Online Parameter Estimation Techniques Comparison Within a Fault Tolerant Flight Control System

Abstract

The results of a study where two online parameter identie cation (PID) methods are compared for application within a fault tolerant e ight control system are described. One of the PID techniques is time-domain based, whereas the second is featured in the frequency domain. The time-domain method was directly suitable for the online estimates of the dimensionless aircraft stability derivatives. The frequency-domain method was modie ed fromitsoriginalformulationtoprovidedirectestimatesofthestabilityderivatives.Thiseffortwasconductedwithin the research activities of the NASA Intelligent Flight Control System F-15 program. The comparison is performed throughdynamicsimulationswithaspecie cproceduretomodeltheaircraftaerodynamicsfollowingtheoccurrence of a battle damage/failure on a primary control surface. The two PID methods show similar performance in terms of accuracy of the estimates, convergence time, and robustness to noise. However, the frequency-domain-based method outperforms the time-domain-based method in terms of computational requirements for online real-time applications. The study has also emphasized the advantages of using ad hoc short preprogrammed maneuvers to provideenoughexcitationfollowingtheoccurrenceoftheactuatorfailuretoallowtheparameterestimationprocess.