Flying-machines are distinguished from balloons and dirigibles in being
“heavier than air,” and consequently raised and supported by dynamic
means alone, by the reaction of the air on surfaces driven through it.
Essentially, the aëroplane may be compared to a kite in which the pull
of the string is replaced by the thrust of the propeller.
On December 17, 1903, the Brothers Wright, in America, made their first
power-flight; while the very first public flight was made in France by
Santos-Dumont on September 14, 1906.
Before it was possible to produce a power-driven aëroplane, experiments
over a long course of years were made with aëroplanes not provided with
propelling apparatus.
In its earliest form the aëroplane consisted of a flat surface moved
through the air in a position slightly inclined from the horizontal; in
its forward movement the plane experiences resistance from the air. As
this resistance is directed partly on the under side, it will be partly
converted into a lifting force. Of these two forces--head resistance or
drift, and the lifting or sustaining force or lift--the first, being
unproductive, must be reduced as far as possible; the second, lift,
must, on the other hand, be raised to the highest possible degree.
This end is achieved by employing, instead of flat surfaces or planes,
surfaces curved in the direction of flight.
THE TWO TYPES.--A _monoplane_ is a machine with a single spread of
surface supporting it. The best known example of a monoplane is the
Bleriot. _Biplanes_ have two supporting surfaces, the one above the
other; the Wright and Farman machines are machines of this type. There
are other machines which have been invented which have more supporting
surfaces than this, the most successful of them all being the Roe
triplane. But at present, at any rate, the advantage lies between the
monoplane and the biplane, the other machines not yet having reached a
sufficiently high standard to be able to compete with them.
The monoplane and the biplane have both their own special uses. The
monoplane is obviously the lighter machine, and its head resistance is
much less, hence it follows logically that its speed will be greater
than that of a biplane. But the biplane is a much more stable machine
than the monoplane; it will therefore probably be safer and will
certainly be able to carry a greater weight.
In the making of aëroplanes wood is usually used for the framework.
Specially selected wood is taken, usually from the spruce, hickory, ash,
or birch, since wood combines in itself the strength and tenacity of
metal without its weight. The fabric with which this frame is covered is
more difficult to obtain, since it must contain in itself all the
qualities of strength, lightness, smoothness, etc., without any
tendencies to shrink, or rot, or burn.
The biplane carries a load of from two and one-half to three and
one-half pounds per square foot of surface; the monoplane from three and
one-half to six pounds per square foot. The load per horse power in each
case is from thirty to forty pounds. In speed the biplane ranges from
thirty-five to forty-five miles per hour, as against forty to sixty
miles per hour attained by the monoplane.
PRACTICAL USES.--From the very first days the value of the aëroplanes,
from a military point of view, has been realized, not as a weapon of
offense so much as of intelligence. It would, in fact, be difficult to
imagine a better means of scouting and reconnoitering than is afforded
by the flying-machine. Its gradually increasing radius of action renders
it available for strategical no less than for tactical reconnaissance;
its easy mode of progress and absence of vibration allow the most
accurate observations to be made and sketch-maps to be drawn. For
dispatch-carrying over difficult country its usefulness is also
considerable. Its employment for purposes of offense is much more
hazardous. On the other hand, it is practically immune from artillery or
rifle fire from the land, especially when flying at a fair altitude.
As a commercial vehicle, and for transport, the aëroplane, owing to its
relatively low carrying power, is restricted in its usefulness. With
increasing reliability, however, it may well assume a portion of the
functions of the motor car.