This DDA40X...

[dtrainBNSF1]

So for Christmas I got myself the DDA40X and since then I've been trying to figure out how to get this thing flying up the hill as it should. I've read the manual, done the math and so far in execution it's been hit or miss.

My goal is to get a consist headed by 4 DDA40Xs up the 1.52% grade of Sherman Hill at 55mph (track speed). I'm particular about this power consist because it's been noted that in the 70s the hottest train on the UP (a Los Angeles train) was upgraded from 3 DDA40Xs to 4. The math indicates that unassisted 1 unit can handle 947t. at track speed. Tried it:worked. So I doubled it. Worked. Tripled it. Worked.

So far it's been "hit". Now comes the "miss".

Quadrupled it. Suddenly I can't get above 45.7mph on the 1% at Wycon. On top of that I'm noticing that at 45mph anything above run2 the amps suddenly dance between 264 and 284, even at run8. What's more, the speed is now dancing at 45.6 and 45.7, like it needs to shift gears or something. It's like trying to drive a steamer at high speed at full cutoff and full throttle - ain't happenin'. This did not happen on my other runs so I don't know what's happening. I think I must have missed something in the other test runs.

Is there a trick to driving this thing that I'm missing here? In any other diesel I've driven it's been as simple as "put it in run8 and watch it go", although in previous tests beyond Borie I haven't had to go over run6 to maintain 55mph in this diesel.

Anybody out there well versed in driving the DDA40X that can shed some light?

[trev123]

How many wagons ?

[Bananarama]

How many wagons ?

He indicated that it was 947 tons and unchanged between adding locos.

[Ericmopar]

It's partly a case of diminishing returns.
What I mean by that is this.
Starting out with one DDA40X and adding another to the lashup is a 100% power increase.
Adding a third loco becomes a 50% power increase over two.
Adding a fourth DDA40X to the lashup is only a 33% hp increase over the first three and so on.
I doubt in real life that U.P. expected a train going uphill to reach line speed. The horsepower for that would be astronomical.

If a train needs 10,000hp to reach 55mph on level ground, it will need 20,000hp to reach 55mph on a 1% grade.
The same train would need 40,000hp to reach 55mph on a 2% grade and so on.
The hp requirements double for every whole percentage point increase in grade. (Assuming a person actually wants to maintain line speed)

In the real world, fast freights like Z trains usually are plugging along at a respectable 20mph up a 1.5 - 2% grade, while a heavy manifest or unit coal train will more likely be dragging it's heels at closer to 10mph. Hence the term "drag" applied to such trains.

That is over simplifying the matter. Lots of things like degrees of curvature, wind and other factors slow a train and will require additional HP or a speed penalty.

[dtrainBNSF1]

I should define just a bit more...

Test 1 was with one unit with 947t. Test 2 was with 2 units at 1894t. and so on and so forth. I ended up with a total trailing tonnage of 3788t. in the final test with 4 units.

I did finally get it to the intended speed of 55mph between Cheyenne and a bit to the west of Borie before the 45mph zone. Coming out of the 45mph zone I couldn't get back up to 55mph until Buford, but all things considering that seems okay.

What I ended up doing was gunning the throttle in Cheyenne coming out of the 35mph zone and 40mph zone. I'd have to understand more about transmissions in order to understand what's going on. It's like I'm forcing the loco to shift gears.

It's partly a case of diminishing returns.
What I mean by that is this.
Starting out with one DDA40X and adding another to the lashup is a 100% power increase.
Adding a third loco becomes a 50% power increase over two.
Adding a fourth DDA40X to the lashup is only a 33% hp increase over the first three and so on.
I doubt in real life that U.P. expected a train going uphill to reach line speed. The horsepower for that would be astronomical.

If a train needs 10,000hp to reach 55mph on level ground, it will need 20,000hp to reach 55mph on a 1% grade.
The same train would need 40,000hp to reach 55mph on a 2% grade and so on.
The hp requirements double for every whole percentage point increase in grade. (Assuming a person actually wants to maintain line speed)

In the real world, fast freights like Z trains usually are plugging along at a respectable 20mph up a 1.5 - 2% grade, while a heavy manifest or unit coal train will more likely be dragging it's heels at closer to 10mph. Hence the term "drag" applied to such trains.

That is over simplifying the matter. Lots of things like degrees of curvature, wind and other factors slow a train and will require additional HP or a speed penalty.

Yeah, no denying that the horsepower required would be astronomical (at least 6.9HPT), but it'd be hard not to reach that requirement with a total of 26400hp on the front end with 4 of these beasts. Accounts at Utahrails.net indicate that trains with Centennials assigned to them did have pretty high horsepower-per-ton ratios (granted today a HPT of 3 or more is high) and were fast accelerators (the acceleration time of these units was so fast that it shaved off 45 minutes from the schedule of North Platte-Los Angeles trains and caused dents in any unit placed in front of them). These units faced grueling schedules with their fast freights, leading to their deterioration and initial retirement. I think it might be reasonable to assume that these engines could achieve more than 20mph on a 1.5% grade. Maybe 30-35mph would more realistic than 55mph based on videos I've seen of stack trains climbing westbound on Sherman Hill.

[Ericmopar]

I should define just a bit more...

Test 1 was with one unit with 947t. Test 2 was with 2 units at 1894t. and so on and so forth. I ended up with a total trailing tonnage of 3788t. in the final test with 4 units.

I did finally get it to the intended speed of 55mph between Cheyenne and a bit to the west of Borie before the 45mph zone. Coming out of the 45mph zone I couldn't get back up to 55mph until Buford, but all things considering that seems okay.

What I ended up doing was gunning the throttle in Cheyenne coming out of the 35mph zone and 40mph zone. I'd have to understand more about transmissions in order to understand what's going on. It's like I'm forcing the loco to shift gears.

It's partly a case of diminishing returns.
What I mean by that is this.
Starting out with one DDA40X and adding another to the lashup is a 100% power increase.
Adding a third loco becomes a 50% power increase over two.
Adding a fourth DDA40X to the lashup is only a 33% hp increase over the first three and so on.
I doubt in real life that U.P. expected a train going uphill to reach line speed. The horsepower for that would be astronomical.

If a train needs 10,000hp to reach 55mph on level ground, it will need 20,000hp to reach 55mph on a 1% grade.
The same train would need 40,000hp to reach 55mph on a 2% grade and so on.
The hp requirements double for every whole percentage point increase in grade. (Assuming a person actually wants to maintain line speed)

In the real world, fast freights like Z trains usually are plugging along at a respectable 20mph up a 1.5 - 2% grade, while a heavy manifest or unit coal train will more likely be dragging it's heels at closer to 10mph. Hence the term "drag" applied to such trains.

That is over simplifying the matter. Lots of things like degrees of curvature, wind and other factors slow a train and will require additional HP or a speed penalty.

Yeah, no denying that the horsepower required would be astronomical (at least 6.9HPT), but it'd be hard not to reach that requirement with a total of 26400hp on the front end with 4 of these beasts. Accounts at Utahrails.net indicate that trains with Centennials assigned to them did have pretty high horsepower-per-ton ratios (granted today a HPT of 3 or more is high) and were fast accelerators (the acceleration time of these units was so fast that it shaved off 45 minutes from the schedule of North Platte-Los Angeles trains and caused dents in any unit placed in front of them). These units faced grueling schedules with their fast freights, leading to their deterioration and initial retirement. I think it might be reasonable to assume that these engines could achieve more than 20mph on a 1.5% grade. Maybe 30-35mph would more realistic than 55mph based on videos I've seen of stack trains climbing westbound on Sherman Hill.

I was just generalizing when I wrote the above. That being said U.P. does run some pretty fast trains over Sherman. On Donner and Cajon getting to speed is moot, because of the track curvatures involved as well as the grades.

[Bananarama]

Maybe 30-35mph would more realistic than 55mph based on videos I've seen of stack trains climbing westbound on Sherman Hill.

Generally speaking, westbounds have always used the 3rd main through Harriman, while eastbounds move over mains 1 and 2. Lighter Z-trains being the exception, however.

[dtrainBNSF1]

Maybe 30-35mph would more realistic than 55mph based on videos I've seen of stack trains climbing westbound on Sherman Hill.

Generally speaking, westbounds have always used the 3rd main through Harriman, while eastbounds move over mains 1 and 2. Lighter Z-trains being the exception, however.

All good info

I was just generalizing when I wrote the above. That being said U.P. does run some pretty fast trains over Sherman. On Donner and Cajon getting to speed is moot, because of the track curvatures involved as well as the grades.

I wish I understood how UP's "equivalent powered axle" system works. All I know about it is that supposedly it can predict more efficiently how much power is needed, what speed the train will travel, and where to place units in train. I have the figures for ES44ACs, SD70Aces, SD70Ms, SD40-2s and SD60Ms, I know that UP will allow no more than 8 units on the headend (powered or otherwise), and that in general no more that 52 equivalent powered axles can be on the head end and up to 62 or so for intermodal trains. How it all works for speed and unit placement...I can't find squat about .

[dtrainBNSF1]

Maybe 30-35mph would more realistic than 55mph based on videos I've seen of stack trains climbing westbound on Sherman Hill.

Generally speaking, westbounds have always used the 3rd main through Harriman, while eastbounds move over mains 1 and 2. Lighter Z-trains being the exception, however.

Do you know anything about the line through Red Butte? It's steeper than main 1&2 from Laramie to Hermosa but it has higher speed limits. Would you suppose that lighter Z trains with more time-sensitive cargo and thus higher HPT travel that route? Just curious.