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Summary
The ducted fan unmanned aerial vehicle (UAV) is capable of both hovering and high-speed cruising, while the transitional flight between hovering and cruising is one of the most challenging flight maneuverings. In this paper, we address the flight mode transition control of a ducted fan UAV with constrained control inputs. During our early flight tests, we have engaged a saturation problem on the control vanes that led to severe crashes. In order to maintain a sufficient control on the attitude suffering from input saturation, we propose a control effectiveness enhancement (CEE) algorithm, which compensates the deficiency on vane control effectiveness by utilizing the thrust-vectored property of the ducted fan UAV. In the meanwhile, to handle the variation of the complex aerodynamic effects acting on the vehicle, we adopt an adaptive full envelope flight control scheme to compensate all of the unmodeled nonlinear dynamics. A sufficient condition is also derived to ensure the stability of the closed-loop system, by which the aircraft is capable of tracking a given velocity trajectory with bounded tracking error. Finally, flight tests are conducted with comparative experiments. The result is satisfactory in accomplishing the desired transition course and resisting the risk of flight failure in the presence of input saturation, verifying the effectiveness of the proposed approach.
