give me some slack

[sooblue]

Well, I have a question for the "old heads".
I was thinking back when I was a kid and remembered how the Soo line would start their trains.
First they backed until all the slack was gone then they started forward.
The effect was the original "rolling thunder".
Then it hit me[B)]
If you are starting a train with a helper or distributed power do you give the extra engines more power and let them pu***he train more or are all the engines working at the same level?
How do you manage slack with distributed power?
I get the picture of an accordian effect with the slack constantly running in and pulling out.
If I had to sit up front it would drive me nuts to have the train do that.[|)]

Sooblue

[Mookie]

QUOTE: Originally posted by sooblue

Well, I have a question for the "old heads".
I was thinking back when I was a kid and remembered how the Soo line would start their trains.
First they backed until all the slack was gone then they started forward.
The effect was the original "rolling thunder".
Then it hit me[B)]
If you are starting a train with a helper or distributed power do you give the extra engines more power and let them pu***he train more or are all the engines working at the same level?
How do you manage slack with distributed power?
I get the picture of an accordian effect with the slack constantly running in and pulling out.
If I had to sit up front it would drive me nuts to have the train do that.[|)]

Sooblue

This is a good question, so will retrieve it and bring it up to the front. Maybe someone will have an answer?

From my vantage point - which isn't the best, but watching the coal trains start up - it seems that they take the slack out with the headend - very gently most of the time and just get it started and then the helper kicks in after they are just about out of the yard limits - right or wrong?

Mookie

[Anonymous]

Of course, you start a train one car at a time, thanks to slack. But passenger trains have no slack. I don't know about distributed power, as we don't use it here. As for helpers, after the air test, I'd tell the helper man I'm starting. I would start opening the throttle [not jerking the throttle out, but not fooling either] and the helper is doing the same. I'm pulling the slack away on the head end, and the helper is shoving the slack towards me. If it's done right, you can get a standing train moving and accelerating pretty quickly [that's on level or modest grades] . If it's not done right, the helper can kick you in the butt. Of course, in situations like Mook is talking, coming out of the yard and such, the helper usually is in one or two notches at most, to keep the slack in on the hind end. Double-heading is a different deal altogether. There the lead engine starts pulling...you let him pull the slack out...after the train is either under way or almost stalled from the lead engine, then the second engine starts pulling...gently, gently, at first. After the whole shebang is moving, both engines can start to open up. That is, if they won't startle Madame Moo's driver! :^)

[sooblue]

There is a lot more to engineering then meets the eye. I love to watch the people who make it look easy.
Their the ones that have taken their work to a higher level. One of art.
Sooblue

[kenneo]

If the road engine can start the train, he does, and the helper is just another box car. If not, you need a bunch of practice and MUST get the whole train moving at the same time. Stopping the train just so is critical here. Trying to start by bunching the slack is asking for big trouble. After the train is started, the helper operates at Run 8 or (16 for a GE) except when slowing or grade changing. Road power controls speed. VERY OVER SIMPLIFIED!

[zardoz]

Did you know that 'slack' was intentionally built into the coupler arrangement so that steam locomotives could start a train? Because of the mechanics of steam locos, they were unalbe to start a train if the slack was stretched.

Of course, a somewhat similar (but for different reasons) situation exists for under-powered trains. Not enough power to start the whole train. Start one car at a time, then use the momentum from the moving cars to help get the others going.

One of the tricks we used to use for starting a train that was entirely on an uphill segment of track was to set enough air so the train would not roll backwards by itself, then back into the train with the locomotives bunching as much slack as possible (but not so much as to cause the back of the train to start moving backwards), then release the brakes and start pulling forward as fast as possible within the limits of coupler stress. This worked well with the old AB brakes, but not so well with the ABD brakes-the ABD released too fast.

Average slack per car: 6 inches
x 150 cars
=75 feet of slack.
Ask any conductor that rode a caboose behind a lousy engineer, and they will tell you about how much impact the slack action can cause the caboose. Many crewmen were injured as the result of lousy train-handling.

An interesting sensation is when you're on the locomotive and are surprised by a run-in of slack. Rather dangerous, too (if you're not seated when the run-in happens, you will be on the floor NOW). Quite a surprise to be drifting along at 10mph and get hit in the rear by your train, and suddenly you're going 15mph! But to feel 600 tons of locomotive be instantly accelerated 5-10mph causes you to really understand the power of a train.

Slack is also why an engineer does not intentionally immediately put a train in emergency after an accident has occured. It takes the air about 10 seconds to traverse the length of a train. If the head-end goes directly into emergency and begins slowing, the rear of the train is still rolling free. If the head-end slows down only 10 mph before the rear sets-up, the rear of the train will 'crash' into the head-end with an impact of 10mph--more than enough to possibly cause a derailment, especially if there are lots of loads behind lots of empties, and even more so if any part of the train is on a curve.

[Mookie]

Very interesting - will put that in Mookie's book of knowledge.

Thanx Zardoz!

[dehusman]

On a distributed power train the slave/DP engines normal operate in concert with the controlling consist. When the lead set have the throttle advance, the rear set advance, when the lead set has the throttle decrease, the rear set decreases, when the head set applies the brakes, the rear set applies the brakes, When the head set releases the brakes, the rear set releases the brakes.

Dave H.

[Mookie]

QUOTE: Originally posted by dehusman

On a distributed power train the slave/DP engines normal operate in concert with the controlling consist. When the lead set have the throttle advance, the rear set advance, when the lead set has the throttle decrease, the rear set decreases, when the head set applies the brakes, the rear set applies the brakes, When the head set releases the brakes, the rear set releases the brakes.

Dave H.

ok - I heard that yesterday on a loaded coal train going east. The helper - as is usually the case - clears the crossing where we are sitting, then I heard it notch up - then notch back down for about 15 seconds then notch back up ( i am not sure what we happening at the head end - but usually when that helper engine clears the overhead signals (going east) I always hear them notch it up at least once. So it would be in unison with the headend, right? BUT....what about when they are in the yards and just starting out of the yards from a dead standstill. Would they be in unison then.

Mookie

[CShaveRR]

Just for the record, DP units can be controlled independently of the lead units when called for, though I think that brake applications would still be done simultaneously.

At the rear of a conventional freight train (no DP), the slack is constantly running in and out...you can hear, if not see, this as the train goes by. Nothing to be alarmed about. I suspect that having motive power on the hind end would move this free-moving area to somewhere in the middle of the train...still not a problem.

Engineers will (or perhaps already have) learn how to use DP to control slack to their advantage. And emergency applications initiated simultaneously at both ends of the train (or from wherever the DP is situated) just have to be safer than applications from just the head end (I believe some EOTs are capable of initiating--or repeating, more accurately--emergency applications as well, so you don't need the DP locomotive for this).

[sooblue]

Very informative,
Thanks Guys.
Sooblue

[Jackflash]

Originally posted by CShaveRR

Just for the record, DP units can be controlled independently of the lead units when called for, though I think that brake applications would still be done simultaneously.

Quite right,, in fact when starting on a grade I will load up the rear DP unit(s)
before releasing the brakes, then when the brakes begain to fall off apply
even more power to the remotes while notching out the head end units
you might have the rear remotes in notch 4 or 5 or 6 and the head end
units in 2, 3 , or 4 after you're moving keep advancing the throttle on the
head end till it matches that of the remote(s) then pu***he "front" button
on the Harris box or DP screen, now the rear units will follow the throttle
of the lead controlling unit, or, you can just leave the rear remote unit(s)
in independent mode, depends on the profile ect. jackflash

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