Aircraft Flap Control System: Proposal of a Simulink Test Bench for Evaluating Innovative Asymmetry Monitoring and Control Techniques

One of the most important requirements in the design of secondary flight control actuation system is the proper limitation of the asymmetry between left and right wing flap surfaces; these asymmetries, that are typically due to mechanical transmission failures, must be timely detected and neutralized in order to guarantee the aircraft safety (especially during takeoff and landing flight phase in which the effects of these asymmetries could generates uncontrollable aircraft attitudes). In particular, when the angular asymmetry exceeds a defined critical value, the flap control system must detect and identify the incoming failure and actuate proper stopping procedures in order to limit this increasing asymmetry; to this purpose, it is necessary to conceive effective control algorithms able to perform an early fault detection avoiding false alarms. In recent applications, the most commonly used architectures employ the reversible actuators with wingtip brakes and centrally located PDU (of a dual motor type for operational reliability) because it is cheaper and more efficient, nevertheless, especially in severe fault conditions (torque shaft break under very high aerodynamic load) could generate unacceptable asymmetries. Therefore the development of enhanced flap actuation systems based on innovative layout or enhanced monitoring and control techniques can improve significantly the operating performances of the secondary flight control systems. In order to evaluate the behaviors of a real flap actuation system, simulating with a proper accuracy its dynamic responses and testing the performances of different monitoring and control algorithms, the authors propose a robust simulation developed in Matlab-Simulink numerical environment. By means the proposed numerical simulation model it is also possible to simulate a wide range of operating conditions (variable aerodynamic load, different mechanical layouts and several hydraulic and mechanical failures), to test new flap control system solutions (alternative architectures, new no-back devices or damping systems) and to evaluate the robustness of the aforesaid asymmetry monitoring techniques.