There was another item observed during the trim tab examination that deserves mentioning. I have seen this on other Lancairs as well. The concept really applies to any hinged control surface.
Wherever flow transitions from one flying surface to another, i.e. wing to aileron or flap, horizontal stab to elevator, or elevator to tab, care must be taken to ensure the trailing surface is in line with or slightly protrudes into the slip stream. (see sketch) Flow readily separates if the in-trail surface is not in proper alignment. Best case is one merely suffers a drag penalty. Worst case is the effectiveness of the surface is compromised. Many control surface designs will intentional project the leading edge into the slipstream during control surface deflection to assure flow remains attached. In the case of the the trim tab, the separated flow served as an excitation on the loose tab. This, in turn, got the elevator oscillating
which was felt in the control stick.
Chris Zavatson
N91CZ
360 std