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Thread: sd70macs pulling coal

  1. #1
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    Default sd70macs pulling coal

    Why do I see BNSF sd70macs only pulling coal drags? I have seen lots of them in executive livery but only with coal drags.

  2. #2
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    Default RE: sd70macs pulling coal

    Because of the technological advances made that made AC traction possible, AC traction is best suited for long heavy drags, because of pulling power and ability to crawl at 2 mph without burning up traction motors.

    Most railroads assign their AC power to long unit drags, such as coal or grain.

  3. #3
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    Default RE: sd70macs pulling coal

    Yea thats why you see CSX AC44's everywhere in VA, KY, and Tennessee (of course, their everywhere).

    On Marias theres alot of BNSF AC44's on grain too

  4. #4
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    Default RE: sd70macs pulling coal

    I only see SD60s doing it.

    http://sgair.net/erick/SIGS/CP_BANNER.JPG

    [font size=1]"The F59PHI and Genesis are the lamest excuses for locomotives Amtrak has ever operated - accept it and move on. Hug an F40 before it's too late!"[/font]

  5. #5
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    Default RE: sd70macs pulling coal

    I've noticed that BNSF if probably the RR that makes the best use of the two types of power. They have a fairly nice fleet of both AC and DC units and seem to use them where they are needed. AC pulls the heavy stuff like coal and grain. While their DC units like the C44-9's pull their fast freight like intermodals.
    CP on the other hand seems to have gone to the other extreme and gone with pretty much only AC units for their new locomotives, and have absolutely no interest in DC power, even for their intermodals.

    James.

  6. #6
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    Default RE: sd70macs pulling coal

    Here is a good article that discusses modern real world railroad considerations and the differences in AC and DC locomotives in service. It also has some interesting info on train weights and consists.
    http://www.trb-agtrans.org/pdf/01-2332_trb.pdf
    Just from a tractive effort perspective, a SD70Mac will weigh from 410,000 to 418,000 pounds and have an ideal adhesion of 41-42% and a dispatch adhesion of about 35-36%. Thus under ideal circumstances, a SD70Mac can generate 175,000 pounds of tractive effort with a heavy unit, and reliably generate 145,000 pounds of tractive effort under normal conditions.
    The SD70M (DC version) will weigh from 405,000 to 415,000 pounds, and have an ideal adhesion of about 36% and a dispatch adhesion of 26-27%. Thus under ideal conditions a SD70M will produce about 150,000 pounds of tractive effort, and reliably generate about 105,000 pounds of tractive effort under normal conditions.
    The AC locomotives can also maintain much higher continuous tractive effort and do so at much slower speeds, which would damage a DC unit as Bradley mentioned. Thus a pair of SD70Macs can start a much heavier train than a pair of SD70M and will be able to crawl slowly over steep grades at high throttle settings that would destroy the SD70M.
    Hope this helps,
    Bob

  7. #7
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    Default RE: sd70macs pulling coal

    Pretty much what Brad said. AC traction allows for really slow speeds when hauling coal trains without traction motor failure. Also, in the dynamic braking mode, DB's are effective to 0mph, unlike thier DC counterparts which DB's die out about 9 mph.

    The electronics on the BNSF SD70MAC's are out of this world. I was VERY impressed with features of IDP such as "The Fence". :D

    >Mike Forster<
    Perth, Western Australia

    [email protected]
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    http://www.trainweb.org/aussiepix

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