Patent ID: 7490792

Claim:
A rotor aircraft, comprising: a fuselage; a rotor shaft extending upward from the fuselage; a rotor mounted to the rotor shaft; a drive mechanism in the fuselage for rotating the rotor shaft; and an isolation assembly mounted between the fuselage and the drive mechanism for allowing translational oscillations of the rotor shaft due to rotation of the rotor, and for isolating at least part of the translational movement of the rotor shaft from the fuselage, the isolation assembly comprising: a pneumatic piston and cylinder operatively coupled between the rotor shaft and the fuselage, the piston and cylinder having an air volume that provides a natural frequency less than the rotational speed of the rotor during flight; a detector for detecting a position of the piston within the cylinder; and an air pressure source for urging the piston to a central position between ends of a stroke of the piston.