Sliding Mode Control Applied for Flutter Suppression of a Nonlinear Aero-elastic System

This paper presents a Sliding Mode Control (SMC) system for the stabilization of an Aero-Servo-Elastic (ASE) system with structural nonlinearities at subsonic flight speed. For this research, a 2 DOF aero-elastic model of a wing section developed, to describe the pitch and plunge motions. For the aim of control, a single control surface associated with SMC technique is used. This control system, in which the Regular Form Approach is used as SMC technique, suppresses flutter as well as the vibration level in sub-critical and post-flutter speeds. For state-space representation of the model, the measured pitch angle, plunge displacement and their derivatives are allocated as state vector, and control surface deflection as input command. For a given initial state conditions, two modes of open loop and closed loop control system are carried out. It is shown that the open loop system with a nonlinear structure in subsonic regimes is unstable and has Limit Cycle Oscillations (LCOs). However, the closed loop system is asymptotically stable and converges to the origin. Therefore, the proposed approach has a good performance for suppressing flutter and LCOs, as well as short time response compared to other nonlinear methods such as State Dependence Riccati Equation or so-called SDRE method.