Bell 407 ground bounce issue
Hi to all helo guys,
iam having some trouble with one of our 407s
It has pretty intense ground bounce going from idle to fly. On idle its fine, on fly its also fine but while spinning the engine up it really vibrates hard passing ~80-90% (pulling the stick out of center helps a bit) After that its smooth and flies very smooth we did T&B and got it to fly awesome but the bounce is still there. We did full collective and cyclic rigging twice now and it helped a bit but the pilot is still concerned.
The back story is we had the mast and transmission sent out for inspection during the annual this february and its had this issue ever since. Could the mast bearing be too loose ?
We also did adjust autorotation rpm a bit
Ive been maintaining this 407 for 6 years now and it did not have this vibration before. Also right now after rigging and T&B its the smoothest flying 407 ive ever been in.
Any insight into this matter would be greatly apreciated