Paul,  did you see the RFI belt drive in  the latest "Contact."  The
rotary version is a 2.5:1,   I wonder what it weighs and if I could
use it on the single rotor, perhaps lightened a bit.  I e-mailed the
designer, Don Parham to find out more.   If you get a chance to look
at it,  I would appreciate your opinion.     Jerry

The prop shaft is cantilevered off a thick plate which puts
the plate in bending. It needs to be very thick and heavy to accept that bending
load. Any deflection will cause the belt to be tighter on the back side of
the pulley and less tight on the front side of the pulley. This could cause
the belt to walk forward. Also for an aircraft it  waste a lot of room under the
cowl by moving the engine down. Apparently not a problem for a Subaru or gyro copter.

At least the lower pulley is supported by an out board
bearing which reduces the bending load on the E-shaft. It still puts
a side load on the e-shaft which is not good. Automotive engines are
not designed for side loads on the crank or e-shaft. It may or may not
cause a problem.  Planetary's put no side load on the e-shaft. I would not
use a belt drive unless there were no other alternatives.
Paul Lamar

The solutions are simple -- gussets from the top half of the plate to
the engine case, blind gussets on the drive side of the plate, or a
longer drive shaft with a dead end.

The better ways for the rotary, however, would be to let the end plate
gusset the drive plate, or (even better) make an end plate with
provision for the upper drive pulley.  In each type, the prop-drive
front-back forces are largely absorbed into the engine case.

Keith Wood



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