Narrow gauge articulated steam locomotives have one or more engine units that can move independently of the main locomotive frames. Articulation allows larger, and more powerful, locomotive to operate on track that has sharp curves. A large number of designs for narrow gauge articulated locomotives have been developed; among the most common are designs by Fairlie, Garratt, Mallett and Meyer.
David Lloyd George at Foxhill Railway.
Merddin Emrys at Parkwood Railway.
The double Fairlie design has two power bogies under a double boiler with a central firebox and a smokebox at each end. The first example of this design was Little Wonder that was built in 1869 for the Ffestiniog Railway. During the original operation of the railway, four double Fairlie locomotives were used and, during the preservation era, three further double Fairlies have been built at the Boston Lodge works.
Pechot-Bourdon locomotives at Monk Ings Bottom Railway.
Despite the Fairlie design being patented, the Pechot-Bourdon locomotive was built for the French narrow gauge military railways from 1888. The Pechot-Bourdon was, to all intents and purposes, a double Fairlie with minor alterations, such as a central steam dome and simplification of the steam and exhaust pipes. By the end of the First World War, over 300 Pechot-Bourdon locomotives had been built.
Single Fairlie Taliesin at Southgate Light Railway.
A derivative of the double Fairlie design is the single Fairlie with one boiler and one powered bogie, the other bogie under the cab being unpowered. The single Fairlie sacrificed bidirectional running for greater coal capacity in a bunker behind the cab and a conventional boiler that was cheaper to maintain. The Ffestiniog Railway has one 0-4-4 single Fairlie and the North Wales Narrow Gauge Railway had three 0-6-4 single Fairlies.
Mahananda at Almondbury Light Railway.
Highland Chief at Great Willowgarth Railway.
Garratt locomotives have an engine bogie at either end, carrying coal and water, with the boiler unit slung between them. The advantage of this design is that the boiler, firebox and ashpan are not restricted in size by the running gear. A larger ashpan allows longer continuous running and a large firebox, with unrestricted air supply, allows for the burning of poor quality fuel. Garratts run equally well in either direction.
NG184 at Almondbury Light Railway.
Drakenberg 60 at Parkwood Railway.
The Mallet design of articulation has a rigidly fixed engine under the rear of the locomotive and a radially swivelling engine under the front. Mallets were powerful engines that were popular on the French narrow gauge systems. Meyer articulated locomotives, by contrast, had two powered bogies under the frames of the locomotive. The firebox is directly above the rear bogie which limits its size, however, the Kitson-Meyer design solved this issue by moving the rear bogie further back under extended frames.
Meyer articulated Monarch at Welshpool & Llanfair Light Railway.
Articulation designs, such as Shay, Climax and Heisler, were used on geared locomotives. The Shay design for articulated gear locomotives originate from North America where they were used primarily for logging and mining operations. Shays coped well with steep and poor quality track as all wheels were driven. In this design, the boiler is offset to the left to counterbalance the weight of the two, or three, steam cylinders mounted vertically on the right.
Two cylinder Shay at the Yorkshire Geared Loco Day.
Three cylinder Shay at Saltersbrook Lane Branch.
The Climax design of articulation geared locomotive had two steam cylinders attached to a transmission located under the centre of the boiler. This transmission unit powered two bogies under the locomotive via driveshafts. Climax locomotives were used principally in the logging industry where many considered them to be superior to Shay locomotives in terms of power and stability on poor quality track.
Climax logging locomotive at Almondbury Light Railway.
Heisler articulated geared locomotive design features two steam cylinders angled at 45 degrees in a V arrangement. Power was transmitted through a drive shaft, in the centre of the frames, to the outer axle on each bogie. The inner axle on each bogie was then driven by a connecting rod. Again a North American locomotive, Heislers had the same low speed power as Shay locomotives but with a higher top speed.
Heisler locomotive Ntinyana at Almondbury Light Railway.
Articulated Lagos Steam Tramway Hunslet at Parkwood Railway.
In addition to Fairlie, Garratt, Mallet, Meyer, Shay, Climax and Heisler, a large number of other, less common, narrow gauge articulated locomotive designs, plus their variants, have been catalogued. Among them were three Hunslet locomotives built in 1910 for the Lagos Steam Tramway. These 0-4-4 engines had four driving wheels rigidly mounted to the frames below the boiler with the cab, and rear accommodation, flexibly mounted and supported by an unpowered bogie.
Shays on parade at Great Willowgarth Railway.
