Constructing the engine carriage, described in Part Two, went much more rapidly than I had expected, partly because of that brief spell of hot weather, which kept me indoors in our shady living room. An advantage of computer modelling is that I could sit in an armchair with my laptop, with no need to venture into my hot workroom. One problem of working this way is that I can get so engrossed in working out the details that my wife has difficulty extracting me, to suggest that it’s time to make a cup of tea!

 

My model of Thunderer’s Engine Carriage

 

I have already mentioned some of the problems with modelling these very early engines, in that reliable information is hard to obtain and several misleading statements have been made over the intervening years. I suspect that, in the present case, there has been some confusion over the considerable difference between Harrison’s Patent drawings and the engine ‘Thunderer’ as it was actually built.  I have tried to stay as close as possible to Wood’s Plate XIII, because he says this was obtained from the builders of ‘Thunderer’.

 

In his text, Wood writes that Fig.8, “is a part of the boiler, which is, in every respect, the same as that shewn in Fig. 1, Plate XI.” I find this a very perplexing when I look at Plate XI, since it seems to bear very little resemblance to the fragment of the boiler shown in Plate XIII.

 

 

Wood Plate XI

 

In his text, Wood describes “… apparatus for generating the steam, .being placed upon one carriage, and the cylinders, and machinery, for propelling the engine, upon another carriage ; each of which is supported by four wheels” Every other reference I have seen, says 6 wheels. Since, I am aiming to be consistent, wherever possible, with Wood’s contemporary description, I have decided to see how the Boiler Carriage might look if running on four 6 foot diameter wheels.

 

NB: I’m now moving into a world of speculation...

 

In favour of Wood is his statement that “we have given a drawing of one, built by Messrs. Hawthorn of' Newcastle-upon-Tyne, for the Great Western railway”. This seems to give contemporary authority to what is shown on his Plate XIII.

 

That, though, has created another problem. Wood’s Plate XIII includes a drawing (Figure 8) of the front end of the boiler carriage, which appears to contradict many of the statements that have been subsequently been made about the appearance of ‘Thunderer’. I measured the dimensions (mm) off the scaled ‘canvas’ created from Plate XIII in ‘Fusion’, and then converted these into feet and inches on the prototype.

 

Wood (1838) Plate XIII Figure 8, with dimensions added

 

According to Colburn’s ‘Locomotive Engineering’ (1871) “The boiler was 44 inches in diameter, and contained I35 tubes l 5/8 inches in diameter and 8 feet 7 inches long, giving 516 square feet of surface. The fire box was of great size, the area of fire grate being 17 ½ square feet, while, by the introduction of a "midfeather" or intermediate water apace, the whole fire box heating surface was 108 ¼ square feet. … The chimney was 16 inches diameter.” This boiler diameter (inside) agrees very well with my own measurement from the ‘canvas’ so, perhaps increases confidence in the other dimensions quoted, including 6 foot diameter wheels.

 

Modelling the Boiler Carriage as described by Wood (1838)

 

I started by extruding a cylinder of 14.67mm diameter and 34.33mm length, to represent the boiler, with reference to Colburn’s figures. I then attached a smokebox to the front end of this boiler, produced by extruding from my ‘canvas’ of Plate XIII in Fusion. I assumed that the grate was approximately square so that, to achieve the quoted area of 17 ½ sq.ft., the length and width should be 16.73mm (in my chosen 4mm scale)

 

The boiler is thought to have had wooden cladding so I extruded a single plank in ‘Fusion’ and then used the ‘circular pattern’ tool to create a compete array of planks around the outer perimeter of my boiler tube. The results of this stage of modelling is shown below:

 

My 3D model of Thunderer’s boiler assembly

 

The height of the chimney and its flared top are speculative, as is the round-topped form of the firebox – I have based both of these features on contemporary practice. I have no idea how access was obtained to the smokebox for cleaning – with no cylinders below, a hatch at the bottom is one possibility.

 

Wood’s Plate XIII shows what appears to be a safety valve behind the chimney. I have added a cover, modelled on Colburn’s drawing for this feature and I've also added a manhole cover on top of the firebox.

 

When it comes to the chassis, I have taken account of Wood’s statement that there were only 4 wheels and Plate XIII shows the front pair to have a diameter of 6 feet, the same as on the Engine carriage. I found, by experiment that an underframe with the same wheelbase as the Engine carriage would fit under this boiler, with an extension at the rear end to form a footplate. Plate XIII also shows the front part of a water tank suspended below the frame.

 

With these features in mind, I copied the framing and wheels from the Engine carriage and added the water tank between the frames. According to an article by Sekon in the Great Western Magazine, April 1910 “The boilers of these engines [Thunderer and Hurricane] were also peculiar, the firebox containing a partition dividing it into two independent sections with a door to each.”

 

In view of the large water tank below the boiler, it occurred to me that coal bunkers could also easily be accommodated an either side of the firebox, turning the vehicle into a self-contained tank engine. The division of the firebox into two separate sections adds plausibility to the idea of their having been two coal bunkers, one on either side of the footplate. Therefore, I have included this speculative feature into my model, as shown below:

 

 

This design diverges considerably from ‘received wisdom’. For example the RTCS Part Two states that “the carrying wheels were four of 4’ 6” and two of 4’ 0” diameter, but how these were arranged under the boiler is not clear.” This does not agree with the leading end of the boiler carriage as illustrated by Wood.

 

We know that ‘Thunderer’ was the first of two engines delivered to the GWR. The second, ‘Hurricane’ had not arrived when Wood was writing his book, so it is possible that some of the features recorded subsequently actually only applied to Hurricane. Hurricane’s engine carriage had a 2-2-2 wheel arrangement with 10 foot diameter driving wheels and no gearing This carriage must have been longer than that for Thunderer, in order to accommodate such large wheels and the motion connected to a central axle. It seems to me entirely plausible that a longer boiler carriage was attached to Hurricane’s longer engine carriage, also with six wheels. The central axle under the boiler would also have made it difficult to include such a large water tank, so a separate tender may have become necessary to carry coal and water. This would have led to the comments about the locomotive being a ‘train in itself’

 

Once I had brought together my two models of the Engine and Boiler carriages of ‘Thunderer’, it was clear that the arrangement I have devised leads to a more compact and purposeful looking locomotive than many later illustrations suggest. I appreciate that I am ignoring a lot of later ‘evidence’ but, without knowing the provenance of the various statements that have been made, I feel comfortable with my interpretation, unless further contemporary information is re-discovered.

 

My 3D model of ‘Thunderer’ as a two-part machine

 

I cannot ‘prove’ that my interpretation is correct but I believe that it is a plausible engineering solution, which conforms to Wood’s description and Figures:

 

Looking at my model and trying to construct a vision of the real engine in my mind, I can see why it made a strong impression on the GWR Directors of the time. In his diary, the Director George Gibbs wrote on 12th May 1838 that “Hammond came for me to Salt Hill with Harrison's engine: and I went backward and forward on it twice. .... Along the greatest part of the four miles the engine ran beautifully smooth and for some way we cleared sixty miles an hour."

 

A couple more views to finish my description of the construction of my model – I added some ‘safety rails’ at front and back:

 

 

 

‘Thunderer’ at Old Paddington

 

As an Addendum, I ‘cut and pasted’ my model of Thunderer, together with Vulcan, into my 3D model of Gooch’s round-house engine shed at Paddington.   A rare glimpse of early operations on the GWR!

 

My model of Paddington Engine Shed ,with Thunderer and Vulcan

 

Having realised the possibilities, I imported a few more of my models of early Broad Gauge stock into my Paddington model, so that I could set up a scene of a train setting out from the Departure Platform for the terminus at Maidenhead.:

 

Old Paddington in 1838, with a train setting out for Maidenhead

 

The above view is from the yard to the West of the old station, with Bishop’s Road bridge in the background. I have shown ‘Thunderer’ as a ‘stern wheeler’, which was probably a safer direction, placing that large revolving drum gear at the back.

 

The following train comprises a Luggage Truck , a closed 2nd-class carriage, a Posting Carriage , and a 4-wheel 1st class carriage [to be described]. The scene also includes Vulcan on the other platform line and a horse box being loaded from the end of the carriage road.

 

In the foreground in another closed 2nd, waiting to be assembled into a train.  In the background, the tunnels under the bridge can be seen, These were for goods trains to reach the goods depot which was on the other side of the bridge.

 

This is, of course, only a static ‘diorama’ but I suggest that it would make a splendid broad gauge scenario for @Annie to create as a 'Trainz' model.

 

Mike