Discrete-time analysis of HHC schemes for helicopter vibration attenuation

Abstract Higher Harmonic Control (HHC) algorithms for helicopter vibration reduction are analysed by taking into account the issues related with their discrete-time implementation. In particular, the periodicity of helicopter dynamics and the presence of two different sampling rates in the control loop are dealt with using a lifted reformulation of the closed loop system, which turns out to be time-invariant. Finally, a numerical investigation of the stability characteristics of HHC control loops is carried out and discussed in order to assess the role of digital implementation in determining the stability and performance of the vibration control system.