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Mallard at York
LNER A4 class 4468 Mallard is an LNER A4 Pacific
class steam locomotive built in the 1930s by the LNER and designed by Sir Nigel Gresley in England. It was designed as an express locomotive with a wind-tunnel tested,
aerodynamic body which allowed it reach speeds of over 100 mph. It was in service until 1963 when it was retired after a lifetime distance of almost 1.5 million miles. It was restored to working order in
1988 to celebrate its 50th anniversary, but at time of writing is out of service without a current boiler certificate. Mallard is
now part of the national collection at the National
Railway Museum in York, England.
The Record
Mallard is the holder of the world speed record for steam
locomotives at 126 mph (approx 202 km/h). The record was achieved on July 3, 1938
on the slight downwards grade of Stoke Bank south of Grantham on the East Coast Main Line, and the highest speed was recorded at
milepost 90¼, between the towns of Little Bytham and Essendine.
Mallard was the perfect vehicle for such an endeavor; one of a class of streamlined locomotives designed for sustained 100+
mph running, it was one of a small number equipped with a double chimney and double Kylchap blastpipe, which
made for improved draughting and better exhaust flow at speed. The A4's three-cylinder design made for better stability at speed,
and the large 6'8" (2032 mm) driving wheels meant that the maximum revolutions per minute was within the capabilities of the
technology of the day.
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 and began to accelerate downhill. The speeds at the end of each mile from the summit were recorded at 87½,
96½, 104, 107, 111½, 116 and 119 mph; half-mile readings after that gave 120¾, 122½, 123, 124¼ and finally 125 mph. The indicator diagrams on the
dynamometer car traced a momentary maximum of 126 mph.
Shortly following the attainment of this record speed, Mallard suffered an overheated inside big end bearing, and had to limp
back to Doncaster for repair. Inaccuracies in the machining and setup of the
Gresley-Holcroft derived motion (which derived the valve motion of the inside 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.
Controversy
Mallard's world record has never been officially exceeded for a steam locomotive, though German locomotives came very close.
Many rumors and stories exist of higher speeds, but Mallard's is the only one with adequate documentation. Certainly many other
steam locomotives were capable of such speeds; the LNER's long, straight, slightly downhill raceway of Stoke Bank played as much
of a part in the record as the locomotive or crew.
It is notable that, unlike the world records for automobiles, there is no
requirement for an average of two runs in both directions, and assistance from gradient or wind has always been acceptable in
rail speed records.
Other locomotives that could probably have exceeded 126 mph include the New York Central's Niagara 4-8-4, the Pennsylvania Railroad's mighty S1 prototype (which is rumored to have exceeded 140 mph in somewhat
debatable accounts) and T1, the Santa Fe's 2900 class 4-8-4s, and last but not
least, the Milwaukee Road's A1 4-4-2 Atlantics and F7 4-6-4 Baltics.
The Milwaukee Road had the fastest scheduled steam-powered passenger trains in the world, with timetables requiring running in
excess of 100 mph; it's certainly known that they exceeded 120 mph on a fairly frequent basis.
The belief is that—as far as can be ascertained—fear of lawsuits, and of a reputation for risk-taking through
record runs, scared all American railroad companies away from official record attempts in the 1930s and 1940s.
Thus, Mallard still holds the crown; a plaque affixed to each side of the locomotive commemorates the feat.
External links
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