Abstract: A damping mechanism is disclosed for damping the oscillations of the rotor hub which are coupled with periodic motions of the fuselage when on the ground, known as ground resonance, and a waddle when in the air. The rotor includes a freely tiltable rotor head mounted on a non-rotatable universal joint having an outer gimbal ring and an inner ring carried by a pylon. The damping mechanism connected between a gimbal ring and the pylon combines the action of a fluid dashpot in tandem with spring means the output of which is connected into the linkage between the pilot stick and the swash plate. The tandem combination of dash pot and spring means delays the signal to the swash plate by about 90.degree. to insert a corrective movement into the swash plate with feathering of the blades to tilt the rotor thrust vector which damps the oscillations of the rotor hub. The invention includes the damping mechanism per se and its combination with the rotor and with the swash plate.

Abstract: A rotorcraft is subject to a rocking motion when on the ground, which is called ground resonance, and in the air which gives the fuselage a waddle type of motion about its center of gravity. both are a form of aeromechanical instability. This fuselage motion is coupled with and accompanied by bending oscillations of the blades with respect to the hub of the rotor of the rotorcraft. An oscillation damper is described which damps the oscillations of the aircraft and thereby eliminates or substantially reduces the rocking and waddle motion of the fuselage. The damper includes a seismic device having a mass-spring combination tuned to the frequency of the rocking motion which will typically be one half or approximately one half of the rotor revolutions per minute at cruising speed and is positioned laterally of and spaced from the center of gravity of the fuselage.