Power by Mazda Peter Garrison For decades the rotary engine has hovered like the Grail before a certain cadre of aeronautical innovators. I don't mean the World War One rotary -- a radial in which the entire engine spun while the crankshaft remained still. I mean the engine generically called the Wankel, in which a triangular rotor whirls inside an oval housing, subdividing it into three combustion chambers of continually varying volume. Wankels are basically quite simple; they have no valves, for one thing. A single-rotor Wankel can, in fact, be compared to a three-cylinder two-stroke, because it has three combustion chambers each of which delivers one power stroke per revolution of the rotor. Beginning in 1958, when Curtiss-Wright acquired a license from the inventor, Felix Wankel, to exploit the technology, a series of prominent corporations, including AVCO Lycoming and John Deere, worked on developing an airworthy Wankel. (On the automotive front, General Motors licensed the technology in 1970, but let the license lapse in 1974.) NASA contributed a good deal of money to development of a 340-hp engine called SCORE, for "Stratified Charge Omnivorous Rotary Engine." The "stratified charge" part of SCORE refers to a method of timing and locating the fuel injection and the spark to ensure complete combustion of a lean mixture in the rotary's awkwardly thin and wide combustion chamber. Incomplete combustion results in emissions problems and also in comparatively high fuel consumption. The "omnivorous" refers to the valuable ability to run on all sorts of fuels, including diesel or jet fuel, regardless of octane rating. By the completion of NASA's study of several competing engine types, the makers of the stratified-charge rotary were reporting fuel specifics superior to those of current recips, and the engine was judged the most promising in a field that included a small turbine and a diesel. But despite all this, the Grail seems no closer. In 1984 John Deere sold off its rotary engine division to Rotary Power International of Wood Ridge, New Jersey, which continues to advertise a line of industrial SCOREs ranging in yield from 15 to 3,000 horsepower, but has announced no further aviation-related developments. The Wankel has attractions beside its indifference to fuel octane. It puts out a lot of power for its size and weight, is virtually vibrationless, and, unlike a horizontally-opposed recip, is nicely shaped to fit in a slender, streamlined nacelle. Several automobile manufacturers, even including a Russian one, have used rotary engines in production vehicles. Mazda of Japan has built millions of rotary-powered cars. Their admirers characterize them as compact, light, powerful, smooth, and highly reliable. Several amateur builders have installed Mazda engines in homebuilts. Running around 6,000 rpm, they require reduction gearing but still come out competitive in weight with, and superior in size and shape to, conventional airplane engines. Russian, German and British firms produce small rotaries for the aircraft market, but the model of choice for American homebuilders seems to be Mazda's two-rotor 13B, nominally an 80-cubic-inch engine rated at 143 hp. Some random cases in point: Since 1994 Tracy Crook of Clearwater, Florida, has been flying an RV-4 powered by a carbureted 13B that he originally bought from a junkyard. He estimates the cost of the entire engine installation, including gearbox and cooling system, at $5,000 - less than a third the cost of an equivalent Lycoming or Continental. He runs it on 87 octane auto gas (or 100LL when auto gas isn't available). Performance is equivalent to that achieved with the more usual 160-hp Lyc: 177-knot top speed, 135-knot economy cruise on 5.5 gallons an hour. Crooks says that a teardown at 600 hours revealed no discernible wear. "I'm convinced," he states, "that it's as reliable as anything Lycoming or Continental ever built, or more so." He anticipates a 2,000-hour TBO, but with overhaul costing only $600 it really doesn't much matter if it turns out to be less. A Canadian builder, Neil Kruiswyk, has a 13B in a Lancair 235. He guesses it would cost $10,000 to duplicate his installation, which weighs 300 pounds complete - about the same as an equivalent Lycoming. Both Kruiswyk and Crook use electronic ignition (as do an increasing number of homebuilders) and have recently converted their engines to fuel injection. Brice Daunay, a Tulsa architect, installed a modified 3-rotor, twin-turbo Mazda 20B engine in a Velocity. (The basic engine is used in a Japanese domestic-market sedan called the Cosmo.) Daunay estimates the cost of the engine at $17,000, and its output at more than 300 hp. It burns about 14 gallons of regular auto gas per hour in cruise. He is very enthusiastic about the engine, which is quiet (it's because of the turbos; rotaries usually aren't), smooth, and, after 70 hours of operation - not a significant duration, of course -- trouble-free. Perhaps the most systematic development work on modifying the Mazda for aircraft was done by Oregon-based Powersport, Inc. Partners Everett Hatch and Steve Beckham eventually arrived at a 167-pound engine delivering 200 hp, but after Hatch's death in a 1997 airplane accident (unrelated to their rotary engine), Beckham sold the company to Ratech Machine of Osceola, Wisconsin. Ratech intends to manufacture engines, and eventually perhaps complete powerplant installations including cowlings, for Van's, GlaStar, and Velocity builders. People willing to dwell on the negative side of rotaries are hard to find. Neither doting homebuilders nor people with something to sell are expected to emphasize the down side. But I did locate one. In his view rotaries, as a class, have not replaced recips because they require comparatively complex and costly processes to manufacture; because they do not fare well running continuously at high power; and because once the "trochoid" - the outer housing - is worn, it cannot be economically reconditioned, and must be discarded. In other words, even though recips have many more parts, they are simpler and cheaper to manufacture and overhaul. None of these objections will deter homebuilders, who are happy to let Mazda bear the cost of tooling; find rotaries to be in fact cheaper to acquire than recips; generally do not run their engines through several overhauls; and find, with Tracy Crook, that wear is in reality not a significant factor. At present, many rotaries in aircraft are prototype installations by individual experimenters. We seem to be at the threshold of a new phase, in which increasing numbers of users will buy ready-to-use engines from what might be termed "amateur manufacturers." This point is similar to the one at which your adorable but obstreperous three-year-old starts nursery school, and you're finally exposed to someone else's opinions of his or her charms. We will soon find out the aviation rotary is really a miracle or a monster.