VHHC in Helicopters

Higher Harmonic Control (HHC) is a method for cancelling the helicopter fuselage vibrations by introducing N/rev oscillations of rotor blades pitch angle (N is the number of rotor blades). This method is effective if both the amplitude and the phase of the oscillations introduced are chosen appropriately, depending on the flight conditions. It is shown in this paper that if the frequency of these oscillations is much greater than N/rev, the phase dependency disappears.