From: "Marvin Kaye" <marv@lancaironline.net>
Subject: Re: Elevator Balance
To: lml
Date: Fri, 03 Oct 2003 12:47:56 -0400
Message-ID: <web-2622951@logan.com>
In-Reply-To: <006d01c389c5$25c49a30$6603a7c0@gamarrdesk>
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Posted for "Giffen A. Marr" <GAMarr@Charter.Net>:

Guy's
You need to remember that the reason the center of gravity of the
control surface must be ahead of the hinge line is to ensure that you
have positive margin and have eliminated the potential for flutter. If
you remember my example about a trailer center of gravity being behind
the wheels will provide you a lesson you will only want to experience
once and will never forget. The same applies to control surfaces, if you
survive. Including in the rest of the control system could lead to not
obtaining the proper control surface balance. Balance the control
surface by it's self. With the rest of the system attached it could mask
the correct balance of the surface. If my memory has not failed me yet,
the air acts like a spring to excite the surface, as your speed goes up,
the spring [air] gets stiffer [higher frequency]. As long as the balance
is ahead of the hinge line, there is natural damping [no excitation], if
it is at or behind the hinge line, it's catastrophic. If any of you have
flown a tail dragger, the same principle applies [the cg is aft of the
wheels (hinge line)] that causes a ground loop [poor pilot damping]. 

Giff Marr
LIV-P/20B