MT prop etc

Category: 912 / 914 Technical Questions 9 months ago

Hi Folks, thank you for adding me to the group. I have a Dyn Aero Sportster with a 912ULS, MT7-A prop and a P-120U controller.

so here goes! On preflight check, the controller as I understand it is set to auto, then engine rpm idle plus 200, ie around 1600 engine rpm. You then select the rpm dial and place to minimum around 1400 prop, RPM is supposed to drop and green light goes out select max rpm, white light goes outrpm increases green light on.....only it doesn’t. Also how do you know what the proprpm is without strobing it? Manifold pressure on shut down is ambient ie 30.5 inches 2035 mbs, on running up to 3500 rpm manifold pressure shows 13.5


any thoughts advice would be welcomed, Many thanks and a happy new year to all!



  • Re: MT prop etc

    by » 9 months ago

    Prop RPM will can be calculated from the engine RPM divided by the gear ratio... (2.43:1 if you have the 'standard' gearbox)

    Thank you said by: Richard Sims

  • Re: MT prop etc

    by » 9 months ago

    This is an MT-P-120U controller issue and the problem should be referred to the MT Factory or dealer.

    Do you have the M-120 Manual?


    The P-120U has a Green Light and a YELLOW light.  No WHITE Light.

    The GREEN Light indicates the prop is in the Full FINE position. (Max RPM)

    The YELLOW LIGHT Indicates a Fault.

    Please restate your problem clearly and what it does and does not do.

    Maybe we can help.


    As the Admin Stated, Prop RPM is Engine RPM / 2.43.

    1400 Engine = 575 Prop. 

    1600  = 660 

    2000 = 825

    3400 =1400 

    5600 = 2300

    5800 = 2385



    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated.

    Thank you said by: RotaxOwner Admin

  • Re: MT prop etc

    by » 9 months ago

    Hi Bill,

    thank you for your message. I ll have another go and see the results! 

    A happy new year to you,


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