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.
Timz has it right. The formula (HP curve) works perfectly between limits. On the low speed end, the limits are motor current and adhesion. At the high speed end its voltage and how fast the motor can spin. Since a 6 axle has 50% more motors to “take” the current, it can go operate on the HP curve to a lower speed before you start toasting the motors. At the high speed end, the voltage and traction motor speed limits are identical for the motors in a SD and a GP, so the HP curve holds up to the same top speed. Between these limits, it makes no difference if you use an SD or a GP.
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.
You might want to check this number…
These two go together
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
Roughly equivalent to a pair of GP60s!
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.
Don’t bother with that-- it’s just a tautology.
Far as we know, any locomotive puts out its maximum TE 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.
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.
OK, a pair of GP40-2s, then…
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
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.
Either way, the Big Boy was not the mythical “super locomotive” that some people make it out to be.
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.
Cheers
lars
Having actually worked with CSXs AC6000, I would say the exact opposite. At 60 MPH, the BIg Boy was well past its power peak, while the AC6000s really pour on the power at 60 to 75 MPH in intermodal / stack train service.
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.
There is nothing exceptional about the Big Boys boiler design. It did have a large grate area, but that was designed to burn the El Crappo coal the UP used in them. A number a large locomotives had more direct heating surface and gas volume areas in their boilers (the Allegheny and all of the Yellowstone types come to mind).
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.
Cheers
lars
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
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.