R44 II - Rough running / Governor?
Looking at some previous points raised on here I can see Im in the right place.
We have an R44 II (Raven) that has developed a problem, i will detail a bit of background first to give 'a bigger picture'
The ship had an over-speed and as a result the engine was removed and the relevant inspection and rectification was carried out. The aircraft was returned to service with both engineers and pilots 'happy' that the ship was serviceable.
The ship has since flown approx 15hrs and has developed a problem. On the first application of power into the 'governor range' 80-102% (not on start up) but regardless of if the governor is on or off we have 'rough running' at 90-95% power and the engine 'hangs' with some harsh vibration. A second later it will clear very harshly causing the ship to yaw and accelerate and try to over speed. This happens the majority of the time but not every time and does not occur in normal flight the problem does not occur unless the engine RPM is dropped below 80% and then bought back in again for example during auto-rotation checks and again the recovery tries to put the ship into an over-speed situation.
It only occurs during this specific and small band of the power range and also the rough running does not sound like a tappet or sticking valve, it sounds more like a rev limiter on a car to use crude terminology.