STABILIZATION OF MOTION OF HELICOPTER ROTOR BLADES USING DELAYED FEEDBACK—MODELLING, COMPUTER SIMULATION AND EXPERIMENTAL VERIFICATION

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 that approximates the motion of a helicopter rotor blade in both hover and forward flight. Analysis of the developed perturbations equation 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 affected 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. The experimental investigation confirms the existence of optimal values of the parameters of the control law, which result in a significant improvement of the stability of the periodic motion of the installation. The experimentally obtained relationship between the optimal control parameters and the period of the motion confirms the results of the analytical investigation of the influence of the control law on the stability margin of uncertain systems.