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912UL Engine vibration on throttle back

in 912 / 914 Technical Questions 12 years ago

  • Re: 912UL Engine vibration on throttle back

    by » 11 years ago

    In some composite props there can be counter weights or even components inside that can come loose and change it's rotating balance properties. This will cause a hard to find vibration. I have seen this 3 times with a few composite props. Unknown and hard to find vibrations may dictate a check with a dynamic prop balance.

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

      
    Report

  • Re: 912UL Engine vibration on throttle back

    by » 11 years ago

    Hi Roger

    Ive just got out of bed after being awake all night :(

    I'm not sure if the Warp Drive prop has this form of construction, I don't know, I just haven't come across it before, although I have had an Ivo prop in the past which sounded like a babies rattle if you tapped one of the blades.

    I am going to change the bearings in the gearbox. It is a resonance rather than a vibration (if you know what I mean), and it is getting worse as if something is wearing.

    I am clutching at straws, but I think/hope this will sort it.

    Any eureka ideas welcome, no matter how daft they may sound.

    In desperation.

    Mark
      
    Report

  • Re: 912UL Engine vibration on throttle back

    by » 11 years ago

    Hi Mark,

    The Warp doesn't have anything inside to come loose.
    Have you done a dynamic prop balance?



    Hi Rob,

    Do you have any ideas on this?

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

      
    Report

  • Re: 912UL Engine vibration on throttle back

    by » 11 years ago

    Hi Roger

    I've not got or know of anyone who can do dynamic prop balancing around my area.

    The thing is, the prop hasn't changed in any way, but one day I started getting a resonant vibration out of the blue that has become worse over the last few hours in that things are starting to crack.

    I'm going to change the gearbox bearings and prop shaft and take it from there.

    I can't think of anything else.

    Mark
      
    Report

  • Re: 912UL Engine vibration on throttle back

    by » 11 years ago

    Hi Mark,

    It sounds like your fault is very similar to mine. It also sounds like you have taken many of the actions that I have taken.

    Today I adjusted my Woodcomp 3 bladed composite prop to reduce the pitch and make it finer. My static RPM increased from 4600 to 5000. This has had an interesting effect on my problem.

    Before the pitch adjustment
    I would cruise at about 4600rpm with the engine smooth, throttling back would result in the vibration which would be particularly bad at around 3000rpm.

    After the pitch adjustment
    I cruised at about 4800-5000rpm but the engine was only smooth when the engine was loaded either by speeding up or climbing slightly. In a level cruise at these rpms the engine was no longer smooth even though the airspeed was the same as before the pitch adjustment.

    However upon throttling back to the 3000rpm range it was nowhere near as rough as with the course pitch setting.

    I am not quite sure what this all means!

    Kevin
      
    Report
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