jeffhergert Coupler strength also plays into it. Here's UP's instructions. https://blet5.files.wordpress.com/2016/05/ssi.pdf Train make-up is covered by Item 5 and 5-C has about placing DP units for where coupler limitations come into play. I've noticed some instructions to train length and length from head consist to DP and between DP consists are similar to the BNSF provided link. Some years ago, a conductor told me about a rider he had that was gathering data. The train they had was a 135 car coal train, 2 x 1 configuration, going east over the Blair subdivision. Something we rarely did at the time. This guy, using computer calculations said their train would top Arlington hill at 12 mph. (Not sure anymore of the exact speed, but 12 is pretty close.) Sure enough, they got down to 12 going over the top. The conductor asked this guy how fast they would've gone over if all 3 engines had been in the front. He did some calculations and said they would've gone over at 3mph, but before they would get over the top a knuckle would've broken due to the stress. Jeff
Coupler strength also plays into it. Here's UP's instructions.
https://blet5.files.wordpress.com/2016/05/ssi.pdf
Train make-up is covered by Item 5 and 5-C has about placing DP units for where coupler limitations come into play.
I've noticed some instructions to train length and length from head consist to DP and between DP consists are similar to the BNSF provided link.
Some years ago, a conductor told me about a rider he had that was gathering data. The train they had was a 135 car coal train, 2 x 1 configuration, going east over the Blair subdivision. Something we rarely did at the time. This guy, using computer calculations said their train would top Arlington hill at 12 mph. (Not sure anymore of the exact speed, but 12 is pretty close.) Sure enough, they got down to 12 going over the top. The conductor asked this guy how fast they would've gone over if all 3 engines had been in the front. He did some calculations and said they would've gone over at 3mph, but before they would get over the top a knuckle would've broken due to the stress.
Jeff
Welcome to my world. That is some of what I do/work with. And really, computers help a WHOLE lot. In fact, it's actually possible to plug in a bunch of data such as amount of cars, weight of the cars, engines, etc etc and make an entire 3D model of the train moving. You can change variables such as grade, and the computer will tell you an educated guess as to what would happened. In reality, I like to say this about Engineers and the professional in general. "Physicists study forces in theory. Engineers study them in practice."
An artist sees the world in colors and patterns. An engineer sees the world in mathematical equations. Both help shape the World and are just as important as the other.
Have not seen anyone address the complications of curve resistance. Believe that for every degree of curve the resistance increases by what ? That may be good use of DPU especially mid train to decrease that rolling resistance ?
Power, weight, and traction distrubition. Well, at least, that's the technical name for what all of you have touched upon and what the OP was asking about. So consider this. How much does a railraod tie weigh? Well, anywhere from 100 to 300lbs, right? So let's just consider 150lbs (it's right in the middle). Now, let's consider the average adult male. Let's say 165lbs, and fairly in shape. You should have no issue straight lifting 50 to 60lbs, or dragging up to your body weight (so 165lbs). If you tried to pick up a railroad tie by yourself, you probably would struggle with it, right? Whereas if you drag it, you can get away with it, right?
So you bring in a second person to pick up the otherside of the tie. Now, you and this second person should have no issue picking up and moving this 150lbs railroad tie. Or, if it's even bigger and heavier such as a piece of rail, you get more people to pick up the rail and move it, say six people. That being said, both of these examples assume that the lift power is distributed evenly throughout the weight that is being lifted. Ie. one on either side of the tie, or two on either side and two in the middle of the piece of rail.
But the problem is, what happens if both people are on one side of the tie attempting to drag it? Or all six people are on one side attempting to drag the rail? It's going to be less effective, and you'll end up dragging the tie/rail. You actually end up putting more work into the same task. The same concept applies to trains. By distributing the power, we can counter act the weight and friction of the train itself. Of course, this depends on how much and what is being transported, as well as the tracks that will have to be crossed in the journey.
The locomotive placement depends on the tonnage of the train, the type of cars in the train, the territory the train is going over and the tractive effort of the engines. Some trains have routes a couple thousand miles long, so even though somebody saw the train on a flat portion of the railroad, a day later it might be in the mountains. There are all sorts of placement restrictions, primarily tonnage and the railroads will balance the placement so there isn't too much tonnage ahead or behind whatever horsepower is in the helper set or sets.
With DPU, the different sets of power can be idled or operated as required by the tonnage and grade.
Dave H. Painted side goes up. My website : wnbranch.com
Electroliner 1935When WWhen you read ALL the conditions, the complexity is great. I don't think I could determine how to set up a train I was to operate. And I am a college graduate.
Rules any more are written by lawyers - so they can be argued in court; not so that railroad employees can actually USE the rules to do their job in compliance with the rules.
Never too old to have a happy childhood!
When WWhen you read ALL the conditions, the complexity is great. I don't think I could determine how to set up a train I was to operate. And I am a college graduate.
I knew there was a lot more to it than what I wrote when I wrote it - and there is, as we can see. Ya learn something new every day!
I didn't know about UP's "fast forties" being the basis of the term, but I had read that GP40's were "slippery" - for exactly the reason given. At 3000 HP, they were 750 HP per axle, at a time that most other locomotives were still (sometime well) under 2500 HP. Curiously, today's 4400 HP six axle locomotives are only 17 HP (per axle) short of that. But wheelslip control has come a long way.
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
VOLKER LANDWEHR Each railroad has its own rules about placement and size of locomotive consists. I have found the following information about BNSF that gives some explanations and the rules: http://nwprr.net/forum/topics/train-tonnage Regards, Volker Edit: More detailed information for BNSF can be found starting on page 70:www.smartlocal933.org/BNSF%20SSI%20No.4.pdf
Each railroad has its own rules about placement and size of locomotive consists.
I have found the following information about BNSF that gives some explanations and the rules: http://nwprr.net/forum/topics/train-tonnage Regards, Volker
Edit: More detailed information for BNSF can be found starting on page 70:www.smartlocal933.org/BNSF%20SSI%20No.4.pdf
Lots of interesting information !
That second linked site: Alot more than just a casual read!
(84 PAGES ! WILL BE ONE TO PRINT AND DIGEST OVER A WEEKEND...)
Mookie I'm going to need a big basket to put all this info in, but when I first read the post, I thought that it might not be placement for that particular location, but for before or after the train leaves or arrives in a new location on their route. Can someone verify this?
I'm going to need a big basket to put all this info in, but when I first read the post, I thought that it might not be placement for that particular location, but for before or after the train leaves or arrives in a new location on their route. Can someone verify this?
Yes, that was one of my thoughts when I made the original post. Perhaps trains were set up differently depending on their destinations, or maybe they would split at some point and go different ways. But there is a long way between Barstow and the next logical split point (Williams, AZ?) si I didn't know whether that made sense.
RME - thank you! Now taking my basket and going to read!
She who has no signature! cinscocom-tmw
MookieCan someone verify this?
Yes, of course.
I do not know the destinations or origins of traffic on the stretch of line the OP is monitoring, but they could easily reflect a number of considerations from 'further along', or even just the operating preferences of other areas or even other railroads involved with run-throughs.
tree68In fact, the GP40 was known to be "slippery."
The GP40 was slippery not because of high speed, but because it only had four axles to put the higher horsepower to the rail (and relatively primitive slip control). Your TE is first adhesion-limited, then motor-heat limited, and only then reduced by the multiplication factor of the gearing relative to armature torque.
As H. Landwehr has pointed out, "Fast Forties" used a higher gearset (59:18, I believe, translating to a nominal 'speed' of 85mph) to match the DD40 family in service. Note that when the Centennials were retired UP rather quickly regeared the Fast Forties, rather than attempting to assign them to 'faster' service pools.
Remember that the 'speed' here is not how fast the locomotive can go when so equipped, it is the fastest you can spin the motor, net of reasonable factor of safety, before its structure suffers. The innocent-sounding fishing term birdsnesting will give you all the mental image you need. When EMD increased the winding reinforcement with the D77/87 motors, the permitted rotational speed went up the equivalent of 5 or 6mph.
Returning to the train question: there are any number of reasons for distributing power differently, and my initial answer would probably NOT be 'because some people making up trains didn't understand there was a better way'. If the train has a heavy, continuous load (like a loaded coal train) then distributed power makes good sense for the reasons already mentioned. (Note that there is a point within the consist, called the 'node', where the effective TE on a coupler or draft gear is zero, and this point moves within the train as power, grade, and resistance change. That is why you hear a banging of slack action when some DPU trains throttle up and down - that is a consequence of the nodal point moving.
If you have a number of empties combined with loads in a different part of the train, the action of conventional DPU may not be for you. Then you might cut a couple of DPU engines into the train in the middle, but not on the rear. Theoretically you could split a long train into two separate ones with a consist built this way simply by closing the air on the hose at the front of the DP consist and uncoupling, assisting some forms of 'precision railroading' where you don't want or need to switch the blocks in the consists immediately.
Note that if you are short of DP locomotives, you may not have enough 'masters' to put into a given train for best use of distributed power, so the OP might be looking at a little insight into how local power is being managed. Are some of the trains destined, ultimately, for routes with more train resistance?
tree68The EMD GP40 and SD40 were often referred to as "fast forties."
To avoid misunderstandings the "Fast Forties" were a number of UP SD40-2s that were geared for 79 mph instead of the standard 69 mph so that they could be paired with the 79 mph DDA40Xs. The 100 locomotives were numbered 8000 to 8099. http://utahrails.net/articles/up-fast-forties.php Regards, Volker
STEVE HINCH I recently spent an afternoon near Amboy, California watching a steady stream of eastbound double-stack container trains on the BNSF transcon. They all typically had 6 locomotives, but on some they were all at the head end while on others they were scattered between front and back, front and middle, or all three locations. Why such a variation on otherwise similar trains traveling the same route?
I recently spent an afternoon near Amboy, California watching a steady stream of eastbound double-stack container trains on the BNSF transcon. They all typically had 6 locomotives, but on some they were all at the head end while on others they were scattered between front and back, front and middle, or all three locations. Why such a variation on otherwise similar trains traveling the same route?
The load factor of the specific train (tonnage behind the engine, and area terrain ) as well as the % of gradient of the line being traveled by that train.
Here in our area Westbounds have traversed the area of the Flint Hills, and we have stackers that will have anywhere from three to four and occasions five units on the headend.
Several time a month we see a very long export stacker that will have two engines on the headend and two more approximately half way back and at least one unit on the rear. Just had an Eastbound go by with about 20 stacks and a string of TOFC.. four units on headend.
Coal trains through here will have three or four units on the head ends and almost always two on the rear. About the same for unit taner trains...Quite a variety of power and placement of that power on a train.
I have to offer my input as opinion - but I suspect it's close to the case. Others can comment on variations to the theme.
Horsepower can serve two different purposes - tractive effort and speed.
The EMD GP40 and SD40 were often referred to as "fast forties." This is because speed takes horsepower. In fact, the GP40 was known to be "slippery." A 5HP lawnmower engine can move quite a bit of train (given the traction), but not very fast. Thus a relatively lightweight train, like I/M, needs it's HP for speed. The light weight of the train means couplers are well within their stated capacities, which leads us to the other extreme.
A long, heavy train may well place more stress on the first couplers behind the locomotives than the couplers can handle. By inserting mid-train and pusher locomotives, instead of putting all the power at the head end, those stresses are reduced. In effect, a train with two locomotives at the head and two at the rear will (assuming a constant grade) have half the train stretched, and half the train in buff.
As I noted, there will be variations on the theme, but this is a start...
Recollection from watching BNSF trains along the Columbia River:
Coal trains almost always have locomotives front and back.
Stack trains almost always only have locomotives on the front.
There is obviously a reason, as opposed to random chance.
Ed
Maybe has something to do with power? This will bring topic back up under someone's nose
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