Output tracking for a non-minimum phase dynamic CTOL aircraft model

A dynamic model for the longitudinal axis of a conventional takeoff and landing (CTOL) aircraft is presented. Non-minimum phase characteristics in this model result from the fact that the process of generating an upward pitch moment produces a small downward force, causing the aircraft to lose altitude. The model is not full state linearizable and the internal dynamics which remain after input-output linearization using the coordinates of the center of mass as outputs are unstable. The CTOL model is not flat with respect to fixed points on the aircraft body. The nonlinear inversion technique produces stable trajectories for the states of the internal dynamics, but the corresponding feedforward force inputs required to track these trajectories are large. Approximate linearization techniques which ignore the coupling between the pitch moment and the vertical and horizontal aircraft dynamics, may be used to calculate inputs of smaller magnitude.