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.
Mallet
Alexisbad on the Harz railway in Germany with 0-4-4-0T 99 5906 (Photo AM Johnson)
Antole Mallet had the concept of taking a large single locomotive similar to normal practice and splitting the rigid wheelbase by having the front engine articulated. The forward power unit pivots at the front of the rear power unit that is part of the normal loco design. Locos can be designed to carry the water in tanks or in a tender.
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.