A review of NASA's propulsion programs for aviation

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NASA TECHNICAL

NASA TM-73831

MEMORANDUM

M M M N78-16055 'i (NASA-Tti-73831) A REVIEW Or VASA'S PROPULSICN PROGRAMS FOR AVIATION (NASA) 21 HC A02/MP A01 CSCL 21A P Unclas G3/07 02580 Q Z OF

A REVIEW NASA'S PROPULSION PROGRAMS

FOR CIVILAVIATION

by Warner L,. Stewart and Richard J. Weber .

e Lewis Research Center Cleveland Ohio 44135 p1` ^` 1^ lr! ?t a^ ?

and Harry W. Johnson fi5 1 NASA Headquarters Washington, D. C, 20546 "^ "'•^°^^F ^ti^^ TECHN.TCAL .PAPER to be presented at the Sixteenth Aerospace Sciences Meeting sponsored by the American Institute of Aeronautics and Astronautics Huntsville, Alabama, January 16-18, 1978

A REVIEW OF NASA'S PROPULSION PROGRAMS FOR CIVIL AVIATION by Warner L. Stewart* NASA-Lewis Research Center Cleveland, Ohio Harry W. Johnson** NASA Headquarters Washington, D.C.

and Richard J. Weber*** NASA-Lewis Research Center Cleveland, Ohio Abstract in the establishment of a special laboratory, the Lewis Research Center, for propulsion research, now Five NASA engine-oriented propulsion programs devoted primarily to jet and fan engine propulsion of major importance to civil aviation are present- systems.

"'. nd and discussed. Included are programs directed at exploring propulsion-system concepts for (1) Through the combined efforts of government and energy-conservative subsonic aircraft (improved industry, the gas turbine engine has developed into current turbofans, advanced turbofans, and ad- a state of high sophistication. Although one might vanced turboprops), (2) supersonic cruise aircraft think that such sophistication both in the engine (variable-cycle engines), (3) general aviation and aircraft would lead to a maturing of the tech- aircraft (improved recipprocating engines and nology, such is not the case. In particular, the small gas turbines), (41 powered-lift aircraft propulsion area presents some very exciting oppor- (advanced turbofans), and (5) advanced rotorcraft.

tunities that could expand and modify the character These programs reflect the opportunities still of aviation dramatically from what we see today.

existing for significant improvements in civil The importance of such advances has been noted in aviation through the application of advanced pro- various studies of future aviation needs (e.g.

pulsion concepts.

Introduction Although NASA's programs include a brr3d range of discipline activities in propulsion related The evolution of aviation to the present areas, and also provide support in many areas to generation of aircraft has taken place over a the military, the scope of this paper will be surprisingly few decades. History has shown that limited to engine programs specifically related to pacing the major advancements in this field has civil aviation. Propulsion work for five major been the development of appropriate propulsion aircraft applications will be described: energy- systems. Indeed, to a great extent, the first conservative subsonic transports, supersonic cruise Wright Brothers' flights were dependent on the transports, general-aviation aircraft, powered-lift attainment of a suitable lightweight engine transports, and rotorcraft. Some comments on system. The era of high-speed high-altitude applications looming on the distant horizon will flight, as we know it now, had to await the ad- also be included.

vent of the gas turbine engine.

Energy-Conservative Subsonic NASA and its predecessor, NACA, have over Transport Propulsion their years of existence contributed in a major way to the advancements in aeronautics. Such con- The commercial fleet of air transports has tributions spanned the complete spectrum of evolved from its initial piston-engine propulsion disciplines - aerodynamics, propulsion, structures, systems, through turbojets, and now to turbofans.

avionirs, stability, etc. The recognition of the In this progression, it was always important to importance of propulsion, in particular, resulted strive for minimum fuel consumption for the sake of better airplane range and operating efficiency.

Due to low fuel costs, however, this was not of *Director of Aeronautics overwhelming importance in comparison with other Fellow AIAA desirable characteristics, such as higher speed, larger size, durability, maintainability, and **Director, Aeronautical Propulsion Division lower noise. But since the oil embargo, the MembEr, AIAA current recognition of dwindling petroleum reserves, and the sudden increase in fuel prices, the ***Chief, Mission Analysis Branch importance of fuel efficiency has come to the fore- Associate Fellow, AIAA front.

As a result of this increased significance of Figure 4 compares current and advanced engines fuel efficiency, NASA in 1976 embarked on a major and lists some of the advanced technology features technology program with the ambitious goal of ul- under consideration. The presently-favored concept timately reducing the required fuel usage in sub- is a two-spool arrangement with direct drive of the sonic commercial aircraft by a factor of two. 3 fan and with mixed exhaust flow. About half of the Part of the achievement of this goal would be sought-for gain is to be achieved through various through improved aerodynamics of the aircraft component improvements beyond the current state-of- (high apsect-ratio wing, super-critical airfoils, the-art. Increased aerodynamic efficiencies, winglets, laminar flow, etc.) as well as by using tighter clearances (including active clearance lightweight aircraft structures through the liberal control), reduced turbine cooling air, and better application of composites.

materials are considered key ingredients. The other half of the gain arises from the improved cycle Major attention was also given to the pro- that can be designed around these better components.

pulsion systems, In this area, three distinct Principal features include a modest increase in programs (improved current turbofans, advanced turbine-inlet temperature, a substantial increase in turbofans, and advanced turboprops) were evolved, cycle pressure ratio, some increase in bypass ratio, each having different goals, risks, and timing. and exhaust mixing.

The program goals of fuel savings and direct operating cost are identified in Figure 1. Project is planned to be an 8-year pro- The E 3 gram that started in 1976. The two major commer- Engine Component Improvement (ECI) cial engine manufacturers are participating on a cost-sharing basis. Preliminary designstudies by This program seeks to make a near-term P&W and GE have just been completed. Initiation of improvement ig ^he existing and near-future air- the detailed design and experimental efforts is plane fleet. 1 0 It thus is limited to whatever expected by March 1978, The ultimate objective of modifications can be economically made to current this program includes the design and testing of an engines, either for future production or through advanced experimental core and an integrated core- retrofit. Through contracts with the manufactur- low spool system. Thus, it is a very major effort.

ers of the JT8D, JT9D, and CF6 engines--which The total program funding is approximately 200 power practically all of the present jet fleet-- million dollars.

it is hoped to achieve at least a 5-percent reduction in fuel usage. At the same time, no High Speed Turboprop penalty in DOC will be accepted. Figure 2 shows cutaway view of an "improved" current engine. On The initial NASA studies of ways to reduce fuel the right-hand side is listed a few of the items consumption considered a wide variety of un, -+en- of potential improvement. tional propulsion systems. 6 , 7 Of these, I., .

felt to have the greatest potential was the ao.,tt^ed Another area of potential improvement is turboprop. As indicated in Figure 1, this approach Illustrated in Figure 3. As indicated, engines has a possible high payoff. However, it also when first placed into service suffer a noticeable represents a high risk.

short-term deterioration in fuel consumption. In the longer term, the rate of loss levels off some- The key characteristic that makes the turboprop what, but still continues. Some, but not all, of of such great interest is the expectation of high this loss is recovered as the engine is period- propulsive efficiency at the flight speeds typical ically repaired. The causes of this deterioration of modern jet transports (Fig. 5). Figure 6 shows are presently not well understood, but are believed a model of an advanced design (provided under to include the items listed on the left-hand side contract to Hamilton Standard) under test in a Lewis of Figure 2. A diagnostic program to identify wind tunnel. It incorporates such features as thin these causes is in process. This should then airfoils, swept leading edges, and multiple blades.

permit finding economically feasible ways to Preliminary experiments suggest tnat the goal of 80 percent propeller efficiency at Mach 0.8 is achiev- minimize the losses, which can be as high as 8 able.

percent.

Many issues must be addressed before turboprops The ECI program, started in 1977, will con- tinue for 5 years and is funded at •:0 million can be accepted as a viable propulsion system.

These include noise and vibration, structural dollars.

design of reduction gears and thin blades (espe- cially using composite materials), propeller/ Energy Efficient Engine (E3) nacelle/wing aerodynamic interactions, and reli- ability/maintainability. These will all be con- The second program 4 ' 5 involves developing sidered in the 'program that was initiated in 1976 and verifying the technology for a future genera- under base technology funding and enters a formal tion of all-new turbofan engines that have rather challenging goals in reducing fuel consumption and project phase in 1978. The first phase is basically DOC. A seen from Figure 1, the goals include a an exploratory activity that will cost 7.4 million dollars over a 3-year period. If successful, later minimum of 12 percent improvement in sfc as com-

pared to the most advanced turbofans of today and hases larger models and subsequent

flight te at least a 5 percent improvement in DOC. The engines must, of course, meet the noise and emission standards that might be in force at that time.

Fuel Specifications, Complex, variable-geometry inlets and exhaust systems are needed with both of these engines. A Another issue that should be discussed when sophisticated control system is necessary to allow considering the fuel consumption of futur- engines all of the components to function in the most is the nature of the fuel that is expecteLi to be effective manner throughout the flight. Advanced available for use by those engines. Present jet components and materials are also desired here as fuels are produced to rather tight tolerances on they were 'in the E3 program.

physical and chemical characteristics. Less stringent specifications would allow wider sources The increasing public sensitivity to aircraft and thus greater availability of aviation fuels. noise is an especially critical issue for supersonic A more extreme situation is the prospect of avia- engines, which require high exhaust velocities for tion fuel being obtained in the future from non- efficient cruising. The corresponding Jet noise petroleum sources such as shale and coal. NASA would be unacceptable if alleviating moasures were has initiated a program to identify the character- not taken. The variable cycle features Just istics of potential future fuels and to assess the mentioned aid considerably in this regard, as they impact of those fuels on engine design and opera- permit takeoff with lower and, hence, quieter tion. Another part of that program includes an velocities. Further quieting can be achieved with evaluation of the energy used in the refining Jet noise suppressors; however, the associated process, in order to minimize the total energy weight and thrust losses impose undesirable penal- required to operate the aircraft. ties.

Supersonic Cruise Transport Propulsion An alternate concept for noise suppression that is applicable to engines that have two exhaust One of the most challenging propulsion goals streams 11 has been explored under this program.

lies in the area of advanced supersonic transports This "coannular" effect is illustrated in Figure 9.

It is generally acknowledged that the feasibility For a given thrust, if the velocity in the outer of such an aircraft depends upon major advance- stream is higher than that of the core stream, tests ments in propulsion. The engine system, including have shown that up to 10 PNdB of noise suppression inlets and nozzles, must operate efficiently at can be achieved. The improvement is reduced, but both supersonic and subsonic conditions, be quiet still substantial, when compared to the case where during takeoff and landing, and have acceptable the two streams are completely mixed before emerging from the nozzle, The data to date has been obtained emissions. Although no development program is in process or even in the offing. NASA since 1973 has only on small-scale experimental nozzles. Also, been engaged in work aimed at advan^ing the state- other noise sources such as core and duct-burner of-the-art in these areas. This wi'il generate noise must still be reckoned with.

the information needed for decision making and preserve the option of undertaking future develop- The recognition that some of the advanced ment. technology elements must be explored on a rather large scale has prompted the initiation of the "variable-cycle engine component" program (Fig. 10).

Variable-Cycle-Engine Technology.

This program 12 uses existing engines as the test- bed to explore several of the critical technologies.

No single engine cycle can completely satisfy all of the conflicting requirements at supersonic The P&W program utilizes the F100 engine as the and subsonic flight conditions as well as meet facility and will explore principally the duct stringent noise goals. Extensive studies of many burner performance and noise and nozzle performance including the coannular effect. GE utilizes a J101 alternative approaches have finally led to the con- engine and will explore the front valving character- cept of the variable-cycle engine as having the istics, as well.as the coannular effects on per- be l s6 potential for satisfying the requirements.

9, formance and noise.

Such an engine would be designed with flexibility in cycle operation and bypass ratio to This variable component test program was allow it to operate more like a turbojet at super- initiated in 1976 as a 5-year effort and is funded sonic cruise conditions, and like a moderate bypass at 22 million dollars. It is expected that it is ratio engine at subsonic conditions.

the first step in a longer range activity that could grow into a variable-cycle experimental Each of the engine companies involved in the program has its preferred variable-cycle engine engine program.

system. The P&W engine (Fig. 7) is a duct burning Emissions turbofan featuring considerable flow variation in the components and a cycle with an inverse turbine One of the major concerns regarding future inlet temperature schedule. As opposed to more supersonic transpo is is that of emissions into conventional engines, takeoff is at a reduced ^3 Primarily, it is feared that the stratosphere.

temperature and maximum inlet temperature is the generation of nitrogen oxides may reduce the employrd at supersonic cruise.

concentration of naturally occurring ozone, permitting more ultraviolet radiation to reach the The GE "double bypass" engine (Fig. B) earth's surface with detrimental consequences to features flow being diverted around the engine in plant and animal life. Although the issue is various ways depending upon the made of operation.

still unresolved, the available studies suggest Valving is provided at both the front and rear that a large reduction in engine NO x production is portions of the engine to permit the desired flow prudent.

distribution.

NASA already had a program under way The AVCO-Lycoming program involves essentially (Experimental Clean Combustor Program) where ad- a new experimental turbofan based upon an upgraded vanced concepts were being explored in an attempt turboshaft engine core (LTS101). It is substan- to substantially reduce emissions from those of tially smaller than the AiResearch engine, having current combustors. This program was expanded in approximately 1600# rated thrust and designed for 1973 to include the problems relevant to super- smaller aircraft flying at somewhat reduced flight sonic aircraft. 14 The favored concepts emerging speeds. A schematic of this engine is shown in from the program are illustrated in Figure 11. In Figure 15. the fan pressure ratio is quite low general, these combustors differ from the conven- (1.31) and the bypass ratio Correspondingly high tional type by possessing two stages - a pilot (9.1). It also has a low emissions combustor, a stage and a main stage. This allows the combustor high work single-stage turbine, and a mixer for to be optimized somewhat independently for sow noise reduction.

emissions both in the vicinity of the airport and at high-altitude cruise, Figure 12 shows that These two Programs were initiated at the this approach offers a considerable improvement beginning of 1977 and are approximately 2 years in over current technology, but substantial further duration. Upon completion of the contract effort, advances are still required to meet the goal of the experimental engines will be delivered to NASA approximately 3 g/kg. for further evaluation.

Several other approaches that promise GATE greater potential reductions are shown in the figure. They are now being explored in a com- Referring again to Figure 13, it is apparent prehensive research program called Stratospheric that there is a large group of aircraft models Cruise Emissions Reduction Program (SCERP). The categorized by horsepower, and flight speeds lower results will be applicable not only to supersonic than those addressed by QCGAT. In fact, about 98 aircraft but also to high-altitude subsonic percent of the 170,000 planes in the present fleet transports. are in this category. Of this large number, turbine power has been able to capture only 10 General Aviation Aircraft Propulsion percent of thu engine market--specifically, turbo- props have sole reign at the higher horsepower part Another area of aircraft propulsion in which of the spectrum. At still smaller sizes, the NASA has recently increased its activities is that reciprocating engine is unchallenged.

related to general aviation. This field of aero- nautics embraces basically all civilian aircraft The purpose of the General Aviation Turbine other than the commercial carriers and, therefore, Engine (GATE) program is to seek advanced tech- nologies that will enhance the attractiveness of covers a wide span of types from single-engine piston aircraft up to the high-speed high- very small civilian turbine engines. Particular altitude business jets. Three major areas of emphasis will be placed upon cost, as this factor activity are currently under way. has been the major deterrent to the extension of the gas turbine engine down to these smaller CQ GAT general aviation applications.

Figure 13 presents a distribution of civil The GATE program is now in the definition stage. Four small-gas-turbine contractors were aviation aircraft by engine horsepower and flight speed. As indicated above, one distinct group in selected to help provide this definition: Detroit the general aviation field is the business jet, Diesel Allison, Teledyne, AiResearch and Williams Research. Elements of this definition program are which is a fairly large aircraft flying at speeds shown in Figure 16 and include (1) a general study similar to those of commercial airliners. The of the market needs for such an engine, (2) Quiet Clean General Aviation Turbofan project determination of engine technologies and design (QCGAT) was initiated with the objective of features that are considered optimum for each air- applying the noise and emissions technology, craft type, (3) an evaluation of the "common core" previously developed for large turbofan engine applications, to the smaller general aviation fan concept to permit, in addition to simplification, the use of the relatively expensive core for a wide engine, and, in particular, provide a means for range of engine types, and (4) the contractor's NASA to transfer this technology to the smaller view of what the GATE program would be in terms of general aviation engine manufacturers. 15 scope, schedule, and cost. The first two phases Two contracts totaling approximately 8 have been completed.

million dollars are currently in process with The results of these studies are intended to Garrett AiResearch and AVCO-Lycoming. The provide the basis for decision making regarding AiResearch program involves an experimental engine proceeding into a subsequent experimental engine using the core from the TFE731. Figure 14 shows a schematic of this experimental engine. Features program.

include a fan of increased diameter and reduced Reciprocating Engine Technology pressure ratio, 1.49, (as compared to the TFE731) which when combined with a jet mixer will reduce As already noted, the vast majority of today's the jet velocity and, hence, noise substantially.

general aircraft are powered by reciprocating It also includes a higher work extraction turbine and a reduced emissions combustor. Its rated engines. One objective of the NASA activity is to aid the industry to reduce emissions. Some of thrust level is 3900#.

the work is being done in-house, For example, advanced technologies that have been incorporated Figure 17 shows the results of tests to correlate In the design. These technologies are important emissions level with ambient temperatures and for other applications besides short haul. They humidity. Other work, some partly funded by FAA, are relevant to many of the present concepts for is being done under contracts with AVCO-Lycoming 3 ply in some degree to all Navy V/STOL vehicles and ap and Teledyne-Continental. These efforts range advanced engines such as E or the advanced turbo- from minimal adjustments to fuel-air ratio and prop.

spark advance through more significant modifica- tions such as variable valve timing and exhaust The QCSEE program is well down the road, with air injection. the OTW engine currently at Lewis for evaluation.

Testing of the UTW engine has been completed at the Another objective is to seek general improve- contractor's site with delivery to take place in ments in the performance and flexibility of the the very near future, 16 engines, included here are lower cooling penal- ties, improved integration with the airframe, and Rotorcraft Propulsion multifuel capability for lessened reliance on specialized aviation gasoline. Over the years of the evolution of the heli- copter, or what is termed herein rotorcraft, the A related activity involves the exploration principal activity has been for military applica- of other advanced propulsion system concepts in tions. Civil applications have been handicapped addition to the gas turbine already discussed. by highpurchase and operating costs, short range, For example, the turbocharged rotary concept low speed, and poor passenger comfort. Neverthe- sketched in Figure 18 is being studied. Another less, the helicopter's unique hovering capability concept being considered is a lightweight Diesel permits its use when no other vehicle will serve.

engine. It is hoped that this program will As a result, in recent years the growth rate for Identify propulsion systems that better meet helicopter sales has been very high.

emissions requirements and have improved perform- ance than the conventional reciprocating engine in In the past, the only significant government use today, support of rotorcraft propulsion system technology has been through the Army. In recent years, this Powered Lift Transport Propulsion effort has been augmented to some degree through a unique joint program where Army-funded civilian For many years it has been suggested that engineers have been located at NASA research cen- one significant method for improving the U.S. air ters and work shoulder-to-shoulder with NASA transporation system would be through the use of personnel. Another joint activity is the Rotor small airfields located in close proximity to the Systems Research Airplane, a flying experimental traveler's residence or business (e.g. ). This facility to test advanced rotor systems. NASA is would both relieve congestion at the major air- now expanding one area of traditional expertise ports and minimize ground travel time. These into a focused program specifically aimed at close-in fields would probably have especially advancing rotorcraft transmission technology. As stringent noise constraints and also be limited indicated in Figure 21, advanced technologies in in available runway lengths. Conventional air- lubricants, bearings, seals, and gears will be craft would be unable to accommodate these applied to improve the mechanical reliability of limitations. However, special short-haul air- these transmissions. Lighter weight will also be planes that employed the propulsion system to aug- a goal of this 5 year, 7 million dollar program, ment the wing lift can be envisioned for this which is just getting under way.

application.

A broader helicopter engine program is also In 1974, NASA initiated the Quiet Clean being contemplated. Although not clearly defineed Short-Haul Experimental Engine (QCSEE) program to at this time, objectives of this program could be explore the propulsion systems needed for such an to explore advanced features for turboshaft engines airplane. A 30-million-dollar contract was such as increased emergency power capability, awarded to BE to design and build two engines better part-power sfc, and improved low-cycle- utilizing an existing core. One engine is fatigue resistance. Also to be explored are ad- intended for under-the-wing (UTW) installation as vanced engine systems that would permit substan- pictured in Figure 19. Lift augmentation is tial increases in cruise speed. Such an engine obtained by deflecting the exhaust jet with the system might be used in an advanced rotorcraft trailing-edge flaps. The other engine is gener- such as that shown in Figure 22, which would ally similar, but is intended for over-the-wing employ a twin rotor system called the "Advancing (OTW) installation utilizing upper-surface blow- Blade Concept",and a "Fan-Shaft" engine, one that ing to obtain jet lift. The prospective air- could operate as a turboshaft unit during the craft using these engines would be similar to the hover mode and as a fan engine at cruise. The Air Force's YC-14 and -15. engine, shown schematically in Figure 23, could be a small version of the QCSEE UTW engine utilizing Many of the features of the engines were the a variable-pitch fan but including a right-angle product of an extremely severe nuise goal of 95 power takeoff within the gearing system. Concepts EPNdB along a 500-foot sideline during both take- such as these will constitute the basis for future off and landing. As a result, the engines are rotorcraft propulsion programs.

relatively high bypass-ratio devices with low fan pressure ratio. Figure 20 lists some of the design values for the UTW version. Also shown is a sketch of the engine, calling out the numerous

Other Horizons in Prulsion This causes drag and weight penalties. Further weight penalties are caused by the necessary insula- The previous sections have described some of tion to prevent boil-off or air condensation.

the technology activities under way or being initiated to advance propulsion technology for The engines, except for the fuel system, are en- civil aircraft. The programs are near term in visioned to be rather conventional. if anything, that they cover aircraft types already in use and the combustor and turbine design problems are that could be expected to achieve operational lessened. The main technical problems are in the status in the next 10-15 years, airframe and fuel system. Other concerns involve the economics of manufacturing and distributing the There are other aircraft on the horizon that fuel to the appropriate airports and the operational could come into being by the turn of the century techniques of refueling the aircraft. Since pure if there were sufficient motivation--principally hydrogen is not found naturally in significant economic. Three of these, under study by NASA, amounts, its general usage is critically dependent will be briefly described here. on the manufacturing process (e.g., conversion from coal or shale). In the long run, it may come Large Cargo Aircraft into use principally as an intermediary for the use of non-fossil-fuel energy (nuclear, fusion, or Predictions have periodically been made for solar) to provide aircraft propulsion power.

a decade or more that the air cargo market was an the brink of an enormous expansion. This has not Hypersonic Aircraft come to pass for numerous reasons, some of which have little to do with the characteristics of the Although supersonic aircraft have not found airplane per se. However, it is clear that, if their way into commercial use in great numbers, the potential market could ,justify its development, there are those who speculate that not only will a much improved, more economical, dedicated air- they come to pass, but that they could be followed by the evolution of a commercial aircraft of even freighter could be constructed, With proper design, it could not only lower direct ton-mile higher speeds, Such aircraft, shown in Figure 26, costs of the airplane but also lead to improve- would operate at extreme altitudes and flight Mach ments in the ground-side costs of the total cargo- numbers (greater than 6) and would require hydrogen handling system, as the fuel so that it could be used as a heat sink to keep the engine, and perhaps the airframe, An approach to such improvements is the con- temperature at tolerable levels.

cept of very large airplanes that are configured The propulsion system indicated on the figure for convenience in loading and inter-modal trans- fers. The spanloader designs illustrated in and considered most attractive at this time is the supersonic combustion ramjet, or Scramjet. This Figure 24 are one way of attaining this objective.

These are being extensively studied by the Langley engine, in the concept illustrated, consists of a combustor mounted on the flattened bottom of the Research Center and its contractors. 'n this fuselage. The forebody acts a compression surface, approach, cargo is contained in the thick wings rather than in the fuselage. The distributed decelerating the airstream and raising its pressure.

weight along the span relieves the bending moments The still-supersonic stream is heated within the combustor and then is expanded against the aft and permits a lighter structure. 17 section of the fuselage. The many unusual problems Whether there are uniquePropulsion problems in fluid flow, combustion, structures, and cooling have been extensively investigated by NASA. An for such aircraft has not yet peen examined in any experimental engine, built under contract to depth The propulsion/airframe integration prob- Garrett, has been successfully tested at simulated ably involves some unusual aspects. Beyond that, there is an opportunity for innovative approaches speeds up to Mach 7. A continuing research program to mechanical and structural design of the engines, on engine components and airplane integration is in if not to the basic thermodynamic cycles. process at the Langley Research Center. Ig Concluding Remarks Hydrogen-Fueled Aircraft This paper has presented a brief description The long-term certainty of diminishing petroleum resources makes it desirable to consider of the major programs under way or being planned by alternative fuels, particularly if the alternative NASA in advancing the propulsion technology for offers other benefits to the airplane. Hydrogen civil aviation. From the discussion, it is clear that NASA's aeronautics program reflects the recog- is a r..andidate fuel in this category. is It nition that advancements in both conventional and possesses a heating value (BTU per pound) nearly three times as high as that of conventional unusual aircraft are paced by advancements in pro- kerosene or JP fuel. This substantially reduces pulsion. It also reflects the confidence that, the fuel weight required for a given range. although substantial improvements have already However, a disadvantage of hydrogen is apparent in been made, vast opportunities still exist for the sketch of a typical hydrogen-fueled transport extending the horizons of aviation in the future.

shown in Figure 25. Even after being liquefied, hydrogen is only one-tenth as dense as kerosene.

The fuel cannot be contained in the limited volume available in the wings; instead the fuse- lage must be enlarged to hold bulky fuel tanks.

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of High Altitude Emissions," Proceedings Of '2 SCAR Conference, NASA CP-001, Pt.2 Nov. 1976, pp. 565-574.

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NGINE DIAGNOSTICS PERFORMANCE IMPROVEMi;.

IAN NICKS ABRADABLE SEALS COMPRESSOR TIP WEAR IMPROVED TURBINE WARPED COMBUSTORS MATERIALS AND COAT,NLS SEAL i EAKAGES CI I ARANCE CONTROI.

ERODED TURBINE BLADES EXHAUST NOZZIE MIXER Figure 2. - Engine component improvement.

CURRENTLY RECOVERED ENGINE PERCENTAGE REPAIR- INCREASEIN , SPECIFIC FUEL — LONG TFRM CONSUMPTION ^^ ENGINE PERFORMANCE ^'- AVERAGE SHORT TERM DETERIOR.iT1ON REPAIRED ENGINE ENGINE TREND

PERFORMANCE i

DETERIORATION EARLY FLEET OPERATION -- FLEET OPERATION —Av FIELD CHECKOUT Figure 3. - Engine component improvement engine diagnostics. SFC per- formance deterioration trends for typical engine.

,DVANCED TECHNOLOGY IMPROVEMENTS • MIXED FLOW EXHAUST • IMPROVED CYCLE • HIGHER TEMPERATURE MATERIALS • IMPROVED COOLING • IMPROVED COMPONENT AERO • ACTIVE CLEARANCE CONTROL • BETTER SEALS/BEARINGS • COMPOSITE FAN • COMPOSITE NACELLE • DIGITAL ELECTRONIC CONTROL CURRENT CYCLE E3 22- 30 OVERALL PRESSURE RATIO 37 - 45 4 - 5 BYPASS RATIO 6 - 9 2200- 2500 COMBUSTOR EXIT TEMP 01` ► 2500 - 2700 Figure 4. - Energy efficient engine.

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QCGAT E3, EC1. TP (COMMERRCIAL GATE \^\\ AIRLINERS) V1 TURBOFAN tBUSINESS v 300 JETS) '/ ^ TURBOPROP (GEN. AVIATION) ^I^ a ECIPROCATING (GEN. AV1,4TION1 < 1 111 -1 1 _1 11,E 60 100 200 400 1010 2000 4000 10 000 80 000 EQUIVALENT SHAFT HORSEPOWER Figure : 1. - u repulsion for civil aviation.

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TASK I FORECAST 1485 G.A. MARKET ESTIMATE MARKET IMPACT OF ADVANCED TECHNOLOGY TURBINES INCLUDE AIRPLANES AND HELICOPTERS IDENTIFY DESIRABLE ENGINE SIZES AND MISSIONS TASK 11 TRADEOFF ANALYSIS TURBOSKAFTIPROP <'1000 SHP TURBOFAN :1500 lb THRUST IDENTIFY HIGH PAYOFF TECHNOLOGIES DETERMINE "OPTIMUM" ENGINE (SIZE, CYCLE, CONFIGURATION', FEATURES) FOR EACH MAJOR APPLICATION COMPARE ADVANCED ENGINES WITH CURRENT ENGINES (TURBINES a RECIPS) SK III EVALUATE COMMON CORE CONCEPT MULTIPLE APPLICATIONS FOR SINGLE CORE, E. G. - TS, W, TF COMMONALITY OF PARTS & DESIGN O:r'ER AIRCRAFT tNGINES `LITOMOTIVE OR OTHER APPLICATIONS T^SK IV RECOMMEND TECHNOLOGY PROGRAM PLAN COMPONENT TECHNOLOGIES EXPLRIMENTAL CORE OR ENGINE PROVIDE BASELINE CONCEPTUAL ENGINE DESIGN Fiyure 16. - Gate study tasks.

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THRUST, lb 17 400

Figure 20. - QCSEE UTW engine.

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Figure 21. - Goals of NASA advanced mechanical components and

transmission technology,

REPRODUCIBILITY UC THE )1M ANAL PAGE IS POOlt Figure 22. - High-speed commercial hPlicopter.

Figure 23. - Helicopter convertible propulsion system.

REPRODUCIBII.M' OF Till' 1100P OMUNAL PAGE W MutINU DOUGLAS v r ,v IN-HOUSE/LTV LOCKHEED-GA Figure 24. - Span-distributed load, cargo aircraft concepts.

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Figure 25. - Hydrogen-fueled transport.

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- r` - M INLET rCOMBUSTOR'~ZNOZZLE Figure 26. - Hypersonic propulsion.

NASA-Lewis-