2.5. DRAWBAR PULL
The drawbar pull (DBP) of a locomotive is its actual pulling
ability; it is the tractive effort less the effort necessary to move
the locomotive itself. In other words, DBP is the effort the
locomotive has left after it moves itself. Tests have shown that it
takes from 16 to 20 pounds of pull per ton to start the average
locomotive or freight car on straight, level track in fair weather
with moderate temperatures. If the locomotives or freight car is
equipped with roller bearings, starting effort required is somewhat
less. However, for military planning purposes, 20 pounds per ton of
total locomotive weight is subtracted from the continuous tractive
effort of the locomotive to establish pulling ability for starting
and pulling a train; this is the force that can be applied at the
drawbar of the locomotive.
It is emphasized that maximum drawbar pull can be exerted only
at low speedsup to 10 miles per hour (mph)after which it drops
off sharply. Drawbar pull at speeds above 10 miles per hour can be
obtained by applying a speed factor to the maximum DBP; however,
speed factors are not included in this text because trains in a
theater rarely travel at average speeds above 10 miles per hour.
For a dieselelectric locomotive weighing 90 tons and having a
continuous tractive effort of 22,500 pounds, drawbar pull is computed
as follows:
Subtract 20 pounds per ton of total locomotive weight from the
continuous tractive effort to get drawbar pull.
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