ANALYSIS OF A MULTI-FUNCTIONAL HIGH-LIFT SYSTEM DRIVEN BY AN ACTIVE DIFFERENTIAL GEAR BOX

Kurzfassung

A flight dynamics evaluation was performed in order to analyse the ability to use the outer flap for roll control as well. Based on the A350 flap system architecture, where the outer flap can be deployed independently from the inner flap by using an active differential gear box, two different concepts were identified as potentially benefitial for the desired purpose. In both concepts the inner ailerons were removed in order to save weight and system complexity and the outer flap performs (all speed) roll control together with the outer (low speed) aileron. Concept 1 comprises the usual flap geometry and the outer aileron, whereas concept 2 comprises an outer flap, which is extended in spanwise direction by the length of the inner aileron. The flight dynamic evaluation revealed that for the use of the outer flaps for regular roll control flap dynamics are necessary of at least 16°/s flap deflection rate in order to fulfill requirements from certification specification CS-25 and handling quality criteria. A system analysis showed that the existing active differential gear box from A350 is unfortunately only able to deflect the flap with a maximum rate of 0.43°/s, or with slight modifications of the existing active differential gear box a maximum deflection rate of 1.4°/s could be feasible. These values showed to be insufficient for regular roll control. Nevertheless, in case of dual loss of hydraulic power the only available roll control could be performed by one remaining pair of ailerons, which are driven by an electrical back-up hydraulic actuator at the A350. In order to still enable roll control, if these electrical back-up hydraulic actuators fail additionally, it was analysed whether the outer flap could be used as emergency roll control with the aforementioned feasible flap dynamics. The results showed that the handling qualities with this flap system ensuring roll control are barely controllable. However, it appears feasible to reach degraded but acceptable handling qualities if the system dynamics could be slightly increased.