Rebuilt Patriot and Rebuilt Scot

Chapelon rebuilt other people's engines, or modified designs. He was never able to produce his own locomotive for the French railway companies that he worked for. So the engines that he is most famous for have the firebox design that they came with. 242A1 is round top, 160A1 is not and so on.

A boiler exists to provide the steam required and there is no good reason to over complicate the design. It is no accident that the LNE Dia 100 is seen as a good example of traditional boiler design. There remains the tendency to view the boiler size as being the solution to the steam supply problem. The exhaust system is the most important thing to get right. Making best use of the steam generated is another area that can, in the view of some, lead to undue complication. Engines become larger than they need to be with the loading gauge becoming an issue where it need not be the case. Safety valves as a general rule sit on top of the boiler or firebox and are no higher than the exhaust exit. Interestingly both the Bulleid Pacifics and 242A1 were exceptions.

So, would the Patriot and Royal Scot classes have been better with a boiler based on the Dia 100? They would have been cheaper to build. As for the Scots, who is aware of the frame cracking issue? And in light of this, would you like to own one?

 

So if Chapelon was a re-builder and modifier of other people's designs how does that leave him vis-a-vis other people like (e.g.) Thompson who followed other designers?

 

Chapelon was rather unique. An original thinker. To compare his work with that of any other locomotive engineer just cannot be done. He had to wait for some time in order to test out his ideas, apply his grasp of thermodynamics. The first exercise in rebuilding a Pacific, that happened to have a very poor reputation compared with other members of the same class, the larger wheeled PO type. These were reasonable enough engines, producing approximately 1850 ihp at express speed. But more was needed and the outcome of Chapelon's work on No. 3566 was an increase to 3000ihp. He had calculated for such a figure and testing was to prove these calculations correct. As rebuilding of the original engines proceeded further improvements raised the sustained ihp to 3,700. If ET had been of the same calibre then the LNE Pacifics should have been capable of peak outputs in excess of 6,000edhp. It is not quite so simple but you get the general idea.

There is rebuilding and there is rebuilding. The PO needed still more power and the adhesion to make use of it. This railway first received Pacifics in 1907, a small wheeled variety and these provided the basic material for the famous 4-8-0s which delivered 4,000ihp for the first batch and 4,400ihp for the second.

From these examples it should be obvious that Chapelon cannot be compared with anyone else. Thinking only moved on under Porta.

 

This is looking like enough thread drift to justify moving elsewhere. But while we're here; is that 6000 figure on the basis of the relative sizes of the PO pacifics and the LNER ones? Or on the basis that Chapelon doubled the original power? The latter wouldn't be valid, because the LNER ones already took some account of Chapelon's principles, albeit not the whole hog.

 

I was only emphasising the fact that for a truly capable locomotive engineer the rebuilding of a locomotive offers a chance to achieve an outstanding improvement in performance. You are looking for great strides forward; not to tread water or even slide backwards. It is not easy, but the general idea is to apply sufficient knowledge to achieve something outstanding, really outstanding.

Chapelon's rebuilds achieved not only a higher power output but a sustainable one at that. The A4s have been credited with crossing the 3000 dbhp mark. But this effort would be transitory. The general target of 40ihp per ton was set in then 1930s. Although the locomotives achieving this target were compounds subsequent work revealed that this target was achievable with simple expansion. If this had been done the A4 class would be capable of 4000hp or more. Throw in compounding, a higher working pressure and you can go further, how far a man like Porta could go with in excess of 100 tons to play with. It might well be too complicated for regular use but the ideas tried would filter into more general use over a period.

So 6000, yes I was in a way being harsh, but the lack of application of the new and the improved to locomotive development in the UK post WW2 is very disappointing. A 4000ihp Pacific would have to be stronger and hence heavier than 103 tons but the W1 was in theory capable of well what exactly? It worked as a pseudo 3 cylinder machine, 242A1 was much larger but the Gresley engine had a far higher working pressure. And this machine was produced before all the more modern work on leakage losses took place. The next step is triple expansion. What exactly is achievable? Chapelon observed that the Rankine Theory did not appear to predict what might be achieved in practice. The steam locomotive so simple and yet a nightmare of complexity.

 

Please explain!

 

This thread now has nothing at all to do with LMS 3-cylinder locos...
But, since we're discussing the subject, one thing about criticising later steam era designers for not developing the best pre-war designs further is quite simply that after 1939 no one needed or wanted locos ( at least not steam locos) for those duties. This was not just blinkered thinking, it was reality check. I am a big fan of Chapelon's, but no one wanted those massively powerful machines. The time was past.

 

The setting of the cranks on the W1 made it function for a period like a 3 cylinder compound, I write for a period because the machine did change over the course of development. The general idea is that both HNG and Chapelon were on convergent paths. The French machine was the one that made it to the finishing post. It was a larger machine, 1 x h.p. cylinder 600mm x 720mm (23.6" x 28.3")and 2 x l.p. cylinders 680mm x 760mm (26.8" x 29.8") the LNE engine had 2 h.p. cylinders either 12" or 10" bore x 26" stroke and 2 l.p. cylinders 20" x 26". The British machine did have one big advantage in that the boiler could work at 475 psi as opposed to the 4-8-4's 300 psi though the limited h.p. cylinder volume was a weakness it has been rated as potentially the UK's most powerful steam locomotive - if only HNG had been able to give it his full attention (guess who was given responsibility for a measure of the locomotive's later development).

Chapelon extrapolated his ideas used on the 4-8-4 and applied them to the Big Boy the result being a 16,000 hp machine and this before all Porta's work on leakage losses, improved exhaust and combustion systems, improved steam flow and valve developments.

O. S. Nock wrote about the 4498 hauled "Border Limited" - the A4 performed rather well but he did make the observation that steam could never equal the performance over Shap of the then modern electric traction. All done and dusted you might think. Then you learn more. Find out what has been achieved elsewhere. 4000ihp, it could be done. More? Yes, but how much more and how to get there.

 

And would non-enthusiasts have wanted to keep working on or travelling behind steam?

 

Traffic did want more powerful locomotives, which is why the ECML ended up with the Deltic. It needed the continuous power output. Easily surpassed with a steam design, and at lower cost.

But back to LMS 4-6-0s of the three cylinder variety. Maybe we need a steam technical section.

 

LMS ............. But powerful, clean, highly cost effective, single manned engines are what we are aiming for here.

 

Very interesting; thank you.

 

Back to Patriots, Scots, and my original question: If, say, I was adapting a model rebuilt Scot into a Patriot, what would I need to change beyond name and number? (Theoretical discussion only as I have no such model)

 

Basically the cab, since the Scots retained their original Fowler type while the Patriots had a Stanier cab. The front buffer beam was also higher on the Scots, and the cover over the inside cylinder between the front frames was different. There are many photos around to illustrate the point, but I don't have any myself, sorry!

 

Yes, time to get back to the rebuilt Scots and Patriots (and I suppose the two rebuilt Jubilees).

The two differences that I have noted in the external appearance of the rebuilds (apart from the cabs as noted above) are that the Scots have an upright rectangular sand box (I think it is) on the running plate just ahead of the Cab, the other is that the Scots have a couple of projections on the glacis plate in front of the smoke box - I think they were there to help with cleaning the smoke box. The Patriots had neither - it took me ages to spot those differences but they are absolutely diagnostic between a rebuilt Scot and a rebuilt Patriot (from what I can see).

As for the two rebuilt Jubilees - I can't spot a difference between them and the rebuilt Patriots.

As for conversions - well starting from a Scot your main task would be switching the Cab from a Fowler to a Stanier. If you started from a Jubilee your cab would already be Stanier but you'd need to move the Top Feed forward as well as adding the sandbox and the smokebox steps.

Hope this helps.

 

Depending on the level of detail you are striving for and what date, but some Scots retained their Fowler driving wheels, some got Stanier 'v' rim wheels, one even had a mix! Similar for Pats. The Scot topfeed cover also changed.

Dave

 

I confess my sins as to being largely bereft of the basic texts pertaining to LMS locomotives.
Can any one give me the basic dimensions of the blastpipe(s)/smokebox/ double chimney on a rebuilt Royal scot (2a boiler) please ?
heights diameters etc....
Ta

 

There are some good diagrams in the Royal Scots and Patriots of the LMS, O S Nock, David and Charles, 1978. ISBN 0 7153 7480 X. You may find a copy at book fairs or on the inescapable E-Bay.

 

See if you can get a copy of LMS Locomotive Profiles No 1 The Rebuilt Royal Scots by Wild Swan Publications

 

The profile of the bottom corners of the front buffer beam are different between rebuilt Scots and Patriots.

Love to know why.