Helper ops

[sirenwerks]

I'm about to lay my hands on an A-B-B-A set of LL FA2s which, upon layout existance, I'm going to want to throw into helper service. Layout will be early 70s and this part of the ops will be heading off layout from semi-urban center via the Modoc Mountains - a locale usually served by SP Tunnel Motors, not the, mostly, 4 axle Alcos I have planned for my home brewed grain and timber sucking bridge route between the Milwaukee Road in Montana and all points California. So the vision of a well-worn A-B-B-A mid-train set of FAs presents as simply sexy to me. But I realized I know smack about helper service. [/size]And even after a year in the new(ish) house, my books are still packed away; office and garage being last on the list of to-dos.
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[/size]I know it's railroad and locale dependent, but I need some ideas of how to design the helpers into the layout... Do helper sets generally get cut out at summit, or travel down grade to help with braking, and come home on the next elevator up and over? If the latter, I need to start looking for another foursome of FAs. If the former, how's that move completed? Helpers cut out, back to the end of the train and push the tail towards the lead, or does the lead reverse to meet the tail after the cut-out?

[coldriver]

I spent a fair amount of time in helper territory all over the PNW back in the 80's to mid-90's.  Practices varied from railroad to railroad and era to era so I think you'll have some flexibility to design your helper operations to match your preferences.  On BN's Stevens Pass helpers almost always stayed cut in all the way down the hill.  Some of this could have been for braking (especially on loaded grain trains) but I believe the primary reason was that the sidings on both sides of Cascade Tunnel were located on 2.2% grades so there was a safety factor involved in performing the cutting out operation on grades that steep.  At least in the era I'm most knowledgeable on braking effort didn't seem to typically be a reason to keep helpers cut in downhill.  The biggest factors seemed to be congestion avoidance and positioning for the next shove - stopping a train to cut out helpers in a location where multiple trains are converging can really gum up the works!   Cutting out helpers at the summit and then having them follow their trains downhill (if the next shove was from the opposite direction) also caused congestion with opposing traffic needing to meet two movements (train and helper) instead of one (train with helper). 
I will say from my own experience with running helpers on the Oregon Joint Line that keeping them cut in downhill can be risky (far moreso than uphill operations), especially when you have operators with limited experience or iffy throttle skills.   But my better operators enjoy the challenge of matching speeds on downhill runs.  I only consider congestion avoidance and next shove positioning (and operator skill!) in deciding whether to keep helpers cut in.  You may have issues with a four unit powered helper depending on your train sizes.  The key to reliable helper operation is to make sure the head end power can't move the train without the helper and vice-versa - you're asking for trouble otherwise because if either consist hesitates you're looking at a run-in or stringline.  Another factor is that a four unit helper takes up a lot of train length - so your sidings may need to be lengthened in helper territory.   I typically run three on the head end and one helper on my 25 car trains up the 2.2%. 

[nkalanaga]

Leaving the helpers on for the downhill run can help with long trains.  With dynamic brakes, much of the braking is on the head end, and the entire weight of the train is pushing the lead units.  Too much weight, and sharp curves, can result in cars being forced out of the front of the train - basically the reverse of "stringlining".  Having DBs in the middle or on the rear can relieve some of the pressure, while still minimizing use of the air brakes.

Also, on Stevens Pass, there are few places to add or remove helpers, without blocking the mainline, so it's easier to run them from Wenatchee(?) to Skykomish and back.  This is also the old electric district, for much the same reason.

[nscalbitz]

What did your prototype  do?
I know nothing about FA2s. but intergenerational helpers are highly improbable to me.

On the Rio Grande, helpers did come in various guise. But the RG mechanicals were balanced and mid-train sets of 4 and 6 axle power varied depending upon zone and terrain and era.

 While several 2nd? Gen GP40s and 30s could appear on the head end, their SD40-2T Tunnel Motors often made up the mid train set and end of train set on heavy hauling coal drags of the 80s I think, until they took over everything with the SD50s and GP30-40s were deprecated to B units. (Needs confirmation).

They couldnt bang in just any earlier GP or SD9s due to mechanical, electrical control needs and traction to match power across the train. So while their passenger era PAs late in life (1960s) did freight duty on manifests, they didnt ever get used as 4800HP helper sets, let alone  with more modern head end power.
YMMV as they say,
dave

[Cajonpassfan]

The practical, model railroad side of helper ops, creates its own limitations. In my experience, model helpers need to be underpowered so that they can only push so many cars in front of them and stall if the front end encounters a problem. An ABBA set of LL FA's can pull paint off the walls and will in my opinion push everything in front of it off the rails the moment the head end should stall. Of course there are many variables that play into this, like car weights, coupler mounts, flange size, fleet consistency, train length, radii and grades, etc. I model a much earlier era, and am still experimenting with rear end helpers, but believe the model physics are comparable.
Still, using helpers can be a blast, especially with sound...
Otto K.

[wazzou]

The practical, model railroad side of helper ops, creates its own limitations. In my experience, model helpers need to be underpowered so that they can only push so many cars in front of them and stall if the front end encounters a problem. An ABBA set of LL FA's can pull paint off the walls and will in my opinion push everything in front of it off the rails the moment the head end should stall. Of course there are many variables that play into this, like car weights, coupler mounts, flange size, fleet consistency, train length, radii and grades, etc. I model a much earlier era, and am still experimenting with rear end helpers, but believe the model physics are comparable.
Still, using helpers can be a blast, especially with sound...
Otto K.

Agree with this.  ^^^

[sirenwerks]

What did your prototype  do?

Dave,


I'm not modeling a prototype, this is a fictional road, based largely on the SP&S. It will basically replace the GN and WP's Inside Gateway, travelling all the way to the Central Valley - Spokane (with a branch east to Missoula) to Sacto. Since the fleet will be all Alco (unless a manufacturer decides to make some 6-axle Baldwins), with 4 and 6-axlke Centuries and 4-axle RS units making up the meat of the power pool, the FAs will represent older power being reassigned to new, less glamorous duties. I was thinking about slugging out some FB1s I have too for road service (ala C&NW), and an RS1 for switching.

[daniel_leavitt2000]

Did the FAs have dynamic brakes? If not, maybe they should be cut off at the summit.

[tehachapifan]

The practical, model railroad side of helper ops, creates its own limitations. In my experience, model helpers need to be underpowered so that they can only push so many cars in front of them and stall if the front end encounters a problem. An ABBA set of LL FA's can pull paint off the walls and will in my opinion push everything in front of it off the rails the moment the head end should stall. Of course there are many variables that play into this, like car weights, coupler mounts, flange size, fleet consistency, train length, radii and grades, etc. I model a much earlier era, and am still experimenting with rear end helpers, but believe the model physics are comparable.
Still, using helpers can be a blast, especially with sound...
Otto K.

I've always toyed with the idea of making some dedicated helper units by removing gears to some of the wheels in one or both trucks, or all of the gears in one truck or some other combination to help with the situation you describe. That said, this was prior to my switching to DCC, where speed matching can be accomplished much better, which I believe should help. However, even with DCC and unmodified locos, I would imagine the complete head-end stall could still create a problem along with a string-line derailment if the helpers should stall or stutter.

[nkalanaga]

I don't know that the SP&S ever had a helper district, but if they did, the FAs would have been as likely a choice as any.  The GN, and BN, ran EMD Fs in helper service well into the second generation era.

Of course, the BN was still running solid sets of Fs in mainline freight service through the 70s...

[OHCR 4218]

From a purely model railroad experience helper operations can be very difficult. The heavier the engine the more its going to cause problems. I have experimented quite a bit with trains approaching realistic size on a layout with many curves crossovers and 2% grades. The best results I've had have been a single engine about 2/3 to 3/5 of the way back into the train. It helps quite a bit to have a few heavy cars directly in front of the locomotive. I've had several incidents in which the helper/helpers have pushed cars off going through a crossover or over a diamond. This happens much more often with a rear helper than mid train. Controlling the rear set individually seems to help quite a lot as well. I have tried consisting them all and this eventually causes issues as the slack bunches in too much. Typically I'll have the rear or mid units 2 speed steps lower than the front to keep from pushing things off.

[Maletrain]

I am no expert at this, but have seen a 100+ car train with mid-train helpers running around a layout for hours without problems, including grades, curves, etc. 

From what I was told, it was basically a conglomeration of 3 trains, each of which traveled at the same speed when not coupled together. The locos were consisted/MUed, but I don't think they were speed-matched.  It apparently took some trial-and-error tinkering to get it to work, so I expect that each layout + equipment roster needs that sort of tinkering to be able to figure-out how to put helpers on various trains to make things work without derailments.

I also expect that trackwork and wiring needs to be solid to avoid sudden halts of locomotives in just one part of the train.

[Cajonpassfan]

I am no expert at this, but have seen a 100+ car train with mid-train helpers running around a layout for hours without problems, including grades, curves, etc. 
.....

Well, actually, as counterintuitive as it sounds, long trains like this are actually more forgiving, possibly because of coupler slack and power/train weight ratio I assume. It's the more modest home layout sized trains, when helper locos overpower the train, where derailments are more difficult to manage. YMMV....
Otto K.

[tehachapifan]

I'm going to guess that body-mount vs. truck-mount couplers on cars may perform better in these situations but, again, this is just a guess.