On Dec 26, 12:15 am, Bertie the Bunyip wrote:
WingFlaps wrote in news:797747ee-e7ec-4c72-b61b-
:



The bottom line is that If the COG of the surface is behind it's
center of lift flutter is promoted. That's why most control surfaces
add weights (depleted uranium!?) to bring the COG forward. On the
preflight you check that that balance weights are there and fixed.
Flutter will destroy the surface, structure and it's hinges pretty
quickly.

Actually, that's not quite correct. the CG of the surface has to be at the
hinge line, not it's Cl. to eliminate this tendency. It's down to the
rididity of the hinge in space, though. The less rigid the greater the need
for balancing. Most wings and stab surfaces are quite flexible, though, so
at least some balance, if not 100% (which would put it at the hinge line)
is reguired for most airplanes.


Err, I didn's say the Cl was at the hinge line (rather that COG must
be forward of control surface lift). But I agree, if the COG _can_ be
put at the the hinge line then not just control surface flutter is
reduced but also flying surface flutter (in this case fin + rudder).
The trouble with the lightt structures in a plane is that balancing
one end (e.g. with a leaded horn) may lead to tortional problems...

Cheers