The phrase “flying a kite” has long been synonymous with the word “wind”. At the beach, you may find a number of kites in the air due to the constant sea breeze.
Yes, you do need wind to fly a kite. The power source for keeping a kite afloat is wind. Wind speed and direction are the most important factors in kite flying; too little wind and your kite can be difficult to launch or to keep afloat, but too much wind and you might be launched into the air, or your kite might get damaged.
Man has always had a fascination with flight, with one of the earliest attempts recorded in Greek mythology as the story of Icarus flying too close to the sun. In modern times, we fly in aeroplanes, or on rockets to the Moon. A kite is like a tethered aircraft – the string stops the kite from flying away with the wind. As a kite has no engines, wind becomes its power source to keep it in the air.
Kite-flying is exciting as a first step to understanding flight. In this article, we will go over what makes a kite fly, basic kite terms, and 2 broad categories of kites.
What Makes A Kite Fly?
There are 4 forces that affect a kite when it is flying: gravity, lift, thrust, and drag. These are the same forces that affects aircraft and even birds.
Gravity
Gravity is a force of attraction that exists between any 2 items. It is the force by which a planet or other body draws objects toward its center. The force of gravity keeps all of the planets in orbit around the sun. Gravity is a downward-acting force.
In this case, gravity between our kite and the Earth causes it to fall to the ground, just as you would when you jump up and land on your feet. It is an invisible force and keeps you on the ground.
In the above diagram, weight is the force that gravity exerts upon a body or item. It shows how gravity is constantly trying to pull your kite down to the ground.
Lift
Lift is the force that stops kites from getting pulled down to the ground when they are flying in the air. In other words, lift is the force that is pushing the kite up and away from the ground. Lift is an upwards-acting force.
Lift is produced by air moving over the top of the kite at a faster speed than the air that is moving over the bottom of the kite. Daniel Bernoulli, an 18th-century Swiss mathematician, is credited with the discovery that the pressure of air becomes lower when it is moving.
The faster air moves, the lower the pressure becomes. Aerodynamic objects such as cars, aircraft, and kites are shaped so that air slows down when travelling under its lower surface – in turn increasing pressure underneath the object – and air will speed up when it is travelling over the upper surface of the object, decreasing the pressure on the upper surface.
Using a kite as an example: as the air pressure above the kite becomes lower, the air pressure below the kite pushes the kite up in order to equalize the pressures above and below the kite. This creates lift to keep the kite afloat in the wind. Lift conventionally acts in an upward direction in order to counter the force of gravity.
The greater the difference between the low pressure and high pressure above and below the kite respectively, the greater the amount of lift produced. In order for all this to happen, air needs to be constantly moving over the kite – this moving air is known as wind.
Lift opposes gravity, and is usually artificially created to overcome the forces of Nature.
Thrust
Thrust is a reaction force described quantitatively by Newton’s third law, When a body pushes in one direction, there is thrust (force) just as large in the opposite direction. Thrust is used to describe how strongly an engine pushes. Thrust is a forward-acting force.
Thrust is most commonly seen when aircraft power up their engines to push air towards the back of the plane at high speeds to move the aircraft forward. Another good example of thrust is how birds move forward through the air by flapping their wings.
Kites do not have engines, and thus cannot produce their own thrust. Instead, kites rely on being held in place in the air as wind moves around it. We hold a kite in place via a piece of string. If there was no wind, you would have to run while holding the kite string attached to the kite. This creates wind for the kite and is a common way to launch kites.
Drag
The next question is then what stops a kite from flying straight over your head and away from you? This is known as drag. Drag is caused by the difference in air pressure between the front and back of the kite and the friction of the air moving over the surface of the kite. Very simply put, when you run forwards, you feel air resistance, which is also known as drag. Drag is also a backward-acting force.
All kites will always have some drag, and some kites are not able to fly without some extra drag being exerted on them. This additional drag is usually created by the tail of the kite, and allows us to make the kite point in the correct direction. Air flowing around the tail pulls the bottom of the kite in the direction that the wind is blowing.
The drag caused by the tail of a kite stops the kite from turning too much to one side or the other. A tail gives a kite lateral stability. If a kite has too small of a tail, it will not be laterally stable, and will move around a lot or even spin. If the kite has too much tail, the kite will be stable, but may be hard to keep flying because of the extra weight from the excess tail.
To launch a kite into the air the force of lift must be greater than the force of gravity. To keep a kite flying steady, all 4 forces must be in balance. Lift must be equal to gravity and thrust must be equal to drag.
Parts of a kite
After talking so much about the forces that come into play when flying a kite, knowledge of the different parts of your kite will help you when you read through the rest of our site, and will help you when you decide to either make your own kite, or when you need some help tweaking your kite.
A spar is the name for any of the sticks which act as the “skeleton” of the kite. The spine is the spar that runs from the top to the bottom of the kite. The cross-spar is the spar that runs from wingtip to wingtip, or left to right. The word frame is can also be used to describe the entire skeleton of a kite.
The leading edges of the kite are the edges which wind flows over first, as they point or lead into the wind. The trailing edges are the edges which the wind flows around last.
The bridle is the line that connects the kite with the flying or kite line that you hold on to. Some kites have a bridle that is connected to the kite itself in 2 places, and other kites use bridles that are attached to the kite in many places. The point where the flying line attaches to the bridle is called the bridling point.
The cover of the kite is called the sail. The sail is pushed against the spine and the cross-spar, dividing the sail into four areas. The two small areas at the top of the kite are called pilot sails. Pilot sails partially control the direction of the kite. The two larger segments are known as driving sails. The driving sails provide most of the lift.
In the picture above, you can see a slightly different kite. This kite is known as a Delta kite due to its triangular shape. You can also see that instead of a bridle, there is a keel. A keel is a piece of material on the bottom of the kite that is usually perpendicular to the rest of the kite when flying in the air. It is similar to the keel of a boat. The keel helps to keep the kite stable, and provides a place to attach the kite line without a bridle – usually at where it is indicated line attachment in the above picture.
The tail of a kite refers to the strips of paper, plastic or fabric which are attached to the trailing edge of a kite in order to increase the drag of the kite. These tails can be slim or thick, long or short. Tails are usually attached to the bottom of a kite, but can also be attached to the wingtips. In the above section about drag, we talk about how tails provide stability to kites.
The spars of a kite can be bowed, or bent, in order to give the cross-spar a dihedral angle. These kites are usually known as bowed kites. In bowed kites, the cross-spar is bent so that the wingtips are at a slight backwards angle to the spine. This helps to make the kite stable. If the kite starts to roll to one side, the wing on that same side presents a greater surface area to the wind. Inversely, the wing on the opposite side appears to reduce in surface area in relation to the wind. More pressure being exerted on the wing with more surface area being exposed to the wind, in turn, forces the kite to return to a stable normal again.
Angle of attack
The bridle is used to control the angle of attack of a kite. This is the angle at which the kite meets the wind.
In aerodynamics, the term “angle of attack” is used to describe the angle between the wing’s chord and the direction of the flow of wind. A wing’s chord refers to to the distance between the front and back of a wing, measured in the direction of the airflow.
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The amount of lift generated by a wing is directly related to the angle of attack. Greater or bigger angles will generate more lift, and in turn generates more drag as the front of the wing, or the kite, turns upwards and creates more friction.
A low angle of attack usually reduces the amount of tension on the kite string. The kite will also fly closer to vertically above the kite flier. This can be very relaxing for a kite flier, and also exciting so for first-timers as they see their kite floating along in the sky.
A high angle of attack normally increases the pull on the flying line as it generates more lift. This can be both fun and challenging as the kite flier will need to have a steady hand to prevent the kite line from snapping and the kite flying away.
There is also a limit called a critical angle of attack. Above this angle, any kite (or wing, for that matter) will produce what is known as wing stall. You may have heard of, or have had, a car stalling – this happens when the engine of a car accidentally stops. You may have also heard of aeroplanes stalling in mid-flight.
Remember how we talked about wind being the engine for kites? When we talk about kites stalling, it is because the layer of air above the kite dissipates as the angle of attack is too high and seemingly cuts off the airflow. In turn, this nullifies the difference in pressure between the upper and lower layers of air. Lift is then reduced to zero, and as there is no more lift, there is no more ‘engine’ for your kite to stay afloat in the air.
How do I prevent a kite from stalling? While it is easy to say: “just alter the angle of attack”, I find that this is something that requires experience.
When I feel that there is too much tension on my kite line, I will let more line out – this in turn lowers the angle of attack . I find that properly made kites will easily balance themselves out once I release some tension on the kite line. Make sure not to release all the kite line, or you may find that your kite will drift away!
If my kite has a low angle of attack, and I want to make it fly higher, or increase its lift, I would usually pull or reel in kite line till the angle is much higher without the kite stalling. This is where experience will come in handy. Once the kite is stable above me, I will then let more kite line out to coax it to fly higher in the sky.
If your kite has stalled and fallen to the ground, the best course is to make your way to where your kite has fallen, check it for any damage, and then try and relaunch it.
Keep in mind that the angle of attack can also be altered to make a kite fly in different wind conditions. A larger angle of attack will enable the kite to utilise more of the wind in light wind conditions. A low angle of attack will allow the kite more stability in strong winds.
Two Types Of Kites
There are 2 types of kites that you may hear from others, or see when you learn more about flying a kite. Both types use wind, but in different ways. Read on to find out more!
Outdoor Kites
Outdoor kites are the most common kites as they are used outdoors. At kite festivals, you can see many different types of kites in flight: from simple diamond-shaped kites, to the triangular Deltas, to fancy novelty kites.
Kites come in all shapes and sizes. Some kites can fly in very light breezes, while others require strong and steady winds. Kites can range from being made of two sticks covered with a sail, to a configuration requiring a complex framework, to without any sticks at all.
Traditionally, kites have been made with bamboo or flexible wood for the spars, fabric or paper for the cover or sail, and string or fibre twisted into string for the kite line. Today, kites are often built with synthetic, ultralight materials.
Flat Kites
Flat kites include all kites that are not bowed in some way. They don’t have to be any particular shape, as long as they are flat. Flat kites are unstable by themselves, and will require tails to stabilize them.
While tailless kites were common in Asia for centuries, it was not until 1893 that William A. Eddy, an American journalist with an interest in meteorology and kite aerial photography, made a significant contribution to kite development in the West. He introduced the commonly-seen tailless, elongated diamond-shaped design. William’s design was known as the Eddy kite, which was an adaptation of an ancient Javanese bowed kite. It was a reliable and popular flier that renewed interest in kite flying.
Bowed Kites
Bowed kites are kites that have a dihedral angle. Bowed kites usually do not have tails as they can easily self-correct in the air. We have a brief section on bowed kites earlier in this page, and you can read it here.
The Rokkaku kite is a traditional Japanese fighting kite that is quite popular in the West as well. It is hexagonal in shape, bowed, and is rarely seen with a tail.
Parafoils
Parafoils are also known as soft kites. These kites have no rigid spars and maintain their shape in flight by the wind filling the chambers or cells. A parachute is a great example of a parafoil. These are easy to fold down for transport, and are much less likely to break on impact.
Sled Kites
Sled kites are similar to parafoils as they are soft kites, and rely on the wind to hold it open. It has several spines running the length of the kite, but no cross-spars. Sleds often have vents cut in the sail, near the bottom of the kite, instead of using a tail. They pull very hard and fly with a high angle of attack.
Box Kites
Box kites are also known as cellular kites. This design involves vertical and horizontal surfaces. Because of these surfaces, which act in a similar way to the dihedral angle on bowed kites, this design does not need a tail. Box kites do well in strong winds and generate a lot of lift.
In Australia, in 1893, British-born explorer and inventor Lawrence Hargrave invented the box kite as part of his research to develop a stable three-dimensional lifting surface for powered manned flight. Hargrave’s box kites were exceptionally steady in strong winds. These kites, flown in tandem with piano wire as kite line, soon replaced the Eddy kite and were used for meteorological work well into the 1920s.
Delta Kites
The delta kite is one of the most popular types of kite that most beginners start out with because it is easy to launch and fly. Delta kites are triangular with a keel holding the spine straight and rigid.
Deltas are also great kites for very light winds, which can be helpful for beginners. They tend to be pushed up and forward so that they lie nearly parallel to the wind, resulting in a low angle of attack. As such, Deltas don’t pull very hard at all. The sail forms a billow, and combined with a keel (instead of a bridle), allows deltas to fly without a tail if one so wishes.
Sport/Stunt Kites
A sport kite, also commonly known as a stunt kite, is a kite that can be manoeuvred in the air. There are 2 common configurations for stunt kites: dual-line and quad-line.
As indicated by their names, dual-line kites have 2 kite lines, and quad-line kites have 4 kite lines. Dual-line kites usually have a triangular shape similar to the Delta (see above picture). Quad-line kites have a “W”-shaped panel (see picture below).
These kites are controlled by the kite flier by adding and releasing tension on the lines. Using a combination of pulls to add tension, and pushes to release tension on the lines, complex tricks and patterns can be flown. Turns, loops, landings, or even flipping the kite end over end are very possible with such kites. Sport kites can be also made to dive or swoop down, while in stall-type manoeuvres they can remain nearly motionless.
Low-wind / Zero-wind / Windless / Indoor Kites
Outdoor kites can be very exciting, especially with stunt kites as various manoeuvres can be performed with them, or with novelty kites as they are aesthetically pleasing to the eye.
However, did you know that you can also fly kites indoors? These kites are also known as low-wind, zero-wind, or windless kites. Indoor kites are designed to fly in a windless environment. While originally designed for indoor use, they can also be flown outdoors when insufficient wind would render traditional kite-flying impossible. They are flown by using the relative wind created by the motion of the kite flier. This motion is typically generated by the user walking slowly backwards, often in a circle, but it can also be achieved with suitable pulls and jerks along the kite line(s).
Many people would attribute the rise of the popularity of indoor kite flying to Connor Doran, who flew his quad-line indoor kite in Season 5 of America’s Got Talent in 2010.
As ultralight materials became more readily available, indoor kites were developed from the idea of flying low-wind kites. Today, indoor kites come in all varieties. There are two-line and four-line indoor kites that are capable of performing most of the same tricks and manoeuvres as an outdoor kites.
Indoor kites are often flown in time to music and indoor kite festivals occur regularly, complete with the same demonstrations and competitions that take place at traditional kite-flying festivals.
Now that you know more about how kites fly, and parts of a kite, go out there and start flying!
