Bob Earley wrote:

Hi Paul,

Could you please discuss the apparent paradox of running a rotary engine at high RPMs, only to run it through a PSRU to reduce prop speed? Is there no way to build a rotary engine/prop that can cruise at 3000 rpm with a direct drive?

The engine is small with very little displacement. In a case like that you need to
run it fast to get HP. Efficient props on the other hand are limited to about
2700 RPM. If you try to run a large diameter (six foot) efficient prop at higher RPM
the 
tips go supersonic and the drag goes through the roof. 

Also, if my understanding is correct, the output shaft turns two times for every rotation of the rotors. Would it be possible to modify the rotor/eccentric shaft interface so the relationship was 1:1? Wouldn't this reduce the load on the engine and provide all the benefits of reduced RPMs?

Actually it is 2:3. No. You would not have a practical rotary. It must be 2:3
other ratios work but it would probably take a billion dollars and 30 years to
develop it.
Seal angle with the rotor housing becomes unfavorable with the following
ratios 3:4 and 4:5. The combustion chamber shapes are even worse.
1:2's don't work as they need external pumping.

Thanks as always.

Bob
Rotary Novice

The diagram is from R.F. Ansdale book on the rotary The Wankel RC Engine.

Paul Lamar
 
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