Brent
Haven’t checked yet to see if the taper is the same- I’m hoping that it is. The big advantage of the Artic Cat engine is a real bell housing with solid attach points. For and aft spacing may be an issue as well as the Rotax has no flywheel before the taper.
For the Geo 1.0/1.3 we would eliminate the tapered shaft entirely and couple directly from the crank to the Rubber Hardy disk with an adapter. This may turn out to be a better design for the Arctic Cat as well. One factor that is often overlooked when converting the snowmobile engines is the lack of flywheel momentum on the crankshaft once the heavy mass of the CVT drive clutch is removed. The tiny Rotax 2 stroke flywheel doesn’t add any significant mass to this combo.
Arctic Cat used only the sheet metal automatic transmission flexplate behind the tapered crank adapter. Couple that with the very low compression of a turbo engine and you will be dealing with heavy resonance spikes building up quickly in the low RPM band. It is still a big question mark as to whether the simple rubber donut coupler of the Rotax Gearbox will work properly with this particular engine package. We had to tune our proven torsional dampening system, standard on all our belt redrives, to dampen the resonance spikes for this engine. It looks like there is just enough room for that type of custom coupling inside the gearbox housing extension. We will only know what works properly when the engine is running again under full prop load on our test stand with this drive combo. Maybe we will luck out and be able to use the existing rubber coupler designed for the two stroke- but I wouldn’t bet on it.
Still need a separate adapter plate to mount the starter as well as mounting points in the correct location for aircraft use. Definitely not a bolt and play operation, but still way simpler than what I’ve seen on the Yamaha conversions to date.
Thanks again for your interest. Think you can see now why we’ve elected to complete at least some preliminary initial testing of these engine packages rather than just have others experimenting with a totally unproven combo. Adapting any gearbox from a two stroke to a 4 stroke application is something that immediately puts the word EXPERIMENTAL in bold type and should be treated with respect. Now that we have seen a number of successful conversions of small 4 strokes, and even larger Suburu engines with this gearbox, we are conservatively willing to explore a bit further in that direction if there is a customer interest in experimenting with that option.
It’s the most powerful engine package we’ve developed to date!!
Jeron Smith
Raven Rotorcraft/ReDrives Inc.
575-737-9656 cell 303-440-6234