Message-ID: <3C79291F.8EF18BE5@ieee.org>
Date: Sun, 24 Feb 2002 09:55:43 -0800
From: "Charles R. Patton" <charles.r.patton@ieee.org>
Reply-To: charles.r.patton@ieee.org
Reply-To: lancair.list@olsusa.com
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To: "lancair.list@olsusa.com" <lancair.list@olsusa.com>
Subject: aileron vibration revisited
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Back at the end of Jan. I wrote to the list about my aileron vibrations
in response to some posts about that subject.  Clark Baker was kind
enough to point out the discussion in May 1999 about aileron vibration. 
That was just the ticket.  With that information I went up and found out
it was tied to engine speed with 2500 rpm being the magic resonance. 
Came back down and took off the ailerons and found they needed the
reinforcement fix on the balance weight web.  With the gracious help of
Hal Woodruff, we installed three 1/2 moon reinforcements on each aileron
to stiffen-up those webs.  Then I rebalanced the ailerons and
reinstalled.  Took it up yesterday - problem entirely solved throughout
entire airspeed and engine rpm range.  Happy camper.

Which leads to the question - why 2500 rpm?  To make calc easy, assume
2400 rpm.  Then 2400 rpm / 60 sec per min = 40 rps.  There's no way I
believe the vibration I felt was 40 pps.  But since a cylinder fires
once every two revs, then there might be a 20 pps component and I could
believe what I felt was in that neighborhood.  Is this correct, that
engines generally do have a strong 1/2 harmonic component or should I
also be worrying about a new item?  (Any discussions I remember about
engine vibration - usually in conjunction with prop resonances -- always
talked about harmonic multiples, not sub-harmonics, hence the question.)

Thanks to the discussion group, it certainly saved me a lot of
head-scratching time - and I can ill afford that as I already have a
bald spot.

Charles R. Patton
360JM
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