A Class of Position Controllers for Underactuated VTOL Vehicles

This technical note proposes a unified framework for stabilizing a hover equilibrium for a class of vertical take-off and landing (VTOL) aircraft using a cascade control architecture which yields almost global stability in the absence of wind gusts. The control design process is partitioned into two decoupled parts: the design of a bounded position controller for a fully actuated point-mass particle, and the design of an attitude stabilizer. The position feedback is then used in an outer loop to provide reference signals for the inner loop attitude stabilizer. A number of sample feedbacks in the proposed controller class are presented, some of which include integral action to compensate for an unknown mass.