stunt kite

Kite

[kahyt]

A kite is a flying tethered object that depends upon the tension of a tethering system. 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 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 or kite buggying. Kites towed behind boats can lift passengers which has had useful military applications in the past.

History

The kite was first invented and popularized 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, kite author Clive Hart and kite expert Tal Streeter hold that kites existed far before that time. 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, 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.

After its appearance in China, the kite migrated to Japan, Korea, Thailand, Burma (Myanmar), India, Arabia, and North Africa, then farther south into the Malay Peninsula, Indonesia, and the islands of Oceania as far east as Easter Island. Since kites made of leaves have been flown in Malaya and the South Seas from time immemorial, the kite could also have been invented independently in that region.

One ancient design, the fighter kite, became popular throughout Asia. Most variations, including the fighter kites of India, Thailand and Japan, are small, flat, roughly diamond-shaped kites made of paper, with a tapered bamboo spine and a balanced bow. Flown without tails that would hinder their agility, these highly maneuverable flat kites have a length of cutting line coated with an abrasive attached to the bridle, which is then tied to a light cotton flying line. Although the rules of kite fighting varied from country to country, the basic combat was to maneuver the swift kite in such a way as to cut the opponent's flying line.

Kite Fighting

Although the rules of kite fighting varied from country to country, the basic combat was to maneuver the swift kite in such a way as to cut the opponent's flying line.

Kite flying began much later in Europe than in Asia. While unambiguous drawings of kites first appeared in print in the Netherlands and England in the 17th century, pennon-type kites that evolved from military banners dating back to Roman times and earlier were flown during the Middle Ages. Joseph Needham says that the earliest European description of a kite comes from the Magia Naturalis written in 1589 by the Italian polymath Giambattista della Porta (1535–1615).

During the 18th century tailless bowed kites were still unknown in Europe. Flying flat arch- or pear-shaped kites with tails had become a popular pastime, mostly among children. The first recorded scientific application of a kite took place in 1749 when Alexander Wilson of Scotland used a kite train (two or more kites flown from a common line) as a meteorologic device for measuring temperature variations at different altitudes.

The next year, in 1750, Benjamin Franklin published a proposal for an experiment to prove that lightning is electricity by flying a kite in a storm that appeared capable of becoming a lightning storm. Benjamin Franklin wisely never preformed his experiment, but on May 10, 1752, Thomas-François Dalibard of France conducted Franklin's experiment (using a 40-foot (12 m)-tall iron rod instead of a kite) and extracted electrical sparks from a cloud.

Materials

Kites typically consist of one or more spars to which a paper or fabric sail is attached, although some, such as foil kites, have no spars at all. Classic kites use bamboo, rattan or some other strong but flexible wood for the spars, paper or light fabrics such as silk for the sails, and are flown on string or twine. Modern kites use synthetic materials, such as ripstop nylon or more exotic fabrics for the sails, fiberglass or carbon fiber for the spars and dacron or dyneema for the kite lines.

Kites can be designed with many different shapes, forms, and sizes. They can take the form of flat geometric designs, boxes and other three-dimensional forms, or modern sparless inflatable designs. Kites flown by children are often simple geometric forms (for example, the diamond). In Asia, children fly dried symmetrical leaves on sewing thread and sled-style kites made from sheets of folded writing paper.

Designs often emulate flying insects, birds, and other beasts, both real and mythical. The finest Chinese kites are made from split bamboo (usually golden bamboo), covered with silk, and hand painted. On larger kites, clever hinges and latches allow the kite to be disassembled and compactly folded for storage or transport. Cheaper mass-produced kites are often made from printed polyester rather than silk.

Tails are used for some single-line kite designs to keep the kite's nose pointing into the wind. Spinners and spinsocks can be attached to the flying line for visual effect. There are rotating wind socks which spin like a turbine. On large display kites these tails, spinners and spinsocks can be 50 feet (15m) long or more.

Modern acrobatic kites use two or four lines to allow fine control of the kite's angle to the wind. Traction kites may have an additional line to de-power the kite and quick-release mechanisms to disengage flyer and kite in an emergency.

Practical uses

Military applications

Kites have been used for military uses in the past for signaling, for delivery of munitions, and for observation, by lifting an observer above the field of battle, and by using kite aerial photography. Kim Yu-Sin (or Kim Yushin), a Korean general, in 637 C.E. rallied his troops to defeat rebels by kite lofting a burning ball. Kites were also used by Admiral Yi of the Joseon (1392-1910) Dynasty of Korea. During the Japanese invasions of Korea (1592-1598), Admiral Yi commanded his navy with kites. His kites had specific markings directing his fleet to perform his order. Admiral Yi was said to have over 300 such kites. The war eventually resulted in a Chinese and Korean victory; the kites played a minor role in the war's conclusion.

In more modern times the British navy also used kites to haul human lookouts high into the air to see over the horizon and possibly the enemy ships, for example with the kite developed by Samuel Franklin Cody. Barrage kites were used to protect London as well as the Pacific coast of the United States during the last century. Kites and kytoons were used for lofting communications antenna. Submarines lofted observers in rotary kites. The Rogallo parawing kite and the Jalbert parafoil kite were used for governable parachutes (free-flying kites) to deliver troops and supplies.

Science and meteorology

Kites have been used for scientific purposes, such as Benjamin Franklin's famous experiment proving that lightning is electricity. Kites were the precursors to aircraft, and were instrumental in the development of early flying craft. Alexander Graham Bell experimented with very large man-lifting kites, as did the Wright brothers and Lawrence Hargrave. Kites had an historical role in lifting scientific instruments to measure atmospheric conditions for weather forecasting.

Radio aerials and light beacons

Kites can be used for radio purposes, by kites carrying antennas for MF, LF or VLF-transmitters. This method was used for the reception station of the first transatlantic transmission by Marconi. Captive balloons may be more convenient for such experiments, because kite-carried antennas require a lot of wind, which may be not always possible with heavy equipment and a ground conductor. It must be taken into account during experiments, that a conductor carried by a kite can lead to a high voltage toward ground, which can endanger people and equipment, if suitable precautions (grounding through resistors or a parallel resonant-circuit tuned to transmission frequency) are not taken.

Kites can be used to carry light effects such as lightsticks or battery powered lights.

Kite traction

Kites can be used to pull people and vehicles downwind. Efficient foil-type kites such as power kites can also be used to sail upwind under the same principles as used by other sailing craft, provided that lateral forces on the ground or in the water are redirected as with the keels, center boards, wheels and ice blades of traditional sailing craft. In the last two decades several kite sailing sports have become popular, such as kite buggying, kite landboarding and kite surfing. Snow kiting has also become popular in recent years.

Kite sailing opens several possibilities not available in traditional sailing:

  • Wind speeds are greater at higher altitudes
  • Kites may be manoeuvered dynamically which increases the force available dramatically
  • There is no need for mechanical structures to withstand bending forces; vehicles or hulls can be very light or dispensed with all together

The German company SkySails has developed ship-pulling kites as a supplemental power source for cargo ships, first tested in January 2008 on the ship MS Beluga Skysails. Trials on this 55 m ship have shown that, in favorable winds, the kite reduces fuel consumption by up to 30%. This system is planned to be in full commercial production late 2008. Kites are available as an auxiliary sail or emergency spinnaker for sailing boats. Self-launching Parafoil kites are attached to the mast.

MS Beluga Skysails is the world's first commercial container cargo ship partially powered by a giant computer-controlled kite (160 m² or 1,722 sq ft). The kite could reduce fuel consumption by 20%. It was launched on 17 December 2007 and was set to leave the northern German port of Bremerhaven to Guanta, Venezuela on January 22, 2008. Stephan Wrage, managing director of SkySails GmbH announced: "During the next few months we will finally be able to prove that our technology works in practice and significantly reduces fuel consumption and emissions." Verena Frank, project manager at Beluga Shipping GmbH, SkySails GmbH's partner further stated that "the project's core concept was using wind energy as auxiliary propulsion power and using wind as a free of charge energy".

Power generation

A conceptual research and development project by Makani Power, based in California and funded by Google.org, is investigating the use of kites in harnessing high altitude wind currents to generate electricity.

A separate Delft University of Technology project has used a 10 kite to generate 10 kilowatts of power.

See also laddermill.

Cultural uses

Kite festivals are a popular form of entertainment throughout the world. They include small local events, traditional festivals which have been held for hundreds of years and major international festivals which bring in kite flyers from overseas to display their unique art kites and demonstrate the latest technical kites.

Asia

Kite flying is popular in many Asian countries, where it often takes the form of 'kite fighting', in which participants try to snag each other's kites or cut other kites down. Fighter kites are usually small, flat, flattened diamond-shaped kites made of paper and bamboo. Tails are not used on fighter kites so that agility and maneuverability are not compromised. In Afghanistan this is known as Gudiparan Bazi. Some kite fighters pass their strings through a mixture of ground glass powder and glue. The resulting strings are very abrasive and can sever the competitor's strings more easily. The abrasive strings can also injure people. During the Taliban rule in Afghanistan, kite flying was banned, among various other recreations.

In Vietnam, kites are flown without tails. Instead small flutes are attached allowing the wind to "hum" a musical tune. There are other forms of sound-making kites. In Bali, large bows are attached to the front of the kites to make a deep throbbing vibration, and in Malaysia row of gourds with sound-slots are use to create a whistle as the kite flies.

The Indian festival of Makar Sankranti is devoted to kite fighting in some states. This spring festival is celebrated every January 15, with millions of people flying kites all over northern India. The states of Bihar, Jharkhand, Gujarat, some part of West Bengal, Rajasthan , and the cities of Ahmedabad, Jaipur, Dhanbad and Hyderabad are particularly notable for their kite fighting festivals. Kite flying in Hyderabad starts a month before the official kite flying festival (Sankranthi). The thread used to fly kites in Hyderabad is known as 'Manjaa'. Highly maneuverable single-string paper and bamboo kites are flown from the rooftops while using line friction in an attempt to cut each other's kite lines, either by letting the line loose at high speed or by pulling the line in a fast and repeated manner. In some Indian cities kite flying/fighting is an important part of other celebrations, including Republic Day, Independence Day, Raksha Bandhan, and Janmashtami.

In Pakistan, kite flying is a popular ritual for the spring festival known as Basant. However, kite flying is currently banned as some kite fliers engage in kite battles by coating their strings with glass or shards of metal, leading to injuries and death. Kite fighting is a very popular sport in Pakistan, mainly centered in Lahore. Kup, Patang, Guda, and Nakhlaoo are some of the kites used in fighting and they vary in balance, weight and speed through the air.

Weifang, Shandong, China promotes itself as the kite capital of the world. It is home to the largest kite museum in the world, which has a display area of 8100m². Weifang hosts an annual international kite festival on the large salt flats south of the city. There are several kite museums in Japan and others in England, Malaysia, Indonesia, Taiwan, Thailand and the USA.

Europe

In Greece and Cyprus, flying kites is a tradition for Clean Monday, the first day of Lent. In the British Overseas Territory of Bermuda, traditional Bermuda kites are made and flown at Easter, to symbolise Christ's ascent. Bermuda kites hold the world records for altitude and duration.

South America

In Chile, it is very popular, especially during Independence Day festivities (September 18).

Popular culture

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 areas or powerful lift can lift the kite flier off the ground or drag them into stationary 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. In Asia, specially in the Indian subcontinent the twine is coated with powdered glass to cut opponent's lines and these deadly strings known as Manja are reported to kill number of pedestrians or motorcyclists each year all over the region.

Types of kites

Types of kite line

See also

References

External links

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