FAST AND HEAVY RAILWAY SERVICE. 245
We will assume a three-car train, motor car and two regular
coaches weighing complete with passengers r14otons. This
demands no special construction; in fact the less departure
from the usual form and appearance of cars the better with
respect to securing traffic.
It is worth while, however, to give the locomotive a
head in the form of a parabolic wedge, which is slightly
better than the wedge of Fig. 127, to vestibule the cars
snugly, and to build the cars as free from pro’ections as is
consistent with usual models.
With these precautions the total equivalent sectional
area could easily be kept within 100 sq. ft. Nearly all of
this, too, can gain advantage from shaping. For the rela-
tive resistance of wedge and plane Fig. 127 gives accurate
values, while the close agreement of the experiments based
on normal surface attests their general accuracy. Adding
one-third to the wedge value for 100 miles per hour to take
account of plane and irregular surfaces, we have a total
atmospheric resistance of ten pounds per _square foot.
The track resistance we will assume at eight pounds per
ton since this value is quite attainable at high speed on a
good track, and furthermore was used in computing the
points shown on Fig 127 sothat if eight poundsis too low,
the air resistances are too high. We may now compute the
total train resistance as follows:
140 tons at 8 lbs., 1120 lbs.
100 sq. ft. at 101bs., 1000 1bs.
Total drawbar pull, 2120 lbs.
At 100 miles per hour, 8800 ft. per minute, this means 565
mechanical horse power developed by the motors. This
power would be raised to about 1300 h. p. in taking a one
per cent grade at the same speed. At 125 miles per hour,
the assumed maximum, the air resistance would rise to
about thirteen pounds per square foot and the horse power
to 733. Even if through increased speed and headwind
the air resistance were doubled, the mnecessary output
would still be below 1000 h. p. We may safely assume