As the aircraft decelerates from max structural cruising speed in a sustained engine under-speed condition from 210 MPH IAS through 140 MPH IAS, a low frequency vibration is felt in the seat of my pants much the same as the two transient RPM Ranges in the Piaggio.
I can tell that it is coming, it gets more pronounced, then subsided in a linear fashion. This only takes place during deceleration at 2000 rpm +-100 rpm. It feels strictly engine/spinny thingy oriented. No Spinner is installed.
It's not that the airplane cannot be operated there, but rather feel obliged to pass through those particular zones expeditiously. Much the same as rotor rpm transient zones for helicopters, the ones that start the funky chicken dance. Chinooks have this well documented on the ground.
Its not really a huge deal, I just am curious if this is a mannerism that is unique to my airplane or something experienced in a fleet. I could speculate but my O-200 experience is almost 10 full hours now, so I'm not going to.
I emailed Gary to start a 63 X 69. I have a 62 X 68 on an 8 in Extension.