Edward Thompson: Wartime C.M.E. Discussion

I think you hit the nail on the head regarding the A4s being given the heavy work. The impression I get was the A4s were a known item, crews got to know them and maintenance was universal and understood. The A2/2 developed different problems at different times (and yes I think when Thompson reported to the various committees about the first rebuild he was being truthful. The engines could haul the same trains occasionally but this seemingly was only for testing or occasional wartime traffic, the rest of the time if was far less than a usual P2 hauled train. Likewise the engines had not yet developed any of the known faults that later caused problems for the class) and as such the shedmasters were wary of them. Only later on when the faults settled down to more regular and predictable faults (if there is such a thing) such as the steam joints on the P1 booster engines did the shedmasters and crews start to get best performances, at which points the locos had been moved elsewhere. The engines did produce some good results on certain types of trains and were preferred over other classes. Just not in Scotland.

Basically Thompson was constrained by the wartime conditions and was not allowed to build a new design, so logically the answer was to rebuild something so that the powers that be (and this included the War Department when it came to materials etc) were happy. The P2s were out of the way and relatively forgotten about by the management so were ideal candidates in that respect. Yes they could have been modified and produced better engines, however Thompson wasn't looking for that, he was looking to trial his ideas for the future.

I didn't go to much into the A2/2s in the new book as I wanted to concentrate on the P2 history but some new light I hope has been shed.

If anyone wants a copy of the book please drop me a message, if bought through us at the A1SLT we get 50% of the cover price towards the next P2.... blatant plug over...

I don't get on here as much as I like but if I can find my notes and pieces from my Kew trips I will see what I can stitch together for interested parties.

 

I think CJ Allen also mentions their slipping propensities.

 

Although that quote for me is an exaggeration (all Pacifics wheel slip) there's absolutely some truth in the adhesive ratio stakes. The A2/2s had a lower adhesive ratio than the other LNER Pacifics.

However as a rule, all of the Thompson Pacifics had a lower adhesive ratio than the other LNER Pacifics.

As we found out in preservation with Blue Peter (to her cost) it is also about the driving and I have seen lots of videos showing Pacifics from the LNER, SR and LMS slip violently over the years. I've even witnessed it on preserved railways and on the mainline.

The issue is one of perception. We know that the Thompson Pacifics had a lower adhesive ratio, but we also know factually that all Pacific locomotives can and do wheelslip. Are the Thompson Pacifics perceived to be worse because of the designer or were they really that bad by comparison? Depends who you ask and what source.

There are of course other stories and factors. Great Northern when rebuilt burned through a set of rails once, slipping violently when starting away from a station. She had a GCR type regulator fitted at the time and water carryover into the valve when starting made it stuck open. The overall conditions - greasy rails, heavy train, lower adhesive ratio, made for one spectacular show of sparks one suspects! After that the later type of LNER balanced regulator was fitted to her and the other Thompson Pacifics fitted with the GCR type regulator.

It must be acknowledged that this was an incredible one off instance and not reflective of the locomotive's ability as a whole - Peter Townend speaking very favourably of 4470 as rebuilt in his books.

 

Andrew, many thanks for your thoughts on this.

 

Since a loco is hardly likely to find itself on a beach, it's not an exaggeration but simply one driver's sardonic remark regarding a loco's propensity to loose its feet. A bit like one driver's opinion of the Swedish 4-6-0 on the NVR. "She rides like she's got square wheels." Now of course the wheels weren't square but she sure was a rough rider. If a loco has a feature that doesn't endear it to the footplate crew, they'll soon find out about it and let everyone know in no uncertain terms.

 

So we're splitting hairs over the interpretation of exaggeration against sardonic...!

I'm struggling with how you can disagree that it's an exaggeration. It's by definition an exaggeration. It can also be sardonic. They're not mutually exclusive of one another.

 

Yes, everyone is agreed the Hoy 2-6-2T were shocking. And yet they were basically an assemblage of standard Horwich parts, all proven in service on other classes. Which just shows... something (not sure what). Maybe that even doing "the right thing" as a CME doesn't necessarily bring success. Relevant to the main topic of this thread? Perhaps. Hoy, meanwhile, seems to have produced nothing but duds, poor chap.

 

Thank you Andrew (ahardy) for your excellent contribution.

If you can scan your Kew LNER Loco Committee notes or provide them in some format I am sure they would be of great interest to very many, and might help resolve some of the technical issues discussed here, and might also provide a better insight into Thompson and his work as CME.

Your book has been ordered!

Cheers.
Julian

 

I quote East Coast Pacifics at work:-

"No 4470 spent many weeks working from Doncaster on slow trains to Grantham. I rode on the locomotive several times in the spring of 1946 on these turns and found 4470 ran and steamed very well indeed with an excellent ride at the low speeds involved. Although this was a waste of a good engine it was suspected that the driving wheels might have moved on the axles after the slipping incident" so qualified praise...

In Nov 1945 4470 was tested against 4466. the coal per mile results were almost identical with the A1 slightly better and "the new A1 was not worked to its maximum capacity, it's steaming was good as also was its acceleration on rising gradients but it tended to slip if not handled carefully" So further qualified praise, but it was working with a double kylchap exhaust against a single chimney A4 but had the same boiler.....

In Sept 1947 No 113 was tested against No 31 and again 113 showed an improvement in coal and water consumption over the single chimney A1. Townend quotes the report on this test as "it was not thought that No 113 rode as well as the A4 as it had a tendency to lateral movement at the fore end and undue sensitiveness to the slight irregularities which occurred in the track. The locomotive has a marked tendency to slip when starting and also on severe gradients and when extra power was required."

His conclusion was " an other wise excellent engine, generally more powerful and easier to work than in it's original form, slightly if anything more economical than the majority of the A4's of the time had been spoiled by the positioning of the outside cylinders and the problems arising therefrom." so, a loco with an A4 boiler and kylchap exhaust was better than a 180 lb A10 with single blastpipe (wow what a surprise - though how much better than an A3, I wonder) and slightly more economical than an A4 with single blastpipe (again, what a surprise given the kylchap was known to produce better steaming and economy)

Praise then? for the performance, yes, though hardly surprising given the advantages it had in boiler and exhaust, but he was thoroughly damning of the front end layout which was a result of Thompson's "obsessions"

1 - Three separate sets of valve gear - not possible with all drive on the centre axle (which was one reason Gresley developed the conjugated gear - he liked to drive on one axle) so divided drive is required whether desired or not

2 - Equal lengths of connecting rod something he liked about GWR design, I believe. Given divided drive, the outer cylinders driving on the centre axle had to be well back or the equal length middle rod driving on the front axle would put the middle cylinder on the buffer beam.

So, no not very favourably. P Townend spoke favourably of what was good and damned that which wasn't.

 

Thank you for reminding me of where that is, I was trying to find it earlier.

The single chimney A4s formed the majority of the top link with the single chimney A3s: there were only five other Pacifics with the double kylchap. So the comparison seems to be about comparing the normal locomotive type against the potential new standard.

In fairness to the A1/1 you have to concede that the permanent way of the railways post war was not brilliant: this doesn't however explain away the Thompson front ends predilection for such lateral movement.

I think we can all agree that the positioning of the cylinders was for the LNER unorthodox and perhaps Thompsons desire for equal length connecting rods was part of that.

You have picked however the only one of the Thompson Pacifics which didn't have all equal length connecting rods. The centre connecting rod was longer than the outside too - which is why 60113 was the longest LNER Pacific, partially.

However all engineering is a trade off

But Thompson accepted that - that's why all of his Pacifics had the double chimney kylchap fitted. He recognised that the A4 boiler was a good steam raiser and that the A4 design could be developed further.

Hence why 60113 is really not as close to a Peppercorn A1 as has been described previously: it's more a post war A4.

Obsessions or engineering choice?

You use the term negatively against Thompson for his choice but where Gresley and conjugated valve gear is concerned he seems immune.

Can they not both be knowledgable engineers with different engineering preferences?

As opposed either one being "obsessed".

But is divided drive, in and of itself, a bad thing?

But this in itself is not a flaw as any GWR or Chapelon follower will tell you. It only appears to be LNER enthusiasts who use this to beat Thompson with a stick with: other engineers happily used equal length connecting rods.

But the use of the words "excellent locomotive" have passed you by, of course.

Like any locomotive they have positives and negatives. Townend disagreed with the positioning of the cylinders. That's accepted: I think we can all agree that on the Thompson Pacifics the execution was off.

But there is nothing wrong with the theory of using cylinder placement or short connecting rods, any more than there is a question over conjugated valve gear.

There's no doubt that Thompson wasn't in the same league as Chapelon: but look at Chapelons Pacific design. The similarity in layout to Thompson Pacifics is surprising. Staniers princess class too. I've made this point before of course -

Thompson seemed to follow engineering trends elsewhere, away from the LNER, where he felt it didn't come up to scratch on the LNER.

On a number of Gresleys engineering choices he agreed - round topped boilers, wheel sizes for standard designs, the kylchap chimney, etc etc - so he appears to have picked and chose what he wanted to keep in his own designs.

There's no shame in that and doesn't make him entirely wrong - it makes him his own engineer.

 

Just what was the logic behind the desire for equal length connecting rods? The only thing that stands out to me is balancing out of the reciprocating masses for each engine of the locomotive, presumably to reduce potential "hammer blow". Or was there more to it?

 

My understanding is that you cannot get exactly even valve events with different length rods. All because of angularity - that at 50% of piston travel the wheel has not rotated exactly 90 degrees.

 

That chocolate brown livery looked so good on those big Nord machines. Well - this is NP and we haven't talked livery for pages!

 

Marsh umber I think (another ex-GNR man ...)

Tom

 

Are you telling me you didn't know where the information was? It seems you were quoting P Townend without checking your references.

Indeed, so it would show up in a better light than if compared to a double chimney A4?

The actual state of the permanent way is not really relevant as this was a comparison between two types of loco on the same track. Do you agree that the loco which handles bad track better is a better loco?

The rods were close in length - and making the centre one longer simply worsens the problem of cylinder spacing. Perhaps the increased axle spacing was the reason?

Indeed - which is why the results of the testing were no surprise - Why didn't Thompson test the A1 against a double kylchap A4? That would eliminate the boiler and exhaust from the equation and show any advantages due to his choice of valve gear, cylinder and rod layout. Perhaps he knew there were no advantages?

I use the word obsessed because he continued to use those features together despite the problems of the P2 rebuilds. To continue using a design that works is engineering choice, to persist with a design with known problems is obsession, in my view. If Gresley had persisted with Watertube boilers despite the problems with 10000, I'd have said he was obsessed.

No, many locos have divided drive, and it was a corollary of using three cylinders and three sets of walschaerts gear with the outer cylinders driving on the middle set

Certainly, but Thompson's application of equal length rods led to a layout that caused problems. The GWR used equal length rods and outer cylinders set well back, with the two inner cylinders set well forward successfully. Choosing the layout could be called an engineering decision, persisting with it despite problems is not.

and you seem to have ignored the previous two words "an otherwise" The boiler and exhaust were fine and those parts were excellent, as were the same parts on a double kylchap A4. I'd say the hopper ashpan and rod driven steamcocks were also excellent aspects. The different type of valve gear doesn't seem to have been mentioned, so perhaps no difference was noted between the two locos. The cylinder and frame layout gave problems.

The chapelon loco you show had a much longer bogie and the rear bogie wheel was just in front of the leading driver. The GWR 4 cylinder locos are much the same. They seemingly didn't have the same frame flexing and riding problems as the Thompson pacifics.

In theory you are right, but in practice, Thompson seems to have got something wrong and he either didn't notice it, wouldn't accept it or simply refused to change.

I made my post because you were exaggerating Peter Townend's view of the A1/1. He didn't comment "very favourably" - he praised what could be praised and criticised the significant parts he felt were wrong.

 

I think a lot of the dispute would have been solved had the rebuilt 4470 been tested against an A3 as opposed to an A1. An A3 is what 4470 The Great Northern should have become in due course. As Lplus comments testing the Kylchap fitted rebuilt 4470 against an A1 was always going to cause controversity.

You can of course read into the above what you want.

Cheers,
Julian

 

Ah, interesting. I think I see the thinking behind this.

 

We've heard that some of the recent cost of sorting out Flying Scotsman was due its having run for some time with an A4 boiler on frames that were originally designed for a 180 psi boiler. Would the same have applied to Great Northern?

 

Hi Jim,

In theory a well designed valve gear can deal with different conn rod lengths. There are lots of examples of 3 cylinder locos where the outside valve gear does not match the inside cylinder set of gear.

There is a particular problem with the type of arrangement used on the GWR Stars, Castles, and Kings due to the outside gear being worked off rocker arms that reverse the direction, but this is getting rather off topic.

I dont think Thompson fully understood the problems in adopting the general cylinder layout of the GWR 4 cylinder locos, and applying it to a 3 cylinder loco. There is an additional problem in that The LNER frame construction for all the Pacifics was rather flimsy when compared to some other Companies such as the GWR and SR. I dont know enough about LMS types to comment on them.

Cheers,
Julian

 

My understanding is that whilst a good design can partially compensate for the inequalities caused by different rod lengths, ultimately its still going to be slightly uneven. You do, if I understand correctly, need separate inside valve gear to do that sort of thing, one of the disadvantages of the conjugated gear being that you can't have such a correction.

But as ever its got to be balanced against other factors. It seems clear that the GWR put a very high priority on even valve events, others less so*. Pearce did some very tricky geometry, refined on the Kings, to minimise the effects of the rockers, the LMS didn't do anything so sophisticated on the Duchesses and apparently accepted the uneven valve events. TBH I have no idea what the implications are in practice: it would be very foolish of me to make suggestions about which design compromises were optimal..

*Cook: "GW locomotives had extreme regularity in their exhaust beats and we certainly could not permit of anything like two beats and a wooffle which was noticeable on some rival lines" (Swindon Steam p62).