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Aviation History
1956
1956 - 0609.PDF
THE COMET 4 ... failure. This was perhaps the most important advantage of theburied installation. It had been considered better to concentrate on a pure poweredsystem for the flying controls, and the reason for this was the consideration that any stand-by system should be as good as theprimary system as' regards effectiveness and pilot-effort. Such dangers as runaway control valves, a seized ram in the booster, ora mechanical failure of any kind in the control circuit and booster mechanism, were all common to the pure powered-control systemand to the powered-control system with manual reversion. The authors believed very strongly that, provided really adequatesafeguards were taken against loss of hydraulic fluid, and that boosters and other valves were duplicated, it was far better to havea simple powered system. During the last six years considerable development had goneinto the Comet's controls. To provide lower elevator gearing for all flying except in the circuit and during take-off and landingthe Comet 4 would have a gear-change device in the elevator system, and "Q-feel" was being incorporated in the elevator.Some of the detailed design improvements made to the Comet since the aircraft flew in its original form on July 27, 1949 were:(1) A change of wing section, eliminating the possibility of a ground stall during take-off. (2) Greatly increased flap areato provide an increase in drag during final approach. (3) The hydraulic equipment in the fuselage had been located in anentirely separate equipment bay remote from any electrical equipment. (4) Considerable development work and a greatdeal of testing had been devoted to improving the flameproof properties of all electrical equipment. (5) Fuel heaters andintegrating flow-meters were provided in the fuel system. (6) A great deal of development had gone into improving engine ventila-tion and the fire-prevention and detection systems. The Comet 4 engine installation was scheduled to be tested in the Rolls-Roycefire tunnel at Hucknall. (7) Dunlop Maxaret anti-skid brakes were fitted and provision made for a tail parachute. Reversethrust was under active development on the Comet 2 and would be fitted to the Comet 4 as soon as a satisfactory system had beendeveloped. (8) Considerable development work was being done to reduce jet noise, although the Comet 4 with its more moderatelypowered engines was not in such great need of noise-reduction as were its more powerful competitors. (9) The flight deck hadbeen largely re-designed to provide for five crew-stations. (10) Full provision was made for automatic blind approach and for cloud-warning search radar. (11) Alternative cabin arrangements had been devised to accommodate either all first-class passengers,mixed-class, or all tourist-class. Mr. Cunningham recounted the flying experience gained sinceJuly 1949, both by de Havilland and by B.O.A.C. It was possible from the Comet's 30,000 hours of airline service to answer someof the controversial questions being discussed today. Firstly, there was absolutely no doubt that passengers preferred jets.Turbulence was a rarity, and the smoothness of the pure jet had to be experienced to be believed (the instruments and radio gave verygood service because of this). The Ghost engines, which reached FLIGHT, 18 May 1956 609 (Left). Close-up of a main-wing spar in its fatigue-testing gan- try. The one-piece cut-outs — compre- hensively strain- gauged—in the spar web tor the engines may be noted to differ from those of the Comet 1, which had bolted ring- pieces. The centre- section structure, separately tested, is here simulated by a V-strut. (Right). A portion of the bottom wing-skin, incorpor- ating an inspection- hole, shown after its fatigue test. a 750 hr overhaul life, were less liable to failure than pistonengines. Noise had never been any real problem, and the air- craft was never towed to the runway before engines were started.Underwing pressure refuelling made rapid transit times possible; normal turnround time was 40 minutes, although times as lowas 25 minutes had been achieved by B.O.A.C. Throughout the Comet 3's recent world tour it fitted into theairports easily and the standard navaids and meteorological facili- ties were found to be very satisfactory, with one exception: therewas a lack of D.M.E., vital to a jet airliner beginning its descent from cruising height at a predetermined distance from its destina-tion, usually 180 n.m. away. The upper air wind forecasts were very accurate throughout the tour and variations in forecast speedshad to be pretty big to have much effect on the flight time. On the mechanical side nothing out of the ordinary in the wayof ground equipment was needed by the Comet except for the provision of kerosene or JP1. The aircraft battery system wascapable of starting all engines when no ground unit was available. The Comet 3 had a high acceleration and a quick unstick, andpower was reduced to cruising setting by the time the end of the runway was crossed; the high rate of climb at the reduced settingmade the aircraft relatively quiet in the vicinity of an airfield. It was hoped for a great improvement with the fitting of theRolls-Royce nozzle, which did not, incidentally, prevent the use of a thrust reverser. There would be some price to pay in efficiencyand weight for the latter, and the authors had no doubt that the Comet 4 could be operated perfectly satisfactorily without suchreversers. If it was said that it was not possible to rely on wheel brakes on icy runways, how was it that North Stars managed tooperate continuously without braking propellers on icy runways? Nevertheless, an experimental reverse-thrust installation was justabout to be flown on a Comet 2. Perhaps the feature most remarked on by pilots convertingfrom a piston-engined transport to the Comet was the lack of deceleration when closing the throttles on landing. This feature,present in most jet aircraft, had been largely overcome by the pro- vision of big wing flaps. Conversion to the Comet was no longerthan that required to convert to another piston engined type: so far as flying and handling were concerned the Comet presentedno big problem, but what had to be impressed upon the jet transport pilot was that he had to stay up high to achieve range,any decision to divert had to be taken quickly and, in general, his mind had to work more quickly. N.Z. AGRICULTURAL AVIATION SHOW THE world's first "agricultural aviation" show is to be held,on November 9th and 10th, at Palmerston North, New Zealand. It is expected that this will be by far the biggestaerial display ever held in the Dominion, and a mass fly-past of 100 aircraft will probably constitute the largest single formationseen in the Southern Hemisphere since the war. The Aviation Industry Association of New Zealand, incollaboration with interested commercial organizations and Government Departments, is organizing the exhibition.Mr. E. R. Curtis, chairman of the committee, said recently that the show would be to a very large extent a display of theoutcome of the New Zealand Meat Producers' Board's decision to loan £250,000 to assist the development of the aerial top-dressing industry. In 1950, said Mr. Curtis, 5,000 tons of fertilizer were spread by the agricultural aviation industry and800 gallons of spray used. Respective figures for 1955 were 350,000 tons and 250,000 gallons.
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