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Thread: Throttle response

  1. #1
    Junior Member
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    Default Throttle response

    Hello,

    I have a slightly disconcerting flat spot/dip in the throttle response most of the way to full power on the takeoff roll, any ideas? Runup is fine, doesn't seem to change with mixture. No roughness, just a smooth pause in the RPM ramp..

    Thanks,
    B

  2. #2
    Senior Member Mark Keneston's Avatar
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    Default Re: Throttle response

    Quote Originally Posted by stretch View Post
    Hello,

    I have a slightly disconcerting flat spot/dip in the throttle response most of the way to full power on the takeoff roll, any ideas? Runup is fine, doesn't seem to change with mixture. No roughness, just a smooth pause in the RPM ramp..

    Thanks,
    B
    Is the run up fine using the carb heat? How many hours on it? How long is this pause? Is it a skip or slight rpm drop? MK
    Cub Crafters
    Factory Direct New & Used Aircraft Sales
    NorthEast & Great Lakes Region
    518.410.9404

  3. #3
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    Default Re: Throttle response

    Quote Originally Posted by Mark Keneston View Post
    Is the run up fine using the carb heat? How many hours on it? How long is this pause? Is it a skip or slight rpm drop? MK
    Hi Mark,

    50 hours, it has done it all along I think. Carb heat on runup gives normal RPM drop and recovery. electroair and mag drops also normal. It's definitely not a skip (that's reserved for my heart rate), and may not even be a drop in RPM so much as a flat spot in the increase in RPM as I 5-count up to full throttle (hard to say without RPM data). It's far enough into the takeoff roll that I'm looking at the runway! Next time I'm up at a safe altitude I'll see what power setting produces it.

    Thanks,
    Ben

  4. #4
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    Default Re: Throttle response

    Most stumbles when pushing throttle forward are caused by too lean of a mixture. Try taking off with carb heat on and see if it's better

    Glenn

  5. #5
    Senior Member Mark Keneston's Avatar
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    Default Re: Throttle response

    Quote Originally Posted by stretch View Post
    Hi Mark,

    50 hours, it has done it all along I think. Carb heat on runup gives normal RPM drop and recovery. electroair and mag drops also normal. It's definitely not a skip (that's reserved for my heart rate), and may not even be a drop in RPM so much as a flat spot in the increase in RPM as I 5-count up to full throttle (hard to say without RPM data). It's far enough into the takeoff roll that I'm looking at the runway! Next time I'm up at a safe altitude I'll see what power setting produces it.

    Thanks,
    Ben
    after review Ben, I'm going to say that you are hearing the pitch of the prop pulling rpm down as you go to full throttle with the prop forward. All of the CS prop cubs I have flown, I hear the engine rev to max and then it flattens just slightly as the prop is grabbing as much air as possible in the forward position. Could this be what your experiencing? If so, I'd say this is normal from my experience in our planes. MK
    Cub Crafters
    Factory Direct New & Used Aircraft Sales
    NorthEast & Great Lakes Region
    518.410.9404

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