Unsourced material may be challenged and removed. Both systems often require redundant backup to deal with failures, which increases weight. The term “fly-by-wire” implies a purely electrically signaled control system. It is used in the fly by wire system in aircraft pdf sense of computer-configured controls, where a computer system is interposed between the operator and the final control actuators or surfaces.
This modifies the manual inputs of the pilot in accordance with control parameters. The flight control computer then calculates what control surface movements will cause the plane to perform that action and issues those commands to the electronic controllers for each surface. The controllers at each surface receive these commands and then move actuators attached to the control surface until it has moved to where the flight control computer commanded it to. Fly-by-wire control systems allow aircraft computers to perform tasks without pilot input.
Automatic stability systems operate in this way. While traditional mechanical or hydraulic control systems usually fail gradually, the loss of all flight control computers immediately renders the aircraft uncontrollable. CCV controls can electronically stabilize the lack of natural stability. A FBW aircraft can be lighter than a similar design with conventional controls.
This is partly due to the lower overall weight of the system components, and partly because the natural stability of the aircraft can be relaxed, slightly for a transport aircraft and more for a maneuverable fighter, which means that the stability surfaces that are part of the aircraft structure can therefore be made smaller. If these structures can be reduced in size, airframe weight is reduced. The advantages of FBW controls were first exploited by the military and then in the commercial airline market. Boeing followed with their 777 and later designs.
Long runs of mechanical and hydraulic connections were replaced with wires and electric servos. The programme was curtailed when the airframe ran out of flight time. Control was through a digital computer with three analogue redundant channels. It flew in April 1972.