Flight Dynamics Modeling and Sliding Mode Control Law Design for Oblique Wing Aircraft

An oblique wing aircraft can continuously vary its wing sweep angle, making it attractive for high-altitude unmanned aerial vehicle (UAV) relay missions that require stable attitude, altitude, and speed for antenna pointing and air-to-ground link consistency. The present work focuses on flight-platform stability as an enabling layer for UAV relay operation rather than on direct optimization of link-level communication metrics. During sweep transitions, however, sweep-dependent mass properties, aerodynamic loads, and control effectiveness introduce coupled attitude disturbances. This study develops a six-degree-of-freedom nonlinear multi-body model using Kane’s formalism to retain products of inertia, center-of-gravity variation, and sweep-dependent control effectiveness in a compact control-oriented form. A minimum-control-energy allocation method is formulated to coordinate the aileron and differential all-moving horizontal tail when aileron roll authority decreases at large sweep angles. An inner/outer-loop sliding-mode controller with auto-throttle is then designed for attitude, altitude, and speed regulation. Closed-loop simulations of 0–30° and 30–60° sweep maneuvers show that altitude and speed remain close to their commands while attitude deviations remain bounded. A 15% aerodynamic-coefficient perturbation case further indicates bounded closed-loop responses under the considered model uncertainty.