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Does anyone recognise this problem and if so what did you find was the cause ?

Our 912S is just over eight years old serviced and maintained on the dot by the same service organisation from new and has given perfect service throughout from new - the engine now has 1650 hours

This summer and several times since, when in the cruise the engine tone will drop and notice a 50 rpm drop with no commanded inputs - this happens with no other discernable reason while otherwise purring along nicely

This is enough to quicken the pulse somewhat ! - this corrects itself after approx 30 seconds and returns to normal and in most flights does not happen again , in some flights it may happen more than once

So far engineers have tried ;

Removing and cleaning all ignition connections
Carb Balancing

If you recognise the above and found out what was causing it or if you think you know what may be causing it please let me know
  • Re: Rev drop in cruise

    by » 9 years ago


    Hi Todd,

    A 50 rpm drop at cruise rpms isn't much and may be caused by simple air fluctuations into the air filter and or carbs. Maybe the air filters or fuel filters needs a little more periodic checking. It could even be caused by turbulent air and the floats bouncing around inside the bowl or maybe something is affecting your fuel flow momentarily in your fuel system. These carbs are self adjusting as we fly so outside forces can have a minor affect on them. Even the wind hitting the prop can change the tone or 50 rpm.
    Bottom line it could be a couple of things, but 50 rpm change can be normal depending on the situation.

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


  • Re: Rev drop in cruise

    by » 9 years ago


    A mate had the same thing happening on his Remos (the rpm drop was more than 50 though), was a faulty/failing ignition module.

    Paul

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