-----------------------------------
Oh I am not surprised. Hard to get a cantilever design to be stiff
enough. Takes REAL large shafts and large and heavy bearings.

Not only that... three things will eventually happen.
The main bearings will go out on the engine, the e-shaft
will crack or the prop shaft will crack due to cyclical bending.

This diagram shows the problem. Notice there is no pre tension at
all of any kind. The belt tension generated is due to the HP
transmitted alone. Save for V, V-Ribbed and cog.

Paul Lamar ...No rotor no motor.
 

Paul ...

In your minds eye can you estimate the probable weight difference
between a gear driven PSRU and a belt driven PSRU. Not sure it can be
done given the numerous variables but I would think you might have a
better idea than the majority. Honestly I'm not even sure what the
average PSRU weighs.

Has anyone built this belt drive PSRU like the one you had attached to
your email or is it just theory? If it has been built do you have any
idea how it is or isn't doing? I'm sure its been built for ultra-lites
and I've seen the one on an email in here for the AC that could land on
water just wondering how his is doing or if he has had any of the
problems you mentioned ... if memory serves the attention was switched
to his significant other's tattoos <LOL>.

And here are the "could ya's"

Isolate the ECC shaft (I assume this is relative to the crankshaft in a
piston engine) with something like a coupling off of an inboard
mercruiser and have the bearings on the inside and outside of the pulleys.

Would having the bearings on the inside and outside of the shafts next
to the pulleys reduce or eliminate the cyclical bending? Its hard to
imagine that much bending in 1, 2 or 3 inches (not sure what the
recommended belt width is) of shaft between the bearings,

The bearing on the prop side would have to deal not only with the load
but thrust too ... is there a bearing that can do that or would you have
to basically have three bearings on the prop shaft, two for load and one
for thrust or pull? (Pusher vs Tractor)

It would "seem" you could use something like a spring loaded idler for
tension like on cars ... would that be feasible?

As for lubrication ... that would take a little tinkering but stranger
things have been done.<G>

Would something like a belt driven PSRU that is semi enclosed (bearings)
need to be cooled?

Speculation and guesstimation,

JOhnZ

"just theory" ????

Whats wrong with theory? :) Theory is a tool. Those that
fail to learn from history (theory) are doomed to repeat it.

Ken Welter builds something similar and has 100's of hours on it.
http://homepage.mac.com/rotarycoot/

A lot depends on what you use for pulleys. Most industrial
system use cast iron which is out of the question for aircraft
use. Ken Welter machines his own cog belt pulleys out of aluminum
and hard anodizes them for good wear characteristics.
I think you could come close to the weight of a gear system
if you used a large thin wall prop shaft and needle bearings.
Needle bearings can also be used for prop thrust bearings
as well. Cheap! The Ross PSRU uses all needle bearings.

"Would having the bearings on the inside and outside of the
shafts next to the pulleys reduce or eliminate the cyclical
bending? " Yes.

I don't think heat would be a problem as you have a lot of
high speed air for cooling.

For more info check out
http://www.rotaryeng.net/psrus.htm

Paul Lamar ...No rotor no motor.

The Rotary Engine NewsLetter. Powered by Linux.
ACRE NL web site. http://www.rotaryeng.net
Copyright 1998-2006 All world wide rights reserved.