Aerodynamics of kites
A kite as a heavier-than-air object and logically should fall under the influence of gravity. But it doesn’t. The reason is that it is an air-foil, and its flight is defined by aerodynamics and Bernoulli’s principle.
Unlike the wings of aeroplanes, sails, bird wings and parachutes, kites can alter or redirect the flow of air around it unevenly so as to create pressure differences. While putting the kite in the air, the angle of the kite diverts the flow of air unevenly over it. This causes the air passing over the kite to move faster than the air passing under.
At this point, according to Bernoulli’s Principle, the faster a current of air moves, the lower its pressure becomes. And, as any physics student will tell you, there is thus a high-pressure build-up below the kite which gives it lift. Gravity tends to pull the kite down while the lift makes the kite float.
When the kite is in equilibrium, four forces — gravity, lift, resistance (drag) from the wind, and the tension of the kite line-cancel out. Drag tends to push the kite horizontally back while the kite line pulls the kite forward. This state keeps kite in steady position.
There are some lato changa, or lazy kites, which respond only when stronger force is applied through the line. This is caused by the low lift-to-drag ratio. If the drag is greater than the lift, the kite will not fly at all.
On a keen breeze, a kite will be at equilibrium and easy to control. When the wind dies down, the kite stalls. But even here, quick lattai action can keep a kite aloft. But there is a penalty: you will have to sacrifice line length. Pulling at the string with a lattai raised above the head is the trademark Nepali way of flying a kite in light breeze.
There are various traditional ways to steer a kite. To take the kite left, for example, wait for the kite to point left and give the lattai a yank pulling it on the right side of your body. Ditto if you want to go down or up. While reeling out the lattai, the kite often rotates, and you have to be careful not to reel in while the nose is pointed down this could put it in an uncontrolled dive. Also remember to allow for delay for the kite to respond to your command, and this delay is always directly proportional to the tension on the line. So, if your line is tight the kite responds immediately, if it is sagging it is sluggish.
Because of the congested urban space, the Nepali roof-top kite flyers are sometimes compelled to yank the lattai to coax their kite up. But field kite flyers have the advantage of a long runway for a kite’s takeoff and get it higher after the launch for it to catch a passing breeze.