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Engine RPM to avoid ?

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Cub Rookie

Apr 16, 2007
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I was involved in a discussion the other day which has brought me to this question. My J-3 has a C-85 and metal prop. The question is: Are there certain engine RPMs to be avoided due to resonant frequencies in the prop or engine? I think that my operation limitations say that T.O. RPM should be 2575 and all other operations should be at 2550.
I have heard that the C-85s like to be run hard but I'm not a big fan of that school of thought. I'm seldom in a big hurry to get anywhere (obviously, I'm flying a Cub) so I like to cruise at a more sedate RPM of something between 2100 to 2300. I only lose a few MPH and probably burn a little Less fuel. I am concerned that instead of preserving the airplane by taking it easy, that I am potentially hurting the engine, prop or airframe by doing this.

Any thoughts ?

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