Flight test based gain tuning using non-parametric frequency domain methods

A novel method to update the controller parameters or gains of a cascaded flight control law, based on inflight maneuver injection is introduced. The method is applicable in situations where differences exists between the design model and the real aircraft, for example due to inaccurate aerodynamic, propulsive or actuator model parameters. The method is based on updating the control law gains through flight test to meet the design requirements on the real system. It is a purely frequency domain, non-parametric method. It is based on the estimation of the closed-loop frequency response, where the plant frequency response is calculated using the known initial linear controller structure and gains. By solving an optimization problem, the resulting closed-loop is shaped by adopting the controller gains to meet the desired requirements. The concept is shown to give very satisfactory results for a medium sized fixed wing aircraft using a high fidelity simulation model.