Locomotive Types
tages can accrue in the matter of flexibility by the copying
of this type. However, a fair amount of lateral play may
be provided if cylinders with valves on top are employed,
and a model locomotive so arranged should be quite as
free on a sharp curve as a bogie engine, but would not,
perhaps, be quite so steady. In real practice many such
engines have leading radial trucks with fairly stiff side
controlling springs. Except in locomotives of this type
having small driving wheels---known sometimes as "mixed
traffic" engines-a long, deep grate is not practicable.
A firegrate which slopes to the forward end may also be used with advantage in these engines, the back end extending over the trailing axle as already mentioned.
The Six-wheeler-single Type.The day of the single- wheeled express locomotive is past. However, in model work very good results can be obtained from such engines, as the weight which may be placed on the driving axle is not limited by considerations of rail strength. The engine depicted in Fig. 18 is a model of a six-wheeled single, de- signed by Mr. J. Ramsbottom for the L.N.W.R. Simplicity in construction is perhaps its only feature from a model- maker's point of view. It is a suitable locomotive to model where the builder desires, for reasons of safety and comfort, not only the largest gauge, but, to reduce cost and labour, the smallest possible engine. A 1 in, or 2 in. scale model, built on the lines of this engine, would be little larger or heavier than a model of a modern 4-6-0 built to a scale of 1 in. to the foot, and would probably prove much less expensive.
In all singles the firebox is more or less unlimited in length and depth. Of course the driving wheels, where they are large in diameter, limit the size of the boiler barrel, but the recent rebuilds of the G.C.R. and G.W.R.17
