Whyte notation

From TrainSpottingWorld, for Rail fans everywhere

The Whyte notation for classifying steam locomotives by wheel arrangement was devised by Frederick Methvan Whyte and came into use in the early 20th century encouraged by an editorial in American Engineer & Railroad Journal (Editorial December 1900). Whyte's system counts the number of leading wheels, then the number of driving wheels, and finally the number of trailing wheels, groups of numbers being separated by dashes. Other classification schemes, like UIC classification and the French system for steam locomotives, count axles rather than wheels.

Thus, a locomotive with two leading axles (and thus four wheels) in front, then three driving axles (six wheels) and followed by one trailing axle (two wheels) is classified as a 4-6-2.

[edit] Method

[edit] Articulated locomotives

Articulated locomotives such as Garratts, which are effectively two locomotives joined by a common boiler, have a + between the arrangements of each engine. Thus, a 'double Pacific' type Garratt is a 4-6-2+2-6-4.

Simpler articulated types such as Mallets, where there are no unpowered axles between powered axles, have extra groups of numbers in the middle. Thus a Big Boy is a 4-8-8-4; there are two leading axles, one group of four driving axles, another group of four driving axles, and then two trailing axles.

[edit] Suffixes

The suffix T indicates a tank locomotive; otherwise, a tender locomotive is assumed. In British practice, this is sometimes extended to indicate the type of tank locomotive: T means side tank, PT pannier tank, ST saddle tank, WT well tank. T+T means a tank locomotive that has a tender for additional coal or water capacity.

[edit] Internal combustion locomotives

In Britain, small diesel and petrol locomotives are usually classified in the same way as steam locomotives, e.g. 0-4-0, 0-6-0, 0-8-0. This may be followed by D for diesel, P petrol, and another letter describing the transmission: E for electric, H hydraulic, M mechanical. Thus 0-6-0DE denotes a six-wheel diesel locomotive with electric transmission. Where the axles are coupled by chains or shafts (rather than side-rods), or are individually driven, the terms 4w, 6w or 8w are generally used. Thus 4wPE indicates a four-wheel petrol locomotive with electric transmission. For large diesel locomotives the UIC classification is used.

[edit] Limitations

The limitations of the Whyte system in classifying locomotives that did not fit the standard steam locomotive pattern led to the design of other forms of classification. Most commonly used in Europe is the UIC classification scheme, based on German practice, which can more completely define the exact layout of a locomotive.

[edit] Naming

In American (and to a lesser extent British) practice, most wheel arrangements in common use were given names, often from the name of the first such locomotive built. (For example, the 2-2-0 is named Planet.) (This naming convention is reminiscent of the naming of warship classes.)

[edit] Common wheel arrangements

Here is a list of the most common wheel arrangements: in the illustration the front of the locomotive is to the left, o is a carrying axle, O a driving axle.

[edit] References

[edit] See also

Wikimedia Commons has media related to: Whyte notation

• AAR wheel arrangement
• Wheel arrangement
• UIC classification
• Category:Locomotives by wheel arrangement