Originally Posted by
Hot and Hi
CoaX Helicopters use rotor tip brakes for yaw control, providing differential torque between the rotors.
Coax I understand bought the design rights to the original Gyrodyne Rotorcycle, developed in the 1950's
Hot and Hi, thanks for that link. An interesting method of directional control.
The web site linked has no response to "rotor tip brakes" when queried, but here are some useful links to systems in that family:
Patent US3015363 - Helicopter-reaction tip brake - Google Patents
Patent US20120282094 - Wind Turbine Blade Tip Brake Apparatus and Method - Google Patents
Gyrodyne RON Rotorcycle - Wikipedia, the free encyclopedia
This link has pictures of the brakes
XRON History
It reminds me a little bit of the Kaman servo flap system, in terms of the linkage going through the blade to create movement of an airfoil (or something) while the rotors are turning.
The patent number 2,835,331 explains and has some figures that help understand the concept.
Patent US2835331 - Directional control system for rotary wing aircraft - Google Patents
From a customer point of view, this looks like a nice feature in terms of lowering noise profile, with the lack of noise from any tail rotor / fenestron.