Any PSRU is less reliable than direct drive.  Part not

installed
will NEVER fail.  ;-)  Back to my wish for a large displ, direct drive,
air cooled rotary with a proper propshaft designed in.   Dream

on!  But it

is a nice dream.

Bill Freeman
Long EZ builder & pilot
BSME, MSME
EAA Technical Counselor

It would have to be a four rotor Bill as the current combustion chamber is
probably right out at the size limits of practicality. In that case I

think

you would have a tough time equaling the current excellent power to weight
ratio. This is intrinsically a high RPM engine.

Paul Lamar

Why intrinsically high RPM, except due to low displacement?  What about
the 21A or the huge pipeline engines?  I can't see why the size can't be
increased
and keep the "excellent" (?) [good, perhaps] power to weight ratio.

Bill
Long EZ builder & pilot
BSME, MSME
EAA Technical Counselor

I think the pipe line engine had BSFC and detonation problems with that
huge combustion
chamber. I could be wrong on this. Perhaps a sphere's surface area to
volume ratio
may get more favorable as the size increases.

I think it would be hard to make a large low speed rotary with the same power
to weight ratio as a high speed rotary. Power of course is proportional to
displacement
times RPM. If you halve the RPM and double the displacement you will wind
up with a heavier rotary I suspect. RPM weighs nothing. With a piston engine
on the other hand high RPM is less desirable as the reciprocating loads
rapidly
increase with higher RPM's.

What do you think about this Jon?

Paul Lamar

I rarely hear about the gear reduction on the PT6 failing at all. Or any of
the turboprop units. And that engine turns at 40,000 rpm then reduced to
2200 rpm or so. So whats the problem? Nice power to weight too. Too bad the
fuel burn is what it is.

Marc Wiese

 
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