With Atlas now offering the N scale 8-40C I can replace some older sentimental favorites with better quality versions. I have several of the Atlas 8-40BWs and I'm quite happy with them. On a real railroad (Santa Fe), what is the differences in the 2 and 3 axle assignment? Would these ever be used together?
If it will pull freight, it can be used. It really doesn't matter what type of loco it is. I've seen just about every imaginable combo out there.
On the Santa Fe, all widenose power was for intermodal (the Super Fleet). Originally, they bought only 4-axle power for this (GP60MS and Bs, B40-8Ws... would've bought B40-8Bs if GE had been willing). They also repainted FP45s for this service (but not F45s or SDP40Fs). Then they switched to buying 6-axle power for the Super Fleet: C40-8Ws, C44-9Ws and SD75Ms. The original intention had been to run Super Fleet power only in color-matched consists. It didn't last. It was much more common to see blue/yellow units on intermodal than silver/red on regular freight, suggesting that Santa Fe nver got enough Super Fleet power for all their intermodal trains.
I believe the two characteristics of HP and CTE (continuous tractive effort) are the deciding factors for what can be pulled, regardless of wheel arrangements. CTE is needed for lugging below about 10mph and HP is needed to maintain higher speeds. Hence for intermodal work a 4,000 HP C or B is pretty much equal, so mixing them is no problem. But for lugging you need the CTE and generally 6 axles will have the edge. (For the same weight 6 and 4 axles should have comparable theoretical tractive efforts, but spreading the load across 6 motors instead of 4 will usually allow a higher Continuous rating.) As for 'reality', I'm sure I've got a video of Cajon Pass which contains a few scenes showing a blue/yellow SantaFe helper set made up of an SD + a GP (probably both EMD, but might have been a mix). I remember it because I did think it odd using a GP in pusher duties. Just shows that what Steve says above is sooo true
With all axles powered, the theoretical TE of any heavier loco is higher than a lighter one, even if the heavier one is a GP and the lighter an SD. Which is why I specified the same weight - eg. an SD40 vs a GP40 ballasted to the same total weight.
I have hadthe Pentrex VHS video on the ATSF Gallup Sub for several years, and when I just watched it a week or so ago, I was surprised at how many of the superfleet locos were 4-axle power; it was very rare to see any 6-axle power although these were probably making there way in to the fleet at the time the video was produced. Jamie
