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From: "Gary Casey" <glcasey@adelphia.net>
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Subject: Re: Elevator Balance
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<<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.>>

Lots of good comments on this subject, but I am puzzled about one thing -
the distribution of the moment balance weights.  I would think that the
destruction of the horizontal tail structure caused by flutter is a
combination of bending and twisting of the horizontal stabilizer induced by
vertical excitation at the hinge point.  If that is true the center hinge
really doesn't count as it is fixed in place.  Therefore, the only elevator
moment that needs to be balanced is out toward the tip.  However, the
"correct" methodology is to install enough lead to balance the WHOLE
elevator and to concentrate it at the tip.  Seems to me that the tip is
being way overbalanced and the root underbalanced.  That thinking would lead
one to reduce the balance weights at the tip drastically as most of the
unbalanced weight of the elevator is at the root, more on one side than the
other because of the trim tab.  Then if it was desired to really balance the
total weight a bob-weight should be located inside the tail.

Then when I look at certificated aircraft it still doesn't make sense.
Cessna usually puts all the elevator balance weights at the tip, but the
aileron balance weights are toward the root near the actuator.  The Cardinal
and Cherokees have all the balance weight for their stabilators at the root.
On the Comanche an extra balance weight can be added at the tip to get a
higher red-line speed.  And on and on.  What I get from all this is that no
one seems to worry about the torsional stiffness of the control surface
itself, but when I look at the elevator on the ES there is a definite lack
of stiffness right at the junction between the balance weight extension and
the rest of the elevator.  Also, our ailerons, while the weights are
"correctly" distributed along the span seem to have a mount for the weights
that doesn't consider stiffness at all and I have heard of these weights
coming loose, probably because of a stiffness issue.

I hope I'm worrying about all this for nothing.

Gary Casey
ES #157