Periodic control of helicopter rotors for attenuation of vibrations in forward flight

The paper is devoted to the design of a control system for the attenuation of vibrations in the main rotor of a helicopter in forward flight. The problem can be formulated as the one of rejecting a periodic disturbance of known frequency acting at the output of a linear time-periodic system. A solution inspired to optimal control design methods is proposed. A major preliminary issue is the estimation of the characteristics of the disturbance, for which two methods are worked out. The performance of the obtained control system is assessed by means of several simulation trials.