Nonlinear and Fault-Tolerant Flight Control Using Multivariate Splines

Abstract

This paper presents a study on fault tolerant flight control of a high per- formance aircraft usingmultivariate splines. The controller is implemented bymak- ing use of spline model based adaptive nonlinear dynamic inversion (NDI). This method, indicated as SANDI, combines NDI control with nonlinear control alloca- tion based on an onboard aerodynamic spline model and a real-time identification routine. The controller is tested for an aileron hardover failure and structural dam- ageswhich change the global aerodynamic properties of the aircraft. It is shown that the controller can quickly tune itself in failure conditionswithout the need of failure detection and monitoring algorithms. Instead, self-tuning innovation based forget- ting is applied to reconfigure the onboard aerodynamicmodel. The controller is able to tune itself each time a model error is detected and does not require any external triggers for re-identification. Multivariate splines have a high local approximation power and are able to accuratelymodel nonlinear aerodynamics over the entire flight envelope of an aircraft. As a result the identification routine gives a robust adaption of the aerodynamicmodel in case of a failure. H.J.