Re: Calculating Motive Power Requirements

Tim O'Connor

  > I'd like to assign motive power based upon tonnage of freight trains.

Grades are a huge consideration --

Rules of thumb --

    5 hp/ton on 0% grade (flat land)
   25 hp/ton on 1% grade
   45 hp/ton on 2% grade
   65 hp/ton of 3% grade

Also remember it takes an equal amount of BRAKING POWER to hold back
a train on a downgrade. This is why dynamic brakes were rapidly adopted
and why dieselization was so swift on steep mountain grades. A diesel
powered train with dynamics can control the train speed with very limited
use of train brakes.

You can make far more complicated calculations, of course. Steam locos
reach peak HP at mid-range speeds (30-40 mph) while diesels can maintain
constant HP. Normal DC traction motors couldn't handle slower speeds than
10 mph for very long or they would overheat. Steam booster trucks worked
only below 20 mph I think. Also, cold freight car bearings have higher
resistance than warm bearings.

And don't get Mike started on Tractive Effort! :-)

Tim O'

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