Antiskid control for aircraft via extremum-seeking

A novel method of antiskid control for transport aircraft is proposed. After robustly stabilizing the hydraulics using an inner-loop controller based on feedback linearization and H/sub /spl infin// theory, a sinusoidal signal of small amplitude is injected into the brake pressure to estimate, in real-time, tyre-runway friction properties. This information is used by the algorithm to keep the friction coefficient slightly less than the maximum allowed by the runway conditions. This results in much smoother braking compared to controllers currently in operation, which try to reach the maximum. Consequently, passenger comfort will be improved and component wear will be reduced, while achieving comparable or better stopping performance. In some cases, several hundred feet of improvement in stopping distance is possible, as demonstrated via realistic simulations based on a detailed model of the MD-90 aircraft.