Kites

Everything there is to know about kites (probably)

What is a Kite?

A kite is a man-made object usually made of flexible fabric such as silk, bamboo or plastic sheet, often but not always stretched over a rigid structure made of wood, plastic or carbon fibre rods.

Due to the kite’s shape, it interferes with the wind causing differences in wind speed, which result in lift.  If the lift created by the kite is greater than the weight of the kite, it flies.  A kite is usually tethered to the ground, a person, vehicle or winch system to control its flight and to stop it from flying away.

A man-made kite takes its name from the bird of prey because its hovering flight characteristics are similar.

People have developed many uses for kites and many specialist designs to help with their particular use.

 

Kites are flown for amusement, ceremonies and competitions and have been used by the military, scientists, meteorologists and by the pioneers of radio and aeroplanes.  A kite can have instruments or lights attached to it, be made to pull a vehicle such as a buggy, surfboard or ice-skater.  There are even underwater kites being developed to create electricity from the sea and river currents.

Kites have a long a varied history and are now enjoyed by hundreds of people in many countries.

How do Kites Fly?

This is a simple question with a fantastically complex answer!

The explanation you will see all over the web and YouTube is the Bernoulli principle…

The Bernoulli Principle

In 1738 professor Daniel Bernoulli discovered that faster travelling air has lower pressure.  Air of greater pressure will move into an area of lower pressure to re-establish equilibrium.  If there is something in the way, like a kite, it will be moved.  If the high-pressure air is below a kite and the low-pressure air above the kite, and the air pressure difference is great enough to overcome the weight of the kite it will move upwards or will have “lift”.

A true kite must create enough lift to overcome it's weight and fly.  Many kites seen at kite festivals are windsocks, flags or drones.  Often tubular in shape, these may look like they are flying but their shape does not create lift and they are simply blown by the direction of the wind.

A kite, on the other hand, affects the wind in some way and causes a difference in wind speed.  The way that it does that is based on its shape…

Flat Kites

Flat kites are square or more commonly seen diamond-shaped kites.

 

Their shape causes an obstacle for the wind to navigate.  The wind has to separate to go around the obstacle creating an area of low pressure behind the kite.  The wind rushes back into this area to return air pressure to equilibrium. 

 

This fast rushing air is at a lower pressure than the wind below the kite.  The wind at higher pressure below the kite tries to move into to lower pressure air but the kite is in the way and so the kite lifts.

Sled Kites and Stunt Kites

Sled kites and stunt kites are different from flat kites because they have three-dimensional shapes.  They are curved and this curved shape causes an even greater difference in airspeed and consequently air pressure making them easier to fly and greater ability to be flown in slower wind speeds.

Power Kites and Leading Edge Inflatable Kites

Power kites like those used for kite surfing and paragliding have a true aerofoil shape, just like an aeroplane wing.  The shape of an aeroplane wing means that air travelling over it travels faster than the air flowing under it and voila, we have conditions for the Bernoulli effect.  Lift.

Whoa there compadre, there’s more.

The Bernoulli principle doesn’t tell the whole story.  The Bernoulli principle is true and does create lift in kites but it also misses other forces acting on the kite.

Angle of Attack

A kite doesn’t sit flat to the wind, it sits at an angle.  This is called the angle of attack. 

 

Air has a mass and due to the kite's angle to the wind, the air is deflected downwards when it comes into contact with the front face of the kite.

 

Conservation of momentum states that every time there is an action there must be an equal and opposite reaction.  If the air has been directed downwards there must be an equal and opposite reaction - in our case, this is good, as the mass of moving air actually pushes the kite into the air.

Wait… There’s more…

Our model hasn’t yet taken into account the turbulence caused by the kite.  This is called drag.  A kite with an efficient way to smooth its movement through the air will have more lift than one that causes lots of turbulent air.

Are we all done? Nope - one more!

And one other important consideration that many explanations leave out is that a kite has edges.

 

Many models represent a kite, or more often an aerofoil or aeroplane wing, as a two-dimensional shape.  They ignore the vortices at the wingtips and the eddy currents at the trailing edges.  The way these forces and currents interact with the kite affect its stability.

Types of Kite

Shapes
Diamond Kite

Perhaps the easiest kite shape to make yourself, diamond kites are popular around the world.

 

The classic or traditional shape is probably the most recognised shape when asked to think about kites.

 

Often seen as kids kites or beginner kites diamond kites are often decorated with bright colours and elaborate tails. 

 

Adding a tail to a diamond kite helps stabilise their flight.

Square / Box Kite

Box kites were invented in 1893 by Lawrence Hargrave in Australia.  Hargrave was trying to develop kites for a manned flying machine.  Hargrave did successfully link several box kites together and lifted him 4.9m off the ground.

A winged box design known as a Code kite following its development by Samuel Franklin Cody was later developed and used for radio transmitting and pilots in World War 2 as liferafts.

Delta Wing

The fourth letter of the Greek alphabet looks like a triangle and is called Delta.

 

Delta kites are easy to fly in a wide range of wind conditions making them an excellent starter kite.

Delta kites originate in China in the 1940s and are thought to be a copy of the shape the Kite bird makes while hovering.

 

Wilbur Green made a prototype that was so successful he patented its keeled kite and sold them under the brand name Gayla.

In 1963 Al Hartig updated the Delta design and named it the Valkyrie.  This new design and a very good step by step DIY build in Kite Tales magazine detailing how to make your own Delta prompted a lot of interest in the delta design.

Sport Kite / Stunt Kite

Similar to the delta wing, a stunt kite is a triangle shape but has extra rods to give a three-dimensional shape and dual control lines allowing it to be manoeuvred in the air.

 

Stunt kites are used by individuals, pairs or teams in display flying competitions, sometimes called areal ballet.

Competitions in the UK are organised by Sport Team and Competitive Kiting (STACK), in the USA by American Kitefliers Association (AKA) and Japan by All-Japanese Sport Kite Association (AJSKA).

 

These organisations agreed to collaborate and formed the International Rule Book Committee (IRBC) in 1996.

Single Line, Dual Line and Quad Line Kites

A lot of beginner kites have a single string to tether the kite to the operator.  Single strings do not allow for much control so in 1972 Peter Powell developed a steerable kite using two control lines.  Pulling on a dual-line alters the kites angle of attack or deforms its shape-changing the flow of air over the kite and pulling it to one side.  Four line kites add to this by also deforming the lower part of the kite or opening a flap, which acts a brake and allows the kite to perform much tighter turns

Power Kites

There are two common types of power kite, the foil and the leading-edge inflatable and two less common, the rigid framed kite and soft single skin kite.

Foil kites consist of a number of cells which air is forced into during flight, bellowing out to create an aerofoil shape.  Some advanced designs have one-way valves which trap air inside the cells giving increased water relaunch capability.

Leading-edge inflatable kites (LEIs) are commonly used by kite surfers because they hold their shape when wet.  As the name suggests, a tube at the front edge of the kite is inflated with a kite pump before use.  The inflated tube is rigid and gives the kite its aerofoil shape.

Power kites have been many uses, most commonly to pull surfboards, buggies, land boards, boats, skis and skaters.  Many kite flyers chose not to use a vehicle and instead like to jump and use the kite to pull them off the ground.

Hang Gliders

A hand glider is an aircraft with many similarities to a delta wing kite.  A rider hangs in a harness below a triangular fabric sail held in a rigid structure with metal or plastic supports.  The pilot controls the hang glider by shifting their body weight from side to side and moving a large metal control frame.

The pioneers of hang gliding glided down the side of small hills.  With huge improvements in wing design, materials and scientific knowledge modern hang gliders are able to use thermal updrafts and wind deflected off mountains to increase flight time considerably.

Paragliders

Paragliding is very similar to hang gliding but the kite used is more like a power kite rather than a delta wing kite.

 

A hang glider is a rigid structure while a paraglider is usually made of woven fabric, sometimes with an inflatable leading edge.  Being flexible allows the craft to be more portable and easier to transport.

Kite Surfing

Kite surfing (or kiteboarding) is an extreme sport combining aspects surfing, sailboarding and kite flying.

 

A kiteboarder uses a power kite to propel their kiteboard and perform tricks and stunts by jumping over man-made ramps and rails or off the tops of waves.

 

Kite surfing has gained huge popularity due to relatively cheap equipment, ease of use and the laidback beach lifestyle.

Kite Buggying

Kite buggies are actually classed as land going boats as many of the technique used to pilot a buggy are similar or the same as sailing a yacht.

A kite buggy is a lightweight go-cart made of metal or carbon fibre.  It has three wheels, two at the back and one at the front, with a seat in the middle in a classic trike formation and the front wheel is steerable using footpegs.

 

The pilot or driver uses a power kite to propel the buggy forward using the power of the wind.  Buggies can reach tremendous speeds up to 70mph allowing for racing similar to dingy racing.  Some extreme riders can jump their buggies using the power of the kite or by travelling over ramps.

Fighting Kites

Extremely popular in India, but found in China, Brazil and some other countries, fighting kites are a traditional past time enjoyed by millions at kite festivals every year.

Most competitors have been creating kites for generations with each family having its own closely guarded adaptations, variations and tactics to give their kite an advantage.

The aim is to snag or cut the control line of the opponent’s kite before they cut yours.

Kites are made to be as nimble as possible to change direction swiftly and beat the other kite flyers reactions.  As such the kites need to be as light as possible, so are made out of thin paper or silk, with a very lightweight frame made out of wood or plastic.

The kite’s control lines often have glass or metal knives attached to them and are strengthened to defeat attacks.

The History of Kites

Speculation has it that kites originated in Asia but no one knows for certain.

The earliest cave painting of kite flying is from Muna Island, in Indonesia and has been dated as C.9000 BC.  The kite pictured is made of Kolope leaf as the skin, bamboo as the frame and pineapple fibres as the string and a very similar design is still in use today by the Muna people.

In China, many believe the kite was invented around the 5th Century BC.  China had many ideal materials for kite building such as silk and bamboo.  It is recorded that paper kites were used in 549 AD for measuring distances, sending messages, signalling during battles, even lifting men for recognisance.  Kites in China have often been decorated with mythological characters and some were fitted with bells, whistles and noisemakers to make sounds while flying.

Known as Patang in India, kites are used in “fighting” competitions with the object is to snag or cut the line of the opposition’s kite.

Kites slowly moved out of China along trade routes and were used all over Polynesia for religious ceremonies as a way to get closer to God and heaven.

Kites didn’t appear in Europe until around 1400 AD and for a long time were just used as entertainment.  In 1752 Benjamin Franklin used a kite to prove lighting was caused by electricity.  Kites were also used by the Wright brothers while developing powered aeroplanes.

How to Fly a Kite

Kite Safety

I know - no one likes safety briefings and no one reads the instructions.  The vast majority of kites are safe and fun, but there are a few dangers that need to be pointed out.

 

First – know your limits.  Even small power kites have a lot of power.  Watch a few crash videos on YouTube if you don’t believe me.  By all means, use small recreational kites in light winds, but if you are stepping up to big delta wings, stunt kites, power kites or surf kites, consider getting instruction from someone who really knows what they are doing.  I am not exaggerating when I say the lessons could save your life.

Fly somewhere safe!

Kite lines can tangle on power lines or get struck by lightning.  Make sure to give yourself plenty of space from overhead obstructions.  Similarly, make sure the wind is coming from an area with few obstructions.  Air that has flown over buildings is gusty and unpredictable.

Kites have rigid structures and can fly fast.  It is unlikely you will be struck by your own kite but it would be easy to hit another person or strangle them with your string.  Stop flying if someone or an animal gets too close.

Kites are easily powerful enough to lift humans off the ground.  This can be good fun so long as it is under control.  The problem comes if it is unexpected, or if the kite pulls you into a dangerous area like over a cliff, into a road or into a lake or the sea for example.  Accidents happen very fast so you need to know what to do instinctively.  Practice your safety drills until they become second nature before flying the kite and remember that launch time is the most likely time for something to go wrong.

Take a note of the wind conditions.  5 – 10mph winds, enough to move the small branches on trees is enough to start with. Progress to 10-15mph only after you have some experience.

Similarly, while concentrating on your kite in the sky, it can be easy to forget what is around you and drift into danger.  It might be a good idea to tether yourself or have a friend near-by who can watch out for dangers.

How to start a kite

With your back to the wind, rest your kite on the ground or have a helper hold the kite at chest height.

 

Make sure your string or strings are not tangled and that you have the correct line in the correct hand.  It is easy to pick up a control bar upside down.  Hold your handle or handles at chest height with your arms bent, shoulder-width apart.

Keeping your feet still, pull your arms backwards and ask your helper to release the kite.  The kite should soar into the air.

The Wind Window

Every kite has a maximum height and maximum distance it can steer to the left and to the right.  This is called the wind window. 

 

At the edges of the wind window, the kite will be stationary or will stall.  In the middle of the wind window, the kite has the most amount of power available.

 

If the wind is too strong and you find yourself not able to manage the kite in the power zone of the wind window, avoid that area.

How to Steer a Kite

Kites with two or four strings can be steered very easily.  If you want your kite to turn left, pull on the left string.  To turn right, pull on the right string.  Once the kite has turned to the direction you want it to fly in, return the strings to equal, otherwise the kite will continue to turn and eventually spiral in circles.  Four-line kites can turn in tighter circles than two-line kites by using their brake lines.

Single line kites can be steered but it is not so easy.  Adjusting the pressure on the control line will cause the kite to become unstable.  A skilled kite flyer can cause the kite to become unstable just long enough to move the kite into the direction wanted, reapplying the pressure to the string at just the right moment to return the kite to stable flight in it’s new direction.

Troubleshooting

Sounds easy right? Well, it does in theory.  We all know, in real life, things don't go to plan.  Here are some tips which may help if your kite is misbehaving.

Diamond kites – out of control.  A diamond kite may need a tail to help smooth its flight.  Experiment with different length tails to see if they correct the erratic flight.

Kite diving, stalling or not stable – Every kite has a balance point and different wind conditions may affect the balance point.  Try adjusting where the control line attaches to the kite, or if your kite has a bridal, experiment where the control line attaches to it, to change the kite’s angle of attack into the wind.

Kite constantly steering to one side – If you are using a two or four line kite, make sure you are not accidentally putting pressure on one line and that the lines are not twisted or tangled.  Check both lines are the same length.  Make sure the kite has been made correctly with all the rods firmly pressed home into any connectors.  Small differences between the left and right side of the kite could change the kite’s shape enough to cause it to steer to one side. If everything checks out, adding a small amount of weight to the side that is turning upward may create stable flight.  It will take some experimenting to get the correct amount of weight.

Kite World Records

The largest kite was a colossal 42m x 25m or 1050 square meters.  A box kite in the shape of Kuwait National flag, it flew for 20 minutes at approximately 20m in the air.

The highest flown kite was in 2014, in New South Wales, Australia.  Robert Moore took 8 attempts over a 10-year period to eventually fly a kite at 4880m above ground level.

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