Placement Of DPU Locomotives In A Train

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Placement Of DPU Locomotives In A Train
Posted by caldreamer on Wednesday, July 24, 2019 4:04 PM

I am trying to figure where DPU locomotives are placed in a train.  Do you use the trailing tonnage, weight no matter how long the train is, and/or both of the above?  How would car lenght fit into the equation of determing DPU placement?  Is there an algorthym that is used to help in the placement of the locomotives?

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Posted by oltmannd on Wednesday, July 24, 2019 5:23 PM

I think the answer is more how you handle them then where you stick them in the train.  As long as you can give the engineer good information about where his train is on the road, he should be able to get the train over the terrain. 

You see lots of big unit trains with the DPU on the rear.  You see lots of CSX merchandise trains with DPUs mid train (I saw a train with two units, 17 cars, then a single unit, then 75 cars.  Headed from Atlanta to Hamlet - or beyond.)

I'd like to see multiple DPUs employed with a locomotive at the head of each block in the train.  Maybe that was what CSX was doing?

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

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Posted by Overmod on Wednesday, July 24, 2019 6:50 PM

caldreamer
I am trying to figure where DPU locomotives are placed in a train. Do you use the trailing tonnage, weight no matter how long the train is, and/or both of the above?

The 'better' answer to this is 'node management' vs. setup complexity.

Of course the power is apportioned in tons per equivalent axle (at the 'ruling' maximum train resistance).  As discussed, with trains of sufficient length or grades/profiles of the wrong character, putting all the power on the head end leads to risk of stringlining, slack run-in and -out, and other issues.  

DPU gets around these by supplying the 'tractive effort' as a combination of pull and push.  You will quickly recognize that this means there will be some point in the intervening consist where the pull from the front exactly balances the push from the rear; there is zero buff or draft at this point and it is called the 'node'.  Note that it can freely move forward or backward in the consist, sometimes very quickly, and you can occasionally hear this as a sharp, fast 'slack action' within part of the train. Why this is important is that the maximum tension in any draft gear forward of the node is then limited to what an equivalent train of that length would be, and the maximum buff force limited to that of an equivalent cut from the node back..

My understanding is that you want some bias of the node toward the rear, with the 'tensile' force set to a reasonable maximum as the vehicle dynamics of a train are better with the couplings stretched than when in buff.  If you have the power distributed within the consist as well as 'top and tail' there is effectively a node in each cut between locomotives, and the buff and draft in each section can be less (for a given number of locomotive units) or the train can be much longer -- this is how the 'world-record' trains were made up and handled, otherwise it'd be Big Liz and the Triplex on steroids.

Of course there are implications for programming and running more complex DPU arrangements, so the added 'advantages' of best distribution may not outweigh the issues involved in setup and running.  If anyone hasn't read Don Oltmann's story about railroading on the ex-PRR in the 2040s (in which the concept of multiple 'blocks' with dedicated power to each factors significantly) you should find and read it now.  It would be a significant gain for a number of actual PSR operating models if DPU could be reliably implemented as Don indicates.

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Posted by Paul_D_North_Jr on Wednesday, July 24, 2019 8:05 PM

Back in the 1960's or so David P. Morgan wrote an essay on the background of Santa Fe's then-President (before the CEO title became all the rage) - John Reed, I believe it was.  Reed had a story that when he was with Santa Fe's Test or Operations Dept., they would locate the 'nodes' by running back and forth on the tops of the boxcars and looking down at the couplers.  

Couldn't do that today . . . 

- PDN. 

"This Fascinating Railroad Business" (title of 1943 book by Robert Selph Henry of the AAR)
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Posted by BaltACD on Wednesday, July 24, 2019 8:53 PM

Paul_D_North_Jr
Back in the 1960's or so David P. Morgan wrote an essay on the background of Santa Fe's then-President (before the CEO title became all the rage) - John Reed, I believe it was.  Reed had a story that when he was with Santa Fe's Test or Operations Dept., they would locate the 'nodes' by running back and forth on the tops of the boxcars and looking down at the couplers.  

Couldn't do that today . . . 

- PDN. 

Would love to see one of todays railroad CEO's run - let alone on the tops of boxcars.

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Posted by caldreamer on Wednesday, July 24, 2019 9:37 PM

Overmod:

  I understand what you are saying about using dpu's to spread the push/pull of a train, but I do not understand what you mean by "As discussed, with trains of sufficient length or grades/profiles of the wrong character"?

     

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Posted by Overmod on Wednesday, July 24, 2019 11:58 PM

caldreamer
I do not understand what you mean by "As discussed, with trains of sufficient length or grades/profiles of the wrong character"?

Specific reference to the thread about the stringline derailment on Horse Shoe a few days ago.  If the train is of sufficient length (or trailing resistance) it becomes impossible to take all the tractive effort through the first few draft gears or couplers, or (as Don calculated) the overturning moment becomes too great and you get a lateral derailment or tipover.  The same 'tractive effort' distributed between pull and push can keep the stresses safely minimized for much heavier overall train weight.

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Posted by CSSHEGEWISCH on Thursday, July 25, 2019 7:00 AM

I recall an article in TRAINS some years back which mentioned the problems that KCS was having with midtrain power causing a bunch of derailments.  At the time, midtrain power was usually placed two thirds of the way back from the front end, primarily to equalize brake response time.  After another derailment, a mid-level manager crunched the numbers and developed a chart for the best positioning of midtrain power under a variety of circumstances.

The daily commute is part of everyday life but I get two rides a day out of it. Paul
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Posted by caldreamer on Thursday, July 25, 2019 8:16 AM

I would love tto see that chart.  How does the track profile affect where dpu locomotives are placed?  I model the BNSF Pikes Peak Subdivision, there is a sag after Palmer Lake southbound then up hill again.. 

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Posted by BaltACD on Thursday, July 25, 2019 8:55 AM

caldreamer
I would love tto see that chart.  How does the track profile affect where dpu locomotives are placed?  I model the BNSF Pikes Peak Subdivision, there is a sag after Palmer Lake southbound then up hill again.. 

I suspect - the chart would only be germain for the territory for which it was created.  One thing that is frequently overlooked by many when creating 'train handling' rules - the physical characteristics of each territory creates situations that are not in place on other territories. (Length of grade, curvature within the grade, superelevation of the various curves, vertical curve in transitioning from one grade situation to the next - both positive and negative)

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Posted by zardoz on Thursday, July 25, 2019 1:39 PM

BaltACD
Would love to see one of todays railroad CEO's run - let alone on the tops of boxcars.

I can think of one or two politicians I'd like to see up there as well.

   23 17 46 11

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Posted by caldreamer on Thursday, July 25, 2019 4:52 PM

BaltACD:

I have been programming for over 54 years, both for the governemt and for myself.  I could easily take their chart and make one of my own for my model railroad.

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Posted by jeffhergert on Thursday, July 25, 2019 6:00 PM


 https://www.up.com/ert/ssi.pdf

If the link doesn't work properly, try Google (it's where I found it on the internet) and use "Union Pacific system special instructions".  Neither way asks me to log in so I'm hoping it will work for everyone. 

Either way, if you can get it to open up, go to Item 5 and go down to Item 5-C.

Have fun.

Jeff

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Posted by zardoz on Thursday, July 25, 2019 6:57 PM

jeffhergert


 https://www.up.com/ert/ssi.pdf

If the link doesn't work properly, try Google (it's where I found it on the internet) and use "Union Pacific system special instructions".  Neither way asks me to log in so I'm hoping it will work for everyone. 

Either way, if you can get it to open up, go to Item 5 and go down to Item 5-C.

Have fun.

Jeff

 

Worked ok for me. Wow--224 pages.

Jeff, do you have to carry these instructions in your grip, or have you memorized them already?Smile, Wink & Grin

   23 17 46 11

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Posted by jeffhergert on Thursday, July 25, 2019 9:46 PM

Even if I memorized them, I'd still have to carry them.  Or their electronic equivalent.  (Ain't gonna happen.  I prefer paper since it doesn't require batteries.)   We have two paper versions available.  One is the standard size, bound like a normal book.  The other is smaller and spiral bound.  I prefer the smaller, spiral bound version as it stays open easier.  

My home terminal won't get the spiral bound versions.  They cost the local manager's budget too much.  So we only get the standard sized one.  (It took about 10 days after they took effect before they actually had them.  It's becoming normal to have some new publication, SSI, time table, rule book, etc to take effect and not have any available until a few days later.)  Other terminals, however...  I snagged a copy at the Council Bluffs yard office.

Jeff

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Posted by caldreamer on Friday, July 26, 2019 8:13 AM

What happens if you get caught without the new timetable,etc?  Would we do not have them in yet work as an excuse?

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Posted by BaltACD on Friday, July 26, 2019 1:51 PM

caldreamer
What happens if you get caught without the new timetable,etc?  Would we do not have them in yet work as an excuse?

At the very least a e-test failure.  Just like ignorance of the law is no excuse, unavilability is also not an excuse.  Railroad Justice! [/sarcasm]

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