if a locomotive can pull 132000 pound force how do you covert that to how much weight it can pull
You are asking how many tons of rolling stock a locomotive with 132,000 lbs of TE can pull? That will depend on a number of factors:
Most railroads have 'tonnage rating' tables for each division on the railroad.
Modeling BNSF and Milwaukee Road in SW Wisconsin
jrbernier You are asking how many tons of rolling stock a locomotive with 132,000 lbs of TE can pull? That will depend on a number of factors: Grades Curvature Short Time rating if this is a DC loco Most railroads have 'tonnage rating' tables for each division on the railroad.
What is the relationship between horsepower and tractive effort? Which is most important in determining how much power to assign to a train?
Rio Grande Valley, CFI,CFII
JPS1What is the relationship between horsepower and tractive effort? Which is most important in determining how much power to assign to a train?
It depends on what you're trying to do. Tractive effort is how much a locomotive can pull. Horsepower is how fast it can pull a load. If you want it to just clear the ruling grade, simply assign enough tractive effort to get it over. If you want it fast, add more units for more horsepower.
conrailfan2596if a locomotive can pull 132000 pound force how do you convert that to how much weight it can pull
You don't. That 132K is STARTING tractive effort and it tells you how much pull the locomotive can exert against its drawbar. It's analogous to torque.
In order to figure out the tonnage of train it can pull, you need to know some other things, some of which are incorporated in 'car factor', compensated grades, etc. -- one good reference for some of the variables might be the Davis formula.
But starting TE won't tell you anything about 'how much weight the locomotive can pull AT SPEED. For that you need to know horsepower, which involves a time factor, and therefore invokes the idea of 'work'. TE is just a force, counteracted at the drawbar by train resistance, and F=MA at the moment of starting. But it takes more power to run the train faster -- look at the definition of horsepower for an idea about this if it isn't intuitive.
A diesel-electric locomotive with very high nominal starting TE will rapidly get to a speed where the effective 'tractive effort' is governed by the maximal horsepower that its prime mover can develop, and where the effective TE corresponding to this reaches the resistance of the train, you will be at the maximum speed that train can reach without external aid (gravity on a downgrade, tailwind, etc.)
conrailfan2596if a locomotive can pull 132000 pound force how do you covert that to how much weight it can pull
JPS1What is the relationship between horsepower and tractive effort?
Next question: how much horsepower does a "4400 hp" diesel produce at its wheel rims, at a given speed. That's not so easy to answer.
timz JPS1 What is the relationship between horsepower and tractive effort? If you're measuring tractive effort at the wheel rim, and you're measuring horsepower there too, then the relationship is dead simple: horsepower equals TE (in pounds) times speed (in miles/hour) divided by 375. Next question: how much horsepower does a "4400 hp" diesel produce at its wheel rims, at a given speed. That's not so easy to answer.
JPS1 What is the relationship between horsepower and tractive effort?
If you're measuring tractive effort at the wheel rim, and you're measuring horsepower there too, then the relationship is dead simple: horsepower equals TE (in pounds) times speed (in miles/hour) divided by 375.
Although 375 is the theoretical number to calculate TE from HP it doesn't take into account losses in the locomotive (air compressor etc) so 308 is often used for practical calculations. So the equation is 308 HP/V But this assumes that the wheel is able to transfer that force to the rail. So a second limiting factor is the coefficient of friction (often called adhesion in railroad circles). This is typically around .20 for DC diesel locomotives and around .40 for AC. Having a higher locomotive weight is beneficial here, hence heavier 6 axle locomotives.
On the pull back side the Davis equation is still often used (although there are arguments about aerodynamic issues especially with the large gaps on double stacks). Extensive tests were performed with large scale models in the Lockheed wind tunnel. These all of which produced more variability that folks wanted to deal with for hand calculations but were incorporated into modern simulation models like TOES (available to AAR members only due to misuse by the legal community). For hand calculations 4lb/ton is still a good # on flat, tangent track, figure 20#/ton/% on grades and for curves resistance is often considered to be 0.8-1.0 #/ton/degree (but very variable based on rail profile and lubrication environment). Hope this helpes.
Buslist Although 375 is the theoretical number to calculate TE from HP it doesn't take into account losses in the locomotive (air compressor etc) so 308 is often used for practical calculations. So the equation is 308 HP/V But this assumes that the wheel is able to transfer that force to the rail. So a second limiting factor is the coefficient of friction (often called adhesion in railroad circles). This is typically around .20 for DC diesel locomotives and around .40 for AC. Having a higher locomotive weight is beneficial here, hence heavier 6 axle locomotives.
My understanding is that in the U.S., the horsepower rating of a locomotive is net auxiliaries (radiator fans, traction motor blowers, air pumps) and prior to losses in the electrical transmission.
Ergo, a 4200 HP locomotive is rated at the shaft of the traction alternator, and the HP delivered to the wheels is that number multiplied by the efficiency of the alternator in combination with the traction motors. I have read that older DC traction motor drives were in the mid 80 percent efficient whereas AC drives are in the mid 90's.
With respect to a passenger locomotive such as the Amtrak Genesis, I think user "schlimm" had posted information that the P42 Genesis isn't "really" 4200 HP at the alternator shaft. This 4200 HP is 1) if the locomotive is not supplying HEP, the motive effort for which is also taken from the main engine shaft but 2) the locomotive is not in the HEP mode, where full engine RPM is not available.
If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
An additional factor is the train's rolling resistance which can vary with outside temperature. Modern trains with roller bearing certainly require less TE to start moving compared to the trains used with steam power in the fifties.
CZ
BuslistFor hand calculations 4lb/ton is still a good # on flat, tangent track, figure 20#/ton/% on grades and for curves resistance is often considered to be 0.8-1.0 #/ton/degree (but very variable based on rail profile and lubrication environment). Hope this helpes.
Agree! Close enough nearly for most practical work.
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
Brake HP = shaft HP out of the diesel engine.
Traction HP = Shaft HP out of the diesel engine that's going to be used for traction (this is the rating. e.g. a SD40-2 is rated at 3000 traction HP)
Net traction HP = electrical power headed to traction motors.
If you are testing an SD40-2 on a load box, to measure these things:
Put a shunt on traction alternator to measure current. Measure voltage. Calculate actual net traction HP. Use gen eff factor to calculate traction HP.
Count cooling fans running, unload air compressor, note that dust bin blower is running. Calculate actual HP of these items by using published standard and correction to actual air temp and pressure.
Add traction HP to the aux HP to get brake HP. Use EMD provided curves to correct from actual conditions back to standard (60 deg F air temp, 28.86 barometer)
I had heard that it take 8 lb to pull a ton on level ground. 132,000 lb could pull 16,000 tons ... on level ground.
the value doubles for a 0.25% grade, is about 3x for a 0.5% grade and 5x for a 1% grade. So it could only pull about 3000 tons up a 1% grade, assuming the entire train is on the grade.
greg - Philadelphia & Reading / Reading
BuslistAlthough 375 is the theoretical number to calculate TE from HP it doesn't take into account...
If you measure tractive effort at the wheel rim, and horsepower somewhere else, then you have to estimate the losses between those two locations. But as I said, when you measure both at the same point, horsepower is speed times tractive effort divided by 375, with no qualifications.
gregcI had heard that it take 8 lb to pull a ton on level ground.
You can do what CN does and simply use HPT and only HPT.
10000 feet and no dynamics? Today is going to be a good day ...
timz gregc I had heard that it take 8 lb to pull a ton on level ground. 8 lb per ton is a reasonable guess if the train is rolling 80 mph.
gregc I had heard that it take 8 lb to pull a ton on level ground.
8 lb per ton is a reasonable guess if the train is rolling 80 mph.
why does speed matter, aside from standing still?
Find a long 0.4% grade and stop a train on it, then release the brakes. Gravity is applying 8 pounds to each ton of the train, slowly accelerating it down the 0.4% grade. What speed will the train eventually reach?
timzFind a long 0.4% grade and stop a train on it, then release the brakes. Gravity is applying 8 pounds to each ton of the train, slowly accelerating it down the 0.4% grade. What speed will the train eventually reach?
Ask Lac Megantic, Quebec - they know a loaded oil train won't make it around at 10 MPH curve without derailing.
Never too old to have a happy childhood!
timz Buslist Although 375 is the theoretical number to calculate TE from HP it doesn't take into account... 375 is the number. It's theoretical in the same sense that 2 plus 2 is theoretically 4. If you measure tractive effort at the wheel rim, and horsepower somewhere else, then you have to estimate the losses between those two locations. But as I said, when you measure both at the same point, horsepower is speed times tractive effort divided by 375, with no qualifications.
Buslist Although 375 is the theoretical number to calculate TE from HP it doesn't take into account...
375 is the number. It's theoretical in the same sense that 2 plus 2 is theoretically 4.
read some of the definitive text books on it, its 308 at the rail that is recommended!! Play what ever games you want. Not my idea those of the experts! Your credentials?
Railroad Transportation Energy Efficiency has a slide (24) that answers my question about the rolling resistance at different speeds as well as correcting my earlier statement - the rolling resistance is < 2 lb/ton for most freight speeds < 30 mph.
it's not 8 lb/ton that I previously mentioned until above 100 mph
Buslist timz Buslist Although 375 is the theoretical number to calculate TE from HP it doesn't take into account... 375 is the number. It's theoretical in the same sense that 2 plus 2 is theoretically 4. If you measure tractive effort at the wheel rim, and horsepower somewhere else, then you have to estimate the losses between those two locations. But as I said, when you measure both at the same point, horsepower is speed times tractive effort divided by 375, with no qualifications. read some of the definitive text books on it, its 308 at the rail that is recommended!! Play what ever games you want. Not my idea those of the experts! Your credentials?
The TE-horsepower relationship is Power=TE x velocity in consistent units. The 375 arises as a conversion facor that accounts for inconsistent units such as pounds, MPH and horsepower.
As Timz stated, if the TE is measured at the wheel rim the tractive horsepower is calculated using 375.
Another example is if a dynamometer car measures the drawbar force and velocity. The DBHP is calculated using the 375.
This is the type of discussion that makes tuning into the Trains' forums worthwhile.
I know enough higher level mathematics to be able to follow the discussion. Thanks for the insights.
Buslist... read some of the definitive text books on it, its 308 at the rail that is recommended!! Play what ever games you want. Not my idea those of the experts! Your credentials?
Since credentials are requested, let's see definitive cites for some of these 'definitive text books' -- and, from you, a detailed explanation of the derivation of 308 as a specific conversion factor.
The 375 is derived from conversion of units definition (HP, lbs force, and units of time and distance all being standardized), so anything much 'other' is someone's empirical modification or 'correction' of a measurement, perhaps akin to the somewhat arbitrary "conservative" use of 85% nominal boiler pressure as the starting point for MEP in the PLAN calculation of steam-locomotive horsepower instead of actually figuring out what the effective pressure at the valve-chest is or how it varies during admission. (Note that 308 is just over 82% of 375, which has me wondering whether it represents the losses in a typical older diesel-electric locomotive; IIRC that 82% is right about what I remember reading in an F-unit manual...)
I do think that using a conservative rating for 'undefinable' losses, or as an allowance for (say) low-speed DC motor derating or slip avoidance, makes sense, and operationally it makes sense to roll all the individual 'correction' factors or adjustments into one guide-number-like one to simplify calculations in the field. But I consider there is as much grave danger in asserting such a number in a theoretical discussion of formula derivation as there in in using spreadsheet formulae that display approximated numbers in the same font and style as "hard" ones -- if there is no explanation of the places where tinkering has been done, readers will have no guide where the mathematics or the assumptions have been 'compromised' -- or whether the assumptions even match the current situation. A couple of Fry's lolog formulae for combustion-gas heat uptake suffer severely from the concatenated use of 'magic' empirical constants that do not adequately reflect many of the characteristics, features, scale or construction of post-1920s large locomotive boiler practice. But you would not recognize this from reading the discussions or papers that included the equations, and to my knowledge even the weighting factors used to arrive at some of the various constants are now lost. Using this without exhaustive (and in some respects impossible) correction will probably leave such an equation a very, very poor predictor of proper design or actual performance.
RME(Note that 308 is just over 82% of 375, which has me wondering...)
It is what the locomotive manufactures tell you to use for generator efficiency. That does not mean that's what it acutally is for all loads, speeds and excitation levels. But, for all practical purposes, it works.
There was some discussion that post Dash 2, Dash 7 locomotives should use a different generator efficiency factor, but I got out of locomotive testing in the early 90s, so I don't really know.
gregc timz gregc I had heard that it take 8 lb to pull a ton on level ground. 8 lb per ton is a reasonable guess if the train is rolling 80 mph. why does speed matter, aside from standing still?
Because rolling resistance has three components. A constant (the wheel/rail interface), a speed dependent portion (viscous bearing friction) and a speed squared portion (aero drag).
gregcRailroad Transportation Energy Efficiency has a slide (24) that answers my question about the rolling resistance at different speeds
timz gregc Railroad Transportation Energy Efficiency has a slide (24) that answers my question about the rolling resistance at different speeds Don't take that graph too seriously. According to it, a 20000-ton train only needs 40000 lb of drawbar pull at 30 mph on the level-- so one C44 could manage that. With 3000 tons the C44 could do maybe 80 mph, says the graph.
gregc Railroad Transportation Energy Efficiency has a slide (24) that answers my question about the rolling resistance at different speeds
Don't take that graph too seriously. According to it, a 20000-ton train only needs 40000 lb of drawbar pull at 30 mph on the level-- so one C44 could manage that. With 3000 tons the C44 could do maybe 80 mph, says the graph.
while the rolling resistance may not be that great on level ground, it goes up rapidly with grade. While it may only be 2 lb/ton on level ground, I believe it is close to 12 lb/ton on 0.5% grade and a 3,000 ton train needs a drawbar pull of 36,000 lbs.
gregcwhile the rolling resistance may not be that great on level ground, it goes up rapidly with grade.
Rolling resistance and gravity 'resistance' are two separate things and should be kept strictly separate. The measure of how 'rolling resistance' increases with grade would include items that change the actual resistance due to train characteristics, as a hypothetical example increased bearing resistance due to weight transfer, or perhaps increased flange force in curves, and not the actual force required to lift the train's weight against gravity. I'd use "train resistance" or some similar term to describe the load that a locomotive's drawbar tractive effort or DBHP have to overcome.
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