British 8 coupled loco's

I have been looking at @S. A. C. Martins discussion of Thompson, in particular over the P2's & a mention of the GWR 47XX's

So why exactly were the only Briish 8 coupled loco's with a very few exceptions heavy freight 2-8-0's?

There were the GWR 47xx's - all 7 of them. By all accounts very good machines but with very limited route availability. The 2 P1 2-8-2's. Again excellent machines but it seems far to powerful to be much use.

Then there were the P2's, and I wont go there.

Certainly the SDJR 7F's acquitted themselves well on passenger trains & many 8F's had dynamic balancing that allowed them to work at up to 60mph. I have seen a photo of a 8F on a 'main line' passenger train at Dawlish of all places.

But nobody built a 'series production' mixed traffic/express 8 coupled loco. All the mixed traffic/express loco's were 6 coupled, as indeed were the 'fast freight' loco's - Granges, LNER Moguls S15's etc although many 8 coupled mixed traffic/express loco's were built for export.

Was there no need for fast 8 coupled loco's or was there some other factor peculiar to theUK?

 

Would it have been that by the time you had an eight-coupled loco with the larger wheels that you tend to want for a passenger engine that the whole thing was getting a bit too big and heavy for UK lines?

 

The 9F was origionally conceived as a 2-8-2 but ended up as a 2-10-0.

I doubt anyone on the S&D considered the 7Fs as acquitting themselves well on passenger duties. They were only used post war out of necessity on summer Saturday workings because there were not enough locos to cover all the required duties. They did the job required but were well out of their comfort zone on these duties and I'm sure the crews would have preferred a more suitable loco had one been available. On a broader picture the same could be said of the 8F. The 60mph balancing that some had was not to work passenger trains but for fast fitted freight work

I guess the answer to you question might have something to do with the restricted British loading gauge

Peter

 

Oops - don't know whats gone wrong here but my response above has come out in a funny format. Can a clever mod correct it please

Thanks, Peter

 

Why would you go to the extra expense of building an 8 coupled locomotive if a six coupled one could do the job?
Its interesting to note that according to Cook when Collett was asked for more 47s he elected to build Castles instead because Castles, athough more expensive, were more flexible at filling in on passenger duties, the 47s being limited to 60mph.

 

I agree, if one is thinking of a 4-8-2, though apparently the LMS did consider one.

With the exception of the Kings, British designers seemed to consider wide fireboxes essential for Class 8, hence all those Pacifics, though Chapelon managed a very powerful 4-8-0. If you're including a rear pony truck and you want 8 coupled wheels for better adhesion without going up to a 4-8-2, you get the P2s.

 

You've managed to knock off a square bracket at the end of the [/QUOTE] tag, pop it back and all will be well!

 

Ability to haul a load is down to the total adhesive weight. The bigger this is, the bigger the load a loco can haul. The civil engineers put a cap on axle load so any increase in adhesion weight has to be by more powered axles. So far, so simple. As highlighted by FS123 above, more driving wheels means a longer wheelbase and the problems coming from that, not only in ability to negotiate curves but also in terms of boiler length. Thus, more driving wheels usually meant smaller driving wheels, which affected practical speeds. Added to this, locomotive engineers were generally of the opinion that, if you wanted to go fast, you had a minimum of driving wheels and the larger the better, which is why single wheelers were popular passenger locos in the mid 19th century and only progressed to four coupled wheels when loads outstripped the capacity of a single driving axle. Of course the 9F's kicked this philosophy out of the window but it was only at the end of steam locomotive production that this happened.

 

The 4700s were a really a specialised express freight loco, they were used on relief passenger trains towards the end of their life but I have read accounts that their riding was less than desirable at speed having a Cartazzi truck on a coupled axle. The long wheelbase necessary for large coupled wheels without restricting the minimum radius the loco can traverse was a conundrum.

 

Maunsell considered a four cylinder freight loco 4-8-0 based on the Lord Nelson for hauling coal from the Kent coalfields. The potential performance was such that trains loaded to the full capacity would have exceeded the length of loops &c; the infrastructure costs made the scheme not worthwhile, with the result that the last batch of S15s were built instead.

Tom

 

Previously the LSWR had used some ROD 2-8-0s, and apparently found it hard to find enough heavy, slow freight for them, so a putative 4-8-0 was stillborn.
Pat
(P.S. I know they were 3ft gauge, but I do wish 1 of the Lough Swilly 4-8-0s had survived.)

 

One of the things perhaps worth considering is axle loads. If we take the US out of the equation, generally British main lines seemed to allow for greater axle loads than elsewhere (another exception being Belgium, home of some surprisingly late Atlantics). So a Chapelon 240P (4-8-0) or the later 241P 4-8-2, with 20 tonnes axle load, was actually only putting 5 tonnes more on the coupled axles than the reality of the GWR Kings (as recently discussed on here, the actual axle load on Kings being approx 25 tons), and maybe 15 tonnes more than an LMS or late LNER Pacific. With longer trains of large continental stock, these were expected to haul 800 tonne trains over sometimes quite heavily graded routes. Same in Germany with the 01 Pacifics, which were the dominant heavy express passenger class despite the existence of 4-6-4 and 4-8-4 classes, built to a 20 tonne axle load.

So perhaps the question is, given likely train lengths and permitted axle loads, why should more 8-coupled types have been built for British service?

 

Thanks to whoever sorted my post out. If there is a way to get it wrong you can be sure I'll find it sooner or later.

Peter

 

Axle-load limits during the "steam era" are certainly a key factor when comparing locomotive designs between countries. The USA and Canada were in a class of their own with 30-ton plus limits. But among other countries, only Belgium and some Australian states seem to have compared with the 22½ ton "double-red" (to use GWR-speak) limits allowed on some British routes. So the SR Schools 4-4-0, GWR King 4-6-0 and LNER V2 2-6-2 were each the heaviest in Europe of their respective wheel arrangements. In most other countries, equivalent locos would have needed the weight spread across extra wheels. So the V2 corresponds to the many European 2-8-2 types built for heavy (or hilly route) passenger and mixed traffic duties.

I see from one of the RCTS books that, after Peppercorn had visited the USA in 1946 and been impressed by New York Central 4-8-4s, outline drawings were prepared for LNER 4-8-2 and 4-8-4 designs. They went no further. Apart from any other considerations, they would have needed 75ft or 80ft turntables.

 

..... not to mention the sort of loadings no longer required after WWII .....

That proposal was new to me. Fascinating stuff. Cheers for posting.

 

There were the GWR 47xx's - all 7 of them.

In fact there were 9.

Best regards

Julian

 

The basic stumbling block in the UK is that as the inventor of railways as we know them we made the mistakes that others following were able to avoid. Essentially our restricted load gauge profile of less than 9' width over cylinders and a height of around 13'. Taking the LNER P2 as an example of 'Superpower', to get 21" cylinders resulted in them being about 1-1/2" wider over that point than an A3, the piston rods centres being the same. This left little or no scope for increasing the width of connecting and coupling rod bearings, let alone any side play to to coupled axles. In other words, the mechanical well-being had to be sacrificed to get the power required.

On t'other hand, in Germany, and taking the Kriegslok BR 52 2-10-0 as an example, they are 3 meters (9' - 10") wide over cylinders - a full 1 foot or 12" more than ours - which means the piston rod centres can be further apart (even with 600 mm/23.6" diameter cylinders), adequate widths for conn and coupling rod bearings, and the 1st and 5th coupled wheels having a side-play of 25mm (1") either side of centre. With thin flanges on the centre driving wheels these locos can cope with pretty sharp curves no problem.

With maximum height of 4550 mm (15', and 2' more than ours!) albeit with removable chimney extensions removed, they could run virtually everywhere in Europe. They could be also built to a maximum width of 3150 mm (10' - 4-1/2") which is some 18" more than permitted here. The 01 Pacifics amongst the larger locos were built to this width.

Thus I cannot but help feel that it was probably best that such projects like LNER and LMS 4-8-2s and 4-8-4s were never built as I suspect that their mechanical reliability would not be good. Also one would be getting beyond the limits of the amount of coal a fireman can shovel, so that would bring lower efficiency of stoker firing (steam to drive the stoker plus coal ground into dust and blown to waste up the chimney), a question of economics really.

As the post-war trend was towards lighter and more frequent trains anyway, which Pacifics could cope with, would such proposed 'Superpower' have been needed? Doubtful that they could have run such trains any faster either.

The P2s pushed things to the limits, and despite the researches and modifications done by the 2007 project group, I still have reservations about the future mechanical well-being of this loco.

 

I'm fairly certain that the same infrastructure issues (length of loops etc) were true about the Gresley P1 locos as well.

 

Its interesting to note that the GWR broad gauge had exactly the same width problems at platform height. Had the GWR won the gauge wars, whilst there would now be no problem with container traffic, super power steam locomotives would have had to have been 4 cylinder compounds with the same restrictions on outside cylinders, but room for massive low pressure cylinders inside.