Help with tractive effort/horsepower

Just a quick, view on your thread. An average freight car, loaded, would weigh between 100-130 tons, not the 40 tons you have calculated. As an average, the roads I worked on, used a ratio of one HP per ton, as long as the grade was at, or less than 1% average. That, as a quick average, would mean your F-7 would be rated for 12-15 cars (loaded), on a railroad with an average grade of 1%. The ruling grade, for the same amount of tonnage/HP would be APPROX., 10% of the average. As the average grade increases, the tonnage rating drops. The "worst" I have run, was .65 ton per HP, with average grade of 1.8%, and ruling grade of 2.2%. This was with high HP, high adhesion locos, though. Regards

Is is possible that the hp/ton ratio for the 2.2% ruling grade was 1.65 instead of .65?

I might have wrote it wrong. It was/is .65 tons per HP, with high adhesion locos. (SD-70/90 series, or GE Dash-9's, or ES locos) Sorry for any confusion

Try to keep in mind that there is a difference in horsepower and tractive efforet. There are those among us (Golden Arm, J Greenwood, UPRR engineer, myself, etc.) that could probably tell you stories about how the railroads learned the hard way things like a 3000 hp GP40 does not equal a 3000 hp SD40.

Simply put, TE is what makes it go, Horsepower makes it go fast.

Ya i got about 3 or 4 stories about tractive effort.

My contractor days, one GP 9 doesnt add up to two SW1500, one UP SD 40-2 out does two GP 9's. (when i got to play engineer back then, all the sand and diesel i could get in those GP's)

UP experiences, a GP 60 doent work in a SD 40-2 yard. Cant replace three 4300 HP units on a local that just barely makes the hill on the branch with two 6000 horse GE's. We had a GE rep. with us that day.

GOLDEN-ARM wrote:The "worst" I have run, was .65 ton per HP, with average grade of 1.8%, and ruling grade of 2.2%. This was with high HP, high adhesion locos, though. Regards

OK.....Where was that at bro? .65 HPT on a 1.8? Your speed at the base of the hill? how many miles of rail on that grade? What speed did you crest the hill? Flange greasers in the curves?

I stopped on a .85 grade with about .75ish HPT with a mixed bag (DC SD 70, dash 8, SD 90, if im remembering right) and just barely gotter going, 8th "rung" before it started to crawl. Ever had a conductor turn in there seat and look right at you with the "Dont you dare pull this ..... er in half " face??... Yes sir, LOL

Speaking extremely generally, a given railroad will usually apply one of two criteria when assigning road locomotives to trains. If the railroad is characterized by relatively steep grades, it will tend to assign locomotives on the basis of tonnage ratings, these being the amount of tons a given locomotive model can be relied upon to move over given segments of the railroad. On the other hand, if the railroad is not characterized by relatively steep grades, it will tend to assign locomotives on the basis of horsepower, because the speed at which a train can move is, except at extremely low speeds, directly proportional to horsepower.

In other words, on a low-grade railroad, horsepower can be the controlling factor because a locomotive consist with enough horsepower to move a train fast enough to maintain its schedule will also produce enough tractive effort to keep the train moving on whatever grades it encounters. However on a high-grade railroad, the tractive-effort-related tonnage rating is the controlling factor. This is because a locomotive consist with enough horsepower to move its train at its scheduled speed on the relatively flat segments of the route will not necessarily produce enough tractive effort to keep the train from stalling on the mountainous segments of the route.

Hello, Boss Boomer; hope this finds you well.

As to your comment on GP-40 vs. SD-40, the difference is not so simple as it is with a highway tractor that sends whatever the power output is to either one or two driving axles mechanically. I think that was your analogy.

With diesel-electric locomotives, there is a major fundamental difference between comparable units built with four and with six driving axles. That difference lies in the fact that a major operational and design factor is traction motor heating, which directly correlates to amperage which naturally is higher at lower locomotive speeds for any given throttle position. The four-axle / six-axle difference comes in when you consider sending the main generator (or alternator) output to either four or six motors. The six-motor unit can run wide open at a lower speed continuously because the wattage is spread over more motors, to put it simply.

Because of this the six-axle unit has a higher continuous tractive effort rating, and achieves this higher rating at a lower speed. That applies to all early types (EMD units through the 1950's, ALCO-GE units before the Centuries, Baldwins and Fairbanks-Morse units too where a given horsepower was available in four or in six axles.)

Further, since you specifically mentioned the GP-40 we must also mention EMD's Performance Control which was designed to match power to adhesion and allow compatible operation with older units at lower speeds. What's that mean? It means simply that the GP-40 limits its power output. It does NOT produce 3000 HP all the time -- as you get down in speed below something like 19 MPH, horsepower begins to drop off (this is done electrically, and the governor maintains proper engine speed) until when you get down to about 12 MPH, the output is actually about 2000 HP. Or, 500 HP per axle. The SD-40 did not have this system, and didn't need it because at full output it was already 500 HP per axle. EMD had this on four-axle units above 2000 HP since the GP-30 and also added it to the SD-45. (GE's systems were different over time; see my site.) Obviously, this works on the way UP in speed the same way.

What THAT means is that when such a system is applied to four-axle units you end up with the same minimum continuous speed as six-axle units. So, then, with older units such as the EMD GP-7 vs. SD-7 you DO have that disparity in minimum speed, that of the SD-7 being much lower; with the later units, such as those you mentioned (GP-40 and SD-40) gadgetry is introduced to match the minimum speeds.

HORSEPOWER -- rated output of the diesel engine itself (Brake Horsepower) or power delivered to the main generator (HP for traction.) Early units were advertised with ratings quoting diesel engine brake horsepower, and later on (by the 1950's) everyone was using "HP for traction." Steam locomotives also had such figures as Indicated Horsepower (developed in the cylinders) and Boiler Horsepower (a largely theoretical figure equating to evaporative capacity but often ignoring the locomotive's ability to really get that out of the boiler.)

TRACTIVE EFFORT -- force exerted on the track in a direction to move the train, measured in pounds. Affected not only by available torque at driving wheel rim but also by coefficient of friction, which is varied by ambient conditions and variable as regards locomotive weight and adhesion / slip / creep detection and control. This is a function of horsepower output and speed.

DRAWBAR PULL -- force exerted on the drawbar of either the back of the tender or the trailing diesel unit. Measured in pounds; tractive effort minus the force needed to move the locomotives.

Hope this simplified explanation helps you on your way!!!

-Will Davis

In response to the question about "high-adhesion", that term could be defined however a given railroad decides to define it. However I've most often seen it used in reference to locomotives that are equipped with microprocessor traction-control systems. These would include EMD 60-series and later models and GE Dash-8 series and later models.

Under any given set of operating conditions, a locomotive has a "factor of adhesion", which is the percentage of its weight that the friction existing between wheel and rail will convert into tractive effort. This percentage will depend on rail conditions and the ability of the locomotive's traction-control system to respond to changes in those conditions. Microprocessor control systems respond more effectively than do earlier systems.

Since a locomotive's tractive effort is the product of its "factor of adhesion" percentage times its weight, heavier locomotives tend to produce higher levels of tractive effort than do lighter locomotives. In the context of tractive effort, the most powerful locomotives currently in regular service in this country are CSXT's class-CW44AH GE AC4400CWs. They are capable of producing 200,000 pounds of tractive effort, which equates to a 46% factor of adhesion.

One other factor to consider on your HO is the time era you are modeling. As Golden Arm says today you can figure about 100 to 140 tons for a loaded car - the car itself weighs roughly 30-35 tons and you can put 100 tons give or take on most cars, again with some exceptions.

But if you're talking about the 1950s and 1960s when your F-7's were everywhere, the empty cars weighed about 25 to 30 tons but could carry only between 50 and 70 tons. So in those days your same F-7 could pull more cars than it would today. Or put another way it took more cars to carry a given number of tons of freight.

Of course back then almost all cars had friction bearings instead of roller bearings so there was more drag, but that's getting too complicated to calculate.

Freight car size and capacity is an evolving process. There is never a drop-dead day when all 50-ton cars become obsolete and are replaced with 70-tonners. So your HO can incorporate some older, smaller cars, whatever the era, and also have some of the latest big ones - whether those big ones are 55 ton or 105 ton depends on what time frame you are dealing with. It probably would not look right to mix a 36-foot wooden boxcar with 286,000 lb capacity coal hoppers, but you do have some leeway to combine older and newer. As you make your models, you may want to give your older cars a weathered, beat-up look, while the latest size can be fairly new and bright.

In today's world...

High Adhesion is a physical design element applied to the engine's trucks where as wheel-slip control is the micro-processor controlled aspect of efficiently getting the most moving power out of an engine. This is most obviously seen in GE's newer locomotives where much of the locomotives systems are computer controlled. Take for example the Dash 9, or the AC4400, AC6000, or the newest ES44AC and the like. These are examples of locomotives with micro-processor controlled wheel-slip systems.

I might be wrong...