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912ULS Vibration Mid-range RPM's

in 912 / 914 Technical Questions 7 years ago
I built my RV-12 in 2011. It has about 350 hours TT. Carbs are well synced and prop has been balanced. Engine runs real smooth at idle and cruise RPM's. Carbs have been overhauled at Lockwood. There has always been increased vibration in the mid RPM ranges, 3000 - 4000 RPM. I have lived with it until now, but it still bugs me. Anybody seen anything similar?

  • Re: 912ULS Vibration Mid-range RPM's

    by » 7 years ago

    You can get a harmonic vibration in that rpm range at times. Many have it, but not everyone. If you synced your carbs down around 2500 rpm then try up around 3500 rpm and it may go away, but it isn't a guarantee.

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

      
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  • Re: 912ULS Vibration Mid-range RPM's

    by » 7 years ago

    Thanks Roger, I didn’t think of that. Makes sense too, since the vibration only shows up in flight, not in a static runup. Apparently no cure then, just avoid that RPM range. I wonder if its a function of the engine, gearboox, or prop, or a combination of all three.
      
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  • Re: 912ULS Vibration Mid-range RPM's

    by » 7 years ago

    Engine's many times have a designed rpm ranges to run in for smooth operation, HP, torque and longevity. Ours is set up to run in the 5'sK range. So we don't run it's cruise life in the 3K-4K rpm range all the time. We do use the lower rpm range when coming into a pattern to land, but that's short term.

    For those that don't know:
    Low rpm Idle is another rpm we stay away from. As an example we don't want to sit for extended times with a 912ULS at1600ish rpm. We just want to treat our engine's right so they don't fail on us and have good longevity.

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

      
    Report
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