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ACRO E-mail Archive Thread: [IAC-L:113] Re: Aileron Rigging

Thread: [IAC-L:113] Re: Aileron Rigging

Message: [IAC-L:113] Re: Aileron Rigging

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From: Finn Jensen <finnjensen at mindspring.com>

Date: Wed, 18 Jun 1997 06:05:14 UTC

Message:

  At 05:37 PM 6/17/97 -0500, you wrote:
>My partner just picked up our Pitts S1S after it had been re-rigged during
the
>annual inspection.  He reported "serious" lateral vibration in the stick, and
>said it felt like some kind of harmonic oscillation.        He called the
>rigger, who told us to take the spades off to see if that fixes it.
(Apparently,
>Harmonic oscillation can come from the square spade, and he mentioned we
might
>want to try a triangular spade) He also mentioned that when he had rigged the
>ailerons, he rigged the top ones slightly up, instead of in-line with the
wing
>as they had been previously.  (He said this puts more tension on the slave
strut
>which should be a good thing)
>
>Now, here's the problem...We had no problem with vibration prior to
re-rigging,
>so I'm wondering why the spades were OK before and not after.  Secondly, has
>anyone heard of rigging the upper ailerons slightly up, and why one would
want
>to do that?
>
>I'm sadly ignorant on this, and before we start trying random fixes, would
like
>more information.  If you can help or know a good source, please respond to
>
>Ana M. Vegega  73761.1371 at compuserve.com
>(415) 572-7151
>Thanks!!!!!!  
>
Many Pitts owners advocate rigging the upper ailerons exactly opposite to
what has been done to your airplane.  In other words, with the lower
ailerons streamlined, the upper ailerons are set to a down deflection equal
to 1/2 the width of the trailing edge.  The rationale is to put a slight
load on the ailerons to prevent "hunting."  I don't know how the factory
sets the ailerons, but it would probably be worth your call to Mark Heiner
at Aviat to ask the question.

You don't mention it, but I assume your airplane has standard Pitts or
Sparcraft wings, and that the ailerons are standard.  I have never heard of
a problem with the square aileron spades with any Pitts S1S.  I certainly
have never had a problem with mine.

There is something definitely wrong with your airplane, and I would ground
it until the entire aileron linkage is carefully inspected from stick grip
to aileron.  I would also have somebody else who really knows the Pitts
biplanes check the rigging. I have never heard of aileron flutter on a
Pitts S1S, but it would be prudent to make sure it won't happen.

Finn Jensen
San Diego>

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