Ultralights have long been defined by their two-stroke engines. Rotax and other brands refined the two-stroke for aircraft use, and today’s two-stroke powerplants deserve their popularity. In the important power-to-weight ratio, two-strokes are hard to beat. Their cost is low, their overhauls cheap; these humble powerplants have lifted many a pilot into the air for many hours. But despite the improvements, despite plentiful businesses to help you maintain your two-stroke engine, and despite a good performance record, two-strokes are still seen as inferior to four-strokes by many aviators. Add to these impressions the regulatory changes many see as inevitable. The blue-smoking two-stroke (even when optimized) presents environmental problems for snowmobiles, watercraft and gas-powered lawn tools. Two-stroke days are numbered—not because of efficiencies, but because of ecological concerns and political decisions. Hail the Four-Stroke General aviation people say, “Well, of course four stroke is better.” But that’s the only kind of engine most of them know, and their aircraft weigh enough to accommodate heavier powerplants.
Turbines for Ultralights?
Just when FAA officials believe they have it figured out, individual actions can introduce new questions. I’m referring to the light-sport aircraft category of new rulemaking proposed by the aviation agency. Consider the turbine engine. Why, you may ask, is turbine power the subject for a column that focuses on the lightest and slowest aircraft? The answer is that turbine engines are actually being used on the these aircraft, and they may be the right power for the use intended. Turbine Tug For two decades, hang gliders have been towed aloft by specially built ultralights. Aircraft like Bobby Bailey’s Dragonfly have succeeded at launching hang glider pilots who live in flat areas like Florida. They don’t need mountains. Just give them a Rotax engine and they’ll take to the skies in swarms. Witness the spring ritual of dual hang gliding competitions in central Florida. Each year as the Sun ‘n Fun fly-in ends, pilots converge from all over the world.
Rotax’s new 912S
Rotax’s new 912S produces more horses per dollar than its 80-hp 912 (no “S”). One of the big success stories in light aviation powerplants is the Rotax 912. The four-stroke engine evolved from Rotax’s two-stroke line and offered a strong 80 horses. Still, some planes need a little more. MORE GET UP AND GO “An airplane that climbs well on the (regular) 912 won’t see much improvement from the 912S,” said one of the leading importers, Phil Lockwood of Lockwood Aviation Supply. “But if your plane climbs a bit marginally with the 912, the 25% power increase in the 912S will make a world of difference.” More power usually means more weight; however, the 912S adds a mere 3.5 pounds over the standard 912. Rotax Aircraft Engines – a division of world aviation leader Bombardier – also offers the 914, a turbocharged version of the 912. The 914 brought power from 80 horses to 115 (with 100 continuous), but comes with a substantial price increase.