Design and development of innovative asymmetry active monitoring techniques for high-lift actuation systems

The aim of this Master thesis is the innovative active monitoring techniques design and developement that reduce the trailing edge high-lift devices asymmetry. Different system failures may cause the control surfaces asymmetry, such as the drive shaft torsion bar braking and the control surface actuators wear and tear. The high-lift system is formed by a Power Drive Unit (PDU) that generates the power transmitted to the reversible actuators by a drive shaft torsion bar. In addition, a wingtip brakes system is implemented to meet the secondary flight controls design requirements considering reversible actuators. The innovative asymmetry active monitoring techniques developed in this project both detect and identify the high-lift device (flap) position asymmetry. Once the failure side is known, the active techniques command the wingtip brakes to stop the failure surface. On the other hand, the operative surface is commanded to reach the failure surface braking position in order to minimize the flap asymmetry. Hence, the vehicle roll dynamic response will be more stable while the aircraft maneuverability after failure will be increased. In particular, four active models have been developed in this project. The control logic inside each model is position-based. Moreover, the control algorithms are using either a differential position step-input algorithm or a relative position ramp-input logic. Furthermore, the active monitoring techniques may include an asymmetry anticipation logic by means of a << dynamic >> position that allows an earlier asymmetry detection in case of high flap speeds after failure. The asymmetry active monitoring techniques have been widely tested in different external conditions, using either wear-free or wear-out actuators and considering every failure side scenario. The external operating conditions consider either low or high aerodynamic loads, which significantly affect the high-lift actuation system dynamics. In consequence, the active models behaviour in terms of time response and stability margin under certain operating conditions depends on the asymmetry control algorithm. Several tests have been conducted to study the active monitoring techniques response on different operating conditions considereing every failure side scenario. In addition, certain aerodynamic borderline conditions have been tested. They consider high aerodynamic loads applied on the control surfaces when they deflect from a starting position that is too close to the mechanical lower limit switch of the flap. The combiation of both high aerodynamic loads and little flap deflection starting positions may not occur on a regular commercial flight but it is useful to evaluate both the robustness and suitability of each new active model. A general comparison of all four active monitoring techniques is performed for each operating condition, in which the most performing models are chosen in each case. Eventually, a single active model has been chosen for any operating scenario analyzed in this project due to either its acceptable or excellent behaviour according to the operating condition.