Quote:
I have taken the aircraft to altitude and lean cut the engine, then whilst gliding I have wind-milled the prop with the mags off (and they both ground perfectly) sure enough at 2200rpm the white noise kicks in on the radio.
That blows the prop vibration theories.
Not sure if it does or not, unless HF stepped on the clutch
the engine would still be rotating , pistons up and down etc.
There could still be a resonating effect that might result in increased vibrations in direction of spin.
This however is where my lack of (any!) practical knowledge of the behavior of prop vibration caused by interaction with engine rotating mass is evident.