I've seen it in prototype operation and I've seen it on film where a locomotive will be put somewhere in the middle of a train to help move a really heavy load such as a coal unit train. But can someone tell me how this actually works.
If the loco in the middle is actually pushing the cars in front of it, then it would take the slack out of the couplers of the locos that were pulling and they would no longer actually be pulling against anything.
Does the loco in the middle actually just keep the slack out of the coupler just in front of it and actually pull everything behind it or what. I can't seem to comprehend how this operation works. If this were the case, then it would appear that it would take a lot of skill on the part of the operator in the middle locomotive.
Couple things (and I'm guessing here, as I don't know for sure, but am pretty confident this is close to the truth): with a helper either at the end or middle of the train, I'm guessing the cars between the head end and the helper "float" to some extent, with pulling strain on the cars behind the head end, but with some (not all) cars pushed by the helper. In any case, the helpers still make their full contribution to moving the train along.
You're correct in guessing that it takes some skill to handle such a train, as it will behave much differently from a train with only head-end power.
So far as operators go, there are no operators in the helpers: they get operated simply as more MUs. (I'm not sure of the details, and am curious how exactly this works: how exactly are the signals communicated between locos? do helper locomotives get different signals from the head-end ones, to make them respond differently? anyone know for sure?)
Back in the the Steam Era, MUs didn't exist. I do know the engineers had to co-ordinate things, usually by whistle blasts I believe. Could be wrong though. How else could they do this before modern communications systems.
Think of it in terms of two separate trains running _very_ close together. If the head loco pulls harder than the mid-train loco then it will begin to pull the mid-train loco as well as it's own train. If the mid-train loco begins to move more than it's share then it will begin to take up the slack and push the wagons ahead of itself. In each case the unloaded loco will have less work to do and will gain on the other.
One limitation of train length is the strength of the couplings and placing motive power at the middle of the train allows the train length to be doubled. Depending upon the stability of pushed wagons, the center loco might be placed somewhere between halfway along the train to 2/3rds along the train. At 2/3rds, the center loco would probably never by pulled by the head loco but would always be pushing in addition to pulling it's own section of train.
There was an article in MR some time in the 1980s in regard to a Canadian ore train (resin casting N scale hoppers) which described the operation with locos at the head, center and rear, the remote ones being radio control MUed from the front loco.
In model form our locos can't be pulled or pushed due to the worm gear drive normally fitted, so trying to recreate this sort of operation is likely to result in the wagons between the separate locos being 'stringlined' on curves. (pulled off the track)
Greg we use 'manned' helpers on our club layout and it works fine as long as the helper engineman keeps an eye on the train to keep from being dragged by the head end where he could stringline the train on a curve or pushing too hard and popping cars out from the train ahead of him. We only use rear helpers and don't do mid train, since we have 'steel framed' cabooses we don't cut the power in ahead of he caboose. We use Digitrax DCC for control.
This is on 140 ft of uncompensated 2.5% grade with four 90 degree curves and one 180 degree curve.
See
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the portion described is from Edgewood on the lower level through Fire Valley to Monashee Summit on the upper level.
Have a look at the main page at
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to see more of the layout including photo tours and a 'cab ride' in MOV format (about six minutes), the cab ride takes you down the helper grade.
I run banked trains - train locos at the head, pusher(s) at the rear on
1:40 gradients and 22" radius hidden spiral. The banker locos have push only couplers and have higher gear reductions and smaller drivers (steam locos) The (model) train locos run slow due to the train load and the bankers run fast due to being "light" so they stay in balance. Perfect pickup is vital because if the train locos were to falter the train would "pop" as the coupler system has almost no slack. Analogue control and 3 crossovers in the spiral.
Uh, my good friend, there is no operator in the midtrain units...they are operated by remote control, radio linked to the lead locomotive...
Likewise, in many cases when pushers are used, there are often no one operating them, but rather radio controlled too. Generally if a pusher will be on the train the whole trip it is radio controlled, but if it is only temporary (such as up a particular hill) then it will be manned and will be added and cut off as needed.
The way it works is that the pusher or mid-train helper pushes against the cars in front of it (and in the case of a mid-train unit) also pulls on the cars behind it...this reduces the drawbar effort of the locomotives in lead position...thereby allowing them to pull easier. Also when cresting hills and you have part of the train going back down hill, you still have power pulling the rest of the train up hill. As a general rule you are supposed to reduce throttle settings when cresting hills to reduce drawbar forces on the Knuckles and drawheads, or you could tear the train in half. Sometimes when you reduce the rear slows down and actually starts pulling the opposite direction increasing the possibility of "getting a knuckle" or ripping a drawhead out of the end a car (or engine). Using mid or rear train helpers helps reduce this possibility in many situations. Also, there are generally restrictions on how many powered axels can be online on the head end of a train, as well as how many axels of dynamic braking can be used. On the Norfolk Southern, just for an example, in most situations if using 6 axel locomotives, You can have up to 3 powered locos online, but only two of them with dynamic brakes operating. But, you have have or or two mid-train (or rear end) helpers operating with all axels online as well as dynamic brakes.
As a general rule, mid-train helpers will be 60% of the way back...so if you had a train with 100 cars, the mid-train unit would be behind the 60th car, with 40 cars trailing it. Of course in the real world, you'd not likely see a midtrain unit on a 100 car train, but rather
150 car train...unless the terrain was extremely demanding.
100 car (or less coal trains) usually have a radio-remote pusher on the rear, due to sheer weight of the loaded cars.
Norfolk Southern runs some coal trains with two locos on the head end and two on the rear. All four are under power on the loaded run, but when the cars are emptied, only the head end locomotive and the rear end locomotive are under power, the ones on the inside are shut down for fuel conservation and because they are unnecessary.
Back in the hey-day of Southern Railway (and early NS) they used a radio-receiver car that was fitted with MU cables and hoses. Southern could use ANY locomotive in their fleet as a mid-train helper (sometimes called a mid-train "slave") . Sometimes they'd have just one in the middle, sometimes more than one. The lead engine had to be equipped with Locotrol (the radio transmitter and control panel for the remote setup). The lead engine would transmit to the radio receiver car, and that car would relay instructions to the locomotives in the middle through the MU setup...which would make them respond as if they were up on the head end MU'd directly to the lead locomotive.
Nowadays, NS and other railroads have locomtoves that are especially equipped with the transmitter/receiver equipment, so as long as the lead locomotive and atleast one of the mid-train locomtives are equipped with "Distributed Power" equipment, you can run them as a "radio train" (or some call it a DP train).
Running a "radio train" is not the same as a regular train, as you have to be careful when cresting hills or you can tear a train apart as I've mentioned above.
On Thu, 09 Aug 2007 10:15:54 -0700, David Nebenzahl wrote: >So far as operators go, there are no operators in the helpers: they get
Ive you put the lead loco in throttle notch 5, the helper will go into
5 as well. Same for dynamic braking. Also if you draw off 15 lbs of air on the lead locomotive, the helper will also draw off 15 lbs.
Something I didn't mention in my other post, is that using either rear or mid-train helpers is also beneficial with the airbrake system, because the brakes come on faster and release faster than they do on a conventional setup where you have all locos on the head end...and most especially on a longer train, where it takes a while for a brake pipe reduction to become effective on the rear of a train (and more-so in cold weather).
I've always thought that modelling a DP/Radio train was the PERFECT use for dummy locomotives. Unfortunately hardly any manufacturer offers dummies any more, and I don't know why... There are some people who'd buy them for collection purposes if nothing else, simply because they are less than half the price of a powered unit.
On 8/10/2007 3:46 PM snipped-for-privacy@earthlink.net spake thus:
While we're on the subject, and since you actually seem to know how this stuff works, I'm curious: since the helpers are linked by radio to the cab, what kind of fail-safe mechanism is there if the communication link is lost? Does the train automatically go into emergency? coast to a safe stop? blink on some dispatcher's screen somewhere?
It helps a lot, but I'm still not sure how the operator determines how much power the helper locomotive needs to do it's job efficiently. Can they tell how much tension is on the couplers and determine the power requirement from that?
And wow, I never even thought about the lead locomotives going down a grade while the helper is still pulling up the grade. This is much more complicated than I first realized.
The whole point of the exercise is to provide sufficient power to move the train! One loco won't do the job, so we add an extra loco. Two locos won't do the job so we add a third etc. Modern locos are MUed so all are driven at compatible power settings. In pre-MU days the banker drivers knew wthe route and how much power was required. Each individual loco could only move a portion of the train so even if the driver got out of sync with the other(s) the worse that would happen would be either his loco became a part of the load and he became very unpopular with the fireman of the other loco, or the loco took more than it's share of the train. Real locos are relatively easily pushed/pulled (except when braked) Loco drivers 'feel' their train so load being taken off or added to their loco is noticed. US couplers have about 1/4" free play (I made that number up :-) in addition to sprung draw gear so taking up the load is noticable.
That's a really good question, and YES you do lose communication with the helper units quite often. I had a train one night that I thought I was never going to get the rear-end helper to link up at all with the head end, but finally after stopping and resetting the system 3 times, it linked. You actually go through a check system before you depart to make sure you have radio communications. To be honest, they've never told me what happens if you lose communication permanently. I would imagine that after so many minutes the unit would probably go into isolation until communication was restored. But helper units are just like EOT's, they do go in and out a lot. EOT's sometimes go out and stay out, and the only way you can fix them is to stop and have someone reset it on the EOT itself (or in some cases replace the battery, if it's battery powered...or replace the whole EOT).
But just for the record, a train wouldn't go into emergency for a situation like that...just as it doesn't go into emergency if the engineer fails to reset the alerter in time...instead the locomotives would automatically draw off a full-service brake application which would bring the train to an easy stop. Going into emergency could cause jack-knifing. You only want to use emergency when there actually is one (i.e. car, truck, pedestrian fouling track, obvious signs of track damage ahead, large trees across track, etc.). And rules state you must also shoot the air from the EOT as well, since it takes awhile for the emergency application to reach the rear of the train...that way you have the application initiated from both ends travelling toward the middle, thus reducing the possibility of jack-knifing.
Well, as I mentioned, if you put the lead engine in notch 4 the helpers go in 4 too, just like the engines that are directly coupled to the lead engine. Not really any way of knowing how much tension is on the couplers that I know of. Most locomotives show how many amps are loading. With Distributed Power, you have a split screen that shows how much the lead locomotive is loading and how much the helper's lead engine is loading. Generally it will be close to the same thing...but no two engines are going to be loading exactly the same amperage. Just for instance say you have 2 engs on the head end and two in the middle (or rear). The lead engine might be loading 750 amps, whereas the lead engine of the helper consist might be loading
735, 749, 762, 780...or whatever. You don't have any way of knowing what any of your other engines are loading unless you have someone physically riding on them to check the ammeters. In fact, a lot of the time on the head end of DP and non-DP trains an engineer will send a conductor or brakeman back to look at the ammeters on the head end trailing units if he suspects one might not be loading.
Some of the newer locomotives read in tractive effort instead of amperage...and I really don't like those, because you see them so infrequently that it's hard to remember how many killopounds of tractive effort equals how many amps...and how many amps you are loading plays a major role in the way you handle a train...especially starting out. You can burn traction motors up, rip out drawheads, break knuckles and do all sorts of mean and nasty things if you don't watch your amperage draw. You can also tell a lot about wheel slip even on locos without wheelslip indicators by watching how your amps fluctuate.
A lot of the time with DP helpers, you will notice that whenever you notch up or down, it takes the helpers a minute or so to react. I've seen times when I thought it wasn't going to, say I notched back from
8 to 3 in 2 second steps (as required by rules) then maybe a minute or so later, I'd see the DP unit notch down to 3 also. Same goes for dynamic braking.
You do have to be a little easier with a DP train. Generally you take t hings a little slower than you would with a regular train...for two reasons...you have to consider those helpers...plus if you are DP, then you are a lot heavier than a normal train...so you have all that additional weight to think about.
Now if you really want to complicate things...let's talk about how the train is built...
Say you have a conventional non-DP train with about 100 cars total and three big six-axel locomotives... Your first 75 or so cars are mostly empties, with a few small blocks of loads scattered randomly through the cut...but on the rear end of the train are about 25 or 30 loaded coal, ballast, cement, sand, etc hoppers. Or even worse 25 or 30 loaded tank cars. A train like this will beat you to death coming down hill, and will create tremendous amounts of backward drawbar force going up hill. Very easy to tear a train in half if you don't watch what you're doing.
Now complicate this with 150 cars, a similar setup and distributed power! Of course usually on DP trains, most of the cars are loaded instead of empty, otherwise you wouldn't need the DP. But there is always the possibilty.
In some cases, say on coal trains...once unloaded, DP units might be moved to the head end of the train...but a lot of the time, the DP units stay on the rear and you just isolate or shut down all but the very head end and very rear end locomotive, as the rest are not needed, and simply wasting fuel. Empties like this you have to watch because they're easier to jack-knife because all the cars are empty and you are pulling and pushing on them at the same time.
With any DP, when you crest a hill you have to use light braking, or the DP unit will slow the cut that still coming up hill down too much. When starting back up hill from a dip, you may need to wait a little longer before going back into power, because the train is already pushing you some, and you don't really need the DP unit to assist in the pushing, as you can get way overspeed...in fact, you may still be in dynamic brake going UPHILL for a bit longer than you would on a regular train.
It's way more than 1/4", I just checked the slack on two HO scale boxcars with Kadees...and they had 1/8" or so slack. Just a guess but I'd say 2 or 3 inches slack in the couplers themselves, and IF you're equipped with cushioned underframed drawheads, you have several feet more slack. In a 100 car train with all cushioned underframes, you can sometimes have several car lengths of slack in the train.
The dummies you see are probably older Athearn units. I don't know of a single current manufacturer who is still offering dummy units of currently manufactured locomotives, except for Athearn's OLDER line of engines which are still being produced...and I'm not sure if they are still making new dummies of those...could be you're seeing what's been in stock for years, as a lot of people just don't want a dummy locomotive.
None of the newer line of Athearns are offered in dummies, nor are Atlas, Proto 2000, Kato, Broadway Limited, Tower 55, Precision Craft Models, etc.
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