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Aviation History
1955
1955 - 0325.PDF
TRANSPORT AIRCRAFT, 1955 . . . Medium-range Transports. Types which can be consideredunder this heading vary greatly in capacity, configuration and cost—from the £300,000 fifty-seater with four turboprops to theex-military piston-engined twin of half the capacity and perhaps one-twenty-fifth of the cost. Broadly speaking, their commontask is the connection of cities over distances of 150 to 1,500 miles, often spanning international frontiers and sometimes involv-ing short sea or ocean crossings. It is in the medium-range market that Vickers-Armstrongs have scored a great success for the Britishaircraft industry with the sale, to date, of nearly 180 Viscounts of which about 50 have been delivered. Performance figures for the Viscount are best quoted in generalterms, since each airline uses a separate model, identified by its own series number, its characteristics being determined by "cus-tomer requirements" and the type of Dart fitted. Progressive development of the Rolls-Royce Dart turboprop has, of course,made possible the considerable increase in size of the production Viscounts. Whereas the early prototype Series 630 had 36 seatsand a gross weight of less than 40,000 lb, the 48-seat Viscounts now being delivered have a gross weight of 60,000 lb. An example of the current-model Viscount is the Series 724for T.C.A., a 48-seater powered by four Dart 506s each delivering 1,400 s.h.p. plus 365 lb thrust (equivalent to about 1,600 h.p.)at take-off. The aircraft has a cruising speed of 320 m.p.h. at 22,000ft and a still-air range of 1,500 miles with an 11,000 lbpayload. Most of the Viscounts ordered but not yet delivered will be ofthe 700D family, this designation denoting the installation of Dart 510s, units offering improved performance and economyover the entire operating range. Take-off rating of the Dart 510 is equivalent to 1,700 e.h.p. Viscounts using this engine will carry230 Imperial gallons more fuel internally than the Series 700s (which have a capacity of 1,720 gallons), effectively postponingthe point at which the payload-range curve begins its descent and making the aircraft more attractive to operators of longer routesin the medium-stage band. The Viscount 700D's operational radius can be still further extended by the fitment of two 145-gallon external "slipper" tanks; these give the aircraft a still-air range of 2,410 miles with a 7,450 lb payload. The latest type of Viscount to be announced is the Series 802,twelve of which have been ordered by B.E.A., with delivery beginning in about 15 months' time. The Viscount Series 800is designed to translate the extra power of the Dart 510s into payload rather than range; over stages of up to 500 miles it willcarry a maximum payload of 14,200 1b, compared with 12,800 lb for the 700D. A 46in fuselage "stretch" will be accompanied bya 65in rearward movement of the aft pressure bulkhead, permitting 14 rows of seats to be installed instead of the customary ten(five-abreast) or 12 (four-abreast). Viscount 800s will thus be able to accommodate up to 70 passengers. Other features includea 5ft by 4ft rectangular forward door for freight loading; adjust- able galley and forward bulkhead; folding seats and strengthenedcabin floor in the forward part of the aircraft for composite passenger/freight duties. All-up weight will be increased by2,000 lb. Vickers viscount 724 for Trans-Canada Air Lines, a 48-seater powered by four Rolls-Royce Dart 506s. Standard American medium-range transports, both powered by two 2,400 h.p. Double Wasps, are the Convairliner 340 (top) and, below it, the Martin 4-0-4. The twin-Avon Caravelle (below) is an ambitious French design due for its first trials this year; from the stage-length viewpoint, it does not fit easily into any of the accepted categories.
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