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Question for the propeller experts among us

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Winginit

Well-Known Member
Joined
Jun 12, 2016
Messages
811
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Is there a formula to compute or at least a rule of thumb to figure how much propeller efficiency is lost as rpms increase ? What I would like to quantify is as efficiency is lost
( in 100 rpms increments) how many additional horsepower would it take to reasonably offset the loss in efficiency ? My thought is that if a reasonably light weight auto engine can be built that gains more than the needed hp as rpms increase, I can get an idea of what hp/rpm level would be needed to maintain roughly similar efficiency.

Basically what I'm thinking is an rpm level that would make about 2/3 of a HP for each cubic inch. A 300 cu in engine making 200 HP and weighing 300 or fewer lbs. It would have to be direct drive to keep the weight down.
 
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