Edward Thompson: Wartime C.M.E. Discussion

Just my feelings.
The very few non stop trains had been better served by 4-4-4s with three cylinders for crew protection and less than six feet drivers for mass saving .
There is a comparison of an outstanding run of 60007 Sir Nigel Gresley (104 tons)and a 9F(84tons) on page 253 of ISBN 0901115959.
If preservation was a big money game to see how far former CMEs were from the ultimate, then the next logical step would be to make a Royal Scott or B16 with five feet wheels.
Kinder to track due to less unsprung mass and the saved mass can be converted to more boiler efficiency.
A Hall with some kind of extra balance could join as well but the Nelsons had too many cylinders for my taste.
A single fireman could be trusted to fire ca 3000 lbs per hour and max 35-40 square feet of grate would have been fine.

 

A very fair point, thank you Tom.

 

The trouble is that in these situations people are all to ready to label opinions that depart from the groupthink as being inflammatory and trolling. And one might even suggest in some circumstances there are those who think that playing the man in the form of making accusations of trolling is an effective way of shutting down an argument that they are unable to defeat by rational means.

Nevertheless there are such things as people who, inadvertently or deliberately, make discussion so unpleasant as to seriously damage the forum. The moderators lot is not an 'appy one ['appy one]. For the rest of us: is it not amusing to put one's tongue in ones cheek and treat the troll as if they were being serious and debate calmly and rationally? Remember your genuine troll wants to provoke angry responses. Why should we give them what they want? And if it turns out they weren't trolling at all, just socially inept, then that's good too.

 

If I've got this right members are being threatened with bans here. With respect, that's not on.
If moderators find that posts are unacceptable THEN take action but having a 'behave or be banned' threat hanging over folk..........that's wrong. IMO.

 

I bet you've never been accosted at a preserved railway on a day out with friends, though Jim, for your views on the GWR like I have for my views on Edward Thompson. I have - several times - particularly in the last five years. A few of them have been positively horrendous experiences, though in the main they are swift exchanges and I walk away when I can. On occasion sworn at quite badly.

Equally, I have also had people come up to me to ask me questions, and that has been much better and much more constructive. Ideas discussed and shared are far better than angry exchanges.

I still find it incredible, given my track record in preservation, and everything that I do and say, that there are those who still think I have been writing the book to undermine Gresley's reputation. Nothing could be further from the truth.

 

No, but then firstly I don't suppose there's a single soul who'd recognise me, and secondly am I not brave enough to stick my head above the parapet when it comes to sacred cows. It is not, I submit, a good thing that there are bullets flying for those who are unwary. We should not be at war with each other.

 

And also coping with coal of variable and often poor quality. The BR standards had wide fireboxes down to Class 6 and as originally planned even down to Class 5.

 

Surely Big Al has merely reminded us that there are terms under which we all participate here, and if we breach those terms we get banned.

I do sometimes struggle to understand Hermod's thinking, but not because of the minor imperfections in his English. He evidently has strong ideas about how steam locos should have been designed, but he is not alone in that.

On his specific issue of wheel sizes: over a long period, as other aspects of design were gradually improved, large wheels became less necessary for high speeds, hence Bulleid's and Riddles' locos having nothing larger than 6'2" driving wheels, as against 6'8" give or take an inch for the Big Four's other top express locos and 7 or 8 feet in earlier times. (I concede that after the war there was perhaps also less inclination to run at high speeds.) I would be interested to know why Peppercorn (and BR after nationalisation) chose to build two versions of his Pacifics, almost identical apart from a 6 inch difference in their driving wheels. Was there really a significant difference in their suitability for various duties?

 

Hermosd's thinking........hmmm.

I feel it can be stated that Gresley introduced the 6'-2" initially with the P2, and in greater numbers with the V2s, yet perhaps quite unwittingly at the time, introduced a new trend later taken up by Bulleid, Thompson, Peppercorn and Riddles.

From shed allocations it would appear that the Peppercorn A1s were more based at sheds serving the faster ECML, and the A2s more in the North-East and Scotland serving hillier routes.

 

I think this is an interesting point not just limited to the Thompson/Peppercorn Pacific story. I vaguely recall the Britannias were originally going to be built in 6' & 6'-6" flavours before a via media of 6'-2" was decided upon. How much of a difference it could have made I cannot guess. 859 Lord Hood's smaller (6'-3") driving wheels didn't seem to make much of a difference in her performance compared to her sisters. The GWR 81XXs also spring to mind. I don't think the question of whether small differences in driving wheel diameter make a significant difference was ever answered but the existence of so many variations attempted by multiple CMEs must surely point to the answer being yes. Why do it otherwise?

Apologies if this seems tangential but I think Peppercorn's Pacifics are as important a corollary to the Thompson story as there can be.

 

Peppercorns pacifics were more Thompson than Gresley but had unequal length conrods?None were conjugated.

The question of wheel-diameter is linked to cylinder number and permanent way.
PreWW1 Germany stated 5 rev per second max for two-cylinder engines and hammerblow per wheel at that speed not to exed 15% of static load on rail.
For three and four cylinders it was 6 rev per second.
The UK Bridge stress recommandation 1927 was that at 6 rev no wheelblow over 5 tons and total engine blow not over 12 tons.
Multicylinder locomotives did blow much less or zero.
It is therefore not unreasonable to say that if a two cylinder /6 feet 6 handles a speed job OK, a threecylinder five feet will as well and allow a larger boiler and be much kinder to track,train and crew.

 

It’s not just about hammer blow - there is piston lubrication which is related to peak piston speed.

In Victorian times, with relatively primitive piston and valve lubrication, locos that were expected to run fast had large wheels so as to have relatively small number of piston strokes per minute and therefore minimise frictional heating of the pistons and valves. There were extreme examples - the Stirling singles had 8’ diameter driving wheels, and I believe a class of 4-2-4T locos on the Bristol and Exeter had 10’ diameter wheels. Such large wheels bought their own problems of centre of gravity, with the boiler having to be mounted above the crank axle; and comparatively low tractive effort limiting the loads that could be reliably hauled uphill.

In the twentieth century, particularly between the wars and after, lubricant technology dramatically improved. At which point, higher piston speeds became acceptable, which in turn meant smaller wheels became available. A 6’2” Pacific in all other respects equal to an earlier 6’8” Pacific potentially accelerated quicker and has a higher TE without necessarily compromising speed. Even so there were limits: I believe one of the reasons Bulleid Pacifics have the comparatively short stroke of 24” (rather than the more normal 26 or 28) is to reduce peak piston speeds at their nominal maximum design speed.

So in your hypothetical example, a 5’ diameter loco going at the same speed as a 6’6” loco will have peak piston speeds about 30% higher, at which point the lubrication may not be up to the job. Indeed, on the rare occasions that they worked fast passenger trains, you can calculate that a 9F at 90mph has approximately equivalent piston speed to an A4 at 120mph, and presumably equivalent demands on the piston and valve lubrication.

Tom

 

If the 9F had three cylinders they could be anything between 16 inch bore/28 stroke or 20/19 .
If made 18/23 there will be space for some lateral movement of first driver.
Still King of mainline?

 

According to a Swindon Junior engineering Society paper I was reading the other day there was a quantum leap in refining technology about 1935.

 

Yes, there was, though it was probably a few years earlier than 1935. My late Grandpa worked for ESSO and dealt with big railway contracts, and had an encyclopedic knowledge and memory of such things from 1927 onwards.

Cheers,

Julian

 

In the context of this thread I find it amusing that some legs of Steam Dreams' Highlands and Islands tour were double-headed by a classic Gresley loco and a classic Thompson one.

 

IIRC once BR authorities found out about high speed exploits with 9Fs, a speed limit was slapped on them pretty smartish.

 

The German standard 4-6-2s also had 2.0m (6ft 7in) coupled wheels from 1925 until the final Bundesbahn pair in 1957, same as the French post-WW2 4-6-4s and 4-8-2s. For comparison, the numerous French mixed traffic 2-8-2s were 1.65m (5ft 5in).

From the end of the single-driver era around 1900, the period 1900-1940 saw express loco coupled wheels generally between 6ft 6in and 7ft 0in in Britain and comparable countries. The range 5ft 5in to 6ft 3in covered most engines for mixed traffic work, passenger work on hilly routes and passenger tanks for fast but short-distance turns.

And then along came that despiser of convention, Sir Oliver Bulleid, and drove his iron horse and coaches through this pattern.