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Hard violent shutdowns

in General Tech Discussion 6 years ago
A 912 ULS with 1821 hrs time has recently started exhibiting a harder and more violent shutdown than was previously noticed. This engine is installed in a Tecnam P92 Echo Sport and at 1731 hrs actually broke several parts of the engine mounting system. I am concerned that this may happen again before we TBO the engine. Any suggestions about where to begin looking to tame this bucking bronco?

Jeffrey Fritts, USAF (ret.)

www.flywwlsa.com

"In aircraft maintenance, good enough is not good enough."

  • Re: Hard violent shutdowns

    by » 6 years ago

    How about a few more details.

    At what rpm is the shutdown commenced?
    Are both ignitions killed at the same time?
    Does a Mag Check show anything abnormal?
    Does the prop reverse direction at the shutdown?

    Check/Clean/Replace Sparkplugs. Carbon buildup... Dieseling?
    Repeat the Mag check before shutdown.
    Run a compression check.

    Check the Engine mount in fine detail.
    It may be the Perpetrator and not the victim.

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.

    Thank you said by: Jeffrey Fritts
      
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  • Re: Hard violent shutdowns

    by » 6 years ago

    Thanks for the quick reply Bill,
    2,000 rpm idle. The carbs are in sync.
    Yes, one mag at a time is used for the shutdown.
    No, all mag checks are normal within limits.
    Now that you mention it yes I believe the prop does reverse direction upon shutdown. The shutdown is so violent I can't be sure. I will watch more closely today while I am checking the other items you have mentioned.
    I am doing a dynamic prop balance and so am starting and stopping the engine several times after an initial warm up to operating temperatures. I let the engine idle several minutes after these high rpm runs before each shutdown. The aircraft is part of a flying club and used primarily for flight training.
    I'll get back to you with the results of the rest of the test.
    Thanks again...

    Jeffrey Fritts, USAF (ret.)

    www.flywwlsa.com

    "In aircraft maintenance, good enough is not good enough."

      
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  • Re: Hard violent shutdowns

    by » 6 years ago

    Prop reversal would indicate a severe preignition condition where the fuel mix ignites well before top dead center and the piston is driven back down causing the prop to reverse.
    If the ignition is OFF, the ignition source must be something else.
    If you have been doing a lot of idling and never getting the heads up to full temperature (100°C+) it is possible that you just have sooty plugs that act like charcoal embers and are igniting the fuel during the shutdown.
    It will only take one!

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.

      
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  • Re: Hard violent shutdowns

    by » 6 years ago

    Lowering the idle speed helps with shut down severity. I use 1550 rpm at the throttle stops, when the engine is running I keep throttle in to maintain 1900 plus idle, usually around 2100.
    Shutdown is smooth and if I delay too long after switching off the first ignition, the engine will quit before I switch off the second ignition.
      
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