Analytical and Computational Modeling of a Stop-Rotor Aircraft With Experimental Validation

Abstract

Stop-rotor aircraft are a class of vertical takeoff and landing (VTOL) vehicle that offer improved efficiency across flight modes through the usage of a single central lifting surface. In VTOL, the central lifting surface rotates like a helicopter blade to achieve an upward force. In forward flight, the central lifting surface locks in place like a conventional fixed-wing aircraft and achieves lift from airflow over the surface. The improved efficiency across flight modes enables more complex mission profiles that balance flight time in VTOL and forward flight, such as package delivery and inspection over a large area. Despite the promise of stop-rotor aircraft, challenges in modeling and control, particularly due to the nonlinear rotor dynamics across flight modes, have limited practical implementation. To this end, this paper presents two types of models: 1. Analytical models, derived from first principles physics, provide insight into the stability and control of the vehicle and demonstrate closed-loop stability of yaw and altitude using classical PID control, 2. Computational models, based on numerical integration of the system's ordinary differential equations, provide full-state dynamics of the vehicle. Validation against bench-top constrained flight tests shows that the analytical models capture over 97% of the variance in the computational results, while the computational models account for up to 40% of the variance observed in experimental data.