In this paper a theoretical framework for nonlinear adaptive flight control is developed and applied to a simplified, over-actuated nonlinear fighter aircraft model. The framework is based on a modular adaptive backstepping scheme with a new type of nonlinear estimator. The nonlinear estimator is constructed using an invariant manifold based approach which allows for prescribed dynamics to be assigned to the estimation error. Attractivity of the manifold is ensured with the addition of dynamic scaling factors and output filters to the design procedure. The properties of the estimator can be exploited by designing a command filtered backstepping control law that renders the closed-loop system input-tostate stable with respect to the parameter estimation error. It is demonstrated that the resulting modular adaptive controller is easier to tune compared to controllers obtained using the classical adaptive backstepping approaches. Furthermore, the performance of the adaptive controller does not suffer from unpredictable dynamical behavior of the parameter update laws. This is illustrated in numerical simulations where several types of realistic failures are introduced in the aircraft model.
A new adaptive nonlinear flight controller is designed for a high fidelity, six degrees of freedom F-16 model for the entire flight envelope. The design is based on a modular approach which separates the design of the control law and the online identifier. The control law design is based on backstepping with nonlinear damping terms to robustify the design against parameter estimation errors and unknown bounded disturbances. The flight envelope is partitioned into hyperboxes, for each hyperbox a locally valid incremental model is estimated based on the linearized equations of motion. A continuous-time formulation of orthogonal least squares is used for identification of these locally valid models. The obtained local models are interpolated by means of B-splines to obtain a smooth model valid for the complete flight envelope. The performance of the resulting nonlinear adaptive control design is evaluated on the F-16 aircraft model for representative flight conditions, maneuvers, and failure cases.
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