Towards an Aircraft with Reduced Lateral Static Stability Using Differential Thrust

Abstract

In the context of aircraft drag reduction, we study the possibility of reducing the area of the vertical tail using Distributed Electric Propulsion (DEP) while maintaining lateral stability with active Differential Thrust (DT). Distributed Electric Propulsion is usually thought of as a mean to increase aerodynamic efficiency by exploiting the beneficial effects of accelerating air around key parts of the aircraft. However, it can also be seen as a collection of actuation devices generating additional moments through Differential Thrust. When the engines are distributed along the lateral axis, the aircraft designer may take advantage of the increase of control authority on yaw to reduce the static stability or the control authority provided by the Vertical Tail (VT). This in turn would allow a reduction of vertical tail surface area. In order to explore and assess this idea, we suggest a framework to compare flight qualities of a traditional configuration versus a configuration using Distributed Electric Propulsion and Differential Thrust. The framework provides information on the flight envelop and stability of the aircraft by computing a map of the equilibrium. Thanks to a global approach, it allows to study any aircraft or DEP configurations in any flight phase. In addition, a key feature of the framework is the inclusion of the VeDSC[1] method to compute analytically the contribution of the vertical tail to lateral stability. It allows to study effects of a 30% reduction of VT surface area. Here are presented the first results and potential of using differential thrust to reduce the area of the vertical tail and the reasons for us to continue developing this framework. * PhD, eric.nguyen-van@isae.fr, eric.nguyen_van@onera.fr † Professor Researcher, daniel.alazard@isae.fr. ‡ Professor Researcher, philippe.pastor@isae.fr. § Research engineer, carsten.doll@onera.fr. Nomenclature CCV = Control Configured Vehicle MDO = MultiDisciplinary Optimization DEP = Distributed Electric Propulsion DT = Differential Thrust VT = Vertical Tail AR = Aspect Ratio ρ = Air density (Kg/m 3) V = Speed (m/s) V s = Stall speed (m/s) V MC = Minimum control speed (m/s) P = Power (W) T = Thrust (N) η = Efficiency (-) S = Wing surface area (m 2) S v = Vertical Tail surface area (m 2) b = Wingspan (m) l F = VT longitudinal position with respect to wing aerodynamic center (m) z v = vertical position of the mean aerodynamic chord of the VT (m) V v = VT volume (-) y = Lateral position of engine (m) m = Mass (Kg) g = Gravitational acceleration (m.s −2) α = Angle of attack (°) β = Side slipe angle (°) φ = Bank angle (°) γ = Climb angle (°) µ = Aerodynamic bank angle (°) Ω = Turning rate (rad.s −1) δ a = Aileron input (°) δ R = Rudder input (°) δ m = Throttle level (-) C D = Drag force coefficient (-) C Y = Lateral force coefficient (-) C L = Lift force coefficient (-) C l = Rolling moment coefficient (-) C m = Pitch moment coefficient (-) C n = Yawing moment coefficient (-) a v = VT lift slope coefficient (-) V SR = Stall velocity (m/s) Subscripts v = Vertical Tail 0 = Nominal condition or sea level b = Body attached frame