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Question On Loco Orient On Multi Loco Trains  
User currently offline2707200X From United States of America, joined Mar 2009, 8713 posts, RR: 1
Posted (2 years 10 months 3 weeks 3 days 21 hours ago) and read 1239 times:

When I see trains with more that one Locomotive, (virtually every cargo train), I see that the first locomotive facing in the direction in which the train is going and I see the locomotives paired behind the first locomotive oriented backward going on reverse. Why is this configuration popular, what are the advantages of rearward facing locomotives behind the forward engine in the front of the train?


"And all I ask is a tall ship and a star to steer her by." John Masefield Sea-Fever
16 replies: All unread, jump to last
 
User currently offlineZANL188 From United States of America, joined Oct 2006, 3566 posts, RR: 0
Reply 1, posted (2 years 10 months 3 weeks 3 days 17 hours ago) and read 1214 times:
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What you are seeing is probably just a coincidence. Although sometimes there are advantages to having the last unit facing the opposite direction of the leading locomotive - the locomotive set won't need to be turned to take another train back in the opposite direction of the first train.


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User currently offlinerfields5421 From United States of America, joined Jul 2007, 7607 posts, RR: 32
Reply 2, posted (2 years 10 months 3 weeks 3 days 13 hours ago) and read 1177 times:

Yes, back to back locomotive pairs goes back to the early days of diesel when turntables started to disappear. As stated above back to back pair does not have to be turned.

Modern diesel electric locomotives have no power or operational advantage is 'forward' or 'reverse' orientations. The traction motors work equally well in either direction.


User currently offlineANITIX87 From United States of America, joined Mar 2005, 3308 posts, RR: 13
Reply 3, posted (2 years 10 months 3 weeks 3 days 12 hours ago) and read 1165 times:
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In a similarly-related question, how exactly does speed get controlled? Is it a throttle setting, or an actual wheel-speed? If a train has 4 locomotives on it, and the conductor sees a 60MPH signal, he'll see it and throttle up for 60MPH. But does the throttle management system tell each locomotive, "OK, you need 55% throttle (or whatever it is) to achieve 60MPH" or does it say, "OK, we need to be doing 60MPH, so based on your gear, just get to the correct throttle setting."

I ask because I assume each locomotive will have slight variances in its gearing or its delivered power (especially if they're old machines). So if all the locomotives are at 55% throttle, one locomotive's "natural" speed at that setting might be 61MPH, which another's might be 58MPH. In that case, you're going to be wasting power on both of them because one is getting slowed down by the train only doing 60, and the other one is getting pulled along by the train's speed, in which case its power production is useless.

Does that make any sense? Or, at least, enough for someone to clarify?

TIS



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User currently offlinerfields5421 From United States of America, joined Jul 2007, 7607 posts, RR: 32
Reply 4, posted (2 years 10 months 3 weeks 3 days 12 hours ago) and read 1155 times:

There is a nice Wikipedia article on diesel electric locomotives - http://en.wikipedia.org/wiki/Diesel_locomotive#Diesel-electric

The Throttle Operation section should answer your question.

Since there are only 9 throttle positions - 1 idle setting and 8 power settings - engineers work by throttle position for gross speed control and use the dynamic braking system to fine tune accoriding to some KCS engineers I know.

Remember a North American diesel electric locomotive has no gearing - it has electrical traction motors attached to the drive axles. The motors turn constantly when the train is in motion. The throttle controls the RPM of the "prime mover" large diesel engine which generates X amount of electricity.

The weight of trains, especially larger ones, evens out any variation in locomotive performance.


User currently offline57AZ From United States of America, joined Nov 2004, 2556 posts, RR: 2
Reply 5, posted (2 years 10 months 3 weeks 3 days 11 hours ago) and read 1145 times:

Actually, it's a little more complicated than what the above posters have indicated. Not all locomotives have the same equipment, even if they are the same type (SD60, etc.). Locomotives are still routinely turned between runs at many terminals on the wye. Often the locomotive for the home road leads for the fact that it may have Automatic Train Control/Automatic Train Stop equipment required that the run through power lacks. Also, the control setups may vary from one railroad to another, causing locomotives to be turned in run through service. For example, most wide cab locomotives have desktop controls, except older Norfolk Southern Railway wide cabs. They have standard control stands as some of the wide cab locomotives have the cab at the rear (like a conventional steam locomotive). On the old Southern Railway and the Norfolk and Western, back to back meant cab end to cab end. N&W had a few dual control stand locomotives so the locomotive could be operated more safely running backwards, but not the Southern.


"When a man runs on railroads over half of his lifetime he is fit for nothing else-and at times he don't know that."
User currently offlineZANL188 From United States of America, joined Oct 2006, 3566 posts, RR: 0
Reply 6, posted (2 years 10 months 3 weeks 3 days 11 hours ago) and read 1138 times:
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Quoting 57AZ (Reply 5):
it's a little more complicated than what the above posters have indicated

if we're going to go that route we may as well explain that what is the "Front" on a locomotive for one railroad is not necessarily the "Front" for what is otherwise an identical locomotive on another railroad. That way we can really confuse the OP. lol. yes, I understand what you're saying about control stands...



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User currently offline57AZ From United States of America, joined Nov 2004, 2556 posts, RR: 2
Reply 7, posted (2 years 10 months 3 weeks 2 days 8 hours ago) and read 1049 times:

In regards to the desktop controls, while they are more ergonomic they do inhibit the ability to safely operate the locomotive in reverse over great distances. Those locomotives must be turned at the terminal or coupled back to back with another locomotive. Also, visibility along the sides of the wide cab locomotives is notoriously poor.


"When a man runs on railroads over half of his lifetime he is fit for nothing else-and at times he don't know that."
User currently offlinejohns624 From United States of America, joined Jul 2008, 936 posts, RR: 0
Reply 8, posted (2 years 10 months 3 weeks 2 days 3 hours ago) and read 1013 times:

Quoting 57AZ (Reply 5):
They have standard control stands as some of the wide cab locomotives have the cab at the rear (like a conventional steam locomotive).

Say what? All wide nose locos have the wide nose end as the front. it's only some of the older conventional nose units that SR and N&W had that ran long hood forward.

Quoting 57AZ (Reply 7):
Also, visibility along the sides of the wide cab locomotives is notoriously poor

There is no such locomotive as a "widecab". All cabs are the same width. It's only the noses that vary in width.


User currently offline57AZ From United States of America, joined Nov 2004, 2556 posts, RR: 2
Reply 9, posted (2 years 10 months 2 weeks 1 day 22 hours ago) and read 878 times:

Quoting johns624 (Reply 8):
Say what? All wide nose locos have the wide nose end as the front. it's only some of the older conventional nose units that SR and N&W had that ran long hood forward.

NS was the last major road to adopt desktop controls and they did indeed run some safety cab locomotives long hood forward. That actually was listed as a contributing factor some years ago where a NS train ran a red board and hit another train that was already in the crossing.



"When a man runs on railroads over half of his lifetime he is fit for nothing else-and at times he don't know that."
User currently offlineKingairTA From United States of America, joined Feb 2009, 458 posts, RR: 0
Reply 10, posted (2 years 10 months 2 weeks 14 hours ago) and read 823 times:

When we build a consist the trailing motors get cut in regaurdless of facing direction. We do have a new rule that on high priority trains that two motors must be facing the direction of travel. This way if the leader dies it can be cut off and put to the rear and the back up can be the leader witbout having to have the power turned.

User currently offlinetimz From United States of America, joined Sep 1999, 6896 posts, RR: 7
Reply 11, posted (2 years 10 months 2 weeks 11 hours ago) and read 790 times:

Quoting rfields5421 (Reply 4):
engineers work by throttle position for gross speed control and use the dynamic braking system to fine tune accoriding to some KCS engineers I know.

Just to clarify-- the locomotive can pull, in one of the eight throttle notches, or it can dynamic-brake. It doesn't do both at the same time. AFAIK if four units are connected together the same is true-- you never have some pulling and some braking.

On the other hand, when a DPU is on the rear of the train... maybe that's what the KCS guys meant.


User currently offline747400sp From United States of America, joined Aug 2003, 3736 posts, RR: 2
Reply 12, posted (2 years 10 months 2 weeks 8 hours ago) and read 773 times:

I have notice that CSX also pair there locomotives for there coal trains out of Newport News VA, back to back.

User currently offlineseattle From United States of America, joined Oct 2009, 63 posts, RR: 0
Reply 13, posted (2 years 10 months 2 weeks 6 hours ago) and read 761 times:

Quoting 2707200X (Thread starter):
what are the advantages of rearward facing locomotives behind the forward engine in the front of the train?

None at all and as already stated mostly coincidense. Most north american freight trains do not have designated power for a certain train. Most of the time when the train gets to it's destination the power is moved around to different consists or scheduled for services and such. The only trains I have seen (other than locals) that require the east most unit facing east or west facing west and so on are on a lot of unit trains like grain and coal trains due to the lack of facilities to turn the leading loco like a balloon track or wye which a yard or terminal would have.

I think the confusion between cab position stems from the termination of "wide cab". Locomotives such as sd-40's, 50's, gp's and for the NS and CSX some dash-9's have what is called a spartan cab. NS has an even more signature variation of them where the controlls of the locomotive are on opposite sides (not ends) within the cab since they were initially meant to be ran "long hood" forward. Wide cabs technical name would be "comfort cab". The comfort cab covers most all SD-60's, 70's, 80's, 90's, 70accte's, ac-4400, majority of dash-9's, and all the evolution series.

Quoting rfields5421 (Reply 4):
use the dynamic braking system to fine tune accoriding to some KCS engineers I know.

For the sake of not being too technical we will say that you have three locomotives on the leading part of the train, all of which are running and all traction motors cut in. Then any power or dynamic controls being conducted from the lead loco are duplicated the same throughout all trailing locomotives through and MU cable connected between the units.

Now if your train was a DPU (distributive power units) train with two units on the front and one on the rear that rear unit is controlled via radio signals from the leading loco. You can "tweek" the way that the DPU unit on the rear runs independantly from the two on the head end. It's called fencing and works well in territories with hills and undulations. If you do not fence the DPU then that locomotive will duplicate the throttle settings that the lead loco is in just like a normal consist.


User currently offlineseattle From United States of America, joined Oct 2009, 63 posts, RR: 0
Reply 14, posted (2 years 10 months 2 weeks 5 hours ago) and read 754 times:

Quoting ANITIX87 (Reply 3):
In a similarly-related question, how exactly does speed get controlled? Is it a throttle setting, or an actual wheel-speed? If a train has 4 locomotives on it, and the conductor sees a 60MPH signal, he'll see it and throttle up for 60MPH. But does the throttle management system tell each locomotive, "OK, you need 55% throttle (or whatever it is) to achieve 60MPH" or does it say, "OK, we need to be doing 60MPH, so based on your gear, just get to the correct throttle setting."

Speed of a locomotive is read from a gear in the number 2 axel from the nose on most all modern deisel locomotives in the US. maintaining a certain speed of a train is (theoretically speaking) no different than maintaining the speed of your car. Gas pedal like throttle notches speeds up, coasting on flat ground like coasting on a train slows down, brake pedal like dynamic brakes or settling air slows faster. now imagine everything you did in your car is the exact same thing that was done in the three cars attatched to your bumper. Now it's your job to maintain a certain speed so normally you would throttle up till you were close to 60mph and make throttle adjustments to stay at 60mph.

When your in run 8 or the highest selling of power then the units behind you are also in run 8 regardless of actual power output between the units. Some put out all 4000HP some half that.

Quoting ANITIX87 (Reply 3):
I ask because I assume each locomotive will have slight variances in its gearing or its delivered power (especially if they're old machines). So if all the locomotives are at 55% throttle, one locomotive's "natural" speed at that setting might be 61MPH, which another's might be 58MPH. In that case, you're going to be wasting power on both of them because one is getting slowed down by the train only doing 60, and the other one is getting pulled along by the train's speed, in which case its power production is useless.

This doesn't really apply to most freight trains given the fact that there are so many other variables to properly maintain speed plus I have never heard or a "natural" speed for a locomotive. Since the locomotive movement is only goverend by throttle position and not actuall MPH.


User currently offline747400sp From United States of America, joined Aug 2003, 3736 posts, RR: 2
Reply 15, posted (2 years 10 months 2 weeks 5 hours ago) and read 751 times:

Quoting seattle (Reply 13):
I think the confusion between cab position stems from the termination of "wide cab". Locomotives such as sd-40's, 50's, gp's and for the NS and CSX some dash-9's have what is called a spartan cab. NS has an even more signature variation of them where the controlls of the locomotive are on opposite sides (not ends) within the cab since they were initially meant to be ran "long hood" forward. Wide cabs technical name would be "comfort cab". The comfort cab covers most all SD-60's, 70's, 80's, 90's, 70accte's, ac-4400, majority of dash-9's, and all the evolution series.






Last year, I was driving under the rail road bridged that cross Hampton Blvd, which NS heavy coal trains run on. The third loco out of a three loco NS coal train, was a SD-70 with a spartan cab. I was a little shocked, so later that day, when this train was pulled up further to wait for it's departing time. Pulled into the parking lot of the Walgreen's next to the NS track, and then a little road closer to the track, to see if I saw right, and yes it was a SD-70 with a spartan cab. BTW, the first loco was a GE Dash-9 and EMD SD-60, both wide cabs, if anybody wanted to know.


User currently offline57AZ From United States of America, joined Nov 2004, 2556 posts, RR: 2
Reply 16, posted (2 years 10 months 1 week 6 days 7 hours ago) and read 697 times:

Quoting seattle (Reply 13):
NS has an even more signature variation of them where the controlls of the locomotive are on opposite sides (not ends) within the cab since they were initially meant to be ran "long hood" forward.

I believe that NS eliminated those locomotives early on (if you're referring to the ex-NW GP-9s). I don't think the dual control stands really met the expectations-certainly didn't do much to enhance safety in my opinion. One control stand alone makes it hard enough to see across the cab-important so that you can see that the other man is alert and awake.



"When a man runs on railroads over half of his lifetime he is fit for nothing else-and at times he don't know that."
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