Locomotive power

[PM Railfan]

In simple laymen terms, it is hard to determine what a single modern locomotive can pull/push. Many variables must be considered....

Ground attitude (level or not), track structure (good or bad, curved or straight), weather (slippery rails from snow or rain), the locos operational statistics (hp, weight, tractive effort, factor of adhesion, etc etc), even down to the engineer. Does he have a good hand at controls or not. No real answer can be given unless you fill in these variables with firm numbers.

Ex: level track, good condition, straight, clear day at 70 degrees, 4400hp comp controlled loco (AC trans with anti wheel slips) at full operational weight (sand, fuel, oil, water), and a highly seasoned engineer. Such a situation could move approx 50 to 75 loaded (100ton) cars. Supposing all cars have good wheel sets and no sticking brakes. Jack it up to 100 cars if empty. (you must make all the cars of equal type, loaded or not to get correct results).

Does it vary betwixt locomotives? Ofcourse it does. Even two 'sister' locomotives can produce minor differences in behavioral performance.

[dehusman]

Railroads also figure pulling capacity based on the service or speed they want the train to go.

Classically railroads had charts that gave the "drag" tonnagefor various classes of engines over each subdivision or between terminals and junctions on the railroad.  The grade and curvature were part of the equation.

Later some roads adopted a horsepower per trailing ton (hp/tt) and different types or classes of trains had different hp/tt requirements.  A unit coal train might have .5 hp/tt while a piggy back train on a flat route had a 2.5 rating and a piggyback on a territory with grades 4 hp/tt.  A 3000 hp SD40-2 on a coal train was worth 6000 tons, on a Z train across Illinois 1200 tons and a Z train in a western state  750 tons.

As various electronic and AC technology came on line straight horsepower became less of a measure of the pulling power of an engine.  Some roads now use a tons per powered axle measure and each class of engine is measured in equivalent powered axles (a powered axle = 10,000 lb TE).  An SD40-2  has 7.1 axles and a C44AC has 12.1 powered axles.  A drag train might allow 500 tons per powered axle while an intermodal train in flat territory 300 tons per axle and one in a mountainous area 200 tons per axle.

[BRAKIE]

Also weather and curves plays a roll in tonnage and a ruling grade can also be a short incline on a sharp curve.

[tomikawaTT]

"A single modern locomotive," can be anything from a recently-constructed six-wheel 'critter' (based on a single truck from a larger diesel) or a genset switcher up to a 6,000hp monster, the diesel equivalent of a Y6b, but capable of higher speed.

"Number of cars," is dependent on state (full or empty) contents (depleted uranium or boxes of ping-pong balls) and railroad profile (flat as a pancake along the Hudson River, darn near vertical in some regions where the parallel watercourse is used for white water kayak competitions.)

So what you have to do is ask, "How much tonnage can a (fill in make and model) pull over a specific ruling grade on a specific railroad."  Then translate tonnage into a number of loaded or empty cars.

My car card/waybill system gives me an empty weight for each car and a weight for whatever it might be carrying.  My locomotives have tonnage ratings based on my specific prototype conditions.  This sometimes results in my doubleheading a train which, in fact, is well within the capacity of a single locomotive.  More rarely, a train of 'empties' proves to be an overload for the single loco assigned.  I attribute that to wet leaves on the track in a rainstorm, and send out a helper to assist.

Chuck (Modeling Central Japan in September, 1964)

[davidmurray]

[quote user="ndbprr"]Of more importance is the tonnage. An engine can pull a higher number of empty cars than full. Every engine has a chart or graph showing maximum tonnage vs. % grade. Every railroad division has a ruling grade which will tell the railroad how many cars to attach based on total tonnage (in theory).

The ruling grade can also be a down grade, in which case the braking power to keep the train from running away is very important.  There was a tlevision show about a case where a dozen covered hoppers were estimated to weigh 40,000 lbs less each than they did.;

 

Plus two engines dynamic brakes were red carded for repare, but sent out anyway.

 

Result was a runaway, derailment, and several deaths.

 

But to the orginal question:  yes a 4000 horsepower locomotive will pull more weight than a 3000 horsepower one.

 

Dave

[ndbprr]

Of more importance is the tonnage. An engine can pull a higher number of empty cars than full. Every engine has a chart or graph showing maximum tonnage vs. % grade. Every railroad division has a ruling grade which will tell the railroad how many cars to attach based on total tonnage (in theory).

[7j43k]

I'm not sure if it qualifies as a modern locomotive anymore, but I did see a Southern Pacific SW1500 pulling 47 cars on the main line in Albany, CA some years ago.  Track was level.

 

Ed

[Tin can man]

I was curious if anyone knew how many cars can a single modern locomotive pull? Does it vary from locomotive to locomotive?