Ben Franklin was not the first example of a kite being used for a scientific experiment, nor was it the last. Few people know that kites today are still very much being used to explore and understand our world. If you do already know this, that’s what makes you a nerd.
The subtle humor of Charles Schulz’s beloved “Peanuts” comic strip (which débuted in 1947) is somewhat of an acquired taste. When they first come across it, many people see little or nothing to it. However, the more they are exposed to the comic, the more they appreciate its delicate profundity. That’s what makes them intellectuals.
Most likely, dear reader, you fall into both categories, which together make you a very well rounded person.
Because of its profound practical and intellectual impact on the world, I believe the kite is eminently qualified to take a prominent place on the list of what I like to call “Extraordinary Ordinary Things.“
What Is a Kite?
It is almost insulting to try to define what a kite is. Everyone who was ever really a kid already knows for the simple reason that everyone who was ever really a kid has almost certainly has built and flown one. However, we are no longer kids, so a scientific description of the kite to go along with our nostalgic memories seems in order.
By simplest definition, a kite is a tethered heavier-than-air flying machine whose wing-like surface reacts against air to lift it into the sky and keep it there.
Kites come in number of different shapes and sizes; however, the classic design consists of four basic components:
- Frame: a backbone structure
- Mainsail: a thin, lightweight material (cloth, paper, or plastic) covering the frame to provide a surface that will react with air to lift the kite into the sky.
- Tether: a thin, strong string to control the kite in the air.
- Tail: a length of narrow, knotted material attached to the bottom of the kite to give it extra stability in flight.
When you flew a kite as a kid (I am assuming dear reader that you did fly kites as a kid), most likely it was what is sometimes called a “cross & paper” kite because this is the easiest type for a child to assemble from a kit, or even build from scratch.
A cross & paper kite consists of a frame (backbone) of light wood in the shape of a cross with a long central bar and a shorter crossbar. The horizontal bar is slightly curved and held in position with a string, giving it the appearance of an archery bow. This basic structure is then covered with a lightweight surface material (mainsail), which is usually thin paper. Finally, a string is attached to the front to act as a tether; which prevents the kite from blowing away and helps the “pilot” guide the craft while it is airborne.
Unlike Charlie Brown, if you knew what you were doing, you wouldn’t have gone into a furious run in order to get your kite into the air. Because if there was no wind or only a very slight wind you wouldn’t have been trying to fly the kite in the first place. When I was a kid, and if there was enough wind (it didn’t require very much), I would usually launch my kite in five simple steps.
- Lay the kite on the ground facing up, i.e. the side where the tether string is attached.
- Stand about 1–2 meters away
- Sharply pull on the string until the kite is slightly off the ground
- Pull slightly hard to raise the kite a bit farther off the ground.
- Once it has been caught by the wind, slowly let out more string to allow the kite to climb higher into the air.
This technique didn’t always work the first time, but it did eventually work.
As with an airplane, the force that raises a kite off the ground and keeps it there is called “lift.” Lift is generated when air moves across the kite’s mainsail, producing low pressure on the upper surface and high pressure on the lower surface.
Perhaps surprisingly, exactly how this differential of pressures occurs is a matter of some discussion. It appears to be more than simply an application of Bernoulli’s principle as you may have been told in school how an airplane achieves lift, which is also somewhat of an over-simplification.
As you will recall, Bernoulli’s principle applies to a laminar flow that is split into two separate streams. With an airplane, one stream passes below the wing and the other passes above. Due to the wing’s curvature, the upper one takes a somewhat longer path than the lower one, before they rejoin each other at the backside of the wing. The different lengths of the two airflow paths create a pressure differential (higher under the wing and lower over the wing), which forces the airplane upwards.
A kite is different. The kite presents a large obstacle to the wind. Air that flows around the edges of the kite swirls in behind the kite in turbulence. The “lift” is the pressure of the moving air hitting the kite. Moreover, because the kite is slightly curved, some of the incoming air is deflected backwards, adding to the turbulence around the edges. The tail of the kite helps stabilize against all this turbulence. This is easily seen if the tail breaks off, in which case the kite goes into violent twists and turns as it plummets to earth.
Wind (air flow) acting on the upper and lower surfaces of the mainsail also generates a horizontal force called “drag.” The vector generated by the lift + drag forces is opposed by the tension of the tether to which the kite is attached.
History of the Kite
A friend of mine once remarked, “Kites have been integral to human history for so long that you could reasonably expect to see them in prehistoric cave paintings.” Though it was meant as a quip, it is true.
The oldest known depiction of a kite dates from the Mesolithic period. It appears in a cave painting on Muna Island, southeast Indonesia. Created more than 11,000 years ago, the painting shows a type of kite known as a kaghati, which the Muna people still use today. Traditionally, a kaghati is constructed with bamboo skin for the frame, kolope leaf for the mainsail, and twisted forest pineapple fiber for the tether. However, in keeping with the times, modern versions of the kaghati have a tether made of cloth or nylon string.
In China, whose culture is almost synonymous with kites, it is commonly believed kites were invented during the 5th century BCE. In part, because 2,500 years ago China was endowed with materials that were ideal for kite making, e.g. strong, lightweight bamboo for the frame; silk fabric for the mainsail; and strong, thin silk woven into string for the tether. Paper, also synonymous with China, appears to have come into use for making the mainsail only around 550 CE, some two millennia later.
Unlike mine and Charlie Brown’s models, the earliest known Chinese kites were flat, not bowed, and had no tail. They were also often rectangular rather than triangular shaped. Later, tailless kites were fitted with a bowline (a type of rope used on old sailing ships) to improve stability and control.
Subsequently, kites made their way from China to India, then Polynesia, and as far as New Zealand. The idea of the kite was rather late arriving in Europe. The first mention of kites in Europe seems to be a mention of seeing them in Asia in the 13th century by the famed explorer Marco Polo. In the 16th and 17th centuries, sailors returning from the Orient brought kites to Europe.
How Are Kites Used?
Kites can be broadly divided into two categories:
- For fun (except for good ol’ Charlie Brown)
- For work, including scientific research
Actually, these categories overlap because elaborate kites designed for fun, particularly at the numerous kite festivals around the world, have sometimes taken their inspiration from kites designed for work, and vice versa.
Kite fanciers can be almost fanatical about them. It boggles the mind to see the incredibly intricate and artistic creations flown at annual kite festivals around the world. As enthused by Eileen Smith, Matador Network Editor-at-Large:
“Bright kites skate across the sky by the dozens—and sometimes the hundreds—in these worldwide kite festivals. There are single kites, single strings that fly tens of kites, and large, complex creations that require a whole team to get up them in the air and flying.”
There are an almost uncountable number of extravagant annual kite-enthusiast get-togethers around the world. Here are just a few of the leading ones; but there are many, many more:
Austin, Texas; Berkeley, California; Bondi Beach, Australia; Brisbane, Australia; Bristol, England; Cleveland, Ohio; Christchurch, New Zealand; Dieppe, New Brunswick, Canada; Himeji, Japan; Lincoln City, Oregon; Moro Bay, California; Portsmouth, England; Rissa, Norway; Singapore; Sumpango, Guatemala; Uiseong, South Korea; Vancouver, Canada; Washington, District of Columbia.
Kites at Work
Kites in ancient times were used mainly for utilitarian purposes such as measuring distances, testing the wind, signaling, and communication for military operations. Anthropomorphic kites, which depicted human beings, were used in religious ceremonies to send prayers to the gods.
Anthropologists have—and still are—using Polynesian kites to investigate and better understand early traditions that are believed to have at one time existed in Asia.
As is well known, in 1752 American scientist and statesman Benjamin Franklin published an account of his kite experiment to demonstrate that lightning is caused by electricity. He had not investigated how this electricity is transmitted. Given the ubiquitous image of the Greek god Zeus hurling lightning bolts down, it may be surprising to learn that lightening in fact starts from the ground and flashes upwards into the sky.
Kites Take Flight
In 1903, the Wright Brothers (Wilbur and Orville Wright) were the first to demonstrate the feasibility of powered heavier-than-air flight at Kitty Hawk, North Carolina. That first flight lasted a scant 59 seconds over a distance of only 272 meters (892 feet). However, they probably would never have gotten off the ground at all except for the pioneering work of Englishman Lawrence Hargraves with kites.
In 1893, Hargraves introduced an entirely new kite design, the “box kite.” As the name implies, this kite is shaped like a box. Several of these boxes can be assembled and linked together to greatly increase the power of the kite to lift things off the ground.
Already interested in the possibility of powered heavier-than-air flight, Hargraves developed concepts for various forms of airplane designs. Most significantly, his experiments were influential in the development of the “cambered airfoil,” a structure with curved surfaces that substantially increases aerodynamic lift. The fin, tail, and wings on modern aircraft are examples of airfoils.
At one point in his experiments, Hargraves even tied several box kites together, then climbed aboard, and was lifted 5 meters off the ground. However, he never actually achieved his dream of powered heavier-than-air flight.
While generally associated with fun, kites have played a full and varied role in the more serious side of life. Here is just a brief overview of their practical applications.
Not surprisingly, the first use of kites in warfare is generally believed to have happened in Asia, and probably in Chinese. During the Song Dynasty (960–1279 CE), they developed a weapon called the Fire Crow consisting of a kite, incendiary powder, a fuse, and a burning stick of incense to frighten the enemy.
However, there is evidence that kites for military purposes may have already been used considerably earlier in Korea. There is evidence to suggest that in 647 CE, Korean general Kim Yu-sin, had already used fire kites (flaming kites) also to frighten the enemy.
In Russia, Prince Oleg of Novgorod is chronicled as having used kites to frighten the enemy, but not fire kites. According to one report, during the 906 siege of Constantinople, the Prince “crafted horses and men of paper, armed and gilded, and lifted them into the air over the city. The Greeks saw them and feared them.”
There are also scattered accounts of kites being used as weapons throughout the Middle Ages.
In the more modern era, during World War I, kites were used to lift human lookouts into the air to spy on the enemy. During World War II, kites were used for anti-aircraft target practice. More importantly, barrage kites (elaborate arrangements of box kite components) were used to protect shipping from enemy air attacks.
Coming right up to date, Palestinians have flown firebomb kites over the Israel-Gaza border to set fire to Israeli crops.
About 250 years ago, meteorologists in Europe began affixing thermometers to kites to make scientific observations of the upper atmosphere.
In the late 1890s, the U.S. Weather Bureau began regular kite observations across the United States. These data-hunting box kites (Hargrave kites) were more than 2 meters (6 feet) high, tethered by thin piano wire attached to a steam-driven reel to hold them in place. The kites carried meteorological instruments known as “meteorographs” to record pressure, temperature, and relative humidity data, recorded on an automated clockwork-driven chart recorder.
Despite their advantages over manned balloon ascents, the days of the meteorological observation kites were numbered due to several inherent limitations. For example, kites could reach an altitude of only about 3 kilometers (less than 2 miles). Moreover, the data could not be recovered and evaluated until after the kite could be brought to the ground and the meteorograph off-loaded. If winds were too strong or too weak, kites were not able to take observations at all.
By 1933, the advent of aircraft carrying meteorographs had essentially ended the era of kites for collecting meteorological data in the sky. Although airplanes were a significant improvement, as with kites they were also unable to fly in poor weather and collected data could not analyze until the plane landed. Additionally, they could fly only to a height of about 5 kilometers (3 miles).
Kites have been used to carry into the air antennas for medium frequency (MF), long frequency (LF), and very long frequency (VLF) transmitters. This is the method used for the reception station of the first transatlantic transmission December 12, 1901 by Italian physicist and radio pioneer Guglielmo Marconi.
Here is a mind-boggling thought. Why not use kites to help cargo ships ply the seven seas? Well, it’s more than just a thought. It has actually been tried, and fairly recently.
In January 2008, the German company SkySails GmbH first tested a ship-pulling kite as supplemental power for moving cargo ships. The trials were conducted on a 55-meter cargo ship called the MS Beluga Skysails. The experimental kite had a surface area of 160 square meters (1,700 square feet) and few at altitudes between 100 to 500 meters (330 to 1,600 ft.).
The results showed that in favorable winds, the kite increased fuel-efficiency by up to 30 percent. At the same time, it also increased the ship’s speed.
While it can’t be said that kite-assisted ships today dominate the waves, they are not all that rare either. Initially conceived for cargo ships, commercial applications today also include zipping up the speed of youths, motorboats, and other pleasure crafts.
The idea of using sails to harness the power of wind to propel ships is almost as ancient as mankind itself. Once ships started becoming machine-powered in the 19th century, someone must have had the idea of also equipping them with a large sail or sails to generate extra speed. However, a large kite has a significant advantage over a large sail.
A well-designed kite can generate up to 25 times more power per unit area than a sail. There are several inherent reasons for this.
- A kite can be flown high above the ship in order to take advantage of stronger, steadier winds.
- A computer-controlled kite can be maneuvered to optimize its position in the airflow.
- Properly designed, a kite can be shaped like an airfoil, resulting in combined forces of lift and drag to pull the ship through the water at maximum efficiency.
- A kite flies in front of the ship, so it doesn’t take of valuable space on the ship’s deck.
- Ship-pulling kites also tend to be safer. Large sails and the large masts they are attached to can act as very large levers, thus destabilizing the ship in severe weather conditions.
The number of sports activities involving kites in almost endless. They include kite boarding, kite buggying, kite buggy jumping, kite fighting, kite land boarding, snow kiting, downhill speed kiting, hang gliding, kite surfing, kite stunt flying, and even kite high jumping.
The kite is often used as an aid in teaching a wide variety of academic subjects such as aerodynamics, art, culture, history, mathematics, materials, physical education, and problem solving.
Kites and Computers
Earlier, I mentioned kite-powered cargo ships, pioneered in the early 2000s, rely on a combination of a very large, aerodynamically designed kite under real-time computer control. A more recent potential application is kite energy production.
A 2007 article in the New Scientist magazine announced: “A new way to harness wind energy may take off now that computers have learned to kite surf.”
Kite surfing (also known as kite boarding) is an extreme sport combining aspects wakeboarding, snowboarding, wind surfing, paragliding, and skate boarding. It uses a large, airfoil-shaped kite for harnessing the power of wind to propel the kite surfer across land, water, or snow.
Researchers have determined energy that can be generated from a kite flying in a figure eight pattern is at least 10 times more than energy generated from a kite simply being held steady in a downwind.
To harvest this energy, researchers experimented with using computer-controlled high-flying kites tethered to turbines. When the kites pull on the tether lines, the turbines turn, generating electricity. The experiment works well in fairly steady winds; however, the computers controlling the kites were less efficient in gusty winds lulls in the wind, often leading to crashes.
To counter the problems, researchers developed a neural network that can learn to steer a kite like a seasoned professional. First, the researchers wrote 20 different software algorithms, using each algorithm to fly simulated kites pulling as hard as possible in a wind of 8 meters/second.
“At first, they (computers) were like blindfolded idiots—they would crash the kite in a quarter-second,” said Inman Harvey, University of Sussex (U.K.) “However, one or two would crash it in a half-second.”
The researchers then “bred” the algorithms that had kept the kites flying the longest (half-second). After 200 generations, the algorithms had evolved the ability not only to fly the kites, but also to fly them in the highly efficient figure of eight style. Moreover, they had developed the ability to reliably cope with strong wind gusts and wind lulls.
Currently, a number of companies have been established and are currently trying to put kite-generated energy on a firm commercial footing.
Kite is also the name of an AI-powered programming assistant to speed up writing Python code for IDEs such as Atom, PyCharm, Sublime, VS Code, Vim, Spyder, and IntelliJ. According to the developer, “Kite is a plug-in for your IDE that uses machine learning to give you useful code completions for Python.” In short, Kite helps programmers write code faster by showing the right information at the right time.
Back to Basics
In popular culture, kites are almost always associated with fun. Perhaps the most exuberant expression of the joy kites bring is in the song “Let’s Go Fly a Kite” in the 1964 Walt Disney feature film “Mary Poppins.” So to end on a happy note (in fact, lots of them) here are the lyrics: Or you can hear it for yourself at: https://www.youtube.com/watch?v=zNSler7jBWs
With a tuppence for paper and string You can have your own set of wings With your feet on the ground You're a bird in a flight With your fist holding tight To the string of your kite (Refrain) Oh oh oh Let's go fly a kite Up to the highest height Let's go fly a kite and send it soaring Up through the atmosphere Up where the air is clear Oh, let's go fly a kite When you send it flyin' up there All at once you're lighter than air You can dance on the breeze Over 'ouses and trees With your fist 'olding tight To the string of your kite (Refrain) Oh oh oh Let's go fly a kite Up to the highest height Let's go fly a kite and send it soaring Up through the atmosphere Up where the air is clear Oh, let's go, fly a kite!