Flight Control System for Ultra-Light Aircraft Conversion to VTOL Unmanned Aircraft Vehicle

This work presents the development, modelling, integration, and validation of a flight control system (FCS) designed to convert a piloted ultra-light aircraft (ULM) into a fully autonomous vertical take-off and landing (VTOL) unmanned aerial vehicle (UAV), while maintaining Optionally Piloted Vehicle (OPV) capability. Unlike conventional ULM autopilots focused mainly on stabilization or pilot assistance, the proposed architecture enables full mission-phase autonomy, including take-off, hover, transition, cruise, approach, and landing, and ensures safe coexistence between autonomous and manual control pathways. A high-fidelity simulation framework was developed in MATLAB/Simulink and Simscape, integrating aerodynamic models derived from XFLR5 and VSPAERO, structural and inertia modelling, propulsion and energy-storage dynamics, and the complete cascaded control structure. Hardware-in-the-Loop (HIL) experiments were conducted using a modular test bench featuring a six-degree-of-freedom force–moment balance and an internal-combustion propulsion unit, allowing the injection of realistic vibration signatures into the control loop. Results demonstrate robust tracking of attitude and angular-rate commands under significant perturbations and AHRS measurement noise, indicating the system’s readiness for initial VTOL flight tests and subsequent transition-mode refinement. Overall, the paper details the control architecture, modelling methodology, simulation environment, and preliminary ground-testing efforts supporting advancement toward Technology Readiness Level 6.