Articulation
All | Mallet | Garratt | Kitson Meyer | Klein-Lindner | Farlie | Geared
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.
Fairlie
Porthmadog on Ffestiniog Railway with 0-4-4-0T Merddin Emrys (Photo AM Johnson)
Robert Fairlie was a Scotsman who took out a patent for his design of double ended articulated engine in 1863. This type of locomotive is essentially two joined back to back sharing a common firebox and controls in a central cab. The power bogies pivot underneath both boilers.
A very famous location that uses this type of machine is the Ffestiniog Railway in North Wales they also have a replica of a single Fairlie design. The Single Fairlie (named Talesin) loco looks like a normal loco with the exception that the powered wheels are in a bogie that pivots under the boiler and the rear of the loco is supported on an un-powered bogie.
Conclusion?
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.
Bibliography
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
Acknowledgements
This article was produced by Andrew Johnson, feedback or contributions about the Leeds engine making industry would be greatly appreciated.