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P2 Locomotive Company and related matters

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

  1. Eightpot

    Eightpot Well-Known Member Friend

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    This AT&SF loco 3752, as far as I can make out, was built in 1928. Was it new with poppet valve gear or was it rebuilt with it later?
     
  2. 30854

    30854 Resident of Nat Pres

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    Just out of interest, I crunched the same numbers for the French Class U1 4-6-4 (the last and IMO the best looking mainline loco constructed for the SNCF in 1949)

    Loco only weight 127 long tons
    Tender weight 83.1 long tons
    All up weight 210.1 long tons
    Rated output 3260 hp

    Giving (loco only) 25.57 hp/ton or with tender 15.57 hp/ton
     
  3. MellishR

    MellishR Part of the furniture Friend

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    That seems to give the lie to the 40 hp per ton figure.
     
  4. Eightpot

    Eightpot Well-Known Member Friend

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    If you have the opportunity to see it at the Mulhouse museum, it is interesting to see that it suffered the same problem that the 'Kings' and 'Princess Royals' had, i.e. loose outside cylinders. The same remedy was applied with blocks of steel welded onto the frames and cylinders to stop them shifting.
     
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  5. S.A.C. Martin

    S.A.C. Martin Part of the furniture

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    upload_2021-6-16_8-25-43.png

    How much more evidence in black and white do you need on this? Thane of Fife as an A2/2 did double the mileage and had double the availability of the P2s. We also have a huge amount of data on the work the A4s were doing, and the W1 too, on that route.

    I sometimes think we enthusiasts get somewhat blinkered in our understanding of what the working railway did. No one is saying a Mikado has worse performance abilities than a Pacific, and I think everyone recognises the maths involved when we're talking about adhesion, and clearly eight coupled wheels is better than six for that specific method of measurement.

    However, it's the work actually being done that mattered to the LNER board and I really don't think we can argue that the P2s were better than the Gresley, Thompson and Peppercorn Pacifics in reality with the evidence we have.

    If we want to talk about how they should have been able to be better - that's a whole different argument.

    I too am impressed with the Vampire modelling but I am calmly awaiting events and seeing how the locomotive performs in reality. Like Tornado, there may be a few little things to clear up on testing but otherwise it should be an impressive locomotive.
     
    Last edited: Jun 16, 2021
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  6. MellishR

    MellishR Part of the furniture Friend

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    That is a very definite statement that the performance of the first rebuilt loco on the road was at least as good as that of the unrebuilt P2s. But have we any idea why the reduction in adhesion weight apparently made no practical difference?

    Also, given the poor availability of the P2s, were some of their turns worked by Gresley Pacifics, and if so how did they compare? I would expect them to have fared worse than the P2s because of their smaller boilers as well as their lower adhesion weight.
     
  7. Jamessquared

    Jamessquared Nat Pres stalwart

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    Not if the turns available were easily within the compass of a smaller loco. For example, if you have a loco designed to haul 600 tons but the traffic available never actually exceeds 500 in normal circumstances, then a 500-ton capable loco can cope just fine. Which comes back to @S.A.C. Martin's point: the measure of a loco is whether it can haul the traffic on offer, not whether it can haul a theoretically greater load but which rarely if ever materialises.

    Tom
     
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  8. S.A.C. Martin

    S.A.C. Martin Part of the furniture

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    Because the extra set of driving wheels on the route simply didn't make that much of a practical difference? Like - they simply weren't required in the first place? What locomotives ran on that route before the Mikados - did they have eight coupled driving wheels?

    The practical difference in a Gresley A4 to a P2 is - what - two extra set of drivers and a few square foot of grate plus a few inches of boiler tubeplate? Controls identical, cab identical, oiling around points and conjugated gear, largely identical? Same tender and therefore water and coal capacity, more or less? Less adhesive weight, that actually doesn't translate into a reasonable difference in performance?

    Thompson could have scrapped the P2s altogether and the Gresley A4s which were working trains on that route could have done the work to a better level of availability and higher mileages by far.

    Where the Gresley P2s are concerned, that focus on the extra set of driving wheels didn't translate into something that was genuinely better than a Gresley A3 or A4. Putting them into a Pacific format gave the class the mechanical reliability and mileages required. That for me is the clincher.

    Do I still want to see a new P2? Hell yes.
     
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  9. huochemi

    huochemi Well-Known Member Friend

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    For one given to seeking truth from the facts (as Chairman Mao put it) you are fond of sweeping assumptions / statements! ;) I suspect the relationship of the number of driven wheels to adhesion is not totally straightforward. In theory, friction is the weight x the coefficient of friction for the material so (again in theory) adhesion is based on weight, not contact area or number of wheels/points of contact (so in theory a single wheeler with an 80t axle load would be as grippy as a P2, and a Formula 1 car would have just as much grip if its wheels were as narrow as those on a pushbike - but they would not last very long). One can postulate that the suspension/track levels and oil on the track etc can alter the theory. A P2's adhesive weight was higher than an A2/2 and I would be inclined to base its extra potential grip on the greater adhesive weight, not the number of driven wheels.
     
  10. S.A.C. Martin

    S.A.C. Martin Part of the furniture

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    I mean I was of course generalising, but the point I was trying to make is that in the practical reality of running trains, did the extra set of wheels/extra weight make a difference to getting the work done? The evidence we have suggests probably not.

    Tom sums it up better than me. I will retire to the comfort of my armchair.
     
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  11. class8mikado

    class8mikado Well-Known Member

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    The one that always puzzles me about the P2. is the size of the wheels.
    Although smaller than the accepted Express Passenger ( as close to 7ft as we can get) wisdom at the time - surely it could have performed its duties just as well with 5ft 8 or less diameter drivers, reducing the coupled wheelbase and overall length by at least a foot
     
  12. toplight

    toplight Well-Known Member

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    The website here gives details of why they were built. https://www.lner.info/locos/P/p2.php

    "The P2s were designed to handle the express passenger traffic on the Edinburgh to Aberdeen main line, which is noted for its steep gradients and tight curves. Double-headed Pacifics were prohibited from the line, so the heaviest traffic was usually handled by double-heading two smaller engines. Gresley sought to overcome this need with a Mikado (2-8-2) design with four driving axles for greater adhesion compared to an A3 Pacific."

    So presumably a single A3 was considered not enough. The A4s were designed later. I have never travelled on the Edinburgh Aberdeen route, Is it particularly steep and curved ?

    I haven't ridden on the footplate much but one ride I did go on was on a pannier tank pulling a train on the Bodmin and Wenford Rly. The line has some very tight curves and the driver didn't adjust the regulator and it was amazing just how much the train would slow down on its own going around a curve and then speed up again on the straights without the regulator even being moved, so the curves caused much more drag than I expected and that was with only about 4 coaches not a full length train.
     
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  13. 30854

    30854 Resident of Nat Pres

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    I wonder just how that 7'-0" dia was arrived at. Presumably, there was an element of keeping reciprocating masses manageable, likely too, concerns over excessive piston speeds. I recall IKB's early specification for BG locos certainly mentioned these, as well as giving the clearest practical demonstration of theory vs fact.

    With the spreeds acheived by later locos with 6'-2" dia coupled wheels, would it be fair to ask whether improvements in metallurgy and lubrication over the intervening century (and a bit) significantly changed several baseline assumptions?
     
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  14. Hermod

    Hermod Member

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    It was due I think to tradition.Drivers should not revolve faster than 5 revolutions per second from two cylinders.
    If it has three or four cylinders it can without much trouble do 7 revolutions per second.
    Seven feet wheels turning 5 or 5 feet wheels turning 7 move at same speed.If piston areas are equal and strokes proportional to driver diameters piston speed will be the same.

    Having selected three cylinders and pony trukcs (Gresley patents) there was no rational reason for 6 feet two drivers apart from looking powerfull and manly.
    A three cylinder 9f would have done better.
     
    Last edited: Jun 16, 2021
  15. 30854

    30854 Resident of Nat Pres

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    Someone's evidently as keen on crank axles as West Sussex County Council are on roundabouts. Are you certain your souped-up 9F's 5'-0" drivers would look sufficiently 'powerful and manly', or just plain 'squat and butch'? ;)
     
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  16. S.A.C. Martin

    S.A.C. Martin Part of the furniture

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    One could argue that Hermod's contributions are more useful in talking out the engineering: because ultimately the "what ifs" do give us an indication of what was possible.
     
  17. Hermod

    Hermod Member

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    As I see it Gresley started selecting three cylinders for everything because then there would be a crank shaft,and if there was a a crankshaft it should be second driver to protect it from abuse from rails and then valve gear becomes difficult and conjugation is a solution and gresley liked conjugations.
    It is my guess that 95 % of LNER locomotives only exceded 5 rev per second when slipping so his obsession was not cheap.


    My madness is another.

    A two cylinder compound can make same work as a two cylinder simple of 10% more mass from 10% less coal but the low ressure cylinder can only sit between frames in UK.
    It is then almost free to balance the whole lot with a spare conrod and then run faster on smaller wheels.
    This obsession has not cost anything.
    Yet
     
  18. W.Williams

    W.Williams Well-Known Member

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    Pulling some snippets from Wiki.


    The second locomotive of the class, No.2002 Earl Marischal was completed by 1935, also at Doncaster, and was fitted with Walschaerts valve gear, as used on Gresley Pacifics, and had a greater superheater heating area of 776.5 sq ft (72.14 m2), obtained by using larger diameter fire tubes.[11] At low cutoffs smoke clearance on No.2002 was unsatisfactory: wind tunnel experiments led to an additional second pair of smoke deflectors being fitted inward of the first.[12]

    No. 2002 proved to be more efficient than 2001, due to a lower cylinder clearance volume and because the stepped-cam cutoff modifications made to No. 2001 reduced economical working relative to the infinitely variable cutoff of No. 2002. Consequently, the following locomotives were built with piston valves.[13]


    The class was rebuilt into Class A2/2 4-6-2 'Pacifics' during 1943/4.[26] According to B. Spencer, an LNER employee, the class was rebuilt due to reliability problems during the difficult conditions of the World War II period, and additionally to take the opportunity to try out a different valve gear arrangement.[27] Other sources supposed that the rebuilding might be because the class's wheelbase was too long for the routes it worked, and that the railway would have been better served if the class had been transferred to more suitable routes.[28]

    Railway author O. S. Nock suggested that Gresley's successor, Edward Thompson, may have made largely unsubstantiated criticisms of the class in order to justify the rebuilding.[26] According to O. Bulleid, the class were not an inefficient design but had been placed into services in which they were under-utilised, leading to poor fuel economy.[29]

    Shortly after being put into service, on 19 June No.2001 was tested with a 19 bogie carriage train of 649 tons on a return journey between Kings Cross, Grantham and Barkston; the locomotive hauled the train at an average speed of over 50 mph, with peak speeds of over 70 mph.[19] Drawbar pulls of around 6 tons at around 60 mph were recorded - representing a peak power output of over 2000 horsepower.[20]


    The Aberdeen road is tricky. Particularly in the winter. Line speeds are still woefully slow in some sections. HST/Azuma timings were/are 4 hours to Edinburgh (400 miles) but a further 3 hours to Aberdeen (130 miles).

    I struggle to see an A3 managing to could cope with 19 bogies on a bleak winters day in the North East. 2000 hp is surely well out of reach of an A3?

    The long wheelbase argument is spurious given that Ferryhill had more than a few WD's allocated to it over the years.

    From a design perspective, Piston valves and infinitely variable cut-off appears to be the holy grail for this machine. In fact, infinitely variable cut-off/runner length is the dream for any reciprocating machine.

    My understanding is that A4's only made regular appearances in Aberdeen post War/BR era. Coronations however did appear daily with LMS Postal's which ran through to BR.

    The question of how often 649 ton loading's came up is one I don't have the information to answer. In LNER days it was clearly often enough to justify the significant capital expenditure of 6 machines.

    To add to all this we have the issues with crank axles, now resolved by the P2 group, but these failures would have plagued the class as being significant and costly in the minds of the company and management. Clearly Thompson saw this as a significant reason to rebuild. The fact the class is so small makes the case that much easier as the capex is specific and importantly, limited, as evidenced by the note above. Easily signed off by the board.

    Further, there is a lot of evidence of double heading post war on the Aberdeen run. It went on daily, so on that basis alone its arguable that the decision to rebuild them was shortsighted and ill-conceived. Had the P2 been given better conditions, ample time and capital investment (prohibited by the war) they may well have seen out their days on the Aberdeen section as untouchable entirely vindicating their inception.
     
    Last edited: Jun 16, 2021
  19. Spamcan81

    Spamcan81 Nat Pres stalwart

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    AFAIK Gresley did not patent three cylinder drives, nor pony trucks. What gives you that idea?
     
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  20. meeee

    meeee Member

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    So what was pulling the services that the P2 would be ideal for? Or did those services not exist?

    Tim
     

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