Reduction of vertical tail using differential thrust : Influence on flight control and certification

The flight control characteristics and certification compliance of a Distributed Electric Propulsion (DEP) aircraft using differential thrust is studied through exploration of flight envelops. Identification of critical flight phases specific to the use of propulsion systems as actuators for flight control is performed. In particular the influence of engine failures on the flight envelop and means of mitigation are given. It is concluded that an aircraft using differential thrust has a most advantageous flight envelop at the point of neutral directional static stability allowing a reduction of 45% of the vertical tail surface area. Additionally, the directional control could be entirely provided by differential thrust, eliminating the need for a rudder. Study of this type of aircraft showed specific failure modes that differ from the actual certification prescriptions. New more relevant definitions and parameters are proposed as basis to demonstrate compliance with high level certification objectives.