Gravity is the force acting upon the kite to pull it down to ground level. The heavier the kite the more force gravity will have therefore the harder it will be to fly it. For this reason most modern kites are made out of very lightweight materials, therefore reducing the effect gravity has on the kite. So if gravity is pulling the kite down to earth, there must be another force that keeps the kite flying in the air, this force is known as lift.
Lift is force that pushes the kite away from the ground and the kite flyer, when you fly a kite it is lift that makes it feel as if the kite is trying to pull away from you. Lift is kept under control by flying the line or lines which the kite flyer controls. Without these lines the kite would blow away or fall to the ground.
To explain lift you need to understand a principle created by Daniel Bernoulli. He discovered that air pressure becomes lower if the air is moving, and the faster the air moves the lower the pressure becomes. This is very important in relation to the shape of a kite. Most modern kites are shaped so that the air travels faster over the top of the kite and slower underneath the kite. The angle at which the kite is being flown can also cause the wind to speed up over the top of the kite. The air pressure below the kite then tries to move upwards, pushing the kite up, in order to try and equalize the high and low pressures. Lift becomes greater when the difference between the high and low pressures increases.
In order for there to be airflow over the kite in the first place there must be thrust, this is the third force acting upon the kite. Thrust is created when the wind blows over a kite being held in one place by the kite flyer, the stronger the wind the more thrust is created. On days with no wind the only way to create thrust would be for the kite flyer to run and pull the kite through the air.
While we are on the subject of wind it may be useful to explain where the wind must be coming from in order for a kite to fly. A kite flyer will always have their kite downwind of them, this means they will have their back to the wind. There is an area called the wind window in which a kite will fly well, outside of this window the kite will stall. Within this wind window there are safe, low power zones out to the sides and there is also a high power zone low down in the middle. The diagram below shows the wind window and the different zones. To be a safe kite flyer you must always have plenty of space and no obstacles downwind of you.
Drag is the final force that acts upon a kite and comes from the tail, the shape of the kite and the materials that the kite is made out of. Drag slows the kite down in the air and can affect how a kite handles, for example a kite with a long tail will have more drag and be more stable when moving from side to side.
These four forces are essential to being able to get a kite to fly, by understanding how these forces affect the kite you can improve your kite flying skills have even more fun.
