Locomotives

I'm trying to help out my son with a problem for a report.  According to some information we've found on the net, George Stephenson's Locomotion #1 could pull a 36 ton load at 4.5 MPH.  We've also found that an SD70Ace has a tractive effort of 137,000 lbs.  What we're trying to do is to compare these two numbers. 

 We can't find the tractive effort of the Locomotion #1, nor can we find a maximum tonnage capability for the SD 70Ace.  Can anyone out there help?

 

Thanks!

Dean P

http://cs.trains.com/trccs/forums/t/162818.aspx

Review the tonnage ratings in the above thread...the 'flatland' rating is on a territory that has a 0.3% ruling grade....3/10th of a foot rise in 100 feet of linear distance.

You're comparing the two engines on level track, right?

Nobody actually knows how many tons an SD70 can pull at low speed on dead level track with its 137,000 lb of tractive effort. For one thing there are two separate questions: (1) how much tonnage can it start from a standstill (2) how much tonnage can it keep moving at some low speed, say 10 mph. The latter may well be more than the former-- it should be well over 50000 tons, maybe over 80000.

As for how much tractive effort Stephenson's engine was exerting: your guess is about as good as ours. I don't suppose that reference to 36 tons at 4.5 mph spelled out how level the track was?

I'm not really sure what we're comparing, which is part of the problem.  I can't assume the 36 tons was on level track, as i think the reference mentioned going up hills. 

 It's not accurate to assume the wheels had the same resistance to starting.  It's not accurate to assume level trackage... 

You mention 50-80k tons.  Can you provide any information on how to calculate that number?  My thoughts would be that if the tractive effort (how much can the SD70 move at 10mph on level track) is 50-80k tons, that would be good enough for what he needs, but we need to be able to show how we got that number. 

He's trying to show how much more a modern loco can pull vis-a-vis the Locomotion #1.  Right now he has two numbers:36 tons (72,000#) for the Locomotion #1 and 137,000 # for the SD70.  The uninformed would just compare those two numbers and be thoroughly unimpressed.  The question is how to get those two numbers to compare.

 

By the way, thanks for the replies!  I/we appreciate it!

Dean P.

Hi,

Can supply a table for an AC6000 from GE's site, here just for level track (note: this loco has something more about 180.000lbf starting force).

Tonnage Table - One AC6000 Loco
trailing tons vs. grade and speed

           balance
           speed (mph)
           |         |
Grade: |10,7   | 15.0    20.0     30.0     40.0    50.0     60.0   70.0    75.0    
0.0%   |60640 | 55771 39124   22236  14090  9370    6424  4459   3701 tons

Have to leave explanations for the term Trailing Tons to GE-engineers. Pulling a train weighting 60.000 tons would be impratical with a single engine.

Enjoy!

lars

 Dean, Check out this site:

http://www.alkrug.vcn.com/rrfacts/hp_te.htm

chad thomas:

 http://www.alkrug.vcn.com/rrfacts/hp_te.htm

Now try it!

dean_1230:

he has two numbers:36 tons (72,000#) for the Locomotion #1 and 137,000 # for the SD70. 

Just to clarify: no point comparing those two numbers. The SD70 is supposed to be able to exert a horizontal force of 137,000 lb at the wheelrims, which means on the level it can likely maintain 10 mph with a train weighing 50000 tons or more. You'd like to be able to compare pulling forces of the two engines, or the trainloads they can pull, but don't mix the two.

If we know the steam pressure, cylinder size and driver diameter of a steam locomotive we can hope to get a reasonable estimate of its tractive effort at low speed.

dean_1230:

Can you provide any information on how to calculate that number?

See the GE table that Lars quoted? They say an AC60 can pull 55771 tons at 15 mph-- where did they get that? Did they try a 55772-ton train and find it couldn't make 15 mph? Presumably not-- those figures are probably all calculated from some formula. They probably are assuming a ton of train weight requires a pulling force at speed V (in miles/hour) of A + BV + CV^2, where A, B and C are constants; if we work backwards thru their numbers we could make a fair guess at what their chosen constants are. But we fans don't have too much idea how realistic their formula is-- GE may not have that good an idea either. Train resistance isn't that simple to measure accurately.

One formula says a loaded coal car (gross weight 143 tons, a typical limit these days) needs less than 190 pounds of pulling force to roll at 10 mph on level track. If that's true, the SD70ACe can maintain 10 mph with a 100,000 ton train. (On second thought-- might be more like 8-9 mph. In any case, it's supposed to be able to keep moving at some low speed, if that formula is right.)

timz:

One formula says a loaded coal car (gross weight 143 tons, a typical limit these days) needs less than 190 pounds of pulling force to roll at 10 mph on level track. If that's true, the SD70ACe can maintain 10 mph with a 100,000 ton train. (On second thought-- might be more like 8-9 mph. In any case, it's supposed to be able to keep moving at some low speed, if that formula is right.)

 

In theory, this is probably true, but getting back to reality, the initial inertial to start the 100,000 train moving probably would be too great for one unit to start it moving.   The record length for a train in the USA was set by the N&W and was close to 500 loaded coal cars if I remember correctly.   Maybe someone has the facts on that train pulled by a bunch of SD45's back in the day.   The N&W train was 500 cars long and weighed about 50000 tons. 

Speaking of out of the USA records, on May 28, 1996, Australia got the tonnage record over 408 KM with ten GE Dash-8s pulling 540 wagonloads (Train Length: 5,892 meters or 3.7 miles) of ore an average 35 MPH. The load was 57,309 tons of ore and 72,191 tonnes of train. This train was a test of Harris Locotrol and had 3 locos, 135 cars, 2 locos, 135 cars, 2 locos, 135 cars, 2 locos, 135 cars, and one loco on the rear.

 In the steam era, the locomotive would take slack on the train by slowly easing back about fifteen to twenty feet on a large coal train and then start forward with as much throttle as possible to get a roll on the train before the total weight was on the draw bar.   You could notice the first few sounds of the chuff were quicker than the speed of the locomotive once the complete weight of the train was moving. 

CZ

 

 

The confusing thing about looking at tractive effort is that on it's own it doesn't tell us anything other than potential. The other thing to consider is adhesion or actual traction. Tractive effort is actually torque as measured at the rail. You can have all the TE in the world but it does no good if you don't have the adhesion (traction) and are just spinning your wheels. Since torque can also be thought of as leverage, we need to look at how this affects potential adhesion. As wheel diameter goes up, TE goes down (all things being equal) at lower speeds. Think of that larger wheel compared to a smaller wheel as a gear in a car. A larger wheel is a higher gear and a smaller wheel is a lower gear. A steam engine with it's larger wheels has less starting TE per the same amount of drawbar horsepower. It sounds confusing but is easy to explain with math if you want me to get that complex with it.

Let's again compare wheel sizes to torque or leverage. We know that a car is going to spin it's wheels best in low gear. In higher gears it doesn't do it as easily if at all. Same thing with steam engines vs diesels and how it relates to adhesion. Our steam engine may have good horsepower but is perpetually stuck in "high gear" with it's larger wheels. That equals less starting TE which will mean it will have a harder time getting a train moving from a stop but it will also mean that it will have a better TE to adhesion ratio. It can get most of it's power down without spinning the wheels. It's not to say that it can't though as steam engines definitely did spin their wheels.

If you get a diesel engine moving with it's smaller diameter wheels, as long as it can maintain adhesion, it can accelerate faster. Again think of this as starting a car out in high gear vs low gear. Now pretend you are doing it on ice. Both can probably break the wheels loose but which one has the potential to accelerate you faster?

However the advantage to the smaller wheels will quickly go away as speed increases. How efficient is your car on the freeway in a lower gear? You don't need as much TE to keep moving the faster you go but at some point your TE will fall below your available adhesion limit which means no matter what you do, you can't go any faster as all you can do is spin your wheels.

It gets confusing and is a bit hard to explain clearly without only bringing up more questions. Needless to say it is an interesting topic that can definitely be explained in far more depth. I am greatly simplifying things and leaving some things out such as available power (or steam) at various speeds.

fredswain:

The confusing thing about looking at tractive effort is that on it's own it doesn't tell us anything other than potential. The other thing to consider is adhesion or actual traction. Tractive effort is actually torque as measured at the rail. You can have all the TE in the world but it does no good if you don't have the adhesion (traction) and are just spinning your wheels. Since torque can also be thought of as leverage, we need to look at how this affects potential adhesion. As wheel diameter goes up, TE goes down (all things being equal) at lower speeds. Think of that larger wheel compared to a smaller wheel as a gear in a car. A larger wheel is a higher gear and a smaller wheel is a lower gear. A steam engine with it's larger wheels has less starting TE per the same amount of drawbar horsepower. It sounds confusing but is easy to explain with math if you want me to get that complex with it.

Let's again compare wheel sizes to torque or leverage. We know that a car is going to spin it's wheels best in low gear. In higher gears it doesn't do it as easily if at all. Same thing with steam engines vs diesels and how it relates to adhesion. Our steam engine may have good horsepower but is perpetually stuck in "high gear" with it's larger wheels. That equals less starting TE which will mean it will have a harder time getting a train moving from a stop but it will also mean that it will have a better TE to adhesion ratio. It can get most of it's power down without spinning the wheels. It's not to say that it can't though as steam engines definitely did spin their wheels.

If you get a diesel engine moving with it's smaller diameter wheels, as long as it can maintain adhesion, it can accelerate faster. Again think of this as starting a car out in high gear vs low gear. Now pretend you are doing it on ice. Both can probably break the wheels loose but which one has the potential to accelerate you faster?

However the advantage to the smaller wheels will quickly go away as speed increases. How efficient is your car on the freeway in a lower gear? You don't need as much TE to keep moving the faster you go but at some point your TE will fall below your available adhesion limit which means no matter what you do, you can't go any faster as all you can do is spin your wheels.

It gets confusing and is a bit hard to explain clearly without only bringing up more questions. Needless to say it is an interesting topic that can definitely be explained in far more depth. I am greatly simplifying things and leaving some things out such as available power (or steam) at various speeds.

And then to throw additional complexity on the diesel electric side of the equation....the various electrical connection transitions that take place to get maximum power at minimum current levels through the traction motors.  Starting a load and then going from slow to fast with it, is a exceedingly complex project in applied physics.

CAZEPHYR:

the initial inertial to start the 100,000 train moving probably would be too great for one unit to start it moving.

Just to clarify-- there's inertia, and there's friction, and the two have nothing to do with each other. If the 100,000-ton train is utterly frictionless, 1 pound of tractive effort will be enough to start it and accelerate it to 10 mph (tho it will take two or three years).

None of us has much idea what tractive effort is needed to break a train loose from a standstill. If the train is sitting on a 0.08% downgrade and we release the brakes, will it start rolling? We certainly don't know, and maybe nobody else does. If that is enough to start it rolling, then we could hope the SD70ACe could start it on the level.

In any case, the resistance formula I mentioned does claim a 100,000 ton coal train would only need a TE of 140,000 lb or so to maintain 9 mph on the level.

fredswain:

 A steam engine with it's larger wheels has less starting TE per the same amount of drawbar horsepower. It sounds confusing but is easy to explain with math if you want me to get that complex with it.

I would be interested in the mathematical explanation if it can be applied to steam-versus-steam or diesel-versus-diesel.   Thank you.

 

 

 

 

JayPotter:

fredswain:

 A steam engine with it's larger wheels has less starting TE per the same amount of drawbar horsepower. It sounds confusing but is easy to explain with math if you want me to get that complex with it.

I would be interested in the mathematical explanation if it can be applied to steam-versus-steam or diesel-versus-diesel.   Thank you.

 

 

 

Hello,

I fear, quoting from wikipedia,  same formula also used at steamlocomotive.com ; so for a 2 cylinder loco :

where

• t is tractive effort
• c is a constant representing losses in pressure and friction; normally 0.85 is used^{[note 9]}
• P is the boiler pressure^{[note 10]}
• d is the piston diameter (bore)
• s is the piston stroke
• D is the driving wheel diameter

( http://en.wikipedia.org/wiki/Tractive_force )

For playing around with that conveniently, see also please

http://www.steamlocomotive.com/misc/TractiveEffort.shtml

, works with actual JAVA-version.

 

Bye

lars

  -edit-

BTW.: for a 4 cylinder artic. simple; multiply the result with x 2 . The formula is just for starting te.

While, on the face of it, there is no comparison between Locomotion and an SD70, I'm sure a relative comparison can be made, based on weight, contact surface, etc.