Vertical take-off and landing (VTOL) aircraft are more and more important as they combine the benefits of both fixed-wing aircraft and rotary-wing aircraft, and tail-sitting is the simplest way to achieve VTOL maneuvers. However, conventional tail-sitting airplanes are made with propellers or duct fans, which have less thrust and less efficiency. This paper introduces a conceptual thrust-vectored unmanned tailsitter which is controlled only by thrust vectors (2 engines) while no other control surfaces, thus, they can achieve larger thrust and better maneuverability. However, this configuration is extremely unstable and hard to control. In order to verify its feasibility, a dynamic model is constructed and a linear control strategy has been established to stabilize the platform in hover mode. Simulation results with reference aero data are presented to show the performance, with small disturbances, and its feasibility is validated.
A state feedback control law based on the sliding mode control method is derived for the aeroelastic response and flutter suppression of a two-dimensional airfoil section with hysteresis nonlinearity in pitch. An observer is constructed to estimate the unavailable state variables of the system. With the control law designed, nonlinear effect of time delay between the control input and actuator is investigated by a numerical approach. The closed-loop system including the observer and nonlinear controller is asymptotically stable. The simulation results show that the observer can give precise estimations for the plunge displacement and the velocities in pitch and plunge and that the controller is effective for flutter suppression. The time delay between the control input and actuator may jeopardize the control performance and cause high-frequency vibrations.
The development of a control strategy appropriate for the suppression of aeroelastic vibration of a two-dimensional nonlinear wing section based on iterative learning control (ILC) theory is described. Structural stiffness in pitch degree of freedom is represented by nonlinear polynomials. The uncontrolled aeroelastic model exhibits limit cycle oscillations beyond a critical value of the freestream velocity. Using a single trailing-edge control surface as the control input, a ILC law under alignment condition is developed to ensure convergence of state tracking error. A novel Barrier Lyapunov Function (BLF) is incorporated in the proposed Barrier Composite Energy Function (BCEF) approach. Numerical simulation results clearly demonstrate the effectiveness of the control strategy toward suppressing aeroelastic vibration in the presence of parameter uncertainties and triangular, sinusoidal, and graded gust loads.
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