The ‘Flying Radiator’

Though it seems incongruous, from immediately after World War I until the early 1930s, a period of more than 10 years, the fastest aircraft in the world were not land-based fighters but float planes.

Though their large, drag-producing floats would seem to argue against high speed, aerodynamically well streamlined floats produced little more drag than the fixed landing gear of aircraft of this period, and high-speed float planes had another aerodynamic advantage.

Because the float planes took off and landed in protected bays, they had very long, smooth “runways” and thus could be designed with short wings with very high wing loadings. This necessitated long take off and landing runs, which the bays provided, unlike land based aircraft that had to fly into and out of short grass strips.

These high-speed floatplanes were a matter of national pride and a symbol of technological excellence. From 1920 to 1931 they completed in a speed competition for seaplanes, the “Coupe d’Aviation Maritime Jacques Schneider,” better known as the Schneider Trophy. The races were held on rivers or on the seaside and were very popular, often drawing crowds of 250,000 spectators, filled with the “zeitgeist” that all was possible and that technology would save the world.

Only the most technologically advanced countries competed ― the U.S., Great Britain, France and Italy ― and the rules were that if an aero club won the club three times in five years, it could retire the cup. Each edition of the race was to be hosted by the previous winning country.

The races were initially held annually. The first two were won by Italy, and Great Britain won one. The U.S. won two in a row, the second flown by Jimmy Doolittle at a speed of more than 230 mph – 60 mph faster than the previous winner.
But just as the U.S. seemed ready to retire the trophy, Italy won in 1926. In 1927 Great Britain won again, and at this point it was decided to hold the races every two years to allow for more developed designs.

During the two year break, the aircraft designer for Britain’s Supermarine Company, Reginald G. Mitchell, refined every aspect of his float plane design. The biggest problem was the high-drag cooling radiators for the engine, so Mitchell designed a system of corrugated copper pipes blended into the fuselage, wing surface and floats the aircraft skin, with the coolant flowing through pipes. Mitchell’s design, the S.6, which he described as a “radiator with wings,” carried a new 1,900 horsepower and won the 1929 cup with a top speed of more than 328 mph.

Great Britain seemed to be on the verge of retiring the cup in 1931 when the Great Depression struck and the British government withdrew support from the project in early 1931, despite an earlier pledge of government support. It seemed like the 1931 trophy would be taken by Italy, France or Germany when an outcry from the British public arose, and the Daily Mail newspapers launched a public appeal that raised enough funds for the Supermarine aircraft to compete in 1931. In a few months, Mitchell re-engined his design, called the S. 6B, to carry a new 2,300 horsepower Rolls Royce.

But when the race was held at Calshot Spit, U.K., on Sept. 13, 1931, accidents had eliminated the other countries’ contestants. In front of a crowd estimated at half a million people, the Supermarine aircraft flew the course and took the cup for Great Britain permanently.

While this ended the completion, the results were far reaching. Reginald Mitchell used the work he put in to streamline his S.6B to his next design ― the immortal Spitfire fighter.

(For questions or comments, contact Dr. Michel at marshall.michel@spangdahlem.af.mil.)