Myths about flight, to fly in the air like a bird is truly an age old dream. History is full of stories and legends about flying through the air like the birds. One such legend is the story of Daedalus and Icarus.
Daedalus, according to Greek myth, served as a builder and craftsman to King Minos. It was Daedalus who built the labyrinth, a maze with so many twists and turns that people who went into the labyrinth never found their way out. Daedalus once fell from favor with King Minos and was confined to the island of Crete. However, Daedalus with his imaginative mind, secretly planned to escape form Crete, with his son, Icarus.
Daedalus built two pairs of large wings out of birds feathers and wax. He
strapped one pair of wings to his son's arms. He attached the other pair to
himself. Then they both leapt into the air and flew.
People saw the two men flying like great birds in the sky and thought they
saw gods. Icarus was so thrilled at being able to fly that he flew higher
and higher toward the sun. Daedalus begged his son to keep away from the
sun, but Icarus flew still higher. The sun's heat melted the wax. The wings
fell apart and Icarus plunged into the sea and drowned. Daedalus flew lower
in the sky and made it safely to land and freedom, but he mourned his son for
the rest of his life.
By 1799, Cayley had made the single most important discovery in the history of aviation. He found that air flowing over the top of a curved, fixed wing will create lift, the upward force that opposes the pull of gravity. Cayley also determined that the larger the wing, and the faster the flow of air over it, the greater the lift will be created. In addition he understood the need for some sort of a tail to give an aircraft horizontal and vertical control.
It wasn't until 1809 that Cayley designed a full-size glider that could carry a person. There is a possibility that he not only built this machine, but that it made a few short hops, piloted by an assistant. Cayley didn't describe the glider in his notebooks, but he did refer to it in his article entitled "On Aerial Navigation," published in 1810. The article dealt with the main problem faced by those trying to design a flying machine "to make a surface support a given weight by the application of power to the resistance of air." It was the first time anyone had written about the principles of aerodynamics. For the next century, anyone seriously interested in science of flight would refer to Cayley's writings.
One man, a systematic engineer from Germany was fascinated with Cayley's discoveries. This man went on and became the first person to truly understand that flying an aircraft demanded more than simply taking off. Otto Lilienthal was his name, and early in his investigations he had decided that flying a powered aircraft was beyond his - or anyone else's - knowledge and ability. So, he set out to learn how to control a flying machine, and thus how to fly.
Lilienthal designed and constructed hang gliders, and starting in 1891 he flew the gliders that he had built from a hill near his home in Berlin. The first of his hang gliders were monoplanes; later he built gliders with two wings.
Each glider had a hole in the middle of the single wing where Lilienthal would hold on while he ran down the hill and jump into the air. He flew these gliders hundreds of times, rising after a short run and skimming a few feet above the ground for 150 feet (46m) or more. He made over 2,000 flights in his own gliders. His moving air was wind currents rising as they struck mountains, or upward drafts created by hot air rising from a ploughed field.
With each successful flight, he learned a little more about how to control a glider in each of the three dimensions of flight: roll - tipping from side to side; pitch- the nose moving up and down; and yaw - turning right to left. Methodically, Lilienthal developed gliders that were more and more controllable and could be flown more steadily and in stronger winds.
There was one problem though, all of his flights ended when the glider dove headlong into the ground. He kept careful notes on the different shaped chambers of his glider wings. He eventually developed a tail with a vertical structure. This acted as a rudder and stabilized his glider. This enabled Lilienthal to gain distance in his future glides, but the glider was still pitching forward and down. For a reason unknown to him he would lose the lifting power of his glider wings very suddenly. He gradually realized there was a relationship between the wing and the angle at which it attacked on coming air. Today this motion is called a "stall".
A stall is the result of the air flow separating as it flows across the top of the wing. The air "burbles" off into space and the wing loses its lifting power. It was due to this stall that Lilienthal fell to his death in 1896.
To fully understand way this occurs "aerodynamically" visit a local airfield. Ask a pilot or aircraft owner if you may measure the width of the upper, cambered surface of an aircraft wing. You will find that the upper surface is two or three inches wider than the lower surface.
Try to picture this wing moving into a stream of air molecules. The air molecules that move over the top of the wing must move faster than those on the bottom of the wing.
Because these air molecules are moving faster than those below the wing, Bernoulli's principle applies. What is Bernoulli's principle? "As the velocity of fluid increases, the pressure in the fluid decreases and conversely, as the velocity of the fluid decreases, the pressure in the fluid increases."
Based on Bernoulli's principle the air pressure will be less above the wing than below it, and the wing will lift.
Now, if the wing is angled up too steeply, this lifting power will be lost. The angle at which this occurs is known as the stall angle. Here, air burbles over the wing surface and lift ceases. The pilot of a glider may feel a shudder or quiver, and then he pitches down. His aircraft stalls. Without sufficient altitude to change the "angle of attack", he dives into the ground.
Today, gliders are equipped with instruments and control surfaces of ailerons and horizontal stabilizers to change the "angle of attack." Because gliders can be towed to five or seven thousand feet, they usually have sufficient height to pull out of a stall.
What began as a curiosity has now evolved into a popular sport. First came the Otto Lilienthal Meet, an informal gathering of visionary self-launched flying enthusiasts. Then came a few regional contests and the national and world meets. Competitions between individuals, teams, clubs, and nations occur every year - and the contest scene continues to grow.
To participate as an observer or as a competitor all you need to do is contact one of the local dealers or schools in your area. There are also several publications Fellow Feathers Flash, in Daly City, California or Wings of Rogallo Newsletter published in Redwood City, California.
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