Development and Evaluation of a Quad-Heli eVTOL Capable of Safe Fly with a Failed Rotor

With advanced air mobility (AAM) vehicles becoming an increasingly popular topic in aviation, the Eagle Flight Research Center (EFRC) at Embry-Riddle Aeronautical University continues to investigate control strategies that enhance aircraft resilience to total power unit failures. Utilizing a distributed electric propulsion (DEP) quad-heli test bed, the EFRC has explored a variety of control laws and hardware configurations to evaluate their effectiveness under failure conditions, including sustained flight with a completely inoperative rotor. The aircraft utilizes a fractional-order PID (FOPID) controller that has recently been developed and shown to outperform conventional PID controller used previously in both nominal and failure scenarios. The use of a FOPID controller offers improved stability and tracking performance. Another development is the implementation of a split-rotation rotor configuration -- where the left-side rotors rotate clockwise and the right-side rotors rotate counterclockwise -- which, when combined with a control law leveraging cyclic rotor inputs for yaw control, provides a robust alternative to conventional quadrotor designs. This configuration leverages the redundancy offered by equipping each of the aircraft's four rotors with full helicopter controls, enhancing the potential for sustained flight in the event of two rotor failures while preserving the maneuverability and controllability characteristic of the conventional configuration. Additionally, to support expanded testing and operational capability, the aircraft has been outfitted with a custom-designed landing gear system, designed and fabricated by the EFRC team.