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Aviation History
1986
1986 - 2149.PDF
33° bank. Engine failure compensation is "nice", says Corps. "The yaw damper has a large, 23° rudder authority. You can lose an engine at 50ft and the aircraft will roll 7-8° and stay there. This gives enough indication of engine failure without making it too easy." Perhaps the most significant capability of the A320 elec tronic flight control system is its ability to protect the air craft from stalling, overspeeding, over loading, excess atti tudes, and even windshear: "The A320 lives in a box—it can't go slow; it can't go too fast," explains Corps. Stall protection should enable the A320 to reach and maintain its maxi mum lift without the pilot exceeding the stall angle-of-attack with his sidestick full back. "The A320 will not stall," maintains Corps. The A320's angle of attack, or "alpha", protection works like this. The aircraft will not penetrate the region above 12 • 8° alpha on its own. At 12-8°, Alpha- PROTECTION activates and an alpha- command control law replaces the usual g control law. At 15°, AlphaFi.ooR activates and full go-around thrust is applied auto matically. Alpha- FLOOR corresponds to 1 • 1 times the lg stal ling speed. If the A320 goes through 12-8° alpha with more than 9° stick input, however, AlphaFLooR is advanced to coin cide with AlphaPROTECTioN- The pilot cannot exceed AlphaLiMiT at around 17° and Airbus hopes to do away with stall warning on the A320. The aircraft cannot exceed AlphaMAx at around 20°, which corresponds to the maximum lift coeffi cient of the wing. The objective of windshear protection is to provide safe, repeatable performance, says Airbus. The pilot simply pulls the sidestick full back to get all the lift avail able, and when AlphaPLOoR is breached, full go-around power is automatically applied. The computers then work to maintain the maximum possible angle of Expanding the Airbus family Billed by Airbus Industrie as "an all- new, short-to-medium-range, single- aisle, twin-engined aircraft", the 120-179-seat A320 will fly in February 1987 and enter airline service early in 1988. The first 20 production aircraft will be A320-100s. With a 66-tonne maxi mum take-off weight and powered by General Electric/Snecma CFM56-5 turbofans, the A320-100 has a 1,750 n.m. range carrying 164 passengers. The A320-200 will follow and has a 72-tonne gross weight enabling it to carry more fuel and giving it a maximum range, with 150 passengers and International Aero Engines (IAE) V.2500 turbofans, of 3,200 n.m. Both engine types are currently rated at 23,5001b thrust and Airbus' own figures give the V.2500-powered A320 a 5 • 3 per cent better fuel burn. Of the 134 firm orders from 12 airlines, 60 are for CFM-powered A320s and 68 for IAE-powered aircraft, with six uncom mitted. Including options, the split is 102 to CFM and 146 to IAE. The A320's main competitor is the Boeing 737-300, and now the stretched 150-seat 737-400. Airbus claims the 737-300 burns 35 per cent more fuel per seat than the V.2500-powered A320 and has a 16 per cent higher operating cost per seat. attack, and lift, without the risk of the aircraft stalling. Overspeed protection is designed to prevent the A320 overshooting its maximum operating airspeed or Mach number. "If you go through the overspeed warning hands off, the aircraft rolls wings level, then automatic elevator pulls the aircraft up with l-75g," explains Corps. Normally maximum bank angle is limited to 65°, but above the overspeed warning this limit is reduced to 40° to leave ^g for recovery. Overspeed protection allows the designers to reduce the margin between maximum operating speed and maximum demonstrated dive speed, by 25kt, and so save structure weight. The A320's angle-of-attack and over- speed protection can not be overridden by the pilot, and neither can its load factor limits of +2-5g and -lg. This is not a disadvantage, Corps emphasises. As with all other transport aircraft, the A320 is designed to a 2-5g maximum load factor with a 1-5-times design margin (3 • 25g) to allow for loss of strength through fatigue, corrosion, repairs, or fractures. Airbus elected to use a miniature side- stick controller because electrically signalled flight con trols no longer required the leverage of a control column to move mechanical linkages. Locating the stick on the side has liberated panel space for larger dis plays on which more information can be presented in a more integrated fashion. When using the sidestick, the pilot's forearm is supported by an armrest and the stick itself is angled inwards and forwards to fit the natural hand posi tion. The stick moves 16° fore or aft, the maximum 221b stick force corre sponding to a demand of 2 • 5g stick back and -lg stick forward. The side- stick moves ±20° sideways, the maxi mum 9-51b inwards stick force (71b outwards) corres ponding to a 10°/sec roll-rate demand. Corps turns the argument for or against sidesticks on its head: "If sidesticks were the normal way for flying aircraft, no one would even consider changing to a control column that makes it difficult for the pilot to get into his seat and which blocks his view of the instrument panel when he's there—besides, thanks to the A320's side- stick and pull-out table, the pilot can at last eat his lunch in comfort". In flight tests of the sidestick-equipped A300 there has been no pilot rejection of the concept, says Airbus. The decision to adopt sidesticks with no mechanical coupling whatsoever gener ated enormous debate, however. If the sticks were not linked in any way and therefore did not follow each other, how FLIGHT INTERNATIONAL, 30 August 1986 87
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