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Aviation History
1960
1960 - 1602.PDF
de Havillond Trident Trident flight deck Trident nose section Below, Trident fuselages THE DE HAVILLAND AIRCRAFT CO LTD Hatfietd, Herts. Telephone: Hatfield 2345 D.H.I2I Trident The three-engined, tripiex-systemed Trident represents a formula that has now been accepted by manufacturers and operators other than the de Havilland-BEA partner- ship that brought it into being nearly three years ago. It is essentially a jet transport for short ranges, i.e. for stage-lengths of up to 1,000 miles; but it can be developed for payload/range capabilities over ranges of up to 2,000 miles and a Mk 2 and other developments are in the project stage with these objectives in mind. The Trident was the result of a general specification issued by BEA to the British aircraft industry in July 1956 for a "second generation" jet airliner. A provisional order was placed in February 1958 with the now defunct Airco consortium headed by D.H.; the whole programme is now, of course, a Hawker Siddeley Group venture, for which de Havilland are technically responsible (Fairey Engineering and Hunting Aircraft remain as subcontractors). The original 121, as provisionally ordered by BEA, was much larger than the design subsequently adopted. It had three Rolls-Royce RB.141s, the steady development of which caused the design to grow too big (though it is not beyond the bounds of possibility that the RB.141 formula could be revived in a developed version). The design was revised round smaller engines, namely three Rolls-Royce RB.163s of 10,1001b static thrust. Maximum weight went down to 105,0001b and searing was reduced from 111 to a limit of about 100 in.all-tourist configuration. The rear-engined arrangement, pioneered by the CaraveUe, confers a wing that lends itself to high-lift devices, and the 121 has good airfield performance as well as good cruise performance. The argument for three engines has been strongly made, and this formula is claimed to be the optimum for this class of jet transport. It is said to satisfy most efficiently the conflicting thrust requirements of take-off and cruise—an aircraft of this class tending to be overpowered on take-off with four engines and overpowered in the cruise with two. Furthermore, a higher aspect ratio for a twin-engined aircraft would be necessary for the one-engine-out take-off case; and this is a further consideration weighting the argument against twin engines. British European Airways signed a firm contract for 24 D.H. Tridents in August 1959. They are scheduled for delivery from the middle of 1963. The first production aircraft is scheduled to fly in December 1961 and six more Tridents will join the flight test programme during 1962. A production rate of six aircraft per month is envisaged, given the orders. The Smiths blind-landing system, to be introduced first as autoflare and then as full automatic landing, is being designed into the Trident right from the start. The associated triplicated and triplex hydraulic, flying-control and autopilot systems are an integral part of the design, and for the first time operators will be able to operate punctual schedules in literally all weathers. Range of the Trident with the maximum payload of about 22,0001b makes possible a stage-length with fuel reserves of more than 1,700 statute miles. Field performance, basically a 6,000ft take-off in standard conditions, is claimed to be exceptional in hotter and higher conditions. As far as economics are concerned, the cost per seat-mile with 82 mixed-class passengers over a thousand-mile range is claimed to be down to the magic figure of Id. With 100 economy-class passengers the cost would be even less. The makers put forward the significant claim that economic8 are not unduly sensitive to changes in cruising altitude, since estimated costs vary only about two per cent for each 10,000ft deviation. A useful feature in an aeroplane of this class is that masifflum landing weight is a very high proportion of maximum take-off weight, of the order of 95 per cent. This gives a high "residual range"—in other words, a capability of landing and taking off again repeatedly without refuelling. The broad strategy of the Trident might be described as a 600 m-pJ- jet with a 6,000ft take-off and "optimized" economics for the shorter trunk-route stages oi up » 1,000 miles.
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