Hey all… I’m building a layout that includes modern stack train ops. I was in Ontario, CA the other day and snagged these pictures of the new gen concrete ties:
I will be prototyping these rails on the mainline section of my track (search my posts for the layout and such)…but the interesting thing comes from real life observation of the operations. I’ve notice the super long trains typically have 1-2 engines around half way through the lineup. Can anyone give me some insight into an operation reason for this?
I can deduce that it is either for repositioning the engines and they are set in a zero drag throttle position (the sound from the mid position engines was a distinctive howling vs. the low rumble of the engines powering the train)… or that they are assisting somehow.
Mid-Train essentially allows two trains to operate in the place of one. Ideally, the front engines are only pulling what’s between them and the Mid-Train helpers, and the MTs are only pulling what’s behind them, while also pushing in the slack just a bit on the front section, further reducing drag on the front part of the consist. Rear-of-train or today’s DPU trains aren’t pushing so much, as reducing drag. Instead of letting the cars stretch out and pull on the lead engines, the rear is pushing the slack back in.
The problem, is getitng the engines into, and out of Mid-Train, which si why you (or at least I) don’t see it much if any at all. It’s more common, and easier, to put the engines at the end of the train, where all one has to do is pop a coupler and go. I’ve even reado of crews poping the coupler lever on the fly, decreasing speed of the Helper hile the train speeds off. can’t do that Mid-Train. And the railroad isn’t in the business of shipping engine around the system because they’ll only need it for 5% of the run. Or at least, they weren’t. With DPU not requiring crews on helpers any more, I have seen UP leave more engines on the backs as trains in neutral. cross over into CSX territory. CSX of couse, is n’t trained on the system and all those engines really do is act as really expensive FREDs.
Howling, I gotta wonder if that’s the Dynamic, but I don’t see why. I’;; bet that by the time you see them, they atre in an area where they don’t need the mid train and yes, they are set in a neutral.
typlically, engines being repositioned will still be kept as deadheads in the lead of the train. Keeps the heaviest weight towards the frint.
Whether the locomotives are in the middle of the train or at the end, they are still Distributed Power Units (DPU). Trains Magazine did an article a while back.about it. The article even talks about, albiet experimental, train consists long enough to have a couple of locomotives at the head end and middle, plus another loco at the end of the train.
DPU’s aren’t just for reducing drag and such. The also allow the brakes to react faster to a brake signal, and since more cars are activating their brakes at one time, brake sooner.
Because of higher cars/tonnage per train DPU’s are more effiecient
Currently DPU’s get their instructions via a radio signal from the lead locomotive, lets call it a head unit. Train length is still limited, especially by terrain, because of the distance the radio signal must travel. However in my situation I mentioned above with mid-train helpers and end-train helpers, one of the loco’s in the mid-train set can relay the signal to the end-train set.
Another arrangement I have seen used is two on the front, a single unit roughly 1/3 back, another single unit 2/3 back and a final single unit on the rear. Train was over 12,000 feet long, mostly double stacks with autoracks at the back. All units were controlled by the engineer from the lead unit, who can do it all together or select individual units (useful on rolling profiles). Spreading out the power reduces many of the stresses, the most obvious one of course being on the drawbars and couplers. The reduced stresses on curvy territory is also beneficial, reducing the chances of stringlining a car (pulling off on the inside of a sharp curve) and actually can allow the same power to haul a couple more cars up grades.
As far as I know, the control signal goes directly from the lead unit to each DPU.
Distributed power. You in effect get two (or more) shorter trains immediately behind each other - less drawbar pull on the couplers between cars (meaning fewer broken knuckles), less slack action, quicker brake action (radio signal between locomotives travels faster than brake line pressure can drop).
