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.