I recently saw a photo of a restored SOU locomotive designated SD-(something), but it was 4-axle. Or was I hallucinating?
I thought SDs were always 6-axle.
IIRC, this engine was being used by a short line, which may have done freight plus tourist-passenger. I was thinking maybe they switched trucks to better navigate sharp curves. But would it still be an SD?
The reason the EMD SD locomotive had six axles is the weight. Unless you somehow reduced the weight, the two axle trucks would be seriously overloaded and I doubt a shortline/tourist operation would have track able to handle the concentrated weight.
Was that EMD’s designation or was it the Carrier’s designation.
In the early days of dieselization the carriers, for the most part, devised their own designations for their diesel power, just like they had for their steam power.
This is not really true. Or rather, it is true and is more true today, but it is not the original reason. the SD7 was designed for traction over speed. Same HP as a GP7, but 50% more traction motors means it can produce more tractive effort. It is also less weight on each axle compared to the GP7 so it can be used on lighter rail. The SD7 weighed more, because there were 2 more traction motors.
With modern locomotives, they simply weigh too much in a freight configuration to be practical at all in a 4 axle model.
Didn’t MILW and some other granger roads, buy SD7’s & 9’s with a smaller than normal fuel tank - so as to reduce the axle loadings on the lightly built track in grain lands.
I can’t say yes or no with respect to the Milw SD-7/9’s, but do remember that the Milw bouht some SDL-39’s for branchline use. I’m assuming the 12 cyl turbo 645 was lighter than the normally aspirated 16 cyl 645, ombined with small tank and lightweight frame.
Probably just a mix up, but a link to the original photo would help…
I don’t think Southern used their own internal locomotive model designations, but they did add a check letter after the road number to prevent wrong numbers from being entered in the computer system.
http://www.srha.net/membersonly/resources/diesel_code_intro.asp
Milwaukee Road, yes.
RailPictures.Net Photo: MILW 512 Milwaukee Road EMD SD7 at Milwaukee, Wisconsin by Tom Farence
So did the Burlington.
Jeff
The SDL39’s rode on EMD GC export 3 axle trucks which were considerably lighter in weight and shorter in wheelbase than the SD Flexicoil trucks in production when they were built. The wheelbase on the GC truck is 146" versus 163" on the SD Flexicoil and fully assembled with 3 motors the GC are about 10K lbs. lighter per truck. Don’t know for sure but the GC truck is only good for a 293,000 lb. loco so the SDL39 must have been no heavier than that.
The SD name was EMD’s designation for 6 axle locomotives of North American size; I’m not aware of any 4 axle locos getting the SD designation from EMD, but RR’s and railfans like to make up their own names in spite of the manufacturer’s designation.
If that’s true, they would be one of the very few railroads that didn’t have their own designation for locomotives.
BTW, OP, are you sure it was “SD” and not “DS” - like a Baldwin DS-4-4-660? (4 axle, 4 motors, 660 HP)
All these posts and no picture? Surely LO can track down the picture he saw and give us a link to it…
I wish I had posted the question at the time. I cannot find where I saw that engine. Sorry.
Do you remember anything else about the locomotive, like the number or a general description? Streamliner? Roadswitcher? End-cab? B-unit?
Well, having worked at GM, here are the official EMD designations (some of them):
https://locomotive.fandom.com/wiki/EMD_Name_Designations
L in SDL39 means Light.
I was always told SD meant Special Duty vs Super Duty so I think that is incorrect on the linked list or I have it wrong. GP meant General Purpose and responsible for the JEEP nickname.
A road-switcher. It is a beautiful-condition unit in Southern Railway black/white/gold. It has a high short hood. It looked bigger than a GP9 or GP7. That’s all I remember.
I’m going to browse my history, but that’s usually a black hole; I look at too many different things.
Got nowhere in the history. Not sure why, but not all my history gets recorded. I think if where I was was linked within something else, then it will not show up in history.
Also, maybe I saw that engine in some YouTube video which contained lots of different things. Plus, if you watch one YouTube video, others get suggested off to the right. If I watch any of those, they don’t show up in history. Like yesterday I know I wound watching a video by that Jawtooth character; that’s not in my history.
I am probably just wrong about that engine …
Super Duty is a Ford truck term.
Was it the video of TVRM’s SOU 5000? That’s a GP38-2 though.
Yes, I’ve only ever heard SD (in EMD terms) to mean Special duty.