Edward Thompson: Wartime C.M.E. Discussion

Not quite so. In late 1908 an H. A. Ivatt LNER Class J1 0-6-0 (GNR Class J21) was turned out new from Doncaster Work as No. 1. Such hardly comes under the heading of being a 'principle express loco'!

 

Can I just say that this is by some margin quite the most ‘up itself’ boring post I have ever read on this forum. And that is some achievement. Couldn’t be bothered to read the second one.

 

You can but I’d like to add yours is one of the least necessary posts I have ever read on this forum (slightly less even than this one) because it says nothing about the debate or even about the post you are criticising, only about your boredom. So what do you think about Thompson?

 

Thompson's pacifics are regarded by many, including me, as awkward looking. A major reason for this is the ungainly location of the outside cylinders. I understand that he had a 'thing' about equal length connecting rods and I've often wondered why he considered this so important. Was it part of an underlying engineering philosophy? Peppercorn quickly reverted to a more traditional cylinder position on his A2, which I doubt was just for the sake of appearance.

 

I believe it was to do with ensuring the valve events for all three cylinders were equal thus removing the syncopation often heard from a Gresley 3 cylinder engine and uneven effort across the cylinder layout placing stress on other parts of the locomotive.....

But I might be totally incorrect so I shall put my head back below the parapet......

 

Equal valve events are obviously ideal, and that could be why Thompson chose equal length connecting rods, but in reality valve events are affected by several other factors. It's rare to hear absolutely uniform exhaust beats from any steam loco when it's working at a short cut-off.

 

unless its GWR

 

Ive yet to hear an off beat GWR loco...

 

Another question why did Thompson not look to Diesel traction as the other CME of his time did with the two English electric prototypes.

 

I have. 7325 during Steam on the Met many years ago. Markedly off beat.

 

The LNER certainly did look to diesel traction. The board invited tenders from manufacturers to build a fleet of 20-something locos of similar spec to 10000/1 and intended to be used in the same way, following a project proposal put together largely by Michael Bonavia (according to his own books at least). Unfortunately the tender date was in 1948, so Riddles made sure that all of the submissions were ignored and the project abandoned.

 

Money?

 

Seems most likely, though much early diesel research was tied in with specific government projects and/or funding, so perhaps it was the same reason the GW wasn't developing electrification.

 

I'd say that you were spot on, and I'd further say that the, shall we say, disadvantages with the B17 came from a combination of divided drive (more or less a requirement with a 2-6-0) monobloc cylinder and Gresley valve gear. This then leads me to ask, what was the reason for the change from single to divided drive on the 3 cylinder pacifics?

 

I understand that divided drive was used by Gresley on the B17 to reduce axle loading and hammerblow on the former GE lines. Gresley's pacifics, which have unified drive on the second axle, have the middle cylinder set higher than the outside two in order to give the middle conrod sufficient clearance over the leading axle. This arrangement surely contributes to the unequal valve events for which (worn) conjugated gear gets all the blame.

I assume that Thompson favoured divided drive so that the cylinders could all be on the same plane and thus more equal valve timing, similar to his reason for equal length conrods. Please correct me if I'm wrong on this.

Could Raven's design, with unified drive on the front driving axle, have offered an alternative way of improving valve events?

 

Due to the divided drive and monobloc on the B17 the middle cylinder is set even higher than it is on the pacifics, thus making the problem even worse, presumably the 3 cylinder moguls suffered similarly, hence the 'Ragtimer' nick- name, divided drive is more or less a requirement on a 3 cylinder 2-6-0 since having the firebox between the frames requires a long box in order to have reasonable grate area, the second axle is generally below the ashpan. The alternative would be for all cylinders to drive the leading axle,as in Ravens design which would require all three rods to be short, which would result in completely the wrong characteristics for a mixed traffic loco. Interestingly James Holdens 'Decapod' had all three cylinders in the horizontal plane, and in order to 'clear the leading axle the middle conrod was of an open lattice design surrounding the leading axle, which was further cranked, although 'sagged' would be more descripive 31/2" to clear. This behomoth also had divided drive (second/third axle) which could lead toward the hammerblow theory for the GE lines, However the only 3 cylinder pacifics to run out of Liverpool Street were unified drive.

 

Surely a question that should be asked about why Peppercorn didn't look to diesels as he was CME in that era.

 

It all gets a bit complicated though. Think about the timescales. You've got to work up some kind of feasibility study for what it will take to do a pilot, not just locomotives, but also the supporting infrastructure and so on, get all that into some kind of reasonable shape with ball park estimates, get that through the board and approved. Now OK in those days they didn't have the sort of endemic vacillation that cripples every major project these days, but even so its a long term project. Surely neither Thompson nor Peppercorn were going to be there long term, and besides I imagine we know very little about what studies and investigations were done on paper that never appeared in metal.

 

I feel like I should just put an FAQs section on the first page of the thread. Good idea? Yay or nay?

RE diesels - Thompson trialled several shunters (DES1-4) - they were very like the 08 shunters that became commonplace.

Thompson took over on the LNER in 1941 (hallo? Second world war?) and his original remit as CME was to reuse or modify existing locomotive stock only when required. LNER was virtually broke hence the loan from the govt.

After the Cox report was published, he had limited permission to build new locomotives using existing components and rebuild more comprehensively older locomotives, but again limited to use of stock components where applicable. All of Thompsons designs used almost exclusively components that were already available. New boiler diagrams still used standard parts and specifications.

So diesel traction - as per the other railway companies, incidentally - wasn't on the cards during the second world war. Oil supplies were difficult to get a hold of - petrol and diesel rationing were in force anyway - coal, which we mined, in its heyday more or less. Why develop diesel traction at that point? Historical context important!

The equal connecting rods were suggested on the A2/2 builds by ED Trask. Thompson went for this idea (given his GWR affection) and all of his 6ft 2in driving wheel Pacifics had identical front end layouts thereafter. The use of three separate sets of valve gear meant that virtually identical valve gear components could be used on all three sets. This is also partially why the middle cylinder was set so far forward ( this was also of course due to driving onto the front axle with divided drive).

Dividing the drive also alleviated the stresses from pistons onto the crank axle. So in the area where they were suspect (all three cylinders driving onto one axle in P2 design), the A2/2s drive was to two axles - they never suffered a failed crank axle again.

 

Bonavia, who had some involvement in the matter, devotes a chapter to it. He notes inter alia [in second half of 1947] "The Board approved the proposal to purchase 25 diesel-electric main line locomotives to replace 32 steam Pacifics...". He sets out the memorandum in Appendix 2. Although a response to tenders was received from six parties, it all got overtaken by nationalisation.

In looking this up I noticed again Bonavia's comment in the previous chapter: "Thompson harped upon the weakness of the motion for the middle cylinder...so much so that Sir Ronald Matthews was once heard to say, "We really cannot build a locomotive policy for the LNER on the basis that everything Gresley did was wrong."