Classical and fuzzy sliding mode control for a nonlinear aeroelastic system with unsteady aerodynamic model

Abstract

This paper proposes a robust solution for the design and stability of nonlinear aeroelastic airfoils of fixed-wing drones that are widely exploited in many fields such as meteorology and surveillance. Therefore, conventional sliding mode and fuzzy sliding mode control algorithms are suggested for the stabilization of a multi-input-multi-output nonlinear aeroelastic model. The aerodynamic lift and moment are expressed based on the Wagner’s function for unsteady aerodynamics, and the flight dynamic model describes the plunge and pitch motions of the aircraft wing section with trailing edge and leading edge control surfaces. The selected two-degree of freedom model that includes aerodynamic and structural nonlinearities interactions, exhibits instability phenomena such as flutter and Limit Cycle Oscillations (LCOs) beyond a critical free-stream velocity. The contribution of this work is to design control algorithms in order to improve the critical flutter speed for the aeroelastic model in which unsteady aerodynamics is introduced. The control laws permit to drive the plunge displacement and pitch angle trajectories to the origin in finite time, and to guarantee a chattering-free system. The obtained results confirm that the established controllers effectively accomplish suppression of LCOs and lead the state trajectories to the origin despite nonlinearities and gust loads.