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Found the thread <!-- l --><a class="postlink-local" href="http://bigbluetrains.com/forum/viewtopic.php?f=54&t=8013">viewtopic.php?f=54&t=8013</a><!-- l --> if a mod would like to merge the two.
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Stephen, I tried to fix your link in the first post but it would not cooperate with me.
Johnathan (Catt) Edwards
"The Ol Furrball"
"I'm old school,I still believe in respect"
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A few times, even back-woods tracks like the one past my house have had wide-cab six axle switchers doing the jobs usually performed by a few GP38-2s and GP40-2s (where was I when this happened? If I didn't see pictures I wouldn't believe it.
In any event, six-axle power in yards isn't all that uncommon. At least in the case of railroads like Conrail and some of its predecessors, they assigned six axle units like SD7s, SD9s, SD38s, and U23Cs as yard power, and these units would stray into local work from time to time. In fact, during the Conrail years, the SD38s were often paired with MT6 road slugs, derived from 6 axle Alco RSD15s.
Granted, this heavy power was usually used in larger yards, particularly as hump engines. Still, they were present.
Modeling New Jersey Under the Wire 1978-1979.
![[Image: logosmall.png]](http://i543.photobucket.com/albums/gg445/CAB_IV/Model%20Trains%202013/logosmall.png)
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Railnet Wrote:Found the thread <!-- l --><a class="postlink-local" href="http://bigbluetrains.com/forum/viewtopic.php?f=54&t=8013">viewtopic.php?f=54&t=8013</a><!-- l --> if a mod would like to merge the two.
Done.
Wayne
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Just for interest, does anyone have a comparison of, say, a GP40 and an SD40? Are they the same unit with different trucks?
David
Moderato ma non troppo
Perth & Exeter Railway Company
Esquesing & Chinguacousy Radial Railway
In model railroading, there are between six and two hundred ways of performing a given task.
Most modellers can get two of them to work.
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Probably the same mechanism and motor, but because the SD is longer, it's likely also heavier. That, along with four more wheels than the GP should make it a better puller.
Wayne
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Just to clarify the GP/SD issue. GP stood for General Purpose and came with 4 wheel trucks. SD stood for Special Duty and came with 6 wheel trucks. A GP unit would cost less than a SD unit as the GP has two fewer traction motors and associated electrical equipment. So who would buy a SD? Heavy haul railroads wanting to maximise tractive effort in tonnage trains sometimes with additional ballast and strangely Granger railroads with light track and restricted bridge limits would specify a SD locomotive with reduced ballast. Go figure!
Interestingly there have been no new orders for GP freight locomotives since Santa Fe's GP 60M order in the 90's, everything has been SD up until the recent BNSF order for AC-C4 equipped locomotives, that is a current standard mainline locomotive with 6 wheel trucks but only 2 AC traction motors per truck. This supposedly gives the locomotive the same tractive effort as a DC equipped SD unit. Personally I am not convinced, but what do I know.
The other thing about GP vs. SD is that until the development of radial trucks SD 6 wheel bogies where know to be harder on the track in curves due to the trucks resistance to following a curve.
As far as GP and SD units in local service today the other thing to note is that the railroad will often de-rate a unit and thus lower its total horsepower by removing the turbocharger unit and associated ductwork to remove a high maintenance item which is not really required to perform the job.
In today's railroad world almost anything goes as far as power goes. You can find locomotives from the first generation diesels through to recent new additions like gen-set and battery powered locomotives being used in local service, it all comes down to the railroad and the tonnages and gradients involved.
Hope this helps.
Mark
Fake It till you Make It, then Fake It some More
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I understood there have been two scenarios when the SD became available.
One is the most prominent reason of better traction but some railroads had a problem with low quality trackage. They ordered an SD7 or SD9 to better distribute the weight on 6 axle. They did not add additional weight and the tank became often a smaller one. That can be spotted easy. MILW had some of those "light weight" SDs. Look at the tiny tank under the huge engine
http://www.rrpicturearchives.net/showPic...?id=155026
Reinhard
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I should clarify my remarks by adding that I was referring to model locomotives, not real ones.
Wayne
