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What Ifs, and Locos that never were.

Discussion in 'Steam Traction' started by Jimc, Feb 27, 2015.

  1. RLinkinS

    RLinkinS Member

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    I think that locos with leading pony trucks were accepted on their merits. The LMS and BR designs performed well the SR design was not so good

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  2. Jamessquared

    Jamessquared Nat Pres stalwart

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    Though after conversion, the U-boats had no real problems at speed. Whereas the L class 4-6-4T with a leading bogie had dreadful problems similar to the K class, and had all manner of subterfuge of water space to try to get round it.

    I think the bottom line was that the track in the 1920s just wasn’t up to having big tank engines working fast, especially on the Eastern section; by the 1940s it had all been completely renewed on a new formation (allowing for the fact that the condition probably wasn’t as good in 1945 as it had been in 1939).

    Herbert Walker is rightly credited with playing a delicate hand to sort out the issue without antagonising either his CME or his Chief Civil Engineer, but my feeling is that had the K class been introduced on the LNER running out of Kings Cross - or even just on the Western Section our of Waterloo - the Maunsell K would today be hailed as the first truly successful example of what became the defining type of modern passenger tank engine.

    Tom
     
  3. RLinkinS

    RLinkinS Member

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    W class 1918 was tried on a passenger train on 13 May 1948 and the riding was poor, so poor that use on passenger trains was effectively banned. The answer to this apparent contradiction is probably that the pony truck side control was good enough for the shorter and lighter 2-6-0s but not for the heavier 2-6-4 tanks.

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  4. 30854

    30854 Resident of Nat Pres

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    Didn't know about that one. I'd imagine the Ws had wheel balancing set up for freight speeds - and I'm thinking here of the ex-LBSC E1s, which on passenger work weren't at all popular, due to the notoriously poor ride at speed being transferred to the leading carriage - examples transferred to the IoW (where they operated the summer flagship service 'The Tourist') eventually being rebalanced for just this reason - so it'd be interesting to learn the detail of the conclusions.
     
  5. Jamessquared

    Jamessquared Nat Pres stalwart

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    There was a brief discussion about the balancing of E1 locos here: https://www.national-preservation.com/threads/balancing-of-inside-cylinder-locomotives.1417801/ From which I draw the conclusion: it's a complex subject! One point from that discussion, obvious I guess but which I hadn't thought about previously, is the relationship between wheel diameter and balance weights; crudely, the smaller the wheel, the more mass you need to give the same effective moment, which then brings its own problems.

    On U boats and side control: my memory is that 1638 swung about quite a lot at the front even at heritage line speeds. I'd always just thought "large cylinder loco" but the quality of the side control would undoubtedly have had an influence. By their nature, the cylinders of a 2-6-0 tend to be further forward than on a 4-6-0 as well, which, relative to the size of the loco, must give a greater moment relative to wherever the nominal centre of mass around which it pivots is.

    The whole business of loco dynamics feels to me like one that is very awkward to analyse by analytical, as opposed to iterative methods. Prior to the availability of computer modelling (which is very good at iterative methods), it sometimes amazes me that designers kept locos on the rails at all!

    Tom
     
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  6. 8126

    8126 Member

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    When the matter of reciprocating balance and side control comes up I always remember this video of 43106 on the MHR, with the lamp on the top bracket furiously wagging back and forth as she worked up the grade, and this with a design introduced after the LMS started to have a more rigorous approach to side control design.

    Rotating and reciprocating balance are both reasonably amenable to analytical design, but with the following caveats:
    • All two cylinder designs have to make some compromise between fore and aft surging, hammer blow, and yawing (the characteristic 43106's lamp is so conveniently exaggerating. As with all compromises, there is no "right" answer for all circumstances (especially as the final variable is always cost).
    • Even "perfectly balanced" three and four cylinder designs (insofar as they exist at all) require the yaw component to be ignored if you want zero wheel hammer blow. If the side control design is good, this doesn't seem to be a problem, but it was rarely done.
    Edit: Worth remembering that the W was a three-cylinder design, so should have been able to have reasonably good reciprocating balance without too much compromise.

    Otherwise, I tend to agree, once the loco suspension and side control comes into it, with a lot of non-linear frictional damping (both designed and otherwise), springs with hysteresis, forces interacting in multiple directions... it gets complicated and any model not supported by real data must be understood to have extremely wide error bars. I don't think it's any coincidence that the A1 trust have made such use of computer models with Tornado and Prince of Wales; Tornado must have had more actual data collected on its loco dynamics than pretty much every other steam locomotive built combined.

    The best approaches prior to this seem to have been a combination of fundamental understanding to understand what variables could be tweaked and how much effect they could have, combined with practical experience of what gave a satisfactory result, as described in Cox's write up of the Indian Pacific issues (which perhaps not coincidentally, involved a French engineer in the investigation). I think a lot fell short of that ideal though. As a slightly different example I was very struck in Holcroft's writings on the E1 class that, for an obviously intelligent man capable of good theoretical understanding of various locomotive issues, the approach to steaming trials with a misbehaving example seemed to be "Throw random tweaks and parts we've already got on the shelf at it until something works." You'd think the first question would be: what is different about this one from all the rest? Still, anyone can be wise when they're not actually having to produce the results and have all the resources of hindsight available....
     
    Last edited: May 11, 2020
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  7. MattA

    MattA Member

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    If you want to see some furious wagging, I'm reminded of this video of L.94 when it visited the Dartmouth Steam Railway - and this was a class of engine that was apparently so kind to the track, relative to its axle loading, because of low hammer blow that its route availability was increased in BR days.
     
  8. RLinkinS

    RLinkinS Member

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    Many years ago I saw a pony truck from a mogul at the Mid Hants. It appeared to have inclined planes on top. Are these what apply the side control in conjunction with a "plunger" with matching angles on the bottom?

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  9. Hermod

    Hermod Member

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    The Maunsell Ws had Cartazzi for front wheels according to WiKi
    This makes fitting a third cylinder on a 2-6-4 more easy than over a Bissel or KraussHelmholts.
    It will be interesting to compare drawings of LMS threecylinder 2-6-4 with the Ws.
     
  10. MattA

    MattA Member

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    I stumbled upon this extract this morning about the LNER Thompson B1s;

    "The firebox plates did tend to fracture, though. This was sufficiently severe that in 1955 there was a plan to replace the boilers with BR Type 3 boilers, as fitted to the BR Standard Class 5MT locomotives. The heavier boiler would have increased the axle loading and reduced the route availability." -
    https://www.lner.info/locos/B/b1thompson.php
     
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  11. Hicks19862

    Hicks19862 Member

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    Anyone want to try and photoshop this? Lol
     
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  12. class8mikado

    class8mikado Part of the furniture

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    presumably a standard 'Cab' would be required at the same time...
     
  13. 60044

    60044 Member

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    Interesting - I have just read this morning that preserved 1264 is having to have welded repairs around the firebox tubeplate and along the 2-top radii. Whast a shame there aren't any spare BR 5MT boilers lying around! (I joke of course!)
     
  14. Hermod

    Hermod Member

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    There are BR test reports for both class 5 and B1 and it is maybe be interesting to se what boiler was most efficient?
    Was the B1 boiler from Sandringhams with another tube layout?
     
  15. bluetrain

    bluetrain Member

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    The B1 boiler (LNER Diagram 100A) was derived from the B17/ Sandringham boiler design (Diagram 100) but had thicker boiler plates to take higher working pressure (up from 200 to 225 psi, or roughly 14 to 16 bar). Most of the B17s were later either rebuilt as 2-cylinder B2 or given the higher pressure 100A boiler to become sub-class B17/6.

    The tube layout remained the same - 24 large flue tubes (5¼in / 133mm outside diameter) and 141 small tubes (2in/ 51mm od).

    Diagram attached of the rebuild that never happened.
     

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  16. Richard Roper

    Richard Roper Well-Known Member

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    Very interesting, not a bad-looking end-product at all! It would take a bit of getting used to seeing a taper-boilered LNER Loco though!

    Richard. :)
     
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  17. Hermod

    Hermod Member

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    The heating surface of the BR3 boiler were very close , grate one square feet greater and boiler mass probably two tons more.
    In 1955 the leading BR steam people were looking for work and most had sung that GWR /Stanier cornered boiler hymn since 1932.
    Same story maybe as building 8Fs during war on all regions.
    Bigger grate means more steam per coal ,but greater loses when standing still.Fairly even.
     
  18. Osmium

    Osmium New Member

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    Is this even true? As in, can it demonstrably be shown that a 9F was better than a 28xx? The 28xx’s were extremely powerful for their size, relentlessly reliable, and were very fuel efficient even compared to designs decades after 2800 was constructed, often better. They were said to be very free steamers and performed without fuss compared to other goods designs during the early days of BR.

    The 28XXs were capable of everything a 9F could do and were a smaller and lighter engine at that, and were likely more efficient.

    I’m not sure how controversial this statement is, but I feel confident in stating that the 28XX was probably the best steam locomotive design ever developed for domestic use in the British isles. Not just goods designs, but designs overall.
     
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  19. 30854

    30854 Resident of Nat Pres

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    I seem to recall Mr.Churchward once suggested a reasonably straightforward scenario, wherein one of his locos might be directly compared with those of another company ......
     
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  20. Jimc

    Jimc Part of the furniture

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    Having regard to date of construction there's certainly a case for that.
    However:
    It would be extremely sad if a 1950s design were not better than a 1900s design, depending on what better is.
    It would be interesting to know what services were actually run by 9Fs that were not within the capabilities of the 28s. Bearing in mind grate size, standard parts etc the 28s were surely cheaper to own and run.
    28s in 1950 were by no means the same as 28s in 1908, cylinders, boiler, chimney, bearings, cabs, weight distribution, construction standards had all changed over the years
    The 28 valve gear was almost certainly better than the 9F for freight work.

    I fear that I rather suspect that many, maybe even most people, stating dogmatically that one was 'better' than the other will make the evaluation on criteria that support their preconceptions!
     
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