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.