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Aviation History
1936
1936 - 0779.PDF
332 FLIGHT. MAKCH 26, 1936. FOR OPEN-SEA RECONNAISSANCE The Saro London General-purpose Flying Boat : Robust Construction and Lozv Maintenance : Simplicity the Keynote of Design LATEST of a long '' family '' of flying boats, the London now being built at the Cowes works of Saunders-Roe, <*l Ltd., is a general purpose twin-engined type in which robustness, low maintenance cost, simplicity of con struction and seaworthiness were aimed at rather than a maximum of performance. The Air Ministry specification to which this machine was built called for these features, and the prototype machine passed its tests without difficulty. The production machines are now coming along, the work having been some what delayed by the necessity to build a new large erecting shop at East Cowes, Isle of Wight, before production in quantities could be under taken. The huge shed is now completed, and the necessary reorganisation of the works is well on the way to completion, so that the machines should be emerging at very short intervals during the immediate future. In its general design the Saro London follows the practice established by British flying boat de signers for a number of years, and is a twin-en gined flying boat with the two Bristol Pegasus III engines mounted on the leading edge of the top plane, a position which gives the airscrews a maximum water clear ance, so that it is only in exceptional conditions that they are not clear of water spray. The hull is of usual two- step type with vee bottom, but an innovation, from the hydrodynamic point of view, is the arrangement of the rear step, which is of less beam than the main hull at that point, so that a fore-and-aft step is between the chine of the step and the chine of the hull proper. In the London the hull beam is considerable, even towards the stern, in order to give a maximum of accommodation for crew, gear, and equipment. On the other hand, the rear step itself should not, for purposes of water performance, be too wide, and the particular step arrangement chosen was an outcome of these considerations. For several years it has been the practice of Mr. H. Knowler, Saunders-Roe chief designer, to use straight-line hull frames. This form is the simplest possible to manu facture, and has the further advantage that panel beating of portions of the hull planking is avoided. A plain vee bottom is, however, apt to be "dirty," as the water is thrown high into the air unless deflected by suitable shap ing of the hull. Some years ago most British flying boat hulls had curved vee bottoms, the vee at the keel being gradually flattened out as the chine was approached. The resulting curvature of the bottom planking called for a certain amount of shaping, and Mr. Knowler evolved a simpler way of achieving the same results. Instead of the straight lines of the bottom frames pointing towards the chines, he pointed them to wards a line some six inches inboard of the chine ; where this straight line cut the horizontal through the two chines he ran horizontal planking, which served to keep down the water, just as the curved bottoms of earlier hulls had done. The vee bottom was, of course, still sufficient to give the desired absorption of shock when alighting. Having evolved this straight-line type of framing for the hull, the Saunders-Roe designers did not wish to spoil the resulting simplicity of construction by introducing in ternal longitudinal stringers such as are commonly used in the construction of flying boat hulls. The stringers re quire a good deal of riveting to the hull planking, and it they are kept continuous from stem to stern the frames have to be cut out to accommodate them. If this is not done it becomes necessary to interrupt the stringers where they cross the frames, and gussets then have to be used for attaching stringers to frames. The scheme ultimately evolved was to form corrugations in the planking itself, spaced some six inches apart. By the stiffness which they introduced these corrugations took the place of riveted-on
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