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British 8 coupled loco's

Discussion in 'Steam Traction' started by johnofwessex, Feb 16, 2020.

  1. 30854

    30854 Part of the furniture

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    ..... and by now, artificial sealing strips would've proved atmospheric propulsion to be the superior system it's proponents claimed all along. ;)

    Edit: had to correct a spelling or two ... damned keboard was set for Spanish! :(
     
    Last edited: Feb 17, 2020
  2. LesterBrown

    LesterBrown Member

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    Or just 2 or 3 massive cylinders inside.
     
  3. LMS2968

    LMS2968 Part of the furniture

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    A three-throw crank axle inside?
     
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  4. 242A1

    242A1 Member

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    Chapelon found that the fitting of a power stoker had a negligible effect on efficiency rather like the removal of superheating from the h.p. cylinders of the 160P. Is a grate area much in excess of 40 sq. ft. required in the UK? In terms of the horsepower needed to work trains probably not, 4,000+ h.p. is obtainable from the grate area mentioned.

    What you do need is adhesion and tractive effort. Once you have reached the maximum permitted axle loading the only way to deliver a higher tractive effort is to increase the number of axles. As for the tractive effort figure itself, we all know that you can make use of boiler working pressure, driving wheel diameter, cylinder dimensions and their number but you can also look at how smoothly you can deliver the power - the less fluctuation the higher a nominal figure you can use, see Barkhousen he did diagrams for turning moments in 1912. Then you have the quality of your railhead conditioning, the effectiveness or otherwise of your sanding system.

    Back to 8-coupled locomotives in the UK. The P1 with booster removed had a nominal tractive effort of 42,446 lbs force, it weighed 94T 16 cwt with an adhesive weight of 69T 5 cwt and a maximum axle load of 17T 15 cwt these figures are for the 43 element superheater. The V2 weighs 93 T 3 cwt has an adhesive weight of 65 T 2 cwt and a maximum axle load of 22 T 0 cwt all supporting a nominal tractive effort of 33,730 lb force. Before looking at the issue of wheel diameter at the time these designs were produced the notion that diving wheels 8 ft or so in diameter were required for high speed work had faded from the scene. On the LNER the 6' 2" wheel was viewed as suitable for some pretty spritely workings and Bulleid made good use of this size on the Southern. The world of railways was moving on and 2 cylinder 8-coupled engines fitted with 5' 10" driving wheels were found to be suitable for working at speeds well in excess of 100 mph.

    The P1 when tested ran at 65 mph however this was an engine that was fitted with short travel valve gear and the cylinders had a valve size to cylinder bore ratio that was not the best for high rotational speeds. A long travel design existed, it was fitted to the later versions of the O2, and the cylinders could be exchanged for the A4 type. The tractive effort could be maintained by using a suitably adjusted diagram 107.

    So would this have been a suitable engine for consideration? It could work heavy freight and fast freight and as for faster workings it would be rather like visiting the Dovregubben vs GermanPacific trials in that the acceleration of the 2-8-4 with driving wheels a fraction over 5' in diameter proved to be of greater value than the ability to run faster, when you eventually got there.

    As for 2007, I wouldn't worry about it. Chassis behaviour has been addressed, front truck design has been changed (the LNER staff suggested that this was the main improvement to be dealt with back in the 1940s) the crank axle is far more robust with improved design and materials and so on. If you have any concerns email David Elliot and please keep us informed if you do, views, analysis and information are greatly valued. Please ask questions if you can, not enough people do.
     
  5. BrightonBaltic

    BrightonBaltic Member

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    Considering how well the 47xx did work, and that there were 0-6-0s with similarly large wheels, I wonder why nobody ever built a close-coupled big-wheeled 0-8-0?
     
  6. BrightonBaltic

    BrightonBaltic Member

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    And supposedly the USA S200 2-8-2 was designed for the British loading gauge, but none ever came here. The Aussies did use them as the NSWGR D59 class, though...
     
  7. Rumpole

    Rumpole Member

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    Didn’t Bulleid also come up with the idea of an eight-coupled loco when in the early stages of developing the Merchant Navy class, only for it to be rejected by the civil engineers?
     
  8. Jamessquared

    Jamessquared Nat Pres stalwart

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    Yes, what became the Merchant Navy started out as a 2-8-2 concept.

    Tom
     
  9. Rumpole

    Rumpole Member

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    And knowing Mr Bulleid’s reputation (and I’m a fan), it probably started off with a view to replacing the C14’s...
     
  10. Jamessquared

    Jamessquared Nat Pres stalwart

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    Ha! Nice one ...

    It’s going off topic just a tiny bit, but was the Drummond C14 technically the last single driver but for a mainline British railway company?


    Tom
     
  11. Dunfanaghy Road

    Dunfanaghy Road Member

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    Interesting thought. His first engines for the NBR were 2-2-2s. If it wasn't for the lamentable 4-6-0s his career almost turned full circle.
    Pat
     
  12. Fred Kerr

    Fred Kerr Part of the furniture

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    Mention of Germany reminds me that in 1975 I was privileged to have a cab ride in a Class 042 2-8-2 which was substituting for an unavailable Class 012 4-6-2 and I asked the driver how much time would be lost by the smaller Class 42 - and he said "None !". He then explained that the smaller wheels of the 042 gave better acceleration which would compensate for the poorer acceleration of the 012 hence maintain the station times if not the point-to-point times.
     
  13. Allegheny

    Allegheny New Member

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    Does the driving wheel diameter make any difference to adhesion, for the same axle loading?
    I'm thinking that a larger diameter wheel would have a larger "contact patch" with the rail - (such as it is)
     
  14. Steve

    Steve Part of the furniture Friend

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    The contact'patch' has nothing to do with wheel diameter. I think that this can be best illustrated by thinking of your cars pneumatic tyres. Let's say the weight on a particular wheel is 600 lb. Let's also say that the air pressure in the tyre is 30 psi. In an equilibrium situation the area of the contact patch will be 600 divided by 30, which is 20 square inches. That is independent of wheel diameter. If your tyre loses air pressure then the contact area will increase. Conversely a higher pressure will have a smaller contact area. Believe it or not it's the same with a steel tyre but the air pressure is replaced by the modulus of elasticity of the steel and the force required to deform the steel and the rail to create the ''patch'. The contact area tends to be an elliptical shape.
    This idea did have others who believed the contact area could be improved.
    http://www.douglas-self.com/MUSEUM/LOCOLOCO/polygon/polygon.htm
     
    Last edited: Feb 28, 2020
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  15. Allegheny

    Allegheny New Member

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    I follow this up to a certain point. The steel would have to deflect further in a small wheel, to acheive the same contact area.
     
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  16. Steve

    Steve Part of the furniture Friend

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    Not sure what you are trying to say. The contact area is the same whatever the wheel diameter.
     
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  17. GWR4707

    GWR4707 Resident of Nat Pres

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    Off the top of my head I don't recall the axle loading of a 47 being any greater than a Castle?
     
  18. Allegheny

    Allegheny New Member

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    OK , referring to the diagram on the attached Wikipedia page
    https://en.wikipedia.org/wiki/Circular_segment
    Take the contact patch as being a segment of a circle, the dimension "h" will be greater for a small wheel than it is for a large wheel, for the same size contact patch.
    By "deflection" I am referring to the "h" dimension.
     
  19. johnofwessex

    johnofwessex Part of the furniture

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    2 verses 4 cylinders perhaps?
     
  20. Jimc

    Jimc Part of the furniture

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    My impression is that the 47s were a bit restricted by the cylinders in where they could go. Platform clearances and the like.
     

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