Expert: Paul Soderman - 6/19/2011

Question
Hello Sir,
A glider that is 70 degree from horizontal fall at free fall vertically.While falling,the angle does not change and land.My question is what cause the angle stay like that.Is it possible that the equilibrium of moment of the main wing which is clockwise and the moment of the stabilizer which is counterclockwise cause this?

And what is dynamic pressure?Does it has something to do with my question?thank you sir.

Answer
Yes,  a simple glider will have a center of gravity aft of the aerodynamic center of the wing and will generate a nose-up pitching moment as does the wing itself.  If those two moments are balanced by a tail that provides a nose down pitching moment the glider can be in equilibrium.  A trim tab and/or elevator on the tail would help establish the right pitching moment.

Dynamic pressure is the product of 0.5*air density*velocity squared, which is the forcing function, if you will, for lift and drag.  It is one of the factors that determines the strength of the lift forces and restoring moments on your glider.  In a weak atmosphere such as on Mars, the restoring moments would be weak.
Paul