Magnetorheological fluid damper feedback linearization control for helicopter rotor application

This study explores the possible use of a magnetorheological (MR) damper with feedback linearization control law for helicopter lag damping applications. Since this control law is based on an assumed damper model, the helicopter may be susceptible to limit cycle instabilities in the presence of model errors due to uncertainties (even if the prescribed damping using feedback linearization control is greater than the system negative damping). For specified uncertainty bounds, a robust control law can be synthesized which will eliminate limit cycle instability by using a much larger value of prescribed damping ratio. The resulting periodic loads in forward flight, however, would be excessively high. To reduce these periodic loads a band-rejecting filter is introduced that eliminates the 1/rev component of velocity from the feedback control signal. By doing so, stability of perturbation motions can be ensured and periodic loads can be drastically reduced, even in the presence of MR damper model errors.