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Increased RPM at take off speed or slippage?

in General Tech Discussion 10 years ago
For the past year we have been working on my My Rotax. During the take off roll the engine seems to increase RPM although no RPM increase is noted. Initially I was told to rebuild the gear box. This has been done twice. It still does it. It always does it on the take off roll at about 140 degrees. We checked the throttle springs to see if it was giving way but no change. Again it is always doing it at the same time. We have synced the carbs rebuilt the gear box. here is a you tube link to a take off roll with the sound of it. it occurs at 54 seconds https://www.youtube.com/watch?v=VIV2nnMe6T4. It never does it after the first take off or when the temp is over 145

Please help. We have taken advice and checked all sorts of things.

  • Re: Increased RPM at take off speed or slippage?

    by » 10 years ago

    Hi William,


    You called this morning. After you answered all my question I'm still not sure what would cause this especially since it doesn't register on the rpm gauge.
    Maybe the gearbox wasn't done quite right. What has me baffled is that you mentioned it only does it below 145F or after first take-off. It seems to be so intermittent and only below a certain temp and only on the first start.

    Maybe Rob, Conrad or one of these others that may have seen this before can come up with something.

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

      
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  • Re: Increased RPM at take off speed or slippage?

    by » 10 years ago

    My friend eric has been helping with me with this perhaps he called this morning. We have rebuilt the gear box twice using two different people. Yes it is always on the first take off below 145 degrees.
      
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  • Re: Increased RPM at take off speed or slippage?

    by » 10 years ago

    Hi William,

    I talked to Eric twice. With the limitations of the problem I haven't a clue right now.

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

      
    Report

  • Re: Increased RPM at take off speed or slippage?

    by » 10 years ago

    William, that is an interesting problem.

    Do you have a 912, 912ULS or 914? Or maybe a 582 with a C or E gearbox?

    The only thing in the transmission of the 912/914 engine that could cause this is the slipper clutch slipping.
    be a good idea to get the slipping torque checked. Rotax have altered the slipping torque a number of times. (completely different to friction torque). Maybe worth having a new slipper clutch fitted in case there is a problem with yours.

    Maybe if it is a 914 it could be an overboost due to a bad control of the wastegate.(faulty sensor, sticking wastegate, bad cable or a faulty TCU.

    Do you have a fixed pitch, ground adjustable, in flight variable pitch or even a constant speed prop? Could be something to do with the prop pitch control.

    Is there anything unusual with your installation? Maybe a few pictures would help.
      
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  • Re: Increased RPM at take off speed or slippage?

    by » 10 years ago

    Hi Conrad,

    Same questions I ask. It's a 912ULS and just had the gearbox serviced. This only happens when the oil temp is below 145F and only the first flight of the day and only for a moment. I think it is on a Flight Design, but don't quote me on that. The gearbox was the first thing I thought of especially since it was just serviced, but the under 145F, only the first start and only for a split second has thrown me.

    Still I guess it could be the gearbox under some odd circumstance and it may be the first thing that should be gone through again?

    I'm kind of at a loss.

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

      
    Report
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