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Swales SD3-15



This single-seater 15m span sailplane is designed especially for use by clubs and small syndicates, with the emphasis on low running costs and capital outlay together with safe flying qualities. Available in two forms, as the SD3-15T with a T-tail and the SD3-15V with a V-tail, the Swales was developed from the Birmingham Guild BG 135 Gipsy, the 13.5m span version of the BG 100/12 designed by J. C.Gibson, K. Emslie and L. P. Moore of Sailplane Design Ltd. Manufacturing rights of the BG 135 were acquired by Yorkshire Sailplanes Ltd, who built a batch of seven as the YS 55 Consort. The BG 135 was itself developed from the earlier and very similar Birmingham Guild Gipsy 12/15 project which, like the BG 100/12, was intended to be a low cost lightweight Standard/Sports Class sailplane in which either a medium-performance 12m wing or a high performance 15m one could be fitted to a common fuselage and tail unit. This was to be achieved by special attention to structural efficiency resulting from efficient wing skin stabilisation, with rigid foam cores, and low cost was achieved by eliminating taper as well as twin-skin sandwich or ribbed forms of construction. The prototype BG 100/12, with a 12m (39ft 4in) span wing, first flew on 7 April 1970 and, like the later SD3-15V, was a cantilever shoulder-wing monoplane of all-metal construction with a V-tail and a large hinged moulded cockpit canopy; a 13.5m span wing was later fitted.
Construction of the prototype SD3-15 began in September 1974 and it first flew in March 1975, being designated SD3-13V. The first prototype SD3-15V first flew in July 1975 and the first SD3-15T made its maiden flight in December 1976, the suffix letter denoting the tail configuration; six SD3-15s had been built by mid-1979; production was then only to order and was restricted to the T-tailed SD3-15T.
Structurally, the SD3-15 is very similar to the BG 135 and BG 100/12 from which it was developed; the constant chord wings have metal and polystyrene ribs and glassfibre reinforced plastic (GRP) wing tips, and the trailing edge flaps also act as air bakes. The plain metal ailerons have foam ribs. The metal skinned semi-monocoque fuselage has a GRP nose cone and is built up on four longerons. The landing gear consists of a non-retractable monowheel with an internally-expanding brake, and a tailskid. Both versions have a metal tail unit with 50% foam ribs; the SD3-15T has a full-span elevator with spring trim while the SD3-15V has all-moving tail surfaces with anti-balance tabs. The cockpit canopy opens sideways to starboard.
Span: 15.0 m / 49 ft 2.5 in
Length: 6.1 m / 20 ft 0 in
Height: 1.30m / 4 ft 3 in
Wing area: 9.57 sq.m / 102.0 sq.ft
Aspect ratio: 23.7
Wing section: Wortmann FX-61-168
Empty weight: 222 kg / 490 lb
Max weight: 330 kg / 728 lb
Water ballast: None
Max wing loading: 34.48 kg/sq.m / 7.06 lb/sq ft
Max speed: 125 mph / 109 kt / 201 km/h (in smooth air)
Max aero-tow speed: 90 mph
Stalling speed: 35 kt / 65 km/h
Max rough air speed: 86 kt / 159 km/h
Min sinking speed: 0.73 m/sec / 2.4 ft/sec at 48.5 mph / 42 kt / 78 km/h
Best glide ratio: 36:1 at 55 mph / 48 kt / 89 km/h




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