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Concorde Fly by wire system
Each of the Flying control surfaces, six elevon and two rudder sections, is controlled by a Power Flying Control unit (PFCU) This is moved by a separate twin-ram electro-hydraulic servo control unit (see diagrame1) These units are supply with hydraulic power and act in response to electrical and mechanical signals. The electrical signals are generated in synchro-transmitted and applied through electrical circuits in which they are amplified and combined with feedback signals from the servo control units and from the auto-stabilisation system. The syschro-transmitters are driven by movements of the control column and rudder pedals on the flight deck. This system is known as ‘fly-by-wire’ and Concorde was the first passenger aircraft to be fitted with type of system. Concorde has a stand-by mechanical signalling system
The ‘nerves’ of the flying controls surface systems, which translate the pilot’s movements into action, are of great importance to both the safety and comfort of Concorde, so therefore there are three of these ‘signalling channels’ as well. The main and standby systems are as spoken about already, electrical: shifts of the control column or rudder pedals are felt by sensors and transmitted along wires to the control units. These channels use specials power-packs which produce their own current at a frequency designed to resist interference. The third system is mechanical, linked to the control column, through a hydraulic jack, directly to the control units.
These three methods of signalling provide plenty of spare capacity; the mechanical backup channel never had to be used during Concorde’s service life. However there is in fact yet another method of moving the control surfaces, this has been added in case the column itself might be partially or wholly jammed. Should this happen, strain gauges measure the actual forces being applied by the pilot can transmit them electrically, through the normal circuits.
Concorde’s ‘fly-by-wire’ system is responsible for many of the features which made her so pleasant to fly on. It’s provided the ability to interpose between the pilot and the controls further signals which refine Concorde’s flying qualities. The first of these is auto-stabilisation, which acts in all three axes (pitch, roll and yaw (to improve Concorde’s natural stability and to smooth out turbulence. It will also apply some rudder control if an engine fails, to counteract the resulting yaw.
Safety flight system
A second electronic box, the Safety Flight System, provides protection against accidentally reaching too high an angle of attack; this could be the equivalent of approaching a stall of other aircraft. The way this works is as follows, firstly by gently opposing the pilot’s demand, then by shaking the stick which is accompanied by a loud rattling noise, and finally by wobbling it quite viciously. Should the pilot be so bent on disaster, that he ignores all of these progressively more insistent messages, the system despairing of his sanity, will put all the elevons firmly down, to decrease the angle of attack and regain a safe flying speed.
Another circuit in the control lines protects Concorde against the reversal. Concorde’s structure also makes it much more resistant to the distorting forces of supersonic flight than aircraft built before her. The electrical singling helps, too. If Concorde gets substantially above its design speed, the outboard elevons are automatically neutralized, so that no twisting is possible. The work of pitching the aircraft up, to reduce speed, is then done by the four inboard elevons, whose hinges are behind the most solid parts of the wings.