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Aviation History
1934
1934 - 0417.PDF
FLIGHT, APRIL 26. 1934 FROM ABOVE : The Scapa " has a normal biplane wing structure, with struts and wires reduced to a minimum. The engines are Rolls-Royce " Kestrels." been issued, but from the fact that the prototype made a flight of ten hours it is evident that the maximum range is considerably in excess of 1,000 miles. Aerodynamic Design Quite remarkable care has been taken in the design of the " Scapa " to reduce head resistance. The hull itself has very clean lines, and on it is mounted a wing structure in which the number of parts has been reduced to a mini- mum. Apart from the slanting struts which carry the two Rolls-Royce " Kestrel " engines, there is but a single pair of inter-plane struts on each side. The engine nacelles themselves are of streamline form, and by placing the water radiators at the rear end of the nacelle, the usual unsightly and drag-producing excrescences are avoided. Lateral stability on the water is ensured by two wing-tip floats, also of low-drag form and mounted each on a single pair of struts. A monoplane tail is carried on the rising stern portion of the hull, to which it is braced by two struts on each side. Above the tail plane are mounted two vertical fins carrying horn-balanced rudders. The " blind " area caused by the tail is not, therefore, large, and the rear guns have a wide field of fire. • ••:-— Military Accommodation The " Scapa " has been designed to be used for recon- naissance, bombing, torpedo transport, and training and navigational instruction. The character of the military load carried will, of course, depend upon which of these functions the machine is fulfilling, but the arrangement of the crew's stations remains the same. In the extreme bows .•there is a special machine-gun mounting, which can be removed and stowed farther aft, leaving the front cockpit free for mooring operations, etc. This cockpit has, in the extreme nose of the hull, a hinged watertight door which is used for bomb sighting. Between the forward cockpit and the wings is the pilots' compartment, which in the " Scapa " is provided with a sliding roof and side windows. The. navigator and engineer are housed aft of the pilots' cabin, between it and the hull frame which carries the front lower wing spar, while slightly farther aft, between the two spar frames, is the W/T operator's station. Behind the wings are the two rear gun positions which, as already mentioned, afford very good tail protection owing to the shape and location of the tail surfaces. If the " Scapa " is being used for extended cruises, pro- vision is made for sleeping accommodation, food and water stowage, cooking table and other special equipment. Stow- age is also arranged for a collapsible dinghy, an engine ladder, an engine maintenance platform and a spare air- screw. Structural Features Light alloys and stainless steel are the chief structural materials of the " Scapa." The stainless steel is used mainly for highly stressed fittings, and the light alloy for planking, frames, wing spars and wing ribs. Doped fabric is used for covering the wings and tail surfaces. Extensive tank tests on models resulted in a hull form which combines low air drag with clean running on the water and good seaworthiness. At the same time, the hull form is not such as to call for very slow and expensive construction. The sides, for example, are flat, so that panel-beating (or " tin bashing " as it is called in the shops) is reduced to a minimum. The underwater portion, between keel and chines, is of curved vee form, the. curva- ture below the chine being designed to keep down the spray. The usual two steps are found in the hull bottom, the main step being approximately under the centre of gravity, while the rear step is placed well aft towards the stern. This arrangement has been found useful in pre- venting porpoising. Normal practice has been followed in the wing structure. Duralumin and Alclad being the materials used for spars and ribs, and stainless steel for fittings. The wings are of equal-span biplane form, and the ailerons, fitted to all four wings, have Frise balances. The one-piece elevator has a horn balance at each end, arranged in a somewhat unusual way. Instead of the horn balance of approxi- 417
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