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Articulation

Articulated Steam Locomotives

This part of my site is dedicated to my special interest: the world of articulated steam locomotives. I will try to give an overview of the many types developed. I will also in due course try to create a complete listing of articulated steam locomotives ever built but this is a gigantic task which may take years to reach any stage completeness (if ever). Any contributions on this area are welcome.

I feel no urge to redo many of the good work done by so many already. So if appropriate and if possible I will suffice to refer to work already underway or finished. Because so many have already created their own site with their own visualization these sites will appear very different. I apologize for that.

A what locomotive?

Most people that I talk to barely have a good idea of what a steam locomotive is. They consider it as a kind of iron dinosaur from an ancient past. They rarely ever realize that the decision to convert to diesel or electric traction is a purely political issue rather than an economical. Time and time again it has been proved that steam locomotives can be operated just as economical as diesels. Only few people, also very few indeed under railway enthusiasts, know anything of the great achievements on modern steam by Porta and others making steam a feasible option for the future.

Unsurprisingly most people have never heard of articulated locomotives either. Maybe in North American or South African circles this concept is a little more known. But as the Netherlands had only one articulated steam locomotive ever, which ran for no more than eight years, you can imagine that most people around me never heard of articulated steam locomotives.

Definition

An articulated locomotive is a locomotive in which one or more of the driven axles are able to take up positions where they do not remain parallel to the others and may take angular positions in curves. The axles may be driven by two separate engines or by a single one.*)

Articulated locomotives can be distinguished in four main groups

1. Fully articulated locomotives All axles are radially adjustable
2. Semi-articulated locomotives At least one axle can take an angular position and at least one can not
3. Temporarily articulated locomotives The locomotive has an auxiliary engine which is radially adjustable but can be switch on and off at will

4.

 

Locomotive that use the tender's weight for propulsion  

On this site I will only address the first two groups. Maybe I will also turn to the other two in a later stage.

Why Articulation?

The quest for increased power meant that locomotives had to be built larger and often longer. This caused problems however. Too large a number of driven axles fixed in a frame causes excessive wear of rails and wheels in sharp curves and increases the chance of derailment. Very often the more power demanding lines with steep inclines were also sharply curved. Since double-heading of engines is wasteful and cost ineffective, two smaller engines could not be used instead of one big one. The solution to the problem of power versus a short wheelbase is articulation, effectively joining two engines in one locomotive. There were, at one point or another, numerous methods of articulation, all of which meant that the rigid wheelbase of the engine was shortened, by placing the driving wheels in one or more independently moving bogies.

*) Lionel Wiener, page 11, Articulated Locomotives, 1930

 

A great many variations on the theme sprung to life as consecutive designers tried to solve the problems of previous designs. The table below gives a brief historical overview. It is not complete yet and will grow over time. Especially the types which were built in small numbers are absent. Anyone able to provide accurate and reliable information about numbers built is requested to contact me.