Essentially the planet carrier becomes part of the prop
shaft doing two jobs. There are only two ball bearings in the
entire PSRU. The forward ball bearing takes the prop thrust.

It is only 7 inches long which is half the length
of Tracy's redrive. Don't get too excited about the weight
as that Allison planet is heavy being designed for over
the road tractor trailer 450 HP diesels towing 50,000 pounds..

The Allison planet and ring gear, sun gear, input shaft is 26.7 pounds alone.

The $30,000 Bell 47 weighs 35 pounds with out the Sonja :-)
Tracy's is 45 pounds. But could be lightened if a 2 inch
hollow prop shaft is used.

This design  picks up 7 inches behind the engine for all aluminum
rotary engines only. Other wise you would have a forward CG
problem. I may not have to move the firewall back on
the Glasair.

This is also much cheaper to make as no long PSRU housing is
needed.

I got some of these ideas from the Bell 47.

Paul Lamar

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