This has probably been asked before, so please pardon my ignorance, but I was watching ‘Trains and Locomotives’ today on RFD and they were showing Norfolk Southern at Horseshoe Curve, and I got to wondering… How come helper units (pushers) are always hooked on the back of the train, instead of MU’d with the lead units?
Only thing I can come up with, is that it’s easier to just uncouple them from the rear of the train and be ready for the return trip, instead of having to unhook the air lines and electrical connections to the lead engines.
I guess another reason is that they can switch onto another track (out of the way of other traffic) after they’ve uncoupled from the rear of the train, thus letting the train continue on it’s way, rather than having to stop the train and wait while the helper locos switch tracks to get out of the way if they were coupled in front of the lead units.
I may have just answered my own question there with common sense, but I’d like someone who knows to affirm or correct me.
You are right in what you are thinking, but there is at least one other reason. If all of the power is on the front end, it can cause too much strain on the coupler knuckles, causing them to break. With the helpers in the back, the forces are more eventhroughout the train, and the equipment doesn’t break as much. I’m sure others can elaborate better than I, but I do know that is an important consideration.
First, pushers aren’t the universal helper mode. Psgr trains generally required head end pushers and the SP ran steam helpers scattered through the train…one mid-train and the second about 12 cars ahead of the caboose. Diesels aren’t simply MUed w/ the road power because that would leave the units stranded after they finished helping. You need an engine crew to return them to help the next train. The N&W would frequently run a pusher in reverse greatly simplifying the return trip.
The couplers and knuckles of a train can only stand do much wieght or pull on them. On a steep grade that limit can easily be exceeded. So helpers are placed in/on the train to add oomph without increasing the strain on the couplers.
On passenger trains the problem wasn’t so much the weight of the train, it was more the speed. So drawbar strength wasn’t the issue. On a passenger train if you put the engines on the headend there is no way that during an accident the cars can be crushede between the two engines. The passengers really hate that.
NS someitimes puts helpers on the front of some trains on Horseshoe Curve. Many times the helpers stay on the train down hill for extra braking. Some western roads use helpers cut in 2/3 the way back as pushing on the rear can pop cars out the middle of the train.
I have seen pictures of WM coal trains with one engine on the point and as many as 7 engines in and behind the train, all massive 2-8-0’s, as helpers. they were in a 1-2-2-3 configuration from the front.
Trains both up and down on horseshoe get helpers to either push westbound or brake eastbound. At Cresson just beyond Galitzen is(or was) a wye and once the train reaches there it is downhill all the way to Pittsburgh. By putting the helpers on the rear the train doesn’t have to stop and it saves time. I believe as I can not recall anything differently all helpers to brake eastbounds go on the front. My logic would say to prevent slack action and keep the train bunched. Have not watched how they cut them off in Altoona but that could also be a crew change point so they need to stop any way.
The one additional use of helpers is to get the train underway. The helpers actually start first, taking the slack out of the train thus making it easier for the head end units to get started and accelerate enough to “make the hill”.
Will
It is easier to add and remove helpers on the hind end. It also distributes the power better, easing the strain on the couplers. Althought the not practiced anymore, in the past, helpers could be cut off on the fly at the top of the grade. Now, it’s common to have the helpers push up the hill and then brake down the other side.
Some roads use DPUs (Distributed Power Units) spaced through out the train. These unmanned enignes, are remotely controled from the lead engine, and stay with the train for the entire trip.
When ruinning trains over the Sierras, the SP used to use helpers spaced two thirds way back in the train as well as rear end helpers. The trains were 125 to 150 cars long. There were as many as 10 engines on a train distributed as needed.
Only roads using DPU are BNSF and UP right now. and the only reason old Bunsniff is using htem is cause we think we have to be like UP( well in dp theory anyway cause our trains are still moving) Have seena set of DP’s in the middle only once msot of ours is at the end of a coal load.
Engineer can control it through the screen ( this is with modern Dash 9 and SD70macs 70’s etc etc) to have it start pushing then release his independent and start the leader moving. Also on hills he can leave it in power whils pushing the rear up while the leader is in dynamic.
I know CSX adn NS dont like DP’s as whenever we get a DP unit train to come by going to chicago we have to unlink and put it on the head end.
Southern Railway (before the NS merger) had a number of mid train helper radio cars and used them quite often. With the era of SD45’s and SD40-2’s and Locotrol equipped locomotives, mid train helpers were quite frequent. With modern radio equipment, they are kind of obsolete, and NS doesn’t use mid train helpers (where I live anyway), so I haven’t seen the radio cars lately.
I always thought passenger helpers had to be on the point, so imagine my surprise one fine April day in 1960 when I looked out the window of the rear vestibule door and found myself staring at the smokebox of a JNR D52, the most powerful road loco they owned! (That line has since been electrified, and today most passenger trains are EMUs with no locomotive.)
The basic rule with helpers can be stated; No locomotive should ever pull on the front coupler or push on the rear coupler of any other locomotive to which it is not directly coupled. Failure to follow that dictum will either string-line the intervening cars or pop them off the outside of curves.
