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.


I saw a video of a twin Comanche on You tuvbe flutterign badly during
tests, but I can't find it now. The other ones there don't illustrate it
very well excepet maybe this one. http://www.youtube.com/watch?v=
8D7YCCLGu5Y
No control surface, but it's the flexibility of the wing that's causing the
problem. It's increasing in amplitude because each subsequent oscillation
is further and when it moves further it increases alpha which in turn
imparts more energy to the next oscillation..


Bertie