I'm reading the Amtrak pictorial "Amtrak: An American Story" and one of the essays states that in the early years Amtrak endeavored to quickly replace the hand-me-down six-axle passenger locomotives with four-axle locomotives that were more suitable for passenger service. The author doesn't provide any more explanation.
Why are 4-axle locomotives more suitable for passenger service than six-axle locomotives?
First, this is referring to B-B vs C-C and not B-B vs A-1-A designations. Mostly, passenger trains don't need the power or adhesion that freight diesels do, under most operating conditions. Weight, track dynamics, power at start, etc., B-B is quite sufficient in most all passenger services in the U.S. today.
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Very interesting, Henry. What I'm also curious about is why the private railroads were using six-axle locomotives for passenger service? Was it for dual-use as passenger/freight?
aegrotatio Very interesting, Henry. What I'm also curious about is why the private railroads were using six-axle locomotives for passenger service? Was it for dual-use as passenger/freight?
The private railroads were not using C-C six-axle locomotives as are being built today. They were using A-1-A six-axle locomotives in the form of EMD E units which only had four powered axles. The center axle of both trucks was unpowered. Most first generation passenger diesels road on A-1-A trucks for improved ride at 100 mph speeds. Remember, there were also many B-B locomotives geared for and operated in passenger service.
As an aside, Santa Fe and Burlington Northern ordered FP-45 passenger locomotives from EMD in the late 60's as replacement power for their first generation passenger units. These were C-C cowled versions of the 20-cylinder, 3600 hp SD-45s. None of these units were ever conveyed to Amtrak.
Mike
MJChittick aegrotatio: Very interesting, Henry. What I'm also curious about is why the private railroads were using six-axle locomotives for passenger service? Was it for dual-use as passenger/freight? The private railroads were not using C-C six-axle locomotives as are being built today. They were using A-1-A six-axle locomotives in the form of EMD E units which only had four powered axles. The center axle of both trucks was unpowered. Most first generation passenger diesels road on A-1-A trucks for improved ride at 100 mph speeds. Remember, there were also many B-B locomotives geared for and operated in passenger service. As an aside, Santa Fe and Burlington Northern ordered FP-45 passenger locomotives from EMD in the late 60's as replacement power for their first generation passenger units. These were C-C cowled versions of the 20-cylinder, 3600 hp SD-45s. None of these units were ever conveyed to Amtrak.
aegrotatio: Very interesting, Henry. What I'm also curious about is why the private railroads were using six-axle locomotives for passenger service? Was it for dual-use as passenger/freight?
Johnny
Deleted
Deggesty Don't forget the Alco passenger locomotives, which also had A-1-A trucks. I am not familar with the Baldwin (except the centipedes) or Fairbanks-Morse, but I believe that they also had A-1-A trucks.
Don't forget the Alco passenger locomotives, which also had A-1-A trucks. I am not familar with the Baldwin (except the centipedes) or Fairbanks-Morse, but I believe that they also had A-1-A trucks.
The OP was referencing the locomotives conveyed to Amtrak in 1971, and I was attempting to keep my response focused. These included no Alco, F-M or Baldwin units; only EMD.
Generally, six-motored locomotives, requiring six axles, can start a heavier train without overloading the traction motors, than four-motored locomotives. The added tractive effort, related to the locomotive's horsepower, is usually needed more in freight service than in passenger service. But there were and are six-wheel truck locomotives that do work well in passenger service, with or without a motor for the center axle. The Amtrak 6-axle early diesels and E60 locomotives simply had six-wheel trucks that were not really designed for high-speed passneger service, except possibly on well-maintained very heavy duty track. They could have been replaced by six-axle locomotives with six-wheel trucks, but that was not what EMD came up with and would have been more expensive. The New Haven EP-5, the Jets, were good passenger locomotives with six axles, and if GE had used that truck, possibly the E60 would have been a successful electric in passenger service.
Aeg...
The short, direct answer to your question is that passenger trains need horsepower not tractive effort. The lighter B-B units are better suited to the service than would be heavier C-C units.
Mac
The E units rode on A-1-A trucks because they were too heavy for four axle trucks, although the longer truck spacing did help the high speed ride. Four powered axles were enough to get over the ruling grade on most routes. It's a neat trick to pack all the equipment and supplies into a four axle and make a reasonable weight.
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
A minor correction to MJChittic's post.
The "BN" FP 45 units were ordered by and delivered to the Great Northern prior to the merger. Shortly before that the GN bought either SDP 40 or SDP 45 units to replace aging F units two for one. GN management could obviously see the end of passenger trains so they bought units that could be instantly diverted to freight service when the opportunity presented itself, as it did.
Mac McCulloch
The weight of the E units was occaisioned by their use of two prime movers in one carbody. The thinking of the time being, that if there were two prime movers in one carbody - if one prime mover failed the passenger train could still continue to destination on the remaining prime mover that continued to operate. Two prime movers plus a steam boiler and the water supply for the boiler all generated additional weight - weight that exeeeded axle loading for a 4 axle locomotive.
oltmannd MJChittick: aegrotatio: Very interesting, Henry. What I'm also curious about is why the private railroads were using six-axle locomotives for passenger service? Was it for dual-use as passenger/freight? The private railroads were not using C-C six-axle locomotives as are being built today. They were using A-1-A six-axle locomotives in the form of EMD E units which only had four powered axles. The center axle of both trucks was unpowered. Most first generation passenger diesels road on A-1-A trucks for improved ride at 100 mph speeds. Remember, there were also many B-B locomotives geared for and operated in passenger service. As an aside, Santa Fe and Burlington Northern ordered FP-45 passenger locomotives from EMD in the late 60's as replacement power for their first generation passenger units. These were C-C cowled versions of the 20-cylinder, 3600 hp SD-45s. None of these units were ever conveyed to Amtrak. The E units rode on A-1-A trucks because they were too heavy for four axle trucks, although the longer truck spacing did help the high speed ride. Four powered axles were enough to get over the ruling grade on most routes. It's a neat trick to pack all the equipment and supplies into a four axle and make a reasonable weight.
MJChittick: aegrotatio: Very interesting, Henry. What I'm also curious about is why the private railroads were using six-axle locomotives for passenger service? Was it for dual-use as passenger/freight? The private railroads were not using C-C six-axle locomotives as are being built today. They were using A-1-A six-axle locomotives in the form of EMD E units which only had four powered axles. The center axle of both trucks was unpowered. Most first generation passenger diesels road on A-1-A trucks for improved ride at 100 mph speeds. Remember, there were also many B-B locomotives geared for and operated in passenger service. As an aside, Santa Fe and Burlington Northern ordered FP-45 passenger locomotives from EMD in the late 60's as replacement power for their first generation passenger units. These were C-C cowled versions of the 20-cylinder, 3600 hp SD-45s. None of these units were ever conveyed to Amtrak.
Never too old to have a happy childhood!
I also assumed the double engine units had A1A trucks for weight reasons. However, when I checked the Second Diesel Spotters Guide I saw that the early EMD 1800 hp double engine units were originally built with 4 axles (B-B), including B&O #50 and ATSF #1 & 1A. The ATSF #1 was rebuilt with a 1B-B1 wheel arrangement. Latter, EMD 1800 hp models EA, E1 & E2 ( using the same 201-A engine pairs) were built as A1A-A1A. The Guide does not explain the reason for the change.
You may want to check out the first of the three part articles on E units that appeared in Railfan & Railroad a couple of years back. The first boxcabs just barely met loading limits with two axle trucks, later units had more weight in part due to steam generators.
- Erik
Alco managed to squeeze 2000 HP out of their 16-244 and built PAs with a single engine, but still needed A-1-A trucks to handle the weight.
You could get all the equipment and supplies jammed into a four axle, but you had to sacrifice HP and/or range - F units and Alco FAs for example.
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