mstull
R.I.P.
Does anyone have experience running a two stroke engine direct drive? I'd like to hear from anyone who's actually flown one... particularly a legal ultralight.
Most 2 stroke engines don't have enough torque to turn a prop direct drive, nor enough power at direct drive RPMs to get decent thrust. I've been looking at trying it with a 605cc, MZ201 twin from Compact Radial Engines. That engine is specifically tuned for low RPM torque, and has enough power in the 3,000 to 4,000 RPM range for my plane.
If this works, it could be a good alternative to the Rotax 447 with B box, for ultralights looking to shed a few pounds. I've been using single cylinder engines with belt re'drive. But I'm really tired of the short belt and pulley life. If it's not too loud, and doesn't vibrate too much, the engine should be very long lasting, cruising at around 3,000 RPM.
Compact Radial Engines also offers 3 or 4 cylinder radials that they always run direct drive. So CRE is the only manufacturer I know of that deals in direct drive 2 strokes.
For those unfamiliar with the concept... Reduction drives multiply engine torque, allowing a much longer prop, that generates much more thrust. The re'drive also divides the RPM, so a modern, high revving engine can turn the prop at a more reasonable prop RPM.
Leon at CRE says he knows that people are using the MZ201 direct drive successfully. He even sells the prop hub for it. And Stuart at Powerfin says their E-2 blade prop should be about the right size, but no garantees. The engine would weigh about 65#, and put out about 35 Hp at 4,000 RPM.
Mark E. Stull
Most 2 stroke engines don't have enough torque to turn a prop direct drive, nor enough power at direct drive RPMs to get decent thrust. I've been looking at trying it with a 605cc, MZ201 twin from Compact Radial Engines. That engine is specifically tuned for low RPM torque, and has enough power in the 3,000 to 4,000 RPM range for my plane.
If this works, it could be a good alternative to the Rotax 447 with B box, for ultralights looking to shed a few pounds. I've been using single cylinder engines with belt re'drive. But I'm really tired of the short belt and pulley life. If it's not too loud, and doesn't vibrate too much, the engine should be very long lasting, cruising at around 3,000 RPM.
Compact Radial Engines also offers 3 or 4 cylinder radials that they always run direct drive. So CRE is the only manufacturer I know of that deals in direct drive 2 strokes.
For those unfamiliar with the concept... Reduction drives multiply engine torque, allowing a much longer prop, that generates much more thrust. The re'drive also divides the RPM, so a modern, high revving engine can turn the prop at a more reasonable prop RPM.
Leon at CRE says he knows that people are using the MZ201 direct drive successfully. He even sells the prop hub for it. And Stuart at Powerfin says their E-2 blade prop should be about the right size, but no garantees. The engine would weigh about 65#, and put out about 35 Hp at 4,000 RPM.
Mark E. Stull
