The extinction of 4-axle units?

[locomutt]

QUOTE: Originally posted by M.W. Hemphill

Locomutt: Actually, practically everything I've ever said on locomotives in this forum can be found in things quite accessible to you: the various Kalmbach diesel spotters books (I would get them all, and read them all, and they're cheap at flea markets), and the four-part series "The Diesel Locomotive from D to L" by Vernon Smith, which appeared in Trains in 1980 (again, easy to find used copies at flea markets or on line). There's little that's changed in 24 years in the diesel business since Smith typed that wonderful series.

Thanks Mark,
Maybe I can retire my 1st edition of The Diesel Spotters Guide.[:)]

[Anonymous]

NS uses GP60's on four intermodels around here, while they were designed for RoadRailer service I have yet to see one on a RoadRailer and I'm sure I never will.

[locomutt]

Thank You,Mark:
I wish our public library had more info on things like this,
and know other places to go to online,to get this info.

[locomutt]

Please correct me if I'm wrong(which I probably am), weren't 6 axles developed
to cut down on wear on lighter trackage?To distribute the weight more evenly?

[Junctionfan]

The only decent 4 axle GE units are the P-42 which is designed for passenger service. GE sells nothing else from what I have seen on GE's website. I would imagine that the P-42 would be excellent roadrailer power.

[Overmod]

See the thread I just posted over there in Mookie's "Why?" thread...

The advantage of the four-axle unit is that it has fewer axles, and less associated cost (e.g., 4 traction motors instead of 6 to stock and maintain, less mass in the truck frames, etc.)

There is still an advantage in very-high-speed service to having two-axle power trucks, in part because the mass of the required sideframes can be less for a given set of guiding characteristics (and the additional mass required for steerable outer axles adds up too). Theoretically a two-axle truck is a bit easier to cross-equalize.

Aside from that, there's a clear advantage geometrically in going to a three-axle steerable truck (such as HTCR-II or FlexiFloat) -- on a main line with transition spirals and "no sharp-radius curves" the effective rigid wheelbase of such a truck is zero. Much more difficult to make this work with a two-axle truck that has a pivot to the carbody. Bolster design, secondary suspension, etc. generally better. Also better weight distribution on the axles during acceleration or braking...

Not much call for power per axle above what existing, stocked designs of TM are putting out. That severely limits the 'viability' of high-horsepower 4-motor units... and about the only place it would pay to build such units 'new' would be in very fast intermodal, or passenger, service.

I think the real point is that the four-motor unit market is quite nicely supplied by the used-equipment market... both with respect to anticipated needs and to a source of low-cost parts for 'new' locomotives (cf. the Green Goat). Seems that the 'minimum' power for RoadRailers is a six-motor unit, and for other mainline trains either a pair or triple of six-motor units. "Road slugs" might benefit from two-axle trucks, to save weight or length, but... see above; nobody buys slugs new and keeps their job for long!

[gabe]

Mookie's GP/SD question reminds me of a question that I have been pondering for some time. Are 4-axle locomotives becoming extinct? I know the GP-60 sold some, but did it sell a lot and is there a successor planned? Does GE even make a 4-axle unit?

Is there any advantage of having a 4-axle unit on a well maintained main line with no sharp-radius curves?

It seems to me as though the 4-axle unit is becoming extinct outside of yard work, can someone tell me how accurate my assessment is?

Thanks,
Gabe