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low rpm

in General Tech Discussion 13 years ago
i should have explained better.the reason i was asking about the low rpm was because i read that the 912 should turn faster than mine is. the most i can get out of it is 5100 on takeoff at cruise i pull it back to about 4000 because it seems to perform well enough. am i flying it at to low rpm? the engine runs fine. starts quickly even when cold and runs smoothly thanks for your reply

  • Re: low rpm

    by » 13 years ago

    thomas,

    You should be able to reach 5800rpm at WOT. (max 5 minutes). 5500rpm continuous. 4000 is a little slow. The engine is designed to cruise at higher rpms. You could cruise all day at 5000-5500rpm and the engine would love it.

    Bill.
      
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  • Re: low rpm

    by » 13 years ago

    I only get 5500 rpm max out of mine and cruse at about 5200 rpm i was told that it will depend on the size prop you are swinging.
      
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  • Re: low rpm

    by » 13 years ago

    Although the engine is designed to run at 5800 for five minutes, A lot of people pitch the prop for a max RPM of 5500. (myself included). Reason is that if you break or lose a throttle cable on one carb, that carb will go to full throttle. The only options then are to go to full throttle on the good carb so the engine stays balanced at 5500RPM or shut down the engine down. If that happens when your max RPM is set at 5800, you can only fly for five more minutes rather than indefinitely. Downside is that you don't have that extra 300RPM in an emergency. It's just a personal choice. Yours sounds like an ideal setup to me.

    Bill.
      
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  • Re: low rpm

    by » 13 years ago

    Hi Thomas,

    You are over pitched on the prop and it is not good and harmful to the engine. It doesn't matter on the size of the prop. You need to setup the engine to a more proper rpm. If you are only getting 5100 max WOT rpm then remove approximately 2 - 2.5 degrees from the prop pitch to get 5500-5600 WOT at your average cruise altitude. Since you have a ground adjustable prop this will give you the best all around performance. Do not run your engine down in the 4K range, it wasn't designed to run it's life there. Once you have the prop setup to get 5500-5600 rpm WOT then a better rpm to cruise at would be 5100-5300. Read the blog about prop pitch.

    http://www.rotax-owner.com/rotax-blog/item/9-understanding-the-ground-adjustable-prop

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
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  • Re: low rpm

    by » 13 years ago

    roger,, thank you for your quick response,, i am almost certain i have a fixed pitch prop. it is made by tonini bros. italy. is the only sulution a prop change?? thanks again tom
      
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