Why does AC traction provide increased adhesion?

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  • Member since
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Posted by Overmod on Monday, July 12, 2021 11:07 PM


... If the wheels are rotating, the brake shoes will clean the wheel surface enhancing adhesion

That's been one of my thoughts...

One of the chief things it does is heat the wheeltread sufficiently not only to dry it and keep it dry as it goes around, but help flash-heat any water or schmutz on the railhead as tread rolls onto the contact patch.

Mechanical 'scraping' is valuable too, but I suspect the heat's the most useful aspect...

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Posted by daveklepper on Tuesday, July 13, 2021 3:31 AM

i appreciate the detailed answers regarding use of the idependent with distributed power.  Thanks.

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Posted by oltmannd on Wednesday, July 14, 2021 9:17 PM

Paul Milenkovic




Don Oltnann may be familiar with what Conrail and then NS might have been doing to increase effective TE with DC motors -- NS was wedded to them for a considerable time past the 'modern AC revolution'.


NS was highly "siloed".  Mechanical ruled the roost for locomotive purchases but didn't really know what was going on on the RR.  In 1998, I asked a Mech Dept exec "why no AC locos?" as part of an informal interview.  (I was shopping myself around prior to the organized "transition" interview process)

They told me, "they cost more and we don't really run trains with more than two units, so AC gets doesn't get us much".  Reality was they were running most merchandise trains with more than two units.  He really was out of touch with what the transportation plan was.    NS was really behind compared to Conrail at many things - mostly because they had nothing pushing them.




Yes, but . . .

If NS was running merchandise trains with more than two units, they were doing it for the horsepower-at-speed, not for the lugging ability?  

The 6000 HP AC locomotive unit, at least in US railroading, would have had the lugging tractive effort for drag freight and the HP in fewer units for merchandise.  But because reasons the 6000 HP size didn't work out?



NS was a notorius "tonnage" railroad up to the adoption of scheduled railroading in 2002.  They would dispatch a particular train only when they had accumulated the maximum tonnage for the locomotives assigned the train.  The assigned locos weren't ALWAYS two SD40s.... Many times it was 3 or 4.

That was the theory.  In practice, about 1/3 of the merchandise trains attempted to run on schedule because of the transit times promised to shippers - notably automotive and chemical shippers.  

The growing intermodal network was nearly always 3 or 4 units per train.

The Mechanical guys in Roanoke weren't keeping up with these changes....which may be why they were all moved to Atlanta a just after TOP was implemented.

A couple SD80MACS could have replaces a trio of SD40s easily on most trains.

-Don (Random stuff, mostly about trains - what else?

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