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Aviation History
1957
1957 - 1601.PDF
FLIGHT, 1 November 1957 689 AIRLINERS OF THE WORLD VANGUARD Vickers-Armstrongs Aircraft) Ltd., Weybridge, Surrey EARLY five years of close consideration by Vickers of asuccessor to the Viscount, culminating in two years of detailed discussion between the firm and B.E.A., led to theCorporation drawing up a specification in the early pan of 1955. Prior to the issue of this specification—which ran to 50 pages andwas probably the most detailed requirement ever given to a manufacturer by an operator—Vickers had studied about 60different configurations for the new aircraft, including several with the high wing at one time favoured by B.E.A. The layout finallyselected incorporated Rolls-Royce Tyne engines, and both air- frame and powerplant have since developed together. The basis of B.E.A.'s specification was for an aircraft that, withthe special characteristic of an exceptionally large underfloor freight hold capable of accepting two-thirds of the maximumpayload at normal densities, would cater for the very seasonal nature of its routes. A profitable volume of low density freight canbe carried when passenger loads are normal, and 2t off-peak periods the Vanguard can be utilized primarily as a freighterwithout any conversion. There are other accrued advantages in freight handling, reduced turn-round time and the large workingspace available for access to systems. Vickers have estimated that a conventional "tube" layout would have cruised only 5 m.p.h.faster and weighed about 1,000 lb less. Since 1954, the design has also been developed to suit Americanrequirements (typified by T.C.A.), an all-freight version study has been made and the take-off weight has been increased to allow themaximum payload to be carried over stage lengths of up to 2,600 st m. A similar development process with the Tyne hasstemmed from Rolls-Royce. AIRFRAME Vickers have employed in the Vanguard acombination of safe-life and fail-safe philosophies, long fatigue life in primary components being combined with multiple loadpaths throughout. Stresses in the pressurized cabin skins have been kept to a maximum of about 12,000 lb/sq in and a safetyfactor of three is employed for the pressurization case. The wing box structure consists of three shear webs; in the event of failureof one, the remainder can deal with the loads. Single heat-treated alloy has been employed for predominantly tension members toobtain better ductility and reduce the likelihood of crack propaga- tion. Fatigue meters will be installed on each aircraft. Fuselage The passenger cabin-underfloor hold combinationof the Vanguard led to the adoption of a "double-bubble" fuselage; the floor datum is at the junction of the two portions. The wholefuselage, with the exception of the nosewheel bay, radome and tail-cone, is pressurized to a dP of 6.5 lb/sq in. Structure is conventional, open frames being fitted to stringersto which large skin panels are flush-riveted. The frames imme- diately adjacent to the door cut-outs are attached directly to theskin; half the load is taken in suitably reinforced plating and half in the boundary members, to guard against a failure of eitherbeing of a catastrophic nature. The windows, 26 by 19in ellipses, are basically identical with those of the Viscount; provision ismade for 35 standard windows, with an additional four over the mainplanes which are also emergency exits, and four "port-hole"type to cater for the higher seating configurations. The areas between the windows are protected by tear-stopping, closely-pitched vertical stiffeners attached directly to the skin. The eleven large windscreen panels are carried in a forged frame. The upperfloor, designed as a passenger and crew floor only, is composed of removable light-alloy panels stiffened by longitudinal channelsections. Rail fixings are employed for seats, bulkheads, and other furnishings. The freight floor is stressed to 150 lb/sq ft witha local intensity of 200 Ib/sq in. Six main doors, four giving access to the passenger compartmentand two to the freight holds, open outwards and are sealed pneumatically. A valve prevents opening at a dP greater than0.2 lb/sq in. The main entrance door, measuring 72 by 41in, is forward on the port side, and there is a second passenger entrancedoor of the same size at the aft end of the cabin. Both doors incorporate built-in hydraulically operated folding stairs. Thelatter are separate from the doors, which hinge outwards on parallel links to lie clear of the fuselage skin when the door is open.Opposite these doors are 64 by 26in emergency exits and pantry service doors and a third emergency exit, 48 by 24in, is providedto the rear of the main passenger door, on the port side. Each freight hold is served by counter-balanced doors 65in wide by46in on the starboard side, split longitudinally and opening up- wards and downwards. Wing Within the 15 per cent section wing (tapering to 13 percent at the tip) is a twin-cell torsion box structure comprising three shear webs and top and bottom integrally stiffened panels.The wing is divided into three main portions, the centre section (which contains no fuel), and the port and starboard mainplanes,each of which has a manufacturing joint immediately outboard of the outer engines. The wing comprises 54 stiffened panels tailoredfrom stretch-levelled duralumin planks varying in length from 12ft to 29ft, in width from 26in to 30in, and in thickness from1.75mm to 2mm. Top surface skins are D.T.D. 5020 (American equivalent 145-T6), and the lower tension skin is machined frommaterial to the U.S. specificatin 24 S-T4. The torsion box and its end ribs form the integral fuel tanks.Access to the interior of die tanks is gained through bolted panels in the top surface of the inner wings, and via access panels in thewebs of the outer wings. Tail The fin is divided into a lower portion attached to thesame frames as the tailplane, and an upper section joined to the lower by suitable fittings and removable pins. The rudder ismade as a single surface with a combined spring and trim tab along
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