Stability analysis and design for aircraft gust alleviation control

Abstract

This paper is concerned with the stability analysis and the development of an on-line two-level gust alleviation control system for a high-speed aircraft operating in an unknown environment. As is well known, such an aircraft experiences dynamic instability in its lateral motion when subjected to the longitudinal and lateral gusts. This is due to the phenomenon of lateral-longitudinal aerodynamic cross-coupling. In the first part of this paper the instability behaviour, in the presence of a longitudinal gust, of two typical high-speed aircraft is analyzed. From theoretical and simulation studies it is shown that for a sinusoidal gust, and for a given configuration, the instability region is a function of both the amplitude and frequency of the gust disturbance. In the second part of the paper, an on-line gust alleviation control system is synthesized for such an aircraft operating over a wide range of unknown environmental conditions. This control system employs a two-level control structure. The controller, however, does not require an explicit knowledge of the aircraft parameters or the environment. Typical simulation results are presented which verify the theoretical predictions.