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Aviation History
1963
1963 - 0666.PDF
638 FLIGHT International, 2 May 1963 TRIDENT . . . set about forming their own group, and agreed with Fairey Aviation and Hunting Aircraft to form a consortium known as the Aircraft Manufacturing Company to build the 121, none of the partners losing their separate identity. The Minister said that this was not quite what he had had in mind, and during the ensuing months of wrangling the airline and the winner of their design competition were unable to conduct any negotiations, or attempt to finalize the 121 specification. Eventually, after he had received the fullest and most detailed information on the design and manufacturing strength of the three partners, and the most binding assurances that they would not fail to meet BEA's requirements, the Minister permitted the programme to proceed. On January 30, 1958, Airco was announced publicly, financed 67 J per cent by de Havilland, 22J per cent by Hunting and ten per cent by Fairey. Hunting were entrusted with the detail design and manufacture of the outer wings, ailerons and flaps, and Fairey with the detail design and manufacture of all tail surfaces. On February 12, 1958, the Ministry of Transport and Civil Aviation announced that BEA were being allowed to negotiate with Airco for 24 "Airco D.H.121" airliners, with an option on 12 more. On August 1 of that year the same Minister gave his per mission for the contract to be completed; but the documents were not signed for more than a year. In the intervening period BEA and de Havilland had both come to the conclusion that the 121 design had been allowed to grow too large, and early in 1959 it was agreed that future traffic trends called for an aircraft of some 30 per cent smaller capacity. At this very late stage the 121 was accordingly cut down to accommodate a mixed-class load of 75 to 80, and Rolls-Royce were forced to abandon the RB.141 and start a smaller unit under the designation RB.163. BEA signed the contract on August 12, 1959, the value of the 24 aircraft and spares being some £28m. In all, the initial service date was delayed by about nine months because of indecision. On July 11, 1960, Mr Duncan Sandys, by now Minister of Aviation, announced that the Government had decided to offer financial help in launching the 121, the money being repaid by a levy on sales of the aircraft (similar to that imposed upon previous civil aircraft and engines receiving such support). By this time de Havilland had become a part of the Hawker Siddeley Group, and had on June 2 announced their intention to undertake the entire 121 programme themselves. Hunting had become part of British Aircraft Corporation, and Fairey had disposed of their British aviation interests (although a new Fairey subsidiary continued to participate in the programme under de Havilland sub-contracts). The 121 was that year named the Trident, and the clouds which had shrouded its early life dispersed. Design Development It is de Havilland's claim that the direct operating cost of the Trident over the stage-lengths originally emphasized by BEA is lower than that of any other aircraft. To some degree this is fortu itous. In 1959 the Trident was going ahead matched to the relatively good airfields of BEA's main network, whilst Boeing were complet ing the design of the 727, which—although it looks very much like the Trident—was planned to meet the demands of US operators serving such difficult points as New York La Guardia and Chicago Midway. Boeing went to great lengths to achieve a shorter field- length than de Havilland, as will be described in next week's issue. At one time many airlines felt that this gave the 727 an operating advantage; but today practically every one of the difficult runways, including that at La Guardia, has been lengthened; while Midway is no longer the main airport for Chicago. As it is, de Havilland calculate according to the ATA formula that cost per mile for the present Trident 1 is nearly 20 per cent lower than that for the 727, and cost per seat-mile some 5 per cent lower. Admittedly de Havil land have now increased the lift coefficient of the later Trident versions; but this has been done not to reduce field-length but to increase aircraft payload and range. Developments of the basic D.H.121 design were under consider ation at Hatfield as early as 1959. There were two main paths along which the aircraft could evolve. The first was simply to make a bigger aircraft, and the Trident 1A was in many respects very similar to the original BEA aeroplane with RB.141 engines. Weighing about 130,0001b, it had a larger wing with the sweep on the outer panels reduced from 35° to 32° and with improved flaps and leading-edge slats in order to meet American Airlines' require ments for a 5,000ft field-length. This would have been a ver\ different aircraft from the Trident 1, would have cost a great deal to develop and was little more attractive than the basic design. Instead de Havilland paid increasing attention to ways of improv ing the existing aircraft; and, as the results of extensive structure and tunnel testing became available, it became evident that the Trident 1 was unexpectedly amenable to "stretching." The first alteration was to seal the wing centre-section and turn it into a l,100gal integral tank (all gallons in this description are Imperial). This raised the weight of the aircraft from 107,0001b to a max of 115,0001b, and required slight local strengthening of the airframe. The resulting aircraft is known as the Trident 1C, and it has a greater range than the Trident 1. BEA decided to have the benefit of the higher takeoff weight of the 1C without incorporating the centre-section fuel system, although the latter can easily be fitted to any of the Trident Is now being built. Meanwhile, tunnel testing to find more lift continued, and results improved steadily. Many studies were made for Tridents with basic wing designs differing in detail from the original structure; and finally it was decided to proceed with a wing of slightly in creased span and flap area, with the leading-edge droop being replaced by slats. Fuel capacity was increased by a further 600gal. This aircraft is designated Trident IE. At the start of the 121 programme de Havilland had accepted that something must be done to increase the camber of a 600 m.p.h wing to make it lift adequately at low speeds, but had no reason to adopt any exotic scheme to achieve a very short field-length. They had therefore chosen the simplest possible solution: a droop ing leading edge in the form of inner and outer sections hinged near the bottom and driven by irreversible ball-bearing screwjacks. Such an arrangement could serve the entire leading edge right in to the body, and hot air could readily be pumped through for de- icing. It required fewer operating jacks and was some 5001b lighter than the best slat system. This is the scheme adopted on the Trident 1 and 1C. Tunnel testing at first showed that only slightly better lift coeffi cients could be achieved with a leading-edge slat. However, after many months of development, a slat giving a worthwhile improve ment over the simpler droop was evolved. The Trident IE has a revised leading edge with four sections of slat driven by screwjacks in a similar manner to the droop leading edge. In addition, a small Kruger flap is provided at the wing root. The Trident IE has 2ft 7in added to the tip of each wing, to improve takeoff performance and reduce induced drag in cruising
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