Some experimental numbers

I thought some numbers might be useful. Here is the model I am using for the initial experiments:

This is a very light and simple model aircraft with a wingspan of 120 cm and a total mass of 184 grms.

With all other joints set rigid, I concentrated on the left wing of the model. With selected spring and damping values which slowed the process down to make it visible, destructive resonance was seen. Resonance was restricted to left/right movement of the wing gradually increasing in amplitude to the point of breakage.

This occurred with a spring stiffness (Kf) of 3600 and a damping coeff (Df) of 1.06 on the Fuselage Left wing joint. The KF of 3600 might appear high; but it corresponds, I think, to a maximum structure limit of 4g on the model. With Df at 1.06, destructive resonance occurred during a flight where no control inputs were made. Increasing the Df to 1.07 eliminated resonance under these conditions. Destructive resonance continued to occur above this value if maximum rudder was held; but ceased with a Df of 1.10.

It is possible that the Df unit is 10 Newtons while the Kf unit is 1 Newton. The critical damping coefficient for Kf = 3600 is 51.55 Newtons for this model. Using a value of Df = 5.155 seems to be correct in the simulator. But this is using my existing too simple math model of the damped spring with the formula sqrt(4 . mass . Kf)

Does a critical damping coeff of 51.55 Newtons appear to be reasonably consistent with a spring stiffness of 3600 Newtons?

Anything particularly strange about these numbers?

Mike