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Standard 8MT 2-8-2 New Build

Discussion in 'Steam Traction' started by pete2hogs, Jul 31, 2014.

  1. Eightpot

    Eightpot Part of the furniture

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    I get the impression that you do not understand the principle of the Krauss-Helmholz truck. It is not a plain version pony truck just pivoting on the leading coupled axle. With the K-H arrangement it acts as a bogie with the leading wheels joined to the leading coupled axle and wheel set, which has provision for sideways movement. The larger Continental load gauge profile (up to 10' - 4-1/2"/ 3150 mm in Germany) permits the spreading out of cylinders more than sufficiently to cater for this sideways movement. Thus with a K-H truck as applied to a 2-8-2 it turns the pony truck effectively into a bogie and as far as wheelbase flexibility is concerned the chassis acts like a 4-6-2. Please have a close look at the photos on post no. 83 to see this.

    According to original Doncaster drawings in my possession a P2 with 21" dia cylinders is only 8' - 11-1/4" over cylinders - that is more than 17" less than permitted in Germany. For comparison an A3 with 19" bore cylinders is 8' - 9-7/8" wide. If you are going to spread the piston rod centres out by a given amount then you will have to reduce the cylinder bore size by twice that amount to keep within the same width. This brings in other problems like if you want the same power from smaller cylinders then jack up the boiler pressure, this will require thicker plates thus increasing the weight. It is all a compromise and UK locos got as big as they could go within the limits of the UK load gauge. If you can't get any useful side play on a leading coupled axle then there is no point in a K-H truck.
     
  2. Jimc

    Jimc Part of the furniture

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    I can't help think that, as evidence for the practicality of a design goes, a drawing from Bulleid that even he wouldn't build, and a concept from Tuplin, well, it doesn't quite run in the first rank...

    Mind you, having mentioned Durrant earlier, if one really wanted a project and a half there was the tank engine he sketched out because he reckoned that double heading iron ore trains to Ebbw Vale with two 9Fs was a bad idea... Working on the basis that if a 9F could get there with a fixed wheelbase and one set of unflanged drivers, it ought to be possible to put an extra axle each end with an inch of sideplay, which with moderate gauge widening ought to be able to transverse 7 chain curves... So yes, it was a proposal for a BR standard 2-14-2. 2 outside cylinders 20*30, 1 inside cylinder 20*28, 275 psi boiler, TE 74,125, Adhesion factor 4.4. He says his management wouldn't even check the calculations, let alone submit the concept to Derby...
    Interesting to note that Durrant's sketch shows the cylinders to be clear of both the leading pair of coupled wheels and the pony truck.
     
  3. Matt37401

    Matt37401 Resident of Nat Pres

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    And what a beast that would have been...
     
  4. MellishR

    MellishR Part of the furniture Friend

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    It can't act quite like an ordinary bogie. A bogie rotates slightly, so that its axis stays roughly in line with the track. If a K-H truck did that, the leading coupled wheel on one side would get closer to the coupled wheel behind, and on the other side they would get further apart. That wouldn't work.
     
  5. Eightpot

    Eightpot Part of the furniture

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    The answer is that it isn't like an ordinary bogie. The leading axle and attendant frame are as one, but the rear end (under the leading coupled axle) is pivoted under the bearing housing above, and around that axle. Thus the lead (pony truck) axle assemble can swing either side of centre independently of the leading coupled axle. There are flanges machined on this latter axle that contains the pivot bearing assembly so that it moves sideways with the axle.The side control spring assembly can be seen about halfway along the frame. The 1st and 3rd photos in post 83 show the pivot assemble under the bearing assembly, however, the machined flanges are inside this outer bearing and not visible. To give an idea of the possibilities of this arrangement, on a Class 52 2-10-0 the permitted sideways movement either side of centre are:- pony truck = 125 mm, lead and trailing coupled axles = 25 mm, with thinned flanges on the centre driving wheels.

    To show the extent of the problem here as compared with the German load gauge profile the Class 44 3-cyl 2-10-0 with 550 mm (say 22") cylinders and the K-H truck has piston rod outside centres of 2260 mm which equates to virtually 7' - 5". In comparison P2 No. 2001 has piston rod centres of only 6' - 8-1/2", that is 8-1/2" less, or putting it another way, 4-1/4" less each side.

    However, as built 2001 had only minimal clearance between crankpin and crosshead - I'd hazard 1/2" at the most - and allowing for initial clearances and wear, it would appear that there is little or no scope for a K-H truck to be fitted without radical redesign, and I have my doubts about that.

    Just out of interest the later Class 86 2-8-2 tank locos were fitted with K-H trucks each end thus effectively converting the chassis to a 4-4-4, so you can't much more flexible than that!
     
  6. 242A1

    242A1 Active Member

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    One of the great things about this forum is that you might have to prod a little but people do respond.

    Yes, U.K. enthusiasts are notoriously parochial. And so were the majority of those involved in the design of locomotives for use here. No rubbish here.

    Designing a locomotive is not easy. Design a good one and that is an achievement. Try to design a truly outstanding one, that is an enormous challenge. Which is why, to date, none exist here.

    The work done is carried out within a number of constraints. It is hemmed in by limits of finance, loading gauge, maximum axle load, works capacity, the human ability you are able to call upon - talent if you like, the mental limits imposed by prejudices and so on.

    K-H and Zara are not the only options. How many axles have you got to play with? But controlled flexibility in the chassis is only one part of the recipe. But if you are building a standard based and recognisably so design all you have to do is stir the mix of standard parts. If you need more ability to deal with curvature it can be delivered without recourse to thinning flanges.

    If you want to go down the outstanding route then that would be for a dedicated thread.
     
  7. ragl

    ragl Well-Known Member

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    What may be considered a good design, well constructed and built in the UK does exist here, S.A.R. No. 3405 at Quainton Road.

    as for the rest of your analysis, I couldn't agree more.

    Cheers

    Alan
     
  8. Lplus

    Lplus Well-Known Member

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    Frankly, that is sheer nonsense
     
  9. Spamcan81

    Spamcan81 Nat Pres stalwart

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    Some are parochial but not all. Same goes for loco designers. You write off much of British loco design but I would ask what engineering background you come from to enable you to make such a judgement?
     
  10. The Saggin' Dragon

    The Saggin' Dragon Nat Pres stalwart Staff Member Moderator

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    He actually writes off most loco designers, except a select few, carefully avoiding the thorny subject of what actually worked as opposed to what could have been, theoretically, a few decimals of a percent more efficient.
     
    Lplus, Spamcan81 and Jamessquared like this.
  11. Sheff

    Sheff Part of the furniture

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    It's my sad duty to report that Phill Taylor, ace graphics artist, who had only just joined Nat Pres, passed away suddenly on Thursday August 21st 2014 aged 47 years. Phill had been of great help to the 5AT and Clan groups, providing artistic impressions of various design options, all at supplied FOC and PDQ . His FB page remains as testimony to his work https://www.facebook.com/groups/AlteredImages101

    RIP Phill, it was a pleasure.
     
    Last edited: Sep 15, 2014
  12. Corbs

    Corbs Well-Known Member

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  13. Eightpot

    Eightpot Part of the furniture

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    Not so much for hauling loose-coupled wagon, more for stopping them.
     
  14. LMS2968

    LMS2968 Well-Known Member

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    To go back a bit, braking was not one of the 9Fs' strongpoints, and an 8F was better. I've been told that the S&DJR allocated ones did work goods, but I've yet to see a photo. S&D men were very concerned at the braking powers of whatever loco they had, with good reason. All the photos show them working passenger trains, two-coach locals in their final year.
     
  15. bristolian

    bristolian Member

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    The reason that 9Fs were not used on S&D freights is because they were too long for the turntables, except that at Bath Green Park.
     

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