What are the pros and cons of one over the other? I understand that A1A means the center axle is the idler and that B1 means that the axle closest to the center of the locomotive (i.e. next to the fuel tank) is the idler.
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I suspect that the context is modern locomotives, such as the SD70ACe-P4 and the ES44C4. The difference likely has to do more with how the weight transfer system is actuated rather than any traction or mechanical advantages.
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16-567D3A Ulrich What are the pros and cons of one over the other? I understand that A1A means the center axle is the idler and that B1 means that the axle closest to the center of the locomotive (i.e. next to the fuel tank) is the idler. The B-1 refers to a front powered B truck, single unpowered idle rear axle,such as would be found at the rear of the EMD LWT-12 Aerotrain locomotives. B-2 is a powered front B truck, with unpowered rear idle B truck such as used on the Baldwin built lightweight Train-X talgo Hydraulic power units...
Ulrich What are the pros and cons of one over the other? I understand that A1A means the center axle is the idler and that B1 means that the axle closest to the center of the locomotive (i.e. next to the fuel tank) is the idler.
The B-1 refers to a front powered B truck, single unpowered idle rear axle,such as would be found at the rear of the EMD LWT-12 Aerotrain locomotives. B-2 is a powered front B truck, with unpowered rear idle B truck such as used on the Baldwin built lightweight Train-X talgo Hydraulic power units...
This has nothing whatsoever to do with the question he asked.
Look at the early history of ATSF diesels for an example of what a 1-B truck vs. an A-1-A involves. Both are three-axle trucks, with one idler axle. The position of that idler axle in the truck frame is the difference.
One difference is in the positioning of nose-suspended traction motors; another will be the effective polar moment of inertia of the motored truck. Having an unpowered axle 'leading' into curves has been considered an advantage for light track standards or low permissible axle loading, and I believe this was the intended rationale behind the ATSF use of a 1-B arrangement.
If you are using a powered 'traction increaser' system that unloads the idler axle to put more weight on the powered axles, it would appear to be easier to apply this to a central axle than to one that is 'leading' or 'trailing' in a truck frame. Presumably weird weight-transfer effects in that latter case are not observed in modern truck designs that use a low-mounted strut for communicating tractive effort to the locomotive chassis. Perhaps tapered loading as on some steam locomotives is valuable?
NorthWest I suspect that the context is modern locomotives, such as the SD70ACe-P4 and the ES44C4. The difference likely has to do more with how the weight transfer system is actuated rather than any traction or mechanical advantages.
This sounds very reasonalbe to me. Don't need to hang the inner-most motor our past the end of the truck.
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
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