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Aviation History
1955
1955 - 0736.PDF
734 FLIGHT, 27 May 1955 JET-AIRLINER SYSTEMS ELECTRICS, HYDRAULICS, AIR CONDITIONING, PRESSURIZATION AND FUEL SUPPLY THE safety and comfort of the passengers and crew of ajet airliner depend to a very large extent on the function-ing of the aircraft's systems; in fact, such services as pressurization, air conditioning and hydraulic power for flying controls become as necessary as the wings themselves. Yet such systems are still comparatively new in conception and there has yet been little opportunity of describing them in operation since the latest air conditioning and powered control equipment has mostly been applied to secret military aircraft. The emergence of the S.E.210 Caravelle, not restricted by security regulations, except for its engines, provides an excellent example of the way in which these new services are incorporated in a large jet aircraft. The descrip- tion might well apply to the Comet and similar projects since a proportion of the components, particularly in the hydraulics, are directly based on de Havilland experience, as well as on S.E.'s own projects in the past, of which the Grognard was one. Taking into account the whole sequence of a commercial flight,it is difficult to attribute major importance to any one system, but since so much of the detail controls and valves are electricallyoperated, the electrical supply may appropriately be dealt with first. This is followed by the hydraulics—which might be termedcritical, since the flight controls depend entirely upon them. Air conditioning and pressurization are hardly less significant, how-ever, and the importance of fuel supply is obvious. Upon these systems, as much as upon the aircraft's structural integrity, doesthe overall efficiency and safety of the jet airliner depend. Though the Caravelle is a French product, many British firmshave a part in it, particularly de Havillands and Rolls-Royce, and Lockheed, Dunlop, H. M. Hobson, Venner, Teddington Controls,Self-Priming Pumps, Flight Refuelling and Graviner, to mention only those here directly concerned. Aero Research, Ltd., are, ofcourse, responsible for Araldite used in the spot-welded and glued stringer/skin structures. The electrical system of the Caravelle has been designed formaximum reliability and also for the greatest possible degree of safety should any failure occur; and, like the odier systems to bedescribed, it is intended for automatic operation, though having full facilities for direct control. There are two engine-driven generators, two mainconverters and one stand-by, two sets of batteries, and a ground-supply connection. Because the Caravelleis designed to start its engines with power from its internal batteries, the main block of these can beswitched either in series for engine starting or in parallel for emergency use. This large block is there-fore called the stand-by battery, and a smaller block the aircraft battery. The whole electrical supply isset up in die three sections, shown in the diagram, which normally operate together but which, in caseof failure, are cut out one after the other. The generators are Bendix 30E029C type, supplying30 v and 375 amp D.C., with a peak power, limited to 30 min, of 400 amp. The aircraft battery is anAmerican Andre Yardley 40 amp hr, 24 v, silver-zinc battery with 15 cells, weighing 11 kg (24 lb) and madeunder licence by Andyar in France. The stand-by block consists of five of these batteries, which, whenconnected in series for engine starting, supply 112 v D.C. Total weight of this block is only 53 kg (116 lb).The English licensee for these batteries is Venner Accumulators, Ltd. The main converters, mounted together with themain generators, are Bendix 1518/1, rated at 115 y, 400 cycles A.C., 2,000 va, and only one at a time isused. The emergency converter is 80 va, and is switched on automatically should the main supply fail.It is run from the aircraft battery. A further supply, transformed to 26 v A.C., is takenfrom the normal 115 v supply to work the position- indicating synchros. It can be seen that a great num-ber of solenoid-operated valves are included in the Caravelle's various systems and in almost all caseswhere direct control from the cockpit is mentioned in subsequent descriptions, it is performed by thismeans. The accompanying diagram shows how the three distributionsystems are linked with batteries and generators. The whole is so arranged that, should one generator fail, unneeded circuits andthe battery charge are cut out. If the second generator fails the next series of non-vital circuits is dropped, the stand-by batteriestake over the whole supply function and the emergency converter is started up. The three distribution circuits are all switched on together assoon as engine revs reach the required level after starting. A master switch isolates all electrical services when the aircraftis on the ground. A series of warning lights in the cockpit indicates to the crew how the system is working. The hydraulic system of the Caravelle is based to a considerableextent on de Havilland experience with die Comet and contains a number of British-made components. Upon it depend the opera-tion of flying controls and the actuation of undercarriage, flaps and several other services, including control-feel simulation, air-brakes, wheel brakes, nosewheel steering and centreing and freight and passenger access doors. It can be seen from this just how important it is that diehydraulic system should be as nearly fail-proof as possible. S.N.C.A.S.E. have therefore designed a system based to someextent on Comet practice, but in many respects improved; and some time ago they constructed a complete working mock-upat Toulouse-Blagnac. This is dimensionally accurate, with all components laid out exacdy where they would be in the aircraft.The only departure is that the aileron and air-brake lines and components have been turned through 90 deg to lie alongsidethe axis of the fuselage, because there was not space in the shop to accommodate the full wing-span. All parts of the system havebeen exhaustively tested, the undercarriage alone having been lowered and raised more than 5,500 times. The weight and massof all control surfaces and other moving parts is simulated on the rig by weights and heavy frames, and the dynamic pressuresupplied to the feel simulator can be varied to reproduce all flight speeds. The controls have already been put through 100,000cycles without a hitch. There are four hydraulic power supplies, identified by colours:green, blue, yellow and red. Green and blue are normal and The Caravelle's electrical system is schematically shown here, with its three main distribution circuits. The numbered supplies are: (I) windscreen demister fan, prototype only, (2) No. 1 converter, (3) No. 2 converter, (4) normal lighting, autopilot and radio, (5) taxying light, converter relays and radio, (6) red system hydraulic pump, (7) yellow system hydraulic pump, (8) port fuel pumps and valve control, navigation lights and lamps, hydraulic system indicators, (9) starboard fuel pumps and valve control, de-icing control, red cockpit lighting, (10) and (11) radio and (12) air- conditioning controls, generator indicators, emergency warning circuits, fire detection and suppression in the engine nacelles. STB'D GENERATORS PORT STANDBY BATTERY 4-Hl ST'B'D CONTACTORS PORT AIRCRAFT BATTERY GROUNDCONNECTION
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