Stabilizing helicopter rotor blades using delayed feedback

Abstract

A new control law for stabilizing the periodic motion of uncertain systems, with particular application to helicopter rotor blades, is presented. The control law uses proportional displacement and velocity feedback with a time delay equal to the period of the motion being stabilized. No knowledge of the dynamics of the system being controlled or the desired trajectory is required. The control law is tested on a two-degree-of-freedom mathematical model which approximates the motion of a helicopter rotor blade in both hover and forward flight. Analysis of the developed perturbation equations shows that a significant improvement in the stability of the motion of the rotor blade is achieved by the appropriate choice of the control parameters. The control law greatly affects the transient states without altering the steady-state motion of the uncontrolled system. This feature is particularly important for helicopters because the steady-state motion of the rotor blades determines the flight path.