Design of a Haptic Feedback System for Flight Envelope Protection

Current Airbus aircraft use a fly-by-wire control device: a passive spring-damper system which generates, without any force feedback, an electrical signal to the flight control computer. Additionally, a hard flight envelope protection system is used which can limit the inputs of the pilot when approaching the edges of the flight envelope. To increase the situation awareness of the pilot, this research aims to provide intuitive information on the flight envelope through haptics, force feedback trough the control device, integrated in the existing Airbus control laws. The goal of this paper is to describe when and how haptics is used in this design. The pilot can get five cues of the flight envelope: when approaching the flight envelope a discrete force cue is given. Next, control inputs which move the aircraft closer to the flight envelope are indicated with an increased spring coefficient. Moving too close to the lower velocity limit activates a stick shaker: a vibration force on the stick. If a stick neutral position is not sufficient to return to the safe flight envelope, the stick is moved forward to the desired control input. Finally, following the automatic Airbus pitch up command during an overspeed condition, the stick is moved back to follow this command. This new system is expected to help identifying the situation and choosing a possible mitigation technique which is evaluated for two scenarios: when the aircraft is moving to the flight envelope, i.e. a windshear, or when the flight envelope moves towards the aircraft.