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Edward Thompson: Both sides of the Story. Discussion 2012 - 2019

Discussion in 'Steam Traction' started by S.A.C. Martin, May 2, 2012.

  1. bluetrain

    bluetrain New Member

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    It was quite common for similar engine classes to appear with differing wheel diameters. The GWR Hall & Grange classes are perhaps a special case from the late steam period, but the GWR in earlier times built large-wheeled and smaller-wheeled versions of its 4-4-0s, as did a number of other railways.

    I think that Samuel Johnson of the Midland Railway may have been the British record-holder for small variations in wheel diameters. Over a short period, he built batches of 2-4-0s with 6ft 3in, 6ft 6in, 6ft 9in and 7ft 0in coupled wheels. I've no idea why!

    Apologies to Mr Martin for going completely off-topic!
     
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  2. bluetrain

    bluetrain New Member

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    4-4-4? Now that really is unusual.

    https://en.wikipedia.org/wiki/4-4-4
     
  3. Hermod

    Hermod New Member

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    It was max 8 car trains running at 60 mph mean speed.
    44 tons adhession is more than enough,but high mean power for many hours,so a decent grate and big ash box is needed
     
  4. Hermod

    Hermod New Member

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    The German 01 and 03 pacifics were two cylinder engines until 130kmh trains were demanded.
    The 03 two cylinder were tried but it was to much wear and tear ,so new ones were made three-cylindered and streamlined.
    When going from two to three they could probably have reduced diameter to next size down 1750mm,but that would be a complete redesign and there was no time.
    The high speed diesel railcars were coming very fast.The steam fraction designed steam hauled look alikes called Henschel-Wegmann trains that tonned between Berlin and Dresden.
    First with two cylinder 2.3mdrivers and then one with three cylinders that still run today and keeps the postWW2 record .186 kmh from memory.
     
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  5. RalphW

    RalphW Part of the furniture Staff Member Administrator Friend

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    In perfect harmony with no pathetic squabbling.
     
  6. Victor

    Victor Part of the furniture Friend

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    :( Back in yer box Victor,:( I posted as I interpreted it, .........and I stand by what I said.

    There are some members on here that can get away with almost anything (and I thought insulting fellow members was against the rules), other well known members (just a few) are 'on the radar' and get slapped down regularly, and yes, banned.
     
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  7. Forestpines

    Forestpines Well-Known Member

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    ES Cox said that experiment showed that, by the late 40s, there was no point:

    "It was quickly perceived from the interchange trials and other trials ... that there was going to be no justification for a step of as little as 6 inches wheel diameter between two otherwise similar types. Not only had the Bulleid Pacifics demonstrated how with a modern front end a 6' 2" wheel diameter was no bar to speeds up to 90mph ... but some tests on the LNER between A1 and A2 Peppercorn Pacifics ... also indicated in a higher power capacity, what little need there was for so fine a distinction."

    - Cox, "British Railways Standard Steam Locomotives" (1966)
     
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  8. M Palmer

    M Palmer New Member

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    Indeed the willingness to experiment & diversify does seem to have diminished between the mid-30s and the late-40s for some reason. I'm certain they made the right decision re the 7MTs but I find the might-have-beens fascinating!

    It occurs to me that the Maunsell Moguls are a microcosm for the debate(s) in this thread. 5'6" or 6' drivers? 2 or 3-cylinder (conjugated or not?)? They certainly illustrate the difference in eras between pre-war (diversity accepted) and post-war (one size fits all).

    Ah now I am definitely about to go off topic! I have the RCTS Standard books 1 & 2. Do you know if I am missing out on anything by not having the Cox book as well. Mainly volumetric considerations!
     
    Last edited: May 18, 2019
  9. Hermod

    Hermod New Member

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    Moguls are not really speed machines.
    GWR dismantled and rebuilt quite some as 4-6-0 due to better behaviour at high speed.
    It could have been made a pure LNER affair :
    Robinson B18 versus
    Raven B16/1 versus
    Gresley B16/2 versus
    Thompson B16/3 and then some Sandringham.
    Material for at least five books and more pages here than 150.
     
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  10. Forestpines

    Forestpines Well-Known Member

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    I certainly wouldn't tell you not to get a copy! It does describe things very much from Cox's personal perspective as a key member of the design team, so I suppose could be described as a little bit rose-tinted
     
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  11. Jimc

    Jimc Well-Known Member

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    That's not what I understand from GWR sources. The running department was asking for more boiler capacity. The Std 4 didn't deliver enough steam at higher speeds and loads. Not altogether surprising as it was basically the same front end as the Std 1 classes. It was the 4700 5'8" wheel 2-8-0 that had a speed limit applied, although RCTS says the 2-6-0 would roll a bit, although nothing like the (4-4-0) Counties.
     
  12. Jamessquared

    Jamessquared Nat Pres stalwart

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    There is a lot of comparative data on the N1 (three cylinder) and N (two cylinder), plus the U and K, in Holcroft, particularly volume 2. The general finding is that the N1s were lighter on coal than the N class at heavy loads, but not on lighter loads. Interestingly, Holcroft seems to ascribe that less to the efficiency of the front end, but more to more even combustion and less spark throwing from six beats per revolution rather than four heavier beats. He is also very keen to point out that any gains from efficiency only really arise when a loco is working; when it is coasting or at rest, there is no gain however sophisticated the front end, a point that is often forgotten when discussing locomotive performance.

    There is also an interesting aside about comparative running of the N class and T9 on the Exeter - Plymouth road. The gradient profile has a significant slog (much of it at 1 in 75) for miles on end, followed by an equally precipitous descent. The N class generally performed better on the climbs, but the T9 could make much of it back on the descents. Although Holcroft doesn't qualify that observation, my guess is that slide valve loco was inherently freer running with steam off.

    I don't think you can ever design a "perfect" loco: every decision (two or more cylinders; slide valve or piston valves; superheated or not; how many wheels; wide or narrow firebox) comes with some sort of trade-off. Even a well-managed set of coal consumption trials doesn't tell you anything about comparative workshop repair costs...

    Tom
     
  13. 8126

    8126 Member

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    I seem to remember the findings were that the three-cylinder versions used similar amounts of water even when they burned less coal, which definitely points to a similarly efficient front end but better combustion efficiency. The three-cylinder Moguls had their valve chests rather scaled down in proportion with the cylinders, so there was no room for an advantage there. One interesting difference in lifetime costs for the three-cylinder variants was that none of them needed the extensive frame surgery received by fifty of the 2-cylinder variants in the late 1950s.

    I'd always assumed that the T9 making it back on the descents in comparison to the N was partly the larger wheels, and partly better stability with the crews being more willing to run fast with a low-slung 4-4-0 than a bigger 2-6-0 with questionable side control on the leading truck. Certainly the T9s appear quite high up in the lists of fast engines wherever it was measured on the Southern; I think one timer had one doing 91 mph near Axminster and I doubt it was coasting at the time.

    In Adams days on the LSWR, there were 7'1" 4-4-0s for working east of Salisbury (such as the T6 class) and 6'7" 4-4-0s for west of Salisbury (such as the T3), where the smaller wheels were considered advantageous for hill climbing. This ignored the inconvenience to sheds (particularly Salisbury) in having marginally different classes for different routes, and also that the small wheeled engines could generally be expected to have to run faster down the hills of the Salisbury-Exeter section than the large wheeled classes on the steady run to London. Drummond quite sensibly standardised on the 6'7" diameter for all his express 4-4-0s.
     
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  14. S.A.C. Martin

    S.A.C. Martin Part of the furniture

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    Nobody should apologise for a very interesting few days discussion. Off topic stuff sometimes yields new ways of thinking - always good.

    Food for thought on the wheel diameters.
     
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  15. Hermod

    Hermod New Member

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    Have bougth Holcroft 2 and look very much forward to read it.
    In the meantime a little international outlook.
    Mr Garbe from Prussia made the P8 (1750mm drivers) as a Fast locomotive and wanted to employ it for plus 110 kmh (level).
    It was of course not allowed to exed the hammerblow limits very clearly defined by police rules pre WW1 and it shutled so much fore and aft thatMinistry said no and limited it to 90kmh.
    It did in very great numbers and worked to the end of steam.
    Good engineering indeed.
    The UK Bridge stress commity made recomandations in 1929 that gave more or less same limits for hammerblow.
    Prussia needed faster trains and made a first try with a 4 cylinder P8 with 2 meter wheels like a Claugton but better valves.
    Not really good and it was the decided to try a four-cylinder de Glenh compound and a three cylinder simple with conjugation.
    All had 2m drivers
    The compound was best(by far) and worked almost to the end in DDR.
    The four cylinder could pull 210 tons with 110 kmh on the level,the three cylinder 230 and the Compound 280.
    The three cylinder had the lowest repair cost.
    Two of the three cylinder version were rebuilt 1933 as three-cylinder 25 bar compound (not conjugated) and outdid almost all other german locomotives in power and fuel economy.
    The missed opportunity is that it was not tried to make a P8 three cylinder compound.

    Cox state that 6 feet two or 6 feet 9 do not matter on three or fourcylinder locomotives but it cannot be not true for two-cylindered.
     
    Last edited: May 19, 2019
  16. Forestpines

    Forestpines Well-Known Member

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    I quoted Cox's words on this above, about the early stages of the Britannia design process. What he said was effectively that: the experience shown with 3-cylindered Pacifics was evidence that there was no need to build both a 6' 2-cylinder Pacific and a 6' 6" 2-cylinder Pacific, because a 6' 2" 2-cylinder Pacific could do the job of both.

    Whether or not you can show on paper that there is theoretically a significant difference in hammerblow between the two, clearly that was not considered to be an important factor on BR in 1948 by the Standard design team.
     
  17. Hermod

    Hermod New Member

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    And that was wrong .
    Neither a 6 feet 2 or 6 feet 9 two cylinder pacific doing 100 mph ocassionally was a good idea.
    According to Adrian Tester ISBN 9780957077904, Britannias became frame crackers.
    Rudyard Kipling was saved from disgracing Cox et al by slow speed and crosstaying when one frame plate parted in two.
    Thinking this thread over it has been become clear where I think Gresley missed the train big time.
    He took a perfectly good B16 in 1937 and fitted conjugation.
    That is many years after he met and befriended Chapelon and many years after the German rebuilding of Three-cylinder into compound.
    Rebuilding the B16 into this form would not have been more work than the conjugating thing apart from rearranging cranks from 120 120 120 degree to 90 135 135.
    No big deal.
    A Chapelonized B16 had been a world beater.
     
  18. Hermod

    Hermod New Member

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    By the way.
    Hammerblowing is something You design into a two-cylinder to avoid shaking crew and train to death or worse.
    Cox mention some testing before WW2 on a Class 5.
    20% reciprocating balance was clearly unacceptable,40% barely so and 60% nice but banned by permanent way department.
    Three cylinder locomotives need no to run smooth but if given,it is to minimize yawing.
     
  19. Hermod

    Hermod New Member

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    On many of the amateur timed high speed exploits going downhill with TWO cylinder locomotives it is maybe more a measure of crew discomfort than locomotive power.
     
  20. Jimc

    Jimc Well-Known Member

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    To me it seems that the problem with the conjugated gear was not in the concept but the detailed engineering. Holcroft's original design had shorter symmetrical arms , the valve on the centre line and the gear behind the cylinders. That would have avoided a whole host of problems, but could only be fitted on a locomotive with all cylinders driving the leading wheels and a relatively small boiler - a 4-4-0 in other words. No use for Gresley! The Gresley variant on the Pacific had problems with valve rod expansion affecting timing, with longer levers and larger bearing loads and so on. The inadequate big end bearing design didn't help either. As James^2 rightly says, every design is a compromise, and its often impossible to tell what the best compromise was with hindsight, let alone for the designer. It doesn't help that we enthusiasts cheerfully ignore some of the design factors that the engineers had to prioritise!
     
    Last edited: May 19, 2019

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