[dpboatnut]

A4''s do have a reverse gear reduction.

That in conjunction with the previously mentioned inefficiency of the prop in reverse are likely responsible for smoothing the vibration, especially if it is the result of inadequate tip clearance. Less clearance than 25 percent of the blade''s diameter and you''re likely to get prop vibration.

I''ve got about an inch and a half clearance on my 2-blade 12x8 and I get the same vibration you mention.

Best,
-Chad