GR grade resistance.
T = one ton (2,000 pounds).
r = percent of ruling grade.
b = one station (100 feet)
thus, GR in pounds per ton may be expressed as:
Assume that the percent of the ruling grade for a division of
railroad is 2.3. You can find the grade resistance as follows:
GR = 20 x 2.3 = 46.0, or 46 pounds per ton of train.
2.8. CURVE RESISTANCE
A curve is necessary each time a rail line changes direction,
and it offers resistance to the progress of a train. No exact means
of determining curve resistance (CR) has been published; however,
military planners use 0.8 pounds per ton of train per degree of
curvature. This means that 0.8 pounds of force or power must be
exerted to move one ton of train around each degree of curvature in
the ruling or sharpest curve on the line. For example, if the ruling
curve for a rail division is 10, you find the curve resistance for
that line by multiplying 0.8 by 10. The CR is 8 pounds per ton of
2.9. WEATHER FACTOR
Weather factor (W) is a percentile expression of the adverse
effects of cold and wet weather on the hauling power of a locomotive.
Experience and tests have proved that when the outside temperature
drops below 32 F., the hauling power of a locomotive decreases. This
decrease results mainly from the changed tolerances between moving
parts of the locomotive caused by contraction of metal and the
increased loss of heat energy from the engine at low temperatures.
Table III gives the loss in hauling power for various degrees of
temperature and also the corresponding weather factor, both in
percent. Look under the temperature column of the table and find