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Rotax 912 ul, severe vibration

in 912 / 914 Technical Questions 8 years ago

  • Re: Rotax 912 ul, severe vibration

    by » 8 years ago

    You can most definitely control the RPM with no problem. What you have to be careful of is over-revving it since there is no load or overheating it since there is no airflow. There is no resonance in the gearbox without the prop, at least there shouldn't be unless you exercise the throttle rapidly.

    As I said previously, done carefully it can be a useful diagnostic test.
      
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  • Re: Rotax 912 ul, severe vibration

    by » 8 years ago

    You shouldn't run the engine without a prop or some load device.

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

      
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  • Re: Rotax 912 ul, severe vibration

    by » 8 years ago

    Hello everyone,

    Maybe not such a good idea running it without the prop after all.

    For further reference I found this video: www.youtube.com/watch?v=PHS05n89kas

    I have the same engine set up, notice the inverted intake manifolds (00:57).
    As mentioned before, the engine rubber material provided for this models is quiet soft and there is that SB ,which I'm planning to perform as soon as I'm back home, to make it more stiff.
    From some other kitfox owners feedback's I think it will help but I'm not quiet sure it will totally cure my problems.

    My engine sounds just as rough, same shake (that you can see the carbs and intake manifolds all over the place) and same fuel overflow. Only that in mine I also experienced air filter and/or carburetor separation.

    In general terms both side carb's are as bad, but the left is maybe a bit worse (from pilot view).

    I think this is a magnified effect: A small shake make it impossible for the carb's needle valve to maintain a constant level in the bowl thus overflowing, thus making an unbalanced mixture, thus making the full thing to try to disintegrate :lol:

    I was trying to contact the user who post this video to see If he eventually found out what was the cause of this problem but no luck.

    Your comments and help is much appreciated!

    Jorge
      
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  • Re: Rotax 912 ul, severe vibration

    by » 8 years ago

    If the rubber engine mounts are more than 5-6 years old they should be replaced and the bolt torque for these double checked.

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

      
    Report

  • Re: Rotax 912 ul, severe vibration

    by » 8 years ago

    This model of aircraft is very challenging to achieve a smooth running engine.
    -The mass of the carbs is moved outwards making the carbs shake more.
    -The throttle cables are short and pull on the carbs as the engine shakes, making the shaking worse.
    -The air filters are heavy; increasing the outboard mass of the carbs.
    -The engine mount has small diameter tubes, allowing more movement.
    Address all these and you will have a nice running engine.
      
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