Supermarine S.4

An advanced monoplane racer, developed by the British for the 1925 Schneider trophy race, was the Supermarine S-4. The Schneider race was an international event for seaplanes. The S-4 is a beautiful, highly streamlined, cantilever monoplane mounted on twin floats. The wing, constructed of a wooden framework covered with plywood, employed flush radiators that were not of the skin type. The wings had landing flaps that could be geared to the ailerons. The rear of the fuselage was of wooden semimonocoque construction, and the forward portion containing the engine was of metal.

The engine had 12 cylinders arranged in 3 banks of 4. The engine gave the appearance of the letter "W"; accordingly, this cylinder arrangement was referred to as a W-type engine. The characteristics of the aircraft contained indicates a drag coefficient of 0.0274, which must be considered quite low in view of the large amount of surface area of the exposed twin floats. The wing loading of about 23 pounds per square foot was high for the period and accounts for the use of the wing trailing-edge flaps.

Another important factor that allowed the use of such a high wing loading was the relatively long take off and landing runs possible with the use of rivers and harbours, as compared with the confined land airfields of the day. The aircraft was destroyed by wing flutter before the 1925 Schneider trophy race. The ailerons on the S-4 were unbalanced, which no doubt contributed to the onset of wing flutter at the high speeds of which the aircraft was capable. Flutter and divergence of cantilever monoplane wings were not understood at that period in the development of aeronautical technology.

Later Supermarine racers, which were quite successful in subsequent. Schneider trophy competitions, employed the more predictable wire-braced monoplane wings. The designer of the Supermarine S-4, R. J. Mitchell, later designed the famous Spitfire fighter of World War II.