High performance needs for modern aircraft such as high altitude and long endurance place demanding requirements on the flight vehicle design. Long endurance necessitates high lift over drag (L/D) and lightweight structures, leading to high aspect ratio, highly flexible wings. These highly flexible wings increase the danger of catastrophic aircraft failure due to flutter, an aeroelastically unstable phenomenon occurring from the interaction of aerodynamic, inertial, and elastic forces acting on the aircraft flying through the air. Hence, active flutter suppression of flexible wing has been studied by many researchers to enable one to expand the flight envelope without weight penalties. Among various control schemes available, sliding mode control (SMC) technique have desirable features applicable for aeroelastic control, i.e. SMC is naturally robust with respect to uncertainties in the system and external disturbances. In addition, SMC offers a systematic approach to the design of variable structure control laws for multivariable systems. However, the application of this control method for active aeroelastic control is rather limited, with most of the related researches were performed for two dimensional airfoil model other than the one for three dimensional composite box beam model.
This paper presents the design of an active flutter suppression system for flexible wing using sliding mode control method. The aerodynamic force generated by the motion of a flexible wing control surface is utilized as control force. For this purpose, aeroservoelastic model is formulated by blending aeroelastic model, control surface actuator model, and gust model. A sliding mode controller is designed for active flutter suppression on the aeroservoelastic model in conjunction with Kalman filter that estimates the system states based on the measured output such as acceleration and strain. Aeroservoelastic modeling approach and controller design method proposed in this paper are validated by comparing the results of aeroelastic analyses and flutter suppression of two dimensional wing model with those from the available literatures and commercial software. The performance of the controller designed is demonstrated via numerical simulation for the representative flexible wing model with trailing edge control surface. Numerical simulations performed show the proposed sliding mode controller is effective in suppressing the flutter of flexible wing even in the presence of disturbances such as gust and system modeling error.