Patent ID: 8413923

Claim:
A method of damping vertical oscillations in a helicopter having a rotor drive-unit and an airframe and which carries an external payload suspended via a lifting gear from a load attachment point on the airframe of the helicopter, the method comprising the steps of: arranging oscillation sensors on the helicopter; providing an actively operated linear actuator operative between the load attachment point and the lifting gear such that the airframe, the linear actuator, and the lifting gear are connected in series; sensing, with the oscillation sensors arranged on the helicopter, excitations at least of a first mode of the vertical oscillations, in which first mode the external load and the rotor drive-unit oscillate together relative to the load attachment point, and of a second mode of the vertical oscillations, in which the second mode the load attachment point oscillates relative to the external load and the rotor drive-unit, with regard to both phase and amplitude of the excitations; and applying, between the load attachment point and the lifting gear with the actively operated linear actuator, forces opposed to the vertical oscillations as a function of the phase and of the amplitude of the sensed excitations.