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Aviation History
1956
1956 - 0885.PDF
6 July 1956 29 FLIGHT CREW STATION TOILETS ACCESS DOOR TO NO 3 FREIGH1 HOLD, CAPTAIN FLIGHT CREW STATION from each other and from the adjoining structure by titanium firewalls.Each engine is secured by two trunnion pads and tie-rods. Two quick- disconnect fittings secure air intakes and roller-mounted jet pipes. Eachengine is an interchangeable unit capable of being readily removed and replaced without disturbing controls. Components, as far as possible,are interchangeable between each installation with the exception of the jet pipes (although inboard pipes and outboard pipes are interchange-able). The underside of each engine is completely exposed for servic- ing by large hinged doors, and further access panels are provided abovefor slinging and for accessory servicing. Most of the accessories, how- ever, are on the underside of the engine and, together with the enginemountings, they are accessible from ground level. Engine control is by means of steel cables. Particular care has been given to cooling, ventilation and de-icing.The compressor zone is cooled by its own intake/outlet system, and the combustion zone has two further air intake/outlet systems. The enginebays are divided by transverse firewalls into separate zones, each with its own fire-detection and fire-extinguishing system. A fuel collector-box of the "self-consuming" type is fitted. A mechanical thrust-reyerser system, to be fitted to the jet pipes oftwo engines, is under active development. SYSTEMS. Cabin Air. The air supply for pressure-conditioningthe cabin is tapped from the compressors of each engine; one engine is sufficient to maintain cabin pressure and conditioning to therequired level. Only cooling is necessary, and this is accomplished by air heat-exchangers and turbine-expander refrigerators of D.H. design. The maximum cabin pressure differential is 8| lb/sq in (8,000ft at45,000fi). Discharge valves control the pressure and automatically dis- pose of used air. Two relief valves limit maximum differential pressureto 9 lb/sq in and also prevent negative pressure of more than \ lb/sq in during a rapid descent. The system is designed for an ultimate pressureof twice normal. Air is drawn from the cabin at the rate of approximately 1,200 cu ft/min and re-circulated with the incoming fresh air. Cabin air is changed completely twenty times per hour and total ventilation is at the rateof not less than 2 to 3 lb of conditioned air per min per person. Temperature is automatically controlled between 60 deg F and 75 deg Fover a range of outside temperatures of —94 deg F to 86 deg F. A humidifier maintains humidity at a minimum of 20 to 30 per cent. Cabinwindows are protected from internal mist by silica-gel containers which dry the air before it enters the sandwich. Pressure control is fully automatic, it being necessary only to pre-select the altitude at which it is required to start pressurizing. This takes care of operation from airports of varying altitudes. Spill valvesprovide basic pressure control, and mass flow and temperature valves, controlled automatically with manual adjustment, regulate air condition-ing. Provision is made for the attachment of a standard air conditioning connection on the ground; there is also a connection for ground pres-surization tests. Electrics. The main electrical supply is from a single-wire earthreturn system operating on a nominal 28-volt D.C. The aircraft structure acts as the earth. The whole system has been fused and engineeredto eliminate as far as possible the likelihood of failure, and the following safety features are noteworthy: (1) Normal distribution is from a single RRST CLASS SEATS PASSENGERENTRY DOOR DIPLOMATIC MAIL LOCKER AND WARDROBE SPACE 2O 15 U)58-| b5O 76-SEAT TOURIST-CLASS 58-SEAT FIRST CLASS VOLUMETRIC CAPACITY 18 2O 22 24 26 28 3O 32 STAGE LENGTH (st miles XIOO) 34 36 busbar which in the event of failure automatically splits into two parts.Services are then maintained by the good half. (2) Certain essential loads—flight instruments, radio—are provided with a secondary busbarin the unlikely event of failure of the above. (3) Should this secondary distribution fail, essential services may be switched to the emergencybatteries for a limited time, during which it should be possible to get at least one alternator back on the line. Power is supplied by four engine-driven 14 kVA alternators, the three-phase output of each being rectified and paralleled before rectification. Each alternator has a continuous rectified output of 350 amp maintainedat 28 volts by carbon-pile regulators. Six 24-volt, 25-amp-hr batteries are installed with switching for series-parallel working; they are in twogroups of three, each group being connected to each half of the dis- tribution system; one battery in each group constitutes the reserve.Five of the batteries are connected in series with a switch for internal engine-starting. D.C. inverter sets provide A.C. at 115 volts 400 cyclesthree-phase for auxiliary power and at 26 volts 400 cycles single-phase by transformers. Sockets for external ground power are provided, andfuses and circuit-breakers are mounted in the control cabin. Crash and inertia switches simultaneously cut off the alternators, isolate thebatteries, discharge fire-extinguishers and actuate a time-delay switch which finally disconnects all circuits except emergency lighting. Hydraulics. The hydraulic system operates the flying controls, under-carriage retraction, flaps, air brakes, wheel brakes and nosewheel steer- ing. Normal pressure is 2,500 Ib/sq in. A single bay under the floorhouses as much as possible of the equipment; this compartment, which is accessible during flight, is isolated from possible sources of ignition.The system comprises four separate circuits, where necessary with independent reservoirs and accumulators, with a colour code as follows: Green: Supplied by pumps driven by the port inner and starboardouter engines, and serving undercarriage retraction, nosewheel steer- ing, flaps, air brakes and wheel brakes. It also provides stand-by powerfor the flying controls. Blue: Supplied by pumps driven by the starboard inner and portouter engines and providing primary power for the flying controls. Red: A stand-by system, supplied by an electrically driven hydraulicpump, providing emergency operation of the undercarriage, flaps and
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