A major variation to the 9F design was imported from Austria, where Dr Adolph Giesl-Gieslingen had developed a draughting system intended to reduce 'back pressure' and enable exhaust to escape even more freely than with a conventional double blastpipe and chimney. His theory was that the smokebox vacuum and, therefore, the forward draught on the exhaust, would be enhanced by using several blastpipe nozzles feeding into a chimney flattened in the direction of travel. It was a combination of a multiple-jet blastpipe and a conventional double chimney. The first application of the Giesl ejector, as it became known, had been on a 2-8-2 of the Baltimore & Ohio Railroad in 1948. It was then used widely and with apparent success on the Austrian Federal Railway (OBB) and in 1956 its progenitors offered it to the British Transport Commission as a way of coping efficiently with poor-quality fuel. Perhaps wary of another Franco-Crosti debacle, Riddles' successor, Roland Bond, firmly declined.
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