Last year (October 2021) I wrote a post under this same title in which I referred to the need for caution, when making models based on published drawings. In some cases, even manufacturers’ drawings, especially in the early days, can be suspect, since the finished product was based more on the skills of individual craftsmen, who trusted their practical knowledge over that emerging from the drawing office!

When I designed my recent model of ‘Vulcan’, I derived the dimensions from sketches by the young Swindon apprentice, E.T. Lane. Although these were only sketches, they were made ‘from life’ and I feel are more likely to represent the actual appearance of his subjects than more polished drawings made many decades later.

Nevertheless, I was perturbed when I realised that my use of these sketches had resulted in the driving wheels of my model appearing to represent a 7 foot prototype diameter, whereas the RCTS book on GWR Locomotives, Part Two, states that the diameter was 8 feet. This statement has been widely repeated in other works ever since. So, I have spent some time examining the evidence more closely

It is in that subtle matter of ‘appearance’ that Lane’s sketches differ markedly from the works drawing of ‘Aeolus’, a sister engine to ‘Vulcan’, both built by the Vulcan Foundry. The works drawing may well indicate 8 ft diameter wheels but, on looking at the wheelbase relative to the driving wheel diameter on the works drawing, the proportions can be seen to be different from the Lane sketch, in which the driving wheel is noticeably smaller

My first step was to photograph my collection of early broad gauge models together, in order to demonstrate their relative proportions:

My Four recent Broad Gauge Models

It was widely reported that the early engines ordered by Brunel had inadequate steam-raising capacity for main-line performance. Daniel Gooch addressed the problem when he designed his Firefly class, of which ‘Argus’ was a member, One of the reasons I had for constructing my models was to help visualise these differences.  The difference between the sizes of the boiler on 'Vulcan' compared with that of 'Argus' is very apparent when the models are placed together.

‘Vulcan’ was a sister engine to ‘Aeolus’, both being from the Vulcan Foundry and all the key dimensions are in agreement between my two models.  My earlier model of ‘Aeolus’ was based on a detailed sketch by E.T. Lane, which had copious annotations giving the dimensions of many features of this engine.  ‘Aeolus’ had been re-built with smaller driving wheels when Lane made his sketches but other key dimensions, including the wheelbase, had not been altered, so far as we know.

It appears, however that when Mike Sharman showed a drawing of ‘Vulcan’, derived from an illustration by G.F. Bird in The Locomotive Magazine, 1901, in his book of Broad Gauge engines, published by Oakwood Press, a scale based on the assumption that the driving wheel diameter was 8 feet was added.

When I placed this Bird drawing below the Works drawing of ‘Aeolus’, aligned to the wheelbase, it is clear that the wheel diameters are considerably smaller in the Bird drawing and, indeed, are a good match to the sketch by Lane. 

Drawings Compared (based on wheelbase)

I suggest that 'Vulcan' may have been delivered with 8 ft drivers in 1838 but that these were changed to 7 ft sometime during the 1840s. I note that Lane indicated on his sketch that the leading carrying wheels had 14 spokes, whereas the trailing wheels had only 12. This difference is borne out in the later photograph of 'Vulcan' as a tank engine, although not in the Bird drawing.  Perhaps it is an indication that 'Vulcan' was re-fitted with wheels salvaged from other engines during the 1840s?

There is an early illustration of Ealing Station, dated 1839, which includes 'Vulcan' (or one of the similar engines in the group) apparently in original form with 8 ft diameter driving wheels.

Extract from illustration of Ealing Station 1839

Overall then, another reminder always to treat published drawings with suspicion. Distortion frequently occurs during publication, so that vertical dimensions may not correspond with horizontal ones! There are plenty of traps for the unwary modeller and I hope that not too many have built models of 'Vulcan' to the dimensions shown in the Oakwood Press book.

I am especially pleased, however, to have found that the late Mike Sharman’s own model of 'Vulcan' does appear to have been based on the proportions shown in the Works Drawing, with its larger (8' diameter) driving wheels. A collection of photos of Mike’s models appeared in Railway Modeller, March 1968, so I was able to compare a good side-on photo of his model with the above drawings. 

I should also be interested to know where Mike's tender design came from - I used a 4-wheel Gooch tender with my own model