Exploring the Mazda Wankel Rotary As an Alternative Aircraft Engine PAUL LAMAR, EAA 171194

Exploring the Mazda Wankel rotary as an alternative aircraft engine PAUL LAMAR, EAA 171194

Aviation headline nine years from now:

Rotary-Powered Racer Bests Warbirds at Reno RENO, NV—Employing turbocharged, twin three-rotor engines, the Rotary Ranger demonstrated what a low cross section, lightweight, reliable, 1,000-horsepower engine can do....

kay, so it hasn't happened yet. But let me convey why such a headline isn't that 1 O outrageous. When married with the proper airframe, a rotary engine could certainly give the old L\_ Li warbirds a run for their money. So why do engine experts seldom in- clude the rotary engine when dis- cussing the merits of auto engine conversions for aircraft? Most likely, it's lack of knowledge. If I could define the criteria for a realistically "perfect" aircraft engine, I think you'd agree that the following attributes are desirable in any aviation powerplant: reliability; robustness; extended time between overhauls (TBO); damage tolerance; smoothness; no shock cooling; abil-

44 FEBRUARY 2002 Perry Mick's Mazda-powered Long- It believed in the rotary engine and valve springs, camshafts, lifters, EZ features a ducted fan shroud giv- solidly understood its superior kine- pushrods, and crankshafts--espe- ing it an extra-futuristic profile. matics. Eventually, Mazda sold more cially at high rpm. The crankshaft in than two million rotary engine-pow- a piston engine, for example, is a ity to run low-cost fuel; low fuel con- ered cars. stress analyst's worst nightmare sumption; low purchase cost; high with its twisting and turning every horsepower-to-weight ratio; com- Why Rotary? which way. pact size; and simplicity. Kinematics is the science of mechan- Wankel engines have no recipro- The Mazda Wankel rotary engine ics that deals with motion, and poor cating motion because every part meets most of these criteria. kinematics and reciprocating mo- moves in a circle or moves in nlore tion have always been the bane of or less the same direction. A two-ro- Wankel HistorY the piston engine. Things stop then tor Wankel engine has only three 1)r. Felix Wankel invented the start up again in the opposite direc- moving parts: two rotors and the ec- eponymous engine in the 1930s, tion twice per revolution. centric shaft, which is analogous to and I use "Wankel engine" in the This reciprocating action creates the piston engine's crankshaft. Un- generic sense to differentiate it from tremendous stress on connecting like a crankshaft, however, the ec- all other rotary engines. Around rods, pistons, piston pins, valves, centric shaft is straight and ex- 19S0, l)r. Wankel built a running pro- totype, but it didn't generate much com- mercial excitement. Several companies were interested in the engine, however. One of them was Toyo Kogyo, known to Americans as Mazda Motors, and it created a state-of- the-art computerized test facility ex- pressly for developing the engine. After a lengthy development period, Mazda started sell- ing cars with rotary engines in 1967. Over the years engineering challenges continued to crop up, and the A B C E other rotary players gave up further development. But Mazda persevered.

Top, Tracy Cook, of Real World Solu- tions (see sidebar page 48), is help- ing aircraft owner Dave Garber get his dual Mazda turbo engine-powered g ~ Reno racer back in shape. Note the dual radiators aft of the cockpit.

Bottom, concept of an over-and-under dual Mazda Cosmo turbocharged three-rotor engines of 1000 hp each installed in a custom-designed Reno O ...... racer.

Spo"t Aviation 4.5 tremely strong. The engine discharges its exhaust aircraft plumbing is a necessity. The turbocharged, gases as the rotor moves over open- Another testament to the engine's 800-hp, two-rotor, 10000 ings in either the rotor housing or bulletproof design is Mazda's track rpm Mazda racing engine of the end housings. This action is sim- record at the 24-hour endurance race stock displacement has demon- ilar to that of a two-cycle piston en- in LeMans, France. Mazda was the strated this strength. Not including gine, but the Wankel is a four-cycle only Japanese car manufacturer to the monster turbo and other acces- engine, and like a four-cycle, four- win the race outright. In 1991 Mazda sories, this powerplant weighs a cylinder engine, it fires twice per fielded a car with a four-rotor version mere 200 pounds. This represents an output shaft revolution. of the two-rotor RX-7 engine, and it unprecedented power-to-weight ra- Because nothing in the Wankel beat all comers, the who's who of ex- tio for all but a turbine engine. reciprocates, stops and starts moving otic European carmakers. Nobody in his or her right mind in the opposite direction, it remains Tearing down the engine after would think of mounting an 800- in perfect balance, just like a turbine the race revealed little or no wear. hp Mazda Wankel engine in a light or an electric motor. It's impossible The following year, LeMans banned general aviation airplane, but it to perfectly balance a piston engine rotary engines from the race. Now, might make an ideal engine for because certain parts oscillate or re- roughly 10 years later, Mazda rac- Unlimited air racing. It does illus- ciprocate—by design—throwing off ing rotaries are either severely trate the robustness of the Mazda its center of gravity. Consequently, handicapped or limited to compet- Wankel engine. the rotary runs smoother than any ing against other Mazda rotaries in Because they do not reciprocate, piston engine. auto racing. the Wankel's rotors are made of Wankel engines cannot fail cata- In homebuilt aircraft, however, rugged cast iron, and unlike the pis- strophically in the "hand grenade" Mazda Wankel engines are seeing a tons in a piston engine, they are fashion, as sometimes occurs with renaissance of sorts for several rea- nearly impossible to melt. A rotary piston engines. One of the worst sons, low cost not being the pri- engine has no exhaust valves to melt things that can happen to a Wankel mary driver. The main reason is or burn, a common problem in air- is an overheated engine caused by durability. The stock engine will run craft engines, and it has no camshafts loss of coolant, but it will still run for many hours at high power with to gall and no lifters to score. and usually will get you to a nearby little or no wear. airport. Cold pressure checking the Like the rotary itself, the engine's coolant system before flight is im- Recent Improvements combustion cycle is unique. portant, and using high quality AX Subscribers to the Aircraft Rotary En-

| 1st Revolution | 2nd Revolution | 3rd Revolution | Shaft Rotation Angle O 90 180 270 360 450 540 630 720 810 900 990 1080 I I I I I I INTAKE COMPRESSION EXPANSION EXHAUST

COMPRESSION EXPANSION EXHAUST INTAKE COMPRESSI(fl

EXPANSION EXHAUST INTAKE COMPRESSION EXPANSION - — _.. —

CHAMBER CHAMBER CHAMBER CHAMBER A: EXPANSION A: EXHAUST A: INTAKE A: COMPRESSION B: EXHAUST B: INTAKE B: EXPANSION B: EXHAUST C: INTAKE C: COMPRESSION C: EXHAUST C: INTAKE OUTPUT SHAFT ANGLE 360 DEGREES OUTPUT SHAFT AN OLE 5« DEGREES OUTPUT SHAFT 180 DECREES OUTPUT SHAFT 000 DEGREES

46 FEBRUARY 2002 ...... / @

Turbocharged Mazda Wankel RX7 engine mounted on the author's Pul- sar/KIS Cruiser with single radiator obliquely mounted under engine. Dia- gram is the author's installation drawings for his rotary powerplant.

improvements, are not required. Based on the wear rate of the stock apex seals and cruising at about 150 hp and 4500 rpm, the projected TBO of a stock Mazda two-rotor engine in aircraft use is about 3,000 hours. Through real-world testing homebuilders have found that mixing STOCK SIDE EXHAUST TYPE COOLING two-cycle oil with the fuel reduces DIAGRAM FOR KIS TR-4 the apex seal wear and the carbon SHORT COWL VERSION deposits inside the engine. The ratio 27.00 [ ) used is about one ounce of two-cycle oil to one gallon of gas. The stock engine injects oil from the crankcase ~INED 0 :RCOBLER INTAKE into the combustion chamber. AL IFOLD ~RCD 2,5 ]NCH CQMpRESSE# Crankcase oil contains certain wear AIR PIPE NOT SHB~4N COOLING' NOT .~aaWN CORE #2-I15 RAI)IATI]R IN F'rNAL RA£[AT[IR NOT SHOVN additives that really make it un- IN FRONT VIEV PJ]~ITION suited to this task, and users disable the oil injector when using the engine in a race car or airplane.

Rotary Specifics INTAKE SOME PARTS NnT • Power-to-Weight Ratio SHn~N FOR CLARITY The power-to-weight ratio of the stock Mazda engine is excellent. De- gine Newsletter and others testing ro- High temperature, 500°F Teflon spite its mostly cast iron housing taries have further improved on what encapsulated silicon water jacket parts, the bare engine weighs 200 Mazda accomplished by using more seals and oil scraper O-rings have pounds. Expensive aluminum end costly high-tech materials for certain also been developed. These increase housings cut this weight by about 50 engine parts. Dr. Francisco Inanette, the engine's ability to withstand in- pounds. for instance, has developed a ceramic advertent overheating, which hap- The firewall forward installed apex seal (which is affixed to the ro- pens occasionally as homebuilders weight of a normally aspirated two- tor) that's so hard and smooth it has relearn pre-World War II lessons rotor Mazda engine with propeller no noticeable wear rate. Nobody has about liquid-cooled aircraft engines. speed reduction unit (PSRU), worn one out vet. These costly materials, although coolant, and radiators runs about the same as a Lycoming O- 320 or O-360--right around 300 pounds. With non-stock peripheral intake ports, a normally aspirated rotary can generate 240 hp on takeoff with excellent durability. • PSRUs Several popular propeller speed reduction units are available. Weigh- ing 40 pounds each, most

Sport Aviation 47 Rotary Suppliers "You install a rotary because you want one," Dave says. Speak Out "I'm saving $8 an hour in fuel, and my annual last year was The homebuilt industry supports several aftermar- $50. A total rebuild would cost me around $2,000. Overall, ket and accessory suppliers for rotary engines. Power- it's a cheaper way to go. But don't try to build the engine Sport Inc. in Osceola, Wisconsin, has been diligently work- yourself, and don't just go to your local garage. They won't ing on a more highly engineered reduction drive. "This do it right." seems to be the main deterrent in using the rotary engine in Tracy Crook of Real World Solutions Inc. (www.rotaryavia- aircraft," says PowerSport Manager Keith Holm. Since the tion.com) says, "I've done a lot of work on the PSRU and the Mazda 13B engine is torsionally stiff, it produces a specific EFI/ignition controller during the past three years and re- resonant frequency at certain cently came out with a higher power settings that can rattle a horsepower version of the PSRU poorly engineered reduction for turbocharged 13B and 20B drive. "Our RD-300 drive has three-rotor engines (300-hp max)." been available for more than a Tracy has flown his rotary-pow- year now," Keith says, "and ered RV-4 for more than 1,000 solves that problem." hours, and he's building an RV-8 PowerSport's drive is rated for that's about a year away from its 300 hp continuous at 2,000 first flight. "There were six ro- hours at an 80 percent duty cy- taries at EAA AirVenture 2001, cle. The 2.29-to-l reduction ratio and there are at least 100 rotary turns the prop at 2620 rpm at its projects currently underway and engine's 6000-rpm limit. Power- more starting all the time," Tracy Sport currently has its rotary en- says. "The auto fuel capability is gine conversion with its propri- definitely a factor in many builders etary electronic engine deciding to look at alternatives." management system and tuned Keith Holm of PowerSport intake and exhaust systems in- warns that plenty of challenges stalled in an RV-6A test aircraft exist for homebuilders consider- (displayed at EAA AirVenture ing rotary power. "Do as much re- Oshkosh 2001). PowerSport's engine produces 215 hp continuous at 6000 rpm—far below the limits of the stock Mazda 13B. You can find out more about PowerSport at its website: www.powersportaviation.com. PowerSport engines are all built from modified new parts directly from Mazda, but other engine builders—and home craftspeople with an engineering bent—start at the salvage yard. Companies like Atkins Rotary Specialties Inc. produce some solid aircraft engines from the bulletproof Mazda 13B. But even a seasoned auto racing pro like Dave Atkins is im- pressed by the PowerSport reduction drive because of its ability to handle high-torque loads. Dave typically uses a highly modified Ross drive, but his high-torque engines can be hard on them. Atkins has pre- sented the Rotary Engines in Aviation forum at EAA AirVen- ture and says, "A lot of people are still afraid of the rotary search as possible to be well informed about the options from the bad press the engine received in the early '70s. available. Be honest with yourself about your mechanical But Mazda fixed most of those problems in 1974." abilities and your project goals." Dave's RV-6, which has flown from the Seattle area to Homebuilders should also check with their insurance car- Oshkosh a half-dozen times, cruises at 160 knots and 8 gph riers to see how a particular engine/airframe combination of unleaded auto fuel. Drag racing in the early 1980s taught will affect their rates. him a lot about the Mazda, and Atkins Rotary Specialties Next year Mazda is introducing the RX-8 to the U.S. mar- (tvtvtv.atkinsrotary.com) uses custom manufactured parts, ket with an updated and more powerful rotary engine, factory parts, and modified parts to build its enhanced avia- known as the Renesis. Even though the engine won't be tion powerplants. One Atkins customer has more than available to the aftermarket for quite some time, it does in- 2,500 hours on his engine, and Dave has never had a cus- dicate a bright future for the rotary. tomer experience an in-flight failure. —Mike DiFrisco

48 FEBRUARY 2002 of them are based on the Rotary User Groups Ford truck automatic trans- Ry Rotary Website (pilots and their projects)—www.members.home.net/flyrotary/ mission planetary gear set. Rotary Engine Website (Paul Lamar)—http://home.earthlink.net/~-rotaryeng/ Ford recently beefed up this transmission by changing the num- degrees lean of peak, and it won't engine burns 0.47 pounds of fuel ber of pinion gears from four to six, burn the exhaust valves—because per hour for each horsepower gener- making it suitable for the three-rotor the engine doesn't have any. At this ated; an air-cooled piston engine engines or the higher power tur- setting, the EGT has dropped into burns about 0.45. If you run the en- bocharged two-rotors. the piston engine range, and the engine full rich at peak power, it will • Turbochargers gine is only slightly less economical burn 0.65, just like an air-cooled pis- Turbochargers, which maintain than an air-cooled piston engine. ton aircraft engine under the same engine power at high altitudes, Tracy Crook, who has a Mazda ro- conditions. The new RX-8 engine is weigh about 35 pounds. To my tary on his RV-4, estimates that his reputed to be much more economi- knowledge, the upper horsepower limits of the turbocharged versions are unknown because nobody has Across Town. run one in an airplane for more than about 100 hours. Or Cross-Country. • Engine Size The two-rotor engine is compara- The Ultimate Off-Road Vehicle. tively tiny. Without any accessories it measures about 12 inches wide, 14 inches high, and 18 inches long. It's quite possible to squeeze a turbocharged two-rotor engine, includ- st seat-mile ing radiators, inside a stock kit air- operating cost. '•• plane cowling. (I've done it with my RPM governor, heater, KIS Cruiser. By comparison, the rotor brake & more. room in a Van's RV cowling would Still priced under $300,000. be considered voluminous.) • Three-Rotor Engines Three-rotor engines develop 50 percent more power than two-rotor engines, and you can import them from Japan. Baa- three-rotor engines weigh less than 300 pounds, and a firewall forward installation would weigh around 400 pounds without a turbocharger. Racing Beat in Ana- heim, California, has a three-rotor turbocharged aircraft engine on the dyno generating 900 hp with about 200 hours of dyno runs so far. The eccentric shaft in the three- rotor is the same diameter as the one in the two-rotor, and it gives no trouble. With exactly the same eccentric shaft diameter, the Mazda LeMans engine was a four-rotor, normally aspirated unit developing 690 hp at 9500 rpm. Many of the other three- and four-rotor parts were similar if not identical to the two-rotor RX-7 engine. • Fuel Consumption The Mazda will happily run 100 For more information, visit SPORT AVIATION on the Web at wvwv.eaa.org

Sport Aviation 49 ca). Th e Power-to-Weight vs. HP Mazda Various Engines happily 3.00 Garrett TSE 231-1 runs on autogas (gas turbine) ——— *. 4 that, right now, is about half the cost of 2.50 avgas. • Cooling Holler Rotary The total heat re- 2.0O jected by a Mazda ro- Garrett TSE 36-1 /(gas turbine) tary is only slightly 1.50 higher than a piston o Wankel LCR 814 1/2 Le Mans / V Mazda Side Q. Rotary/ Engine——^ ^p,^ E||^ne O) engine. All engines en Midwest Harrier / /Midwest Hawk /maM|a 138 Rotary o Rotary \ S / Rotary if have a heat balance, X 1.00 which is the distribu- ' / Lycoming 0-235 Lycoming IO-360-AIA / / /Continental 10-470-H tion of energy con- ^•' . / * t * *^ tained in the fuel due 0.50 1 \ "* * ^ to burning it. Some Wankel ^ * energy is rejected to R™"r?7 FMW-Z"»C the coolant as waste 0.00 , D 50 100 150 200 250 300 350 400 450 50 heat, some goes out Rated Horsepower the exhaust, and the remainder comes out the shaft as rejecting about the same amount of All internal combustion engines do mechanical energy. One horsepower horsepower to the coolant, about the same more or less by only a few is equal to 746 watts, and an engine 150 kilowatts. percentage points. A Wankel en- generating about 200 hp would be This is not unique to the Wankel! gine's heat balance differs by only single-digit percentages compared to rthe r Airplane A Perron Can Pv»;lJ/< all other forms of internal intermit- Mustang II "A great cross country tent combustion engines. (A gas tur- Two Place machine. At 200 mph, bine is an internal continuous com- 1,000 miies a day is 35 Years Proven / a piece of cake... bustion engine, in case you were Reliability 800+ Built My Mustang II wondering.) operates on 1 60 hp and has to be the most economical So Why Not a Wankel? airplane for its and versatility." To be frank, you'll have a consider- Midget Mustang Single Seater George J. Linkis, able engineering challenge installing Prbf/Gwner/Builder N13GL Also Available a rotary engine in your airplane. The 1 FAST/SIMPLE CONSTRUCTION Mustang Aeronautics, Inc. engine itself is not the problem; WITH QUICK BUILD ' AIRFRAME HTS START UNDER $ 10,000 1470 Temple Cily • Troy • Ml • 48084 careful planning is absolutely neces- Phone (248) 649-6818 • Fax (248) 649-0098 sary with any non-aircraft or auto www.MustangAero.com engine conversion. You can ease this challenge by making mechanical Don t Guess! Fly sate with Angle-ot-AttacK drawings and mock-up models before starting the building and instal- Voice Warnings lation process. Accurate and Affordable No Ugly Probes or Moving Parts You may have to design and build True full range AGA Instrument component parts like the motor Lightweight and Easy to Install mount, oil pan, alternator mount, Landing Gear Warning Option Patents 6,271,769 81 & Pending and intake manifold and modify the water pump inlets and outlets. As (952)474-4154 the engine becomes more popular, Proprietary Software Systems many of these unique aircraft-spe- 950 Iris Circle cific parts should eventually become Excelsior MN 55331 available to home craftspeople. On the upside, overhauling the rotary engine is trivial by Lycoming For more information, visit SPORT AVIATION on the Web at wmv.eaa.oig

50 FEBRUARY 2002 or Continental standards. $3,000. The 1993 models and later turbocharged two-rotor rotary engine. Strict attention to cooling details sell for more than $15,000 because Paid edits the 3-year-old e-mail Air- is essential. Most rotary home- they were more expensive and so- craft Rotary Engine Newsletter, builders have trouble with cooling, phisticated cars to begin with. which has about 1,000 subscribers. He and many have simply given up. With all it has going for it, the is married to Robin Lamar, a full-time The exact shape of the ducting to Wankel rotary just may be the light United Airlines mechanic, sometime the radiator is critical, and sealing aircraft engine of the future. c£*. A&P teacher, president of the Associa- the cowl properly to prevent back tion of Women Aircraft Mechanics, and pressure on the radiator is essential. A former aerospace and (Chaparral winner of the prestigious Aviation Tech- The design of the cowl flaps and the race car engineer, Paul Lamar invented nician of the Year award given by opening around them are other im- and manufactured computerized auto- Women in Aviation International. portant considerations. Wankel en- motive performance test eijidpment. Paid Robin has no time left over to help Paul gines reject a third of their cooling lias been an EAA member for 25 years, build his airplane. heat through the oil, so a good oil owns a Cessna J82, and has logged For more information visit cooler is mandatory, and the stock about 3,000 hours. Now retired, he's http://home.earthlink.net/~ro Mazda RX-7 oil cooler works well. building a KIS Cruiser with a Mazda taryeng/. The Wankel engine is ideal for turbocharging because of the shape of the combustion chamber, the in- herent low compression ratio, and Shape Meta/ the lack of exhaust valves. You'll need an intercooler to keep the intake temperature down. High intake manifold temperatures lead to deto- nation, which can fracture apex seals with consequent scoring of the rotor housing and rotors. The engine will not fail catastrophically under this scenario, but it will run somewhat low on power. A good muffler is essential with a Wankel because the exhaust port opens much more rapidly than in a Your Warbird could be a prizewinner if you shape its piston engine and emits supersonic cowling with a MetalAce shock waves. This will not be a prob- English Wheel. When you want the lem on the new Mazda RX-8 motor, finest, most precise Panels, Doors. which has side housing exhaust ports Wheel Pants, Etc., use the finest, most that open and close more gradually. precise English Wheel...MetalAce. A turbocharger helps quiet the No English Wheel is more rugged engine and adds no weight be- or versatile than a MetalAce. cause it replaces the muffler. In the 1989 to 1992 RX-7 model years, To receive more information Mazda built a good turbocharger about the 22B or our other fine for aircraft use. Later, dual tur- products, log on to bochargers were too complicated www.ratd.com or call us at and less reliable, while earlier ones -800-828-2043 today. just plain cracked. When purchasing a Mazda en- The MetalAce 22B gine for aircraft use, it's best to buy a offers excellent running car because it comes with a portability and Met a I flee versatility for lot of parts you can use, including aircraft restorers. M.icle in the USA ENGLISH WHEELS the alternator, ignition coils, fuel in- Craftsmen know. jectors, starters, oil coolers, etc. Good Mazda vintages are 1989 and Manufactured in the USA by Right Angle Tool • 1-800-828-2043 later. 1992 and earlier second-gener- 1-309-827-6878 • 13958 Roberto Rd. • Bloomington, IL 61704 www.ratd.com ation RX-7s can be had for less than For more information, visit SPORT AVIATION un the Web at www.eaa.org

Sport Aviation 51