Leeds Engine:More Reading: Articulation


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Over the years as locomotives have been developed and made more powerful it has been necessary to aid traction by putting the power to the rail on more driven wheels. In the early years many locos only had a single powered axle with other wheels to add support for the weight of the loco. Initially the favoured layout was to have a six wheeled loco with a pair of axles coupled together and the third as support. When locos get longer, bigger and more powerful they run on more axles many of which are coupled together.

One of the largest locos built were the Russian AA class 4-14-4 with a coupled wheelbase of 33 feet as you can imagine they struggled to keep the loco on the track whilst going round curved tracks. The solution to this problem is to build an articulated loco. Below are some of the methods used by various designers to get powerful locos to travel on curved tracks. The other costly solution to the problem is to provide many smaller locos running together.

Geared Articulation
There are a few more methods of articulation for steam locomotives. These are derived from having the cylinders on the main rigid part of the locomotive and then the transmission is taken to the powered trucks by means of rotating shafting. There are a few different types:-

Shay locomotive at Roaring Camp Railroad USA

Shay at Roaring Camp Railroad California (Photo AM Johnson).
Heisler - with this the cylinders are formed into a V under the boiler. Transmission is taken to the bogies via shafting inside the frames. Avonside built a few locos and some the designs were later built by Hunslet when they had taken them over.
Shay - these locos have an unbalanced appearance as the shafting and cylinders are located on one side and the rotational motion is clearly visible.
Climax - The cylinders are inclined in the conventional position to avoid the movement of the forward powered truck. Transmission is by shafting similar to a Heisler.

Note that each loco type may be more suitable for different applications and must not look upon the Garratt as the best because of the quantities built or the Mallet as the one of the most powerful. Recently on the Welsh Highland it has been possible to compare Mallet, Garratt and Fairlie locos together.

Donald Binns, Ktson Meyer Articulated Locomotives
AE Durrant, Garratt Locomotives of the World
David Joy, Engines that bend - NG articulated locomotives
André Chapelon, La Locomotiva a Vapeur

This article was produced by Andrew Johnson, feedback or contributions about the Leeds engine making industry would be greatly appreciated.