Analysis of a multi-functional high-lift system driven by an active differential gear box

Abstract

A flight dynamics evaluation was performed to analyse the ability to use the outer flap for roll control as well. Based on the Airbus A350 flap system architecture, where the outer flap can be deployed independently from the inner flap using a so-called active differential gear box (ADGB), two different concepts were identified as potentially beneficial for the desired purpose. In both concepts, the inner ailerons were removed 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. Roll spoilers were not considered in the presented analyses. The flight dynamics evaluation revealed that a flap deflection rate of at least 16�/s is necessary to fulfil requirements from certification specification CS-25 and handling quality criteria. A system analysis showed that theexisting ADGB is only able to deflect the flap with a maximum rate of 0.43�/s or 1.4�/s with slight modifications of the existing ADGB. These values showed to be insufficient for regular roll control. Nevertheless, in case of a 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 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.