Message-ID: <002001c1daef$c8a54dc0$464db041@f3g6s4>
Reply-To: "Dan Schaefer" <dfs155@earthlink.net>
Reply-To: lancair.list@olsusa.com
From: "Dan Schaefer" <dfs155@earthlink.net>
To: "Lancair list" <lancair.list@olsusa.com>
Subject: Trim tab counter balance
Date: Wed, 3 Apr 2002 01:11:56 -0800
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Trim tabs can and do flutter depending on the application. Sloppy linkage on
a non counter-balanced trim tab (the most common type) is the main culprit
on a tab that has a propensity to flutter. Because of the small size of a
typical trim tab, it's natural frequency (the frequency at which it's likely
to flutter) tends to be high and at the speeds of our aircraft, unlikely to
be excited. But I'd never allow my tab linkage to become loose enough to
test that theory.

FWIW, to illustrate, not too long ago, maybe 5 - 8 years or so (at my age,
that doesn't feel like all that long ago) a common twin - don't remember the
type - had an AD issued regarding maximum play at the trailing edge of it's
pitch trim tab. The AD came about due to an incident where the pilot noted a
powerful vibration or "buzz" in the controls. The guy was lucky and got the
airplane on the ground. The post mortem revealed that the trim tab could be
moved up and down about +/- 1/4 to 3/8 inch. The airplane manual listed the
limits of +/- 1/16 inch. After the fix, the problem did not recur.

The conclusion was that the trim tab experienced flutter.

Dan Schaefer


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