EAA Sport Aviation - February 2010

manufacturers (e.g., Rotax and Jabiru) who
started from scratch to design their new engines.

Compared to those engines and some of the small Continentals, Lycomings, Franklins, as well as some old inline designs, the VW looks—and is—simple. Parts are readily available at low prices, and the engine design is straightforward. People, regular people, feel they can work on a VW. Regular people can even build them, without needing an extensive shop, lots of special tools, and a Ph.D. in engineering. Four major U.S. specialty manufacturers offer effective solutions to the trickiest parts of building; all give good customer support.

Revmaster R-2200

Flexibility of design and years of work allow direct drive from either end of the crankshaft or from belted reduction drives in various ratios. Inverted oil systems are developed and proven; ignition, carburetion, and fuel injection come in many forms. Several engine-mount configurations bolt right up. Perhaps most fun of all: You can build or order an aviation-ready VW in many configurations, from 1600 cc all the way to 2. 5 liters.

WHAT TO EXPECT FROM A VW

Most VW installations are direct-drive. This means top horsepower is achieved at relatively high prop rpm—3400 is typical. Consequently, propeller diameter is Mach-limited to about 62 inches. (The 2700 rpm limit of many aero engines allows similar Mach numbers with props up to 78 inches in diameter. Some “known truths” about higher propeller efficiency with lower rpm still arise, though the engineering tends to refute them.)

Properly converted engines can range in output from about 60 hp to just over 80, with some very large Revmaster-made specialty engines coming in higher. Claimed weights vary, but generally consider the installed weight of a starter-equipped engine with exhaust (but no muffler) to fall midway between that of a Rotax 912 and a Continental O-200. Fuel burn is largely operator-dependent, but 4-5 gph is generally achievable.

VW engines run well on just about any gasoline,
but they are subject to power loss in proportion to
ethanol content and reduced octane and will expe-
rience lead buildup from 100LL avgas.

Time between overhauls is almost entirely builder- and operator-dependent. Since most recreationally flown aircraft see fewer than 50 hours of flight each year, rebuilds are more often due to neglect or disuse than to wear. Fly 500 hours a year, use good gas and oil, and maintain the engine properly, and you can probably count on three or four years before you’ll need to do anything important inside the engine.

Maintenance is infrequent and simple, adjustments are minimal, and parts are widely available. The valve lash is a five-minute job; electronic ignition timing is typically fixed by design. Oil changes are cheap (the original VW holds just 2 quarts of automotive oil; a cooler and inexpensive automotive filter add more capacity). Wear parts (cylinders, heads, pistons and rings, bearings, valves, and seats) are auto-priced. The camshaft rides in replaceable bearings, too.

WHAT TO CONSIDER

When deciding to build an aircraft, engine choice is as important as airframe choice. Aircraft mission, realistic flying plans, the builder’s mechanical ability, familiarity with engine systems, and the desire to know your powerplant are balanced against the decisions to build or buy a VW engine or engine kit. The configuration and sophistication of the ultimate choice often comes down to the time available, the desire for involvement, and the budget of the customer.

Airframes generally dictate whether the ( typical) pulley-end or (more “aviation-y”) flywheel-end direct drive is preferred; sometimes (as in a gyroplane or PPC), there may be room for a re-drive. After that, it’s time to specify displacement (closely related to horsepower), ignition, carburetion, oil systems, engine cooling, carb heat—any of the myriad choices that allow the VW to be tailored to the builder’s exact taste and needs.

Four companies in the United States offer aviation conversions for the VW: Revmaster, Great Plains, AeroConversions (AeroVee), and Hummel. Each offers advice and support, and each company has options others don’t. All (except AeroConversions) offer finished, test-run engines, plus parts à la carte. (AeroConversions supplies complete engine kits only, plus support parts for kit customers.)