Supermarine S.4
Revolutionary British monoplane for the 1925 Schneider Trophy.
The Supermarine S.4 was a British single-engined monoplane built by Supermarine for the 1925 Schneider Trophy contest. Designed by R. J. Mitchell, it was considered revolutionary for its unbraced cantilever wing and wooden construction. Less than a month after its first flight, it set a world seaplane speed record of 226.752 mph.
Quick Facts
- Country of origin
- United Kingdom
- Manufacturer
- Supermarine
- Designer
- R. J. Mitchell
- First flight
- 24 August 1925
- Number built
- 1
Facts from the source article.
Design and development
In 1925, R. J. Mitchell began work on a new aircraft for that year's Schneider Trophy competition, a decision jointly made by Napier and Supermarine on 18 March 1925. This design contrasted sharply with the flying boats Mitchell had entered in previous Schneider races, which won in 1922 and placed third in 1923. The S.4 designation was Mitchell's own, with "S" standing for Schneider; he considered the three earlier Supermarine Sea Lion entrants as S.1, S.2, and S.3. The Air Ministry gave British teams more freedom than the U.S. government allowed its designers. The S.4 was a monoplane seaplane with an unbraced cantilever wing and semi-monocoque fuselage, powered by a specially developed Napier Lion producing 700 hp for short periods. It was built mostly of wood: the single-piece unbraced wing had two spars with spruce flanges and plywood webs, covered with plywood braced by stringers. The fuselage used diagonally laid spruce planking over plywood formers around a pair of steel A-frames, which attached the engine bearers, wing spars, and floats. The single-step floats were metal. Although the S.4 lacked newly designed surface radiators, it was aerodynamic and considered aesthetically pleasing.
Operational history
The S.4, carrying civil registration G-EBLP and Air Ministry serial N197, first flew on 24 August 1925, with Mitchell watching from a motorboat alongside Lord Mountbatten. Testing occurred at Calshot due to the long take-off runs required. Chief test pilot Henry Biard was reportedly uneasy with the S.4, disliking its unbraced wings and the cockpit position far behind the wings, which restricted forward view, especially during take-off and landing. On its maiden flight, this limited visibility nearly caused a collision with an ocean liner. On 13 September 1925, over a 1.864-mile straight course on Southampton Water, the S.4 raised the world seaplane speed record and British speed record to 226.752 mph, creating a press sensation when announced a month later. The S.4, along with two Gloster III biplanes, was shipped to Baltimore for the Schneider Trophy competition aboard the SS Minnewaska at no charge. During the voyage, Biard injured his wrist playing tennis. Bad weather at Bay Shore Park gave competitors little practice time; aircraft remained crated while canvas hangars were erected on the beach. Biard caught influenza but recovered enough to compete. Wind blew down the hangar holding the S.4, and a falling pole damaged its rear end. The aircraft was repaired in time for navigation trials on 23 October 1925. During these trials, the S.4 initially performed well, but on return to shore the control column oscillated violently and Biard lost control at high speed. The S.4 stalled and fell flat into the sea from 100 ft. Biard, initially unconscious while strapped in, resurfaced from the sea bed and clung to floating wreckage. The first rescue launch broke down; a second launch rescued him. Mitchell, aboard the rescue boat, jokingly asked Biard if the water was warm. Biard was later found to have broken two ribs.
Legacy
The Supermarine S.4 was a groundbreaking aircraft that was far more advanced than its contemporaries, establishing a design philosophy that would endure through the 1930s and 1940s. It featured cutting-edge floats, considered the most sophisticated of their time, and a wing without external bracing wires—a first for any Supermarine plane. Aviation historian John D. Anderson observed that the S.4 showed Mitchell’s readiness to blend new technology with a proven conceptual design approach, calling it a revolution that shaped every subsequent Schneider Trophy racer. The 1926 Schneider winner, the Italian Macchi M.39, bore a clear resemblance to the S.4. Mitchell applied lessons from the S.4 when creating its successor, the Supermarine S.5. The S.4 is often called Mitchell’s first major triumph. Footage of its construction and first flight, along with drawings, appears in Leslie Howard’s 1942 film about Mitchell, The First of the Few. The S.5 incorporated wire-braced monoplane wings to counter the wing flutter thought to have caused the S.4’s crash. It also had a narrower fuselage and sleeker floats for better speed. The biggest performance gain—roughly 24 mph—came from surface radiators, which cut drag. After the S.4’s loss, tests on a model at the National Physics Laboratory revealed that its Lamblin radiators created a third of the aircraft’s drag; without them, the S.4 would have been the world’s cleanest monoplane.
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