Incorporating a
hub spring into a conventional 2-blade teetering rotor will result in more cyclical control authority and less chance of tail-boom incursion. Unfortunately, this hub spring will generate a 2P vibration when the tip-path-plane is tilted in respect to the mast.
It appears that the following concept will provide the above two advantages while minimizing the 2P vibration.
The basic idea consists of locating a 'trim-tube' between the teetering head and the mast. Hub springs are installed between the teetering head and the trim-tube, and 2 linear actuators are installed between this rotating trim-tube and a stationary support.
For the very interested or for constructive criticisms;
Rotor - Hub - 2-blade - CVJ+HS