Question on real trains (slack)

[Anonymous]

My dad and I were sitting out side watching the trains go by and the coal train that was passing had a pusher(like most here do). Anyway we starting thinking, how do they control the slack between the engines. Do they keep things scrunched up or what. The part that really confuses me is when a train is going over a hill with one half going down and the other half going up. How do they control that? Please help an easily confused soul. [:D]


Thanks,
Jeremy

[M636C]

Jeremy,

The system I'm familiar with is the GE/Harris "Locotrol", and not the latest versions, but remote control locomotives aren't just run in "multiple unit" with the lead locomotives. There is a seperate miniature control stand, the ones I know being fitted above the standard AAR Control Stand, in a small box a lot like a model railroad controller. The locomotive driver has to judge where the remote locomotive is, and it should keep pushing up a hill even after the lead units are over the crest and have cut off power. When going through a dip, the remote locomotive should not start pushing on the falling grade or the cars would bunch up in the bottom of the dip. So the driver is in fact driving two separate locomotives in different places at the same time.

I've seen an iron ore train made up of two sets of two locomotives and 100 cars each. When it reached the unloading yard, the train was split into two equal parts. The first train ran forward and stopped in a siding, and the second train followed into a parallel track next to it. As it rolled past me, I realised that there was nobody in the cab of either unit - it was still being driven from the lead unit of the first half of the train.

A really bad acident occurred on the Queensland Goonyella line with a 150 car coal train hauled by four electric locomotives. the train was passing through mountains and the radio link to the remote units was lost. The lead units stopped but the trailing units 100 cars back kept pushing. The 100 cars ended up at right angles to the track (like a folded concertina) and the pusher locomotives were wrecked. They were shovelling coal off the track for weeks.

Peter

[cacole]

Hmmm, that's an interesting question that I had never thought about. I have seen videos of loaded 100-car SP coal trains on the Tennessee Pass line in Colorado with five lead units, four mid-train helpers, and three end-of-train pushers, all C-44s. There's no mention in the narrative of how they control slack with these monster lashups, but they are going up and down hills and through tunnels. I think the theory is that if all engines are exerting equal pressure on the couplers, they are not going to run in or pull out slack once the train is rolling. These trains undoubtedly used radios for communications between the crews, so they would all know when to apply the throttle and when to begin braking. As the train passed through a tunnel, the lead units probably had to ease off on the throttle and begin setting their dynamic brakes, but the mid-train and pusher locomotives would still be throttled up until they got to the crest of the hill.

[dharmon]

Jeremy check out this thread on Trains:

http://www.trains.com/community/forum/topic.asp?page=-1&TOPIC_ID=17609&REPLY_ID=156715#156715

[Anonymous]

Thanks all for the great info. There is alot more to the protoyoes we model then one thinks. Thanks again.

Jeremy

[Anonymous]

The experience and judgment of the helper engineer has a lot to do with successful operation of a train up and over a steep grade. Engine crews become intimately familiar with the railroads over which they work, so they will be able to anticipate the grades and curves which they will be facing (often in darkness or inclement weather). Also, crews will be advised of the numbers of loaded and empty cars in their trains and of the gross tonnage, and can make good estimates about train handling based on that information.

Steam engines provided information to their crews as to how hard they were working by the sounds of their exhausts; diesels and electrics were more subtle in terms of sounds--but were equipped with ammeters to show how hard they were working.

The comment from Australia about the Locotrol system brought back memories. Milwaukee Road also use Locotrol in its mountainous helper districts, beginning in the late 1960s. A number of Milwaukee trains went on the ground when tunnels interfered with Locotrol radio signals.