In this study, a multi-input/multi-output (MIMO) time-delay feedback controller is designed to actively suppress the flutter instability of a multiple-actuated-wing (MAW) wind tunnel model in the low subsonic flow regime. The unsteady aerodynamic forces of the MAW model are computed based on the doublet-lattice method (DLM). As the first attempt, the conventional linear quadratic-Gaussian (LQG) controller is designed to actively suppress the flutter of the MAW model. However, because of the time delay in the control loop, the wind tunnel tests illustrate that the LQG-controlled MAW model has no guaranteed stability margins. To compensate the time delay, hence, a time-delay filter, approximated via the first-order Pade approximation, is added to the LQG controller. Based on the time-delay feedback controller, a new digital control system is constructed by using a fixed-point and embedded digital signal processor (DSP) of high performance. Then, a number of wind tunnel tests are implemented based on the digital control system. The experimental results show that the present time-delay feedback controller can expand the flutter boundary of the MAW model and suppress the flutter instability of the open-loop aeroelastic system effectively. ª 2014 Production and hosting by Elsevier Ltd. on behalf of CSAA & BUAA.

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= reference length of half-chord b j = breakpoint of the jth segment c 0 , c 1 , c 2 , c 3 , c 4 = coefficients of interpolation polynomial D = generalized damping matrix fV = cubic spline function of flow velocity f i = frequency corresponding to the flow velocity at the ith step g = added structural damping for k method Im = imaginary part of complex number j = sequence number of segment K = generalized stiffness matrix k = reduced frequency k j = the jth reduced frequency in which the generalized aerodynamic matrix is computed M = Mach number M = generalized mass matrix n = number of reduced frequencies for computing aerodynamic influence matrices n a = number of frequency data in a set p = Laplace variable Q s p = rational function approximation for generalized aerodynamic matrix Q 0 j , Q 1 j , Q 2 j = complex-valued coefficient matrices of the jth segment q = vector of generalized coordinates V = flow velocity V i = flow velocity at the ith step = flow density

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