On-line parameter estimation for restructurable flight control systems

This paper describes the results of a study where an on-line parameter identification (PID) technique is used for determining on-line the mathematical model of an aircraft that has sustained damage to a primary control surface. The mathematical model at post-failure conditions can then be used by a failure accommodation scheme to compute on-line the compensating control signal to command the remaining healthy control surfaces for a safe continuation and/or termination of the flight. Specific criteria for the use of an on-line PID for these critical flight conditions are first discussed. The methodology is illustrated through simulations of a fighter jet at subsonic flight conditions featuring a novel modeling procedure to characterize the post-failure/damage aerodynamic conditions. The simulations have shown the potential of this on-line PID within a fault tolerant flight control system. The results have also highlighted the importance of conducting an ‘ad hoc’ small amplitude and short-duration PID maneuver immediately following a positive failure detection to enhance the reliability of the on-line estimated parameters used in the accommodation scheme.