The A4 class was designed by Sir Nigel Gresley as an express locomotive type to power high-speed streamlined trains. The wind-tunnel-tested,[1] aerodynamic body and high power allowed the class to reach speeds of over 100 miles per hour (160 km/h), though in everyday service it was relatively uncommon for any steam hauled service in the UK to reach even 90 mph, much less 100. Mallard was in service until 1963, when it was retired, having covered almost one and a half million miles (2.4 million km).
It was restored to working order in the 1980s, but has not operated since, apart from hauling some specials between York and Scarborough in July 1986 and a couple of runs between York and Harrogate/Leeds around Easter 1987. Mallard is now part of the National Collection at the United Kingdom's National Railway Museum in York. On the weekend of 5 July 2008, Mallard was taken outside for the first time in years and displayed alongside her A4 sisters, thus reuniting all four A4s extant in the UK for the first time since preservation. She departed the museum for Locomotion, the NRM's outbase at Shildon on the 23 June 2010, where she was a static exhibit, until she was hauled back to York on 19 July 2011 and put back on display in its original location in the Great Hall.
The locomotive is 70 ft (21 m) long and weighs 165 tons, including the tender. It is painted LNER garter blue with red wheels and steel rims.
Mallard is the holder of the official world speed record for steam locomotives at 125.88 mph (202.58 km/h). The record was achieved on 3 July 1938 on the slight downward grade of Stoke Bank south of Grantham on the East Coast Main Line, and the highest speed was recorded at milepost 90¼, between Little Bytham and Essendine. It broke the German (DRG Class 05) 002's 1936 record of 124.5 mph (200.4 km/h).
Mallard was the perfect vehicle for such an endeavour; one of the A4 class of streamlined locomotives designed for sustained 100+ mph (160+ km/h) running, it was one of a small number built with a double chimney and double Kylchap blastpipe, which made for improved draughting and better exhaust flow at speed; the remainder of the class were retro-fitted in the late 1950s. The A4's three-cylinder design made for stability at speed, and the large 6 ft 8 in (2.03 m) driving wheels meant that the maximum revolutions per minute was within the capabilities of the technology of the day. Mallard was five months old, meaning that it was sufficiently broken-in to run freely, but not overly worn. Selected to crew the locomotive on its record attempt were driver Joseph Duddington (a man renowned within the LNER for taking calculated risks) and fireman Thomas Bray.[2]
The locomotive had previously had problems with the big end bearing for the middle cylinder, so a "stink bomb" of aniseed oil was placed inside the big end, that would be released if it overheated. Shortly after the attainment of this record speed, Mallard suffered an overheated middle big end and had to limp onwards to Peterborough after setting the record. It then travelled to Doncaster for repair. This had been foreseen by the publicity department, who had many pictures taken for the press, in case Mallard did not make it back to Kings Cross. The (Edwardian period) Ivatt Atlantic that replaced Mallard at Peterborough was only just in sight when the head of publicity started handing out the pictures. Inaccuracies in the machining and setup of the Gresley-Holcroft derived motion (which derived the valve motion of the inside (middle) cylinder from those of the other two, avoiding a hard-to-maintain valve gear linkage between the frames) meant that the inside cylinder of the A4 did more work at high speed than the two outside cylinders; this overloading was mostly responsible for the failure.
Mallard builder's plate with works' number 1870.
Stoke Bank had a descending gradient of between 1:178 and 1:200. Mallard, with six coaches plus a dynamometer car in tow, topped Stoke Summit at 75 mph (121 km/h) and began to accelerate downhill. The speeds at the end of each mile (1.6 km) from the summit were recorded at: 87½, 96½, 104, 107, 111½, 116 and 119 mph (141, 155, 167, 172, 179, 187 and 192 km/h); half-mile (800 m) readings after that gave 120¾, 122½, 123, 124¼ and finally 125 mph (194, 197, 198, 200 and 201 km/h). The speed recorded by instruments in the dynamometer car reached a momentary maximum of 126 mph (203 km/h).
On arrival at King`s Cross (just after the run) driver Joe Duddington and Inspector Sid Jenkins were quoted as saying that they thought a speed of 130 mph would have been possible if the train hadn`t had to slow for the junctions at Essendine. In addition at the time of the run there were permanent way restriction to 15 mph just north of Grantham which slowed the train as they sought to build up maximum speed before reaching the high speed downhill section just beyond Stoke tunnel.
http://en.wikipedia.org/wiki/LNER_Class_A4_4468_Mallard
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