Kite
From Wikipedia, the free encyclopedia
A kite is a flying tethered aircraft that depends upon the tension of a tethering system.[1] The necessary lift that makes the kite wing fly is generated when air (or in some cases water)[2][3][4] 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.[5] The anchor point of the kite line may be static or moving (e.g., the towing of a kite by a running person, boat,[6] or vehicle).[7][8]
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 were develop strongly by Domina Jalbert. Kytoons have been made in toy-scale as well as military large scale.[9][10]
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[11] which has had useful military applications in the past.[12]
Contents[hide] |
[edit] History
Kites were used approximately 2,800 years ago in China[13], 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.[14] 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.[15] Ancient and medieval Chinese sources list other uses of kites for measuring distances, testing the wind, lifting men, signaling, and communication for military operations.[15] 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.[16] 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 performed 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.[17][18]
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 (see Focke Achgelis Fa 330 for example). Since then they are used mainly for recreation due to a vast improvement in technology.
[edit] 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, fibreglass or carbon fibre 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.[13]
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 (15 m) 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.
[edit] Practical uses
[edit] 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.
According to Samguk Sagi, in 637, Kim Yu-sin, a Korean general of Silla rallied his troops to defeat rebels by lofting a kite with a straw man which looked like a burning ball flying to the sky.[19]
Russian chronicles mention prince Oleg of Novgorod use kites during the siege of Constantinople in 906 A.D.: "and he crafted horses and men of paper, armed and gilded, and lifted them into the air over the city; the Greeks saw them and feared".
Kites were also used by Admiral Yi of the Joseon Dynasty (1392-1910) 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.[20] The war eventually resulted in a 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.[21] Barrage kites were used to protect London as well as the Pacific coast of the United States during the last century.[22][23] Kites and kytoons were used for lofting communications antenna.[24] Submarines lofted observers in rotary kites.[25] The Rogallo parawing kite[26] and the Jalbert parafoil kite were used for governable parachutes (free-flying kites) to deliver troops and supplies.[27]
[edit] 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 the traditional 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 a historical role in lifting scientific instruments to measure atmospheric conditions for weather forecasting.
[edit] 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.
[edit] 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.[28] 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.[29] Kites are available as an auxiliary sail or emergency spinnaker for sailing boats. Self-launching Parafoil kites are attached to the mast.[citation needed]
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".[30]
[edit] 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.[31]
A separate Delft University of Technology project has used a 10 m² kite to generate 10 kilowatts of power.[32]
See also laddermill.
At the KULeuven, there also is a research group investigating the use of kites for power generation. But rather than flexible kites, they use a rigid wing structure, like a plane, because of the higher gliding number, easier control and better understanding of plane dynamics. A small prototype is being built.
[edit] 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.
[edit] 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.[33] 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, kite flying is the most popular game of Asia, and is known in Dari 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 used to create a whistle as the kite flies.[citation needed]
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, Punjab and the cities of Ahmedabad, Vadodara, Jaipur, Dhanbad, Varansi 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. An international kite festival is held every year before Uttarayan for three days in Vadodara, Surat and Ahmedabad. These three cities are the main sites where kite flying is observed on 14 and 15 January every year. The 14th known as 'Uttarayan' and 15th known as 'Vasi Uttarayan'. People start flying kites early in the morning and continue until the evening. Playing music to accompany kite-flying is a common sight. The kite is known as 'Patang' in Gujarat and other places in India. People start preparations before 15 days ahead to buy kites and cords for their kites.
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 8100 m2. 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 UK, Malaysia, Indonesia, Taiwan, Thailand and the USA.
[edit] 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.[13]
[edit] South America
In Chile, it is very popular, especially during Independence Day festivities (September 18).
In Guyana, kites are flown at Easter and is an activity participated in by all ethnic and religious groups. Kites are generally not flown at any other time of year. Kites start appearing in the sky in the weeks leading up to Easter and school children are taken to parks for the activity. It all culminates in a massive airborne celebration on Easter Monday especially in Georgetown, the capital, and other coastal areas. The history of the practice is not entirely clear but given that Easter is a Christian festival, it is said that the flying kite is symbolic of the Risen Lord. Moore[34] describes the phenomenon in the 19th century as follows:
A very popular Creole pastime was the flying of kites. Easter Monday, a public holiday, was the great kite-flying day on the sea wall in Georgetown and on open lands in villages. Young and old alike, male and female, appeared to be seized by kite-flying mania. Easter 1885 serves as a good example. “The appearance of the sky all over Georgetown, but especially towards the Sea Wall, was very striking, the air being thick with kites of all shapes and sizes, covered with gaily coloured paper, all riding bravely on the strong wind"
(His quotation is from a letter to The Creole newspaper of December 29, 1858). The exact origins of the practice of kite flying (exclusively) at Easter are unclear. Brereton and Yelvington[35] speculate that kite flying was introduced by Chinese indentured immigrants to the then colony of British Guyana in the mid 19th century. The author of an article in the Guyana Chronicle newspaper of May 6, 2007 is more certain:
Kite flying originated as a Chinese tradition to mark the beginning of spring. However, because the plantation owners were ever so suspicious of the planter class [read, plantation workers], the Chinese claimed that it represented the resurrection of Jesus Christ. It was a clever argument, as at that time, Christians celebrated Easter to the glory of the risen Christ.
[edit] Popular culture
- The Kite Runner, a 2005 novel by Khaled Hosseini dramatizes the role of kite fighting in pre-war Kabul.
- The Peanuts cartoon character Charlie Brown was often depicted having flown his kite into a tree as a metaphor for life's adversities.
[edit] 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 kite fliers 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.[37][38]. One method to obtain the glass was to break fluorescent light bulbs. The same problem has been reported in the Philippines and in Brazil.[13].
[edit] Kite designs
- Bermuda kite
- Bowed kite, eg Rokkaku
- Cellular or box kite
- Chapi-chapi
- Delta kite
- Foil, parafoil or bow kite
- Malay kite see also wau bulan
- Tetrahedral kite
[edit] Kite types
- Expanded polystyrene kite
- Fighter kite
- Indoor kite
- Inflatable single-line kite
- Kytoon
- Man-lifting kite
- Rogallo parawing kite
- Stunt kite
- Water kite
No comments:
Post a Comment