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Aviation History
1955
1955 - 0069.PDF
69 (Left) The first and second production Bri- tannias drawn up behind the three-bay assembly building. G-ANBB, the second aircraft, is seen immediately below un- dergoing a pre-flight test, with the first Bri- tannia 300 fuselage vis- ible to the right. In the third view, ground-run- ning of Proteus 705s is seen from an unusual angle. "Flight" photographs when performance measurements have been required at com-paratively low levels, the equivalent cabin "altitude" has been some 2,000ft below sea level. Though the Britannia cabin wasdesigned for a maximum differential pressure of 8i lb/sq in, the differential has temporarily been restricted to 6f lb as a pre-cautionary measure pending further data from current research into pressure-fatigue problems. A maximum differential pressure of 6f lb allows 5,000ft con-ditions to be maintained in die cabin at altitudes of up to 25,000ft, increasing to an equivalent cabin altitude of 10,000ft at35,000ft. The maximum height reached by Britannias—and then only at the end of the longest stages—will be 35,000-36,O0Oft.Bristol's confidence in the structural design of the Britannia's pressure-cabin is reinforced, therefore, by the knowledge that itcan be operated at less than its designed working pressure without prejudice to economy or appreciable effect on comfort. Every aircraft development programme is susceptible to addi-tions or alterations in die light of later aeronautical knowledge. In the case of the Britannia, the outstanding example is theA.R.B.'s revision of pressure-cabin test requirements, which have not yet been fully determined. It is not, however, the only example.An aircraft of the Britannia's size and technically novel concept does not achieve certification on the basis of the airworthiness andperformance requirements in force at the time of its design: new requirements emerge throughout its development Life, somewritten around unique features of the new aircraft concerned, others reflecting experience built up from the operation of earlieraircraft of comparable function. One or two examples may be quoted. The Britannia will be the first British transport with landingdistances scheduled to include the braking effect of airscrew pitch reversal. The establishment of these distances (which vary,of course, according to the landing weight and other factors) in- volves an exhaustive series of tests, which must take into accountall the combinations of unfavourable conditions which could be met by airline pilots. It must be shown, for instance, that theaircraft can be brought safely to a standstill on a wet runway in a cross-wind with an inboard airscrew feathered; one outboardairscrew delivering full negative thrust in reverse pitch; and the other delivering full positive thrust after failure of the reversingmechanism on touchdown. This unpleasant set of circumstances has been among the emergencies simulated during the test pro-gramme at Filton. Approach speed is another of the variables which affect landingdistance. In the past, calculations have assumed that an aircraft crosses the 50ft screen at its approved approach speed, a certainpercentage being added to the measured distance by way of a safety margin. Observations at a number of airports have shownthat, in practice, "over-the-hedge" speeds are usually some way above the operating-manual value. This has resulted in the evolu-tion of a "rational" or "reference" method of calculating landing distances, entailing the assumption of a higher approach speed butallowing a smaller percentage addition to the measured distance. The method has been applied during the Britannia performancetrials, with the result that the aircraft has to be brought over the threshold some 15 kt faster man the approved speed for finalapproach; the touch-down must, of course, be made at the correct speed. Four of Bristol's pilots, in addition to Mr. Pegg, are qualifiedBritannia captains. Two of the three B.O.A.C. crews (each con- sisting of two pilots, a navigator, an engineer and a radio officer)have taken up residence at Bristol and the third is due there next month. The first Britannia flight by an all-B.O.A.C. crew,incidentally, took place some two weeks ago. 'THE BRIDGES AT TOKO-RI" THE film of this name, based on die story by James A.Mitchener, began its London run at the Odeon cinema, Leicester Square, last week. It is to be hoped that Flight readerswill not be dissuaded from seeing this excellent picture of carrier life during the Korean War either by the posters advertising thefilm or by recollections of misguided criticism of die book. While the photography remains carrier-borne or follows theactivities of the ship's Panther squadron, the film is at its best. True, there are sequences which will cause some of our Fleet AirArm stiff upper lips to break into a faint amused curve, but these are mainly due to differences between the British and AmericanNavies and not to faults in the film. Certainly the film has its faults: the problems of the pilot'swife are over-simplified in true Hollywood fashion, and much of what Mitchener wrote has had to be omitted, or only very brieflyimplied. But, as in die Fighting Lady films, die atmo- sphere and strange rituals of carrier flying have been well cap-tured and, happily, the new film has no happy ending. For these reasons alone the film of "Toko-Ri" would be well worthseeing.
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