Abstract
AbstractTurbulence and gusts cause variations in the aerodynamic forces and moments applied to the structure of aircraft, resulting in passenger discomfort and dynamic loads on the structure that it must be designed to support. By designing Gust Load Alleviation (GLA) systems, two objectives can be achieved: first, realizing higher passenger comfort; and second, reducing the dynamic structural loads, which allows the design of lighter structures. In this paper, a methodology for designing combined feedback/feedforward GLA systems is proposed. The methodology relies on the availability of a wind profile ahead of the aircraft measured by a Doppler LIDAR sensor, and is based on $H_{\infty}$-optimal control techniques and a discrete-time preview-control problem formulation. Moreover, to allow design trade-offs between those two objectives (to achieve design flexibility) as well as to allow specification of robustness criteria, a variant of the problem using multi-channel $H_{\infty}$-optimal control techniques is introduced. The methodology developed in this paper is intended to be applied to large aircraft, e.g. transport aircraft or business jets. The simulation results show the effectiveness of the proposed design methodology in accounting for the measured wind profile to achieve the two mentioned objectives, while ensuring both design flexibility and controller robustness and optimality.
Highlights
As per Part 25 of the FAA Airworthiness Standards(1) and CS-25 of the EASA Certification Specifications(2), the strength requirements on an aircraft structure are specified in terms of limit loads and ultimate loads
By designing Gust Load Alleviation (GLA) systems, the dynamic structural loads can be reduced, allowing for the design of lighter structures
5.1 Impact of the preview horizon on the performance of the GLA system
Summary
As per Part 25 of the FAA Airworthiness Standards(1) and CS-25 of the EASA Certification Specifications(2), the strength requirements on an aircraft structure are specified in terms of limit loads (the maximum loads to be expected in service) and ultimate loads (the limit loads multiplied by prescribed factors of safety). The manufacturer must determine (for all critical combinations of parameters on and within the boundaries of the structural design envelope) the applicable structural design loads resulting from likely externally or internally applied pressures, forces or moments that may occur. For proof of a structure, compliance with these strength requirements must be demonstrated for each critical loading condition, considering all of these applied loads. Of particular interest in this paper are the loads resulting from gust and turbulence conditions. Turbulence and gusts cause variations of the aerodynamic forces and moments applied to the structure of aircraft. By designing Gust Load Alleviation (GLA) systems, the dynamic structural loads can be reduced, allowing for the design of lighter structures (assuming that the sizing/critical cases result from the gust and turbulence loads). The ride quality can be enhanced, resulting in improved passenger comfort
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