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Locomotives recorded power.

Discussion in 'Steam Traction' started by maddog, Aug 11, 2016.

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  1. maddog

    maddog New Member

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    I've searched but couldn't find anything. I was just wondering if there was a list of locomotive classes ordered by maximum recorded power, or at least grouped together in divisions of say 100hp or 250hp. As I understand it the Duchesses top the list but other classes are something of a mystery, or at least don't seem to be recorded in one place.

    The maximum power isn't particularly useful i know given that you can supply more steam than boiler can give continuously but it'd be interesting to see how classes compare in performance.
     
  2. LMS2968

    LMS2968 Part of the furniture

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    A point here is that looking at power restricts the discussion to class 8 express passenger engines. Power is defined as Force (Tractive Effort - and this means the TE being delivered at the time, not the Nominal Tractive Effort quoted in the ABCs) x Velocity (speed will do). The thing is that the power needed to move a train rises in proportion with the increase in tonnage, but with the square of velocity. So if you take a train of 300 tons running at 30 mph, raising the tonnage to 600 but maintaining the 30 mph doubles the required power. But, if you stay at 300 tons but raise speed to 60 mph, you need four times the power output from the engine. This is why British goods engines have almost always been smaller than passenger classes: the lack of continuous brakes kept speeds low, so high power outputs were just not necessary. Brute strength often was.
     
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  3. Steve

    Steve Resident of Nat Pres Friend

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    You also need to define where you are measuring this power. The power produced at the cylinder (known as indicated or cylinder horsepower) or the power produced at the drawbar (drawbar horsepower) are different. The former includes that required to move the locomotive which, in itself, can be quite substantial. The operating people are only interested in the drawbar horsepower because that dictates the load that can be hauled.
    AFAIK, the record measured power output for a British loco is held by (4)6234 Duchess of Abercorn at 3350 ihp but I'm sure someone will quickly jump in if this is wrong.
     
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  4. maddog

    maddog New Member

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    Drawbar horsepower would seem to be the fairest comparison. In Peter Smith's "Mendips Engineman" he says about the time Baron Vuillet logged a run where 2000 drawbar horsepower was achieved with a 9f.
    I suppose I am looking for the express types especially the 8Ps and 7Ps.
    It really isn't a particularly simple subject is it!
     
  5. Andrew Young

    Andrew Young New Member

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    As I understand it 46229 exceeded 3350 on the S&C in the eighties and I think that I read that a few yrs ago in Steam Railway. However here- https://books.google.co.uk/books?id...mAEAQ6AEIhQEwEw#v=onepage&q=46229 ihp&f=false -it suggests it also(or maybe only lol)was in 1985 out of Marylebone. Book is
    Giants of Steam: The Great Men and Machines of Rail's Golden Age
    By Jonathan Glancey

    and claims a figure up to 3700ihp
     
  6. LMS2968

    LMS2968 Part of the furniture

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    The problem here is how you measure Indicated Horse Power. Really this requires that the loco is 'indicated', i.e. that the pressures in the cylinder(s) is measured throughout at least one return stroke of the piston(s). To my knowledge, this has never been done in preservation. The figures for 6229 involve calculating the power at the drawbar from known factors: train weight, speed and gradient, then applying these to a formula to produce the d.b.h.p. So this is not actually measured but estimated. This estimated figure is then extrapolated into a further formula to produce an i.h.p. figure. It can be seen that such an approximation based on another approximation is not guaranteed to be accurate, and certainly no basis for a claim for 'The Most Powerful Loco In Britain', but it's all we have to go on.

    There are better records from 6234's trials on 26th February 1939, which ran a twenty coach 607 tons train from Crewe to Glasgow and return. The ex-LYR dynamometer car was behind the loco and recorded a maximum of 2,511 Drawbar Horsepower between Carlisle and Plumpton. Some of the engine's power output was diverted to lifting the engine itself against the gradient, so the Equivalent Drawbar Horse Power (what would have gone into the first coach for the same power output on a level road) was calculated at 2,890. The i.h.p. was then calculated at 3,348 (some sources misquote this as 3,248). It is known that both preserved class members to access the main line have exceeded 6234's performance and therefore power output.

    Other contender included the A4s and their various runs at well above 100 mph. These were usually record attempts and are known to have breached the 3,000 i.h.p. barrier, but not by as much as might be thought: they were usually on short trains (so lower aerodynamic resistance) and with a good deal of assistance from gravity. As far as I know, only Mallard topped, 3,100 i.h.p., but I'm open to persuasion.
     
    Last edited: Aug 12, 2016
  7. JJG Koopmans

    JJG Koopmans Member

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    That information is available in the BR test reports of the Rugby tests in the 1950's. All are available in the NRM library and some can be found as .pdf on the web.
    Kind regards
    Jos Koopmans
     
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  8. Enterprise

    Enterprise Part of the furniture

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    There are several muddled up concepts here. The most obvious: power does not rise in proportion with velocity squared except that very roughly air resistance is proportional to velocity squared; the power required to accelerate a train is quite different to that needed to maintain a steady speed. There are others.
     
  9. LMS2968

    LMS2968 Part of the furniture

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    Up to a point, yes, but we can get a bit overwhelming with the maths and keeping it simple illustrates a point. But Power is Energy given or used per hour; in this case the energy is Kinetic, and the formula for KE is Mass x Velocity squared over two. We are though talking of constant speed; acceleration requires different parameters. Realistically, this is why the engineers conducting the testing tried for constant speed (the LMS Mobile Testing Units were built with this in mind), which eliminated one of the variables so allowing a more accurate assessment of the other readings.
     
  10. Enterprise

    Enterprise Part of the furniture

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    You are very much muddying the waters. Your relationship for KE is correct but irrelevant. What point is illustrated by your incorrect mathematics?
     
  11. LMS2968

    LMS2968 Part of the furniture

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    Look at the title, Locomotives Recorded Power. Power, as said, is energy over time, and the energy, as said, is Kinetic.

    What I was pointing out is that 'power', in this context, is difficult to evaluate and therefore draw comparisons. It's more than just Loco Number XXX put out this amount of power, so that's and end of it. It isn't.
     
  12. Jimc

    Jimc Part of the furniture

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    I quite agree with the premise that true power is hard to evaluate. But the kinetic energy of a train is only really important when you want to stop it. The headline figure should surely be drawbar horsepower, both short term and sustained, and measured, not estimated.
     
  13. tedarchbold

    tedarchbold New Member

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    As horsepower is merely tractive effort at speed, it is rather simple to convert the LMS/BR power ratings to horsepower bands:

    0P = 448 HP and under
    1P = 448-597 HP
    2P = 597-747 HP
    3P = 747-895 HP
    4P = 895-1045 HP
    5P = 1045-1194 HP
    6P = 1194-1344 HP
    7P = 1344-1493 HP
    8P = 1493 and up

    0F = 425 HP and under
    1F = 425-538 HP
    2F = 538-650 HP
    3F = 650-762 HP
    4F = 762-874 HP
    5F = 874-986 HP
    6F = 986-1098 HP
    7F = 1098-1210 HP
    8F = 1210-1322 HP
    9F= 1322 and up
     
  14. Jimc

    Jimc Part of the furniture

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    I think it could be argued that to equate nominal tractive effort with actual delivered power output is at best highly simplistic.
     
    Last edited: Aug 12, 2016
  15. LMS2968

    LMS2968 Part of the furniture

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    The point that seems to be missed, Jim, is that the KE the train has comes from somewhere, and that somewhere is the loco and its power output.

    To be honest, I'm sorry I responded to this thread. My intention was to point out that goods engines cannot and are not designed to produce the power output of the largest passenger engines. Having done that, it seemed reasonable to provide some reason why this is so, but in simple terms.

    By the way, I used to teach this to Engineering Degree undergraduates. One thing you learn in teaching: don't overcomplicate the subject beyond the level the students can deal with. We could enlarge on the theory, but there might not be many readers after the first sentence!
     
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  16. johnofwessex

    johnofwessex Resident of Nat Pres

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    I have enjoyed your contribution.

    I am trying to get my head around the difference between steam - constant force & Diesel - constant horse power and how this affects performance, in particular hill climbing
     
  17. Steve

    Steve Resident of Nat Pres Friend

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    It can get even more complicated in this case. A diesel is, as you say, a constant horsepower machine in simple terms with a maximum horsepower set by its control system. A steam loco has no such equivalent and also has a huge reserve of energy in the boiler so, for short periods can produce power beyond its constant power ability. A steam engine isn't, however, a constant torque (force) machine. The torque will reduce as speed increases for a variety of reasons.
     
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  18. Steve

    Steve Resident of Nat Pres Friend

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    It's a tad more complicated than that. The LMS & BR power ratings were based on different criteria. The maximum power output of a locomotive is certainly not in the ranges that you have quoted. There is a very good explanation of the two systems in the RCTS book on the Standard Steam Locomotives, vol 5.
     
  19. tedarchbold

    tedarchbold New Member

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    I went from the information provided on wikipedia, which gives a series of tractive effort ranges at 50 mph for passenger and 25 mph for freight. All I did was turn it into hp.
     
  20. LMS2968

    LMS2968 Part of the furniture

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    Yes, that would explain it.

    If only life were that simple!
     

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