light twins?

Thanks Corky,

My assumptions about the rotary were not based on experience, so it's good
to learn something new.

I would have expected the rotary to have less spiky torque output than a
piston, but perhaps the wobble of the rotor along its ellipsoidal path
creates enough inertia to cause some sizable spikes.

I may post a question about this to the Mazda newsletter -- once Paul gets
back from Osh. I'm sure there will be some people there with good insight on
this.

I still have to think though that maximum torque is the limiting factor in
both gear and belt design. Even if torsional vibration is an issue (with the
rotary or any engine), the way to address that is to dampen the spikes and
prevent harmonics from causing destructive resonance. Just using bigger
stronger gears is one approach, but not really the most elegant -- or
lightweight.

I notice that Tracy uses rubber doughnuts between the flywheel and the
gearbox coupling, just for that reason I would assume.

Your story is just another reminder that gearboxes are one of the big
bugaboos of any auto engine conversion -- and torsional vibration (or
resonance) is always the culprit. I know that in the Subaru community there
is not really a box that I would consider completely trustworthy.

I was hoping the rotary was less of a problem in this area. Darn.

Regards,

Gordon.




"Corky Scott" wrote in message
...
On Thu, 28 Jul 2005 16:08:46 -0400, "Gordon Arnaut"
wrote:

Still, compared to a piston engine, the rotary is a pussy cat when it
comes
to torsional issues, because it does not have the lever-arm effect of the
crankshaft throws to worry about -- which creates the bulk of the
torsional
flex in a piston engine.

This may not be accurate Gordon. There was a company based up in
Washington State that produced a planetary gear box as a PSRU for the
Mazda rotory and they had a HORRENDOUS developmental period with many,
repeat many broken boxes.

They finally got something that was extremely professional looking as
machined aluminum can be, and robust and long lived. They had it on
the front of an RX4 and flew it to various air shows. One of the
developmental partners was killed in an airplane crash and for a while
the psru was still available but I don't know if it still is.

The big issue, the one that was busting props and tearing their boxes
apart was torsional vibration. I remember reading that they claimed
there was something about the rotory engine that gave it a really
powerful torque spike.

I think they eventually solved the problem with some kind of cushion
drive. But for a while it was busting one attempt after another on
the test stand, and a bunch of dead stick landings.

Corky Scott