I'm wondering how HP and TE relate to number of axles? I've asked about TE before and have finally understood that, but now I'm wondering about say Continuous TE of a GP40 compared to an SD40. The formulas I have use HP (I assumed the hp made at a given rpm that matched with a given throttle notch) that only figure HP and speed but not number axles, so in the formulas I have (TE= HP x 308/MPH) would make no difference between a 4 axle unit and 6 axle unit. Is the power assentially increased by 50% because an SD has 50% more axles than a GP?
Using the formula, a 3000 hp unit has
92,400 lb TE at 10 mph
924,000 lb TE at 1 mph
9,240,000 lb TE at 0.1 mph
The formula assumes the unit is transmitting 308/375 of its rated power to the wheel rims, which is a reasonable assumption at 30 mph, for both units-- but as speed drops the assumption eventually fails. It fails sooner for the four-axle.
Let's say the SD40 really can produce 92,400 lb TE at 10 mph: it might be running 1100 amps thru each traction motor at that speed. Dunno how many amps would have to go thru each of a GP40's motors to get 92,400 lb-- too many-- but in any case the wheels would have started to slip before the amps reached that level. Motor heating and slipping-- those are the limits on a unit's TE at low speed, and a six-axle unit has an advantage on both of those.
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
You can get as technical as you want but a locomotive is always going to be limited by how much it can pull by how heavy it is.The more weight you have the more power you can put to your wheels and the more it can pull.You can have all the horsepower in the world but if you don't have the weight to keep the wheels from spinning your locomotive is out of luck.It is this very reason the big steam locomotives could pull the very heavy and long trains that they did back in the day.The modern day locomotives may have nearly twice the tractive effort of a Big boy but do I believe they could pull a two mile train with one locomotive?No way.A big boy could because it had around 80 tons of weight per driving axle.Your average modern day 6 axle locomotive weighs a little over 200 tons giving it around 33 tons per axle.
Your six axle locomotives pull more than a four axle because they are almost always turbocharged,have more weight,and have two more traction motors.
Thomas 9011A big boy could because it had around 80 tons of weight per driving axle.
Thomas 9011Your six axle locomotives pull more than a four axle because they ....,have more weight,and have two more traction motors.
horsepower = pulling force x speed
pulling force is proportional to traction motor current
maxiumum pulling force for a locomotive is limited by the thermal limit for traction motor current or adhesion
Thomas,
Your assumptions have some flaws. Weight on drivers affects 'adhesion' - TE is the same no matter what the weight is(see the above formula). The weight on the drivers will affect the 'wheel slip'. Most locomotives are in the 60,000-70,000 lb axle loading range. A lot of this has to do with bridge ratings. Now, how much 'deliverable' TE is another matter...
As far as 80 tons per axle on a Big Boy - You are just plain wrong. That would be 160,000 lb axle loading - I can think of no bridges capable of carrying that load. IIRC, the C&O 2-6-6-6 engines had something like 72,000 axle loading, and they were the heavy axle loading engines of the steam era. Most sources rate the Big Boy at about 7,000 hp at 40 mph, and with an axle loading of 67,500 lbs/axle. The TE generally is listed as about 135,000 lbs.
Jim
Modeling BNSF and Milwaukee Road in SW Wisconsin
jrbernierMost sources rate the Big Boy at about 7,000 hp at 40 mph, and with an axle loading of 67,500 lbs/axle. The TE generally is listed as about 135,000 lbs.
I think I found part of where I got confused. I was also given the formula for TE (might have been starting TE) of Locomotive Weight x Adhesion, sticking with the GP40 240,000 x 25%= 60,000 lbs. I was under the impression a locomotive couldn't produce more TE than that figure, but as I understand now that TE figure is just for the locomotive sitting at rest. So I assume now then that the CTE figure given which is at a mph, like say 73,000 lbs @ 12 mph is the slowest continual speed a loco could go before roasting its motors? I think I just got confuzzled again.
MILW-RODR I was also given the formula for TE (might have been starting TE) of Locomotive Weight x Adhesion
MILW-RODRas I understand now that TE figure is just for the locomotive sitting at rest.
Say an SD40 is in Run 8 at 20 mph when they hit the foot of an upgrade, and speed starts to drop. TE, and current thru the motors, increases as speed drops. When speed reaches 11 mph (with a PF17-equipped, 62:15-geared unit) each motor is getting 1050 amps; it so happens that at that amperage the motor blower can just keep up-- motor temperature will rise to the allowed maximum, but not beyond. So the unit can keep going indefinitely as long as speed doesn't drop further.
(So actually the "Continuous TE" rating depends on ambient temperature, but by how much we don't know.)
I was way off.Too many numbers to remember.I was thinking 80,000 pounds not 80 tons.I checked the figures and weight per driving axle was 67,800 pounds for the big boy.
oltmanndjrbernierMost sources rate the Big Boy at about 7,000 hp at 40 mph, and with an axle loading of 67,500 lbs/axle. The TE generally is listed as about 135,000 lbs.Roughly equivalent to a pair of GP60s!
GP40-2oltmanndjrbernierMost sources rate the Big Boy at about 7,000 hp at 40 mph, and with an axle loading of 67,500 lbs/axle. The TE generally is listed as about 135,000 lbs.Roughly equivalent to a pair of GP60s! The Big Boy might have put out 5,800 HP @ 40 MPH in typical running condition. Maybe 6000 HP if in exceptional condition. That 7,000 HP figure is total BS.
Big Boy:
indicated HP: 6680@40
Calculated DBHP: 6000@40
Actual DBHP: 6100@40
Peak DBHP: 6290@41
If we may calculate the indicate HP of the peak, we may get a value of ~7000ihp. They were equal to 5 F3-units at this speed. The 1943 tests are not such a good indicator of Big Boys capacity.
Cheers
lars
oltmannd OK, a pair of GP40-2s, then...
Yep, that sounds right on.
1 Big Boy = 2 GP40-2s
Or
1 Big Boy = 1 AC6000, with the AC6000 having a large advantage in TE, adhesion and operating efficiency.
Big Boy may become equal to a AC6000 at speeds between 25-60mph, though the 5000DBHP+ of BB at 60mph (extrapolated) seems a little bit low.
Lars LocoBig Boy may become equal to a AC6000 at speeds between 25-60mph, though the 5000DBHP+ of BB at 60mph (extrapolated) seems a little bit low. Cheers lars
Lars LocoGP40-2oltmanndjrbernierMost sources rate the Big Boy at about 7,000 hp at 40 mph, and with an axle loading of 67,500 lbs/axle. The TE generally is listed as about 135,000 lbs.Roughly equivalent to a pair of GP60s! The Big Boy might have put out 5,800 HP @ 40 MPH in typical running condition. Maybe 6000 HP if in exceptional condition. That 7,000 HP figure is total BS. Big Boy: indicated HP: 6680@40 Calculated DBHP: 6000@40 Actual DBHP: 6100@40 Peak DBHP: 6290@41 If we may calculate the indicate HP of the peak, we may get a value of ~7000ihp. They were equal to 5 F3-units at this speed. The 1943 tests are not such a good indicator of Big Boys capacity. Cheers lars
Kratville has stated in the past that he believed, as a class of locomotives in their typical operating condition, the Big Boy was a 5,800 HP locomotive. He stated the particular one that produced the 6100 HP in a test was in exceptional operating condition at the time.
GP-40,
Sir, thank you for the information.
I did not read that Kratville has stated that before, at least not in his BB-book.
Source for the 6680ihp is K.'s "Challenger"-book, the comparison with the F3-units came from "Motive Power West", I think.
Sir,
I really would like to join a ride how a AC6000s really pour on power, you can bet.
This table was puplished by GE, though may be outdated: Trailing tons vs speed:
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
Yes, the AC6000 gives the BB a hard time here, but I suppose it could handle those tonnages at those speeds as well.
Do you have any actual tractive-forces table for the GE?
Kind Regards
Lars Loco Do you have any actual tractive-forces table for the GE? Kind Regards lars
Can I discuss specifics? Sorry, No.
If Jay Potter is following this thread, he may be able to chime in. Jay has a way of "extracting" CSX inside information. LOL
Here is a teaser about how much power at speed the big GE ACs have. Granted, these are only the 44s, but you can see a pair of them have no trouble pulling 130 loaded coal cars at 50 mph.
GP40-2Lars Loco Do you have any actual tractive-forces table for the GE? Kind Regards lars Do I have CSX test data? Yes. Can I discuss specifics? Sorry, No. If Jay Potter is following this thread, he may be able to chime in. Jay has a way of "extracting" CSX inside information. LOL Here is a teaser about how much power at speed the big GE ACs have. Granted, these are only the 44s, but you can see a pair of them have no trouble pulling 130 loaded coal cars at 50 mph. www.youtube.com/watch?v=gOYeLGlzHxE
If Jay Potter is following this thread, he may be able to chime in. Jay has a way of "extracting" CSX inside information. LOL Here is a teaser about how much power at speed the big GE ACs have. Granted, these are only the 44s, but you can see a pair of them have no trouble pulling 130 loaded coal cars at 50 mph. www.youtube.com/watch?v=gOYeLGlzHxE
Sir, I hope Mr. Potter can join us, as a knowing and informative person he is indeed.
As I read, CSX is consequently not only shifting freight, as well as a lot of bits and bytes while improving their steering-software. As I told, my data may be outdated, and , if I am not completely out of whack, 33.000lbf of pulling force in the high 60ties for an AC6000. The best I can say for BB is 25.000 to 30000lbf @70mph.
Thanx for the link!
-edit-
A single GE AC4400 is probably capable enough, to take 4000tons of load with the speed of a Big Boy up to Wasatch, replacing them one by one. With an AC6000, you may take 300,400, 500tons more.
I'm not at all familiar with how steam locomotives perform; and my familiarity with diesel performance is pretty much limited to the adhesion segment of tractive-effort curves, as opposed to the horsepower segment. So I don't rely on, or even deal with, formulas very much. But if I were going to apply a tractive-effort formula to an AC6000CW in notch eight at a speed of around 11 or more miles per hour, it would be (TE in pounds) equals (6000) times (factor X) divided by (speed in miles per hour), with factor X being a number somewhere between around 329 and around 337. Again, I'm not sure how useful the result of that calculation would be.
Tractive effort is how hard a locomotive can pull. For a diesel electric locomotive this number is maximum at very low speed and is limited only by either the adhesion of the wheels to the rail or by the amp rating of the traction motors. A GP7 at 1500 HP and GP 40 at 3000 HP have very similar tractive effort, about 68,000 lbs at 10 MPH or there abouts. Newer locomotives have some extra electronics in them that can boost this number by about 15% by watching wheel RPM and ground speed.
Railroads are limited by how much weight a wheel can put on a rail. Adhesion between the wheel and rail is a direct function of the weight on the wheel. Thus, having 6 axles allows a locomotive to be heavier than having four axles. The main determiner of tractive effort is the adhesion between the wheel and rail. More weight = more adhesion. Thus an SD 7 at 1500 HP and an SD 40-2 at 3000 HP have about 98,000 lbs maximum sustained tractive effort. Again, AC drives and wheel slip electronics allow this number to be increased by about 15%.
Steam engines were different. Their tractive effort peak occured at a much higher speed. They were not as good at starting a train as a modern diesel. Thus on the DMIR, two SD9 locomotives with a combined 3500 HP can readily handle the same weight train as a Yellowstone 2-8-8-4 with a theoretical 6000+ horsepower available. They just climb the hills a little slower. For iron ore trains, this is no big deal.
Thus three four axle locomotives have about the same tractive effort as two six axle locomotives. Three GP 38's perform essentially the same as two SD 40's, both with 12 driving axles and 6000 HP.
Tractive effort determines whether or not you can climb the hill at any speed. A farm tractor can climb a very steep hill, but will do it slowly. It has high tractive effort but low horsepower.
The other part of the equation is horsepower. As speed increases, tractive effort is limited more and more by the horsepower the diesel engine can apply to generating electricity for the traction motors. As traction motor speed increases, tractive effort decreases because it is limited by the output of the diesel engine.
This is where horsepower comes in. Given a train weight and track grade, doubling the horsepower will roughly double the speed that the train will have climbing the hill, again keeping things like traction motor heat ratings, drawbar strength and the like in mind.
Horsepower determines how fast you will climb the hill. Going back to the tractor analogy, a Corvette can climb the same steep hill much faster than a farm tractor.
There are some interesting developments in this. GE just delivered some EVO type locomotives to BNSF with A1A trucks. These trucks do not have a traction motor on the center axle.
Track can handle much heavier wheel loadings at low speed than at high speed. Also AC drives and traction motors can handle much more current and deliver much more torque to the wheel than the wheel can normally transmit to the rail. In low speed tough pulling situations, these locomotives actually hydraulically lift most of the weight off the center axle, transmitting it to the outer axles and increasing the tractive effort on those axles.
At higher speeds where tractive effort is limited more by diesel horsepower than by adhesion, the weight is put back on the center axle to keep the axle loadings at speed within a tolerable range. The main advantage of this is two fewer traction motors per locomotive at the expense of some relatively minor suspension complications.
These locomotives are said to have similar performance to a standard GE EVO locomotive with six powered axles.
Clear as mud, but an engineering description.
Back in the good old days it was my impression that builders and railroads calculated steam locomotive starting tractive effort by arbitrarily using 75% of maximum boiler pressure. Under normal conditions steam locomotives operated much closer to 100% than 75%. If this is the case, any attempt to accurately compare diesel starting TE with published steam TE would be somewhat meaningless.
JayPotterI'm not at all familiar with how steam locomotives perform; and my familiarity with diesel performance is pretty much limited to the adhesion segment of tractive-effort curves, as opposed to the horsepower segment. So I don't rely on, or even deal with, formulas very much. But if I were going to apply a tractive-effort formula to an AC6000CW in notch eight at a speed of around 11 or more miles per hour, it would be (TE in pounds) equals (6000) times (factor X) divided by (speed in miles per hour), with factor X being a number somewhere between around 329 and around 337. Again, I'm not sure how useful the result of that calculation would be.
Lars,
Here is a video of a single CSX AC6000 pulling 92 coal cars at a good clip.
Valleylineit was my impression that builders and railroads calculated steam locomotive starting tractive effort by arbitrarily using 75% of maximum boiler pressure.
ValleylineUnder normal conditions steam locomotives operated much closer to 100% than 75%.
ValleylineIf this is the case, any attempt to accurately compare diesel starting TE with published steam TE would be somewhat meaningless.
Thank you GP40-2,
trainspotting at youtube is always fun and with a big sub-woofer almost becomes real...
Some years ago, I gained those GE-tables for an AC6000 tonnages vs speed/grade it became clear, that nothing, maybe except the Allegheny at upper speeds, comes close to it.
- a link hopefully for your interest, why not 12-Axle Power?
http://books.google.de/books?id=HtwDAAAAMBAJ&pg=PA81&dq=8500+horsepower+turbine+popular+mechanics&cd=1#v=onepage&q=&f=false
One more thing, beside those horsepower-factors puplished here by Mr. Oltmannd and Jay, is it safe to assume that modern engines will always deliver ~90% of the prime movers output into drawbar-force over their entire speed-range ?
My understanding of the TE vs speed for a steam locomotive is that it is maximum at 0 speed when the full operating boiler pressure is applied to the cylinder. As steam starts to flow, cylinder pressure drops due to friction of flow thru the throttle, pipes and valves.
AC motors have a starting torque about 50% of their max due to the severe lag between the rotating field and the stationary rotor fields. As the AC motor starts to turn that lag is reduced and the two fields (stator and rotor) align for stronger pull. The variable frequency systems in AC motors reduce the lag at low speeds and allow the AC motor to have higher torque at low speeds.
The electric motor starting advantage is due to the fact we can overload the system for a few minutes (at ratings well beyond that of the generator and motors). We cannot overload the steam engine by doubling the boiler pressure for a short time.
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