Output tracking control design of a helicopter model based on approximate linearization

Output tracking control of a helicopter model is investigated. The model is derived from Newton-Euler equations by assuming that the helicopter body is rigid. First, we show that for several choices of output variables exact input-output linearization fails to linearize the whole state space and results in having unstable zero dynamics. By neglecting the couplings between moments and forces, we show that the approximated system with dynamic decoupling is full state linearizable by choosing positions and heading as outputs. We prove that bounded tracking is achieved by applying the approximate control. Next, we derive a diffeomorphism showing that an approximation of the system is differentially flat, thus state trajectory and nominal inputs can be generated from a given output trajectory. Simulation results using both output tracking controllers based on exact and approximate input-output linearization are presented for comparison