civil and military aircraft thatcould supercede all current aircraft bythe turn of the century. NASA'sAeronautics Research and TechnologyProgram is focused on those emerg-ing technologies that will make thesevehicles possible. Potential vehicleapplications are described below andthe key or enabling technologies areidentified. In addition to vehicle spe-cific technologies, strong emphasis isbeing placed on fundamental disci-plinary research that addresses majortechnological opportunities which arebroadly applicable to all classes of air-craft or which will enable entirelynew systems or aircraft not yetdefined.Hypersonic Cruise/TransatmosphericVehicles: Fully reusable manned vehi-cles with horizontal takeoff and land-ing capability, able to cruise and ma-neuver into and out of theatmosphere and to provide rapid,long-range transport between inter-continental earth destinations. Thekey to these missions is developmentof air-breathing propulsion systemtechnology providing horizontal take-off, acceleration through the transonicand supersonic speed range, and sus-tained operation at hypersonic speeds.Other crucial technology challengesinclude actively cooled thermal struc-tures for peak and sustained heatloads, revolutionary concepts forhighly integrated airframe and pro-pulsion systems, and advanced com-putational methods to address thecomplex flow, structures and integra-tion phenomena associated with veryhigh speed vehicles.

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Long Range Supersonic Cruise: Passen-ger aircraft that feature transpacificrange at cruise speeds of two-to-fourtimes the speed of sound. The criticaltechnology challenges include vari-able cycle propulsion providing noiselevels acceptable to the communityand with a substantial reduction infuel consumption and extended-lifehigh sustained engine operating tem-peratures; reduction in airframe structures weight fraction; and increasingcruise lift/drag through improvedaerodynamics including supersoniclaminar flow.Supermaneuverable Aircraft: Tacticalaircraft capable of supersonic cruiseand maneuver throughout the speedrange with short take-off and verticallanding (STOVL) capability. The keytechnology challenges involve STOVcapability with minimum perfor-mance penalty, supersonic maneuver-ability, and effective low-speed con-trol at up to 90 degreesangle-of-attack.Transcentury Transport: An entirelynew generation of fuel efficient, af-fordable, technically superior sub-sonic transport aircraft. The key technology challenges involve reductionof fuel consumption with advancedturboprop propulsion systems; reduc-tion of viscous drag with laminar floand turbulence control; reduction ofstructural weight with advahced composite materials and concepts; andfully integrated flight controls and oerating systems that interface with aflexible and modernized National Aspace System.

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i Introduction

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Next Generation Rotorcraft: Quiet, jetsmooth, highly automated helicoptersand revolutionary new rotorcraft withunprecedented high speed capabilitiesfor both military and civil roles. Thetechnology challenges include reduc-tion of external noise and airframe vi-brations through validated predictionand design methods; reduction ofcrew workload in performing complexpiloting tasks through cockpit auto-mation and emerging concepts inman-machine interfaces; and integrat-ing new enabling technologies in ma-terials, controls, and aerodynamicsinto innovative configurations whichcombine the utility of the low diskloading rotor with the high speed ca-pability of a fixed wing.Fundamental Disciplinary Research:Technology areas with broad applica-tion to safety, efficiency and perfor-mance of a broad range of aircrafttypes or that have the potential to en-able entirely new aircraft systems.Goals for this research include: Validate computational methods

for analysis and prediction ofcomplex external and internalflows, structural mechanics, con-trol theoretics and their interac-tions to enable confident, practi-cal application for aircraft andengine design.

Provide design and validationmethods for highly reliable, inte-grated, and interactive control ofaerodynamics, structures, andpropulsion for optimumconfiguration.

Laser illumination of leading edge vortices

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Computer generated spatial grid systemfor vehicle aerodynamic flow calculations


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II Introduction

Develop technology for humanerror tolerant and computer-aided piloting systems and forwindshear modeling anddetection.

Develop methodologies to designsophisticated, intelligent auto-mated systems to enhance crewperformance of complex tasksand provide dramatic advances invehicle performance and agility.

Develop design methodologiesand life prediction modelingtechniques for advanced hightemperature materials such as ce-ramics, ceramic composites, car-bon carbon and metal matrixcomposites to enable their appli-cation in high-performance, un-cooled turbine engines.

Enhance aeronautical facility ca-pability by improving productiv-ity and integrity of major facilitiesand extending capability in criti-cal areas.

The far-term focus of the NASAAeronautics Research and TechnologyProgram is intended to provide re-sults well in advance of specific appli-cations and to provide long-term, in-dependent research and technologywhich is not driven by the develop-ment and operational pressures oftenencountered by the DoD and indus-try. Fundamental research in the tra-ditional aeronautical disciplines isemphasized in addition to research

directed at interaction among disci-plines, components, and subsystems.Ongoing and planned research in theredirected program will provide thetechnological foundation for securingand maintaining world leadership inaeronautics for the United States.

The 1986 Annual Report focuseson key technical accomplishmentsand research highlights of the NASAAeronautics Research and TechnologyProgram. The Report is divided intotwo principal sectionsmvehicle tech-nology and discipline research. Thevehicle technology section includesactivities that are focused on, orclearly applicable to, a particular classof vehicles. Frequently, this researchinvolves the testing of innovative sys-tems in a realistic environment. Aero-nautical discipline research includesactivities in the traditional areas ofaerodynamics, propulsion, materialsand structures, information sciencesand human factors, and flight systemsand safety. This research is aimed atestablishing and maintaining a solidfoundation of technology, embracingall of the relevant disciplines to pro-vide a wellspring of ideas, conceptsand emerging technologies to catalyzenew advancements in aeronautics.Brief descriptions of NASA's orga-nizational structure, unique facilities,university program, and the Aeronau-tics Advisory Committee are pre-sented in the concluding section ofthe report.


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Vehicle Technology

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HYPERSONICHypersonic TechnologyOne of the key technology thrusts ofthe aeronautics program being pur-sued by NASA is the technologyfoundation for hypersonic vehicles.The program focuses on vehicle con-figuration studies, propulsion, andmaterials and structures. Recentaccomplishments in these areas, com-bined with earlier progress in hyper-sonic research, established the foun-dation for the National Aero-SpacePlane (NASP) program. The NASPprogram, which is jointly funded byDoD and NASA, focuses technologydevelopment toward a flight researchvehicle, the X-30, which will be usedto validate and demonstrate the suc-cessful merging of aeronautics andspace technologies across the speedrange from takeoff to orbitalvelocities.

This merging of aeronautics andspace technologies into an aerospacevehicle powered by an airbreathingpropulsion system, provides the po-tential for an entirely new class of ve-hicles for the next century, rangingfrom hypersonic aircraft to a single-stage-to-orbit space transportationsystem. These vehicles would havethe ability to take off from and landon conventional runways, sustain hy-personic cruise flight in the atmo-sphere, or accelerate into space. Thetrans-atmospheric capability madepossible by this technology willgreatly enhance the operational po-tential of both military and civil air-craft and significantly cut the cost ofdelivering payloads to orbit.

National Aero-Space Plane concept11


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The technical challenges of anaerospace plane are formidable andthe list of essential technologies islong. During 1986, NASA addresseda number of the major technology is-sues with significant accomplishmentsin propulsion, high temperature struc-tures, and computational fluiddynamics.

One of the key enabling technol-ogies for an aerospace plane is in thearea of hypersonic propulsion. Test-ing in the Langley Research Centerwind tunnels has demonstrated thatmeasured thrust levels of a supersoniccombustion ramjet (SCRAMJET) en-gine module, the system required forairbreathing propulsion above Mach6, agreed well with theoretical predic-tions for airframe integratedSCRAMJET engines. Using theseground facility data, projections madeto flight indicated that thrust signifi-cantly greater than vehicle drag canbe achieved at both Mach 4 andMach 7.

Successful experimental and analyt-ical progress on variable geometrySCRAMJET configurations wasachieved with the successful testing ofthe variable geometry inlet configura-tion at Mach 4. Companion analyticalprogress was achieved with thedevelopment of a Navier-Stokes flowanalysis for the transition section ofthe engine combustion section forcross-section changes from square tocircular. A square inlet configurationwould permit integration with the ve-hicle contours while a circular com-bustion section would reduce struc-tural complexity at high pressures.This configuration reduces the com-plex integration problems associated

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Variable geometry SCRAMJET engine inlet

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with SCRAMJET propulsion systemswhich use the underside of the vehi-cle for airflow compression prior toentering the inlet. These 1986 accom-plishments are significant steps inachieving a hypersonic propulsionsystem that can be operated over abroad range of speed-altitudecombinations.In related engine structures re-

search, an advanced technology fuelinjection strut for the SCRAMJET en-gine was fabricated in 1986 using acomplex brazing process. Two short-ened versions of a full-size flight-weight article were successfully as-sembled. This effort demonstrated thefeasibility of this design approach and

preparations are now underway totest the strut assembly with burningfuel in the Langley Research Centerpropulsion test facilities.

Accomplishments in aerothermalairframe structures also includedprogress with a promising concept

, under investigation for the fabricationof load-carrying honeycomb panelshigh-temperature super-alloys. Apanel array of super-alloy honeycombmaterial was successfully tested in1986 in the Langley Research CenterHigh Temperature Tunnel uhder hy-personic flow conditions.

The development of an optimumintegrated vehicle design through thintegration of a hypersonic propul-sion system with the airframe de-mands unprecedented technologicalsophistication. NASA's Numerical


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Hypersonic Facilities Complex, LangleyResearch Center

I Vehicle Technology

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Aerodynamic Simulation capability,now in operation, provided vital sup-port to the technology developmentprogram by enabling the calculationof the complex flow fields for variousaerospace plane configurations. Thiscapability to provide solutions ofNavier-Stokes equations that definethe air flow around NASP configura-tions at high Mach numbers allowsanalysis and prediction of vehicleaerodynamic loadings and aero-ther-modynamic interactions at Machnumbers beyond the capability of ex-isting ground test facilities.

cepts. In addition, the facilities areused to perform basic fluid mechanicsstudies, to establish data bases forverification of computer codes, and todevelop measurement and testingtechniques. The research in aerother-modynamics, structures, and propul-sion technologies requires unique fa-cilities that simulate the high energyenvironment of hypersonic flight.Small-scale tests for screening poten-tial propulsion system component de-signs are performed in a Mach 4blowdown tunnel. In addition, theMach 4 and the Mach 7 SCRAMJET

Test Facilities at the Langley ResearchCenter provide free-jet tunnel flow forsubscale SCRAMJET engine tests.

Two major facilities are also beingmodified to expand NASA's hyper-sonic testing capabilities: the 8-footHigh Temperature Tunnel at theLangley Research Center foraerothermal structures testing and forlarge-scale and multi-module air-frame-integrated SCRAMJET tests,and the Propulsion Systems Labora-tory (PSL) at the Lewis Research Cen-ter for subsonic and supersonic pro-pulsion systems tests.

Hypersonic FacilitiesNASA hypersonic facilities representa major, and unique, national asset.These facilities range in Mach Num- ......ber capability from Mach 6 to Mach20. The Hypersonic Facilities Com-plex at Langley Research Center in-cludes the Hypersonic CF 4(tetraflouromethane) Tunnel with aMach 6 capability, the Mach 6 HighReynolds Number Tunnel, the 20-inch Mach 6 Tunnel, the Mach 8Variable Density Tunnel, the 31-inchMach 10 Tunnel, the Hypersonic Ni-trogen Tunnel (Mach 17), and the Hy-personic Helium Tunnel and its openjet leg (Mach 20). Key hypersonic fa-cilities at the Ames Research Centerinclude the 3.5 Foot Tunnel, arcjets,and High Enthalpy Facility.

These NASA hypersonic test facili-ties are used to study the aerody-namic and aerothermal phenomenaassociated with the development ofadvanced aerospace transportationsystems, including trans-atmosphericand hypersonic transport vehicle con-

Fuel injection strut for SCRAMJET engine

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SUPERSONICIt has been 24 years since the 1962 An-glo-French agreement to build the Con-corde was signed. On January 21st of1986, the Concorde fleet completed 10years of active commercial service. Tenyears is long enough for the novelty tohave worn off, yet it is evident that thereis a steady demand for high speed trans-portation, even at premium fares.During 1986 NASA continued several

technology efforts that are applicable tosupersonic aircraft. These include researchin aerodynamics, materials and structures,propulsion, and systems.In aerodynamics, much of the appli-

cable research was focused on reducingdrag to provide more efficient sustainedsupersonic cruise capability for militaryaircraft. This involves tailoring the con-figuration to reduce wave drag, interfer-ence drag, and induced drag and surfacechanges to reduce friction drag and reducesurface heating. Increased effort is beingaimed at determining the feasibility forlaminar boundary layer flow retention atsupersonic speeds. During the past year,the first exploratory flight tests were con-ducted on an F-106 aircraft at Langley Re-search Center to develop instrumentationfor research on skin friction dragreduction.

In materials and structures, research ef-forts have concentrated on the develop-ment of advanced composite and ceramicmaterials for the high-temperature envi-ronment in the engines and on the air-

frames of high speed vehicles. Studies areunderway that indicate major improve-ments are possible for supersonic aircraftengines by the application of advancedhigh-temperature materials. In propulsion,research efforts have been initiated to in-vestigate the feasibility for supersonic fansin future supersonic aircraft turbofanengines.In systems, research efforts are under-

way to develop automation technology in-corporating artificial intelligence to im-prove the operational efficiency and safetyof all aircraft. This can be particularlyvaluable for future high-speed transport

aircraft because of their large fuel and rel-atively small payload fractions.This year, in order to better focus

NASA's technology efforts, two majorcontracted studies were initiated withBoeing and McDonnell-Douglas to exam-ine the opportunities for new high-speedcivil transport aircraft. These studies willevaluate conceptual designs ranging inspeed capability from new supersonictransports to "Orient Express" hypersonictransports. The studies will evaluate thetechnical feasibili ty and economic viabilityof these conceptual designs and identifythe crit ical technology requirements.

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Supersonic cruise transport aircraftconcept

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F-111 Mission Adaptive Wing (MAW)aircraft

II Vehicle Technology

HIGHPERFORMANCENASA's high performance aircraft re-search program is an integral and criticalpart of the overall aeronautics programthat is structured to develop and maturetechnologies that have important militaryand civil applications. NASA and the mili-tary, historically, have worked closely to-gether to identify and develop aeronauti-cal technologies which require flightresearch to fully explore, validate, andmature the technologies for application ina military aircraft. These technology pro-grams are carefully selected to demon-strate a significant improvement in perfor-mance or to show a new capability thatpotentially has high payoff.NASA has also traditionally had a rolein applying its knowledge, people and fa-

cilities to assist the military in solvingchallenges encountered with operationalaircraft. Finally, it should be recognizedthat certain synergies exist between themilitary and civil technology develop-ments. The military strives to expand theperformance envelope while the civil sec-tor tends to concentrate on lower produc-tion costs, maintainability, and high reli-ability. This in turn results in militaryaircraft being more affordable and civilaircraft having increased performance.Mission Adaptive WingThe joint NASA/Air Force Mission Adap-tive Wing program has produced results

in 1986 which will directly enhance mili-tary and civil aircraft capabilities. Thevariable camber wing technology offersthe potential for significant aerodynamicimprovements when compared with cur-rent fixed-airfoil technology. Increasedrange of up to 25 percent, increased op-erating ceiling by 15 percent, and in-creased sustained maneuver capability of20 percent are achievable. The F-111 air-craft, one of a number of high perfor-mance military testbed aircraft on loan toNASA, was modified to incorporate aflexible wing surface structure allowingthe implementation of the variable cam-ber wing concept.

Supporting ground based research andanalytical studies indicated that if a wing'sairfoil shape could be adapted to a widerange of mission flight conditions, a sig-

nificant overall improvement in perfor-mance could be achieved. Phase I flighttests of the manual flight control systemwith the Advanced Fighter TechnologyIntegration (AFTI/F-111) aircraft havebeen completed. The next phase of testingis now underway using automatic, in-flight adjustment of variable camber basedon measured flight conditions.

The Phase I flight tests cleared theflight envelope to Mach 1.3 at an altitudeof 40,000 feet. Performance data were ob-tained which agreed with predictions. Inaddition, airfoil pressure distribution mea-surements were obtained and they com-pare well with wind tunnel data. The ini-tial checkout of a deflection measurementsystem, which is used to measure theshape of the wing in flight, was accom-plished. Structural load distributio_charateristics have also been determinedand compared with analytical predictions.

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High angle-of-attack free flight model in 30-by 60-foot Wind Tunnel

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SupermaneuverabilityIn 1986, high angle-of-attack flight tech-nology for high performance aircraft wasaccelerated. The area of interest was thebehavior of these aircraft configurations atangles-of-attack approaching 90 degrees(also referred to as high-alpha flight).Achieving stable and controllable flight atthese angles to the free stream airflow of-fers the potential for dramatic payoffs inagility, performance, and safety. Collec-tively the technology is referred to as"supermaneuverability."Unprecedented high angle-of-attack, or

"high-alpha," capabilities utilizing propul-sive control concepts were demonstratedwith free-flying models and simulationstudies. The key to this achievement wasthe advancement in propulsive flight con-trol technology that couples the propul-sion system and flight control in a quickresponse, integrated system.Free flight model tests in the Langley

Research Center 30- by 60-foot WindTunnel using an F-18 with propulsiveflight control confirmed the ability toachieve incredibly stable performance andfull maneuverability at an 80-degree nose-up angle-of-attack relative to the oncom-ing airstream.The wind tunnel model and simulationinvestigations were complemented by ex-perimental and computational analyses offorebody flows and vortex flows to studythe aerodynamics of high-alpha flight.Water tunnel model tests of the F-18 con-figuration conducted at the Ames Re-search Center, Dryden Flight Research Fa-cility confirmed that, by making flowinjections in the airstream near the noseof the aircraft, the vortex flow over the

vehicle can be altered to achieve favorableaerodynamic changes and overall dragreduction.Additional flow investigations were car-

ded out in July 1986 in the Langley Re-search Center 4-by 7-Meter Wind Tunnel.Oil flow patterns on an F-18 model illus-trated that the inherent aerodynamic flowasymmetry in the region of the tip of theaircraft nose at high angle-of-attack playsa key role in the loss of control. Furtherresearch in the understanding and controlof this flow characteristic will offer signifi-cant payoff in the ability to design forhigh-alpha flight.Preparations are now underway to con-

duct a full-scale flight research programutilizing a modified Navy F-18 aircraft.Initial flights began in the fall of 1986with the emphasis on acquiring aerody-

F-18model water tunnel flow studies

Oil flow studies of F-18at high angle-of-at-tack in 4- by 7-Meter Tunnel

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namic data for correlation with wind tun-nel results. Next, conceptual designs willbe tested for a thrust vectoring system forthe F-18 research vehicle. Modification ofthe research aircraft with such a systemwill allow full-scale flight verification ofwind tunnel results.Vertical and Short Take Off and Land-ing TechnologyAdvances in propulsion system thrust-

to-weight ratios, propulsive lift control,and the understanding of low speed aero-dynamics combine to open new opportu-nities for state-of-the-art advances in ver-tical and short take off and landing (V/STOL) aircraft technology, as well as fornew short take off and vertical landingaircraft (STOVL) concepts.The United States and the United King-dom signed a joint research agreement in1986 to foster collaboration in the devel-

opment of advanced STOVL (ASTOVL)technologies aimed at reducing the tech-nological risk associated with potentialASTOVL aircraft development. The twocountries have agreed upon a conceptualevaluation model to be used to assess dif-ferent concepts. During 1986, NASA per-formed an internal evaluation of four air-craft configurations: vectored thrust,ejector augmentation, tandem fan and re-mote augmented lift propulsion. In a re-lated 1986 activity, NASA entered into anagreement with Canada to build and testa full-scale STOVL wind tunnel model.The model, an E-7 transonic aircraft con-figuration, utilizes an ejector thrust aug-mentation system for low speed STOVLoperations.As part of the continuing V/STOL

technology program, the Ames ResearchCenter conducted wind tunnel tests of a1/10 scale E-7 V/STOL fighter at Machnumbers ranging from 1.6 to 2.2. Thegenerally favorable agreement of predic-

E-7V/STOL aircraft wind tunnel model

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I VehicleTechnolo

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tions and high speed test results for the E-7 confirmed the aerodynamic viability ofthe design as a high performance fighteraircraft. The tests also resolved many un-certainties and established a large, com-prehensive design base for realistic V/STOL configurations.Oblique Wing TechnologyAchieving efficient flight performance atboth high and low speed has been a chal-lenge to aircraft designers. The obliquewing concept offers the promise of meet-ing this challenge for high performanceaircraft. The concept, first envisioned over40 years ago, incorporates a wing that

pivots in to form oblique angles with theairplane's fuselage in high speed flightforming a low aspect ratio wing configura-tion to minimize drag. The wing is posi-tioned in a high aspect ratio position atright angles to the fuselage during takeoff and landing and low-speed flight.

Precursor research, analytical studies,wind tunnel investigations, and prelimi-nary flight tests with the low speed AD-1research aircraft have provided the confi-dence and data base required to constructand flight test a full scale vehicle based onthe NASA F-8 flight research aircraft in ajoint NASA/Navy program. In 1986 thepreliminary design was completed for a300 square-foot aeroelastically tailored

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F-8 obliquewing technology demonstratoraircraft illustration.....................................

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X-29 Forward Swept Wing aircraft

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wing for the F-8 oblique wing demonstra-tion. The subsequent detail design, fab-rication and aircraft modification will leadto flight validation of the concept at su-personic speeds.Forward Swept Wing TechnologyIn 1980, NASA, Air Force and the De-fense Advanced Research Projects Agencyembarked on designing, building and test-ing a forward swept wing fighter class air-craft. This design was projected to offerboth performance advantages and a newoption in configuration integration. At thesame time, the opportunity was seized totest several other emerging technologiesof high potential. These included relaxedstatic stabil ity; three surface longitudinalcontrol; aeroelastically tailored, composite,thin supercritical wing; close coupledwing and canard; and digital flight controlsystem. The successful integration ofthese technologies was demonstrated in1986 as the flight envelope expansionprogram was completed.During the envelope expansion flight

program, preliminary research data wereacquired that validated the performancepredictions at the design flight conditions.Detailed engineering data have been col-lected by each of the engineering disci-plines for correlation, comparison and im-provement of prediction methodology.Major new test and analysis techniqueswere developed including the ability to dodetailed flight controls analysis in realtime and the ability to extract stability andcontrol derivatives from a highly unstableaircraft. Predictions of structural loadswere verified throughout the flight enve-lope which included high speed, high dy-namic pressure, operating conditions.

Improvement of Operational AircraftFrequently, at the direct request of themilitary services, the expertise and facili-ties of NASA are utilized to solve tech-nical problems and develop improve-ments for operational military aircraft.In 1986, at the request of the Navy,

NASA developed and tested aerodynamicmodifications that provide options for sig-nificant improvement in the safety and ef-fectiveness of the EA-6B aircraft. As theEA-6B configuration evolved from the1960's, A-6 aircraft weight increased fromthe original 36,000 pounds to 55,000pounds without a corresponding increasein wing area. This degradation in maneu-ver margin has contributed to the air-craft's high accident rate.

NASA completed wind tunnel studiesof the EA-6B configuration in the LangleyResearch Center National Transonic Facil-ity. The results of the tests in this uniquefacil ity formed the basis for recommendedconfiguration modifications which includethe addition of a small vertical tail exten-sion, addition of a wing root/body strake,and an airfoil leading and trailing edgemodification. These modifications im-prove the EA-6B lift at low speed and in-crease the directional stability at high an-gles of attack, thus reducing stall/spintendencies. The Navy is currently initiat-ing an EA-6B test program to evaluate therecommended modifications in flight priorto incorporating them into the aircraftfleet.

SUBSONICNASA works closely with manufacturers,airlines, and the Federal Aviation Admin-istration to advance the technology forsubsonic transport aircraft. This close rela-tionship is essential to the timely intro-duction of new technology to assure theUnited States retains its preeminent posi-tion in this important world market. Theresearch activities in the subsonic pro-gram are coupled directly to technologyapplication programs in industry. In thisway the timely transfer of research resultsto new aircraft developments is enhancedin keeping with current aeronautical re-search and technology policy.

A major goal of the subsonic transportprogram is to establish the technologythat will enable the doubling of the fuelefficiency of today's best transport aircraft,while substantially increasing their pro-ductivity and affordability.Advanced Turboprop ProgramA number of accomplishments in ad-vanced turboprop research directed to theimprovement of subsonic transport pro-pulsion system efficiency were realized in1986. Earlier analysis and wind tunnelstudies clearly showed the potential to use15 to 30 percent less fuel while maintain-ing cruise speed, cabin comfort and noiselevels of current comparable turbofantransports. Lewis Research Center aug-mented both analytical and expe_mentalpropfan research in support of increasedindustrial activity in the advanced turbo-

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Propfan Test Assessment (PTA) aircraftmodel in the 4- by 7-Meter Wind Tunnel

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_fNAL PAGE'_0" " TOGRAPH

Large scale propfan ground test

IIVehicle Technology

OR_G_NAE PAGECOLOR PHOTOGRAPH

.......

prop area in 1986. This effort includedboth counter-rotating propellers and drivesystems. Full scale advanced turbo-proppropulsion system ground testing andflight demonstration activities were begunby NASA and industry in 1986.The objective of the NASA Propfan

Test Assessment (PTA) program is to con-duct flight tests to verify blade structures,aerodynamics, and acoustics prediction ca-pability. In preparation for the flight testproject, a 1/9-scale model of the PTA air-craft configuration was tested in the Lang-ley Research Center 4- by 7-Meter WindTunnel during August, 1986. The windtunnel data verify the safety-of-flightaerodynamics and that theoretical designand analysis methods predict the nacelleand nacelle/slipstream flow with suffi-cient accuracy for design purposes.The PTA wind tunnel results also de-fined the extent to which the installationof a propfan on a complete aircraft con-

figuration affects the aerodynamic perfor-mance. In addition, the speed/altitude ca-pability and buffet margins were definedfor the PTA aircraft. The analytical codefor predicting aircraft flutter characteristicswas also verified in high speed wind tun-nel testing.

Ground testing of a large scale (nine-foot diameter) propfan was also com-pleted in 1986. The aerodynamic resultswere close to those predicted, thus satisfy-ing ground testing requirements prior toflight evaluation of the structural andaerodynamic characteristics of the propfaninstallation on a Gulfstream II twinjettransport.

During 1986 significant progress wasachieved in the joint NASA/General Elec-tric Unducted Fan (UDF) program. Thisadvanced turboprop concept incorporatestwo unducted, counter-rotating fans witheight highly swept blades on each fan.Studies have shown that two counter-ro-

Unducted Fan (UDF) turboprop propulsionsystem


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24

tating fans can totally eliminate the wakeswirl that exists in single fan designs. Theswirl elimination results in an 8 percentincrease in propulsion system efficiency.The UDF system was successfully groundtested in preparation for flight testing.The 100-hour ground test demonstratedthrust levels of over 25,000 pounds withacceptable engine vibration and propfanstress levels.

Both near-field and far-field noise mea-surements-taken over a range of tipspeeds, power settings, and blade sweep-indicated that significant noise reductionswere achievable, and projections indicatethat the counter-rotating propeller designsshould meet community noise levelrequirements.First flight tests of the UDF on a modi-

fied Boeing 727 were completed success-fully in August, 1986. In-flight perfor-mance and acoustics evaluations wereconducted. Currently, General Electric, inconjunction with McDonnell Douglas, ispreparing for additional flight evaluationon a modified McDonnell Douglas MD 80aircraft.

lent flow over airfoils can be achieved bya favorable pressure gradient stabilizationknown as natural laminar flow (NLF), orby a small amount of surface suctionknown as laminar flow control (LFC), or acombination of these known as hybridlaminar flow control (HLFC). The tech-nical challenge is to devise a means formaintaining the smooth flow as far alongthe surfaces as possible and delaying thetendency for the flow to transition fromlaminar to turbulent flow. During 1986,these laminar-flow concepts were investi-gated with promising results.Recent NLF airfoil research in the Lang-

ley Research Center Low-TurbulencePressure Tunnel (LTPT) demonstratedthat extensive natural laminar flow can bemaintained over properly designed airfoilsurfaces at design lift conditions, resultingin profile drag reductions of 33 percent.A full size proof-of-concept wing incor-

Aircraft Drag ReductionReducing viscous drag caused by skinfriction is a key objective in aerodynamicsresearch since it accounts for roughly one-half of an aircraft's total drag when flyingat normal cruise speed. Laminar boundarylayer flow and turbulence control tech-niques can significantly reduce viscousaerodynamic drag, thereby contributing tooverall aircraft drag reductions of up to 40percent.

Laminar Flow: A promising approach toachieving reduced drag is to sustainsmooth, non-turbulent (laminar) flow inthe layer of air in contact with the aircraftairfoil and fuselage surfaces. Non-turbu-

Full scale natural laminar flow (NLF) winginstalled on Cessna 210 aircraft

ORIGINAL PAGEOOLOR PHOTOGRAPH

Flight test of UDF on modified Boeing 727aircraft

porating the new NLF airfoil was de-signed by the Langley Research Centerand fabricated by Cessna. Wind tunneland flight tests in 1986, utilizing a Cessna210 aircraft, confirm that the airfoilachieves natural laminar flow over 70%of the upper and lower surfaces over abroad range of operating conditions. Theaircraft cruise speed increased 14 knots atthe same power setting, which is the ulti-mate demonstration of improved aerody-namic efficiency.

Another NLF accomplishment in 1986was the successful flight testing of a con-toured glove installed on the wing of aBoeing 757 aircraft in the region of intenseacoustic radiation from the turbofan en-gine. The flight tests confirmed that thedesired laminar flow can be maintainednot only in a quiet environment but alsoin close proximity to engine noise.Recent NASA research in laminar flow


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Laminar flow control (LFC)installation onJetstar wing

control (LFC) indicated that significantamounts of laminar flow may be sus-tained on wing surfaces having a moder-ate sweep angle, typical of commercialtransports. In order to verify this potentialin flight, laminar flow control gloves withsuction through tiny slots or perforationswere installed on the leading edge of thewings of a JetStar aircraft to investigatetheir effectiveness. The 1986 flight testingconfirmed the technique and demon-strated that laminar flow over the criticalleading edge of the wing could beachieved without undue maintenanceburden while operating in a typical airlineenvironment. This was particularly note-worthy because of earlier concerns that in-sect and other airborne debris might de-grade the suction surfaces of the laminarcontrol system.Laminar flow control research accom-plishments in 1986 set the stage for thenext phase of research which will concen-trate on hybrid laminar flow controlcombining the best features of active lam-inar flow control and natural laminarflow to achieve significant drag reduc-tion with less system complexity.Turbulent Flow: Research in turbulencecontrol encompasses techniques such aslarge eddy break-up (LEBU) devices andriblets, whose small streamwise groovesinhibit the lateral spread of small turbu-lent eddies. These concepts have the po-tential of reducing turbulent skin-frict ion-drag on surfaces where laminar flow isdifficult to achieve. These techniqueshave progressed through the laboratorydevelopment phase to the point of beingready for flight validation. In 1986 windtunnel tests the drag reduction associatedwith LEBU devices and riblets was dem-onstrated to be additive. Also, computa-tional fluid dynamic codes were devel-oped to predict the flow physics of bothdevices.

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JetStar aircraft with laminar flow control(LFC) wing glove installed for flightinvestigation

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ROTORCRAFTThe nation's continued leadership in mili-tary and civil rotary wing technology de-pends on a strong and broad-based re-search program. NASA, in cooperationwith other government agencies and in-dustry, carries out a rotorcraft programthat addresses fundamental research inaerodynamics, structural dynamics, acous-tics, guidance, stability and control, pro-pulsion and drive, and human factors.This research is conducted through an-alytical and experimental programs whichfocus on critical areas of technologicalneed in order to exploit the full potentialof this unique vehicle class.The U.S. Army and NASA work hand-in-hand on rotorcraft research. This is

made possible by an arrangement of col-located Army laboratories at the NASAaeronautical research centers. Joint pro-grams with the Defense Advanced Re-search Projects Agency (DARPA), theFederal Aviation Administration, and theU.S. helicopter industry result in a con-structive and closely coordinated nationalresearch effort in rotorcraft technology.In 1986 there were a number of signifi-

cant accomplishments in the areas of re-duced noise, improved rotor performance,enhanced flying qualifies, and high speedperformance. Reducing rotorcraft noise isessential to secure community acceptanceand to reduce military detectability. Noisereduction has received special emphasis

with the research cooperation achieved byNASA, the United States rotorcraft indus-try (under the umbrella of the AmericanHelicopter Society), the U.S. Army, theFederal Aviation Administration, and theHelicopter Association International. As aresult of this unique cooperative programa new helicopter total system noise pre-diction code called ROTONET has beendeveloped and made available to industryin its initial operational phase.

A major rotor system noise experimentwas completed in 1986. The experimentmeasured rotor broadband noise sys-tematically over a range of conditions in acontrolled environment for the first time.The results of this broadband test are be-ing included in ROTONET. In addition,comprehensive blade-vortex interaction(BVI) data were obtained that will enablethe development of a semi-empirical BVInoise methodology.A promising tool for significantly reduc-ing the internal noise caused by helicoptertransmission was developed. This tool is acomputer program for gear tooth contactanalysis and determination of gear cuttingmachine parameters that will provide spi-ral bevel gears with zero kinematic error.Transmission gears produced with thiscode will operate with less vibration,leading to more reliable, longer life andquieter transmission designs.A major rotor system improvement was

demonstrated in 1986 with the use of anadvanced rotor blade design tested on ascale model UH-60 rotor. The modelblade utilized advanced airfoils, a uniqueplanform shape, a high degree of twistand aeroelastic tailoring to increase rotorperformance and reduce vibration. Thewind tunnel tests showed such a signifi-cant performance improvement, especiallyat high altitude, that the U.S. Army is se-riously evaluating this blade design as aproduct improvement for the UH-60Blackhawk helicopter.In the area of flying qualifies, a cooper-

ative program with the U.S. Army utiliz-ing the CH-47 variable stability researchhelicopter and ground based simulatorshas resulted in a major update to the out-dated mili tary specifications for rotorcraftflying qualifies with a focus on theArmy's light helicopter (LHX) program.This research will continue with a goal ofcompletely redefining flying qualifies cri-teria for new helicopters.Increased forward flight speed is a tech-

nology focus which leads to new and in-novative configurations such as the TiltRotor and the X-Wing. By converting froma pure helicopter mode to a more efficientwing-lift mode, it is possible to double, oreven triple, rotorcraft cruise speeds,thereby vastly improving the productivityof rotorcraft. Other benefits of higherspeed wing-borne flight include reducednoise and vibration, and enhanced mili-tary effectiveness.

Scale model UH-60 rotor in TransonicDynamics Tunnel2


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RSRA/XTWjngflight research aircraft

A significant advancement was made intilt rotor research in 1986. An experimentwas conducted applying circulation con-trol to the trailing edge of a tilt rotor wingwhich was enmeshed in the downwardflow from the hovering proprotors. Theresults verified analytical calculations thatthe downward force on the wing can bereduced by 25 %, making possible promis-ing design alternatives for future tilt rotoraircraft which will enable more efficienthigher forward flight speeds.

An important rotorcraft milestone wasreached in August 1986 with the comple-tion of the fabrication and assembly ofthe Rotor Systems Research AircraftRSRA/X-Wing research vehicle. The X-Wing rotor is a four-bladed, extremelystiff, rotor system utilizing circulation con-trol aerodynamics for lift and control. Inhover and low speed flight the rotor sys-tem rotates as a conventional helicopterrotor. In high speed forward flight the ro-tor rotation is stopped and a fixed X-Wingconfiguration results. The RSRA/X-Wingvehicle was shipped to Dryden Flight Re-search Facility at Edwards Air Force Base,California to begin preparation for flightresearch.

This joint DARPA/NASA programcontinues the effort to advance the state oftechnology in high speed rotorcraft flightand in several other key technology areas.The X-Wing rotor is a fully composite ro-tor/wing which incorporates the thickestload beating composite structure everbuilt. In addition, the quadraplex flightcontrol system has over 60 control effec-tors controlling complexpneumodynamics, and circulation controlaerodynamics.

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ORIGINAL PAGECOlOR PHOTOGRAI_

The potential national benefits of tilt ro-tor technology are being assessed in a

i joint study initiated in 1986 by NASA! with the Department of Transportation

and the Department of Defense. Thei study will document economic factors re-i !ated to civil tilt rotor development, the

base of the V-22and follow-on tilt rotor programs, emerg-and potential designs toaccommodate them, and the effects on

the National Airspace System.

XV-15 Tilt Rotor Research Aircraft flightdemonstration in New York City

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ORIGINAL PAGE'C-Ot..OR PP_TO_RAPH Discipline Research

AERODYNAMICSThe increased emphasis on technologythrusts that are responsive to new aero-nautical opportunities and national needshas led to the pursuit of aerodynamics re-search tasks that focus on innovative an-alytical techniques, unconventional air-craft configurations, new operatingregimes, and more sophisticated instru-mentation and testing techniques.The NASA disciplinary research in

aerodynamics is a tightly interwoven pro-gram of theoretical analyses, numericalsimulation, wind-tunnel testing, instru-mentation and where necessary, flight re-search. The basic, on-going, research un-derlies and enables the advancement ofaeronautical vehicles through the applica-tion of new technology.Major emphasis is being placed on thedevelopment and application of computa-

tional fluid dynamics for the prediction ofcomplex aerodynamic phenomena. This ismade possible by the rapidly growingsupercomputer capabilities now available.Computational Fluid DynamicsWith the increasing availability ofsupercomputers, the discipline of com-putational fluid dynamics (CFD) is nowproviding powerful analytical, simulation,and predictive tools to address the basicphysics of aerodynamic flow fields. NewCFD tools are being used to advance theunderstanding of the complex flow envi-ronment of advanced aircraft configura-tions and to permit aerodynamic optimi-zation of the new aircraft designs.During 1986, significant progress was

achieved in CFD techniques. Computa-tions are now possible for three-dimen-

Computer generated flow stream tracelines over F-16 aircraft configuration


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ORIGINAL PAGECOLOR PHOTOGRAPN

sional, viscous compressible flows con-taining separated flow regions whereas,previously, only simple aerodynamicflows for complex configurations weresolvable.Thus, the computation of flow over re-

alistic wing-body combinations are nowpossible. As an example, the new tech-niques were used at the Ames ResearchCenter to calculate the streamlines overan F-16 high performance aircraft configu-ration utilizing a new 3-D grid scheme.This accomplishment marked the firstcomplete flow field solution for viscous 3-D flows around an actual aircraftconfiguration.

The new CFD techniques were alsoused in 1986 in support of the NationalAero-Space Plane (NASP) effort. BaselineCFD calculations of pressure contours onthe vehicle surfaces and in the surround-ing flow field were performed. Achievingthe solution of Navier-Stokes equations athigh Mach number forms the base for fu-ture analysis and predictionefforts in support of NASP. This is espe-cially important in the investigation of ve-hicle aerodynamics and aerothermo-dynamics where ground test facilities arecurrently inadequate.

Successful computations of hypersonicwing/body surface pressure contourswere also performed in 1986. These CFDcalculations were carried out for a flightenvironment of Mach 25, a 5 degree an-gle of attack and a 3000 degree R walltemperature.

The rapid advances in supercomputertechnology are directly responsible for thenew progress in CFD. A major 1986 mile-stone in CFD supercomputer capabilitywas the opening of the Numerical Aero-dynamic Simulation (NAS) facility at theAmes Research Center on July 21. Thenew facility will be fully operational inMarch of 1987. The NAS currently uti-lizes a Cray-2 supercomputer having amemory of 256 million words. Future

plans at NAS are to continue its pathfind-ing role in state-of-the-art computer sys-tems as a requisite for pioneering aerody-namics research and development.Combined DoD/NASA programs requir-ing secure processing are also planned.

In a related activity, a complete end-to-end, high-speed mainframe computernetworking subsystem, utilizing the Pro-gram Support Communications Network(PSCN) as the communications medium,was implemented in 1986. In addition toproviding access to the Amessupercomputers, the PSCN provides ageneral purpose network to allow centerusers to interface with the computer main-frames as a total system. The ComputerNetworking Subsystem (CNS), which is

one of PSCN's services, is designed to ex-change large bulk files between largemainfame computer facilities located atAmes Research Center, Dryden Flight Re-search Facility, Langley Research Center,and Lewis Research Center. The CNS isintended to improve the effectiveness andproductivity of large mainframe comput-ers in support of the aeronautics researchand technology program.The CNS began operation in March of1986 at the transmission rate of 56

kilobaud and has been upgraded to itscurrent 224 kilobaud rate. During the on-going development the satellite networkis being heavily used to provide LangleyResearch Center with access to the Cyber205 located at the Ames Research Center.

Numerical simulation of hypersonic aircraftconfiguration surface pressure map

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tion utilizing liquid crystal technique

m Discipline Research

Experimental Aerodynamics and TestTechniquesThe National Transonic Facility (NTF) atthe Langley Research Center plays an im-portant role in experimental aerodynam-ics. This cryogenic wind tunnel facility al-lows true simulation of full-scale flightReynolds number. This capability makespossible the independent investigation ofcompressibility, viscosity andaeroelasticity effects_a powerful newtool in validating new computationalcodes. The NTF has been utilized in"problem-solving" testing as well as re-search investigations. Extensive tests wereconducted on an EA-6B aircraft modelwhere low speed stability and lift wereimproved significantly. This tunnel hasalso provided data which aided in thevalidation of existing CFD codes. An ex-ample of this was the favorable compari-son of data taken on the Pathfinder I ge-neric transport model with a shock waveprediction code.The recent completion of the Fluid Me-

chanics Laboratory at the Ames ResearchCenter is a major new capability for theexperimental aerodynamics program. Thislaboratory contains a number of small re-search facilities that are used for funda-mental fluid physics investigations. The-ory and experiment are being closelyintegrated in this environment in studiesin turbulence modeling, vortex flow, highangle-of-attack flows, and other complexfluid phenomena. This facility will pro-mote cooperative activities with the uni-versity community, the aerospace indus-try, and with other government researchorganizations.Another advancement in experimental

test techniques was achieved in 1986 withthe initiation of operations of the adaptivewall pilot wind tunnel at Langley Re-search Center. The adaptive wall tunnelhas greatly improved transonic wind tun-nel test fidelity by eliminating wall distur-

EA-6B aircraft model in National TransonicFacility (NTF) cryogenic wind tunnel

bances which would otherwise propagatetoward the model, distorting test condi-tions, and compromising test accuracy.Three airfoils were tested in 1986_a cali-bration airfoil (NACA 0012), and two ad-vanced airfoils developed by Boeing.The application of laser holography ad-

vanced significantly in 1986. Using sev-eral laser beams focused at a point, thefirst non-intrusive detailed measurementof a rotor flow field was made. Using thistechnique and automatically scanning theflow under a helicopter model in theLangley Research Center 4-by 7-MeterTunnel, the first comprehensive measure-ment of the rotor downwash wasachieved. This database is an importantcontribution to the understanding and

prediction of rotor loads, noise, andvibration.Important progress was also achieved

in the use of liquid crystal coatings tostudy boundary layer behavior in flight.The key to the technique is the tendencyof the liquid crystal to change color in re-sponse to changes in shear stress and tem-perature. In 1986 a Learjet 28/29 wasused to successfully develop the liquidcrystal technique for in flight boundarylayer investigations. Using liquid crystalcoatings, the boundary layer transition ona winglet of the Learjet was displayed inflight at 300 knots and 50,000 ft. altitude.The significance of this achievement wasthat it demonstrated the first method forhigh-al-titude, cold temperature boundarylayer behavior visualization.

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PROPULSIONAdvanced propulsion technology is thekey to achieving order of magnitude im-provements in new aeronautical vehicleconcepts. For example, hypersonic flight iscritically dependent on new propulsionsystems, advancements in supersoniccruise and subsonic transport performanceare dependent on more efficient propul-sion systems, and the successful achieve-ment of high speed rotorcraft operationrequires new, innovative propulsion sys-tem concepts.In each instance the newpropulsion system technology must bebuilt upon a solid base of research in theareas of internal computational fluid me-chanics, advanced control concepts, andnew instrumentation techniques.

Computer graphic display of stress distr i-bution on turbine engine exhaust duct

34

ORIGINAL PAGECOLOR e HOTQGRAPI'II

Specific propulsion concepts which arebeing investigated at both a componentand system level at the Lewis ResearchCenter include small turbine engines,powered lift concepts in support of ad-vanced short take-off and vertical landingaircraft configurations, propulsion for su-personic cruise aircraft and for hypersonicaircraft. Rotary cycle engines and uniquepropulsion systems for high speed rotor-craft applications are also elements of thecurrent aeropropulsion program. Combin-ing these research areas with focused dis-cipline research in areas such as new hightemperature materials enables advances inpropulsion systems technologies whichare critical to the successful developmentof new vehicle concepts.Internal Fluid Mechanics

Discipline research in internal fluid me-chanics (IFM) is providing the analytical

tools to describe the complex flow inturbomachinery, high speed inlets, ex-haust nozzles and ducts, and chemicallyreacting flows in combustors. The abilityto describe the flow in more than onestage of turbomachinery was recentlydemonstrated with a new code developedby the Lewis Research Center. The codeuses an average-passage approach to de-scribe the extremely complex flow fieldwhile also reducing computer calculationtime to a manageable level using thehighest speed computers currently avail-able. In addition to code development, iis necessary to perform experiments tovalidate the complex phenomena pre-dicted by the codes. A recent experimentused a sophisticated laser measurementsystem to develop a unique data set de-scribing the structure of a normal shockinteracting with a boundary layer and thflow field downstream of the shock.


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InstrumentationLaser velocimetry has become a valuabletechnique for acquiring detailedturbomachinery internal flow field mea-surements. By combining an interferom-eter and a conventional laser velocimeterinto a single optical system, the system iscapable of measuring three velocity com-ponents using two laser beams and re-quires only single port optical access tothe internal flow field. The system wasfirst used successfully in 1986 to measureradial velocity components as small asone percent of the axial velocity compo-nent. The system is currently being usedto investigate the flow field within a tur-bine vane annular cascade in whichflowpath convergence generates large ra-dial velocity components. Results of theseexperiments compare favorably with an-alytical predictions.High temperature electronics technol-ogy is a key element in achieving success-ful advances in propulsion system tech-nology. Silicon carbide, because of itswide temperature capability for electronicdevices and because of its wide range offrequency output, is an ideal instrumenta-tion material for use in aeropropulsion ex-perimental rigs and in operational aircraftengines. These characteristics also makesilicon carbide a potential candidate foruse in spacecraft where heat dissipation isof cri tical concern. Significant progresswas made in 1986 in high temperaturetransistor technology with the demonstra-tion of the ability of silicon carbide de-vices, manufactured at the Lewis ResearchCenter from silicon carbide crystals grownthere, to retain diode characteristics up to300 degrees C.In addition, the first successful dem-

onstration of plasma etching was accom-plished on silicon carbide crystals to formhigh quality semi-conductor device geom-etries. It was also discovered thatantiphase boundaries in the crystals alters

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IIDiscipline Research

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the electronic structure and thus affectsdevice characteristics, particularly as tem-peratures increase. This discovery pointsthe way to the production of improved sil-icon carbide crystals for integrated sensorsfor aerospace propulsion control systemscapable of operation above 600 degrees C.Intermittent Combustion TechnologyIntermittent combustion engines offer in-herently low cost for general aviation andcommuter applications but have been re-

stricted to the use of aviation gas whichhas become more difficult to obtain andthus expensive. Research is currently un-derway on stratified charge rotary engineswhich have the capability to operate onseveral different fuels, including jet fuel,as well as offer improved efficiency andpower relative to current engines.The intermittent combustion researchprogram is structured to improve powerdensit ies and efficiencies for stratifiedcharge rotary engines. A major accom-plishment of the NASA/Deere an_t Co.stratified charge rotary engine programwas the attainment of 160 Horsepower(HP) from a 40 cubic inch single rotor en-gine, the highest power density everachieved in this type of engine. Using ahigh speed electronic fuel control system

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and jet fuel, a fuel consumption wasachieved comparable with today's generalaviation engines. The ultimate goal is toreduce fuel consumption by approxi-mately 30% using optimized fuel controland ignition systems in conjunction withdesign improvements developed on thebasis of validated analytical airflow mod-eling codes. Turbocompounding, adiabaticcomponents, lightweight rotors, and re-duced friction schemes are also being in-vestigated. The first laser holographicvisualization of airflow in the combustionchamber of a rotary engine was success-fully obtained in 1986 and will be usedalong with other methods of determiningairflow to validate a multi-dimensionalairflow model for a rotary internal com-bustion engine.

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Small Turbine Engine TechnologyThe primary objective of the small turbineengine program is to raise the perfor-mance level of small turbine engines tomore nearly match that of large engines.Work continues to be focused on provid-ing fundamental experimental data to en-able an understanding of the design pa-rameters that affect componentperformance as size is reduced. Small en-gine component technology studies werecompleted which determined that hightemperature materials, such as ceramicsfor the hot section; improved aerodynam-ics; and advanced cycles, includingrecuperators, have the potential of reduc-ing fuel use by 20-50% with a cor-responding reduction in direct operatingcosts of 12-20%. A scaled centrifugal com-pressor program was completed demon-

strating that the effects of tip clearance,blade thickness, and surface roughnesscould be properly accounted for, leavingthe effect of aerodynamic scaling as thefundamental cause of efficiency change.A new structural analysis code was

completed in 1986 which predicts fastfracture probability for ceramic turbinecomponents. Also, experimental evalua-tion of an advanced ceramic matrix com-bustor liner provided a 300 degree F in-crease in turbine inlet temperature yeteliminates film cooling requirements. Ananalytical model for predicting flow fieldsvelocity and temperature trends in theturns of a reverse flow combustor was de-veloped under contract to industry.STOVL TechnologiesThe advanced short take-off and verticallanding (ASTOVL) program at the LewisResearch Center is providing a technologybase in the area of propulsive lift systems,attitude control systems, light weight de-flecting and vectoring nozzles, and inte-grated flight and propulsion controls forapplication to advanced military super-sonic powered lift aircraft configurations.The 1986 completion of the Powered LiftTest Rig, which can provide adequate airflow rates and pressure ratios to simulatetypical engine performance, will makepossible the full scale assessment of vari-ous lift augmentation systems. The rig iscapable of measuring axial thrust up to30,000 lbs., vertical thrust to 20,000 lbs.,and lateral thrust up to 3,000 lbs.


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Convertible EngineThe completion of the convertible engineprogram in 1986 at the Lewis ResearchCenter has successfully demonstrated thatthis type of propulsion system is viable forfuture advanced rotorcraft concepts suchas the X-wing, folding tilt rotor, and ad-vancing blade concept configurations. Thejoint NASA/DARPA program used aTF34 engine, with variable fan inlet guidevanes for thrust modulation, to evaluateimproved fan hub design and map thesteady state and transient performanceand stability of this concept over the fullrange of engine operation. The variableguide vane engine system was found tobe inherently stable and controllable in allmodes of operation. Utilizing this type ofpropulsion concept to provide power ineither a forward or vertical mode will en-

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able a 20 percent reduction in direct op-erating costs compared to using separateengines to achieve the two flight modes.The application of this technology is nowunderway and the General Electric Com-pany expects to make available a flight-rated, convertible engine demonstrator inthe early 1990s.Transmission TechnologyThe rotorcraft transmission programachieved several significant accomplish-ments in FY86. The first rigorous analyti-cal study of transmission dynamic load ef-fect on gear pitting fatigue life wascompleted which showed that operatingspeed and contact ratio significantly affectcomponent life. A 3600 HP split torquehelicopter transmission design study was

Convertible fan/shaft turbine engineground test installation

completed which provides a 15 percentweight reduction, improved reliability, a 9percent reduction in power losses, and ap-proximately a 35 percent reduction innoise. This design provides for a possiblereplacement of the Blackhawk helicoptertransmission and includes growth poten-tial from 3000 HP to 4500 HP.In addition, a life and reliability com-

puter program was completed which willserve as a valuable tool for evaluatingpreliminary designs and for evaluatingcompeting helicopter transmission de-signs. Using inputs such as transmissionconfiguration, load, and speed, the ex-pected life of transmission componentsand systems can thus be predicted. Theprogram also provides information whichcan be used to support fleet operations toplan spare parts requirements based uponthe predicted life of the components.

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MATERIALSANDSTRUCTURESSignificant improvements in the per-formance, durability and economy offuture civil and military aircraft re-quires that advancements in the tech-nology base in materials and struc-tures be achieved. To meet thenational goal in hypersonics alone,new materials and structural conceptsmust be developed that can with-stand high aerothermal loa_ng cyclesin airframes that are lightweight andincorporate complex intersectingstructural surfaces.

In addition, the development ofnew, validated analytical predictionmethods for complex, lightweight,high temperature structures has re-sulted in increased emphasis on com-putational structural mechanics(CSM), optimization techniques, andintegrated active control concepts forflutter suppression, relaxed static sta-bility, gust load alleviation and ma-neuver load control.High Temperature StructuralMaterials

Ceramics are attractive high tempera-ture structural materials because oftheir strength, low density, environ-mental resistance and net shapefabricability. However, the brittle na-ture of ceramics makes these materi-als sensitive to minute flaws and de-fects. Enhancement of ceramictoughness, via the addition of parti-

High temperature test of ceramic materialturbine vane

cles or whiskers to deflect and arrestcracks and toughening and strength-ening of ceramics by fabrication ofcontinuous ceramic filament rein-forced ceramics, can permit ceramicparts to be more forgiving of flawsand to exhibit tensile behavior morecomparable to ductile metals.Significant progress in ceramictoughness technology was accom-plished in 1986 with the Lewis Re-search Center development of an ap-proach to strong, tough, hightemperature ceramic-ceramic compos-ites that utilize continuous silicon car-bide fibers to reinforce reactionbonded silicon nitride matrices. Thehigh fiber content in the ceramic com-posite impacts improved fracturetoughness and ultimate strength overstate-of-the-art monolithic materials.The most important aspect of thisaccomplishment is that a failure inthis new ceramic composite occurs ina more stable, progressive mannerthan the catastrophic fracture ofmonolithic materials.SiC Fibers Strengthen and ToughenReaction-Bonded Si3N4Ultimate Strength, 10 3 P Si140

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Composite structure geodesic stiffened .compression panel

Composite StructuresComposite materials are finding in-creased use in current and future air-frame designs because they arelighter and stiffer than conventionalmetallic aircraft structural materials.The composite program is directed to-ward the development of new poly-meric systems and concepts for inno-vative structures for large wings andfuselages with improved toughness,fabricability, consistency of proper-ties, and weight/cost reductions.

One example of the breakthroughsin composite structures research in1986 is the development of the geo-desic stiffened compression panelwith isogrid construction geometry.This structural concept, developed atthe Langley Research Center, has re-sulted in major steps towards produc-ing cost effective, damage tolerant air-frame designs. The geodesic orthogridwall panel concept provides 30%lower weight than a correspondingskin/stringer aluminum structure,and is over 40% lower in cost. Cur-rent design practice with conventionallayup techniques results in double thecost of aluminum structures with onlyequivalent weight savings.Computational StructuralMechanicsNASA has initiated a focused multi-center activity in computational struc-tural mechanics (CSM) with the keyobjectives of (1) developing accurate,efficient and innovative computa-tional methods for very large andcomplex aerospace structures and, (2)exploiting the newest and most pow-erful computers available. A signifi-

Aeroelastic model of "active flexible wing"aircraft in Transonic Dynamics Tunnelcant 1986 accomplishment of CSM isthe detailed analysis of an advanced,uncooled turbomachinery turbineblade. This component is subjected tosevere cyclic thermal and mechanicalloading, and the blade materialcharacteristics become highly nonlin-ear in critical locations during normaloperation. A detailed analysis of thisproblem is beyond the scope of tradi-tional analytical methods on conven-tional computers. Advanced computa-tional methods are demonstrating thecapabil ity to significantly reduce solu-tion time with improved accuracy.These methods are currently beingused on a state-of-the-art CRAY XMPvector processing supercomputer, butare being installed on a more power-ful CRAY 2 supercomputer.

AeroelasticityNASA is a leader in the study of aicraft aeroelasticity, including the phnomena of divergenece and flutter.Structural deformations of the aircrcan couple with the aerodynamicforces acting on it to produce unstabconditions in which the deformationsgrow excessively large. This conditican lead to the destruction of the acraft. The avoidance or control ofthese unstable aeroelastic phenomenare critical to the successful flightadvanced aircraft configurations.

An innovative scheme was recenproposed to the Air Force by Rockwell International in which the fleibility of the wing would be used

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rectly to control aeroelastic response.This involves elastically deformingthe wing shape instead of just mov-ing control surfaces. The approachhas the potential of saving severalthousand pounds of structural weight.A model of an "active flexiblewing" was successfully tested in theTransonic Dynamics Tunnel (TDT) atLangley Research Center in 1986. Ini-tial testing has been completed and avaluable database obtained to validatethe predicted advantages of the con-cept. Rolling moment coefficients,which correlated well with predic-tions, were experimentally deter-mined. Additional testing will be con-ducted in the TDT to support thedevelopment of a complete controlsystem for aeroelastic tailoring.

Numerical Aerodynamics Simulation facilitycomputer complex

INFORMATIONSCIENCES ANDHUMANFACTORSIncreasing emphasis is being placedon the significant payoffs that can oc-cur from the infusion of the disci-plines of information sciences and hu-man factors into the process ofapplying advanced technology to fu-ture generations of aeronautical vehi-cles. The research challenges rangefrom the basic understanding of newcomputational concepts to the theo-retical basis for reliable fault-tolerant

systems, from the exploitation of newcontrol and guidance concepts to thedefinition of readily adaptable artifi-cial intelligence concepts, and fromreliable workload prediction tech-niques to sophisticated techniques foranalytically modeling the behavior ofhuman pilots in high workload cock-pit environments.

These challenges are the driversthat establish the priorities of the re-search efforts in NASA's informationsciences and human factors program.The enabling technologies emergingfrom this rapidly expanding field ofscience will provide the key to under-standing, applying, and controlling anew family of aeronautical vehiclessuch as rotorcraft that can fly nap-of-the-earth in all weather, high perfor-

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mance aircraft that can maneuver at90 degree angle of attack, transportsthat can fly more safely in the Na-tional Airspace System, ortransatomspheric vehicles that canoperate routinely across the bound-aries of the atmosphere and space.Computer ScienceSignificant accomplishments in com-puter science took place in 1986 thatprovide the leading edge technologynecessary to aggressively and effec-tively realize the tremendous com-putational potential of the NationalAerodynamic Simulation (NAS) facil-ity and the Computer NetworkingSubsystem (CNS).

During 1986, a concurrent proces-sor test bed became operational at theResearch Institute for AdvancedComputer Science (RIACS) at AmesResearch Center. Among the equip-ment in the test bed are a maintimesharing system that supports 20users, an Intel Hypercube that sup-ports concurrent programming re-search, and an IRIS 1500 work stationthat supports Numerical Aerody-namic Simulation Graphics tasks andRIACS graphics. Research is beingconducted in architectures for com-putational physics and in graphics forcomputational and experimentalphysics.Initial demonstrations were suc-cessfully accomplished in 1986 usinga new special purpose computer. Aparallel architecture computer forsimulating flows governed by theNavier-Stokes equations is being de-veloped by Professor Nosenchuck ofPrinceton University under a grantfrom Langley Research Center. Thiscomputer is capable of peak processorspeeds of 960 Mflops.

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Computational science mathematicalrepresentation of surfaces on spheresSignificant progress was achieved

in finding improved techniques forvisualizing depth in three-dimen-sional computer graphics images. Anew stereo imaging capability hasbeen developed and demonstrated onan IRIS workstation. In addition, IRIScan now be used for interactive view-ing of Cray 2 simulations utilizing adirect Cray 2-IRIS interconnectscheme.

Other 1986 computer scienceaccomplishments include improvedmapping of mathematical functionson the surfaces of spheres. Thisachievement evolved from research indynamic displays of data on closedsurfaces carried out under sponsoredresearch at the University of Arizona.Related display research at the Uni-versity of Utah resulted in high qual-ity 3-D solid modeling techniquesand computer generated "transpar-ent" displays showing hiddensurfaces.

Controls and Guidance

Controls and guidance research isproviding advanced technology en-abling the exploitation of new avion-ics concepts to dramatically improvethe operational capabilities of newcivil and military aircraft. Major ad-vances in aircraft control designmethodologies, reliability validationtechniques, and guidance and displayconcepts are taking place that will in-crease the efficiency and effectivenessof the next generation of aircraft androtorcraft.

Important progress was made inthe critical area of fault tolerant datamanagement system concepts. In1986 an Advanced Informatibn Pro-cessing System (AIPS) design was developed that provides triplex, duplex,and simplex processing capability.Corollary efforts addressing sensorsand effectors were combined with theAIPS development to achieve a totalsystems level approach to faulttolerance.


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