Flap failure and aircraft controllability: Developments in asymmetry monitoring techniques

The asymmetry limitation between left and right wing flap surfaces is one of the most severe requirements for the design of the actuation and control system. When the position asymmetry exceeds a defined value, it must be detected and limited by appropriate monitoring devices equipped with a suitable software. In the design of a new flap control system the development of the asymmetry monitoring subsystem plays a very important role and, together with the flap system layout selection, it was and still is a debated matter in the industrial field. The currently used monitoring technique is based on the differential position detection between left and right surfaces. Their use generally slightly reduces the asymmetry, but in some cases it may have an unreliable behavior. In order to overcome the shortcomings of the previous models, in this work the authors propose new different monitoring strategies and assess their positive effects on the maximum asymmetry following a torque tube failure; in particular, the asymmetry reduction coming from the employment of the proposed techniques in the considered operative conditions (typical deployment / retraction flap actuations), with respect to a previous type of technique, can be evaluated in the order of 30%.