Disbonding of the bushes from the wooden ribs inside the tail planes can have
fatal
consequences. Potentially it could allow the tail plane to migrate sideways
(outboard) along the torque tube until disengaging from the drive pins and
the tail plane would whip up and down destructively.
Some builders make the recess around the pip-pin head too large, so that the
distance
between the inboard side of the pip-pin head and the side wall of the recess
is greater than the length of the drive pins. Therefore if the bush through
which the pip-pin passes was to disbond (as one of mine did), nothing could
stop the tail plane from drifting sideways.
I favour "belt and braces" back-up solutions to such problems and I also like
solutions
to be simple. So I bonded a little piece of plywood into each pip-pin
recess on the inboard side, to fill the gap between the pip-pin head and the
inboard sidewall of each recess.
This was done in addition to other modification instructions to beef up the
joints
in the tail plane torque tube assembly. I have no free play up and down at
the trailing edge of either tail plane.
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http://forums.matronics.com/viewtopic.php?p=498677#498677
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