Quote:
The test train consisted of three of the "Coronation" twin sets, plus the dynamometer car, seven vehicles in all weighing 240 tons."
From milepost 100, speeds at the end of each successive mile were 87½, 96½, 104, 107, 111½, 116, 119 m.p.h. (milepost 93), and then, at the ensuing half-miles, 120¾, 122½, 123, 124¼ and finally 125 m.p.h. at milepost 90¼, while the dynamometer record for a very short distance revealed the tremendous maximum of 126 m.p.h., the figure usually quoted, and at which the 6 ft. 8 in. driving wheels were doing more than 500 revolutions a minute. All this was at 40 per cent. cut-off with full regulator, increased between mileposts 94¼ and 93 to 45 per cent. Five miles (posts 94 to 89) were reeled off at an average of 120.4 m.p.h., and speed actually exceeded 120 m.p.h. for three miles continuously (posts 92¾ to 89¾). So the record was secure; Mallard had travelled faster, not only than the L.M.S.R. Coronation, but also than all other steam locomotives in the world whose high speed performances, properly authenticated by a sequence of passing times, are on record.
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The test was on a slight down slope, not conducted with any redundancy, hardly what we'd accept as official today. But! it was 1938 and the Germans had set the existing record of 124.5 in 1936. So the Brits pulled a tw, claiming the record and repeating the dubious claim over and over. It WWII had ended differently, it might be challenged.
They claim when Gresley designed the A-4 series he did a lot of wind tunnel sculpting. It was a big departure from previous steam locomotive design and streamlining imperative as speed was one big objective from the start. He wanted to build locomotives to run over 100mph in daily service, although they were rarely called on to do that. But the Mallard was special, this engine got a couple extra tweaks like a double chimney and double
Kylchap blastpipe, for better draughting and exhaust flow at speed. The Kylchap mixes steam with boiler exhaust in four stages to create a jet stream that sucks the exhaust out better at speed.