A plane ten
feet square, for example, would not need any great inclination,
nor would it require a speed higher than a few hundred feet a
second to bear a man. What is of yet more importance, the higher
the speed the less the inclination required, and, if we leave out
of consideration the friction of the air and the resistance
arising from any object which the machine may carry, the less the
horse-power expended in driving the plane.
[Illustration]
Maxim exemplified this by experiment several years ago. He found
that, with a small inclination, he could readily give his
aeroplane, when it slid forward upon ways, such a speed that it
would rise from the ways of itself. The whole problem of the
successful flying-machine is, therefore, that of arranging an
aeroplane that shall move through the air with the requisite
speed.
The practical difficulties in the way of realizing the movement of
such an object are obvious. The aeroplane must have its
propellers. These must be driven by an engine with a source of
power. Weight is an essential quality of every engine. The
propellers must be made of metal, which has its weakness, and
which is liable to give way when its speed attains a certain
limit.
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