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I have 912 ULS fitted to an Aeroprakt A32, with a two-bladed MT constant speed propeller. Total time 60 Hours since new.

The aircraft has vibration, reminiscent of an unbalanced propeller, peaking between 2200 and 2400 RPM. High RPM it's perfect and the propeller has been dynamically balanced at high RPM where the vibration is not apparent. Carbs have been overhauled and synced, still shaking. Carbs were transposed with another aircraft and the problem was still there, so I'm pretty sure that's not the issue. Trigger coil gaps checked. Modules changed. Spark plugs changed. Compression checked. Intake manifold o-rings changed. Carb sockets changed. Air filters cleaned. Throttle cables changed. I haven't pulled the gearbox as the engine is still quite new, but I'm running out of ideas. 

If anyone can assist me, I'd be extremely grateful.

PS. I have 3 other nearly identical aircraft and they are smooth, so I leaning away from it being a harmonic issue with the two-bladed prop, but who knows!

  • Re: Vibration at 2200-2400RPM

    by » one month ago


    I have had similar issues with 2 x 912UL engines. I went through everything that you have also done and I couldn't solve the problem so I just live with it now. One of the engines I have owned for a long time and that used to be smooth so something has definitely changed on that one. I don't know the full history of the second engine but I am guessing that it didn't leave the factory with a vibration.

    I would be interested to know if you manage to resolve your problem but unfortunately I cannot offer any other advice.


  • Re: Vibration at 2200-2400RPM

    by » one month ago


    Can you temporarily switch out the prop with one of the other aircraft?


  • Re: Vibration at 2200-2400RPM

    by » one month ago


    What gearbox is on the engine?
    Which Clutch?
    Is it the type where if you turn the prop back and forth, it resists all motion...
    Or the type that has a few inches of free play before resisting?

    What Gearbox Model and Serial ????


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


  • Re: Vibration at 2200-2400RPM

    by » one month ago


    Kevin Stewart wrote:

    I have had similar issues with 2 x 912UL engines. I went through everything that you have also done and I couldn't solve the problem so I just live with it now. One of the engines I have owned for a long time and that used to be smooth so something has definitely changed on that one. I don't know the full history of the second engine but I am guessing that it didn't leave the factory with a vibration.

    I would be interested to know if you manage to resolve your problem but unfortunately I cannot offer any other advice.

    Unfortunately that isn't an option. Demanding customer, he won't accept that.


  • Re: Vibration at 2200-2400RPM

    by » 4 weeks ago


    Is the carb choke slightly open?  Just read that this can cause low RPM roughness when it does not go back to stop.


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