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Kite Flying

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Author: Marc Rosner

Kites are readily available for purchase in many stores. However, the experience of flying a kite is much more rewarding when you have constructed the kite yourself. By experimenting with the design, and trying to obtain the maximum possible altitude, you can learn about aerodynamics and engineering.

Kites have different functions. Fighting kites are used to attack each other in contests. Acrobatic kites can dive, loop, and perform figure eights. Some kites are designed to appeal to the eye and ear. These kites range in form from simple diamond shapes to figures resembling birds, animals, and mythological creatures, including dragons up to 30 m long. The kites are usually multicolored and may carry bamboo pipes and other instruments that emit musical sounds.

Materials

  • thin spruce sticks 0.5 cm thick, or 1/4-in. dowel stock
  • fine-tooth wood saw (requires adult help)
  • meterstick
  • knife (requires adult help)
  • glue
  • 160 m of thin nylon string, available at hardware stores (not wire!)
  • scissors
  • kite cloth (newspaper, closely woven silk, or Mylar)
  • kite string spool
  • strip of cloth for tail
  • 4 paper cups or pint-sized ice cream cartons (if not using cloth)
  • bamboo (optional)
  • small camera or weather-sensing instruments (optional)

Procedure

  1. Construct a simple diamond-shaped kite—a pair of crossed sticks covered with paper.
    1. Have an adult use a fine-tooth wood saw to cut the sticks. Make the spline, or vertical stick, 100 cm long, and the spar, or horizontal stick, 67 cm long. Have adult use a knife to make a 2-mm notch at both ends of each stick.
    2. Position the sticks so that the middle of the spar crosses the middle of the spline 33 cm from the top of the spline. Fasten the sticks together where they cross, using a drop of glue and a binding of string.
    3. When the glue dries, run a string around the sticks through the notches.
    4. Cut a piece of kite cloth as shown, fold the edges over the string, and secure it with glue.
    5. Fit the kite with a bridle, a short span of string tied to the top and bottom ends of the spline on the cloth-covered side of the kite, and a span tied to each end of the spar. (The length of each span is determined by the dimensions and flexibility of the kite.) Adjust the bridle length so that the strings become taut when pulled 30 cm from the cloth at a point directly above where the sticks cross.
    6. Kite Flying

    7. Wind 150 m of string on a spool. This is your flying string. Temporarily tie the free end of the flying string to the bridle at the point determined in step Ie. The point at which the flying string is attached to the bridle determines the angle at which the air strikes the kite: the angle of attack.
    8. Diamond kites are unstable until you fit them with a tail to hold them upright. A tail can simply be a strip of cloth tied to the base of the spline. Alternatively you can provide the kite with a tail that consists of a series of wind cones (see figure). The cones can be made by removing the bottoms from four paper containers, such as paper cups or ice cream cartons. Connect the cups with nylon string.
  2. Kites, like the mainsail of a sailboat, perform best at angles of attack ranging from about 20 to 25 degrees, greater than the angle at which an airplane wing meets the wind because of the pronounced curvature of the paper. The exact angle of attack at which a kite performs best depends on the strength of the wind and must be determined experimentally. The adjustment is accomplished by shifting the flying string toward the top of the kite.
  3. Fly your kite in a safe place, such as an open field at least 1 km from any power lines or airports. Never fly a kite when the string is wet or the weather is bad.
  4. The stabilizing force is provided partly by the weight of the tail, partly by friction between the tail and the moving air, and partly by turbulence generated in the airstream by the tail. The last two forces are known as drag. The amount of stability required increases with the speed of the wind. A kite that flies nicely with a short tail during a light breeze will spin out of control in a stiff wind. Yet a kite with a long tail that flies well in a stiff wind may not fly in a light breeze.
    1. To launch your kite, grasp the spool of flying string in one hand and the bottom of the kite in the other.
    2. A circular kite can be made by bending bamboo into a hoop.
    3. Incline the kite at an angle of about 25 degrees into the wind, with the cloth side facing the wind, and let it go.
    4. As the kite rises, play out the flying string at a rate that allows the kite to continue its ascent.
  5. Experiment with different design changes. You can vary the following:
  1. The length of the spline and the spar.
  2. The shape of the kite. For example, three sticks of equal length can be crossed to make a hexagonal kite.
  3. The construction materials.
  4. The length and weight of the tail.
  5. The number of kites. You can send up a train of two or more kites.
  6. The payload (cargo). For example, you can send up a small camera or weather-sensing instruments.
On May 5, 1910, the uppermost unit in a train of 10 Weather Bureau kites carried a payload of meteorological instruments to an altitude of 8,000 m. The kite exerted a pull of nearly 0.25 ton on the 14.5-km flying string of piano wire.

References

The Great Kite Book by Norman Schmidt (New York: Sterling, 1998).

Making Kites (Step-by-Step) by David Michael and David Jefferis (Stanwood, Wa.: Kingfisher, 1993).

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