OK gents, here is the response from Dr. Niewoehner regarding the balancing/flutter/pivot interaction. I'm afraid it may not solve much here in our debate, other than to illustrate that, as been suggested already, we are probably at a point with these larger jets that some actual and legitimate engineering must take place in their design.

Sluggo-

The thread is predictably confusing two issues, since we refer to both mass balancing and aerodynamic balancing.

Aero balancing is done by ensuring the aero center of the surface in question is aft of its hinge. Too far aft and you'll get lots of deformation. On GA airplanes with sizable horns (or rudder on a Corsair), the horn pulls the aero center closer to the hinge, reducing control forces. The F4U Corsair had a huge rudder, for example.

Mass balancing is done to pull the CG of the surface close to the hinge or pivot. Small horns on GA airplanes are filled with ballast to do just this. Lower mass moment of inertia on the surface about its pivot raises its natural frequency, just as lighter guitar strings vibrate faster. Raising the frequency of the pitch deformation pushes the flutter speed higher, hopefully above the operating speed.

In manned airplanes, we don't eliminate flutter. Rather, we seek to push the flutter speed 15% above Vne.

Again, flutter is the interaction of structural rigidity (and dynamics), with mass properties, and aero properties. So, all of the above play against one another, with both aero and mass balancing as part of the tool kit.

Rob

Robert Niewoehner
David F. Rogers Professor of Aeronautics
CAPT, USN (ret), PhD, CFI
Aerospace Engineering Dept
United States Naval Academy