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Gnosspelius was head of the research department of Short Brothers, for whom he had devised an ingenious mechanism for testing aerofoil sections, the Gnosspelius Aerodynamic Pendulum.[2] Tests using this had indicated that incorporating a small step into the upper surface of the wing at the point of its greatest thickness would reduce drag, and Gnosspelius had started work on the design of a small glider using this discovery when, in early 1923, two prizes intended to promote the development of light aircraft were announced.
He accordingly revised his design to use a 679 cc Blackburne Tomtit V-twin motorcycle engine, driving a pair of chain-driven 4 ft (1.2 m) diameter pusher propellers[1] running at two-thirds of the engine speed. The resulting aircraft was a single-seat high-wing monoplane with a circular section monocoquefuselage made of spruce planking built up over elm hoops, with spruce frames for local reinforcement. The wing used the RAF 19 section, modified by the inclusion of a 3⁄8 in (10 mm) step in the upper surface. The thin wing section dictated the use of four spars, these being box sections with spruce flanges and 3-ply webs, and was built in three sections, the sections outboard of the propeller shafts being removable for ease of transportation. The wing had a parallel-chord centre section and outer sections with the leading edge swept-back to meet the fourth wing spar at the tip. The engine was mounted on duralumin bearers between the two centre spars. Wide-span ailerons were hinged to the rearmost wing spar, operated by torque-tubes with dog clutches at the junction between the centre section and the removable outer panels. The fixed undercarriage consisted of a pair of wheels on a short axle carried inside the fuselage, the lower part of the wheels projecting through slots.
Two aircraft were built by Shorts and the first one, registered G-EBGN, first flew on 26 May 1923 piloted by Short test pilot John Lankester Parker.[1] The second aircraft was unregistered and was flown at Lympne as No. 19; it crashed at Cramlington on 18 June 1926 killing the pilot.[1]
