Flight Testing a Trajectory Control System on a Subscale Transitioning VTOL Aircraft

This paper presents the development, optimization, and flight testing of the trajectory control system (TCS), a novel middle-loop controller designed for vertical takeoff and landing (VTOL) aircraft. The proposed flight control architecture is configuration-independent, making it applicable to a wide range of VTOL designs, including hybrid and transitioning aircraft. The system enables intuitive and efficient control across all flight modes, from hover to forward flight, while minimizing pilot workload. To achieve this, an explicit model-following (EMF) inner-loop control structure is integrated with a trajectory-based middle-loop controller. The control laws were optimized using a formal optimization framework and validated through piloted flight experiments on a subscale aircraft. Flight test results demonstrate that the system provides stable, predictable, and low-workload operation, even for pilots with minimal training. Furthermore, the control approach maintains consistent performance across varying speeds and configurations, highlighting its robustness and adaptability. These findings support the feasibility of implementing this approach in future VTOL designs to enhance operational simplicity and safety.