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  1. #1
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    Default Vibrations

    2007 Sport Cub, 300 hrs.: Has anyone experienced the vibrations described as follows.

    In the air or on the ground, as the RPM is increased from approx. 1,600 RPM to approx. 2,200 RPM, or the reverse, a noticeable vibration is felt - strongest at approx. 1,900 rpm. Have tried switching to one mag. Have tried varying mixture. None of this altered the vibration.

    Prop Sensenich Wood with about 200 hrs. Was removed from plane and stored for 4 years, then reinstalled 2 yrs ago. Prior owner dynamically balanced it about 1-1/2 years ago. Vibration status prior to balancing, not known.

    Has anyone had this problem or even heard of it.

    Thanks for your patience. LBlack

  2. #2
    Administrator Pete D's Avatar
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    Default Re: Vibrations

    Take a look at the engine mount rubbers, they may be worn and the engine mount bolt(s) may be near the case.

    Also look at the spinner for wobble. Have someone stand a couple of wing spans to the side, inline with the prop and watch the spinner as it runs.
    Pete Dougherty
    R & D Shop Manager
    Cub Crafters Inc

  3. #3
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    Default Re: Vibrations

    Quote Originally Posted by Pete D View Post
    Take a look at the engine mount rubbers, they may be worn and the engine mount bolt(s) may be near the case.

    Also look at the spinner for wobble. Have someone stand a couple of wing spans to the side, inline with the prop and watch the spinner as it runs.
    -----------------------
    Thanks, Pete. I'll add these to my list of things to check. A couple of questions. First one is a stupid one: Which case are you referring to? Next, do you know of a way to strengthen the spinner bulkhead? It seems a bit too flexible.

  4. #4
    Senior Member chipallen's Avatar
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    Default Re: Vibrations

    Mark,

    I've owned a couple of Sport Cubs with Sensenich composite, ground-adjustable props and Bendix mags. Several years ago, at Oshkosh, a few of us met with Sensenich and Continental (TCM) to discuss the ongoing problems; broken mag shafts, prop vibration, etc. Both of my Sport Cubs had several instances of broken prop bolts, broken mag drive shafts, etc. Originally, we thought the vibrations were simply propeller related, but after the prop bolts began breaking, Sensenich rebuilt the hub (no charge), and things returned to normal. At the time, Continental claimed that the Sensenich composite prop (and it's inherent lack of mass) in conjunction with the Bendix mags were setting up a harmonic vibration than eventually took out the magneto. Based on a lot of telephone conversations with Sensenich and TCM engineering, it was determined that there are two solutions to this problem. First, get rid of the composite, ground-adjustable prop and install a metal prop, or get rid of the Bendix mags and go to Slicks. I changed the mags out on my second Sport Cub and the mag issues went away as did the vibration. Flew it about 250 hours, sold it, and the current owner has had no problems at all. See the attached bulletin from Sensenich.
    Sensenich Harmonics.pdf

    Chip Allen

    SWT Aviation, Inc.
    Cubcrafters Southeast Sales Center
    Marietta, GA

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

    Quote Originally Posted by chipallen View Post
    Mark,

    I've owned a couple of Sport Cubs with Sensenich composite, ground-adjustable props and Bendix mags. Several years ago, at Oshkosh, a few of us met with Sensenich and Continental (TCM) to discuss the ongoing problems; broken mag shafts, prop vibration, etc. Both of my Sport Cubs had several instances of broken prop bolts, broken mag drive shafts, etc. Originally, we thought the vibrations were simply propeller related, but after the prop bolts began breaking, Sensenich rebuilt the hub (no charge), and things returned to normal. At the time, Continental claimed that the Sensenich composite prop (and it's inherent lack of mass) in conjunction with the Bendix mags were setting up a harmonic vibration than eventually took out the magneto. Based on a lot of telephone conversations with Sensenich and TCM engineering, it was determined that there are two solutions to this problem. First, get rid of the composite, ground-adjustable prop and install a metal prop, or get rid of the Bendix mags and go to Slicks. I changed the mags out on my second Sport Cub and the mag issues went away as did the vibration. Flew it about 250 hours, sold it, and the current owner has had no problems at all. See the attached bulletin from Sensenich.
    Sensenich Harmonics.pdf
    Chip

    LBlack here will appreciate that info for sure. Maybe he had the composite on prior and damaged the mags??? MK
    Cub Crafters
    Factory Direct New & Used Aircraft Sales
    NorthEast & Great Lakes Region
    518.410.9404

  6. #6
    Senior Member chipallen's Avatar
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    Default Re: Vibrations

    Quote Originally Posted by Mark Keneston View Post
    Chip

    LBlack here will appreciate that info for sure. Maybe he had the composite on prior and damaged the mags??? MK
    From several years ago, I'm not aware of any magneto failures on Sport Cubs that were running aluminum props. I think they all had the "infamous" Sensenich composite / Bendix mag combination.

    Chip Allen

    SWT Aviation, Inc.
    Cubcrafters Southeast Sales Center
    Marietta, GA

  7. #7
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    Default Re: Vibrations

    Quote Originally Posted by chipallen View Post
    From several years ago, I'm not aware of any magneto failures on Sport Cubs that were running aluminum props. I think they all had the "infamous" Sensenich composite / Bendix mag combination.
    Thanks for all your helpful comments. Our 2007 Sport Cub was delivered to the original owner with the Sensenich wood prop. At 104 hrs, I was replaced with the Sensenich ground adjustable composite prop. Then at 234 hrs, the wood one was reinstalled. The plane has Bendix mags.

    We plan to inspect the mags as the result of your comments.

    Thanks again.

  8. #8
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    Default Re: Vibrations

    Thanks very much, Clay and Mark.

    The vibrations seem to be associated with a power reduction, specifically when passing through about 2,000 rpm in a rapid power reduction. Not so noticeable if the rpm is slowly decreased through 2,000. If fact, if during the reduction and the rpm is stopped at 2,000 - no vibrations. It seems to be a dynamic thing.

    Another idea offered is that it could be an induction air leak. As the throttle is closed, momentarily more outside air is pulled into the induction system, leaning the air/fuel during the throttle reduction. Comments?

    Thanks again.

  9. #9
    Senior Member Clay Hammond's Avatar
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    Default Re: Vibrations

    Both possibilities. Only way to run it down is to start eliminating possibilities. List them all out and then start picking them off one by one until the vibes are eliminated or start to mitigate. It might not be one single thing...that is always the bugaboo. Keep at it though and it will resolve. Only takes a combination of time, knowledge and/or money. Usually all of the above!
    _______________________
    Clay Hammond

  10. #10
    Senior Member Mark Keneston's Avatar
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    Default Re: Vibrations

    Quote Originally Posted by Clay Hammond View Post
    Both possibilities. Only way to run it down is to start eliminating possibilities. List them all out and then start picking them off one by one until the vibes are eliminated or start to mitigate. It might not be one single thing...that is always the bugaboo. Keep at it though and it will resolve. Only takes a combination of time, knowledge and/or money. Usually all of the above!
    Clay is right, hunt and peck. I feel like mags or prop damaged. MK
    Cub Crafters
    Factory Direct New & Used Aircraft Sales
    NorthEast & Great Lakes Region
    518.410.9404

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