During 1925, R. J. Mitchell was working on a new aircraft to compete in that year's Schneider Trophy competition. The decision to begin the design process was made jointly by Napier and Supermarine on 18 March 1925. Following the success of the Americans during the previous contest, Mitchell was fully aware of the need to reduce drag to increase speed. Supermarine's new design was for a mid-wing cantilever floatplane which resembled a French monoplane, the Bernard SIMB V.2, which had broken the flight airspeed record in December 1924. The new design was in marked contrast to the flying boats Mitchell had designed for previous Schneider Trophy races, which had won in 1922 and come third behind the American Curtiss CR seaplanes in 1923.
The designation S.4 was given by Mitchell, "S" standing for Schneider. He regarded the three previous Schneider Trophy entrants (the Supermarine Sea Lion series) as S.1, S.2, and S.3. The S.4 was the first Schneider Trophy entrant to be supported by the British government, who agreed to buy the aircraft if Supermarine and Napier covered the initial costs of development and construction.[6] The Air Ministry provided the British teams with greater freedom than was given by the US government to their designers.
The S.4 was a monoplane seaplane with an unbraced cantilever wing and semi-monocoque fuselage, powered by a specially developed version of the Napier Lion, developed to produce 700 horsepower (520 kW) over a short period.[8] The aircraft was primarily constructed from wood: the single-piece unbraced wing had two spars with spruce flanges and plywood webs, and was covered with plywood braced by stringers. The fuselage had a covering of diagonally laid spruce planking over plywood formers constructed around a pair of steel A-frames, to which the engine bearers and wing spars were attached and which carried the floats. The single-step floats were metal. The S.4 lacked the newly designed surface radiators, at that time still unavailable, but it was aerodynamic and also judged to be aesthetically pleasing.
In September 1925, the magazine Flight reported:
Perhaps one may describe the Supermarine-Napier S.4 as having the appearance of having been designed in an inspired moment, but having all that is considered best in British construction incorporated in its details. That the design is bold, no one will deny, and we think the greatest credit is due to Mr. R. J. Mitchell, chief designer of the Supermarine Aviation Works, for his courage in breaking away from stereotyped methods and striking out on entirely novel lines.
Photo-Description:
Supermarine S.5 replica
Thorpe Park. Basic scan of slide taken on 7 August 1981
