There was a time in the 1980s when the Rotax two-stroke engines, the 503 and 582, dominated the lower-priced range of the kitplane world. Kitfoxes and Avids with two-strokes were very common, for example. There were even designs like the composite Aero Designs Pulsar that got pretty respectable performance (130 mph cruise) on just a 64 hp 582. That seems to have petered out in the 1990s and early 2000s as the Rotax 912 came to dominate.
Fast forward to 2018 and there are some pretty impressive, well-proven two-strokes engines, often with liquid cooled heads and lower max power RPMs, available from the paramotor, powered parachute, and light gyroplane world. Many of them offer comparable power to the old Rotax two-strokes at lower weight, fuel consumption, and noise levels with claims of higher TBO and better reliablity.
Take the 48 hp Simonini Victor 1 Plus, for example, which the manufacturer presents as a direct competitor to the 503, comparing all the specs: http://www.simoniniusa.com/?page=Engines&Engine=Victor-1-Plus. It comes complete with accessories (muffler, electric start, etc.) for a little over $6k and seems perfect for a single-seater or a very light two-seater like a motorglider. There is also the Polini Thor 250DS at only 37 hp but under $5,000 all in. For around $8-9k you can still get a 582 or equivalent Hirth engine in the 60-70 hp range, and for about $10-11k you can get a 100 hp engine from Hirth or Simonini. This when even the basic 80 hp Rotax 912UL runs close to $20k by the time you get it completely set up.
These numbers seem to suggest that a complete, flying, two-stroke single-seat kit around $15k is possible, less if built from plans. Ditto a two-seat, two-stroke kit around $20k. These would be complete, flying aircraft for less than the cost of the Onex and Sonex B airframe kits alone.
So why does no one seem to be designing for two-strokes anymore?
Fast forward to 2018 and there are some pretty impressive, well-proven two-strokes engines, often with liquid cooled heads and lower max power RPMs, available from the paramotor, powered parachute, and light gyroplane world. Many of them offer comparable power to the old Rotax two-strokes at lower weight, fuel consumption, and noise levels with claims of higher TBO and better reliablity.
Take the 48 hp Simonini Victor 1 Plus, for example, which the manufacturer presents as a direct competitor to the 503, comparing all the specs: http://www.simoniniusa.com/?page=Engines&Engine=Victor-1-Plus. It comes complete with accessories (muffler, electric start, etc.) for a little over $6k and seems perfect for a single-seater or a very light two-seater like a motorglider. There is also the Polini Thor 250DS at only 37 hp but under $5,000 all in. For around $8-9k you can still get a 582 or equivalent Hirth engine in the 60-70 hp range, and for about $10-11k you can get a 100 hp engine from Hirth or Simonini. This when even the basic 80 hp Rotax 912UL runs close to $20k by the time you get it completely set up.
These numbers seem to suggest that a complete, flying, two-stroke single-seat kit around $15k is possible, less if built from plans. Ditto a two-seat, two-stroke kit around $20k. These would be complete, flying aircraft for less than the cost of the Onex and Sonex B airframe kits alone.
So why does no one seem to be designing for two-strokes anymore?
