Let’s take your average freight train, in this case one that has enough locomotive power to deal with the ruling grade on the line (according to guidelines), but not much more.
Let’s say that on level ground, the engineer rolls forward slowly, taking up slack. Then, once all slack is stretched out, he stops without letting any slack occur. The train is fully stretched out. (This is hypothetical.) Could he now start the train moving, allatonce?
If the answer to the above is Yes, let’s say this train proceeds until it is on the ruling grade and suddenly the engineer needs to bighole it. (Let’s say he sees people on the track, but stops before hitting them, then the people leave.) Now the train is stopped on the ruling grade, with no slack. Can the engineer get the train going? Or will they have to double the hill?
Forgot that junk about going in emergency! Trains stopping on a grade is a common occurance, happens every day. And, barring unusual circumstances, the train moves away.
From what I’ve heard over time, starting a train from bunched was a practice necessitated by the old friction bearings. The oil in the journals was the practial equivalent of roller or ball bearings.
A standing car would push the oil from between the axle and the bearing, leaving a metal on metal situation. Trying to start an entire train in that condition might require more “oomph” than the power could provide.
Starting the train from bunched meant starting only one car at a time, even if it was only a foot or less. The rolling car would quickly pick up the film of oil between the axle and the bearing surface and roll more easily.
With roller bearings, this phenomenon doesn’t really exist. The only force to overcome is inertia. I would suppose that starting from bunched might make a little difference, but the need for it would be rare.
Starting from bunched, however, is one reason cabooses are gone. The last car in the train would suddenly go from zero to however fast the locomotive had gotten up to - often enough to knock crew members off their feet.
I recall a situation from my youth, seeing a train of coal hoppers apparently stalled on the grade through Milford, MI (Saginaw line). As I watched from a crossing mid-train, several attempts were made to get the train moving by bunching the train, then pulling out the slack. My most notable memory is the bang-bang-bang-bang-bang-bang-bang-bang-bang of the empty hoppers
As to the noise of slack as it ran in, the most notable example that I remember came one night back in the mid-sixties, when I lived on the main line of the IC 55 miles south of Jackson, Mississippi. I heard a great bang out front, went out, and learned that a southbound freight had to get out of the way of the City of New Orleans–by backing over onto the wrong main. The engineer had started braking right after passing the crossover switches, which were ground throw switches (talk about knowing your territory–no switchstands). The conductor or rear brakeman told him when the rear had passed the switches by throwing a lit fusee up in the air; they had plenty of time to line the switches before the caboose reached them. I did not count the cars, but from previous countings, I would say that there were about 180 cars on the freight. The engineer stopped the freight short of the fouling point–and the City was right at the SB fouling point when the switches were lined for through operation, and was moving when I saw its engine; it obviously had crept up after passing the previous signal.
One way the world has improved since the age of steam. In the ‘bad old days’ the engine could pull any train it could start, but (1) it could only start limited resistance ‘at one time’ without risking slip (or stall) and (2) it needed to get up to particular speed to start winding the reverse back to good cutoff without peaky torque issues, and to get reasonable horsepower at higher cyclic. That meant that an engineer might well be getting the head end to relatively high speed by the time the last few draft gears were coming out - and interestingly high rates of short-term acceleration would be observed… perhaps especially if the brother running the engine didn’t care for snakes… [}:)]
Nowadays with AC drive and roller bearings, the start can be made keeping constant speed once above a couple of mph until the whole train is stretched, then throttled up from there. While most hydraulic underframes work better in buff than in draft, there’s still a longer travel and better accommodation of any transient run-ins that might produce ‘shock’ accelerations.
In other words boring homogeneous conveyor belt computer controlled ho-hum verses human on the spot ingenuity, the ‘I think I can’ workings effects of steam and man, a drama fit for the stage. Well worth watching and listening to.
Can he release the brakes and start the train without it rolling backwards down the hill? If a six-axle AC unit has 5000 trailing tons on a 1% grade? Sounds doubtful, doesn’t it? Next question: can he bunch some slack with the brakes partially released?
None of us has a good idea of what today’s units can be relied on to haul up a given grade. On a long 1% grade, say – with 6000 trailing tons in 50 cars, would an ES44 have a 90% chance of making the grade, or more, or less, on a dry day? So we don’t know how tough a given tonnage rating is, so we don’t know how much margin a unit has to restart on the grade.
As for how much it can start on the level – first thing to find out is how much pull is needed to start the train rolling. So park the train on a carefully-measured 0.1% grade and release the brakes. Does it start rolling, just by gravity? If not, try 0.2%; I’m guessing that will be enough.
My basic question, I guess, was really about two things:
How close do the power-needs guidelines cut it regarding the ruling grade (particularly if, say, that one grade is an outlier in relation to the others)?
How much part does inertia/momentum play in the guidelines and in actual practice? Seems like you guys are saying “little or none.”
I had been wondering if the supposition was that (for example) 90% of the time, or more, the train would have a good head of (figurative) steam up when it arrived at the hill; and in the unlikely event the train had to stop on the grade, they could always double the hill. The idea being: don’t use more power than necessary, so it can be used elsewhere.
Are power guidelines adjusted in the winter, to account for slippery rails and snowdrifts?
For you engineers: have you ever used the entire load of sand on one trip?
On the pre-PSR CSX the Power Corordinators tried their level best to apply exact power to the tonnage rating of a train over the ruling grade of the ENTIRE TRIP - many of the territories the train operated over had tonnage rating much higher than the tonnage rating of the ruling grade. In the case of mountain grades where manned helpers were used, it was expected the maximimun number of powered helper axles would have the proper rating to get the train over the ruling grade. The PoCo’s would take great delight in powering at 15,985 ton train with power rated for 16K tons. Tonnage rating was ‘Gospel’. Some trains made the grade, a few didn’t. Some trains with 17K tons and power rated for 16K tons also made the grade. There are a lot of conditions that enter into a train successfully climbing a grade - weather (hot, cold, wet, dry, snow, ice); exactly where the tonnage is in relation to the max grade segment, are the grease
What a crock of BS! Where do you guys come from???
A good engineer would gently pull out the slack until the rear notified him that the cab was moving.
CN took the tonnage ratings out of most subdivision timetables years ago. Probably so crews can’t complain too hard or refuse a overtonnage train.
Starting a heavy train on a grade is indeed an art. Stopping with the train stretched is normally beneficial (so the slack won’t roll out backwards, potentially hard enough to break a knuckle), but I’ve had to take slack (bunch it up) to start particularly underpowered trains a few times.
From observation, it seems that DC power will reliably make it up grades as long as the horsepower per ton (HPT) ratio is .1 to .2 greater than the grade. AC power HPT needs to be equal to the grade. As an example, the ruling westbound grade on CN’s mainlines from Edmonton, AB to the Pacific coast is 0.4%. Trains with all DC power are often loaded down to 0.6 or 0.5 HPT, while trains with AC power are dispatched at about 0.4 HPT. These trains occasionally stall on certain hills in rain/snow or when the Dispatcher stops them in a bad place (as Balt noted), but most of
Do they ever assign tonnage that the engine couldn’t start, if it happened to get stopped on the steepest upgrade? Dunno how often they do it now, but it used to be common on UP coal trains east from Cheyenne. The climb is 2.7 miles averaging 0.65% compensated, and a pair of SD40-2s would use momentum from the preceding downgrade to take 13000 tons over the top.
By the way: the tonnage ratings in the timetable are just for show – don’t assume they’re realistic. When UP had ratings in the Spec Instr a few years ago, they said GP60s were good for 3400 tons on 1%.
Offhand, I can think of at least two locations between Edmonton and Vancouver that have short westbound stretches of 0.6% or 0.7%. They are both on single track, so it is rare for a train to stop there, but some have stalled in the past.
Soon after this type of operation began, the 0.4 HPT AC-powered trains ‘discovered’ a bunch of new places where it is a bad idea to stop them in the rain.
I would go so far as to say that higher horsepower modern locomotives are getting back into the steam territory of being able to move a greater tonnage than they can start. Especially when it is raining or they are out of sand.
On that note, I have never used up a full sandbox’s worth on one shift, but I have seen a number of locomotives run out enroute, or simply get released from the shop with no sand at all.
When starting a train and at low speeds, horsepower really doesn’t matter as much as weight-on-drivers and wheelslip control. From experience switching with each of them, I think a SD40-2 would out-pull a SD60, Dash-8 or Dash-9, and be about equal to a SD70.
A 1800 HP GP9RM-slug pair will out pull any of the above at slow speeds, despite having less than half the HP. Why? It weighs more, and has two more traction motors.
Lol ok.
Maybe as long as the train kept moving above 30 mph, but we know how
Gotta tell my Mom’s story… when she was young (6 or 7) her family moved from Indiana to Kansas. Her Father and brother drove a truck with their belongings while her and her Mother took a train; they rode as paying passengers in a caboose of a freight train. (She said they saw her Father and brother waiting at grade crossings a couple of times on the trip. She waived, but they didn’t see her.)
At one stop, she said she was up prancing around, trying to stomp on flies, which were thick in the caboose on the hot summer afternoon. A man in a dark blue suit came in the back door and told her, “Little girl, you’d better sit down.” She said she had been told not to talk to strangers and she was not about to pay any attention to this man. “Who was he to tell me what to do!” She turned around to face the other end of the caboose and continued stomp at flies.
A moment later she heard some banging coming from the front of the train and she suddenly was sitting on the floor. She got up and sat next to her mother. But she had a hard time sitting still because her bottom hurt. She said that the man in the dark blue suit laughed at her, but she would not look at him.
I never thought to ask her if she was able to kill any flies stomping on them or in the act of suddenly sitting on the floor.
Yes, however, we had one certain turnaround job that we knew to begin with that we would have to double the hill. And, unless they timed things right so that a returning set of pushers were available, that is what we did.
I have ridden in cabs a number of times - some starts were gentle, some were less than gentle - you soon learned where the welded rail was and wasn’t. Depending upon the engineer and the train - the inroute slack action could be severe.