Vertical takeoff and landing (VTOL) aircraft provide interesting examples of nonlinear non-minimum phase systems. We introduce a new approach to output tracking for VTOL aircraft. First the nonminimum phase aircraft model is decomposed into a minimum phase part and a non-minimum phase part. For the minimum phase part dynamic inversion is used. The nonminimum phase part is simpler than the original and linear control can be used to achieve output tracking with stability. A robust control design methodology is proposed that incorporates perturbations that arise due to the tracking commands; this leads to restrictions on the class of tracking commands. The resulting control laws are nonlinear. Computer simulations indicate that the controllers are efficient and robust with respect to aircraft parameter uncertainties.
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