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P2 Locomotive Company and related matters

Discussion in 'Steam Traction' started by class8mikado, Sep 13, 2013.

  1. Steve

    Steve Resident of Nat Pres Friend

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    But the beats come from two 2-cyl engines. The question of uneven beats was originally raised with regard to variation in power . I'm not sure that 'Sir Nigel Gresley's' explanation of length of exhaust passages being a key factor holds water, though. What speed does steam travel down a pipe?
     
  2. class8mikado

    class8mikado Well-Known Member

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    IIRC gresley locomotives all drive onto the same axle ( as opposed to different axles for thompsons and pepps) in which case if the three cranks are at 120degrees and the middle cylinder is not in the same horizontal plane ( to clear the forward coupled axle ) an offset beat is inevitable and not an indication of poor valve setting. The only detrimental effect being a slightly uneven flow through the exhaust . Not convinced that the additional length of travel of a foot or so through the exhaust passages would have a noticeable effect...
     
  3. irwellsteam

    irwellsteam Active Member

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  4. Spamcan81

    Spamcan81 Nat Pres stalwart

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    The B17s had divided drive but I think that was the NBL influence.
     
  5. class8mikado

    class8mikado Well-Known Member

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    Whichever valve gear is chosen its inevitable that the Double kylchap, probably to the same dimensions as Tornado, will be used. With this giving a fairly soft exhaust the shortcomings of the original design as a smoke deflector may become problematic. Be interesting what alteration is made to overcome this...:confused:
     
  6. Steve

    Steve Resident of Nat Pres Friend

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    But the cranks aren't at 120° I think the middle one is at 117°/123° but I can't immediately confirm that.
     
  7. philw2

    philw2 Member

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    Surely, if the middle cylinder is higher than the others it will be at a greater inclination than the others but the cylinder centreline will still be perpendicular to the axle/crank pin centreline irrespective of divided drive. In this case, the setting between the centre crankpin and the other crankpins will not be 120 degrees. It will be more like 119/241 degrees with one and 121/239 with the other; the outside crankpins remaining at 120 degrees. You will have max. efficiency but unequal beats.
    The only scenario with equal beats is when all three cylinders are at the same level and inclination; possibly when the middle cylinder drives the forward axle.
     
  8. Spamcan81

    Spamcan81 Nat Pres stalwart

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    The exhaust on 2001 as built was no problem and the deflection provided by the front end was fine. After switching to Kylchap however, the softer blast require auxiliary deflectors a la 2002.
    If poppet valves are chosen then I can't see the original front end shrouding being an issue
     
  9. class8mikado

    class8mikado Well-Known Member

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    Ah but whilst poppet valves do have quite a sharp release, unless you open up the blast pipe a little to compensate the fire will get ripped up on starting/ working hard so you should still end up with a soft exhaust...
    The Idea behind the P2 Shape and the original Merchant Navy shape neglects one issue, that is creating a pressure -to -velocity system around the chimney by this scoop shape method you create a low pressure /stagnant area elsewhere ( down the flanks of the locomotive, infront of the cab windows ) which is where the air flow is going to be drawn once past the chimney.
    Creating 'vents' on either side at the back of the 'scoop' should solve this and if its done carefully you'd be hard pushed to notice the change on a P2 where as the
    'Gill Slit' on the Spam Cans is unavoidably obvious (but not bad looking for all that.)
     
  10. Pesmo

    Pesmo Active Member

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    I wonder, should we have two long term separate threads to avoid confusion ? One for the Doncaster P2 and the other for the P2SLC ?
     
  11. 242A1

    242A1 Active Member

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    High peak exhaust events should be avoided. 2001 was infamous for having a high fuel consumption and no modern day fireman would thank you for foisting on them an unmodified recreation of this engine. The clearance volumes were recognised by the LNE as a problem and they could never equal the percentages achieved by the piston valve fitted members of the class. Coupled with the limited range of cut-off positions available with the modified Lentz gear and the rebuilding of 2001 was inevitable.
    Just what is the aim of this project? A faithful reproduction of the original? Or is it being used more as a device to facilitate the construction of a 2-8-2? The cylinder size is no longer as the original, neither is the boiler pressure. The original valve gear proved to be less than satisfactory, the LNE settled on traditional piston valves which proved satisfactory. The project will have to use poppet valves if a 2001 alike is the aim with Lentz out and the unprototypical BC gear in. Will the peculiarities of the original frame plate construction be followed? The change to the front truck away from the swing link type is unavoidable and rightly so. The exhaust system will come under the magnifying glass and the original front end screening could well have to be changed. So, what will be faithful to the original design apart from the wheel arrangement? Or should the project be called a locomotive based on and inspired by the LNER P2 class?
     
  12. Spamcan81

    Spamcan81 Nat Pres stalwart

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    As with many LNER Classes that had modifications to some class members, a sub class designation was introduced so 2007 could logically be called Class P2/4.
     
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  13. S.A.C. Martin

    S.A.C. Martin Well-Known Member

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    The annual mileages Thompson's Pacifics made post-war were as high (and sometimes higher) than any of the other "Big Four" express locomotives, only really eclipsed by those express passenger locomotives from their own region (which, FYI, were higher than all of the region's locomotives by far, particularly the Peppercorn a1). If they were such "failures" (and they weren't, people just say that from a wholly anti-Thompson perspective) then why were they not rebuilt en-masse like Bulleid's Pacifics? Why did they continue to be run for a good fifteen years post-war? Because they were more than adequate for the job asked of them. They were designed as mixed traffic Pacifics and by reasonable, constructive and balanced accounts read even the A2/2s did sterling work on express and express goods work.

    Without Thompson's work on the Pacifics, you wouldn't have had the Peppercorn A1s or Tornado.

    Please. The only reason you don't want a Thompson debate is because the anti-Thompson side of the debate is fraudulent at best, with a lot of hearsay and rather patronising dismissal of locomotives which were never as bad as they have been made out to be by railway enthusiasts.
     
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  14. Spamcan81

    Spamcan81 Nat Pres stalwart

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    The Thompson's weren't rebuilt a la Bulleids, they were simply withdrawn, the first LNER Pacifics to suffer that fate. Not only that but there wasn't that many of them and Peppercorn made immediate changes to the design. They had their problems, the long wheelbase made them somewhat light footed and the angular outside steampipes were prone to leakage at the joints. Both features were dispensed with by Peppercorn whose A2s were held in much higher regard than their Thompson predecessors. You dismiss any criticism of Thompson as hearsay yet your support has a similar basis unless you are old enough to have had first hand experience of them and I doubt that. To say without Thompson there would be no Peppercorns nor a Tornado is nonsense. Had Peppercorn been Gresley's successor then he would introduced his own designs anyway and I suspect they would have been little different than those he designed after succeeding Thompson.
     
  15. S.A.C. Martin

    S.A.C. Martin Well-Known Member

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    Absolutely, will not argue with any of that. But they were withdrawn at the dawn of the diesel revolution, not because they were poor machines, but because they were in the smallest classes. This is absolute fact - the smallest classes throughout the major regions were withdrawn first. The Thompson Pacifics were smallest in number, and were dispensed with first. That is not a reflection on their ability but their numbers.

    I don't dismiss criticism of Thompson: on the contrary, there is much to be critical of in his locomotive policy and he certainly rubbed people up the wrong way. However in order to have a balanced opinion and a factual debate, we have to dispense with some of the phrases which are commonplace and used far too often to describe locomotives which were merely average and by no means exceptional as the A4 Pacifics and Peppercorn A1s were. The Thompson Pacifics had their advantages in many respects, not necessarily outweighed by their flaws but they were not failures. The word implies unusable, awful, and many people do use that word to describe these locomotives which is factually incorrect (certainly not borne out by the fact they continued to be used in their mixed traffic role until their withdrawal in the late 50s and early 60s).

    I think it's fair to say that because it is true. Gresley had continued to use the conjugated valve gear in his excellent but expensive V4 locomotive and there is nothing to suggest he wouldn't have continued to use it - and his successors - ad infinitum until steam's passing. Only those with the benefit of hindsight after Gresley and Thompson have suggested this change, and it bears little resemblance to the facts of the matter.

    Thompson removed the conjugated valve gear - used three sets of walschaerts - Peppercorn took over and removed the flaws from the otherwise Thompson and Gresley respect main line Pacific to perfect the breed. Without Thompson, we don't get the Peppercorn A1s in the form we know and love them in, like it or loathe it.

    I'm no Thompson lover: perhaps an apologist these days but only because people will be entirely dismissive of locomotives which cannot have been so awful to have continued to have been used, almost entirely unmodified, since their building. It's not fair and it doesn't present a constructive and balanced view of the man (who like any other had flaws - perhaps more than most - but was working under a fair amount of pressure).

    I've been researching and writing a book on Edward Thompson for nearly three years now, having interviewed a fair few people, read as much as I can and got views here and elsewhere. Whether or not I lived through the times of his Pacifics is irrelevant: I've done more than most to research him as much possible to make my own mind up. Many people only go by the populist and loudest views which only give one side of the story. If I've learned one thing from working at the service, there are two sides to every story and it's the one which isn't heard which needs to be to make discussion balanced and fair.
     
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  16. Spamcan81

    Spamcan81 Nat Pres stalwart

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    Research away. I can point to well researched books on the Bulleid Pacifics. One upholding the view that the rebuilds were superior and another debunking that fact. Disagree whole heartedly that without Thompson we wouldn't have had the A1s. If Peppercorn had taken over in 1941, I remain convinced we would have had Peppercorn Pacifics anyway. He patently wasn't an admirer of the conjugated gear otherwise he would have reverted to it so three sets of Walschaerts and divided drive would have come about anyway IMO.
     
  17. S.A.C. Martin

    S.A.C. Martin Well-Known Member

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    The problem is, there was no chance of Peppercorn taking over due to seniority (not getting Bulleid, Thompson was the next in line) - and arguably if Gresley hadn't died, and made it to Nationalisation, we'd have not had the Peppercorns at all due to the standard range.

    I've read a few books on the Bulleids and have a great admiration for their design. My point above was made simply to highlight that the authorities considered the Bulleids flawed enough to rebuild the entire Merchant Navy class and a large proportion of the WC/BoB but made no such efforts on any of the Thompson Pacifics. That in itself must say something of the locomotives - not being awful but adequate for the duties which they found themselves on.
     
  18. maddog

    maddog New Member

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    I feel sorry for Thompson in how he is deemed the butcher, Gresley engines are for some reason seen in the same way that copper clad locomotives were/are on the GWR. In his attempts to ultimately improve upon a set up he inherited has been vilified. Working in the circumstances that he was of WW2, faced with a fleet full of many different classes of seemingly little if any standardisation relying on somewhat flawed components in daring to change ultimately for the better he seems to of upset those who think Gresley could do no wrong, of which there seems to be many.

    Just imagine if Stanier had effectively continued the LMS small engine policy, that his predecessors at LMS had (albeit from what little i understand, unwillingly) rather than dare to build such effective engines as he did
     
  19. Sir Nigel Gresley

    Sir Nigel Gresley Active Member

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    It is not my explanation, but that of probably the world's current expert on the testing of steam locomotive. As "uncle Rudi" has now retired, perhaps you would like to apply for his job at Meiningen (if you know where that is, and what the works achieved under the stringent lack 0f resources conditions in communist East Germany).

    As mentioned by other contributors, the crank settings of Gresley 3-cylinder locos (except for D49 & B17) are not 120°, owing to the inclined middle cylinder, but the power-strokes are, nevertheless, evenly-spaced. The uneven acoustic beat is due to the differing lengths of the exhaust pipes; the only disadvantage of this being the effect of the relatively uneven draught on the fire (and perhaps on the integrity of the smokebox).
     
  20. Spamcan81

    Spamcan81 Nat Pres stalwart

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    So when 4771 ran with the most even beat I've ever heard from a Gresley loco, or any other three cylinder loco, would this have been due to valve timing being set to allow for the differing length of exhaust pipes?
     

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