Supermarine S.6B  (S1595)  [@ Science Museum]

The Supermarine "S" series were one of the major technical achievements in British aviation between the two world wars. The series produced a line of racing seaplanes designed by R. J. Mitchell who went on to design the famous and innovative Spitfire.

Jaques Schneider, the French Under-Secretary for Air, first announced the Schneider prize for seaplanes in 1911, with a prize of the then huge amount of £1,000. The purpose of the competition was to encourage progress in civil aviation but became a contest primarily about speed. In the twenties the competition acted as a spur to aircraft development with the result that aircraft speeds rose from 150 mph at the end of the WW1 to over 400 mph in 1931.

The first event, held in Monaco in 1913, was won by the French pilot Maurice Prevost in a Deperdussin with an average speed of 45.75 mph. Britain won the trophy in 1914 in Monaco with C.H.Pixton flying a Sopwith Tabloid at an average speed of 86.7 mph. The competition was suspended throughout WW1 and re-established in 1919 when Supermarine entered for the first time with the Sea Lion. Held in Bournemouth in foggy conditions and with the mistaken application of the rules by the judges no body actually won. The Sea Lion retired due to sustained damage in practice.

Both of the 1920 and 1921 events were held in Venice and won by the Italians flying a Savoia S12 (107.2 mph) and a Macchi M7 (117.2 mph) respectively. Under the Schneider Trophy (photograph, left, shows the original Schneider Trophy at the Science Museum), if Italy won for a third consecutive time then it would keep the Trophy. Under mounting pressure from the British press for our aircraft industry to respond, Supermarine took up the challenge with the Mitchell designed Sea Lion 2. Based upon the previous Sea Lion biplane, the new entry was of a more streamlined design with a reduced wingspan and all superfluous fittings including the landing gear removed. With the Italians acknowledged as the world leaders in aviation design a victory looked certain. Challenging them in the 1922 competition, around the Bay of Naples, were the French and the Sea Lion. With an average speed of 145.7 mph the Sea Lion’s pilot, Henri Biard, managed victory over the Italians by just 2.5 mph. The Sea Lion's win had not only boosted the company but Mitchell’s profile as a designer.

For the 1923 Schneider race, which was held at the Isle of Wight, Supermarine entered the Sea Lion 3 which was basically the Sea Lion 2 but with a modified hull and a more powerful Napier engine. Needless to say the plane was beaten by a Curtiss R3 biplane, with its compact D12 engine, of the United States Navy (piloted by T. Rittenhouse) which attained speeds of over 177 mph. The Fairey Aircraft Company was so impressed with the new engine that it purchased some and fitted them to the new Fairey Fox. The Fox was a light bomber and so fast that it could not be caught by any contemporary RAF fighter. The 1924 contest was declared void since no other nation turned up to challenge the Americans.

Mitchell realized that there was a basic design problem with the biplane – the large lifting surfaces of the wings, while allowing aircraft to remain lightweight, resulted in a large amount of drag. His solution, still powered by the Napier Lion engine, was the innovative S.4 with its ultra-streamlined fuselage, twin floats instead of the flying boat design, and cantilever wings with no external bracing. During trials on Southampton Water, the plane shattered the world speed record, reaching 226.75 mph. During the 1925 Schneider competition over Chesapeake Bay, at Baltimore in the USA, the S.4 developed a violent wing flutter at 8,000 feet forcing the plane into the sea at high speed. Fortunately Biard survived, but with severe injuries, and the revolutionary S.4 was written off. Later research suggested that the S.4’s wing flutter might have been caused by over large ailerons, though it may also be possible that Biard, unused to such an innovative machine, misjudged a turn and stalled it. The race was won by a Curtiss R3C flown by James Doolittle of the USA with an average speed of 232.5 mph. Doolittle later went on to win fame with his audacious raid on Tokyo during WW2 when 16 B.25B Mitchells were lunched from the aircraft carrier USS Hornet.

Supported by Supermarine and now the Air Ministry, Mitchell started work on improving the S.4, particularly dealing with the rigidity of the wings and the poor visibility. The S.5 (photograph - below) had a low wing, supported by wire braces to overcome the flutter problem, while the largely metal fuselage was much narrower than on the S.4 which meant that the fuel had to be carried in the floats. Further streamlining was achieved by removing the obtrusive radiators of the S.4 and replacing them with double-skinned surface coolers made of copper sheet. Despite the very advanced features of the S.5 in one way it was actually a "step backwards" from the radical S.4 in that it used external bracing wires to strengthen the wing. The S.5 was not ready for the 1926 Schneider competition which was won in the USA by the Italians. Major de Barnardi piloted a Macchi M39 to victory with at an average speed of 246.5 mph. With the RAF providing serving pilots from the High Speed Flight, both 1st and 2nd places were taken by S.5s in the 1927 Venice based competition. Flight Lieutenant Sidney Webster piloted the winning S.5 to victory at an average speed of 281.65 mph. In fact the British aircraft industry was there in strength with entries from the Gloster and Shorts companies as well. The engine shown above is a Lion V11. It was a specially designed and geared racing engine and was fitted to the Supermarine and Gloster seaplane racers.

Supermarine S.5  (photograph of a photograph)  [@ RAF Hendon]

The photograph shows an S.5, with its Lion engine, on the slipway at the Supermarine Aviation Works at Woolston, Southampton.

All nations now agreed to a two year gap between races as aircraft and engines were getting more complex and two years would be needed to introduce the innovations. Following the success in the Schneider competition Supermarine was floated on the Stock Exchange in 1927 and in the following year the entire share capital was bought by Vickers Aviation, a subsidiary of the giant Vickers Armstrong armaments and shipbuilding group. Supermarine was essentially acquired for the design talents of Mitchell whose contract now prevented him from leaving Supermarine/Vickers before 1934.

In 1928 there was a crash of an S.5 in which Flt Lt Kinkead of the High Speed Flight was killed. However, by early 1928 Mitchell had decided that in order to seek significant improvements to the performance of the S.5 the Napier Lion engine needed a design replacement. Mitchell visited Sir Henry Royce who at the time of the visit was working on a new engine called the Buzzard which offered a substantial increase in performance over previous models. After discussions with Mitchell he agreed to adapt the Buzzard for use by Supermarine. What he built, after just six months of redesigning, was the potent 37-litre "R" [photograph - below] engine, which featured a large supercharger and gave over 1,900 horsepower.

  

Designed around the "R" engine, the S.6A was a physically larger aircraft than the S.5 so as to accommodate the larger engine. With wings made of the lightweight alloy duralumin it had a similar appearance to the S.5. On 7th September 1929 Flight Lieutenant H. R. D. Waghorn piloted the S.6A to a Schneider victory at an average speed of 328.6 mph, over 43 mph faster than the Italian who finished second. A few days after the race Squadron Leader A. H. Orlebar raised the world speed record in the S.6A to 357.7 mph.

Supermarine S.6A  (N248)  [@ Solent Sky Museum]

N248 was one of two S.6 seaplanes ordered by the Air Ministry in 1928 (along with two Gloster VIs) for the 11th Schneider Trophy Contest of 1929. Bearing the Race number 8, N248 was flown by Flight Officer R. L. R. Atcherley who was disqualified for turning inside one of the marker pylons. However, he did set up new World Speed Records for the 50 and 100 km closed circuits of 331 and 332 mph respectively. In 1931 N248, together with its sister, N247, was modified to bring it up to the S.6B standard. In the 1950s it was put on display on the Royal Pier in Southampton bearing the incorrect serial number S1596 (i.e. the second S.6B, S1595 being the other). It was later removed from the Pier and stored by the RAF, only appearing for special events such as the RAF's Jubilee Review. In 1976 it returned to Southampton for display in the R.J.Mitchell Memorial Museum and then its true identity came to light. N248 was then taken to the British Hovercraft Corporation at Cowes (the old Saunders-Roe aviation works) where it was stripped down and repainted in its 1931 colour scheme before being returned to Southampton for display in the Museum.

Supermarine S.6A  (N248)  [@ Solent Sky Museum]

The Labour government of Ramsay MacDonald, beset by economic crisis, announced that it would not provide any funds to support the British Schneider entry. According to the Air Minister, the Trophy was “in the nature of a sporting contest”, so private enterprise would have to meet the costs. At the eleventh hour, rescue came in the form of a £100,000 cheque from Lady Houston, reputedly the richest woman in England. Mitchell, under severe time pressure, set about modifying the S.6A. The S.6B had an extended fuselage to accommodate the more powerful "R" engine (now giving 2,350 horsepower) and the associated extra fuel and cooling surfaces. During the Schneider week, held in September 1931 at Calshot, near Southampton,  S1595 piloted by Flight Lieutenant Boothman reached a world record speed of 379.05 mph (average speed of 340.1 mph). Unfortunately the French and Italians were forced to withdraw because of engine trouble and Britain enjoyed an uncontested victory.

Supermarine S.6B  (S1595)  [@ Science Museum]

S1595 represents one of the major technical achievements in British aviation between the two world wars. It is the aeroplane that won the 1931 Schneider Trophy outright for Britain. Two weeks later Flight Lieutenant George Stainforth broke the 400 mph barrier by flying S1595 at 407.5 mph, an astonishing speed in an era still dominated by biplanes.

It was inevitable that the Air Ministry/RAF would want to utilize the exceptional talents of Mitchell for military purposes; unfortunately, the appropriate political will power was absent. Eventually the Schneider competition gave birth to the Spitfire, the Italian Macchi fighters and established the low drag liquid cooled engine as the fast fighter designer’s principal choice for power. Only later in the WW2 did the approach change with the success of the German FW 190 and the American Corsair and Thunderbolt.