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2 Answers

Operating at 75% Power C172SP

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Aircraft Systems, General Aviation

Hello CFI's,

During my PPL training I was instructed to cruise at around 2400 RPM (C172SP), any time I'd get over that my first CFI would get a little antsy.  However, in the POH it states the standard cruise RPM of 75% power is 2500 RPM at sea level.      

Is there any reason why I shouldn't  cruise at 2500 RPM on my CC flights (I wouldn't mind having the  few extra kts to save on my bill after I land ;)?   Now I understand that as I climb, I will be losing RPM's and of course leaning properly will keep the RPM's up until a certain alt but if she'll do 2500, is there any reason to not cruise at the power setting? 

Thanks for the info! 

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2 Answers



  1. Lucas on Jul 30, 2014

    Hey Stephen
    You are absolutely correct as long as you stay within the Green Arc of the Tachometer you are fine. Some Tachometers have a caution range between 2200 and 2400 RPM (indicated by a yellow segment). You want to avoid running in those RPM because of vibration problems. Also always follow the recommendation of the POH. Your flight instructor probably flies in many different airplanes and for some of them 2500 RPM might be too much but if the POH of that particular plane tells you to cruise at 2500 RPM for 75% horse power than thats just fine.

    Cheers
    Lucas
    http://passfaaexams.com/

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  2. Russ Roslewski on Aug 04, 2014

    On XC flights that’s known as “full rental power” and I see no reason to not fly at that power setting – you’re right it may save you a few minutes and a few dollars.

    On local flights, I often have my students pull the power back a little further – not only aren’t we going anywhere in particular, but the faster we go, the further we get from the airport, the further we have to come back anyway. So might as well do it at a “low cruise” setting.

    In addition, that helps reduce the noise of the engine which helps make the airport a good neighbor to the surrounding population.

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