Allen Chan wrote:

Hi,

I have a question about rotary engines and aviation.
Is it possible to get rid of the PSRU, by machining a
new rotary crankshaft which yields a RPM in the
aviation range (<=2,700 RPM) rather than the automtive
range?

Allen Chan

No. Every part is precisely related to every other part.
ANY change in any one part's dimension would prevent the engine from
being assembled and consequently it would not work. It can 
however be scaled up or down.

The wankel rotary is a high RPM engine by nature. Since
HP is proportional to RPM if you reduced the RPM by half the HP would also
be half while the weight would stay the same. Thus you would
lose its excellent power to weight ratio advantage. 

The high displacement low speed aircraft engine  on the other hand 
is designed from scratch to be a low RPM engine. Every part is designed 
with that in mind to minimize the weight. the parts are only strong enough
to withstand the red line. If you run it at higher RPMs you 
risk catastrophic failure. A reduction in life is also guaranteed.

The rotary on the other hand to can run up to 10,000 RPM for many hours and 
therein lies its HP to weight ratio advantage. It is like an electric 
motor in that regard.

Here is a picture of a wankel rotary that was designed to generate a lot
of HP at 750 RPM. It obviously weighs a lot.

Paul Lamar
 
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