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Draughting arrangements for Bulleid Pacifics including the Giesl ejector

Discussion in 'Steam Traction' started by jamesd, Oct 14, 2014.

  1. martin1656

    martin1656 Resident of Nat Pres Friend

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    And if i remember correctly, there were issues with drifting exhaust obscuring the crews vision when Tangmere was on the mainline, Might the rail vehicles acceptance body have a view on future operations of un rebuilt Bulleid Pacific's because of this problem, , so it might make sence to reduce this visibility problem down to an acceptable level?
     
  2. 30854

    30854 Resident of Nat Pres

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    With respect to @Big Al that ain't exactly the original appearance, as it features the full 'Southern' roundel, rather than the 'inverted horseshoe' initially fitted to 21C1 and hastily amended due to superstition on the part of enginemen.
     
  3. Jamessquared

    Jamessquared Nat Pres stalwart

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    Not to mention the cast brass number plates and "Southern" lettering, soon discarded on weight grounds. (How they got all that brass past the wartime austerity measures is an interesting question!)

    To be honest, the first five locos were pretty radical in appearance; things settled down after that into more or less the final form, but the first few were all somewhat different from each other.

    This would look pretty dramatic if you could just "discover" in the archives that it was actually 35001 and not 35011 that had wound up at Barry all those years ago ...

    https://transportsofdelight.smugmug...SOUTHERN-RAILWAY/SOUTHERN-RAILWAY/i-LDCWPLd/A

    Tom
     
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  4. Big Al

    Big Al Nat Pres stalwart Staff Member Moderator

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    As you say, there was tweaking from Day 1 to the early locos of which the change to a full roundel was one, for obvious reasons. (Nice to see that feedback led to a quick response.) I used that image of Royal Mail at Salisbury as it illustrates what I believe became the accepted version of the original design that is quite distinctive from how the locos appeared later and would set GSN as different from those light pacifics that still exist.
     
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  5. Sheff

    Sheff Well-Known Member

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    All of this presumes the loco is going mainline. Is that not the case? If it’s just going to be a show pony for heritage lines then I’m out.
     
  6. class8mikado

    class8mikado Well-Known Member

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    Don't think anyone is suggesting 'real 'wind tunnel testing.
     
    Last edited: Apr 11, 2021
  7. JJG Koopmans

    JJG Koopmans Member

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    The book of Roger Mannion, "The Southern Pacifics" gives some details on page 85 on the testing of a 1/10 scale model in the wind tunnel of the University of Southampton early 1943.
    This book also has drawings of the original smokebox version and the Ell modified one on page 54 and 160 resp.
    Kind regards
    Jos
     
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  8. Allegheny

    Allegheny Member

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    Was the blastpipe size changed at all?
     
  9. JJG Koopmans

    JJG Koopmans Member

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    No, 5 orifices of 2 5/8 in. diam.
    Kind regards
    Jos
     
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  10. Spinner

    Spinner Member

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    That original (or as introduced) casing is as ugly as a hat full of, well, blurters. The second version is far more visually acceptable. I thought that making 35011 aesthetically pleasing was part of the remit. You do not want to produce a locomotive so ugly that it scares passengers away. Similarly, that shape kept the exhaust over the locomotive, reducing visibility, which was the operational reason for the, as someone else has called it, 'production version.'

    Part of the attraction in traveling behind a 'cased in' 35011 will be based on doing something that people did in the 1940s and 1950s. The 'production version' of the casing is depicted in many photographs etc, making brand recognition work in filing the carriages that 35011 will be hauling.
     
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  11. srapley

    srapley New Member

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    My understanding, backed up by some of the CFD we've done of a MN and looking at the papers from the 40s on the aerodynamics of the front end of an A4 and a Duchess, the front end works well when there is no cross wind. Unfortunately, due to the fairly trapezoidal cross-section, if there is any cross wind, a low pressure region develops on the leeward side of the locomotive, as the top corner of the casing is too sharp for the flow to remain attached; on an A4 I would hazard a guess the detachment occurs much lower down . If the exhaust is too weak to get out of the low pressure region on the top of the casing (which during the transient exhaust cycle 6 times per revolution of the wheels it is), it then gets pulled into that low pressure region. The deflectors do help a lot, but there will always be a condition with the air-smoothed casing where you can get obscuration. On P2 2001 with it's Lentz valve gear the exhaust was sharp and it worked well, on 2002 with Walschaerts the exhaust was softer and didn't get clear, hence the second set of deflectors. Our members will be getting more details of this in the next issue of The Packet, which will be published soon...
     
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  12. srapley

    srapley New Member

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    We looked at some of these things in CFD (virtual wind tunnel); the problem with changing the contour of the smoke deflector is if it's not parallel to the railway track, it could obscure the drivers view. I believe the original design, and the 2nd batch design were tested in a wind tunnel at Southampton University in the 1940s (Bulleid acknowledges the work done there in his 1945 paper) but the details of that testing weren't published as far as I know. Again, our members will be getting more details of this in the next issue of The Packet, which will be published soon...
     
  13. srapley

    srapley New Member

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    I'd be interested in seeing that!
     
  14. srapley

    srapley New Member

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    The intention is the 2nd batch casing design, with deflectors
     
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  15. srapley

    srapley New Member

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    The plan is to go mainline and have deflectors, as GSN had when built in 1944. The deflectors are necessary for mainline running. The draughting is primarily about improving the performance/efficiency of the locomotive, but with an eye on exhaust clearance at the same time.
     
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  16. srapley

    srapley New Member

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    There's a few papers on the subject, correct. One on smoke deflectors on Maunsell locomotives, one on the development of the A4 & Duchess front-ends...
     
  17. srapley

    srapley New Member

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    We're definitely targetting mainline running; the time, effort and expense we're putting into recreate the original drawings, the cost of the new components, etc. is essentially the same whether we mainline certify or not, but we have a collective vision of recreating something like this (though probably with the latter cab). Having GSN purely on a heritage line at 25mph is like taking your Ferrari to Tesco to do the shopping, it doesn't use the power of the machine (we will visit Heritage lines of course, if they'll have us)
    [​IMG]
     
    Last edited: Apr 12, 2021
  18. class8mikado

    class8mikado Well-Known Member

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    Vision Shared. i think a membership is required...
     
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  19. srapley

    srapley New Member

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    I'll have to have another read of this book. The issue which the wind tunnel testing didn't solve (possibly didn't address) is cross-wind effects, which is where the exhaust obscuration really comes from. The deflectors combatted that to some extent, but no design can be perfected for all conditions (apologies to all if my posts are drawing this thread away from draughting from a perfomance point of view)
     
  20. srapley

    srapley New Member

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    Have a look at our website, it is very, very easy to sign up for membership, thanks to our excellent Membership Secretary https://35011gsn.co.uk/membership.html
     
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