244 POWER DISTRIBUTION FOR ELECTRIC RAILROADS.
The normal resistances encountered by a moving
rain may be roughly classified as friction, grades and air
resistance. ‘The first mentioned, including all the ordinary
tractive resistances, is usually ter or twelve pounds per
ton of moving weight on good track. Anything below ten
pounds is unusually good and few railway engineers would
care to count on anything below eight pounds even under
the most favorable circumstances, although lower results
are probably now and then reached at high speeds.
The atmospheric resistance used to be taken as varying
with the square of the speed, but the work of Crosby and
Pounds per sq. ft.of cross-section
102220 30 40 50 €0 70 80 90 100° ‘110 - 120 - 130
Miles per Hour Street Ry.Journal
FIG. 127.
recent experiments with fast running trains have made it
certain that up to speeds of fully 125 miles per hour the
air resistance increases very little faster than the speed.
Moreover it can be greatly lessened by shaping the front of
the locomotive into a plane or parabolic wedge. Fig. 127
shows the results of Crosby’s experiments with whirling
bodies in addition to several points approximately estab-
lished by direct experiments on moving trains. The latter
are somewhat uncertain owing to insufficient data concern-
ing exposed surfaces, but the results given have been taken
as large as the data permit, so that they are over rather
than under the real resistances.
From these data we can calculate the power required
to drive a given train at, say, one hundred miles per hour.
e ——erererre:
e e E——T——