Abstract
Gust load alleviation functions are mainly designed for two objectives: first, alleviating the structural loads resulting from turbulence or gust encounter, and hence reducing the structural fatigue and/or weight; and second, enhancing the ride qualities, and hence the passengers’ comfort. Whilst load alleviation functions can improve both aspects, the designer will still need to make design trade-offs between these two objectives and also between various types and locations of the structural loads. The possible emergence of affordable and reliable remote wind sensor techniques (e.g., Doppler LIDAR) in the future leads to considering new types of load alleviation functions as these sensors would permit anticipating the near future gusts and other types of turbulence. In this paper, we propose a preview control design methodology for the design of a load alleviation function with such anticipation capabilities, based on recent advancements on discrete-time reduced-order multi-channel H_infty techniques. The methodology is illustrated on the DLR Discus-2c flexible sailplane model.
Highlights
Turbulence and gusts are causing dynamic variations of the aerodynamic forces and moments that are applied to the aircraft structure
The controller was synthesized by two different methods of the H∞ optimal control: full-order based on the work of [4, 5], and fixedstructure based on the method presented in [6, 7], and implemented in the MATLAB Robust Control Toolbox
Regardless of the choice of the control designers regarding the plants Pi and the constraints possibly imposed on the controllers Ki, the multi-channel control synthesis technique optimizes a program of the form given by Eq (1), where Twi→zi = Fl(Pi, Ki) is the closed-loop transfer function obtained by the lower linear fractional transformation of plant Pi and controller Ki: minimize maxi ‖‖‖Twi→zi = Fl(Pi, Ki)‖‖‖∞
Summary
Turbulence and gusts are causing dynamic variations of the aerodynamic forces and moments that are applied to the aircraft structure. The formulation of the feedforward load alleviation is made with a preview control problem formulation that is similar to the approach of [8], but in output feedback setting and adapted to a different application Their simulation results showed that the structural loads and the normal load factor at pilot location (a ride quality index) had been greatly reduced compared to the case of no control (i.e., open loop) and to the case of feedback-only control. Fezans were used in [3] forced combining all the design objectives into a one single performance channel, which led to including unwanted cross-coupling terms in the H∞ norm of the overall transfer function This mono-channel formulation limits the control designers in expressing the control design criteria, which makes it difficult to perform the fine tuning needed when designing more complex load alleviation systems.
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