Under the

Whyte notation Whyte notation is a classification method for steam locomotives, and some internal combustion locomotives and electric locomotives, by wheel arrangement. It was devised by Frederick Methvan Whyte, and came into use in the early twentieth cen ...

for the classification of steam locomotives by

wheel arrangement In rail transport, a wheel arrangement or wheel configuration is a system of classifying the way in which wheels are distributed under a locomotive. Several notations exist to describe the wheel assemblies of a locomotive by type, position, and c ...

, the is a Garratt

articulated locomotive An articulated locomotive is a steam locomotive (rarely, an electric locomotive) with one or more engine units that can move independent of the main frame. Articulation allows the operation of locomotives that would otherwise be too large to neg ...

. The wheel arrangement is effectively two 4-6-0 ten-wheeler locomotives operating back to back, with the

boiler A boiler is a closed vessel in which fluid (generally water) is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, centr ...

and cab suspended between the two swivelling power units. Each power unit has two pairs of

leading wheel 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 ...

s in a leading bogie, followed by three coupled pairs of driving wheels and no trailing wheels. A similar wheel arrangement exists for Mallet type locomotives, but is referred to as . On a Mallet locomotive, only the front engine unit swivels while the rear unit is rigid in relation to the main frame.

Overview

This was a rare wheel arrangement for Garratt locomotives, with only seven locomotives built for two South American customers. * The first was for the metre-gauge Mogyana Railway of Brazil, with five examples built by

Beyer, Peacock and Company Beyer, Peacock and Company was an English railway locomotive manufacturer with a factory in Openshaw, Manchester. Founded by Charles Beyer, Richard Peacock and Henry Robertson, it traded from 1854 until 1966. The company exported locomotives, ...

in 1912 and 1914. * The other was two locomotives built for the 3-foot gauge ''Ferrocarril Pacifico de Colombia'' by

Armstrong Whitworth Sir W G Armstrong Whitworth & Co Ltd was a major British manufacturing company of the early years of the 20th century. With headquarters in Elswick, Newcastle upon Tyne, Armstrong Whitworth built armaments, ships, locomotives, automobiles and ...

in 1924.

References

6,4-6-0 66,4-6-0+0-6-4 {{steam-loco-stub