A A, B B, C C C

ChrisDante Jul 25, 2003

  1. ChrisDante

    ChrisDante TrainBoard Member

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    I've been around trains for a long time, but mostly steam and I was always wondering what those letters meant when talking about diesel engine wheel sets.

    What does A B A mean?

    How are diesel engine wheel arraingements classified?

    If anyone can help, I would appreciate the info.

    Thanks,
     
  2. rray

    rray Staff Member

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    an A unit would be the lead locomotive, with the cab nose facing forward. The B unit would be the middle engine, that has no cab, and is controlled via multi unit cables, and the C unit is identical to the A unit, just turned facing backwards.

    I think that arangement was popular for passenger trains, and the ABA set did not have to be turned at the end of the line. They must have used a passing siding to move the locomotives to front of the train for the return trip.
     
  3. rray

    rray Staff Member

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    Oh, and the wheel arangements... a -B unit has 4 axles, and a -C unit has 6 axles. For some reason the naming changed over time from say... "U-30-C" to "Dash 40-C" with the "-C" AKA "Dash C" meaning 6 axles on the locomotive where a "Dash B" would be 4 axle.


    The 6 axle locomotives would serve a role like a Northern 4-8-4 locomotive, hauling a lot of freight, or long passenger trains, and the 4 axle would serve more like a 2-8-0 or 4-6-2 Pacific, doing shorter faster work like short passenger or freight I think. [​IMG]

    [ 25. July 2003, 03:35: Message edited by: pray59 ]
     
  4. Doug F

    Doug F TrainBoard Member

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    I think that you are confusing two different things in describing diesels.

    In describing the wheel arraingement the use of letters represent the wheels on the engine.

    A unit described as B+B means that the unit has two trucks each having two powered axles.

    Another unit might be a C+C. having two trucks each having three powered axles.

    Some of the older passenger units were A-1-A+A-1-A. These units had two trucks where each had two powered axles on the outside with a non-powered axle between them.

    This is the same terminology used to describe electric locomotives. Diesel engines are electrics that carry their own generators rather than getting the power from overhead wires.

    On rare occasions you may find engines described as differing combinations. One unusual combo was the early Santa Fe road diesel that powered the first Super Chief. This engine at one time was a 1-B+B. This means that the leading truck had three axles, the first was non-powered, followed by two powered axles and the rear truck was two axles , both of which were powered.

    When describing an engine lashup of different units the A-B-B-A represents the way the engines are hooked together and operated under the control of one unit. The cab units were designated as A units and the cabless units were called B's. Thus an A-B-B-A lashup would be an engine with a cab, followed by two cabless units, then another unit with a cab. There could be differing hookups of these engines. A-A, A-B-A, A-B-B, etc. There would almost always be an A unit on the front of any lashup. Some B units did have controls but they were only used in the confines of yards and served the purpose of moving the units in servicing and making up the consists.

    I hope that this helps your understanding of the terminology used with diesels.

    Doug
     
  5. GP30

    GP30 TrainBoard Member

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    EMDs are classified as GP's having 4 axles, SD's having 6 and DD's used to have 8. :eek:
     
  6. Alan

    Alan Staff Member TrainBoard Supporter

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    In the UK a little more information is given in the wheel arrangement notation.

    A 4 axle locomotive can be either B-B or Bo-Bo. A B-B has one motor or drive powereing both axles of a truck, as in a hydraulic drive, whereas a Bo-Bo has a seperate motor for each axle (the norm these days).

    In the early days our diesel locomotives were much heavier and needed more axles to spread the load so used A1A-A1A already mentioned where the middle axle of a 3 axle truck was unpowered, or 1Co-Co1 where the outer axles of the 4 axle trucks were unpowered. As developments brought down weight the 1Co-Co1 was replaced with Co-Co arrangement. All units these days are either Bo-Bo or Co-Co. In the USA these would be described as B-B or C-C.
     
  7. ChrisDante

    ChrisDante TrainBoard Member

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    Thank you all very much for the information. I've been around trains for 40 yrs and am still learning new things.

    Thanks again
     

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