Continuous Traction Effort vs # of pull-able rail cars

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Continuous Traction Effort vs # of pull-able rail cars

  • The one I used is called "1970 modified Davis Eq."  Don't recall where I found it.

    -Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/

  • Thanks to all for the answers, I believe me, I know that straight and level track is NEVER straight and level... 

    And again, I have seen a single locomotive start a cut of cars that seems "impossible" for it to move, but has indeed, moved it;, but I have always wondered how the "powers that be" have determined exactly what each locomotive is "rated" for as far as car numbers.  Now I've got something to not only work with for grins and giggles, but gives me a better idea of what the "real guys" do. 

    Now, if I could only find a CSX tonnage ratings book for the area I'm in (CSX Dothan Subdivision), I think I'd be set...

  • Bama,

    As others have mentioned real world ratings are in tons between two points, not cars. For each train there will be a consist that will include somewhere on it loads, empties, tons, and feet. These are the important numbers for train dispatching.

    Mac

  • Mac, you're right.  I've heard those exact things broadcast on various scanner feeds when a train is coming out, or heading into a yard.  But with those tonnage limits, (and some rough calculations/guesstimates) I could more, or less, come up with a max # of cars based on the power on the head end.

  • BamaCSX83

     

    Now, if I could only find a CSX tonnage ratings book for the area I'm in (CSX Dothan Subdivision), I think I'd be set...

    DEPART - ARRIVE - SD402  SD50 C40-8 ES44D SD70MA CW44C CW44AH
    NASHVL - BIRMIN -  2650  3150  3400  3700  4350  4600   5000
    BIRMIN - MONTGL -  4200  5000  5450  5850  6900  7350   7950
    MONTGL - DOTHAN -  2800  3300  3600  3900  4600  4900   5300
    DOTHAN - WAYCRO -  4050  4800  5250  5650  6650  7050   7650

    WAYCRO - DOTHAN -  3250  3850  4200  4550  5350  5650   6150
    DOTHAN - MONTGL -  2850  3350  3700  3950  4700  4950   5400
    MONTGL - BIRMIN -  3350  3950  4350  4650  5500  5850   6350

     

    Forum formating doesn't provide accuracy in tabular data.

    Never too old to have a happy childhood!

  • Bama,

    The railroad operates first and foremost on tonnage. Conversion from tons to cars is imprecise since mixed freight cars have various weights depending on whether loaded or empty. Car count does become a limiting factor in terms of siding length. It is very handy to have your trains short enough to fit in the sidings.

    Mac

  • PNWRMNM

    Bama,

    The railroad operates first and foremost on tonnage. Conversion from tons to cars is imprecise since mixed freight cars have various weights depending on whether loaded or empty. Car count does become a limiting factor in terms of siding length. It is very handy to have your trains short enough to fit in the sidings.

    Mac

    And even that can be 'fudged', by setting policy that trains in one direction must fit the sidings and trains in the other direction can exceed siding length.  Makes it a little more difficult for the Train Dispatcher but it is a workable strategy.

    Never too old to have a happy childhood!

  • BamaCSX83
    if I could only find a CSX tonnage ratings book for the area I'm in (CSX Dothan Subdivision), I think I'd be set...

    Best not to trust "tonnage ratings" that much. Some RRs try to be realistic and some don't bother; none of us here is much of an expert on which is which.

  • timz

    BamaCSX83
    if I could only find a CSX tonnage ratings book for the area I'm in (CSX Dothan Subdivision), I think I'd be set...

    Best not to trust "tonnage ratings" that much. Some RRs try to be realistic and some don't bother; none of us here is much of an expert on which is which.

    What I posted is what is used for the 'Bow Line' from Waycross to Birmingham that includes the Dothan Sub

    Never too old to have a happy childhood!

  • Found 2 cents, here they are....

    For DC locomotives, empirically determined, but based on calculations, a territory is determined to need a supply of horse power per ton of trailing load. The territory may include momentum grades, where an over-tonnage train may not be able to start but in a continuous train movement the train will lose speed but not stall before getting over the grade's summit. The phrase "making a run for the hill," comes to mind.

    Hp/T ratings average out all the results of the more intricate calculations, and may include or exclude local factors like the mile of 1 per cent at the Martinez Bridge on the way from Oakland to Roseville, where exploiting short time amperage  ratings allowed 3-tenths of a horse power per ton to let me get 5800 tons over the 'road.

    Where Windy Point, near Palm Springs, and Midway on SP's Altamont trackage made tonnage ratings based on the formulas seem fictional, Hp/T usually worked. Not always.....most of the trips.

    Many formulaic conclusions may never fail. Hp/T may never  fail but also...as the weight of cars increases the effects of train resistance diminishes.

    On Cuesta, the grade from San Luis Obispo toward San Francisco, I fired trains that were limited to 4250 tons with only power on the point.

    Now, on the point, 5400 tons is the limit....roller bearings....no solid bearings....heavier cars...with less surface area for wind to affect... 


  • As to Cuesta I suspect the difference is due to grade E couplers and knuckles rather than grade C.

    Mac

  • Should not the values in th modified Davis formula be modified depending on revular journals or roller bearings?

  • Tonnage ratings my carrier uses are based upon how much tonnage the locomotive can keep moving just above its Minimum Continuous Speed on whatever the ruling grade is.

    Personally, I take exception to this, because like it or not a train with max tonnage for it's engine consist will have some form of mechanical trouble and stop on the ruling grade for the territory.  While the locomotive consist may be able to keep the max tonnage moving - there  is not enough power to START the train on the grade.  To get the train moving again, assistance will have to be secured.  Assigning tonnage rating based upon MCS is a gamble, the gamble being whether the train stops on the ruling grade or not.

    Never too old to have a happy childhood!

  • daveklepper

    Should not the values in th modified Davis formula be modified depending on revular journals or roller bearings?

    No.

    A well designed plain bearing only has a  higher coefficient of friction when first starting. Higher torque is needed only to break the the oil film. Once running, the oil film becomes hydrodynamic in nature, and the friction is similar to a roller bearing.

    The main advantage of a roller bearing on a rail car is the reduced maintenance vs. a plain bearing.

  • OK, now that we've settled all this, what about weather?  (Always glad to add a kink to a discussion Devil )

    Hump yard computers, even in my day (early 70s), took journal temperature into account when calculating the retardation required for each car.  I seem to recall a Davis variation that had an adjustment for temperature and maybe humidity but the details are hazy (no pun intended).  But I clearly remember assigning extra power when snow was in the forecast.

    Of course, on the Central in those days, it was unthinkable to assign only as much power as the tonnage required unless it was a low priority train.  SVs, for example, always had four, five, or six of the newest GP40s available.  Nobody ever got fired for overpowering an SV but a late SV could get somebody terminated.

    Chuck
    Allen, TX