Comparison: Steam vs. Diesel

[KeithA2]

This web page by a professor of mining engineering at OSU may be quite useful:
http://www.mg.mtu.edu/~frotuony/mg336/chap02.htm
Go to Chpt 2 "Rail (Locomotive) Haulage.

There is a formula relating Tractive Effort and Horsepower under the section entitled "Motor Horsepower". There is also an email contact for additional questions.

Hope this helps.

Cheers,
Keith Albrandt

[Anonymous]

Well,
This is a deep subject, and one that's fun to talk about. However, as you can clearly see, the answer to your question is no. What your question askes is to compare apples and oranges. The different mecanical dynamics and even chemical variations in fuels can effect performance in each type of locomotive.
What are you actually trying to find out? How much tonnage can each pull? How fast they can pull a given load? How quickly can they accelerate a given load to a certain speed? What are their ablities to maintain a given velocity? Etc.....

[Anonymous]

I think some guys dont understand the laws of physics at work here.More tractive effort dosen,t mean more power.More TE allows more power to be applied.It works that way for all vehicles.Take for instance your car on a gravel road.It is easy to spin your tires on loose gravel from a start. But as your speed increases it becomes harder to spin your tires.Once you get going say maybe 20 mph or so you cant spin your tires even with the pedal to the floor.The friction between the gravel and your tires is the same at 20 mph as it is at 2 mph.The difference is speed.The faster a object travels,the less friction that is required to apply a given amount of power.So to put it in a nutshell below 20-25 mph most road locomotives are not able to use all of their horsepower.If they did their wheels would spin like crazy.Trains Mag did an article on this a few years ago.They had a graph which showed that an SD40 has to travel almost 25 mph before it can use all of its horespower.Sure some models may have better wheel slip control and better weight distribution but you can,t ignore gravity and friction.I am sure we have all seen GP40's and SD40's moving at 10 or 12 mph in notch 8 but believe me they weren't using all their HP.Thats because the amount of power going through to the traction motors is regulated on all locomotives.As speed increases more power is allowed to be applied.With high speed trains HP becomes more important because at 70 mph adhesion isn't a problem.What you need is brute HP to move tonnage fast.But on mine runs and drag frieghts TE is more important.I was looking at an old Rio Grande timetable and on the 3% grade up Tennessee Pass. When placing helpers on the rear of a train just ahead of the caboose it states that no more than 18 powered axles are to shove the train.The timetable dosen't care if its F units or SD45's.As long as the weight per axle is somewhat consistent,each axle will pull or pu***he train with the same amount of force,at slow speeds regargless of the type of unit.Limiting the number of axles keeps from shoving the train off the track.I have always been interested in how RR's use power and adhesion and I have found in my travels that very few railfans understand it.
Ron

[BRAKIE]

Gregg,Yes,I was speaking about mine runs.And as you said there was some pretty hairy grades,also you are correct about different engines handling differently.I know of one mines location it took 4-5 SD35s to pull the a 50-60 car train,it WAS very hairy with a grade of1.9% up and down on the return trip!BTW we would set the retainers on the cars before we would even think about descending the grade even with DBs thanks for your input.I have also seen SW1200 lugging a loooong cut of cars!

[thirdrail1]

Brakie, tractive effort and horsepower are not at all the same. For 14 years, the AN Railroad pulled a 100 car, 12,000 ton unit coal train from the loading terminal to the departure track with a single 1200 HP SW9. OTOH, it took a minimum of 5 SW1500's or GP15T's to get it over the road. The SW9 had the tractive effort to get the train moving on flat ground, but not the horsepower to get it up to 40 MPH or up a 1.5 mile 1 percent grade. If you are talking about mine runs, I am sure there were some pretty hairy grades involved and different types of power behave differently. Heck, the AN had 8 SW1500's, and the one with the worst fuel consumption used twice as much as the best, so different locomotives of the same type don't all do the same work either!

[BRAKIE]

Now,being the head brakeman on both of those runs,I know this.The 1.4% grade coming out of the hollow where the mine was located,had a pretty sharp curve in it.And the GP38 tonnage rating was not that close to the 40s on that branch.Ok?Therefore the extra 38 was due to the tonnage rating against the train tonnage,OK?I have worked this branch with 4 GP35s which tonnage rating was less then idea for that branch.3 lowly GP9s could work this train with the sanders open all the way.This may not make since,but trust me it is the way it was.I am told that the G9 2-8-0 haul the same tonnage,this was told to me by the engineer that ran that branch for 40 years.He also stated give him a H6 and he would pull the whole mine along with the train.I did not disagree with him.If you really wanted some fun try using 2 GP30 on the same train!Then,if that is not enough fun for you try it with 3 GP15! What a joke! We stalled and had to double the train.BTW you are pretty keen on engines!

[Anonymous]

GP40s and GP38s do weigh the same. Look it up. You will find some variation because the railroad ordered some with extra ballast, or one has a full size fuel tank and the other a small one. You will find some GP38s that weigh somewhat more than some GP40s, and also the opposite due to the optional equipment ordered by the railroad. On the PRR the SD40s weighed much more than the SD45s because the PRR ordered the SD40s weighed down with thousands of pounds of concrete. They wanted the SD45s for speed, so you keep them light for maximum speed, but with lower tractive effort. The SD40s were ordered to pull mineral service trains, thus you maximize weight so there is more tractive effort making the locomotive able to pull more tonnage, but at a lower speed.

The reason they put three GP38s on the same train they put two GP40s is obvious. They wanted to run the train at the same speed each day. So you put on the same Horsepower. Three 2000 HP GP38s is the same as two 3000 HP GP40s, a total of 6000 horsepower in both cases. So if two locomotives have enough Tractive effort to pull the train, then two GP40s can pull the train at the same speed as three GP38s. But the three GP38s could still pull a train half again longer than what the two GP40s could manage, albeit at a lower speed.

[BRAKIE]

Mike,That is very true.speaking of GP7/9 dancing I met some old timers that would really walk the walk with them! I am yet to hear any old engineer knock a GP7/9.

[CHESSIEMIKE]

May I Jump in? Mhen you are out on the road the numbers of T.E. and H.P. are not the only thing you deal with! Lets also compare how fast the engines load and if you have control over when the locomotives make the transisions (series-series, series-parallel, parallel-parallel). This can make a bige difference, and yes some of those "old timers" could make a GP7/9 really dance.

[BRAKIE]

A GP40 and GP38 does not weight the same.There is no way a 38 will out lug a 40.If they could pull the same,why did chessie put 3 38s on a mine run then the next day on the same run put 2 40s on it.Both days the train was the same tonnage? I have heard to many engineers #### &&*** 38s! wounldn't pull a @@!## hat off your head!Yeah the railroaders back then had a dirty mouth.

[Anonymous]

You are wrong. If you have two locomotives that weigh the same, have the same number of drivers, but one has 4000 HP and the other 2000 HP, they will both be able to start and pull identical trains. That is a result of Tractive Effort!

Now when you reach the balancing speed for 2000 HP the lower horspower locomotive will stop acclerating its train. But the 4000 HP locomotive will be able to continue to accelerate. That is HORSEPOWER not Tractive Effort.

If the locomotive are identical in weight and drivers the Tractive Effort is identical and at identical speeds they can pull identical trains. Only when you want to go faster or accelerate faster does the horsepower do anything for you.

[BRAKIE]

Carl,Spaking as a former Chessie brakeman,I will say this.On the mine runs most engines would perfer a GP7/9 over the 38s.The GP40 would follow the GP7/9 in perference on mind runs.Some of the engineers I have talked to was not worried about the T.E has much as they were handling.I have heard some very choich words used on the 38s.These are the type of words I can not repeat here.I know of 1 old engineer that perfered the C&O G9 2-8-0 over any diesel! I will not go into the GP30 on mine runs.That is a whole different story.A interesting story to say the least.

[CShaveRR]

You said it yourself..."at speed". I just looked over the specs for GP38s and GP40s on the C&O (a road that would really be concerned about tractive effort!), and tractive effort was pretty much equal among those two models, and the GP39s as well. The variations in t.e. were generally within 1000 pounds (about two percent), and the weight of the units might account for that.

[BRAKIE]

Whoa up! There is no way a 2,000 hp unit will out pull a 4,000hp unit.It would take 4 GP38s to pull the same train as 2 GP40s,at speed.Have you ever wonder why it took a A-B-A set of E8s to do the same job as that J3a?

[Anonymous]

That is correct. The diesel engine is identical, except for the substitution of a turbocharger instead of a blower. There is little or no weight difference. And often, the railroad has the unit ballasted to a specified weight anyway.

[Anonymous]

dont a GP40 have 3'000 horsepower and is tubrocharged. and a GP38 2'000 horsepower without a tubrocharger.

[Anonymous]

You are trying to compare two different things. Tractive effort is more dependent on the weight on drivers than on the Horsepower of the Locomotive. This is truer in diesels than in steam because the power is applied more smoothly and because most diesels have all the weight on drivers.

For example, a GP38 and a GP40 that are equipped identically would have identical tractive effort. So they could each start the same train. But the GP40 could haul that train at a higher speed since it has more horsepower.

[favuprailroadfan]

It all depends on what kind of research you are doing. If you would let me know, I would really be willing to help you in your research. It don't matter what it is I will try to help you in any way possible.

Dru

[thirdrail1]

There really is no valid comparison. For example, an NYC J3a Hudson had a fairly low tractive effort, yet was a comparatively high horsepower machine, but its maximum horsepower was developed at passenger train speeds. Until the new highest horsepower Diesels, all Diesels had 40 inch diameter drive wheels, whereas steam power had drive wheels varying from 50 to 84 inches in diameter. Maximum horsepower was achieved at various speeds for steam locomotives, depending on design. Diesels achieve maximum horsepower at starting.

[Anonymous]

Does anyone have a reasonably simple way to compare the tractive effort of a steam locomotive to the horsepower output of a diesel? I'd like to be able to make a relatively valid comparison while conducting my research.