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BR Standard class 6 No. 72010 'Hengist' and Clan Discussion Thread

Discussion in 'Steam Traction' started by Bulleid Pacific, Nov 23, 2009.

  1. Sheff

    Sheff Resident of Nat Pres

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    I think that would be an absolute last resort. With a multiple valve regulator and steam chest pressure gauge drivers have the tools to they need to control any tendency to slip. Working pressure could also be limited if found necessary by adjusting the safety valve setting.


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  2. 30854

    30854 Resident of Nat Pres

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    Apologies if this is a stupid question, but with regard to increasing the TE (courtesy of an increase in boiler pressure), whilst I take the point about the balance between power and the ability to put that power down in a useful fashion, what is the effect of such an increase when it comes to a train in motion, on encountering adverse gradients? Put another way, is that excess power which can cause such impressive displays of slipping from a standing start, any more useful as a reserve to maintain line speed with a load?

    At a design level, the example which comes to mind is that of the reduction in cylinder diameter of the Fairburn 4MT, to satisfy BR loading gauge requirements, dictating the increase in designed BP of the BR Standard 2-6-4T. Pretty much the opposite of considerations for 72010, but does that increase in power which comes with increasing BP whilst retaining the original cylinder size have any bearing on the ability of the frame design to cope with increased forces?
     
  3. class8mikado

    class8mikado Part of the furniture

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    Well at any given cut-off there is more output at the cylinders, so to achieve any given state of running you should have less steam needed - either by way of lower cut off or less than full regulator.
    I dont have any concerns about the frame design as its essentially an improved Britannia frame; a redesign undertaken by BR, which together with a hint of metric creep in frame plate thickness suggesting that Hengists frames are more than capable of handling the new forces which are still somewhat less than those generated by the 20 inch Cylinders of a Britannia.

    Sheffs coments they are entirely pertinent ; whatever tools/ aids are available a tendency to slip is still an unwelcome worry and limiting boiler pressure increase another 'adjustment' option. Running in trials are going to be interesting.
     
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  4. MellishR

    MellishR Resident of Nat Pres Friend

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    Don't all steam locos (not to mention other kinds) have a tendency to slip in some circumstances? Part of a driver's skill is to be aware when slipping may occur and to be able to control it when it does. Given some of the other tweaks to the original Class 6 design to improve Hengist's performance, a modest increase in tractive effort seems quite reasonable.
     
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  5. S.A.C. Martin

    S.A.C. Martin Part of the furniture

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    “Slipping” is a ridiculous measure of a locomotives worth and rarely are there any factual records on this.
     
  6. LMS2968

    LMS2968 Part of the furniture

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    Alternatively, some types were more prone to it than others. Pacifics tended to be light on their feet, but outdone by Atlantics, which took second place to singles. It is said that the driver of a Stanier three-cylinder 2-6-4T on the LTSR could wind it into full gear and shove the regulator full open from the start, and it walk away without slipping. A bit of an odd one, and I don't know of any other class where you would try that.
     
  7. 240P15

    240P15 Well-Known Member

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    "Rain and laefage at the rails, it`s like driving on green soap" Retired norwegian driver (of steam)

    Knut:)
     
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  8. Bill2

    Bill2 New Member

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    One other class said to be capable of working with full regulator from the start was the King Arthur on the Southern. Only on a dry rail...
     
  9. class8mikado

    class8mikado Part of the furniture

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    Surprised that a Lord Nelson wouldnt do the same....
     
  10. class8mikado

    class8mikado Part of the furniture

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    An unusually fatuous statement Mr Martin, if slipping /adhesion is such a worthless quality why are the vast majority of steam engines 0-6-0's and not 2-2-2's , and why did Churchward select the 4-6-0 above the 4-4-2, and why did the pacific arrangement ever come into being when a 4-4-4 would do... i could go on right to the point where rebuilding a 2-8-2 as a 4 -6-2 makes it less effective at the job it was designed for ( however much its reliability/availability was improved)
     
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  11. 30854

    30854 Resident of Nat Pres

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    Would that be down to the constant torque provided by four cylinders? I'd imagine, with their reserves of power, Mr Maunsell's V class took a steady hand on the regulator to avoid slipping like billy-o.
     
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  12. John Petley

    John Petley Part of the furniture

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    Indeed. it's a great credit to the Bricklayers Arms and St Leonard's crews in the years before 1957 that day in day out, including when the rails were wet, with a "Schools" they would take sometimes as many as 11 coaches from a standing start at Tonbridge up a very nasty incline including both a short section as steep as 1 in 47 and some rather sharp curvature. Not surprisingly, in the preservation era, few tour operators have tried an any unassisted run over this section of line with steam. Braunton went that way in September 2020, but the train did have a 47 on the back.

    Incidentally, two other classes which I gather had a good reputation for surefootedness were the GWR 42xx 2-8-0 tanks and the LSWR Adams 4-4-0s. I have never heard a 42xx slip and they do sometimes take some fairly hefty loads on the Dartmouth line. 4253 will soon be able to vouch for the class's surefootedness only a few miles from where I'm currently typing this in a few months' time, hopefully while 563 could do likewise at Swanage next year if all goes well.

    Sorry - this has rather degenerated into thread drift, but an interesting diversion nonetheless.
     
    Last edited: Jan 5, 2022
  13. S.A.C. Martin

    S.A.C. Martin Part of the furniture

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    Fatuous, possibly.

    The reason I say it is because there’s more than hint of the old wives tales when discussing adhesion. The Thompson Pacific nonsense - and it is utter nonsense - is based on a belief that the Pacific couldn’t do the job of the mikado.

    When all evidence suggests strongly the pacific was better, and not just in reliability/availability stakes.

    I rather think we need to get a grip where discussions like this are concerned - I’m all for the theoretical advantages of more driving wheels equals more adhesion but the practicality of a locomotives value extends past just two extra driving wheels, and to whether that theoretical advantage was actually realized in practice.

    From my point of view when looking over the LNERs vast dataset I have, it’s pretty damn clear that six coupled and eight coupled mixed traffic and goods locomotives were the mainstay of the work and arguing the toss over mikados and Pacifics ignores the blatantly obvious: what were the traffic needs and were they met?

    Not a single person has questioned the use of Gresley A4s or the W1 on the P2s work and yet fundamentally the same principle applies when discussing the Thompson or Peppercorn equivalents.
     
  14. class8mikado

    class8mikado Part of the furniture

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    Think you have it in the Nutshell 'whether that theoretical advantage was actually realized in practice'. But at the stage where one is making a tool that other people will use it easy to forget the skilled hand is what gets the best out of that tool rather than the tool itself
     
  15. LMS2968

    LMS2968 Part of the furniture

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    Well, yes, although I don't think that's how you meant it. But the Factor of Adhesion has its practical applications and is why heavy goods engines have more than six coupled wheels, and Riddles, possibly mistakenly, went for ten instead of eight with the 9Fs. And while passenger engines did not have to start the same weights of train, they did have to get them on the move, which could be entertaining to watch when a big power output overcame their ability to 'get a grip'. They were also inclined to slip at speed. A case in point was the L&YR Atlantics, not perhaps the most powerful of engines by modern standards, but they were prone to this and were known to slip even with steam off!
     
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  16. Richard Roper

    Richard Roper Well-Known Member

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    I've seen it done once on the KWVR at Oakworth with 48431... No rear truck or bogie though, so no problem of unloading the rear drivers. It made a right racket too!

    Richard.
     
  17. MellishR

    MellishR Resident of Nat Pres Friend

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    Other things being equal, more driving wheels are obviously better, as Churchward verified – but other things are not always equal, as with the P2s. If their other flaws could have been rectified without sacrificing one pair of driving wheels, they would have retained their greater adhesion, which would surely have been beneficial sometimes.

    But back to Hengist; this particular thread drift started with the suggestion that its increased boiler pressure and thus increased nominal TE could be a disadvantage. That would be so only on the occasions when slipping is likely, and then only if the driver tries to use more TE than the wheels can deliver. How often is a steam loco actually asked to deliver its full nominal TE anyway?
     
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  18. 30854

    30854 Resident of Nat Pres

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    Point of Order: Not actually thread drift (for once!), as the discussion concerns a subject directly addressed on the project's website. The considerations and relevant exemplars likewise cannot be considered thread drift ..... at least, not so far as anything posted so far goes. Give it time!

    Interesting question about when max TE is needed. My guess, FWIW, is starting (or restarting) a load from rest, but ties in with my own question concerning how 72010's possible BP increase factors in laying down increased power on adverse gradients.
     
  19. Sheff

    Sheff Resident of Nat Pres

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    FWIW I think we need to careful, if I can make the comparison with the automotive world, not to confuse torque and power.
     
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  20. 30854

    30854 Resident of Nat Pres

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    Agreed. Equally FWIW, I've always regarded TE as no more than an indicator of potential, useful on paper, less so on a rail surface. Put simply, an assumption is needed that all other relevant factors are equal. We could all name several class comparisons which give the lie to that .... not all of them six coupled!
     
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