Compound helicopters, those having a rotor blade and a small wing, possess rear propulsion propeller adjacent to the tail rotor. The tail gearbox is driven through a drive train coupled to the main rotor drive shaft. In such aircraft the tail rotor is in operation when the propulsion propeller is turning, and vice versa. A mechanism is provided herein for stopping or feathering the tail rotor when driving the propulsion propeller, or for stopping the propulsion propeller when the tail rotor is in operation.