The LEADING WHEEL or LEADING AXLE or PILOT WHEEL of a steam locomotive is an unpowered wheel or axle located in front of the driving wheels. The axle or axles of the leading wheels are normally located on a leading truck . Leading wheels are used to help the locomotive negotiate curves and to support the front portion of the boiler.
Importantly, the leading bogie does not have simple rotational motion
about a vertical pivot, as might first be thought. It must also be
free to slip sideways to a small extent (otherwise the locomotive is
unable to follow curves accurately – a point lost on the 19th
century railway pioneers), and some kind of springing mechanism is
normally included to control this movement and give a tendency to
return to centre. The sliding bogie of this type was patented by
William Adams in 1865. The first use of leading wheels is commonly
John B. Jervis
Locomotives without leading trucks are generally regarded as unsuitable for high speed use. The British Railway Inspectorate condemned the practice in 1895, following an accident involving two 0-4-4s at Doublebois , Cornwall, on the Great Western Railway . Other designers, however, persisted with the practice and the famous 0-4-2 Gladstone class passenger expresses of the London, Brighton and South Coast Railway remained in trouble-free service until 1933. A single leading axle (known as a pony truck ) increases stability somewhat, while a four-wheel leading truck is almost essential for high-speed operation.
The highest number of leading wheels on a single locomotive is six as
seen on the
* ^ Simmons, Jack; Biddle, Gordon (1997). The Oxford Companion to British Railway History. Oxford: Oxford University Press. ISBN 0-19-211697-5 . * ^ Rolt, Lionel (1955). Red for Danger. London: Bodley Head . ISBN 0-7153-7292-0 . * ^ Gladstone at the National Railway Museum, York accessed 22 December 2006.
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Locomotive running and valve gear
VALVE GEAR TYPES
* Allan * Baker * Bagnall-Price * Baguley * Bulleid * Caprotti * Gab * Gooch * Gresley * Hackworth * Joy * Kuhn slide * Lentz * Southern * Stephenson * Walschaerts
AAR type A switcher truck
OTHER RUNNING GEAR ELEMENTS