Thanks for the video Paul.
What's kinda sad is that those particular SD40-2's are also rather familiar to me...saw them many many times.
How fast the time flies.
John
All this talk about comparing steam locomotives to diesels is all very interesting but all of you seem to have forgotten the most important aspect of all, the respective power curves of both power types. A diesel electric developes maximum horsepower and tractive effort starting out and both rapidly diminish as speed increases due to the fact that the traction motors (all electric motors for that matter) act as generators. As the speed of the traction motors increases so does the amount of back voltage and it takes more and more horse power to counteract this force. That's why it takes so many diesels to make a train go fast.
A steam locomotive on the other hand has a far different horse power and tractive effort curve. As the steam locomotive starts to pull at low speed it develops its lowest tractive effort and horsepower, that's why a steam locomotive's starting tractive effort number is so important. It determines the tonnage of the train it can pull without needing helpers to get going. As the speed increases so does the tractive effort and horse power. At what speed these level out and then fall off is determined by driver diameter, boiler pressure, rate of steam production,cylinder stroke, valve gear timing and the weight of the locomotive.
That's why a Challenger putting out 5000 hp at 40mph is the equivalent of four or five high horse power diesels, because those diesels have only about 5000 effective hp and similar tractive effort at that speed. Some calculations even suggest that the Challeger uses less btus than than diesels to get the job done but that's another subject entirely.
It all comes down to something very simple: A steam locomotive can pull a train at speed that it can't start on it's own, a diesel locomotive can start a train on it's own that it can't pull at speed. Hope this helps.
P.S. That was a great video that started this thread and thanks for posting it!
Yardmaster01...That's why a Challenger putting out 5000 hp at 40mph is the equivalent of four or five high horse power diesels, because those diesels have only about 5000 effective hp and similar tractive effort at that speed.
...That's why a Challenger putting out 5000 hp at 40mph is the equivalent of four or five high horse power diesels, because those diesels have only about 5000 effective hp and similar tractive effort at that speed.
Perhaps you would be so kind as to show us EMD or GE tractive effort curves for the above mentioned units at 40 MPH to confirm your statement.
Yardmaster01Some calculations even suggest that the Challeger uses less btus than than diesels to get the job done but that's another subject entirely.
Maybe where he went wrong was reading this
CAZEPHYRfive GE's had pulled the train into Cheyenne from the west.
and concluding the 4-6+6-4 could equal five GEs. Hopefully CAZEPHYR would disavow any such implication.
We could clarify the situation if somebody had clocked the five GEs up the west side of Sherman Hill with the stack train. Given the train's tonnage, it would be easy to calculate that if they were really only good for 1000 hp per unit at 40 mph they couldn't possibly make the speed they actually did make up the 0.82%.
Sorry guys, didn't mean to ruffle any feathers. When I referred to "high horse power" diesels I was thinking of SD 40-2's, (They're putting these things in museums already!) shows how old I'm getting. The Challenger at speed is probably the equivalent of 1 1/2 or maybe 2 at best of today's most modern power. At start the king of tractive effort and horsepower is still the gear reduced electric motor, be it straight electric or diesel electric.
The fact remains that the more you try to push an electric motor the more it pushes back. Effective horse power drops off following a descending logarithmic curve. I have my old college engineering texts with the relevent data but I'm not computer savvy enough to figure out how to get them posted. (Principles of Electric Generation and Use, McMillan Publishing, 4th ed. 1977, page 279-283)
Back EMF (Electro- Mechanical Force) is the major impediment in the usage of electric propulsion. Engineers try to design electric propulsion systems to stay in the "sweet spot" of the electric motor so that the motor isn't running too far along the bottom of the curve. The sweet spot of diesel electric locomotives tends to be in the range of 5 to 35 mph, over 35 and the back EMF becomes ever greater and horsepower transmission efficiency decreases thereby lowering effective horsepower and tractive effort.
Staight electric locomotives overcome the back EMF problem somewhat by having a relatively large amount of available horsepower to drive the traction motors and can then run at a higher speed. As far as their traction motors are concerned, they "see" the available horsepower as virtually infinite. This principle allows today's high speed trains to generate the speeds that they do.
Southern Pacific tried to get around the back EMF problem by trialing the Krause-Maffei diesel hydraulic locomotives. While they did indeed have tremendous low end pulling power and maintained that power farther into the speed band, they leaked like sieves and tended to overheat.
Steam locomotives develop their highest tractive effort and horsepower farther along the speed curve than the previously mentioned types and there-in actually lies their greatest detriment as far as most efficient utillization. Most railroads never ran their trains at a high enough speed to take advantage of the potential horsepower, although the Norfolk and Western was the main exception to that rule. They had the Y class for low speed lugging, the superlative A class for high speed heavy tonnage and the 600 class 4-8-4's for low tonnage high speed passenger trains. Railroads like UP and DM&IR wasted the huge horsepower potential of their large simple articulateds lugging high tonnage trains up steep grades at low speeds.
The diesel on the other hand had the advantage of utillizing ALL of it's horsepower right from the start. If you wanted to go faster, you just added more units. This is still true today. When you get right down to it, railroading is a relatively low speed undertaking with most of today's diesels operating in the low end of the speed band and thus being most efficiently used.
As far as saying that the Challenger was using less btus to do the job, that was an extrapollation on my part from studies the NYC did that found their Niagara's were more thermally efficient AT SPEED than the EMD FT locomtives it took to replace them. The NYC found that it took 2 FT's to replace one Niagara at 70 mph, an FT consisting of four 1200 hp permanently coupled units or EIGHT total units. Now one might postulate that the Challenger is a larger locomotive than the Niagara and so it would take more diesel electric horsepower to replace it at speed. I neglected to take into account the higher efficiency of today's modern power and if I was wrong on this will gladly concede the point.
Didn't mean to get so long winded and as said before, didn't mean to ruffle any feathers. Hope some more people chime in on this and correct any inaccuracies. This thread has been fascinating!
Yardmaster01...I have my old college engineering texts with the relevent data but I'm not computer savvy enough to figure out how to get them posted. (Principles of Electric Generation and Use, McMillan Publishing, 4th ed. 1977, page 279-283)
I'm sure a engineering book from 1977 does not delve into microprocessor controlled frequency drive AC motors. Which is to say a lot has changed in diesel-electric locomotive performance since the time of the SD40-2s, or the time of the FTs.
Given feltonhill's accurate statement that a Challenger is a 4600 HP locomotive @ 40 mph, that gives it a 500 hp advantage over a 4400 HP AC @ 40 MPH and about 900 HP less than an AC6000 @ 40 MPH.
The "sweet spot" on an AC is actually at higher speeds, which is why CSX has used ACs on intermodal from the get go (a trend that I now see the other Class 1s engaging in).
You will get no argument from me that the late steam designs were indeed powerful (not as powerful as some railfans like to pretend they are), and it wasn't until the last 15 years or so that D-E technology has progressed to the point of being able to give both high low speed tractive effort and high speed horsepower from a single unit.
Thanks for the feedback GP 40-2, can't fault your logic. It sucks to admit I'm turning into an antique like the machines I love. 1977 seems like yesterday..... At least back then I could stand trackside and watch the occasional F-unit or Alco roar by.
Yardmaster01 The sweet spot of diesel electric locomotives tends to be in the range of 5 to 35 mph, over 35 and the back EMF becomes ever greater and horsepower transmission efficiency decreases thereby lowering effective horsepower and tractive effort.
Like most railfans, you have basically no idea what speed an SD40-2 would make on a given grade with a given tonnage-- for whatever reason, railfans in this country aren't much interested in that. (Not interested enough to go out a take a proper look, anyway.) But various railroads have long steady grades with parallel highways, where you can pace the trains in your car and get a good idea of their speed. If by chance you live in California you can pace SFe trains up a steady 1.0% grade eastward from Essex; I fear few? no? freights climb that hill at 60+ mph now, but SD40-2s used to take the 991 train up there at that speed, overcoming the back EMF just as they're supposed to.
Yardmaster01 The NYC found that it took 2 FT's to replace one Niagara at 70 mph, an FT consisting of four 1200 hp permanently coupled units or EIGHT total units.
Yardmaster01studies the NYC did that found their Niagara's were more thermally efficient AT SPEED than the EMD FT locomtives
There is no way to get around the laws of physics, even in railroading.
timz You've got the wrong idea about back EMF, which is just nature's way of keeping us from getting something for nothing. We want to get mechanical work out of a motor, so we have to put electrical work into it-- that is, we have to shove the current past the "back EMF". An SD40-2 succeeds in doing that at 60-70 mph just as well as it does at 20-30 mph. [snip]
How 'bout a little help here in understanding the 'back EMF' = 'back ElectroMotive Force' concept, also known as 'counter-electromotive force' ? [And no, it's not an ailment peculiar to GM's diesels, or one that GE's are immune from . . . ]
I've done a little Internet research on this, but it's hard to find something that applies directly to railroad locomotive motors. I gather that the back EMF - mainly in the form of voltage - results from the motor's armature spinning in the magnetic field that's created by the electric current running through the stator coils. It's also proportional to the motor speed - slow speed, little back EMF; fast speed, lots of back EMF. So it's also a 'feedback loop' or 'check-and-balance' kind of arrangement on an unloaded motor just going faster and faster . . .
I also understand that the rearrangement of the motor circuits from the series to series-parallel and then to full parallel is a method to boost the voltage to overcome this - for a 600 volt DC generator and C-C trucks, the voltage across each motor would then change from 100 volts (600 volts/ 6 motors) to 300 volts (600 volts / 2 sets of 3 motors each) to 600 volts (600 volts across each motor). Is that correct, or not ?
Feel free to correct anything that's wrong, not quite right, or needs further explanation, whatever is most convenient. Thanks.
- Paul North.
Paul_D_North_Jrtimz You've got the wrong idea about back EMF, which is just nature's way of keeping us from getting something for nothing. We want to get mechanical work out of a motor, so we have to put electrical work into it-- that is, we have to shove the current past the "back EMF". An SD40-2 succeeds in doing that at 60-70 mph just as well as it does at 20-30 mph. [snip] How 'bout a little help here in understanding the 'back EMF' = 'back ElectroMotive Force' concept, also known as 'counter-electromotive force' ? [And no, it's not an ailment peculiar to GM's diesels, or one that GE's are immune from . . . ] I've done a little Internet research on this, but it's hard to find something that applies directly to railroad locomotive motors. I gather that the back EMF - mainly in the form of voltage - results from the motor's armature spinning in the magnetic field that's created by the electric current running through the stator coils. It's also proportional to the motor speed - slow speed, little back EMF; fast speed, lots of back EMF. So it's also a 'feedback loop' or 'check-and-balance' kind of arrangement on an unloaded motor just going faster and faster . . . I also understand that the rearrangement of the motor circuits from the series to series-parallel and then to full parallel is a method to boost the voltage to overcome this - for a 600 volt DC generator and C-C trucks, the voltage across each motor would then change from 100 volts (600 volts/ 6 motors) to 300 volts (600 volts / 2 sets of 3 motors each) to 600 volts (600 volts across each motor). Is that correct, or not ? Feel free to correct anything that's wrong, not quite right, or needs further explanation, whatever is most convenient. Thanks. - Paul North.
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
In Paul Kiefer's book, A Practical Evaluation of Railroad Motive Power, the only reference I saw was either 2-unit or 3-unit E7's in comparison to a Niagara. IIRC, it took three units to equal the performance of a single Niagara, but two units were close enough, and more economical.
Paul_D_North_Jra 600 volt DC generator and C-C trucks, the voltage across each motor would then change from 100 volts (600 volts/ 6 motors) to 300 volts (600 volts / 2 sets of 3 motors each) to 600 volts (600 volts across each motor).
The other possibility was field shunting-- not used on any locomotive since... 1972?
Wasn't Paul Kiefer the Chief of Motive Power on the New York Central or some high post? I suppose that book is out of print and hard to get and, oh well.
I think that the narrative was that from a HP standpoint, a single Superpower steam locomotive -- Northern, Challenger, and so on -- matched not just a Diesel but a multi-unit Diesel consist, to within certain bounds. That is, back in the day when an FT was what, 1300 HP and an E7 was 2000 HP.
The (multi-unit) Diesel had the steam locomotive beat hands down on weight on powered axles and probably on lugging ability, but as far as I could tell, you could "flog" a steam locomotive until you lost your steam (by using too much) whereas you could do expensive damage to a Diesel consist by exceeding short-time ratings.
But these days, a 4500 HP six-axle AC-motored microprocessor-wheel-slip-controlled Diesel is probably a match for anything steam in both HP and lugging ability. If they were able to pull that consist with a Challenger, they should be able to manage it with a single modern AC Diesel. That they have at least 2 (or maybe 3) such units on a modern intermodal is that they want some reserve for an on-road unit failure, be able to run through without helpers or locomotive changes for grades on certain divisions, have acceleration to meet schedules.
If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
Paul Milenkovic I suppose that book is out of print and hard to get and, oh well.
Paul Milenkovic a 4500 HP six-axle AC-motored microprocessor-wheel-slip-controlled Diesel is probably a match for anything steam in both HP and lugging ability.
As far as I know, EMD ALWAYS used field shunting, as well switching from series to parallel motor connections, on all locomotives that used dc generators. (Possibly some switchers may have been exceptions.) This may have been changed once they started with alternators and rectifiers, and certainly was dropped with any ac motor locomotives.
timzPaul_D_North_Jra 600 volt DC generator and C-C trucks, the voltage across each motor would then change from 100 volts (600 volts/ 6 motors) to 300 volts (600 volts / 2 sets of 3 motors each) to 600 volts (600 volts across each motor). That's the general idea, except that AFAIK no road diesel ever connected all its motors up in one series string-- no need to do so, I assume. Some C-Cs did go from two strings of three motors, to three pairs, to straight parallel, but none? of the post-1965 models needed that initial two-strings-of-three stage. Since circa 1980? all locomotives use parallel connection of the motors all the time; the reconnection (if any) is done in the alternator/generator instead. The other possibility was field shunting-- not used on any locomotive since... 1972?
The first loco with gen transition I can remember was the SD50.
Paul_D_North_JrHow 'bout a little help here in understanding the 'back EMF' = 'back ElectroMotive Force' concept, also known as 'counter-electromotive force' ? [And no, it's not an ailment peculiar to GM's diesels, or one that GE's are immune from . . . ]
Paul,
An analogy that might help is to think of a water turbine - the "back EMF" of a motor corresponds to the "back pressure" of a water turbine that corresponds to the work transmitted to the output shaft - with electric current being equivalent to water flow. The power available from water under pressure (conversely the power required from a pump to generate water under pressure) is the flow times the pressure drop, 1 cubic foot per second at 1,000 psi has the same potential power as 1,000 cubic feet per second at 1 psi. Similarly, DC power is volts times amps.
Getting on to DC motors, the EMF is proportional to the armature speed times the strength of the magnetic field produced by the field windings. The magnetic field strength is proportional to the field current up until the iron in the motor frame starts saturating. The torque from a motor is proportional to the armature current times the magnetic field generated by the field windings.
The series motor has the field current equal to the armature current, so for a constant armature voltage (assuming no field saturation), as speed increases, the current through the armature needs to decrease to maintain the same EMF. Since diesel locomotives operate in a constant power more for a given prime mover speed, this means that the generator voltage needs to increase with increasing track speed. One problem is that there are limits as to how high the voltage can go before the generator (or motor) starts having troubles (e.g. arcing). One way of getting around that is to re-arrange the series/parallel connections of the motors - which reduces the strain on the generator. Field shunting is another means - this allows the armature current to increase without increasing the field (hence without increasing the back EMF).
Hope this helps,
- Erik
timzClose to a match, against most steam in most situations. NY Central did do actual tests too, and the time their 4-8-4 took to accelerate 22-car trains to 75 mph will be hard for an AC44 to match.
From a standing start, I would put my money on the AC44. If they were to start a race where they were drifting at say 25mph, then I might go for the steamer. It would be a half mile down the road before that GE started to load up.
.
Yes, that is a good question. A heavyweight coach with A/C would be in the order of 147K lbs, so 22 of them would come to about 1,600 tons, plus or minus for the different cars comprising a train. I would think an AC44 would be able to start that tonnage with ease, and it would surely out-pull a Niagara until perhaps 25 mph.
-Crandell
BigJimtimzClose to a match, against most steam in most situations. NY Central did do actual tests too, and the time their 4-8-4 took to accelerate 22-car trains to 75 mph will be hard for an AC44 to match.What kind of tonnage did those 22 cars weigh?
Offhand I'm guessing the 4-8-4 would have more of an advantage in the 25-70 race than in the 0-70. It's more powerful over most of that range-- but then it has to be, to make up for its extra 250? tons.
timzNY Central did do actual tests too, and the time their 4-8-4 took to accelerate 22-car trains to 75 mph will be hard for an AC44 to match
timz:This statement leaves many questions unanswered.
1. What year was the test conducted?
2. Were the cars three axel or 2 axel trucks? 3 axels track and ride better.
3. Did the cars have axel generators?
a.. Were the generators belt driven or geared?
4. Was it summer and was the A/C running and what kind of A/C? electromechanical or some other kind that did not drag the train?
5. Friction bearings or roller bearings or a mix?
6. Tight lock couplers or type "E"?
7. Streamlining or connventional cars?
8. Car profiles all the same?
9. Other factors that someone may think of.?
"0 to 75 mph in 9.00 minutes and 37200 ft (averaging less than 0.03% downgrade). "
Gee whiz! That's seven miles! Welp, I'll double my bet on the diesel. Can I use an SD40-2? Can I? Can I?
blue streak 1This statement leaves many questions unanswered.
BigJimCan I use an SD40-2?
With 15 cars 1005 tons, the 4-8-4 allegedly reached 75 in 5.02 minutes, 19400 ft. If the single-unit diesels can win any race, that's the one to try for, since the 4-8-4's weight disadvantage has the greatest effect.
timz BigJimCan I use an SD40-2? If you do, don't bet on yourself. With 15 cars 1005 tons, the 4-8-4 allegedly reached 75 in 5.02 minutes, 19400 ft. If the single-unit diesels can win any race, that's the one to try for, since the 4-8-4's weight disadvantage has the greatest effect.
Knowing the parameters of the bet is limited to the gearing speed of the diesel, change the top speed to at least 90 mph and see which engine will win. After all, we are talking about a 1946 steam locomotive that was designed and put into service sixty four years ago and was designed to run at 90 mph or more on a passenger train against a 2009 freight locomotive that is geared for 75 mph. They also were used in freight and did well in that asignment even with the 79" drivers.
This one is a sure bet for the 4-8-4.
Hardly a good comparison.
CZ
CAZEPHYRtimz BigJimCan I use an SD40-2? If you do, don't bet on yourself. With 15 cars 1005 tons, the 4-8-4 allegedly reached 75 in 5.02 minutes, 19400 ft. If the single-unit diesels can win any race, that's the one to try for, since the 4-8-4's weight disadvantage has the greatest effect. Knowing the parameters of the bet is limited to the gearing speed of the diesel, change the top speed to at least 90 mph and see which engine will win. After all, we are talking about a 1946 steam locomotive that was designed and put into service sixty four years ago and was designed to run at 90 mph or more on a passenger train against a 2009 freight locomotive that is geared for 75 mph. They also were used in freight and did well in that asignment even with the 79" drivers. This one is a sure bet for the 4-8-4. Hardly a good comparison. CZ
Hang on, guys...I have the Broadway Limited Imports versions of each of those in HO scale. I'll test them and get right back. How about best out of three trials?
Did someone say "lunch"? On the NYC? I'll have the Welch rarebit, with bacon rashers and sliced tomatoes, and a bottle of Genesee beer, please. Yes, I wrote it down.... Thank you!
Hays
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