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Aviation History
1984
1984 - 0475.PDF
panels below the PFD/ND displays. In the A320 Airbus commits its engine instru ments to a CRT display for the first time —to the upper of two displays on the centre panel. These two displays show the information output of the Ecam (electronic centralised aircraft monitor). The upper screen shows engine performance and warnings in dial and digital form; the lower shows systems and fuel management information in diagram and digital form, and checklists. In case of display failure, almost any information (from Efis or Ecam) can be shown on almost any screen. On the coaming above the centre panel is each pilot's Efis control and, as standard, the flight control unit. Airbus has studied the possibility of providing addi tional data on the PFD beyond that to which pilots are accustomed. For example, symbols showing the actual flight vector relative to the horizon in addition to the aircraft attitude and a "total energy vector" symbol, which would show the extreme flight vector which you could ask of the aircraft. Although this information may be made optional, Airbus believes that few pilots would actually use it because the "crossed bars" of the flight director provide them with all that they normally want to know in terms of performance demand. Flying the A320 For manual flight control the captain has a small sidestick to his left, operated with his left forearm resting on an adjustable armrest, and the copilot's sidestick is to his right. The two throttle levers are in the conventional posi tion on the centre pedestal, as are the flap levers. Fly-by-wire means that heavyweight pilot muscle is irrelevant and useless in controlling the airliner; hence the abandonment of the large, conventional control column. Allowing the controls to become heavier to operate as the aeroplane goes faster either naturally, or though artificial feel has also become pointless. This is because the flight augmentation com puter, through which the sidestick-generated signals are processed, protects the aircraft against control-stick displacements which would overstress the airframe. So the A320 pilot will fly with his wrist, moving the sidestick against a spring force which is constant at all airspeeds and all aircraft attitudes. The pilot needs to rethink what he is actually doing when he operates this new form of control column, because although he is moving it as required in the normal three-axis sense he is not directly demanding control surface movement. Instead he is demanding a specific g force (during wings-level flight) which is directly proportional to the stick displacement he selects. As soon as he releases the stick it springs central, and by doing that he is commanding the aircraft to fly to lg (vertical g) in what ever flight path he has selected. While the aircraft remains on this flightpath speed may vary but no manual trimming is required — there is no trim switch on the sidestick—trimming is auto matic. To turn, the pilot selects a sideways displace ment on the stick which gives the bank (thus the rate of turn) which he wants, and he holds it there. No back pressure is required on the stick unless the pilot requires a turn of 33° bank or more. The aircraft continues to maintain, in its turn, the flightpath which keeps the vertical g vector at a value of one. Beyond that bank angle back-pressure is required to maintain a level turn. These are the plans for sidestick flying at the moment. There may be modifications to the planned flight augmentation computer program by the time the A320 is certificated. These ideas — sidestick position and size, and handling through a computer which gives no "feel" feedback (real or arti ficial) to the pilot —may sound strange. But all types of Adoption of side- sticks frees the lower front panel for a pull-out table for each pilot. The cathode ray tube displays are slightly larger than those flying on the A310, and the one in the upper centre displays engine parameters (A310 has electro mechanical engine instruments) AIRBUS UPDATE transport aircraft pilots who flew the testbed A300 with the computer-linked sidestick received it enthusiastically, however sceptically they had approached it. This includes test pilots, current airline pilots, certification authority pilots, and Flight (see Flight, December 24, page 1687 for full sidestick flying report). The flight augmentation computer, part of the three- computer automatic flight system, also controls manoeu vring load and speed limits, making the aircraft unstressable and unstallable. Manual operation can take the aircraft deliberately beyond normal operating limits, but not beyond maximum limits. For exam ple, if the pilot held the nose down when the aircraft approached VNK (never-exceed speed) the aircraft would defy him and pull up at a steady 1.5g until it was within normal operating limits. There is protection at the low speed end, too, via an angle-of-attack (alpha) sensor which is linked to the computer (see December 24 issue). All this sounds fine provided that the electrics and electronics continue to work. But Airbus knows that whatever systems duplication and triplication there is, the certificating authorities will require some form of mechan ical backup. How easy is it to fly an airliner with just tail- plane trim and rudder? Aero- formation, Airbus' aircrew and groundcrew training organisation, let David Learmount try it out in one of their A310 simulators. Having taken-off and climbed the simulator to 3,000ft on a long "downwind leg" the engineer simulated jammed elevators and the crew abandoned all use of the control column. The Flight man in the left hand seat was given a 180° turn to carry out, followed by an ILS approach from 3,000ft, using only pitch trim and rudder. The "first officer" handled the throttles. There was no problem at all in carrying out the simulated approach and landing, so it seems that a fully type- qualified pilot would be able to get his A320 safely home on the mechanical backup controls with which Airbus intends to fit its new fly-by- wire airliner. FLIGHT International, 24 March 1984 737
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