Short Knuckleduster
| R.24/31 (S.18 Knuckleduster) | |
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| Short S.18 'Knuckleduster' (K3574), at Felixstowe, 1934 | |
| Role | General purpose flying-boat |
| Manufacturer | Short Brothers |
| Designer | (Sir) Arthur Gouge |
| First flight | 30 November 1933 |
| Retired | 1938 |
| Status | Prototype |
| Primary users | Short Brothers Marine Aircraft Experimental Establishment (MAEE), Felixstowe |
| Produced | Rochester |
| Number built | 1 |
The Short R.24/31 (or Short S.18 and nicknamed the Knuckleduster) was a British twin-engined, high-wing cantilever gull winged monoplane flying-boat designed and built by Short to Air Ministry specification R.24/31 for a "General Purpose Open Sea Patrol Flying Boat". The contract also specified the use of the experimental Rolls-Royce Goshawk engine. The Saunders-Roe London and the Supermarine Stranraer competed successfully for this contract.
Although it never saw military service, the Knuckleduster provided useful information on the steam-cooling of engines and the handling of monoplane flying-boats; much experimental data gathered contributed to the design of the successful Empire and Short Sunderland aircraft.
The British Air Ministry issued its Specification R.24/31 for a "General Purpose Open Sea Patrol Flying Boat" in 1931 and ordered one prototype from each of Saunders-Roe, Supermarine and Shorts. Whereas the other two companies opted for traditional biplane designs, Shorts decided to produce a more modern, all-metal monoplane aircraft with the experimental steam-cooled, cast block Rolls-Royce Goshawk engine, itself a development of the smaller Kestrel engine.
The Knuckleduster's straight-sided hull was of all-metal (Alclad) box-section construction, from the bow as far as the pointed main step at the rear of the planing bottom; aft of the main step the fuselage was of monocoque construction. The central section of the hull was boxed and braced by diagonal frames to bear the loads from the wing-root attachments.
The wing sections inboard of the engines were attached at a 30° dihedral angle, thus providing sufficient clearance for the airscrews from water-spray during takeoff. The wings were designed for high torsional stiffness, each comprising a box-spar with four tapered stainless steel tubular booms. Fuel tanks were mounted within the wings; sprung and braced wingtip floats were fitted. The wing surfaces were of fabric.
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