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what is the expected pulling power of a loco?

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  • Member since
    July 2009
  • From: lavale, md
  • 4,678 posts
Posted by gregc on Saturday, January 11, 2020 5:42 AM

SeeYou190
I have a terribly hard time believing any mathmatical formula that ends with basically a 12 ounce locomotive should pull X many cars.

while nothing is exact ("~"), expectations should be within limits and variables that matter understood.

balanced weight determines pulling power of model locos just as it does prototypes.   size (length) and number of drivers do not.   Weight can be added.

the resistance (oz) for a # of cars also depends on weight and wheel friction.  Wheel friction varies but can be improved.   Observing that a loco cannot pull an "expected number of cars" suggests upgrading to metal wheels or making the effort to check the rollability of the trucks (simple incline) and tune them.

 

SeeYou190
I guess that is why Model Railroader actually measures the pull of every locomotve they review, rather than just weigh it.

not every modeler has an appropriate gauge to measure pull strength, but it's easy to weigh a loco and estimate the pulling power (i.e. min 20%)

 

SeeYou190
I'll bet that if I take two locomotives that are mathmatically indentical, load them up with cars, and send them up a 3% S-curved grade made with Kato Unitrack 28" radius sections that they WILL NOT both max out at the same number of 4 ounce cars all with indentical Kadee trucks.

sure.   but how much of a difference, 1 or 2 cars, not 10.

greg - Philadelphia & Reading / Reading

  • Member since
    January 2009
  • From: Maryland
  • 12,897 posts
Posted by ATLANTIC CENTRAL on Saturday, January 11, 2020 9:47 AM

mvlandsw

ATLANTIC CENTRAL wrote the following post 2 hours ago:

"Prototype railroads did lots of testing and calculations, but at the end of the day, they just needed to know how much tonnage a given loco could move (and stop/hold still) over the ruling grades of a given section of the line."

Almost all of the "holding still" is done by the air brakes on prototype cars. I did hear of a modeler who ran long trains of cars loaded with real iron ore up steep grades using rear end helper locomotives. After the helpers were cut off if the train went down grade too fast it could not be stopped. Even with the power shut of the weight of the train would slide the locomotives down the grade.

Mark Vinski

 

Not exactly, read this:

http://hm.evilgeniustech.com/alkrug.vcn.com/rrfacts/hp_te.htm

Sheldon

    

  • Member since
    January 2004
  • From: Canada, eh?
  • 13,375 posts
Posted by doctorwayne on Saturday, January 11, 2020 2:40 PM

Thanks for posting that link, Sheldon.  I've always enjoyed the way Al explains things so that even I can understand it.

Wayne

  • Member since
    December 2001
  • 1,190 posts
Posted by mvlandsw on Monday, January 13, 2020 2:30 AM

ATLANTIC CENTRAL
 
mvlandsw

ATLANTIC CENTRAL wrote the following post 2 hours ago:

"Prototype railroads did lots of testing and calculations, but at the end of the day, they just needed to know how much tonnage a given loco could move (and stop/hold still) over the ruling grades of a given section of the line."

Almost all of the "holding still" is done by the air brakes on prototype cars. I did hear of a modeler who ran long trains of cars loaded with real iron ore up steep grades using rear end helper locomotives. After the helpers were cut off if the train went down grade too fast it could not be stopped. Even with the power shut of the weight of the train would slide the locomotives down the grade.

Mark Vinski

 

 

 

Not exactly, read this:

http://hm.evilgeniustech.com/alkrug.vcn.com/rrfacts/hp_te.htm

Sheldon

 

From the linked article " Therefore these locomotives, with their brakes set, will hold the train on the hill "

This assumes that the locomotive brakes can keep the wheels from turning. My experience is that they cannot be depended upon to do that. Then as they roll along the rails they find rail conditions where the adhesion is lower and they begin to slide.

Mark Vinski

Mark Vinski

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