What does SD mean, like SD70 and SD40?
Special Duty, as compared to GP - General Purpose.
RS = Road Switcher, BTW.
IIRC, it comes from the early days of Dieseldom, when pretty much everything freight had four axles. It would take some special requirement to require six axles, so such a locomotive would be built to handle some special duty...
Today, of course, the designations are relatively meaningless in that context. One could argue that these days, the SD is really general purpose and the GP is used to fill special duties....
Locomotive designators is really kind of an interesting study...
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Special Duty, Super Duty, or Six axel duty, depending on who you talked to on different railroads or around EMD.. GP was General Purpose as EMD sent out its first GP7's and 9's with that designation, the SD9's having six axels. All GP designated units had four axel trucks and became Geeps although purists insist that the only real Geep was either a 7 or a 9. I am a purist.
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When EMD introduced its first six-motor locomotive in 1952, it designated it as the SD7; and the "SD" signified "special duty", which referred primarily to the fact that the six motors made it better suited than four-motor units for low-speed heavy-tonnage assignments. When EMD introduced the "40" series locomotives (including the SD-38, SD40, and SD45), it ceased marketing SDs as "special duty" locomotives and began referring to them as "mainline" locomotives; however it never changed the letter designation. So I guess that "SD" no longer means a special-duty EMD locomotive but still means a six-motor EMD locomotive.
Just corroborating / 'piling on', but also with a citation to the Trains article on 'Locomotive Model Abbreviations' in the ''ABCs of Railroading'' series - http://www.trains.com/trn/default.aspx?c=ss&id=13 - at:
http://www.trains.com/trn/default.aspx?c=a&id=207
GP = General Purpose SD = Special Duty
- PDN.
Paul_D_North_Jr http://www.trains.com/trn/default.aspx?c=a&id=207 GP = General Purpose SD = Special Duty
When EMD introduced the "60"-series locomotives, it stopped referring to GP's as "general purpose" locomotives and began including them, along with the SDs, in the "mainline" locomotive category.
Yes
SD = special duty
GP = general purpose
RS = road switcher
Also, for example ON EMD’s SD Series, “M” Designation means wide cab like SD70M, SD60M SD40-2M etc.
You probably know this already but with the GE product ES mean Evolution Series, AC means alternating current.
On the older loco’s Alco “C” Means Century Series.
Hope this helps,
Justin
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IIRC the early SD units could be ordered either with C-C arrangement (two three-axle trucks, all six axles powered) or A1A-A1A where the center axle in each truck was an unpowered idler. The A1A trucks were usefull for railroads that didn't need the additional lugging power of six motors vs. four, but wanted to spread out the weight per axle so they could use them on lighter rails.
Alco originally used "DL" (Diesel Locomotive) in the names of their diesels, if memory serves what came to be called an RS-11 was referred to by Alco as a DL-600(??) Also RSD units had six wheel trucks, RS units had two axle trucks. The Century series was mainly different from the contemporary RS and RSD lines of the sixties in that the Century series had the cab pushed forward to allow room for a steam boiler for passenger service...even though few were ever ordered with steam generators.
It meant Special Duty, more referring to early diesels when six axle power wasn't the norm. GP was indeed General Purpose, and referred to as Geeps. I believe pronounced the same as the military vehicles but spelled differently.
Don't confuse C-C with A-1-A! C-C meant all three axels were powered while A-1-A indicated a powered axel-an idler axel- a powered axel. I never heard a PA or E unit ever considered SD; SD was Special Duty with six powered axels. GP was prounounced Geep, but only GP7's and 9's are officially accepted as Geeps, everything after that are "G-P's" but often miscalled Geeps. As I said, I am a purist.
You are right, E units were definitely not SDs. THe A1A truck was used to help distribute the weight over more axles on these big units, but only 4 powered. This of course also helped with their speed with a highed HP per axle rating.
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I never even tried to figure out all the Alco designations, then you figure in MLW and it really gets confusing. EMD to the best of my knowledge never did have an A1A hood unit, though they certainly experimented with some fancy trucks over the years.
Between 1958 and 1960, EMD (Canada), known then as General Motors Diesel (GMD, Ltd) in London, ON built 101 light road switcher units for Canadian consuption only, the GMD1. Of these the majority (83) were equipped with A-1-A Flexicoil trucks. The remaining 18 were built with B-B Flexicoil trucks and steam generators for the CN. The A-1-A GMD1s were built for CN and Northern Alberta.
Mike
The Alco RS series came in 3 wheel arrangements. B-B, A1A- A1A, and C-C. The 4 axle unit was the standard RS, the A1A version was the RSC, and the C-C models were RSD. With ALCO Centuries, the first number was the number of powered axles, the 2nd and 3rd # were horsepower in 100's. Thus a C430 was a four axle, 3,000 hp unit. A C630 was a six axle, 3,000 hp unit.
I believe that with Montreal built units , the numbers were the same but the letter was M instead of C. Thus the M630 was a Montreal built six axle, 3,000 hp unit. Maybe someone out there can verify this.
pajrr I believe that with Montreal built units , the numbers were the same but the letter was M instead of C. Thus the M630 was a Montreal built six axle, 3,000 hp unit. Maybe someone out there can verify this.
Nearly correct, but the switch to the "M" designation occurred after ALCO ceased to build locomotives. The C424s built by MLW were C424s, and in fact MLW outshopped the first Century model rather than Schenectady. The first MLW C630s seem to be designated as C630M, although this might possibly be of railfan origin. MLW used the Dofasco High Adhesion truck, quite different from the ALCO equivalent, for all the 6-motor production. The M-series included the M630, M636, M640 and several variants of the M420.
The final freight models from MLW, the HR412 and HR616, used yet another system. The first digit was the number of axles and the next two were the number of cylinders. HR stood for "High Reliability" but it seems they didn't quite match the reliability of the SD40-2.
John
CShaveRRI've never heard of an EMD hood unit with A1A trucks. Alco had some: I think the RSC-3 was the A1A-A1A equivalent of an RS-3 (the C-C version was an RSD-5). I believe every Alco locomotive model had its DL specification as well. For some reason, certain models (DL640, for one), were better known by this specification than by their actual model designation (RS-27).
All EMD E units were A-1-A! And the FL9's of New Haven fame were B-B in front and A-1-A on the rear truck. I don't believe there were any others in the EMD stable. ALCO/GE had the PA of course. I am not sure if any other manufacturer had an A-1-A locomotive. All other units were either B-B, C-C or D-D. Alco/GE RS were B-B but the RSC was a C-C unit, not A-1-A.
henry6All EMD E units were A-1-A! And the FL9's of New Haven fame were B-B in front and A-1-A on the rear truck. I don't believe there were any others in the EMD stable. ALCO/GE had the PA of course. I am not sure if any other manufacturer had an A-1-A locomotive. All other units were either B-B, C-C or D-D. Alco/GE RS were B-B but the RSC was a C-C unit, not A-1-A.
Alco RSC locomotives had A1A trucks, the much more common early C-C trucked Alco hood-units were type RSD. Seaboard Air Line and the Soo Line RR bought most of the RSC Alcos. Baldwin also built A1A trucked locomotives. They built A1A Cab Units for the PRR with the shark-nose model DR6-4-2000 and hood units for various railroads including models AS416. Early Fairbanks Morse "Erie-built" passenger locomotives were also A1A trucked.
henry6 I am not sure if any other manufacturer had an A-1-A locomotive.
I am not sure if any other manufacturer had an A-1-A locomotive.
FWIW, BNSF's new GE AC44C4 locomotives, #6600 - 6624, which were released earlier this year are configured with a pretty interesting A-1-A wheel arrangement:
http://tinyurl.com/m5khhe
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Trainfan I did some quick fact checking and found that EMD/GMD built over 500 A1A-A1A hood units. They also built some 1B-B1 hood units. It all just depends on where you look stuff up.
Ed
trainfan1221 I never even tried to figure out all the Alco designations, then you figure in MLW and it really gets confusing. EMD to the best of my knowledge never did have an A1A hood unit, though they certainly experimented with some fancy trucks over the years.
Mike: GMD also built 10 A1A-A1A G8s for CN.
MJChittick Between 1958 and 1960, EMD (Canada), known then as General Motors Diesel (GMD, Ltd) in London, ON built 101 light road switcher units for Canadian consuption only, the GMD1. Of these the majority (83) were equipped with A-1-A Flexicoil trucks. The remaining 18 were built with B-B Flexicoil trucks and steam generators for the CN. The A-1-A GMD1s were built for CN and Northern Alberta.
Ted: I found that GE is reluctant to build A1A-A1A locomotives, but did build some in the past. There were GE A1A-A1A switchers built by GE licensees as early as 1950. Also GE exported some A1A-A1A U15s to the Sudan in 1975 and 1981 plus built some A1A-A1A U18s for Indonesia in 1977. So this new move by GE and BNSF with the AC44C4 will be interesting to watch to see if it is developed further or if more orders come in for the type.
Ted Marshall henry6 I am not sure if any other manufacturer had an A-1-A locomotive. FWIW, BNSF's new GE AC44C4 locomotives, #6600 - 6624, which were released earlier this year are configured with a pretty interesting A-1-A wheel arrangement: http://tinyurl.com/m5khhe After an extended absense from the list, it's great to be back. Hello gang...
Some "C-Liners" were built with a B-A1A configuration - I suspect to deal with the weight of a boiler. That sure would raise Cain with defect detector axle counts....
YES! OF COURSE! BALDWIN SHARKS WERE A-1-A! In may semi sleep mode last night I kept thinking Baldwin but not Sharks!!! And the FM Erie builds I do believe had an A-1-A for Canada but not sure of the US...the B-B--A-1-A makes sense knowing their use on the LIRR. I was not aware of any road switcher having an A-1-A wheel arragement but I also gave up keeping close tabs on locomotives after the SD45s!
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