JimC

Don't underestimate the weight problem - I believe a current nuclear flask is about 50 tons for 2.5 tones payload. A nuclear reactor will always be best used to power electric trains.

Also the time scale to turn vegetation into coal and/or oil by natural processes is a bit long term...

The trouble with any discussion on nuclear power tech is that it's almost impossible to find reliable information sources. So many/much lies, grinding axes, spin and disinformation. Looking at the authorship of that Guardian article I wouldn't rate it much better than Wikipedia. I think we can be reasonably certain, though, that nuclear power will never be appropriate for heritage steam operation. Arguably discussion of any alternate power source should include not only the likely effects on passenger numbers, but also the likely effect on volunteer numbers.

Isn't part of the trouble the longevity of steam? As late as my 1958 Observers book I count 28 pre group classes on the LMS from six different companies. I don't deny the desirability of consolidating design, but there was a huge legacy. Attitudes to treatment of salaried staff were arguably different too in those days when "job for life" was nearer being a thing than it is now.

Indeed, but the pattern is subtly different too. Compare, for example, the top rows of the flue tubes, straight at the smokebox end, gently arched at the firebox end. The differences are small, but exist.

Indeed, that would be the case if the boiler were truly a cone shape. But its not. The vertical cross sections are all circular, as can be seen on GWR cross sections, and they have to be, because the tube plates at each end are circular, and so all the intermediate cross sections are circular too. I did once look up what the shape of a taper boiler is officially called by mathematicians, but its something complicated and I have forgotten again. Another little bit of trivia - the arrangement of tubes at each end of at least some GWR taper boilers is not really the same, and the tubes in the boiler are not parallel. Here's an extract from a GWR drawing of tube plates on a Standard 7 (47xx) boiler and its evident how the extra space at the firebox end is used, presumably to give more water circulation round the tubes.

Another possibility would be 1391. The last absorbed locomotives in the 1300 series were 0-8-0s up to 1390, so a Cambrian 0-4-2 could have got 1391. In real life it was allocated to an ex LSWR 46 class Adams Radial from the Brecon and Merthyr, but that was absorbed after the Cambrian and in the event it never carried the number.

If you assume a GWR reboilering anything is up for grabs, although a GW boiler would surely have had a bigger dome. As for a number, tricky. Numbers were allocated by wheel arrangement, but no 0-4-2s were absorbed to give us a clue. 1337 might work, being after absorbed 2-4-0s. It was on an absorbed Manning Wardle that was scrapped in 1926, but we can imagine it going earlier.

Not sure you can really rebut it, since its true, but its just as true of big tank engines, and in both cases its not that great a number in percentage terms. One may as well get excited about the loss of braking adhesion on a tender engine when the tender is empty, which seems to me a much bigger deal, especially with unfitted trains.

Its not easy. The 15 was already heavier on the leading two pairs of wheels than the trailing ones. If you move the rear axle back it gets even more front heavy. If anything the leading wheels need to go forward to make the weight balance more even, but of course they can't go forward because of the cylinders. Here's a sketch of the boiler, wheels and motion of the 1500 with the 9400 wheels superimposed. 1500 wheels in red, 94 wheels in blue. They're aligned with the boiler in the same place. As can be seen the 94 takes advantage of the inside cylinders to have the leading wheels a good bit further forward, and consequently the trailing wheels can go further back. I hadn't appreciated until I sketched this just how very constrained the design of the 1500 was. It looks to my inexpert eye as if the only way they could have got a longer wheelbase on the 15 would have been to give an extended smokebox and mount the main part of the boiler further back, but that would have added weight to what was already a heavy locomotive. There was a 1945 study of a 2-6-0 outside cylinder pannier tank, and I now understand much better than I did before why this was considered.

As Riddles err, didn't?

Thinking on Hawksworth building more Castles rather than Counties, it's an interesting thought that while the Counties had his name on, he had most likely done a good deal of the actual design work on the Castle. Town Councillor and Justice of the Peace suggests a rather formal character, but he also sang in the Parish choir which is usually more sociable. A Hawksworth BR might not have had so many low powered designs, but the big challenge for a Swindon trained CME would probably have been adapting to the "different" build and maintenance standards on some of the other lines. Presumably Cook would have been solidly employed going round the factories improving engineering precision.

I wonder if anything so small did more damage to the railways in general and steam in particular than self cleaning smokeboxes? In an era of increasing white collar employment who wanted to travel to the office on a filthy railway if they could travel in a clean car or bus? To my mind its a classic example of the sort of blinkered short term thinking that accelerated the move to road transport.

You could argue that they did. There was a great deal of common DNA. But a Pacific costs a lot more money without adding that much extra capability, so why would you build one if you didn't have to. And a substantial part of the theoretical extra carrying capacity of the trailing wheel is taken up with carrying the extra weight of wheel and truck. Its worth noting that inter alia A4, Merchant Navy and Princess Coronation were all too heavy for GWR red routes, and indeed the published axle weights for the Princess Coronation exceed those for the King. Even the original Gresley A1 was half a ton heavier on each driving wheel than the Castle, which was on the red route limit.

There's a good deal of truth in that. GWR standard boilers came in distinct families, based on, amongst other things, the flanging blocks. Both barrel and firebox could be longer or shorter. These families can be identified. Std 6, 7, 8 used the same (the Bear's set) Std 1 and 4 Std 2, 3, 10 . Metro, Std 11, Std 21 Class P (Dean Goods), Class N, Std 9 Classes U, R, V, S, SS, Std 16 Most out of place were the two boilers designed against really big weight issues, the Castle, which was originally a Std 7 with a smaller diameter barrel, and the Manor. It must have pleased Hawksworth that the government had bought him a set of blocks intermediate between the Castle and Std 1 sets, which gave him more options.

This is what I don't understand about the proposition. The King boiler used the same flanging blocks as the Great Bear and the Std 7 (47xx) boilers, being intermediate in length between the two and having the same diameters. The Bear had pretty much a modified Star chassis and cylinders, and the Std 7 boiler on Star proposal that was abandoned due to weight problems was obviously also on a Star chassis, so there seems no obvious reason why the boiler couldn't have fitted over 6'8.5 wheels. There may of course have been more subtle reasons, which is why I'm so keen to hear if there's a good source for it. Its not in Holcroft or Cook to my knowledge, or even AFAICS in Nock.

You've said this before, but I have trouble believing it. Its not something I've come across in any of my reading, and there are two items of evidence against it. I would be very interested in a source. The first is that the boiler barrel diameters of the King are the same as those of the Bear, which did have 6'8.5 in wheels, and the second is that, admittedly at a cost of horribly squashed boiler furniture, preserved Kings have been cut down to well below the GWR loading gauge. Its also interesting that the boiler pitch of the Kings is identical to that of the 47s, which again had the same barrel diameters as the Bear, but with 5'8 wheels presumably had no clearance problems. [later] The surviving weight diagrams for the 1920 proposals for Star and Saint fitted with Std 7 boilers (ie the 47xx boiler) show a pitch of 9'0", 0.75" higher than the King. On the one hand that suggests that the drawing office may have taken advantage of the smaller wheels to drop the boiler a tad, but on the other it suggests that a higher pitch could have been fitted within the gauge. OTOH one must also be aware of the corners of the box. I've attached an extract from a GWR King cross section that does suggest that although tight, the boiler could have gone up to 9'0" pitch. (Note that the original c/s was right side only, I mirrored it, hence the extra ejector, lamp bracket etc.)

The smaller wheel diameter was established early on in the design AIUI. It was something of a feature that driving wheels on express locomotives became smaller over the 20thC, and it can be argued the King started a trend that was followed by the Merchants and Britannias. The technical GWR sources state that the over 40K mark was achieved by taking the early Kings out to what was in IC terms first rebore on the cylinders, and there are hints that by no means all of them left the works with the cylinders taken out the extra quarter of an inch.

It was Walschaerts, but the implementation, according to the late Don Ashton, who was something of an expert on these things, was far better than on any LMS locomotive.

But the Castle was already in existence as a freer running machine with a lower nominal tractive effort. Surely the extra brute power was the business need?

The ARLE also had a 2-8-0 design, albeit less advanced than the 2-6-0 proposals. Its interesting that although Churchward appears to have been greatly involved in the ARLE proposals, by and large the result was rather less sophisticated than the Churchward standards with parallel round top boilers and 180psi boiler pressure.

Don't forget the "Felix Pole" mineral wagons.

Or the MSWJR Beyer Peacock 2-6-0s.

Ideas will come. But an exercise might be to imagine a traffic that one's favourite railway did not have, but maybe could have had, and see if one can imagine a locomotive for it. Eliminating double heading is always a favourite, although given the UK loading gauge its hard to avoid the Garratt option. High frequency, fast acceleration suburban traffic is another. SR enthusiasts are a bit thin on the ground, but imagine heavy fast container traffic from Southampton Docks. What would Bulleid have built? Or supposing Bulleid hadn't been appointed? If there had been more continuity from Maunsell what express locomotives might there have been? And what might have replaced all those Victoria tank engines? Or supposing the SR electrification had all been short range, but clean air acts came in sooner? Can you imagine mixed mode steam/electric? I'm having a bit more trouble imagining options for my own favourite to the west. The railcars provide all too easy a model for suburban electrification for example.

"Far too cheap" he said, looking at his royalty statements...