Self-Adapative Notch Filter for the V-22 Flight Control System

The notch filter is essentially an inverse dynamic compensator. It has great performance when the aircraft's structural modes are nearly identical to the models of the structural modes which were used to design the notch filter. Unfortunately, for a variety of reasons it is very difficult to precisely predict the structural dynamics of the aircraft. Often the uncertainty in the ability to predict the structural dynamics is handled by designing a filter with a wider notch that can accommodate expected variations in the structural modal frequencies. The downside to this solution is that unwanted phase shift is introduced at the frequencies where the pilot is providing closed loop control. The result is pilot induced oscillation. An adaptive notch filter offers the potential of tuning each filters so that it can provide the necessary structural mode suppression while minimizing the introduced phased shift. A neural network based parameter identification technique is proposed as a means to solve, on-line, for the parameters of a state space model that contains both rigid body and structural degrees of freedom. The identified state model then will provide the data base for updating the characteristics of the notch filter.