Periodic analysis of Higher Harmonic Control techniques for helicopter vibration attenuation

The class of Higher Harmonic Control (HHC) lgorithms for helicopter vibration reduction is analysed and a simple derivation of the state space form for such compensators is derived. A characterisation of these compensators in terms of the Harmonic Transfer Function for periodic systems is also proposed. Finally, a numerical investigation of the stability characteristics of HHC control loops is carried out and discussed. In particular, it is shown that the periodicity of rotor dynamics plays a major role in determining the closed loop behaviour of the helicopter.