Paul_D_North_Jrit's sometimes true that a longer and heavier train can get up a short, steep grade easier than a shorter and lighter train.
PDN just gave you an example.
To second that, the eastern roads had a love affair with the GP40 series over SD's ... Those rascals got awful slippery on tougher grades and longer trains with as much HP often overtook 'em on serious grades. Saw it on Raton in the '80's with GP40X/GP50 pig trains vs merchandise& coal drags out of York Canyon/ C&W Jansen on adjacent tracks
The Operating people set the ruling grade on a district (it can change on a whim) and some of this comes down to some wonky lines of thought attached to train handling, tunnels and other fun stuff in the dispatcher's office..
And not mentioned yet are the compensated grades when curvature is fudged in at roughly 0.04%/Degree IIRC
mudchicken And not mentioned yet are the compensated grades when curvature is fudged in at roughly 0.04%/Degree IIRC
Thanks to Chris / CopCarSS for my avatar.
I have been searching the web for more info but can't find it now. There is a riddle or poser about a RR somewhere in the Northeast U.S. that would require a double header if the train was short, but if a few cars were added then a single engine could take the train up out of a valley. Something about the ruling grade was short and the engine could be helped if the tail of the train was still on the preceding downgrade, so a short train needed an extra engine, but a long train didn't. Anybody remember that riddle and have more detail about it?
Semper Vaporo
Pkgs.
This gaggle is wild...flying without GPS...and it might be helped by considering the empirical physical traits of trains...
If your finger in a yo-yo string is the locomotive, then the string is your trailing train including the spinning wood spool.
To move the spool (yo-yo )up the string if it's stopped at the ultimate length of the string, jerk it to start it.
If the spool is dropping to the extreme of its string's length, then only a little upward vertical physical encouragement is needed when it's at the bottom of its string travel
The yo-yo is the train, that part behind the locomotive, does what a loose string with weight at its end does.
So if a consideration about the ups and downs of grades endures, think that the string represents the breaking strength of the train's couplers. The braking strength of the cars and locomotives is sequentially applied and affected by the grades,the ups and flats and downs, the strength of the string to which the yo-yo is attached.
The train is your finger the string and the yo- yo communicating, the capability of this whole thing to not break and stay together.
A DPU group changes everything I've just written.
t.
Murphy Siding mudchicken And not mentioned yet are the compensated grades when curvature is fudged in at roughly 0.04%/Degree IIRC fudged in?? Don't railroads have surveyors to tell them what those real numbers are?
Murphy,
I think you are reacting to MC's "fudged in". He means, I think "figured at" or "taken as". FWIW my 1972 edition of Management of Train Operation and Train Handling gives the factor for curve resistance as equal to 0.05 % grade per degree of curve, or a resistance of 1 pound per ton. Curve resistance is known in the vernacular as "curve bind".
Most mountain grade railroads are compenstated for curve bind by reducing the grade in an amount sufficient to offset the increased resistance due to the curves. A five degree curve would be reduced by .25% of grade through the curve and a 10 degree by .5%. On a one percent compensated grade these are significant figures. I would not be surprised to find five degree curves on a 1% grade, but 10 degree curves are either special situations to dodge an obstruction, or a common maximum curve in mountain territory.
MC also alludes to the fact that someone will tell the engineers who are to lay out a line what standards of construction to apply. For example, what the maximum acceptible ruling grade will be, the sharpest allowable curve, and whether or not to compensate for the grade.
Once a line is in operation, if the grade is compensated then tonnage ratings can be figured based on the compensated grade, say 2.2%, with no further ado. If the grade is not compensated then the ruling grade must be figured based on the combination of the grade, say 2.2%, plus the worst curve bind. One of the more famous uncompensated grades is Tehachapi which is 2.2% uncompensated. SP figured eastward (toward Los Angeles) tonnage ratings as if the grade was 2.64% IIRC.
Mac
timzBut 90% of the time the climb isn't that constant, and there's no official formula for calculating (or even defining) "ruling grade" when the steepest part of the climb is a quarter-mile or half-mile or even a mile long. The question is always the same: are you going to assume a running start, or are you going to plan on a train being stopped on the steepest part of the climb? If the latter, how long a train are you going to assume?
I'd have to say, for the most part, the significant grades on Conrail WERE constant. The big exception, that could occasionally cause trouble, was the PRR line south out of Cleveland where an ore train could stall, but the same tonnage in open top hoppers, would be fine.
Generally, the drag tonnage was calculated through TPC simulations, but you could use that to back into the ruling grade with enough precision and accuracy that it usually matched up with what you saw on the track charts.
In practical terms, you need to keep a little cushion in your drag ratings. You never really know the true tonnage of at train until it is too late to do anything about it, anyway - if at all.
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
Quite a bit of this is well over my head, but a very good book is James E. Vance, Jr.'s "The North American Railroad". There is considerable discussion on the building of the PRR thru Pennsylvania.
Ed
oltmannd. ..........The big exception, that could occasionally cause trouble, was the PRR line south out of Cleveland where an ore train could stall, but the same tonnage in open top hoppers, would be fine...............
Murphy Siding oltmannd. ..........The big exception, that could occasionally cause trouble, was the PRR line south out of Cleveland where an ore train could stall, but the same tonnage in open top hoppers, would be fine............... Hmmmm... that almost sounds like the old riddle: "Which weighs more, a pound of iron, or a puond of feathers?". Why would an ore train stall, and the same tonnage in open top hoppers not stall?
A ore train with Jenny's would be very short for the tonnage being handled. Normal open top hoppers with the same tonnage would be almost twice as long. A short grade would have the entirety of the jenny train on the grade. The longer open top hopper train would only have part of the train on the same short grade at any one point in time, thus actually having less tonnage actually on the grade, even though both trains could have the same gross tonnage.
Never too old to have a happy childhood!
oltmanndfor the most part, the significant grades on Conrail WERE constant.
PNWRMNMMost mountain grade railroads are compenstated for curve bind
Some or all of the 3.3% in the Siskiyous is compensated, but offhand I don't think of any other pre-1900 climb that is.
I'm guessing 0.04% per degree of curve is more common than 0.05.
Ruling grade is not a mathmatical point on a route. It is a operating reality in moving tonnage trains over a territory - long or short - it don't matter. It is that area of a route where a train is most likely to stall for lack of sufficient motive power for the tonnage. Each line segment has it's own ruling grade - the ruling grade is direction dependent on most line segments - as what goes down in one direction, goes up in the opposite direction.
Lets run a train from A to Z.A to C - tonnage rating for a SD40 is 4000 tons per unitC to G - SD40 = 6000 tonsG to M - SD40 = 3000 tonsM to Q - SD40 = 12000 tonsQ to R - SD40 = 2000 tonsR to Z - SD40 = 10000 tons
Build & power a train to run A to Z without a helper being required over the ruling grade.
BaltACDlong or short - it don't matter.
Again, I'd have to dig out the charts, so you'll have to take my word for it.
We regularly deal with two major grades on our line. Purgatory hill approaches 2%, but is only a couple of miles long.
Big Moose Hill varies around 1.1%, but is five miles worth.
It's been said that if crews made it up Purgatory, they knew they'd make Big Moose. On the other hand, I don't know that helpers were used on Purgatory Hill, but I know they were used on Big Moose Hill.
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
BaltACD Ruling grade is not a mathmatical point on a route. It is a operating reality in moving tonnage trains over a territory - long or short - it don't matter. It is that area of a route where a train is most likely to stall for lack of sufficient motive power for the tonnage. Each line segment has it's own ruling grade - the ruling grade is direction dependent on most line segments - as what goes down in one direction, goes up in the opposite direction. Lets run a train from A to Z.A to C - tonnage rating for a SD40 is 4000 tons per unitC to G - SD40 = 6000 tonsG to M - SD40 = 3000 tonsM to Q - SD40 = 12000 tonsQ to R - SD40 = 2000 tonsR to Z - SD40 = 10000 tons Build & power a train to run A to Z without a helper being required over the ruling grade.
Murphy SidingWho at a railroad is in charge of building and powering trains...
I believe the answer at the bigger railroads is the power desk, or whoever serves in that capacity at smaller lines.
As I see it, the premise of the second part of Balt's post is to point out that if you have a train of 24,000 tons (just to throw a number out), you need to divide that by the tonnage rating for a given district.
Just to look at a short section, from M to Q, you can get by with two SD40's.
From Q to R, you'll need 12...
For the rest of your trip, from R to Z, three will do (unless they're short of power, then those poor souls will have to slug it out with two...)
Odds are that from Q to R, you'll see some helpers used.
Looking at the overall profile that Balt shows you, the power desk might shoot for that 4000 ton rating and give you six units, then add help for the areas where you need it. But it all depends...
Betcha' you've been involved in a situation where everything worked until...it didn't.
Your Q to R, 2000 tons, preceded by greater ratings each side o Q to R, suggests a grade normally surmounted by the momentum from the preceding grade with the engines power.
My guess is that a train stopped on that grade from Q to R and its crew couldn't start it.
Thus that is the ruling grade.
Coupler endurance, if a railroad was willing to assign enough power to the head end of it to start it there, will always rule.
I had 11,800 tons for Roseville to Schellville, which included a couple of miles of 1.8% on the Branch from Suisun to Lombard, 4 SD-45s and 2 SD-40s and 4 SD9s.
I griped to the Dspr's office before leaving RV.
"Your train needs 1.5 horse power per ton and you've got it."
Guess?
I asked once more for directions to double the hill....too much coupler resistance I said.
Ordered to go, mutiny not appreciated, or condoned,, I went.....
.
Full-throttle. holding the independent brake valve handle in the position which prevents the engine brakes from applying, the break-in-two happened, at about 11 MPH, 5 cars back at a brand new knuckle;. stopped a car length apart....some of us know what a car-length apart means on a 1.8% grade.
Ruling grades are long or momentum, and they include the physics of,... of, physic's. involving limits and capability's.
t
Murphy Siding BaltACD Ruling grade is not a mathmatical point on a route. It is a operating reality in moving tonnage trains over a territory - long or short - it don't matter. It is that area of a route where a train is most likely to stall for lack of sufficient motive power for the tonnage. Each line segment has it's own ruling grade - the ruling grade is direction dependent on most line segments - as what goes down in one direction, goes up in the opposite direction. Lets run a train from A to Z.A to C - tonnage rating for a SD40 is 4000 tons per unitC to G - SD40 = 6000 tonsG to M - SD40 = 3000 tonsM to Q - SD40 = 12000 tonsQ to R - SD40 = 2000 tonsR to Z - SD40 = 10000 tons Build & power a train to run A to Z without a helper being required over the ruling grade. To be honest, I don't even understand the premise of the second half of this post- but it does intrigue me. Who at a railroad is in charge of building and powering trains- such as in your example?
The premise is - this is what todays railroad operations is involved in. Moving traffic from A to Z in the most efficient manner possible (as well as moving traffic between all the intermediate segments), which considers manpower, motive power, running time, siding size and/or double track, maintenance of way curfews on the route, terminal facilities at intermediate locations - with changes in any of the identifed resource areas having a affect on determining the best solution. The continuing operation is a 24 x 7 x 365 juggling act as all the resources and traffic volumes are constantly changing.
Around here, power assignment is done at a system office in Atlanta. In general, there is a "plan" for each scheduled train, which is designed to help keep the power balanced across the network and fit the typical train sizes, but particular power assignment will vary with fluctuation in traffic. It also has to take into account pickups and setouts en route - some or which are imperfectly known at the time of the power assignment.
Unit train OD pairs and train tonnages are well known and power requirements are repeatable. The trick is getting the power to the train when things are tight.
Could you explain the O-D concept, please?
JayPotter Could you explain the O-D concept, please?
Origin to Destination - Assigned power stays on the train for the complete trip.
I was under the impression that it also refers to the type of traffic carried by unit trains.
BaltACD Lets run a train from A to Z.A to C - tonnage rating for a SD40 is 4000 tons per unitC to G - SD40 = 6000 tonsG to M - SD40 = 3000 tonsM to Q - SD40 = 12000 tonsQ to R - SD40 = 2000 tonsR to Z - SD40 = 10000 tons Build & power a train to run A to Z without a helper being required over the ruling grade.
The problem as given is a simple one. First questioin is how heavy a train can we run over the ruling grade. That depends on coupler limits which are, IIRC, 240,000# for grade C and 360,000 pounds for grade E. Last I knew figure grade E on unit train, including stack train, equipment and grade C on everything else.
At MCS an SD40 generates about 90,000# of TE. Three generate 270,000# of TE. A 6,000 ton train will offer 270,000 pounds of resistance on the grade. I am over limit for grade C. Now I have three choices. One is to with a 6000 ton limit and hope I do not break too many trains. Two is to drop to 5300 tons which will give just under 240,000# of resistance. Three is to see if there is a regular block of at least 700 tons with E couplers that I can reliably get on the head end of the train. If that is the case, I can run 6,000 tons safely. All this assumes DPU not yet invented. With grade E couplers my limit is 360,000#, and 4 units generate 360,000# TE, so all should be well with an 8000 ton train.
Balt has simplified the problem hugely by NOT allowing helpers, and by not telling us how long these line segments are and what traffic density is over each of them. If they are 200 mile long crew districts, we have a 1200 mile run. Assuming equal segment length, a fact NOT in evidence, our train is grossly overpowered over about half the route. In addition, odds are that the ruling grade on each segment is much shorter than a crew district, a situation that encourages helpers.
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