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Aviation History
1953
1953 - 0379.PDF
ENGINEERING the VISCOUNT Structural Design and Equipment of the World's First Turboprop Airliner A FTER collating the facts for this article the writer is r\ more than convinced that whoever buys a Viscount gets his money's worth. Without any doubt, there has never before been so completely equipped an airliner of this size. The most significant single feature, of course, is the Dart powerplant (pages 368-371). But Vickers-Armstrongs have built around these engines a truly fine aircraft, and one which will do much to enhance the prestige of the British aircraft industry. Much of the development work entailed in bringing the Viscount to the operational stage was, either directly or indirectly, caused by the high cruising altitude decided upon. But, far from being a "premature test-bed of an airliner," as a transatlantic spokesman once kindly put it, the Viscount is today a well-proven (2,600 hours flying) vehicle with clearly pronounced characteristics of safety and comfort: it carries its kerosine fuel in flexible-bag tanks, and it has bigger windows and better furnishing than any of its competitors. When its other virtues are allied with its smooth flight and economic appeal it becomes an overwhelmingly attractive proposition to the operator of stage-lengths under 1,200 miles. The Airframe.—The fuselage is a conventional modern stressed-skin structure and, except for the rear portion, the tail cone and the nosewheel bay, is pressurized throughout to a differen tial of 6J lb/sq in. It is built up on standard frames formed from two or more segments of channel section, in 20 or 22 gauge, with swaged webs and lipped flanges. Each frame includes a floor beam or, between stations 26 and 112 (the numbers denote inches from the nose), a strong, braced web carrying the pressure-roof ove£ the nosewheel well. Special frames at the wing leading-edge, spar and trailing-edge stations provide six wing-attachments on each side; further built-up frames are provided carrying the attachments for the tail surfaces. The stringers pass outside the frames and through incisions in shear members, the latter acting as links between the skin and the frames. The skin itself is Alclad sheet in from 22 to 18 gauge, flush-riveted to the stringers and reinforced with heavier gauges around openings. The panels are lap-jointed. The rivets in thicker parts of the skin are dimpled and those used at seam joints or boundaries in the pressure cabin are mushroom-headed. The flight-deck floor, which extends from the nose to station 132 (the pressure wall behind the nosewheel bay), is formed from sections of lap-jointed sheet, carrying many pipe adaptors for the various controls and systems. From station 132 the floor of the passenger cabin extends a distance of some 53ft to the rear pressure-bulkhead, and in the Viscount 701 is made from multi ply birch panels, stiffened with Z-section transverse beams and top-hat-section stringers. Each panel is edged with metal and those along the central gangway are secured with 4 B.A. counter sunk screws to permit access to the underfloor services; the remainder of the floor is flush-riveted. A pressure differential of 6| lb/sq in is, in the present state of knowledge, bound to influence the structure greatly. As an example of such influence, the windscreen and hood assembly of the Viscount is noteworthy. Abaft the pilots' cockpit the fuselage begins to taper towards the nose; some discontinuity in skin is, therefore, unavoidable if circular section is to be maintained. The solution adopted is similar to that employed on the Canberra. A large aperture is left over the cockpit, around which is built a ring of heavy-gauge section which acts as a base for the hood. The hood itself is a 22-gauge Alclad dome, braced by pressings 'and channels and secured to the hood ring by |in bolts and rivets. Around the front are inserted five window-frames, and the whole assembly is finally faired-in with falsework to preserve a smooth external contour. The flooring in the Viscount is entirely at one level. Beneath it he the nose landing-gear in its unpressurized bay; the forward freight hold; and a mass of air-conditioning, cabin-pressure and de-icing equipment and ducting. The prominent scoop under the rear fuselage collects cooling air for the cabin heat-exchangers, as will be described later. There are five main doors: two on the port side; one to star board, giving access to the rear freight hold; and two on the lower
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