Tehachapi, BC

[Lemosteam]

Please pardon my ignorance, how does the helper or DPU separate from the train during ops, or does it stay with the train?  I've always been curious how this is done on a model railroad.  If I ever get to model horseshoe Curve, I want to be able to incorporate helper service.  This might be where a DCC operated coupler would come in handy!  Especially if a second controller were in the mix.

I thought both videos were great!

[3DTrains]

I believe modern DPU service would remain with the train for its entire journey, while helper service in the SP era, locos would be cut-in mid-train at Bena and removed at Summit.

[C855B]

I believe modern DPU service would remain with the train for its entire journey, while helper service in the SP era, locos would be cut-in mid-train at Bena and removed at Summit.

Clarity to add to that...  in the '70s, when SP started running DPU ("remotes" back then), remotes were cut-in roughly 2/3 into the train at West Colton and removed at the destination (IIRC), or possibly Roseville, and vice versa. Helpers, usually a brace of SD9's, were put ahead of or behind the caboose - not clear why or when the distinction was made - at Sand Cut (helper pocket west of Bena), and then cut off at Summit.

[Lemosteam]

So how does one perform a cut-in/cut-out during an layout ops session?  Does the train have to stop or can it be done on the fly?

[Scottl]

I have a video of this operation in the 1990s on Rio Grande/SP Tennessee Pass line where pretty much every train had helpers.  At the summit, they stop, cut the train and move the helpers out.  It seems like a long process, facilitated by the presence of a short house track at the summit.   A block of tunnel motors or some AC units, depending on what the train was.

[Ian MacMillan]

I have a video of this operation in the 1990s on Rio Grande/SP Tennessee Pass line where pretty much every train had helpers.  At the summit, they stop, cut the train and move the helpers out.  It seems like a long process, facilitated by the presence of a short house track at the summit.   A block of tunnel motors or some AC units, depending on what the train was.

I have a simlar video Rio Grand Odyssey and I really like it.

When I had my Pittsburgh Line layout in N back in the early 2000's I had helper operations. Rear helpers were added or removed in Altoona pretty much like the prototype. It added a lot of operational interest.

[Smike]

What a great video! Thanks for sharing! The pre planning and execution on the track work really shines in the flawless and smooth running.

[jagged ben]

I'm pretty sure I could add another 10 cars without too much trouble (...) but I would definitely need another unit somewhere.

The 'somewhere' will depend on how many cars you can push or pull up your grades.  Most likely the 5th unit will make more sense on the rear.  The 6th unit might work front or rear.   

Your limiting factor on the number of units up front is the number of cars that can be pulled through your 18" curves without string-lining.    If it only takes 3 units to pull that number of cars without slipping and stalling, then there's no point in adding more units up front.  (That doesn't mean you can't necessarily add more units up front, but you'll need them to pull with less power per unit or the string-lining will still happen.  That either means using slower DC units, or using separate control in DCC and running the front units slower.)

In a corresponding manner, your number of rear units will be limited by the number of cars that can be safely pushed up the hill without "accordioning" the cars in front of the locos.  (Again, you could add more units but they'd have to run slower to keep from pushing too many cars).   Your max feasible train length with DPUs will be slightly under the total sum that you can pull with the front and push with the rear.  The slightly under is because you need at least a couple cars worth of flexibility for the transition point between the cars that are pulled and pushed.

BTW, I don't do DPUs pushing any long cars that have truck mounted couplers, e.g. 89' intermodal cars and autoracks.   Tried pushing some autoracks once, was a big failure.  Maybe someday I will try a single helper on the back if I get those cars all body mounted.    But long cars reduce the train length that can be pushed or pulled.

One thing I have definitely noticed is that it's counter-productive to use multiple units at the head end if they're not decently speed matched.  They tend to fight each other rather than pull the train.  I'm hoping DCC speed matching will help that situation.  In the meantime, I have enough units to pick & choose for match.

Well, yeah.  To be clear, I haven't speed matched my units. But then again I (so far) only use Kato Dash-9s, (and occasionally SD40-2s) which is itself kind of way of speed matching.   Tried an Atlas Dash-8 in the consist once and it didn't work out.  Anyway, a bad speed mismatch means balky performance and not getting efficient power out of your consist.   It's counter productive at either end of the train, because if one end doesn't perform as required then the other end will be pulling or pushing too many cars, and if that happens on a hard curve your train will be on the ground.

[GaryHinshaw]

A few more thoughts on pusher and dpu ops.

* Lemo, as people have noted, the current practice on Tehachapi is to run the "dupes" (DPU's) straight through, not to cut them off anywhere on the modeled portion of the line.  They are important not only for their additional horsepower, but also (perhaps more importantly) for the extra dynamic braking.  Having distributed power also greatly reduces track wear in curves.  (This line is almost nothing but curves.)  My favorite train on the hill is the westbound loaded grain train BNSF runs from the midwest to Stockton: roughly 12,000 tons of grain that have to be eased down the mountain.  This runs with 4 units up front, 3 at mid-train, and two in the rear, mostly for braking.  I've often wondered what it feels like in the cab as you start down the hill with that load behind you.  One day I am going to try running this with 3x2x1 units.

* I'm not yet sure how I will handle live helpers, vs. dupes, but I will probably have a mix of both in real ops sessions.  It will depend on how big a crew is available (and will fit), how busy the schedule is, and how reliable the dupes end up being with DCC.

* jb, on the prototype, I tend not to see dupes on auto-rack trains, and often not on inter-modals either.  Way back in May, I posted a similar video of the first train on the Loop: a 14' rack train with no dupes.  (Temprary track and wiring at the time.)  Fortunately, there was no sign of the cars wanting to string-line then, and that's close to the longest train I'd run in a session.  Much longer than that starts to visually dominate the layout.    So I will probably run the racks and most inter-modals with only head-end power.  I'm a little concerned about running a lot of racks down grade with truck-mounted couplers and lo-pro wheels - will have to try that soon.

-gfh

[jagged ben]

* jb, on the prototype, I tend not to see dupes on auto-rack trains, and often not on inter-modals either. 

Yeah, that's true these days, especially on the rack trains.  However, ATSF and SP used to have rear and mid helpers on intermodals, and that's something I'd like to try.   They also used to mix autoracks in regular manifests (still happens sometimes) which also had helpers.  I guess that stuff is out of your era.

I have run DPUs on one train with an 89' Trainworx autoparts car (body mounted couplers from the factory) and while it didn't spell disaster in the first few feet the way it did with Red Caboose autoracks, I did have to re-rail the car in front of it a couple times.

Way back in May, I posted a similar video of the first train on the Loop: a 14' rack train with no dupes.  (Temprary track and wiring at the time.)  Fortunately, there was no sign of the cars wanting to string-line then, and that's close to the longest train I'd run in a session.  Much longer than that starts to visually dominate the layout.    So I will probably run the racks and most inter-modals with only head-end power.  I'm a little concerned about running a lot of racks down grade with truck-mounted couplers and lo-pro wheels - will have to try that soon.

Nice video, not sure if I missed it before or if I forgot about it.    It's a good sign you can get that train through your curves (although I wonder if body-mounting those racks will change anything).  You should be able to do whatever you want with DPUs if that's as long a train as you'll ever want to run.   

[eric220]

I've seen DPU units on the rear of UP intermodals headed into the Port of Oakland. Usually just one on the end.

[C855B]

I've seen DPU units on the rear of UP intermodals headed into the Port of Oakland. Usually just one on the end.

Yes... 2-3 years ago UP started routinely running DPU on intermodals over the ex-SSW. I was a little surprised by this since one of the basic assumptions in DPU ops is low variability in load distribution along the length of the train, but apparently load handling algorithms account for that now. Unit trains such as coal or grain were naturals for DPU, but beyond that gets complicated. I have yet to see a mixed commodities train with (modern) DPU, not to say that they haven't happened, but if so, not as a matter of course.

Of course, there was the infamous UP intermodal test train of two years ago - 3.5 miles long, four sets of power - head end + 3 DPU sets, 12-14 locos total. I think the biggest result of the "test" was that it tested the patience of people who lived in the L.A. basin, clogging up traffic at grade crossings on several major surface streets with a train that never seemed to end. But if you want an over-the-top example of intermodal with DPU, there you go.

[Scottl]

CN runs mixed freight DPUs through here pretty frequently.   I understood it was because they have gone to very long trains and they want to reduce coupler stress and failures.

[jagged ben]

In my experience DPUs are much more common on stack trains than on TOFC trains.  And yes, UP seems to do it more on intermodals than BNSF does.

A stack train probably has more even load distribution than a TOFC train.  More of a unit train.

[GaryHinshaw]

A bit more follow-up:

* The main UP intermodal over the Pass is the LA-Portaland stack train (which might have a Bay Area component - I'm not sure); as Eric notes, this routinely has at least one DPU and it's not uncommon for it to have a 1+1 configuration.  (I'm going to need a bunch of green HUB Group cans soon if I'm going to model this train though!)  As jb notes, the BNSF intermodals with TOFC almost never have DPU's.

* The majority of the manifest trains over the hill have DPU's...  And I have seen some rack trains with them.

* I ran a 35-car 15' manifest through the Loop last night with DPU's.  It was too long to fit in Walong siding - just like most of the proto trains, but it ran flawlessly.  The other sidings on the layout could accommodate this length, so long trains like this could fit into the ops plan.

-gfh