Overmod Backshop I was under the impression that a 38 and a 40 could haul the same train but the 40 could do it faster. And burning much less fuel in the higher notches. But of course if they have the same traction motors, you could expect both the characteristics up to where the TMs come out of low-speed limitation (in the 10 to 12mph range, iirc, but someone here will have a more exact figure) but down the rectangular hyperbola of engine power until the Roots engine starts to run out of efficient air to use for combustion...
Backshop I was under the impression that a 38 and a 40 could haul the same train but the 40 could do it faster.
And burning much less fuel in the higher notches.
But of course if they have the same traction motors, you could expect both the characteristics up to where the TMs come out of low-speed limitation (in the 10 to 12mph range, iirc, but someone here will have a more exact figure) but down the rectangular hyperbola of engine power until the Roots engine starts to run out of efficient air to use for combustion...
MCS for and SD40 is about 11 mph. For an SD38, about 8 mph. Both will have the same TE, the 40 just gets you a bit more speed with that TE.
Yes, the roots blowers run out of breath after notch 6 or so, and fuel efficiency suffers. My hazy memory thinks it's in the 15% range in notch 8.
But, same train, same route. SD38 vs SD40, both will get you there. SD38 will take longer and use a bit less fuel. The going slower part outweighs the lower fuel efficiency part.
If you're running a drag RR and you can get your crews from A to B reliably with the 38s, they are a better choice.
If you are running a train scheduled RR, you want the 40s for your road trains.
If you are running a yard, you want the 38s. They don't burn enough fuel in that service for fuel economy to matter.
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
BackshopI was under the impression that a 38 and a 40 could haul the same train but the 40 could do it faster.
I was under the impression that a 38 and a 40 could haul the same train but the 40 could do it faster. They do have the same/similar starting and continuous TE.
I thought we established a few posts ago, from a good source, that the traction motors in the SD38-2 and SD40-2 were common, and the difference in power between the units was in the engine construction. What might be likelier is that the amount of achievable dynamic braking current might be limited to match the capability of the prime mover: why pay for more braking power than for the load you could lift to the top of a particular grade? So I think it's a cost thing, but an artificial economizing.
wjstixIt would make sense to me, since an SD-38 had much lower horsepower, it's motors would generate less heat, so would require smaller fans?
The HP is of the diesel prime mover, not the electric traction motors, which are probably exactly the same as an SD40. So quite against what you're suggesting, it makes more sense that the DB capacity is the same, since it's the same set of traction motors, so that's based more on the number of axles/motors and irrelevent to the engine HP.
Chris van der Heide
My Algoma Central Railway Modeling Blog
What Backshop said got me thinking - the way regenerative / dynamic braking works on electric locomotives is that when doing downhill, the traction motors in the trucks can be adjusted to generate electricity, which can then be fed back into the overhead wire via the pantograph. With a diesel, there's no way to use the electricity generated, so it's used to create heat, which is then vented out of the loco body via a fan.
It would make sense to me, since an SD-38 had much lower horsepower, it's motors would generate less heat, so would require smaller fans? At least to me, that makes more sense than suggesting some railroad forced EMD to build them that way against their better judgment.
Which brings us back around to the question of why. Obviously prior to the 38/40 series, 36" dynamics were fairly typical on SD units.
YoHo1975 It really looks like it would be hard to fit 48" fans with the paper Air Filter in the way...on the other hand the 38-2 does so.
It really looks like it would be hard to fit 48" fans with the paper Air Filter in the way...on the other hand the 38-2 does so.
It does look tight. Although, I can't imagine they wouldn't fit...
JayBee Here you can see two SD38AC locomotives on the Missabe. The smaller 36" dynamic brake fans are obvious. Missabe 200 Every photo I can find showing DM&IR, EJ&E, B&LE or BNSF SD38-2s seem to show 48" dynamic brake fans.
Here you can see two SD38AC locomotives on the Missabe. The smaller 36" dynamic brake fans are obvious.
Missabe 200
Every photo I can find showing DM&IR, EJ&E, B&LE or BNSF SD38-2s seem to show 48" dynamic brake fans.
Here's a total SWAG...
The RR spec'd 36" fans to be compatible with the older locomotives in the fleet. Perhaps they didn't use DB very often.
RR: "We want the same fans on our new locomotives as our current fleet"
EMD: "No." (they always say "no" right away - to everything non-standard)
RR: "okay. Cancel the order."
EMD: "Well....we can't do the engine cooling fans - air flow - housing design - new radiator core design - blah blah blah, but you can have 36" DB fans. You just will be limited how much DB they have..."
RR: "Okay then! Deal!"
YoHo1975It looks like the big 38 style access cabinet (never understood what that was) might be limiting the space for the fans.
That's a housing for paper air filters. (engine air intake)
200 also has an older style 3" fan for the radiator. Which is very interesting.
The orange and black unit behind it also Shows the 36" fans.
It looks like the big 38 style access cabinet (never understood what that was) might be limiting the space for the fans.
timz Seems unlikely EMD would give the SD38 punier dynamics. 4000 braking horsepower would be just as useful on an SD38 as on an SD40, so if the SD40 needs two 48-inch fans you'd think the SD38 would need them too.
Seems unlikely EMD would give the SD38 punier dynamics. 4000 braking horsepower would be just as useful on an SD38 as on an SD40, so if the SD40 needs two 48-inch fans you'd think the SD38 would need them too.
Didn't we have a prior thread where either Pneudyne or bogie_engineer discussed the history of fan types on these EMDs?
Yeah, this is specific to the Dynamic Brake fans.
Backshop As far as I know, all have 48" fans. Some have the shorter radiator section without the divider in the middle, but all have the full size fans. It makes sense...SD40 3000hp with 3 fans, SD38 2000hp with 2 fans.
As far as I know, all have 48" fans. Some have the shorter radiator section without the divider in the middle, but all have the full size fans. It makes sense...SD40 3000hp with 3 fans, SD38 2000hp with 2 fans.
I think that you will find that the three fans are radiator fans, not for the dynamic brake.
.
Hi all, I had it pointed out to me that some (all?) SD38s had 36" Dynamic brake fans vs. the more common 48"
And these fans were "high shroud" but not the same fans as Say the F2/F3 nor the midddle fan on the 35 series.
I did a google search for more info on this, but it turned up empty. I don't have the physical books I'd need to learn more about this and was curious if anyone could provide details on this? Why the dual 36"? was it all units or just some?
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