RVTD and Hei-Kiwi;
Thanks for the information.
Mart,
The Kaman helicopters (at least the intermeshing ones) have very soft rotors, and this is necessary for a servo-flap to act as a primary flight-control. The increasing rigidity of modern rotors may preclude the use of servo-flaps for primary control.
To my knowledge, current R&D in servo-flap technology is only for reduced noise and vibration.
Now if some company with deep pockets would like to fund this......
Dave