Evening star. [volume] (Washington, D.C.) 1854-1972, 1930-05-18
BY PHILLIP r. WHEELER,
Engine Test Laboratory, Bureau of
standards

| StAnuaruS,
Do YOU know that the average auto
mobile would be more nearly streamltned
| II 1t were driven backward? Do you
| know what streamltne shape Is? Do
| you know how it affects you who drive
an automobile and why bodies are tend
| ing toward that shape?
You are buying more gasoline today
| than you would If your car were more
| perfectly streamlined Motion in the
air takes power and the faster the
motion the more power Is required.
| Streamlining reduces the power neces-
Sary by smoothing ths curves of the
body surface so that there is minimum
| of disturbance created in the air as the
body moves through It.
The air may exert large forces. It
produces WsterspoutS at sea and lorna
, does on the land. We cannot see it,
! yet it levels villages and mows paths
through forests. We ride on the air
in our tires and it holds us up when
We fly in an atrplane.
Even the engine under the hood
breatheS air and it is the expansion of
heated air which produces the power to
send one speeding over the boulevard.
We often speak or hear some one
speak of a vacuum or suction. A
vacuum, as ordinarily used, Is a name
applied to any region of low pressure.
When standing still in the air an auto
mobile or any other object has equal
pressure on all sides of it, but when
the body is given motion the air
through which it is moving acts accord
in gto certain laws of nature.
Air Holds Car Back.
There will be an increase in pressure
on the front parts moving against the
air and a decrease in pressure on the
rear parts moving away from the air.
Both of these changes tend to hold the
car back and make the engine work
harder to keep the car in motion. The
| reduction in pressure behind a moving
automobile is caused by the inertia of
the air and its failure to close in be-
! hind as fast as the back of the body
moves away from it, This reduction in
pressure on the rear may be as great as
the increase on the front parts, so that
the shape of the rear half of a car is
| as important as that Of the front half
that is, providing the car is to be de-
signed to gain low air resistance and
not just to appear in accordance with
somebody's idea Of what car ought to
look like.
IF the speed is doubled these changes
in pressure at the front and the rear,
as great, but four times as great in
stead. At 40 miles an hour the force
required to move through the air is only
one-fourth as great as at 40 and only
one-ninth as great as at so miles an
hour. That Is, air resistance increases
as the square of the speed.
The power which the engine must de-
liver to overcome the air resistance in
creases still more rapidly, for it in
creases both as the air resistance and
as the speed. At 60 miles an hour the
horsepower required to overcome the air
resistance is q times as great as at 20
miles an hour.
According to some figures supplied by
DR.. H. L. Dryden, chief Of the aerody-
namical physics section Of the Bureau
OF Standards, the air resistance of
certain light sedan model at so miles
per hour amounts to about 100 pounds
and about 80 horsepower Is required to
overcome the air resistance. Some ex-
periments made In Germany have
automobile with the same projected
area for which the air resistance is only
70 pounds and for which only IL horse
power Is required. If some method
could be found to deal with the dis
turbance produced by the wheels, the
values for very good streamline model
might be overwhelmingly, an air
resistance Of only 20 pounds, requiring
AZ Horsepower instead Of the 100 pounds
and 80 horsepower of the present mod
els. At the present time these ex-
tremely low figures have not been ap-
preached In q practical vehicle.
streamlining Reduces Resistance.
Thus it Is seen that the air resistance
OF one body may be several times as
great as that Of another body OF the
same size or frontal area. This Is be-
cause streamlining allows q body to
move through the air with a minimum
OF disturbance and therefore with a
minimum Of resistance. With stream
line body or shape the air parts at the
front follows the surface of the body
and comes gradually together at the
back, giving minimum change In pres
sure at both places. Bringing q body
gradually to a point or line at the back
allows the air to close together without
region Of low pressure behind.
Nature furnishes us with examples of
nicely streamlined bodies. The curves
Of the pretty speckled trout. the gamey
black bass and the silver bellied salmon,
as well as many others, make good
streamlined bodies. They move rapidly
through the water which behaves much
WIG &oAAAC 90 U4NC OIL 0Alo hCNduoC Va
their shape, they move with the least
possible resistance to forward motion
This means that If they had to burn
gasoline, they would burn small amounts
and that II they had to have an engine,
its horsepower output would always be
kept at minimum.
There are other beauties whom Nature
has endowed with perfect curves Among
these are the swtfthying duck, the sleek
geese and even the pretty songster who
wakes you on a bright Spring morning
The soaring gull and the hawk are some
of Natures masterpieces. The eagle at
his lofty height surveys the world from
many points of the compass because of
the ease with which he can move from
place to place. Travel gets these crea-
lures of the air their living, protects
them from danger and perhaps carries
them to a warmer climate when the
cold comes.
Man Models After Nature.
Man has modelled his airplanes after
them. He makes planes In streamline
form with as few projecting parts as
possible. Just putting a streamline
cowling or specially shaped air-shield
around the landing wheels may add
from 5 to is miles an hour to the top
speed of the plane. Putting we'll de-
signed cowling around the engine may
add like amount to the speed. Which
means that the plane will require less
pasoIine and poWer or else with the