Date: Wed, 16 Jun 1999 09:03:59 -0400
From: "Douglas L. Dodson, Jr." <73773.1546@compuserve.com>
Subject: Control Surface Balancing
Sender: "Douglas L. Dodson, Jr." <73773.1546@compuserve.com>
To: Blind.Copy.Receiver@compuserve.com
Message-ID: <199906160907_MC2-799E-24D9@compuserve.com>
Mime-Version: 1.0

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>>
>> Can any of our more technical brethren in the aerodynamic field give
us some pointers as to what we are trying to achieve by balancing and to
what degree of balance we should aspire to? <<

OK, 100% mass balance theoretically eliminates the possibility of
control surface flutter.  This is only theoretical, however, since no
bearing or bolt is a perfect fit and some small amount of slop will always
remain in the hinges and control system, and all structural modes are still
there.

The next issue is 100% of what?  Including the bellcrank that mates the
two elevator surfaces is overkill in my opinion, but here is how I would do
it.  After the surfaces are painted, balance each one individually.  Then
connect the two together, and split any additional weight between the left
and right.  Don't remove any weight even it after they are connected it
appears to require less.

Bottom line is over-balanced is conservative.  A particular design may
not require 100% counterbalance to prevent control surface flutter in the
desired envelope, but 100% should give the maximum protection.  More than
that will not add flutter margin nor will it take away.

Hope this helps.


 - Doug Dodson
   Glasair II-S FT
   Flight Test Engineer, CFI-A,G
   Baby Dragon IF1 Race Team
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