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Old 4th March 2017, 21:08   #1
StirlingRatty
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Default Single wheelers

I am trying to understand the reasons for the move from large single wheel locomotives to multi coupled ones. What was the technological advance that caused that move?
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Old 4th March 2017, 21:15   #2
Elecman
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Increasing train weights meaning the single wheelers were unable to start the loaded trains due to lack of available adhesion
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Old 5th March 2017, 11:43   #3
Flying Phil
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Would improved lubricants/lubrication also have enabled higher piston speeds, thus enabling smaller (coupled) driving wheels to rotate faster for higher speed?
I did see the Stirling Single on the GCR years ago and it was so effortlessly elegant - but only on a three/four coach train!

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Old 5th March 2017, 14:03   #4
Taunton
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One technological advance was improved steel for coupling rods, which previously had been too prone to failure with higher power transmitted, due to the stresses they sustain at the joints (more so than connecting rods).
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Old 5th March 2017, 14:44   #5
70014IronDuke
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Surely the fundamental reason was economic, rather than technical as such.

for reasons of economy, you wanted ever bigger locomotives to producethe power to pull heavier loads (and/or faster).

The crew of two remained the same, plus the guard. So obvoiusly, it was cheaper to run one big loco + (say) 10 coaches, than two trains with smaller locos and 5 coaches. (Or maybe 6 coaches, as two would be BSKs )

But, you simply could not build a 70 tonne locomotive and put it on one pair of driving wheels - either the axle loading would be so much it would break all the rails and bridges, or, if you used unpowered axles to spead the load (eg into a 4-2-2 arrangement) you lost adhesive weight - ie your single driving axle would be VERY prone to slipping.

The only solution was to expand the number of driving wheels/axles, initially to x-4-x arrangements, and later to x-6-x, x-8-x and even (in the UK) to 2-10-0s.

But it's like every system known in the universe: you develop some aspect to maximise its particular performance, only for other limiting parameters to take effect - eg as noted about, the coupling rods failed (for a period) or, eg the poor fireman was unable to shovel in enough coal to feed the massive grates needed to utilise the massive boilers etc etc
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Old 7th March 2017, 17:07   #6
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Originally Posted by 70014IronDuke View Post
So obvoiusly, it was cheaper to run one big loco + (say) 10 coaches, than two trains with smaller locos and 5 coaches.
Midland Railway did not get that memo!
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Old 7th March 2017, 18:54   #7
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Midland Railway did not get that memo!
Probably why the LMS based their motive power engineering department in Crewe not Derby!
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Old 7th March 2017, 21:40   #8
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Probably why the LMS based their motive power engineering department in Crewe not Derby!
But still heavily influenced by Derby practice until Stanier arrived in the early 30s.
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Old 13th March 2017, 12:35   #9
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"M is for Midland with engines galore
Two on each train and asking for more!"
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Old 20th March 2017, 00:44   #10
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Midland Railway did not get that memo!
No - but even Midland Railway found it had to replace single-wheelers by 4-4-0s.
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Old 20th March 2017, 18:12   #11
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No - but even Midland Railway found it had to replace single-wheelers by 4-4-0s.
While the widespread need for double-heading in steam days made little sense on the LMS, and its BR successor region, the original Midland Railway offer of comparatively short trains departing often from St Pancras was perhaps an early example of a company recognising the attractions of high service frequency to customers.
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Old 20th March 2017, 20:17   #12
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I still don't understand why the Midland didn't build bigger engines, at least when they got far enough north that the routes were hilly and I believe most trains needed double heading. It's not as if Derby couldn't build large locos, as they did for the S&D.
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Old 20th March 2017, 22:43   #13
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One explanation as to why the rival GNR and successor LNER always built locos able to handle the largest trains singlehandedly was a long held understanding that there was a 'ban' on double-heading by the civil engineer on lines into Kings Cross. After the end of steam, my father, who was by then the local divisional traction and rolling stock engineer, wanted to investigate the truth behind this apparent 'ban' as part of the research for his book about the LNER pacifics. There was no formal documentation of the restriction in any sectional appendix or other publication he could find, so what was its source? Informal approaches to friendly colleagues in the the civil engineers resulted in bridge inspectors being dispatched to carry out detailed investigations of the Welwyn viaduct and a bridge at Newark, believed to be the problem structures. From these enquiries, the civil engineer concluded there was in fact no substance whatsoever to any supposed restriction! Double heading then came in very useful as a method for ferrying deltics, working in multiple, between London and Doncaster for the routine engine swaps that were part of the maintenance regime for the class.
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Old 21st March 2017, 07:00   #14
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One explanation as to why the rival GNR and successor LNER always built locos able to handle the largest trains singlehandedly was a long held understanding that there was a 'ban' on double-heading by the civil engineer.
Gerry Fiennes, in "I tried to Run a Railway" commented on this; when the Deltics were under consideration to replace the lower powered pioneer diesels which didn't have the performance, another senior manager said "Why don't you double-head". And that was where the restricted length of Kings Cross station (which it has compared to other termini) came into play. Fiennes, the Deltic champion, retorted "yes, two locomotives on EACH end with a platform turnround, triple-car dining set (which the ECML long had), and you end up with space left for about three coaches".

Certainly during WW2 when maximum train lengths were required it was not uncommon apparently to have four or five coaches off the platform there, and the train engine actually just into Gasworks Tunnel, all blocking much else.
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Old 21st March 2017, 11:26   #15
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Quote:
Originally Posted by MarkyT View Post
While the widespread need for double-heading in steam days made little sense on the LMS, and its BR successor region, the original Midland Railway offer of comparatively short trains departing often from St Pancras was perhaps an early example of a company recognising the attractions of high service frequency to customers.
You have saved me writing the same thing (more or less). The London extension in particular needed this kind of service - and still does to some extent today. Very different population centres north of Luton compared to, say, the ECML, where you only really had Huntingdon and Peterborough north of Hitchin pre 1970. I remember when the local service north of Hitchin was incredibly poor in the early 60s - one four-car DMU every four hours, plus two up and two down commuter trains to/from KX in the peak.

But going back to the original point, although compounds were quite big locomotives when first introduced, the Midland surely could have used a decent Class 5 type 4-6-0 on the difficult routes such as Peak Forest and the S&C.
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