Design of a nonlinear dynamic inversion controller for trajectory following and maneuvering for fixed wing aircraft

This paper presents the design of a robust linear controller that can be used for trajectory following and maneuvering of fixed-wing aircraft using Nonlinear Dynamic Inversion (NDI) principles. The design addresses control coupling to exploit multiple redundant controls. It can also be easily extended to state decoupling. The design procedure exploits the nature of the equations of motion written in the wind axis resulting in a cascaded linear controller structure with inner and outer loops. A systematic methodology is evolved which uses only the relevant stability and control derivatives in the control synthesis, as opposed to the inversion of the complete nonlinear equations used in conventional NDI designs. The tuning of the control gains is based on the requirements of adequate trajectory following and robustness to control surface failures. Finally, it is shown how a series of controllers can be derived depending on the sensor complement available on the aircraft. The proposed approach is ideal for fixed-wing Unmanned Aerial Vehicles (UAVs).