Trimming & non-linear autopilot for the GSACM model

This report describes design and implementation of a trimming routine and a nonlinear controller for simultaneous attitude and velocity control of a small single engine fighter aircraft. The controller is very general and should be applicable to other thrust and moment controlled vehicles (rigid bodies) moving in a gas or fluid as well, such as various forms of unmanned aircraft and underwater vehicles. It is based on multi-input backstepping theory and utilizes a combination of two motions to archive the control. One is a geodesic movement on the sphere of unit norm quaternions for oriention control and the other is a rotation of the body velocity vector into the right direction combined with thrust control of the engine to set its magnitude. The controller is capable of controlling the orientation and velocity to trimmed values for straight path flight or constant angular velocity turn for large region of deviations from these values. A proof of the stabilizing properties of the controller is given. The aircraft, trim routine and controller are implemented in the Modelica language and simulated in the Dymola environment. The model for the aircraft is referred to as the GSACM model and is based on the Admire model. Simulations are presented to illustrate the performance of the controller under various flight conditions.