A kite is a tethered aircraft. The necessary lift that makes the kite wing fly is generated when air (or in some cases water) flows over and under the kite's wing, producing low pressure above the wing and high pressure below it.
This deflection also generates horizontal drag along the direction of the wind. The resultant force vector from the lift and drag force components is opposed by the tension of the one or more lines or tethers. The anchor point of the kite line may be static or moving (e.g., the towing of a kite by a running person, boat or vehicle).
Kites are usually heavier-than-air, but there is a second category of lighter-than-air kite called a kytoon which may be filled with hydrogen, hot air, methane, or helium; these stay aloft with or without wind; at calm they float; at wind they receive lift from buoyancy and aerodynamic lift. Kytoons have been made in toy-scale as well as military large scale.
Kites may be flown for recreation, art or other practical uses. Sport kites can be flown in aerial ballet, sometimes as part of a competition. Power kites are multi-line steerable kites designed to generate large forces which can be used to power activities such as kite surfing, kite landboarding, kite buggying and a new trend snow kiting. Kites towed behind boats can lift passengers which has had useful military applications in the past.
Kites were used approximately 2,800 years ago in China, where materials ideal for kite building were readily available: silk fabric for sail material; fine, high-tensile-strength silk for flying line; and resilient bamboo for a strong, lightweight framework. Alternatively, the kite authors Clive Hart and Tal Streeter hold that leaf kites existed far before that time in what is now Indonesia, based on their interpretation of cave paintings on Muna Island off Sulawesi. The kite was said to be the invention of the famous 5th century BC Chinese philosophers Mozi and Lu Ban. By at least 549 AD paper kites were being flown, as it was recorded in that year a paper kite was used as a message for a rescue mission. Ancient and medieval Chinese sources list other uses of kites for measuring distances, testing the wind, lifting men, signalling, and communication for military operations. The earliest known Chinese kites were flat (not bowed) and often rectangular. Later, tailless kites incorporated a stabilizing bowline. Kites were decorated with mythological motifs and legendary figures; some were fitted with strings and whistles to make musical sounds while flying.
Stories of kites were brought to Europe by Marco Polo towards the end of the 13th century, and kites were brought back by sailors from Japan and Malaysia in the 16th and 17th centuries.
The period from 1860 to about 1910 became the "golden age of kiting". Kites started to be used for scientific purposes, especially in meteorology, aeronautics, wireless communications and photography; reliable manned kites were developed as well as power kites. Invention of powered airplane diminished interest in kites.World War II saw a limited use of kites for military purposes. Since then they are used mainly for recreation due to a vast improvement in technology.
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