Vertical Tail Reduction Through Differential Thrust: An Initial Assessment of Aero-Propulsive Effects on Lateral-Directional Stability and Control in Engine Inoperative Conditions

Differential thrust can be used for directional control on distributed electric propulsion aircraft. This thesis presents an assessment of flight dynamics and control of differential thrust aircraft under engine inoperative conditions with minimum control speed. A methodology consisting of an aerodynamic data acquisition module and a non-linear six-degrees-of-freedom flight dynamics model is proposed. The data acquisition module uses FlightStream solver to capture the aerodynamic performance data. The assessment consists of studying the aero-propulsive effects, control of the aircraft, rudder removal, and vertical tailplane size reduction. The directional control is achieved in the flight dynamics model by using a proportional–integral–derivative controller to generate a yaw command, which is distributed to the propulsors by thrust mapping. Additionally, drag mode is investigated, in which the outermost idling propulsors are used to generate maximum drag, allowing the non-idling inner propulsors to produce more thrust. A modified version of the NASA X-57 aircraft is selected as the case study aircraft. Results show that during the engine inoperative conditions at minimum control speed, the aircraft experiences significant loss in thrust and power augmented lift due to the failed propulsors and the directional control effort. Therefore, the stall and minimum control speed are increased, and the aircraft must accelerate to prevent a stall. Consequently, the aircraft experiences a temporary reduction in altitude during the recovery maneuver. Vertical tailplane reduction is seen possible, with differential thrust fully replacing the performance of the rudder. It was seen that the response time of the directional control has a significant impact on the maximum yawing angle and temporary altitude reduction. Finally, the use of drag mode reduced the maximum yaw angle and increased the climb gradient.Aerospace Engineerin