LINEAR CONTROL ISSUES IN THE HIGHER HARMONIC CONTROL OF HELICOPTER VIBRATIONS

Classical linear control theory is used to develop a framework in which the performance of active vibration control algorithms can be evaluated in terms of compensator structure, closed loop vibration levels, and sensitivity to modeling errors due to changing flight conditions. This framework leads to the interpretation of current vibration control algorithms as classical narrow band disturbance rejection problems. Moreover, current HHC algorithms are quite robust with respect to errors in the T matrix, so that real time adaptation of the T matrix is probably not crucial to satisfactory performance.