I don't know how I missed this back in 1990 but it was republished
in the RV Aviator book.

Something I never thought about was if you have a climb prop
on your airplane your engine is probably generating more
HP at top speed. Interesting. The rotary, just like a direct drive
aircraft engine, generates more HP in direct proportion to RPM.
This is because, like a direct drive aircraft engine, it is not
breathing limited. Most large displacement piston engines start 
to become breathing limited about 5,000 RPM. Smaller piston engines
and the rotary to a lesser extent become breathing limited around
7,000 to 8,000. The main reason for this is the piston engine poppet valve.

A peripheral port rotary will keep generating more power right up to
the point the rotor bearing fails due to centrifugal force overcoming
oil pressure in the bearing. I digress too much. Getting back to
fixed pitch props.

I divided the climb rate by ten and multiplied the max speed and the
climb rate together. That is the first added column on the right.

The second added column is a number proportional to MPG at 2600 prop cruise RPM.
Cruise speed divided by HP.

What blew me away was the mediocre performance of the constant speed 
prop in this regard. I suspect something is wrong with this data.
Either that or the CS blade twist was all wrong for 180 MPH or so.

Paul Lamar
 
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