Unified Energy Control for Wide-Speed-Range Tilt-Body Flight

Tail-sitter vertical takeoff and landing (VTOL) aircraft face universal control challenges during transitional flight, stemming from intrinsic thrust–attitude coupling and severe aerodynamic nonlinearities. To overcome the fundamental limitations of conventional, phased controllers, this paper proposes and validates a novel control architecture—the Nonlinear Total Energy Control System (NTECS)—for a tilt-body aircraft, an advanced tail-sitter platform. The design is based on a preceding systematic analysis of the flight envelope, in which the tilt-body’s challenging transition corridor is rigorously characterized. Its core innovation reframes the longitudinal control problem as total energy management, realized through a dual-component architecture comprising feedforward and feedback elements. The feedforward component is a model-based nonlinear controller designed to compensate for aerodynamic nonlinearities across the flight envelope and to ensure high-performance tracking. In parallel, the feedback structure regulates energy distribution and magnitude through coordinated pitch and thrust control. Flight test results confirm that this single, unified framework achieves robust, wide-speed-range flight from hover to high-speed cruise—a capability beyond the reach of traditional methods. The principles developed in this work offer a viable pathway to enhancing flight safety and operational versatility for the broader class of tail-sitter aircraft.