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Cruise MAP 912UL

in 912 / 914 Technical Questions 11 years ago
Hi. The book says to use 27.2 MAP @ 5000 rpm, but I read somewhere that to avoid the risk of detonation you shouldn't go under 5200 for that MAP. What MAP should I use then when cruising at 5000? I'm confused :(

  • Re: Cruise MAP 912UL

    by » 11 years ago

    Hi Allan,


    Are you running a ground adjustable prop or an in flight adjustable prop?

    For the 912UL or ULS the manifold pressure will usually be 1" to 1.5" lower than ambient and most people don't even have or use a MAP gauge for the 912, but most probably use a ground adjustable prop too. I wouldn't worry about the MAP. Set the prop pitch correctly and cruise at 5000 rpm or more and your engine will be happy.

    Add a turbo to the mix and or an in flight adjustable prop and it will be different.

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

      
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  • Re: Cruise MAP 912UL

    by » 11 years ago

    Hi. Yes it's an inflight adjustable prop. When I was flying the other day at about 3500ft I used WOT and adjusted the prop to bring the rpm down to 5k. The MAP gauge read 27.2 which is what the book says to use. The trouble is I read on a Rotax service document dated 28/7/09 that "Continuous use of engine speed below 5200rpm with WOT should be avoided".
      
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  • Re: Cruise MAP 912UL

    by » 11 years ago

    Hi Allan,

    With my 912ULS and Woodcomp SR 3000/3 CS Prop I use 4600rpm and 22in MAP in the cruise, or to go a bit faster I use 4800 rpm and 24in MAP, or faster still 5000rpm and 26in MAP.
    The engine though to me seems at its happiest at 4600/22 or 4800/24 in the cruise.

    Hope this helps,

    Alan
      
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  • Re: Cruise MAP 912UL

    by » 11 years ago

    Hi. Thanks. My POH shows 5000/27.2 & 4800/26.5 so I think I will compromise and use 5000/26.5 which is basically what you suggest. I want good performance but I definately don't want detonation:(
    Allan
      
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