Multi-variable aircraft directional control with anti-skid differential brakes

The paper deals with the design of a fault-tolerant control system of the runway dynamics for small jet aircrafts, in which hydraulic differential brakes are used as a stand-by directional command, to be activated in case of electro-mechanical nose-wheel steering failure. The directional control system is composed of four nested feedback loops, respectively acting on the brake pressures, the wheels’ slip ratio, the aircraft heading and the ground path. The study, performed by integrating detailed models of hydraulic brakes and electro-mechanical nosewheel steering in a light jet aircraft simulator, aims at demonstrating that, in case of nose-wheel steering jamming, the redundant control architecture is capable to assure safe and satisfactory operations, but only if the differential brakes are activated with minimum fault detection latency. Simulation results allow highlighting and characterizing, at different runway conditions, the effects of jamming detection latency on the directional stability when the aircraft crosses severe lateral gusts.