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Aviation History
1949
1949 - 1661.PDF
FLIGHT, 29 September 1949 425 If it is borne in mind that up to 100 hours' laboratory work will be entailed for every hour of flight testing, the duration of the ground tests which preceded the first flight —and during which the instrumentation was being adjusted —is readily accounted for. The reward for the elaborate instrumentation described should be a mass of unique tech- nical records of immense significance. Radio and Intercommunication * . For early flight trails the Brabazon I has V.H.F. and M.F. W/T communications equipment, Marconi automatic direction-finding, Gee, and a radio altimeter. All flight crew stations have facilities for any three receivers and any two transmitters, together with intercomm. There are three separate intercomm. channels, with no fewer than 49 points; any two or all three channels can be mixed, or, as for the first flight, all three can be fed together to the flight deck. Availability of three channels means that the flight observers can conduct three separate tests simultaneously without cross-talk on one channel interfer- ing with conversations on the other two or the flight deck. The chief observer is stationed at the navigator's position and controls channel mixing and selection. Pressurization and Air-conditioning The 143ft pressure-hull section of the Brabazon I ex-tends between pressure diaphragms at frame F.1029, forming the front wall of the cockpit, and R.680, aft ofthe passenger compartment. In the Brabazon I the maxi- mum differential pressure is 5.5 lb/sq in and the cabinaltitude-equivalent at 25,000ft is 8,000ft. The decision to power the Brabazon II with Proteus turboprops, witha consequent increase in cruising height from 25,000ft to some 35,000ft, has necessitated the development of centri-fugal blowers capable of producing a higher differential pressure than those for the Mk. I. As might be imagined, the expansion of the fuselageunder pressure presented formidable problems, and although under normal conditions the internal pressuredifference causes an increase of only -Jin in length and Jin in diameter, the effect of extremes of temperature(between minus 60 deg C and plus 40 deg C) is a length- wide expansion of fully 4£in. One square inch of leakagearea over the whole fuselage is permitted. The principal components of the air-conditioning andpressurization system are two Marshall blowers, two coolers, three heaters, three discharge valves, four inwardrelief valves, a safety valve, re-circulating fans and booster fans. Air circulates from the aft hold, through a heater, fordistribution through ducts to the cabins. Thence it is extracted through grilles in the floor and returned tothe aft hold. To keep the air fresh about 25 per cent new air is added every cycle; this is collected by wing-rootintakes and is fed into a mixing box with the recirculating air from the aft hold, before passing through a heater forducting to the cabins. Though a small amount of air is continuously escaping through joints in the fuselageplating, most of the air to be displaced to make way for new air leaves the fuselage through reducing valves.These valves prevent differential pressure from building up dangerously (e.g., as in a dive). Should cold air berequired, the heater is switched off and coolers in the supply system from the wing-root ducts are brought in. In the event of failure of the two Marshall blowers,direct ventilation is obtained by opening spill-valves on the main leading-edge intakes for the pressurizing system. Air entering the. pressurization intakes is filtered andpassed to the blowers (driven by the inboard accessory gear boxes), which force air on to the cold air mixingboxes of two heaters. Vibrations set up in the air intakes are damped out by passing the air through silencersmounted in series, one in each wing, and one in the fuse- lage. The ^tir passed through the blowers having beencompressed and heated, it is ducted to cooler units in each wing. Mass-flow units are provided to measure the H/draulkal unit for power operation of rudder. flow of air. Flow is controlled by spill valves on the intake which, when opened, allow air to escape into the wings. Twenty oxygen cylinders are provided for emergency use. Gust Alleviation To relieve the wing loads sustained in gusty weathera "gust alleviator" was considered desirable, and is but one of numerous novelties first developed for the Braba-zon. Various suggestions received careful attention before a promising method—precursor to that now fittedto the Mk. I—was evolved. It has been estimated that without the alleviator the weight of the Mk. I wing wouldhave been increased by about 7,000 lb, and that of the Mk. II by 13,000 lb. In collaboration with the R.A.E., a Lan-caster has been fitted experimentally with a Brabazon- type alleviator. The pitot of the alleviator is mounted in the extremenose of the fuselage and produces a differential pressure on a diaphragm with change of vertical component ofwind. The deflection of the diaphragm operates the aileron power-control units through an electrical circuit,which causes the ailerons to be deflected simultaneously in proportion to gust intensity, thus reducing suddenvariations in wing loading. Fire Precautions The automatic fire-extinguishing system provides pro- tection for the port and starboard wing anti-icing heaters, tail anti-icing heaters, cabin conditioning heaters, each engine and its air intakes, the forward and aft luggage holds and the electrical distribution centre. There are four banks of eight extinguishers for the engines alone, two in each bank having dual heads for '' second shot'' operation on either engine of a pair. In addition to the fifty automatic units, hand-operated extinguishers are strategically placed. Anti-icing Thermal anti-icing systems serve the main planes, tail-plane and fin. Two Radiation heaters are fitted in each inner wing, just outboard of Nos. 1 and 8 engines, andeach pair is fed with air from an aperture which derives its supply from the outboard engine air intake. Eachaperture has an inlet flap, operated by a hydraulic jack, electrically controlled from the engine fire panel, and byclosing the flaps each heater system can be isolated in the event of fire. Being normally open, the flap venti-lates the wing interior in the region of the fuel bags. From the heaters, air is ducted along the leading edge to thedouble skin of the outer wings. The tail anti-icing sys- tem, with heaters, is self-contained. The "birdproof" windscreen, comprising several layersof different types of glass and a Perspex panel fin thick, is demisted by hot-air circulation. Although controls for air-screw anti-icing are fitted at the 2nd engineer's station, the present wooden airscrews do not have the necessaryequipment.
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