Message-ID: <000f01c1ac31$03d12e20$990eb43f@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: High speed vibration in a 360
Date: Sat, 2 Feb 2002 13:31:43 -0800
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<<A friend's 320 had a vibration and it turned out to be the curved area of
the ailerons where the weights are attached. He removed the ailerons and
installed a 2 thin webs between the curved area and the front spar of the
aileron and presto no more vibration.>>

After installing the counterweights on my 235 ailerons, I noted that the
mounting (the extension of the lower aileron skin) was somewhat flexible, or
"springy". It looked like the weights could vibrate if something excited
them at the correct frequency.

Having done a lot of vibration testing of new equipment for large aircraft
in my life, and seeing the havoc that can be visited upon materials when and
if the excitation just happens to coincide with the part's natural frequency
(resonant frequency), I also decided to install the webs at each end of the
weight mounting. By stiffening the assembly, I figured that it would raise
the natural frequency enough to avoid the problem. Seemed to have worked as
I have never had even the slightest stick buzz, and I have opened my flight
envelope to red-line (for the 235, that's 247 MPH indicated) plus a small
margin - very carefully, I might add!

If you add the webs, however, be sure to leave a small opening at what will
be the lowest point to allow drainage as rain can get in there and (without
the drain holes) fill up the area behind the weights.

Dan Schaefer


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