A New Complement for Air and Spacecraft: A Man/A Computer

Abstract

Abstract Until today the links between the pilot (stick, pedal, throttle) and the servo-jacks acting upon the control surfaces on the fuel vanes consist of cables or rods with a lot of mechanical or hydraulic compensating devices. Reduction of frictions, hysteresis and other non linearities are encountering tremendous difficulties due to the size of modern carrier and also that, in flight, static and dynamic deformations of a plane, are difficult to compensate. Once the fly-by-wire concept has been accepted, the design of the plane enters a completely new way. Three themes will be developed in this paper. a) the reliability of a fly-by-wire system (which includes digital computer inserted between the controls and the actuators) has to be proved to be at a level higher than 10-8 fatal failure per hour of flight. b) What has to be Implemented first ? The tremendous field of an electronically controlled plane must be carefully opened because of the vulnerability to electromagnetic interferences, namely lightning, of the control system of the plane. The rapide growing up of composite materials replacing metallic material, would increase this vulnerability if nothing is done. The loss of electricity on board must be proved to be smaller than 10-8 per hour of flight. c) The expected gains from this concept may be classified as follow : • control of the flight enveloppe on a continuous basis so that the plane must not reach any point in the border of it. Stall conditions overspeed, buffeting of flutter become impossible. • The plane is automatically trimmed, this means that it appears like a neutral stability plane at any time. • Reduction of the margin of inherent positive stability. • control of the wing loads during manoeuvers or in turbulence. • Gust alleviation. If an estimate of the local wind in front of the plane can be achieved -let say 10 or 50 meters ahead of the plane-computation of the setting of the control surfaces at the correct time, i.e. when the gust reaches the wing, would decrease the randem load which would have appeared if no such control had been performed. • Side sticks instead of the control column : the need for a massive control column disappears once electric signals are used between controls and actuators. The signals resulting from the motion of the 2 sticks have to be interpreted through a logic. • This papers will refer to the general concept of fly-by-wire ; however experience gained through the A 320 will be developed in order to give an idea of the present “State of the Art” in this matter.