Lateral control allocation using ailerons and roll spoilers for fly-by-wire aircraft

Abstract

© The Author(s), under exclusive licence to The Brazilian Society of Mechanical Sciences and Engineering 2024.To perform maneuvers in a fly-by-wire aircraft, a pilot usually commands the yoke or the stick. This command is interpreted by a Flight control computer (FCC), which activates actuators of the control surfaces. To roll large aircraft, it is usual to employ ailerons and roll spoilers as control surfaces. The amount of deflection shared with each control surface is known as control allocation, and it is computed by flight control laws, algorithms embedded in the FCC. This work compares two methods of control allocation to roll aircraft, taking advantage of the flexibility given by fly-by-wire architecture, to compute adequate deflections of ailerons and roll spoilers that comply with requirements of performance, stability and handling qualities. Moreover, it presents alternatives to deal with possible nonlinearities of the roll spoilers. As a first method, it was considered a dead zone for roll spoilers, such that roll spoilers deflect only after certain deflection of ailerons. As a second method, it was considered that ailerons and roll spoilers work together whenever required. The study of the two methods covers real aspects for design in the whole flight envelope, in order to implement in a FCC: study of the bare-airframe (large-heavy transport/cargo aircraft adopted in this case), definition of objectives, control architecture, linear design, nonlinear integration and pilot-in-the-loop simulations. As result, pros and cons of each method are presented. In one hand, the first method is a conservative approach to deal with nonlinear behavior of roll spoilers around small deflections for example but can expose ailerons to rate saturation when deflecting alone in scenarios with poor control power. On the other hand, the second method alleviates the work of the ailerons, but it assumes a reliable model for design, which might be hard to develop. The results were validated with offline simulations and with pilots in a flight simulator.

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