One of the simplest forms of the aeroplane is the common kite. This
takes various forms. It is usually made of a framework of three light
strips of wood crossing a little above the center and secured at the
outer ends by similar strips, or strong cord tautly drawn and making
when covered with paper a six-sided figure. From the corners of the
framework cords are drawn to a common point near the center and there
firmly united. At this point of union is attached the twine which is
held in the hand of the kite flyer. From the base of the kite is
suspended a string with light horizontal paper rolls, each about the
size of a lead pencil, tied at intervals of a few inches, and forming
the tail which steadies the kite in air. The paper surface of the kite
is the plane on which the pressure of the air current and the power
applied to the string is to lift the kite upward. As this simple form of
the kite has but one plane, it may be considered a monoplane. The box
kite presents two such surfaces joined together at the sides by the ends
of the "box," and may therefore be called a biplane.
When the boy flies his kite he first determines the direction of the
wind and runs in that direction. In other words he flies his kite
against the wind. The pressure of the moving current against the under
surface keeps the kite aloft. When the boy runs against the wind, moving
the kite forward with him, this pressure is increased and the kite tends
to rise higher and higher. If instead of the long string and the boy
there could be placed with the kite itself a very light motor that would
give to it the same forward impulse, the kite would float through the
air without boy or string and we would have a small aeroplane flying
machine--a monoplane. If there were two kites, with parallel surfaces a
few inches apart, united with light framework so that the air would pass
between them, we should have a biplane. For many years the great problem
in aviation was to get an engine of sufficient lightness and power to
propel monoplanes, biplanes and multiplanes at an upward angle through
the air.