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I am buying a new plane with a Rotax engine and constant speed 3 blade prop. I have some very basic questions since I'm unfamiliar with high rev engines:
Propellers are efficient at low RPM, but engines bog down if they run too low RPM. Does Rotax have a recommendation table for RPM and FF or MP for fast, normal and econ cruise settings to help quantify the optimal combinations? For example, 4000RPM at full throttle would be legal, but both wasteful and harmful. I see no guidelines.
Does operating the engine at max continuous 5500 for long cruise, or at lower power settings for econ cruise have an effect on wear or engine reliability? Is there any wisdom in running the engine at lower RPMs?
My old TCM engine had tables for max, 75%, 65% and 55% rpm/MP/FF settings and I don't see that here. Could you tell me the values associated with those percentages for the 912ULS? Does Rotax consider those percentages useful as targets for normal, economy or loitering RPMs?
Thank you for any advice you can offer.
  • Re: operational guidance

    by » 8 years ago


    Riley,
    the Rotax engine runs well at its continuous power setting. 5200-5400 is what is indicated on most of the Rotax Tachometers which are notorious for being about 200 RPM Slow. Check your tach with a measuring devise. That said, My 80 HP 912 is smooth and happy at 5400. I can fly at 4000 RPM if I want to fly it slower but the slower RPM can be a drag on the engine unless I am straight and level. The engine is made to be flown at its cruise setting. At 4.5 to 5 GPH, your wasting your time looking for fuel economy. "FEEL" the transitory vibrations in your plane between 4000 and 5400, its going to be clear to you that the motor likes being at its higher RPM range. Keep the carbs balanced and the fuel clean and you will fly it for years without issue. Stay Stock, no mods, the manufacturer has millions of flight hours "as is". You won't improve performance AND longevity. Hope that helps.

    Thank you said by: Riley Stevens

  • Re: operational guidance

    by » 8 years ago


    Keep the cruise rpms between 5000 - 5500 rpm and you'll be fine. This engine wasn't designed to cruise in the 4K's for its life.

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


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