it's a prop plane, prop/spinner/etc.. are all perfectly in balance, the vibration is simply from 16,300 RPM high resonance and the design of the plane makes it impossible to mount the tank anywhere that allows more then a marginal amount of foam between the tank and formers. the only way to get room for foam is to move the tank away from the engine a good 18" which is unacceptable due to limited access in those areas or spray the canopy and remove the cockpit which I'd rather avoid if possible. none of my old ducted fans had these problems because i was always able to get at least 1/2" of foam around the tank, on this setup the formers are only slightly larger then the tank so to keep the stock location and have foam, I'd have to remove the former completely.

Joe, thanks for the comment on the UAT seams nobody else had that answer.

kc