Document
NASA / TM--1998-208411 AIAA-98-3116
General Aviation Light Aircraft Propulsion:
From the 1940's to the Next Century
Leo A. Burkardt Lewis Research Center, Cleveland, Ohio Prepared for the 34th Joint Propulsion Conference cosponsored by AIAA, ASME, SAE, and ASEE Cleveland, Ohio, July 12-15, 1998 National Aeronautics and Space Administration Lewis Research Center
July 1998
Trade names or manufacturers' names are used in this report for identification only. This usage does not constitute an official endorsement, either expressed or implied, by the National Aeronautics and Space Administration.
Available from National Technical Information Service NASA Center for Aerospace Information 7121 Standard Drive 5287 Port Royal Road Hanover, MD 21076 Springfield, VA 22100 Price Code: A03 Price Code: A03 AIAA- 98--3116 GENERAL AVIATION LIGHT AIRCRAI_£ PROPULSION: FROM THE 1940'S TO THE NEXT CENTURY Leo A. Burkardt* NASA Lewis Research Center Cleveland, OH 44135-3191 It appears that we are now at a turning point in the Summary history of light aircraft engines, with new technologies and manufacturing techniques within reach that will Current general aviation light aircraft are powered have a major impact on the light aircraft engines of the by engines that were originally designed in the 1940's.
future. NASA's General Aviation Propulsion (GAP) This paper gives a brief history of light aircraft engine program is developing two new light aircraft demon- development, explaining why the air-cooled, horizon- stration engines, in cooperation with industry, which tally opposed piston engine became the dominant will provide a revolutionary quantum leap over current engine for this class of aircraft. Current engines are engines in affordability, ease of use, and comfort. This fairly efficient, and their designs have been updated paper describes the program, the engines being through the years, but their basic design and operational developed, and their impact on the industry.
characteristics are archaic in comparison to modern engine designs, such as those used in the automotive Evolution of the Light Aircraft Engine industry. There have been some innovative engine developments, but in general they have not been com- The internal combustion piston engine was the first mercially successful. This paper gives some insight into manufacturable engine that had a high enough power- the reasons for this lack of success. There is now to-weight ratio to meet the requirements of powered, renewed interest in developing modern propulsion heavier-than-air flight. Figure 1 shows the Wright systems for light aircraft, in the forefront of which is brothers' engine, which powered the first successful NASA's General Aviation Propulsion (GAP) program.
heavier-than-air aircraft flight in 1903. This was a This paper gives an overview of the engines being liquid-cooled, four-stroke, spark-ignited, internal com- developed in the GAP program, what they will mean to bustion piston engine--just one of many possible con- the general aviation community, and why NASA and its figurations of the internal combustion piston engine.
industry partners believe that these new engine develop- Over the years, most of the possible configurations have ments will bring about a new era in general aviation been tried with more or less success. This paper covers light aircraft.
only the "standard piston" engine, that is, an engine Introduction with a piston that reciprocates within a cylinder con- nected to a crank shaft via a connecting rod (fig. 2).
This is by far the most successful type of internal com- Light aircraft engines have had a long history of bustion engine. Other types, including cam engines and development. The first successful aircraft engine was vane engines, have been proposed and tried, but in gen- the Wright brothers' engine, which powered their eral have not been successful because of mechanical Wright Flyer in its first flight in 1903. Since that time, design difficulties and/or lack of adequate materials.
practically every piston engine configuration imaginable Over the years, the cooling method has probably has been tried. Mechanical layouts from inline to radial been one of the most controversial configuration issues and beyond were proposed and built. Two- and four- with respect to aircraft engines. Both liquid and air stroke engine designs were used with spark and com- cooling have advantages and disadvantages, and there is pression ignition. Air cooling and liquid cooling were no clear answer to which is better. The type of cooling tried. Engines using every combination of these selected depends in large part on the preferences of the mechanical layouts, cycle types, and cooling types have designer and end user. In the early years, most medium been successfully flown. Yet today, the air-cooled, to high power output engines were water cooled, with horizontally opposed, four-stroke, spark-ignited engine the exception of the infamous rotary engines, because is the only configuration to survive as a mass-produced, air-cooling techniques were not developed sufficiently certified light aircraft piston engine. The reasons for this to handle the high heat loads of these more powerful and why the turbine engine has not been able to pene- engines. Air-cooling techniques improved considerably trate the light aircraft market to any significant extent over the years, as evidenced by the increase in cooling are explored in this paper.
area per horsepower. In the mid-1920's typical cooling *Aerospace Engineer, Member AIAA and SAE.
NASA/TM--1998-208411 1 Two-stroke engines can attain higher power-to-
areas were on the order of 25 in.2/hp, and by the mid-
weight ratios because a two-stroke engine has one 1940's they were on the order of 35 in.2/hp. With these power impulse with every stroke of the piston, whereas improvements in air-cooling techniques, air cooling was a four-stroke engine requires two piston strokes for also successfully used on high power output engines.
every power impulse. Therefore, if everything were Air-cooled engines tend to be lighter and simpler. When equal, a two-stroke engine would develop twice the running at high power outputs, though, they usually power of a four-stroke engine running at the same require rich fuel mixtures, with the heat of vaporization speed. In reality, that does not quite hold true because of the extra unburned fuel being used to help cool the of the less efficient breathing associated with the two- engine. This results in poor fuel economy and high stroke process.
emissions at high power. Air-cooled engines can also be The major drawback of the two-stroke configu- sensitive to what is called thermal shock; that is, over- ration is its lower fuel efficiency when it is applied to cooling during sudden reductions in power, which may spark-ignition engines, as much as 60-percent greater result in engine damage.
fuel consumption. Until recently, in virtually all spark- Liquid cooling allows better control of the engine ignition engines, the fuel and air were premixed before heat loads, which enables more efficient fuel usage, they were taken into the cylinder to ensure a homoge- results in less cylinder distortion, and permits tighter neous air-fuel mixture for proper ignition and burning design tolerances. The radiator can be placed in its most when the spark was produced. Also, premixing the fuel efficient location in the airframe for drag reduction and through carburetion or manifold injection is mechani- structural efficiency. However, liquid cooling has the cally much simpler and less expensive than direct in- disadvantage of introducing another subsystem to the cylinder fuel injection. Because intake and exhaust must engine, which adds weight, cost, and additional occur simultaneously in a two-stroke engine, it is inevi- mechanical failure modes.
table that some of the fresh fuel-air mixture will be lost Historically, most light aircraft engines have been through the exhaust port, wasting fuel. As the art of air-cooled because of the importance of simplicity and piston engine design progressed, reliability increased.
lower cost in this class of aircraft. This has continued to By the mid-1910's, the two-stroke engine's lack of fuel be the trend to the present day with essentially all of efficiency resulted in its no longer being a major player today's commercial light aircraft engines being air- except for very small engines.
cooled.
The final major engine configuration issue was the The preferred cycle type was settled by the 1920's.
mechanical layout of the engine: that is, its shape and Two- or four-stroke cycles can be used with either spark the alignment of its cylinders. The four basic types or compression ignition (fig. 3). (Compression-ignition were the inline engine, the V-engine, the horizontally engines are more commonly referred to as diesel opposed engine, and the radial engine (fig. 4). Progres- engines.) Compression-ignition engines require high sing from the inline to the radial configuration, for a compression ratios (greater than 14:1) because gas given power output the engine usually becomes lighter.
temperatures above the fuel auto-ignition point must be However, it grows in frontal area, which tends to developed during the compression process for the fuel increase drag. Mechanical layout also affects the to ignite. The high compression ratio requires a heavy difficulty of cooling an air-cooled engine. Much more structure to withstand the stresses developed. Therefore, attention to the air ducting system is needed to ensure although compression-ignition engines tend to be more good cooling of cylinders that fall directly behind other fuel efficient because of the high compression ratio, cylinders, as occurs in all configurations other than the they are also much heavier than spark-ignition engines radial configuration, with the inline configuration being of equivalent power. Because aircraft greatly benefit the worst case of this. The inline engine tends to be from lightweight components, compression-ignition heavier than the radial because of the long, multiple- engines never were major players as aircraft throw crankshaft, which is more massive than the short, powerplants.
single-throw crankshaft of the radial. Additional mass is In the early years, two-stroke engines were given required for stiffness in long inline configurations, and much consideration for aircraft because of their greater additional counter weighting is required to overcome reliability and power-to-weight ratio in comparison to the rocking moments, which do not exist in a radial four-stroke engines. Two-stroke engines tend to have configuration.
fewer moving parts because the piston is used to open A special, interesting case of the radial engine was and close the intake and exhaust ports; a separate the rotary engine. In this engine, the crankshaft was mechanical valve system is needed for four-stroke fixed to the airframe and the engine case rotated with designs. Also, fuel and oil are mixed and used for lubri- the propeller. This type of engine was very popular in cation in most two-stroke designs--so as long as the World War I because it was light, smooth running, and engine is getting fuel, it is being lubricated. These two had very good cooling characteristics. Its smoothness design features made early two-stroke engines much was due, in part, to the fact that the pistons did not more reliable than the four-stroke engines of that time.
reciprocate with respect to the aircraft but merely NASA/TM-- 1998-208411 2 size class are short and compact with little to no weight
orbited ina circle. Also, the spinning case acted as a
penalty in comparison to radial engines. Finally, since a flywheel, which smoothed out the torque pulses. How- small number of cylinders are lined up on each side of ever, this also had the detrimental effect of causing the engine, air cooling is not a major problem. For these large gyroscopic forces during maneuvering, which the reasons, the air-cooled, horizontally opposed engine has pilot had to compensate for. The main drawbacks of the virtually displaced all other piston engine configura- rotary engine that made it unsuitable for general tions in the light aircraft arena.
aviation were its extreme unreliability and the difficulty The granddaddy of all horizontally opposed of putting an exhaust manifold and carbureted fuel-air engines is the Continental A--40 (fig. 6). This engine delivery system on a rotating engine. The unreliability of these engines was due in part to extreme efforts to was 115 in. 3 in displacement, produced 37 hp at reduce weight for military purposes; however, even with 2500 rpm, and weighed 144 lb. Introduced in 1931, the that consideration, they tended to be less reliable than A-40 was the first popular horizontally opposed engine their contemporary water-cooled inline counterparts.
with more than two cylinders. It had many of the desir- The lack of an exhaust manifold made them very able qualities still looked for in general aviation light unpleasant to fly behind, and the primitive fuel supply aircraft engines today. It was smooth, reliable, easy to system resulted in poor fuel efficiency and lack of start, and inexpensive.
throttleability.
By the late 1930's, there were three major manu- From the mid-1920's to the mid-1930's, the air- facturers of horizontally opposed engines for light air- cooled inline engine was considered to be the best light craft: Continental, Franklin, and Lycoming. In 1938, aircraft engine. It was lighter and simpler than the Continental introduced the A-50, which a year later was liquid-cooled inline engine and produced less drag than upgraded to the A-65 shown in figure 7. The A-65 pro- the radial engine. The high drag of radial engines was duced 65 hp at 2300 rpm.
overcome with the invention of the NACA cowl in the Compare this engine with the currently produced early 1930' s, making radial engines competitive for Continental IO-240-B (fig. 8), and the design heritage higher speed aircraft by the mid-1930's.
of today's Continental engines is immediately apparent.
For single-engine aircraft, figure 5 shows a major Virtually all engines currently produced by Continental disadvantage that all other configurations have in com- and Lycoming were originally designed in the 1940's or parison to the horizontally opposed configuration. The 1950's. These were excellent engines when they were Cessna 182, which has a horizontally opposed engine, introduced, and they are still good engines today. Fur- has much better over-the-nose visibility than the Cessna thermore, the designs have been improved over the 190, which has a radial engine. The horizontal configu- years, with upgrades such as the replacement of carbur- ration allows a higher thrust line with better forward etion with modem electronic fuel injection. Most of visibility than do any of the other configurations.
these improvements have dealt with engine perfor- An inverted inline or V-configuration would give mance, whereas the manufacturing method and the a high thrust line also, but it is not as easy to accom- human factor aspects of the propulsion system have modate retractable front landing gear. A particular essentially been unaddressed. These two categories consideration with inverted engines is the problem of include aspects such as noise, vibration, ease of use, hydraulic lock. Oil can drain down past the piston into and engine cost; and these are the areas where today's the combustion chamber. If the engine sits unused for piston aircraft engines pale in comparison to modern awhile, a volume of oil larger than the combustion automotive engines.
chamber volume at the piston's top-dead-center can There were some attempts at new designs in the drain into the combustion chamber. If it is not drained 1970's and 1980's. Continental developed and intro- before someone tries to start the engine, the piston will duced to the market the compact, lightweight, high- push up against the oil when the engine is cranked, and revving Tiara and the liquid-cooled Voyager series since oil is incompressible, it will not be able to extend engines (fig. 9). Lycoming participated early on in the to full top-dead-center and the engine will be damaged.
development of the Wankel engine (fig. 10) for aircraft The horizontally opposed piston engine integrates use. Wankel engine development was discontinued, well with modem single-engine aircraft. There is little after many years of effort, in the early 1990's. There to no additional drag penalty because the engine fits were still some mechanical reliability problems, and within the width of the side-by-side seating arrangement after all was said and done, there did not appear to be of virtually all post-World War II light aircraft designs.
that much advantage to the engine over standard It allows a high thrust line with good over-the-nose engines. Its one major advantage was its stratified- visibility. Compared with a radial engine with the same charge combustion system, which enabled it to run on number of cylinders, an opposed engine would be almost any liquid fuel. However, the great promises of heavier; however, because of balance considerations, low cost and weight were never realized. The stratified- for the same smoothness of operation, a radial engine charge combustion system reduced the fuel-to-air ratio requires more smaller cylinders than an opposed engine the engine could accommodate, and this, coupled with does. Therefore, in practice, opposed engines in this the required gearbox to reduce high crankshaft speeds NASA/TM-- 1998-208411 to those usable by the propeller, resulted in a power-to- 1000 aircraft per year. In this market, few innovative weight ratio not much better than that of other engines. new products were developed and a pilot could buy good used aircraft with the same performance and com- These systems also increased engine cost, so this engine fort characteristics as a new aircraft for less than half never made it to market. The Continental engines, on the other hand, were not successful in the market.
the price. The light aircraft market has muddled along Why weren't these innovative engines successful? in this condition for the last 15 years.
We appear to be at a critical time in the light There are many factors, but the basic reason is that they offered nothing except minor benefits in performance aircraft market, and there is optimism in the industry over engines already in the marketplace. In a thriving that the market is ripe for a turnaround. The average age market, such benefits could have been justified; but in a of the light aircraft fleet is 29 years. Consumer elec- depressed market, the cost of incorporating these tronics, materials, and engine technologies have pro- engines into aircraft was greater than the profits they gressed to the point where major performance, comfort, and price advances are feasible for light aircraft.
would produce.
Some of these advances are very prominent in home-built aircraft. Home-built aircraft now outstrip Turbine Engines every certified production aircraft in performance and Turbine engines make very good aircraft engines modem avionics. Light aircraft pilots are hungry for these advances and this accounts, in part, for the popu- as is evidenced by their complete takeover of aviation propulsion except for the light aircraft market. Turbine larity of home-built aircraft.
engines, such as the Allison Model 250 (fig. 11), have The General Aviation Revitalization Act passed been introduced into this market. However, they have by Congress in 1994 relieves some of the burden on manufacturers by limiting their liability to 18 years. In not made major inroads into the market and mainly find addition, the industry is actively promoting new pilot use in niche markets. Although most turbine engines are not quite as fuel efficient as piston engines, they are recruiting and training programs.
much lighter, which helps to reduce aircraft weight and Finally, foreign manufacturers are beginning to show interest in this market. For example, Toyota's partially offsets their higher fuel usage rate. In every other way it can be argued that turbine engines are prototype aircraft engine based on the Lexus V8 auto- superior to piston engines for aircraft applications. They motive engine was type certified recently, meaning that have an Achilles heal, however: they are extremely the engine design meets Federal Aviation Administra- tion (FAA) requirements. Before Toyota can produce expensive. In the light aircraft marketplace, that is an the engine in quantity, they will also need a production overwhelming detriment. A turbine engine propulsion certificate, which certifies that the manufacturing system can cost more than the piston-powered aircraft that it might be considered for. Therefore, turbine facility produces engines that conform to the type certificate.
engines have only been able to penetrate, to a small extent, the top-of-the-line luxury light aircraft market.
The Challenge General Aviation Light Aircraft Marketplace For the light aircraft market to be reinvigorated and the United States to maintain leadership in this market, The general aviation light aircraft market once modem aircraft that meet the needs and desires of the thrived, having a sales trend that generally followed the gross national product. Single-engine aircraft general aviation customer must be developed. Both sales peaked at over 14,000 aircraft per year in 1978 traditional light aircraft customers and the potential new customer base of those who need affordable, fast, (fig. 12). However, just after this peak, sales began to sharply decline. Many factors contributed to this efficient cross-country transportation need to be considered.
decline, including a reduction in investment incentives, the oil crisis, the loss of postwar government pilot train- An enabling part of this challenge is the develop- ment of new light aircraft engines. The NASA Aero- ing incentives, and a sharp increase in liability costs nautics Advisory Committee's General Aviation Task spread over a smaller sales volume. The interesting thing to notice is that there was a similar decline in the Force Report of September, 1993, states that "replacing late 1960's; however, as the economy picked up in the today's outdated light aircraft propulsion systems is perhaps the most important factor in revitalizing the 1970's, so did aircraft sales. This resurgence did not occur in the 1980's.
light aircraft market." There is an old axiom: "New Figure 12 shows the mean price of single-engine engines beget new aircraft."
aircraft over the mean average family income for these In spite of the age of their design, today's engines same years. Aircraft prices began to rise sharply at this do perform well. However, as depicted in figure 13, downturn, and new aircraft became unaffordable for today's engines leave much to be desired. Turbine most individuals, forcing sales down even further and engines would redress all of these problem areas, but as keeping them at a severely depressed level of less than discussed earlier and depicted in figure 14, their cost NASA/TM-- 1998-208411 airport neighbors and aircraft passengers. As seen in
must bedrastically reduced before they can become
figure 16, this engine together with the quiet propeller viable engines for this class of aircraft.
will more than meet expected future noise regulations.
To meet the propulsion challenge, NASA has Leaded gasoline will be a thing of the past. GAP's IC joined with industry and the FAA in the General engine will burn jet fuel at a low fuel consumption rate Aviation Propulsion (GAP) program to develop two of 0.36 lb/hp-hr instead of the 0.41 to 0.49 lb/hp-hr for new engines that will be the forerunners of the next today's engines. Special care is being taken in the generation of general aviation light aircraft engines.
design of the engine to ensure smooth, vibration-free These engines will change our concept of general operation. There will be no fuel-air mixture or propeller aviation propulsion systems. They will bring about a pitch control to contend with. Instead, a single power revolution in affordability, ease of use, and perfor- lever will control the engine and propeller. The engine mance. With their smooth, quiet operation, they will will provide the same kind of quiet, easy-to-use power provide a level of comfort never before enjoyed in that has become the standard in the automotive world.
general aviation light aircraft. These new engines prom- Along with these vast improvements in engine operation ise to be the key to creating new demand for aircraft and and performance, unique design features and the to revitalizing the U.S. general aviation industry. The development of low-cost manufacturing methods will potential is especially strong when the benefits of the have the potential to reduce engine costs to 50-percent new propulsion systems are coupled with those of cock- of those of current engines.
pit and airframe technologies being developed by the The GAP compression-ignition engine will be NASA-FAA-industry Advanced General Aviation flight demonstrated on a Cirrus SR20, Lancair Transport Experiments (AGATE) consortium.
Columbia, and Piper Seneca IV (fig. 17) in the year NASA's GAP program consists of two elements: 2000.
the Intermittent Combustion (IC) Engine Element and the Turbine Engine Element. By the year 2000, NASA GAP Program Turbine Engine Element and its industry partners will develop a revolutionary new piston engine in the IC Engine Element and a revo- GAP's Turbine Engine Element will demonstrate a lutionary new turbofan engine in the Turbine Engine new propulsion system concept for higher performance Element. That year, both of these engines will be flight light aircraft. These aircraft usually have four to six demonstrated to the public for the first time at the seats and cruise at more than 200 kt.
Experimental Aircraft Association's AirVenture '00.
Reducing the price of small turbine engines by an Commercially produced engines based on these engines order of magnitude (from hundreds of thousands to and manufacturing technologies will soon follow.
tens of thousands of dollars) is the primary goal of the Turbine Engine Element.
GAP Program Intermittent Combustion Engine Element Williams International and its partners (Bell Helicopter, California Drop Forge, Cessna Aircraft, GAP's Intermittent Combustion (IC) Engine Chichester-Miles Consultants, Cirrus Design, Forged Element will demonstrate a new propulsion system for Metals, New Piper Aircraft, and VisionAire; subcon- entry-level aircraft. Such aircraft usually have a single tractors Producto Machine, Scaled Composites, and engine, no more than four seats, cruise at less than Unison; and consultant Raytheon Aircraft) have teamed 200 kt, and are easy to handle. The goal of the IC with NASA to develop a truly revolutionary turbine Engine Element is to reduce engine prices by one half engine that will set a new standard for general aviation while substantially improving reliability, maintainabil- engines. The FJX-2 high bypass ratio turbofan engine ity, ease of use, and passenger comfort.
(fig. 18) will produce 700 lb of thrust and weigh less To achieve this goal, Teledyne Continental Motors than 100 lb. This is a weight advantage of 3 or more and its partners (Aerotronics, Cirrus Design, Hartzell over current piston propulsion systems with similar Propeller, Lancair International, New Piper Aircraft, and subcontractor Perkins Technology) teamed with capabilities.
With a bypass ratio of approximately 4:1, the NASA to develop a highly advanced piston engine FJX-2 will be fuel efficient and, more importantly, very (fig. 15). This engine incorporates many innovations. It quiet. It will be 20-dBA quieter than the current Stage 3 is a horizontally opposed, four-cylinder, liquid-cooled, regulation for turbofan aircraft, and as shown in figure two-stroke, compression-ignition engine. Compression- 19, the FJX-2 will even be very quiet in comparison to ignition engines are well known as very reliable but today's piston aircraft (which, in general, fall close to heavy. However, combining the two-stroke operating the current regulation line).
cycle with innovative lightweight construction will Emphasis will be placed on simplifying and result in an engine that is lighter than today's aircraft reducing the number of parts. For example, there will engines. The engine will produce 200 hp.
be no mechanical power takeoff and all aircraft power This IC engine will be combined with advanced requirements will be supplied electrically. Such low- design, low-speed propellers (from related NASA- cost design techniques, combined with the development industry research) to offer very quiet operation for both NASA/TM--1998-208411 of advanced automated manufacturing methods will realized, especially when these engines are combined lead to a turbine engine with the unprecedented poten- with advances in airframes and avionics being devel- tial of being cost competitive with piston engines. oped in the AGATE program. Commercial derivatives Aircraft powered by commercial derivatives of these engines will provide a previously unheard of level of comfort and convenience, and there will be a of GAP's turbine engine will have the performance to avoid bad weather and minimize travel time. By taking true revolution in the performance-to-price ratio. Hying advantage of the weight and aerodynamic integration will not only be fun, it will be comfortable and affordable!
benefits of this engine, such aircraft will do this with a takeoff-to-landing fuel burn equivalent to or less than References that for today's comparable piston-powered aircraft (fig. 20).
The FJX-2 will be demonstrated in the year 2000 1. Smith, H.H., "Aircraft Piston Engines," McGraw- Hill, New York, 1981.
on the V-Jet II (fig. 21). This aircraft was specially built to demonstrate the revolutionary benefits of this 2. Wagner, W., "Continental! Its Motors and Its engine for future light aircraft designs. People," William Wagner, Aero Publishers, Fallbrook, CA, 1983.
Conclusions 3. White, G., 'q'he Allied Aircraft Piston Engines of World War II," Society of Automotive Engineers, Warrendale, PA, 1985.
New engines enable new aircraft. With the two new engines being developed in the GAP program, general 4. Whittier, B., "Light Plane Heritage," Experimenter, vol. 17, no. 3, Mar. 1997.
aviation will take an exciting leap forward. The poten- tial for an invigorated general aviation market will be NASA/TM--1998-20841 I 6 Figure 1 .mWdght brothers' Wright Flyer enginH liquid-cooled, four-stroke, spark-ignited, internal combustion engine. (Copyright National Air and Space Museum; used with permission.)
Cylinder Connecting rod Crankshaft Figure 2.--Standard piston engine.
NASA/TM--1998-208411 7 Intake Compression Power Exhaust Compression Power stroke stroke stroke stroke stroke stroke Four-stroke cycle Two-stroke cycle
l&l
Spark ignites fuel High-temperature air resulting from high compression ignites fuel Spark ignition Compression ignition Figure 3.--Engine cycle types.
V Inline Horizontally opposed Radial Figure 4.--Engine mechanical layouts.
NASA/TM-- 1998-208411 8 Figure 6._ontinental A-40--first popular, horizontally Figure 5.--Radial (Cessna 190) versus horizontally opposed engine. It produced 37 hp at 2500 rpm.
opposed (Cessna 182) engine installation.
(Copyright Teledyne Continental Motors; used with (Copyright Cessna; used with permission.)
permission.)
Figure 8._ontinental IO-2_ currently used, Figure 7._ontinental A-65_a horizontally opposed horizontally opposed engine. (Copyright Teledyne engine producing 65 hp at 2300 rpm. (Copyright Continental Motors; used with permission.)
Teledyne Continental Motors; used with permission.)
NASA/TM-- 1998-208411 9 Figure 10.---Rotary Power lntemational's Model 2013R Figure 9._ntinental Voyager 200---a liquid-cooled Wankel engine.
engine. (Copyright Teledyne Continental Motors; used with permission.)
Actual aircraft sales 16x103 Price/FMAl -- -- 5 \ I', O
,0
d) "O cL 8 2.
¢) <_ 1 -- 0 0 65 70 75 80 65 90 95 Year Figure 12.--Single-engine aircraft sales and price Figure 11 ._Allison Model 250--a light aimraft turbine per family mean annual income (FMAI).
engine. (Copyright Allison Engine Co.; used with permission.)
NASA/TM-- 1998-208411 10 FUEL HighAVGAScost MAINTENANCE EMISSIONS COST COMFORT 7,_4fill_=lll_'_ +'+' '+" ___J Figure 13.--Why light aircraft need new engines.
I I GAP Turbine Engine Technology Low vibration High reliability Multifuel capability Low weight Low emissions Fuel usage Low maintenance Low installation drag Turbine engine disadvantages Turbine engine advantages Figure 14.--Turbine engines are desirable but very expensive.
NASAFFM--1998-208411 11 90 m ICAO noise -- limits J ,_- .........
= 6o
Current/j_ J p _ " "O / ,J --" 75 /
>= /
O Proposed," == 70 ......
-, GAP piston o -- engine noise z 65 6O
I I I I
0 500 1000 1500 2000 Maximum takeoff weight, kg Figure 15._GAP piston engine--an innovative, Figure 16.--GAP piston engine noise compared with horizontally opposed, four-cylinder, liquid-cooled, International Civil Aviation Organization (ICAO) two-stroke, compression-ignition engine.
noise limits for propeller aircraft.
Figure 17.--GAP piston engine flight demonstration aircraft.
NASA/TM-- 1998-208411 12 90-- _ ICAO noise S ..........
limits J, ,,_
<=80
Curre_ js _ / // --" 75 -- / / > _ Proposed/ FJX-2 engine .¢_ ....... _ noise O z 65 6O 55 I I L I 0 500 1000 1500 2000 Maximum takeoff weight, kg Figure 19.mFJX-2 noise compared with International Figure 18.---GAP FJX-2 turbofan engine.
Civil Aviation Organization (ICAO) noise limits for propeller aircraft.
Weight, Ib Range, mi Figure 21 .--V-Jet II turbofan (FJX-2) demonstration Figure 20.DAircraft performance estimate for typical aircraft.
single-engine turbofan.
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1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED July 1998 Technical Memorandum 4. TITLE AND SUBTITLE 5. FUNDING NUMBERS General Aviation Light Aircraft Propulsion: From the 1940's to the Next Century WU-523-12-13-00 6. AUTHOR(S) Leo A. Burkardt 8. PERFORMING ORGANBATION 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) REPORT NUMBER National Aeronautics and Space Administration Lewis Research Center E-11246 Cleveland, Ohio 44135-3191 10. SPONSORING/MONITORING 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) AGENCY REPORT NUMBER National Aeronautics and Space Administration NASA TM--1998-208411 Washington, DC 20546-0001 AIAA-98-3116 11. SUPPLEMENTARY NOTES Prepared for the 34th Joint Propulsion Conference cosponsored by AIAA, ASME, SAE, and ASEE, Cleveland, Ohio, July 12-15, 1998. Responsible person, Leo A. Burkardt, organization code 2200, (216) 977-7021.
12b. DISTRIBUTION CODE 12a. DISTRIBUTION/AVAILABILITY STATEMENT Unclassified - Unlimited Subject Category: 07 Distribution: Nonstandard This publication is available from the NASA Center for AeroSpace Information, (301) 621-0390.
13. ABSTRACT (Maximum 200 words) Current general aviation light aircraft are powered by engines that were originally designed in the 1940's. This paper gives a brief history of light aircraft engine development, explaining why the air-cooled, horizontally opposed piston engine became the dominant engine for this class of aircraft. Current engines are fairly efficient, and their designs have been updated through the years, but their basic design and operational characteristics are archaic in comparison to modem engine designs, such as those used in the automotive industry. There have been some innovative engine develop- ments, but in general they have not been commercially successful. This paper gives some insight into the reasons for this lack of success. There is now renewed interest in developing modem propulsion systems for light aircraft, in the fore- front of which is NASA's General Aviation Propulsion (GAP) program. This paper gives an overview of the engines being developed in the GAP program, what they will mean to the general aviation community, and why NASA and its industry partners believe that these new engine developments will bring about a new era in general aviation light aircraft.
15. NUMBER OF PAGES 14. SUBJECT TERMS 16. PRICE CODE Propulsion; Aircraft; Engines A03 20. LIMITATION OF ABSTRACT 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIRCATION 17. SECURITY CLASSIFICATION OF ABSTRACT OF REPORT OF THIS PAGE Unclassified Unclassified Unclassified Standard Form 298 (Rev. 2-89) NSN 7540-01-280-5500 Prescribed by ANSI Std. Z39-1B 298-102