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Tornado

Discussion in 'Steam Traction' started by Leander's Shovel, Oct 20, 2007.

  1. Bikermike

    Bikermike Member

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    So empirically, it would seem you can flog a 1930s/50s tech 6'2" driver to 100mph on a regular basis without any immediate problem (query if there would be cumulative issues), which would suggest the theory needs revisiting/clarifying
     
  2. 30567

    30567 Well-Known Member Friend

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    Slight hyperbole I feel ; @gricerdon wrote a HR article on over 100mph runs and he and @Big Al may be able to comment authoritatively. My reading of it re SR pacifics is --- 90mph relatively common ; 100 mph rare and very rare pre 1966.
     
  3. 35B

    35B Resident of Nat Pres

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    It did matter if they broke the track and underline structures, though.
     
  4. Johnb

    Johnb Resident of Nat Pres

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    How would that happen?
     
  5. Jamessquared

    Jamessquared Nat Pres stalwart

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    There was a blanket speed limit of 90mph on the Southern region. So the 100mph+ runs only really started very late, since they would have been distinctly frowned upon before then, but in the last few weeks there was rather more of an attitude of "if not now, when?"

    As I recall, Bulleid Pacifics have rather short piston strokes (24"stroke; cf 26" stroke on a Gresley A4; 28" stroke on a GWR King). That was a conscious design choice to ensure piston speeds didn't get too high at higher speeds despite the relatively small wheel diameter. In turn, that drove the need for high boiler pressure (280psi as originally built) to ensure the locos had sufficient power while having comparatively small cylinders.

    Tom
     
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  6. 35B

    35B Resident of Nat Pres

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    Hammerblow


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  7. Johnb

    Johnb Resident of Nat Pres

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    Not an issue on a three cylinder loco and I stand to be corrected but I don’t think it increases with speed
     
  8. GWR4707

    GWR4707 Resident of Nat Pres

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    We clocked 96 with a mixed traffic loco with 6'2 wheels on a tour in the 80's
     
  9. Flying Phil

    Flying Phil Well-Known Member

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    I believe that BR 9F's, with 5 foot diameter driving wheels, were regularly in the 80 mph range and even up to 90 on one or two occasions so Tornado should be comfortable at those or even higher speeds.
    I still think the EBOR episode was more to do with the winter maintenance re-bore/re ringing and the centre valve seizing as it was at its hottest. Although it had been run-in, after it was not at the sustained high speed of the EBOR. The previous 100mph run was done after several years main line running.
     
  10. Big Al

    Big Al Nat Pres stalwart Staff Member Moderator

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    Just a detail. The Southern limit was 85 mph and I've lost count of the number of times when a Bulleid has taken me at that speed on the flat or downhill. 90 was not unusual west of Basingstoke on the ACE and we know that Clan Line clocked 104 way back in 1961 long before the excitement of 1966/67 when 90+ became almost normal. Fleet by name and also to describe what went on there!

    Few can argue against a loco with 6ft 2in drivers being capable of three figures and to touch 90 when appropriate is really beyond debate....except to ask why you would do it with a steam locomotive on the main line. I've been at speed when it was necessary to keep ahead of a service train but it wasn't done for fun and neither was the loco any the worse for the experience. But I wouldn't recommend it especially if it isn't necessary.

    For me the debate about Tornado running at speeds of up to 90 is academic. I'll be convinced when someone shows me a path on the ECML that will work on 90 mph max but won't on 75.
     
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  11. huochemi

    huochemi Well-Known Member Friend

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    Although it is a complicated subject, I don't think it is correct to say that 3 cylinder locos do not have hammer blow, rather that balancing the reciprocating parts presents different considerations. In his paper of 1941 "Balancing of Locomotive Reciprocating Parts", Cox notes that the MNs had no reciprocating balance and nil hammer blow, but that seems to have been quite unusual. Incidentally, the per cylinder reciprocating weight was greater on the MN than on the Duchess, King or A4. One of the complications is that you can balance out the axle but have hammer blow on individual wheels e.g. again from Cox, a Jubilee at an unlikely 115mph would have a per wheel hammer blow of 7.8 tons but a per axle hammer blow of 0.6 tons (cf a Duchess which was 3.35 tons and nil respectively). There is of course the hammer blow which arises on joints and track irregularities from unsprung weight, which is difficult to mitigate in a steam loco, but became a major issue for diesel and electric locos. This hammer blow is destructive of track even if the hammer blow from reciprocating parts is eliminated. (there is at least one ILE paper on this, McClean, 1937 "The Hammer Blow with Axle-hung Electric Traction Motors").

    The use of piston speed as a factor is interesting, when of course the piston spends its whole time accelerating and decelerating, and presumably what loco engineers meant was the maximum speed. One of the interesting and non-intuitive issues that arises from an examination of the piston and connecting rod assembly is that the piston appears to complete the front half of its cycle quicker than the rear half (if you draw an arc with the centre at the little end and the radius being the distance to the centre of the driving axle, the arc cuts the crankpin circle top and bottom in front of the perpendicular from the wheel centre).

    Edit. I probably did not explain that very well, but the radius is of course the distance between centres of the little and big ends of the connecting rod, and the arc is drawn when the piston is midway between its front and rear extreme positions / the crosshead is mid-stroke. The attached graph from one of Phillipson's series on steam loco design in The Locomotive in 1931 shows a graph of the velocity of the piston relative to the cycle of the crank pin, showing the asymmetry between front and rear parts of the stroke.
     

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    Last edited: Oct 2, 2020
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  12. LMS2968

    LMS2968 Part of the furniture

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    No, it increases with the square of speed, so doubling your speed quadruples the hammerblow. And you can and do get it with three (and four) cylinder engines. If the drive is divided, the two driven wheelsets will produce individual hamerblow, but this will be out of phase and largely cancelled out overall. If driving on the same axle but with unequal length (and weight) connecting rods it will arise again, but in neither case will it be as severe as with a two cylinder engine.
     
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  13. 242A1

    242A1 Member

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    It depends what you call modern. The AAR rules have been established for years, we are not talking state of the current art here but how the US railroads and locomotive companies designed and built their engines. If we are taking about the design speed as and when built, Gresley was disappointed with the performance of 4468 and wanted another attempt but war intervened. 130 mph is what was expected and given the performance of the single chimney fitted Silver Link on on Sept. 27th 1935 I can well understand the feelings of HNG and his staff.
     
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  14. Steve

    Steve Part of the furniture Friend

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    But we aren't talking about one off attempts at a speed record; we are talking about reaching a sensible conclusion on a realistic speed for an existing steam loco.
     
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  15. 242A1

    242A1 Member

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    True enough, but looking at what a locomotive was designed to achieve is one part of this. You could, given the time and money investigate what each design ought to be capable of but instrumentation is costly, so is running checks on material specifications, running the whole design through a full analysis of its design using currently available technology again costly. So we are left looking at the established record, what did these engines achieve in regular service, what were they expected to achieve in that service. You then look at costs, what did it cost to run these engines at their expected level of performance and how does this translate into what it might be expected to cost today.
    A glance at the national network and the schedules being worked to today and the gulf in performance that exists between heritage traction and current types raises the question with regard to how, where and when we might continue to be accommodated.

    Suppose it could be agreed that in order to be allowed onto the network on what might be termed primary routes we ad to come up with a plan. Reduced weight trains with increased fares to make these viable. This should allow for improved acceleration, but what speed should we be aiming for? Well given a suitable piece of modern traction on the rear we can have our relics pushed up to speeds that no responsible locomotive owner would find acceptable.

    We have some of what we call new builds of which only one is completed. But what are these really? The designs date from the 1930s and 40s and though a number of improvements have been included and these engines benefit from newer materials and construction techniques they are still essentially old designs.

    If you want a realistic speed for today then accept the existing limits. What engines would and could do in the past is an interesting subject. Many performance records exist, many examples of achievable schedules. But then there were spare engines, extensive locomotive works to conduct repairs, many trains to work to drive revenue. We should be responsible preservationists and accept and understand the limits that our situation imposes on us.

    Or maybe we should have built a 5AT.
     
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  16. MellishR

    MellishR Part of the furniture Friend

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    The 5AT was specifically intended to be able to pull economically viable loads at speeds fitting in with the modern railway. I find it very sad that the project never gathered enough support.

    Although Tornado is in most respects a 1940s design (and British 1940s at that, with limited incorporation of Chapelon's improvements) it has been somewhat updated, it was intended and is being maintained to be able to run well above 75 mph when appropriate, and it has plenty of power for pulling enough coaches. So it would be good for that capability to be used.
     
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  17. Jamessquared

    Jamessquared Nat Pres stalwart

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    5AT was always a dead end. Firstly, I don't think it was "heritage enough" in appearance to be a draw for the core market. Maybe that market can't distinguish a Black 5 from a Standard 5, but they can certainly tell the difference between a heritage experience and one that isn't. If you booked a vintage Rolls Royce for your wedding and the car that turned up on the day was a modern Mercedes, you'd be annoyed, even though in almost any way you care to mention the modern car would be superior.

    Secondly, and more significantly, to provide operational resilience, you need a pool of locos; and the schedules and loads have to be based around what the least capable of those locos can manage, not the most capable. If you have a loco that can comfortably run 120 miles between water stops, you still can't build schedules on that assumption in case it has to be substituted late for one that can only do 80 miles. So in practical terms, having a single very capable locomotive does not allow its capabilities to be exploited.

    We should be grateful for what we have, which is a reasonably varied fleet of old machines that can still be seen in operation. They are interesting because they are old and show a different mechanical era, not because they have some wizard tweak that converts them from "unbelievably inefficient" to merely "really inefficient".

    Tom
     
  18. Sheff

    Sheff Well-Known Member

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    It’s all about the engineering challenge involved. Maybe too niche for many. But certain elements are already up and running on locos old and new.


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  19. 242A1

    242A1 Member

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    As Sheff states elements of the work carried out in the design work carried out for the 5AT are already being included on locomotives.

    The engine did not have to look as depicted, it could have had a far more "Heritage" appearance. Without the large tender it would not have had the projected range but even with a version of what would appear to be a BR1F it would have superior range to any currently existing type.

    If you build one locomotive you can build more. And if the general public cannot tell the difference between the historic and the not so you can guarantee that one very important body would notice.

    The efficiency angle is an interesting one. Chapelon carried out some calculations when it came efficiency. As steam locomotives went at the time his designs were the most efficient, but they did not represent what could be achieved merely what had been achieved to that date. He wanted to know just how efficiently the raw energy source that was being used, coal, was being converted to what we might call power at the drawbar. Now I haven't found the calculations (given how things that are politically inconvenient disappear no real surprise there) but the result, that is another matter. The compounds made better use of the coal than the electrics when all losses had been taken into account. This could be considered to tie in with Brown "The Economics of Diesel Traction on U.S. Railways". Getting more towards the current times deliberate omission remains a common currency, the French offshore windfarms provide an interesting story. And don't mention the Drax fiasco.

    Yes, technology has moved on since Chapelon ran his numbers but it should be remembered that neither side has stood still. The steam locomotive might not have been the most efficient machine in the world, the human body is not all that efficient either but both are outstanding when compared with the efficiency of growing our food, I have come across figures of 1.5% for this.
     
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  20. Bikermike

    Bikermike Member

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    Just to dig this up briefly, I'm reading M. Jackman "Engineman SR" (one of those Bradford Barton footplate memory books) on the train, and in early 50s (he's back from Malaya for National Service and it's before 1957, he talks about running BoB Sptifire Tonbridge to Ashford and touching the ton on that run, so it may not have been official, but it seems that they did manage it from time to time. And some stuff about several timed 95mph runs behind Lord Nelsons on the Bournemouth run (unspecified but in relation to the 1948 loco exchanges).

    That and thrashing the bejasus out of Schools at every possible opportunity...
     
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