This paper concerns the flight controller design of aircraft that has significant changes in aerodynamic characteristics and addresses the flight controller design of a quad-tilt-wing unmanned aerial vehicle that has vertical takeoff and landing as well as high-speed cruise capabilities. The quad-tilt-wing unmanned aerial vehicle has a tandem wing that tilts between vertical to horizontal positions. This configuration change significantly alters its aerodynamic characteristics, and therefore requires a gain-scheduled flight controller. The gain-scheduled flight controller, which consists of a gain-scheduled stability augmentation system, a gain-scheduled control augmentation system, and a gain-scheduled turn coordinator, is also required to be robust against modeling errors because the motion dynamics of the quad-tilt-wing unmanned aerial vehicle are inherently unstable at almost all wing tilt angles and the precise aerodynamic characteristics are not available. To this end, this paper proposes a design method for structured gain-scheduled flight controllers by combining a conventional gain-scheduled controller design method and multiple-model approach to satisfy the robustness requirement, and it designs a gain-scheduled flight controller for the quad-tilt-wing unmanned aerial vehicle. The effectiveness of the method is demonstrated by flight tests during which the quad-tilt-wing unmanned aerial vehicle successfully achieved full conversion flight: that is, vertical takeoff, accelerating transition, high-speed cruise, decelerating transition, and vertical landing, as well as super-short takeoff.