Kites fly according to the same aerodynamic principles. Instead of a motor the kite uses a line to the ground to prevent the kite being blown backwards as the wind flows over the surface of the kite. An aeroplane uses an engine to create its own thrust and to move through the air, while a kite uses the existing wind, and the flying line to hold it into that wind, to generate thrust. Consequently, if there is no wind there is no thrust, and the kite will not fly. If there isn't any wind, you can create some for your kite by running with the kite. Running at five kilometers per hour with a kite in still air is the same as standing still with a kite in a five kilometer per hour breeze. In both cases there is a five kilometer per hour movement of air over the surface of the kite. If the wind is strong enough for the kite to generate sufficient lift to overcome the weight of the kite, and the kite is not producing too much drag, then the kite will fly.
If an aerofoil is looked at in cross section, it is obvious that the upper surface is curved and the lower surface is more or less flat. The aerofoil acts as a wedge, cutting the airflow into two streams, one passing over the aerofoil, and one passing under it. The streams of air intermingle again after they have passed the aerofoil and reach the back, or trailing edge, of the aerofoil. The curved, upper surface is longer from front to back than the flat, lower surface, so air must move faster over the aerofoil in order to reach the trailing edge of the aerofoil at the same time as the air that has traveled along the lower surface. Tilting an aerofoil so that its leading edge is higher than its trailing edge increases the distance that the upper stream of air has to travel, and as the time taken by the stream of air to travel from leading to trailing edge is not increased, the air pressure is further reduced. This means that more lift is produced when an aerofoil is tilted so that its leading edge is higher than its trailing edge. The angle of this tilt is called the angle of attack. As the angle of attack increases, the air above the upper surface starts to become turbulent, and slows down, which reduces the amount of lift. If the angle of attack becomes excessive, the turbulence becomes severe enough to slow the airflow over the wing to the point where no lift is produced
2007-08-14 00:33:30
·
answer #2
·
answered by Anonymous
·
0⤊
0⤋