BR Standard Class 9F - Design Features

Design Features

The 9F was designed at both Derby and Brighton Works in 1951 to operate freight trains of up to 900 tons (914 tonnes) at 35 mph (56 km/h) with maximum fuel efficiency. The original proposal was for a boiler from the BR Standard Class 7 Britannia 4-6-2, adapting it to a 2-8-2 wheel arrangement, but Riddles eventually settled upon a 2-10-0 type because it had been successfully utilised on some of his previous Austerity locomotives; distributing the adhesive weight over five axles gave a maximum axle load of only 15 tons, 10 cwt. However, in order to clear the rear coupled wheels the grate had to be set higher, thus reducing firebox volume. There were many problems associated with locomotives of such a long wheelbase, but these were solved by the design team through a series of compromises. The driving wheels were 5 feet 0 inches (1.52 m) in diameter, and the centre driving wheels were without flanges, whilst those on the second and fourth coupled wheels were reduced in depth. This enabled the locomotive to round curves of a radius as small as 400 feet (120 m). As on all other BR standard steam locomotives the leading wheels were 3 feet 0 inches (0.91 m) in diameter.

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