An anti-skid braking system for aircraft via Mixed-Slip-Deceleration control and Sliding Mode Observer

For both safety and technological reasons, aircraft anti-skid control systems are typically based on the wheel speed measurement only, which yields a self-contained landing-gear subsystem, but makes the anti-skid performance sub-optimal. For a better exploitation of the available tire-runway grip, a modulating control technique is herein proposed: it ensures improved closed-loop properties but requires the estimation of the aircraft velocity, which cannot be directly measured. In this paper, an aircraft landing gear control-oriented model is presented considering the distinctive effect of the gear walk dynamics. A Mixed Slip and Deceleration anti-skid controller is introduced to suitably leverage the runway available grip. Then, a Sliding Mode Observer is proposed to estimate aircraft wheel slip and, based on a non linear curve fitting procedure, it allows also to retrieve road friction conditions. Finally, simulation results of the implemented model are shown in order to quantitatively asses the combined estimation and control performance.