Unpowered Aircraft

A kite is an aircraft consisting of one or more wings tethered to an anchor system. Frequently a wing of a kite is referenced as "kite". The necessary lift that sustains the kite in flight is generated when air flows above the kite's surface, producing low pressure above and high pressure below the wings. The interaction with the wind 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 one or more of the lines or tethers to which the kite is attached. The anchor point of the kite line may be static or moving (e.g., the towing of a kite by a running person, boat, free-falling anchors as in paragliders and fugitive parakites or vehicle).
The same principles can be used in water and experiments have also been made with lighter-than-air kites (kytoons)



History

Kites were invented 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.
The kite has been claimed as the invention of the 5th-century BC Chinese philosophers Mozi (also Mo Di) and Lu Ban (also Gongshu Ban). By AD 549 paper kites were certainly being flown, as it was recorded that in that year a paper kite was used as a message for a rescue mission. Ancient and medieval Chinese sources describe kites being used for measuring distances, testing the wind, lifting men, signaling, 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. From China, kite was introduced to Cambodia, India, Japan, Korea and western world


After its introduction into India, the kite further evolved into the fighter kite, known as the patang in India, where thousands are flown every year on festivals such as Makar Sankranti.
Kites were known throughout Polynesia, as far as New Zealand, with the assumption being that the knowledge diffused from China along with the people. Anthropomorphic kites made from cloth and wood were used in religious ceremonies to send prayers to the gods. Polynesian kite traditions are used by anthropologists get an idea of early "primitive" Asian traditions that are believed to have at one time existed in Asia.

Kites were late to arrive in Europe, although windsock-like banners were known and used by the Romans. Stories of kites were first 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. Although they were initially regarded as mere curiosities, by the 18th and 19th centuries kites were being used as vehicles for scientific research.

In 1750 Benjamin Franklin published a proposal for an experiment to prove that lightning was caused by electricity by flying a kite in a storm that appeared capable of becoming a lightning storm. It is not known whether Franklin ever performed his experiment, but on May 10, 1752, Thomas-François Dalibard of France conducted a similar experiment (using a 40-foot (12 m) iron rod instead of a kite) and extracted electrical sparks from a cloud.

Kites were also instrumental in the research of the Wright brothers when developing the first airplane in the late 1800s. Over the next 70 years, many new kite designs were developed, and often patented. These included Eddy's tail-less diamond kite, the tetrahedral kite, the flexible kite, the sled kite, and the parafoil kite, which helped to develop the modern hang-gliders. In fact, 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; many different designs of man-lifting kite were developed as well as power kites.
The development of mechanically powered airplane diminished interest in kites. World War II saw a limited use of kites for military purposes (see Focke Achgelis Fa 330 for an example). Since then they are used mainly for recreation

General safety issues

There are safety issues involved in kite-flying, more so with power kites. Kite lines can strike and tangle on electrical power lines, causing power blackouts and running the risk of electrocuting the kite flier. Wet kite lines or wire can act as a conductor for static electricity and lightning when the weather is stormy. Kites with large surface area or powerful lift can lift kite fliers off the ground or drag them into other objects. In urban areas there is usually a ceiling on how high a kite can be flown, to prevent the kite and line infringing on the airspace of helicopters and light aircraft.