Psychot Given the constant striving for locomotive uniformity and interchangability at the Class 1’s, it bewilders me that they would introduce locomotives into their fleet that can/should only be used for certain applications, just to save a few bucks. I would think the complications they’re introducing into their locomotive management system would far outweigh the up-front savings.
Given the constant striving for locomotive uniformity and interchangability at the Class 1’s, it bewilders me that they would introduce locomotives into their fleet that can/should only be used for certain applications, just to save a few bucks. I would think the complications they’re introducing into their locomotive management system would far outweigh the up-front savings.
BNSF is a big enough system that some specialization is not a problem.
In the DC-motor era, the locomotive was limited more by traction motor overheating than by the diesel, except in high-speed less-than-heavy service.
In the current AC-motor era, the diesel is usually the overall limiting factor.
cefinkjrI believe one reason for development of the six-axle SD (and possibly the reason for the Special Duty tag) was that they could be used on branch lines with lighter rail.
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This was also my understanding of the reason for introducing the SD series of locomotives. They were much better suited to service on lines with lighter rail.
-Kevin
Living the dream.
SeeYou190 cefinkjr I believe one reason for development of the six-axle SD (and possibly the reason for the Special Duty tag) was that they could be used on branch lines with lighter rail. . This was also my understanding of the reason for introducing the SD series of locomotives. They were much better suited to service on lines with lighter rail.. -Kevin
cefinkjr I believe one reason for development of the six-axle SD (and possibly the reason for the Special Duty tag) was that they could be used on branch lines with lighter rail. .
This was also my understanding of the reason for introducing the SD series of locomotives. They were much better suited to service on lines with lighter rail..
And then the railroads figured out - if you made the SD's heavier, you could haul more tonnage.
Never too old to have a happy childhood!
The SD "Special Duty" was designed originally for slow, heavy drag freight. The SD-7 was first built in 1952. I believe you are thinking of ALCO's RSC-2 (1946), with an A-1-A truck designed to put a lower axle weight on branch lines with light rails.
By my calculations a GP7 has a axle load of 61,500 lbs, a F7 is slightly higher.
A SD7's axle load is 51,500 lbs, almost 10,000 lbs less than the GP7.
Of course, putting 2 extra axles under the GP7 would give an even lower axle loading.
This is essentially what Canadian National got EMD to do with the custom-designed GMD1. Its frame is nearly as long as a GP9, yet it has 6 axles, a smaller 12-cylinder engine, and a very small fuel tank. Its axle load is about the same as a RSC-series, under 40,000 lbs.
Greetings from Alberta
-an Articulate Malcontent
SD70DudeBy my calculations a GP7 has a axle load of 61,500 lbs, a F7 is slightly higher. A SD7's axle load is 51,500 lbs, almost 10,000 lbs less than the GP7.
The point to remember is that the SD7 and GP7 have the same engine, which severely horsepower-limits the six-motor version as it gets into the rectangular-hyperbola part of the horsepower curve. Then the longer wheelbase and wackier riding of the Flexicoil trucks dramatically limit higher speed (in those days) and you of course have much more 'weight per available horsepower' to tote around.
Only when larger diesel engine capacity gave the ability for six axles to have the power density of "one and a half GP units" at comparable wheelslip did you see the four-motor units go out of vogue completely. Icing on the cake was practical radial steering on the HTCR trucks, which have an effective rigid wheelbase of zero, considerably less than any combination of lateral will provide in a swing-hanger Blomberg truck ... and two-axle radial steering is an iffy business at best.
CN's passenger GMD1's had two-axle Flexcoils, and were initially geared for over 80 mph.
Didn't SP have some early SD's with steam generators for the Peninsula Commute?
SP got ten SDP45s about 1967 for their long-distance trains. They ended up on the Peninsula after Amtrak started getting SDP40Fs.
The SDP45s had 60:17 gearing for some of their lives, but SP limit was 70 mph for almost all of their lives. Of course, Santa Fe allowed its FP45s 90 mph -- think they were 59:18.
And SDP40Fs were high-geared, too ... well, that didn't turn out quite so well.
Gearing speed is different from ride quality or induced track damage. I believe there are other examples where high speed and Flexicoil trucks turned out not to 'play well together' from the standpoint of track maintenance, which was more the 'side' I was addressing.
Postwar CN did do a very good job of maintaining the track on its mainlines, so that may have covered up any issues with the 1900-series GMD1's. They were eventually re-geared to a lower speed, but I believe this was more a function of train cancellations and the creation of GO Transit bumping them off regular passenger assignments.
I don't imagine the crews enjoyed their ride quality at 80 mph very much.
They were still used as backup passenger power but were not popular in this role due to the lower gearing. There is a story in a old issue of CN Lines (the CN historical society's magazine) about the Montreal motive power director being forced to assign a pair of them to a priority evening train, only to receive calls from the Stationmaster, Trainmaster, and Superintendent complaining about the delays this would cause. His honest response was that they were the only passenger power left in the terminal, and their only other choice was to cancel the train.
Overmod And SDP40Fs were high-geared, too ... well, that didn't turn out quite so well. Gearing speed is different from ride quality or induced track damage. I believe there are other examples where high speed and Flexicoil trucks turned out not to 'play well together' from the standpoint of track maintenance, which was more the 'side' I was addressing.
What is a Flexicoil truck and how does it contribute to track stresses?
Don Oltmann once explained that the Pioneer III inside-bearing truck that goes on an Amfleet car has a very simple primary suspension consisting of slabs of rubber (elastomere) between the axle journals and the truck frame. I also heard that Amtrak is not fond of the Pioneer III design from track wear? Being an oddball design?
It seems that Amtrak has replaced almost every different truck design with the more conventional pedestal truck where the journals slide up and down in a slot? The Horizon cars were originally in commuter service, especially in Boston, with some variant of an inside-bearing truck, and Amtrak's were purchased with a pedestal truck? The Superliner I's had some European-inspired design but the Superliner II's reverted to pedestal trucks?
One of the problems the European-style trucks address is to produce increased stiffness of the axle against yaw relative to the truck frame, using automotive-type radius arms rather than a sliding guide of the pedestal style? The Pioneer III may also offer similar stiffness with the "rubber slab" connection? When a pedestal truck is worn, doesn't it allow the axle to yaw within the guides, creating an unsteady ride at high speed? Do the newer pedestal trucks incorporate something akin to Franklin self-adjusting wedges to counteract this effect?
If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
Paul MilenkovicWhat is a Flexicoil truck and how does it contribute to track stresses?
The Flexicoil is the EMD 'replacement' for the Blomberg three-axle design. It uses independent coil springs for both vertical springing and some control of lateral motion. It is neither designed nor intended as a high-speed design, and that would likely be true even if frame-mounted motors or a monomoteur arrangement, with Cardan shaft or similar drive, were used in it. I will see if I can find some drawings or views that show the arrangement; if anyone knows of them, please save me time.
Don Oltmann once explained that the Pioneer III inside-bearing truck that goes on an Amfleet car has a very simple primary suspension consisting of slabs of rubber (elastomer) between the axle journals and the truck frame.
A little 1970s-era design methodology: the formula for passenger suspension from Nystrom on was 'stiff primary springing, soft secondary springing' more for ride quality than good guiding, track-following, or lateral compliance -- but those considerations are important, too, and account for much of the three-axis strut design you see in the 'last generations' of ISH and OSH pedestal trucks.
All the rage by the '70s were chevron-sprung trucks, which implemented the primary suspension via composite (Fabreeka-style) springs like the ones originally used for lateral on pedestal tenders, but now angled (hence the 'chevron') to provide both vertical and lateral compliance under load. This gave about the best axle-to-frame primary performance, while facilitating very soft and long-travel secondary springing -- not the very long outside springs on designs like the ALP-44, or the air-bag arrangement on the Amfleet cars.
I have to run for a while, so more on the 'rest' later...
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