The kite is a heavier-than-air object, so why does it fly? How does it counteract gravity and soar up into the sky? Some basic aerodynamic principles answer these questions and make skillful kite fliers.

There are three forces that act upon a kite to keep it aloft -- gravity, lift, and drag. The first force, gravity, is the force that pulls the kite downward. The second, lift, is the upward force, caused by the wind. This force enables the kite to defy the law of gravity. The third force, drag, is the resistance of the air to the movement of the kite.

It is the ratio between lift and drag that determines how well a particular kite will fly. If the amount of drag is much greater than the amount of lift, the kite will not get off the ground. If the combined forces of gravity and drag equal the force of lift, the kite will float in one place. On the other hand, if the combined forces are greater, the kite may dive to the ground.

The wind is the major factor in making the kite airborne. When the face is tipped forward into the wind, the kite begins to rise. The wind pushes against it forcing it backward and upward. Simultaneously the flying line pulls downward and holds the kite steady so that it can keep its angle of flight. Frequently, without warning, changes in the wind cause a kite to lose its angle of flight. It no longer catches the wind and falls. For example, if the kite flies directly overhead, it will flatten out, become parallel to the ground, and lose altitude.

Some aerodynamic principles show how the wind affects the flight of the kite. For example, a kite is like an airplane wing. Both stay up because of the movement of air around their surfaces. To make the air rush over and under its wings, an airplane is pushed or pulled through the air by its jet engines. A kite, however, is lighter and all wing. It is secured by the string while the air rushes around the kite itself.

Air that rushes along under the surface of an airplane wing (or a kite) tends to push the wing or kite upward. The air, however, that flows over the upper surface of the wing or kite provides even more lifting power.

A Swiss scientist, Daniel Bernoulli, explained this about 200 years ago. He discovered that water flowing rapidly through a pipe presses against the inside of the pipe with less force than water flowing slowly. This effect also occurs with air.

Air that flows over the curved upper surface of an airplane wing travels a longer path than air that flows under the wing. The air flowing over the wing, therefore, has to flow faster than the surrounding air in order to keep up with it. The slower flowing air pushes up the lower surface of the wing with greater force than the faster moving air pushing down on the upper surface. This provides the extra force needed to lift the airplane off the ground and keep it up in the air.

If a kite is held so that the wind is blowing against one side, the paper surface bulges somewhat like the top of an airplane wing. When the kite is flying, the weight of the string holds down the front surface so that air flows over the curved upper surface just like it does over an airplane wing. This produces the lift that keeps the kite in the air

 
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