Harald:

That spring balance is such a good idea that it's known as "SAS," or Stability Augmentation System. If you check many light aircraft, they have this sort of spring centering the elevator.

It's not for flutter prevention, though, it keeps gravity from pulling the elevator off center, leading to less effort needed to maintain level flight. In some cases the spring tension can be altered in flight to change elevator sensitivity. I don't know of any full scale installations on rudder or aileron surfaces, give it a try and let us know.

There are many toy r/c models, Wal-Mart $20 sort that do not have proportional control, using magnetic actuators for deflection and a spring to center the surface for level flight. Or straight driving - cheap cars use it too.

I thought you had gone off-line, Harald, no notes, no posts, recently I see you have come back to life. All the best to you.

If you tune your spring.
. Will the ailerons ring?

Bill.