Having wandered into South Devon territory with my atmospheric caper, I started to look at some of the steam engines used on that line. I realised that, although I have modelled several early passenger engines, including the Firefly class, I have not tackled any of the early goods engines.

The Leo class 2-4-0 were built as goods engines, starting in 1841. It was soon realised, however, that they had insufficient adhesion weight, so all the engines were converted to carry saddle tanks. We are very fortunate that the young draftsman, E.T.Lane made sketches of ‘Leo’ both before and after conversion at Swindon Works in 1849. In fact, his two sketches were dated 13th September 1849 and 21st September 1849, which indicates how rapidly the conversion was carried out! Although these are only notebook sketches, I found that overlaying the two versions showed how similar they are and indicates that the sketches are actually rather accurate. Many of the key dimensions are written on the sketches, although the later one only shows those which changed as a result of conversion. Unusually, he also sketched end elevations for the tank engine.

Sketches by E.T.Lane of Leo at Swindon in 1849

I decided that the saddle tank version was the one I would like to model and so I started to examine the available information in more detail. I should mention that there was a later ‘upgrade’ to many of these engines, when larger bunkers were fitted and that there are a few photos available of the larger-bunkered form. They must have been useful engines, because many of them survived until the great cull of Broad Gauge stock in the 1870s.

I have mentioned before that caution is needed when taking dimension from drawings. In the present case, G.F. Bird made some more ‘finished-looking’ drawings, clearly based on Lane’s sketches, early in the 20th century. When I looked at one of these, reproduced in Mike Sharman’s book of Broad Gauge drawings, I thought that the tank tops looked very low, in comparison to the Lane sketches drawn from life. This could be seen clearly when I overlaid the Bird drawing over the Lane versions:

Three drawings overlaid

There are actually three drawings here – the first by Lane as a tender engine (Red), the second by Lane after conversion to a tank engine (Black), and the Bird drawing (Blue). Considering they are described as ‘sketches’, the Lane versions appear remarkably consistent in their scaling but the Bird drawing is very different in its portrayal of the tank.

Fortunately, there is a good photo of ‘Aries’ (Leo-class) standing outside Faringdon shed, probably in the late 1860s by which time its bunker had been enlarged. Although it is not quite side-on, it is possible to compare the overall height of the tank with the diameter of the driving wheels (known to be 5 feet). The result looks to be much closer to the Lane sketches than to the much later Bird drawing (overlaid in red).

Comparison of photo with Bird drawing

To take the matter further, I decided to create a 3D model that I could then align with the photograph, to check how well the Lane dimensions agreed. I extruded the tank body, using ‘Fusion 360’, from one of the Lane end-elevation sketches and created the boiler as a cylinder, scaled from the prototype dimensions of 8’ 6” length by 3’ 6” diameter, as shown below:

Extruding from drawings in Fusion 360

I copied the frames and buffer beams, by extruding in my usual way, and ‘borrowed’ a Haycock-style firebox from my earlier ‘Firefly’ model.  Next, I assembled all these parts together, within ‘Fusion 360’, and then imported the photo of ‘Aries’ at Faringdon as a ‘canvas’. I could now rotate my basic 3D model until it appeared to be in a similar orientation to that shown in the photograph.

Model and ‘Canvas’ in Fusion 360

I then overlaid the model and photograph, in order to compare the major dimensions. The result, shown below, confirms that the Lane sketches are an accurate representation of the height of the saddle tank.

Overlay of my 3D model and photo of ‘Aries’

This is one of those rare occasions when one of the early engine designs survived long enough to appear in a good photograph. I have used 3D modelling as a research tool, to validate Lane’s sketch and to show that the much later Bird drawing is not accurate.

Having got this far, I suppose can now proceed with a complete model of a Leo-class tank engine. According to Ian Pope & Paul Karau’s book “The Forest of Dean Branch, Vol.1”, the former station master at Cinderford recorded that the line was opened with a Leo-class engine ‘Virgo’, so I even have an excuse to include this engine in my ‘Bullo Pill’ collection .

Mike