On Fri, 11 Dec 2009 07:07:43 -0800, Andy wrote:

Hmmm...maybe you're right. I'm not an expert on aeroelastics. My
thinking was that flutter at its core is like a mass-spring-damper
system. Given that the input aerodynamic forces don't change with mass
loading, adding mass to the wing ought to make it respond less in
bending to the input force because it has more inertia. I would expect
most of the bending resistance would be structural (spring) resistance
rather than inertial (mass) resistance, so the effect could be small.
The lower natural frequency of the wing would correspond to a lower
speed for flutter onset, but the aerodynamic forces would be lower as a
function of the square of the speed, so what's the net effect? With
enough mass might you not get any flutter at all? May there also be
harmonic effects related to how many bending "waves" you get along the
span?

I remember hearing a talk about this a few years ago. Anything that moves
the wing section CG forward relative to the effective CP will reduce the
tendency of the surface to flutter - hence lead in control surface
leading edges and the recommended lead in the tip LE of the modified
ASW-22.

All modern gliders carry water in front of the spar. As a result the CG
moves forward and you'd expect some increase on the speed at which
flutter starts.


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martin@ | Martin Gregorie
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