Britannia. Why single chimney?

[Forester]

Always believed the small chimney spoiled the appearance of the otherwise impressive Riddles Britannia class.

 

Why were they given single chimneys?

Would they have performed better with double or multiple blastpipes and large chimneys? Was this considered?

 

Plenty of discussion about the 8P draughting but I've never seen any discussion of the 7MT arrangement, contemporary or in preservation.

 

Thoughts anyone?

[Bon Accord]

Ditto, I've always thought the Brits would have been low hanging fruit for some double chimney experimentation and am surprised it wasn't attempted.

[The Johnster]

The Britannias steamed pretty well as they were.  A double chimney does not always improve a loco's performance over that with a single chimney, and can in some cases lead to a 'soft' exhaust which cannot clear properly and lead to steam hanging down around the boiler and obscuring the crew's forward vision, even on locos fitted with smoke deflectors.  It is a matter of subjective personal opinion, but I find the Brits to be fine looking engines with the chimneys they've got, while preferring my 9Fs to have double chimneys!

 

I am not qualified to answer the question of whether they'd have performed better with a double chimney, but modern computer modelling might be able to provide an answer.  As they only had two cylinders to exhaust, a multiple blastpipe would not have been needed, though you might argue that a double one could have been used.

 

I have no idea if a double chimney, blastpipe, or any arrangement other than that actually provided, was ever considered for the Britannias, either in the design stage or as a retrofit alteration.

[pH]

Always believed the small chimney spoiled the appearance of the otherwise impressive Riddles Britannia class.

 

Why were they given single chimneys?

Would they have performed better with double or multiple blastpipes and large chimneys? Was this considered?

 

Plenty of discussion about the 8P draughting but I've never seen any discussion of the 7MT arrangement, contemporary or in preservation.

 

Thoughts anyone?

 

Information below is from “British Pacific Locomotives” by C.J. Allen and Loco Profile #12 “BR Britannias”.

 

The original design proposal for what became the Britannias included a double blastpipe and chimney. (It also, apparently, specified outside bearings for all carrying wheels!) However, this was dropped as a result of testing done at Swindon and on the Rugby test plant. This showed arrangements, like double blastpipes, designed to reduce back pressure at steaming rates close to maximum did not produce optimum performance at low output. A single blastpipe arrangement was more versatile over the whole range of output. The Britannias were classed as ‘mixed traffic’ engines (power class 7MT), were expected to perform various types of work, most of it probably at moderate power outputs, and so it was decided to fit a single blastpipe and chimney. If continued research (neither publication says there ever was any more research done) showed that there were possible advantages to a different arrangement, it could be looked at again.  

[Forester]

Information below is from “British Pacific Locomotives” by C.J. Allen and Loco Profile #12 “BR Britannias”.

 

The original design proposal for what became the Britannias included a double blastpipe and chimney. (It also, apparently, specified outside bearings for all carrying wheels!) However, this was dropped as a result of testing done at Swindon and on the Rugby test plant. This showed arrangements, like double blastpipes, designed to reduce back pressure at steaming rates close to maximum did not produce optimum performance at low output. A single blastpipe arrangement was more versatile over the whole range of output. The Britannias were classed as ‘mixed traffic’ engines (power class 7MT), were expected to perform various types of work, most of it probably at moderate power outputs, and so it was decided to fit a single blastpipe and chimney. If continued research (neither publication says there ever was any more research done) showed that there were possible advantages to a different arrangement, it could be looked at again.  

 

Thanks for the quote.

 

I always thought the Britannia 7MT classification fell into the same category as calling the Merchant Navy class "Mixed Traffic". At least the first MNs were tried and photographed on heavy goods trains.  Early publicity photos of Britannia were never on mixed traffic work, always on named expresses,

I do acknowledge that much later in life the Brits genuinely ended up as 7MTs on heavy goods as well as passenger trains. But by that stage most pacifics were doing the same as steam ran down.

 

Fair points though.

[APOLLO]

Some Brits steaming well here, near the end of their working lives.

 

http://www.rmweb.co.uk/community/index.php?/topic/67100-apollos-grand-days-out/page-2&do=findComment&comment=940913

 

Brit15

[jonny777]

Always believed the small chimney spoiled the appearance of the otherwise impressive Riddles Britannia class.

 

Why were they given single chimneys?

Would they have performed better with double or multiple blastpipes and large chimneys? Was this considered?

 

Plenty of discussion about the 8P draughting but I've never seen any discussion of the 7MT arrangement, contemporary or in preservation.

 

Thoughts anyone?

 

If you read ES Cox on BR Standards, you get the impression that the recent tests at the time had shown the opposite to the perceived wisdom, which had recently been discovered; that is a narrowing of chimney diameter with a reduction in taper had improved steaming rates by a large amount.

 

Cox cites the Ivatt 4MT (flying pig) which saw an 89% increase in steam production with a reduction in chimney diameter of 1.5 inches; and this in addition to the improvements gained by the substitution of a single chimney for the original double variety.

 

He also mentions the Manor class which leapt from 10000lb of steam per hour to 22000lb after narrowing of the chimney dimensions.

 

Prior to this research work ( by S O Ell at Swindon ) it had been proposed to fit all the larger standards with double chimneys, but this was changed to correctly dimensioned single ones until research work on double blastpipes had been completed.

Edited June 17, 2017 by jonny777

[newbryford]

Thanks for the quote.

 

I always thought the Britannia 7MT classification fell into the same category as calling the Merchant Navy class "Mixed Traffic". At least the first MNs were tried and photographed on heavy goods trains.  Early publicity photos of Britannia were never on mixed traffic work, always on named expresses,

I do acknowledge that much later in life the Brits genuinely ended up as 7MTs on heavy goods as well as passenger trains. But by that stage most pacifics were doing the same as steam ran down.

 

Fair points though.

 

I always thought that by calling the MN's as mixed traffic locos meant that they could be built during WW2.

 

Quoting from Wikipedia.

The new design was intended for express passenger and semi-fast work in Southern England, though it had to be equally adept at freight workings due to the nominal "mixed traffic" classification Bulleid applied to the class for them to be built during wartime.^[Administrative measures had been put in place by the wartime government, preventing the construction of express passenger locomotives, due to shortages of materials and a need for locomotives with freight-hauling capabilities.Classifying a design as "mixed traffic" neatly circumvented this restriction.

 

 

Cheers,

Mick

[D854_Tiger]

Don't forget many of those classes that did receive double chimneys, such as the Castles, didn't receive them until around the same time as the Britannias were being built.

 

Any subsequent development of the Britannias, had it been considered or needed, would then have most likely ran head first into the decision to do away with steam altogether, after which all further steam locomotive development, even including scheduled rebuilds (such as the West Country class), pretty much came to an end.

[DCB]

I always thought the Britannia started as an LMS proposal for as large wide boiler mixed traffic loco like the LNER V2 with a target like the MN to run 600 tons at 60 mph, not 400 at 75mph as per Express Passenger locos.  Obviously the design morphed and lost its way gaining a leading bogie, losing a couple of much needed tons of axle weight and being tarted up to look like something vaguely German which I suppose saw and liked when out abroad in 1944/45.

 

Back in the late 1940s the only double chimneys used successfully in the UK were on three and four cylinder locos. The LNER had about a dozen  4X A4  1 X A 3  1 X A1(?)  W1(?) and some A 2s, The LMS 50? Duchesses, Turbomotive and Jubilee/ Scot rebuilds.   The 2 cylinder ones,  Flying Pigs, the first County, Black Fives were pretty lame, some were re converted to single chimney with great improvement, so once the decision to fit the Brit with only two cylinders had been reached there was no successful UK double chimney arrangement to copy.   

 

Also in the late 40s small blastpipe orifices and more superheat which reduces exhaust pressure were the fashion as there was a desire to burn huge amounts of cheap coal instead of sensible amounts of decent coal, Kings, etc had their variable blastpipes (Jumper tops) removed and the nozzles sleeved.

 

Whether the Brits would have been better with double chimneys is difficult to answer, they may have been faster but they seemed plenty fast enough already, but Riddles would have been in deep doo doo if his shiny new nationalised loco hadn't steamed.

 

The 9F is a bit of an enigma, After the first batch they were fitted with 4MT regulators which effectively meant they couldn't be opened up beyond 2/3rds throttle.  This only seemed to affect them while running very fast at full regulator ( as in slipping furiously)  which is odd.

Their initial duties were at Ebbw Vale  where the GW plotted a King Boilered 2-10-0 at one time and actually tested Kings on these heavy (Iron ore?) trains, very successfully.  More successfully than the 9Fs managed initially.  It could be said a King could cope with 9F duties just as capably as a 9F could run King turns. 

Ell discovered 9Fs would be more economical pulling 600 ton at 60 mph with double chimneys so they altered the ones under construction and the few that had heavy general overhauls at Swindon pre 1960 ish, the fact they didn't actually get to pull 600 tons at 60 mph was sort of forgotten, so they ended up with a heavy goods loco capable of 2000 hp and 92 MPH   Whooppee.   The design really vindicated itself when 92220 pulled a 410 ton Pines Express single handed over the S&D on the last day.  

 

The use of a big powerful loco like the 9F running at such high rotational speeds was unprecedented in the UK, Churchward disliked asymmetric crossheads as they gave uneven piston wear and excessive piston and ring wear seemed to be the 9Fs achilles heel.

Maybe if they had been fitted with LMS style cylinders and valve gear they would have suffered less wear and been more useful on fast workings.

 

The other question which bugs me is why on earth didn't they put the Brit Boiler and trailing truck on Duke of Gloucester

Edited June 17, 2017 by DavidCBroad

[John_Miles]

If you read ES Cox on BR Standards, you get the impression that the recent tests at the time had shown the opposite to the perceived wisdom, which had recently been discovered; that is a narrowing of chimney diameter with a reduction in taper had improved steaming rates by a large amount.

 

Cox cites the Ivatt 4MT (flying pig) which saw an 89% increase in steam production with a reduction in chimney diameter of 1.5 inches; and this in addition to the improvements gained by the substitution of a single chimney for the original double variety.

 

He also mentions the Manor class which leapt from 10000lb of steam per hour to 22000lb after narrowing of the chimney dimensions.

 

Prior to this research work ( by S O Ell at Swindon ) it had been proposed to fit all the larger standards with double chimneys, but this was changed to correctly dimensioned single ones until research work on double blastpipes had been completed.

 

Cox is not the best of sources to quote. There are suspicions that he falsified results from the Rugby test plant and some of his writings on LMS locos have been shown to be biased.

[D854_Tiger]

Cox is not the best of sources to quote. There are suspicions that he falsified results from the Rugby test plant and some of his writings on LMS locos have been shown to be biased.

 

He was an engineer that pretty much guarantees he was always up for some handbags at twenty paces.

 

I now this because I am also an engineer.

[Phil Bullock]

IIRC fitting double chimneys to standard 4MT 4-6-0s raised their performance - albeit transiently one would assume due to the size of the boiler - to 5MT equivalent

 

Phil

[The Johnster]

I always thought the Britannia started as an LMS proposal for as large wide boiler mixed traffic loco like the LNER V2 with a target like the MN to run 600 tons at 60 mph, not 400 at 75mph as per Express Passenger locos.  Obviously the design morphed and lost its way gaining a leading bogie, losing a couple of much needed tons of axle weight and being tarted up to look like something vaguely German which I suppose saw and liked when out abroad in 1944/45.

 

Back in the late 1940s the only double chimneys used successfully in the UK were on three and four cylinder locos. The LNER had about a dozen  4X A4  1 X A 3  1 X A1(?)  W1(?) and some A 2s, The LMS 50? Duchesses, Turbomotive and Jubilee/ Scot rebuilds.   The 2 cylinder ones,  Flying Pigs, the first County, Black Fives were pretty lame, some were re converted to single chimney with great improvement, so once the decision to fit the Brit with only two cylinders had been reached there was no successful UK double chimney arrangement to copy.   

 

Also in the late 40s small blastpipe orifices and more superheat which reduces exhaust pressure were the fashion as there was a desire to burn huge amounts of cheap coal instead of sensible amounts of decent coal, Kings, etc had their variable blastpipes (Jumper tops) removed and the nozzles sleeved.

 

Whether the Brits would have been better with double chimneys is difficult to answer, they may have been faster but they seemed plenty fast enough already, but Riddles would have been in deep doo doo if his shiny new nationalised loco hadn't steamed.

 

The 9F is a bit of an enigma, After the first batch they were fitted with 4MT regulators which effectively meant they couldn't be opened up beyond 2/3rds throttle.  This only seemed to affect them while running very fast at full regulator ( as in slipping furiously)  which is odd.

Their initial duties were at Ebbw Vale  where the GW plotted a King Boilered 2-10-0 at one time and actually tested Kings on these heavy (Iron ore?) trains, very successfully.  More successfully than the 9Fs managed initially.  It could be said a King could cope with 9F duties just as capably as a 9F could run King turns. 

Ell discovered 9Fs would be more economical pulling 600 ton at 60 mph with double chimneys so they altered the ones under construction and the few that had heavy general overhauls at Swindon pre 1960 ish, the fact they didn't actually get to pull 600 tons at 60 mph was sort of forgotten, so they ended up with a heavy goods loco capable of 2000 hp and 92 MPH   Whooppee.   The design really vindicated itself when 92220 pulled a 410 ton Pines Express single handed over the S&D on the last day.  

 

The use of a big powerful loco like the 9F running at such high rotational speeds was unprecedented in the UK, Churchward disliked asymmetric crossheads as they gave uneven piston wear and excessive piston and ring wear seemed to be the 9Fs achilles heel.

Maybe if they had been fitted with LMS style cylinders and valve gear they would have suffered less wear and been more useful on fast workings.

 

The other question which bugs me is why on earth didn't they put the Brit Boiler and trailing truck on Duke of Gloucester

 

Yes, iron ore trains to Ebbw Vale steelworks from Newport Docks, heavy loads on a steeply graded and sharply curved route.  The initial trials with 9Fs in 1954 were notorious for the heavy smoke screen the locos left all the way up the Ebbw valley.  It is, at least in my opinion, significant that later allocations of 9Fs to Ebbw Junction shed were double chimneyed locos and included the unique Geisl Ejector fitted 92250.  The GW apparently proposed a 2-10-2 tank which would have looked like a 72xx on steroids for this route, with a 'King' boiler, but it was rejected on the grounds that the frames would not have coped with the sharp curvature and water leakage from the tanks would have been at an unacceptable level in consequence.  It would probably have been the heaviest axle load on the GW.

 

Evening Star, when first allocated to Canton in the summer of 1960, was used on the 'Red Dragon' and kept time with the train despite the difference in driving wheel diameter from a Britannia's 6'2".  Apparently, when management at Paddington noticed that the big green engine on the 'Dragon' had more driving wheels than it should have, Canton were promptly instructed to stop messing about (it is possible that this was not the actual term used) and put the loco on the freight work it was designed for...  A similar exploit on the ECML with a 9F substituting for a failed Pacific and running at over 90mph was another vindication of this excellent design that hardly needed vindicating!

 

A Brit boiler might not have had the capacity to feed 3 cylinders at high output; the Duke of Gloucester was conceived as an express passenger 8P for the WCM, to run as fast as possible up Shap and Beattock, whereas the Britannia was a mixed traffic 7MT to be suitable for fast freight work as well as passenger duties less strenuous than 8P work.  I am not stating this to be the reason that the Brit boiler was not used on the 'Duke', but suggesting it as a possibility, nor am I suggesting that it worked on the Duke as originally built...

Edited June 18, 2017 by The Johnster

[34theletterbetweenB&D]

The simple fact is that the steam loco exhaust set up is always a compromise: from a power production perspective the selected arrangement should be the one obtaining the most efficient entrainment of the combustion product for least energy, over the target speed range of the design. ideally a variable exhaust configuration would be used - the 'jumper top' blastpipe fitting is an attempt at this - but the brutal truth was that the smokebox environment was so filthy that no such mechanism remained sufficiently reliable in service while steam was the majority power supplier for rail transport. Modern technology can do it. Read Chapelon and his followers for more.

[Grovenor]

Cox is not the best of sources to quote. There are suspicions that he falsified results from the Rugby test plant and some of his writings on LMS locos have been shown to be biased.

Biased or not, Cox was in charge of the design team and a published source, it would seem likely those thinking him biased ahve an opposing bias.

Can you advise of a more unbiased source from someone equally in the know?

Regards

[slilley]

I always thought that by calling the MN's as mixed traffic locos meant that they could be built during WW2.

 

Quoting from Wikipedia.

The new design was intended for express passenger and semi-fast work in Southern England, though it had to be equally adept at freight workings due to the nominal "mixed traffic" classification Bulleid applied to the class for them to be built during wartime.^[Administrative measures had been put in place by the wartime government, preventing the construction of express passenger locomotives, due to shortages of materials and a need for locomotives with freight-hauling capabilities.Classifying a design as "mixed traffic" neatly circumvented this restriction.

 

 

Cheers,

Mick

 

 

But dont forget the first batch of MNs was ordered before World War 2 broke out.

[John_Miles]

Biased or not, Cox was in charge of the design team and a published source, it would seem likely those thinking him biased ahve an opposing bias.

Can you advise of a more unbiased source from someone equally in the know?

Regards

 

The various publications of Adrian Tester.

[The Johnster]

All of which opens a debate as to driving wheel diameter.  Several locomotive designs had appeared before the Britannias were drawn up featuring 6'2" diameter ones including the GW King and LNER P2, (pre-war and predating the Merchant Navies), Hawksworth Counties, and Thompson/Peppercon pacifics, all ostensibly express passenger locos, as well as the 'mixed traffic' Merchant Navies.  It could be argued that Collett would have preferred larger Star/Castle driving wheels on the King but was constrained by the size of the boiler as well as axle load considerations.  Notwithstanding a driving wheel whose diameter would have been considered small for an express loco prior to the grouping, modern lubricants meant that all of these locos could run at express speeds of approaching and sometimes exceeding 100mph on a daily basis without issues arising from that.

 

But the generally accepted diameter for fast mixed traffic locos was around 6', as on GW Hall, LMS Black 5, and LNER B1, 2 of those designs predating the Merchant Navy.  We are coming down to splitting hairs here; indeed the LNER's pre-war fast mixed traffic loco was the V2, with a driving wheel diameter of, yes, 6'2".  Tyre wear in service would take this dimension very close to and possibly under 6', so the difference between an express passenger loco and a mixed traffic one becomes a little blurred if you are taking driving wheel diameter as the defining factor!

 

And you cannot argue that the MN's 3 cylinders made it a 'luxury express engine' either, as the mixed traffic LNER V2 was a 3 cylinder beast.  I am not sure that the story that Bullied blagged the MN's during wartime with the mixed traffic argument stands close scrutiny, but since that sort of scrutiny of decisions taken in closed boardrooms nearly 80 years ago cannot be made, it is an academic point; it would not be the only piece of railway mythology to be proved suspect.  The claim was certainly made at the time of the MN's introduction, and Hawksworth was known to be quite upset over it having had some of his ideas refused by the Ministry of Supply, but it is difficult to argue with Bullied's claim that the MN's were mixed traffic locos whatever your suspicions, or at least it would have been difficult to argue it with Bullied!  In any case he was only doing the best he could for his railway as he saw it.  Thompson on the LNER built 3 cylinder pacifics during wartime without claiming them to be mixed traffic locos and nobody seems to have commented on the fact, although the locos were and still are controversial in other respects.  If the restriction on express passenger locos could be circumvented in this way as the Wikipedia entry claims, they'd have all been at it...

 

By the late 40s and early 50s 6'2" had become an accepted standard size for express work, and rotational speeds considered less of a barrier to fast running than they had been, arguably resulting in increased hammer blow. 

 

Personally, I am happy to give Bullied the benefit of the doubt, though Hawksworth wouldn't have!  Having done that, I cannot argue that the 'Britannia' was anything other than a fast mixed traffic loco, and a very successful one at that, which justified it's 7MT power rating.

 

BR Standard 8P 71000 Duke of Gloucester had 6'2" driving wheels, and whatever that loco's problems were as built, the size of her driving wheels was never one of them.

Edited June 18, 2017 by The Johnster

[New Haven Neil]

I think scrutiny of the Great Central's many changes of driving wheel diameters on successive 4-6-0's proves that it makes little difference when the change is in inches.  It seems there was a belief at the time that driving wheel diameter was some kind of magic ingredient - it isn't.  As valve gear, valve design and metallurgy advanced, it became ever less so.  By the time of the standards I think two sizes would have done the lot.

[The Johnster]

I think scrutiny of the Great Central's many changes of driving wheel diameters on successive 4-6-0's proves that it makes little difference when the change is in inches.  It seems there was a belief at the time that driving wheel diameter was some kind of magic ingredient - it isn't.  As valve gear, valve design and metallurgy advanced, it became ever less so.  By the time of the standards I think two sizes would have done the lot.

 

Back in Victorian days, a large diameter driving wheel (and some of the singles were very large indeed) was desirable in that it increased speed of travel but reduced the speed of piston strokes, making life easier for the indifferent lubricants they had in those days.  The largest wheels were not needed by the turn of the 20th century, and within a few years of that became increasingly difficult to house beneath boilers that were increasing in size and diameter.  There has to be room beneath the boiler for not only the axles, which sit a few inches higher at the tope than half the wheel diameter, but internal motion, eccentrics, and so on, especially with multi-cylinder or compound designs.  The Midland compounds, for example, had 7' driving wheels and, by the time they were being produced for the LMS, a smallish boiler.  They were fast enough engines in their day, but never record breakers.

 

The GC's experimentation with driving wheel diameters was repeated on the GW by Collett, who either messed around with or did his best to improve on (depending on your opinion) the range of standard sizes from the Churchward era.  As well as coming up with a more or less pure Churchward loco that hadn't actually been built, the Grange, he introduced new driving wheels of 5'6" and 5'3" diameter and fitted them to large prairies and 43xx moguls in an attempt to improve tractive effort; little difference was made.

 

You are right in my view, by the time of the grouping the differences in driving wheel size were becoming less important and not only the BR standards, but the Big Four could probably have done everything they needed to with no more than 3 wheel sizes; a sub 5' wheel is still necessary for heavy slow unfitted mineral work, which did not exceed 25mph and lasted well into the 1960s.