Vehicles - Gliders

Gliders

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Although there have been many myths and legends about people trying to fly or glide, the first person to write about the principle of "lift" was Sir George Cayley.

By 1799, Cayley had made the single most important discovery in the history of aviation (flying). He found that air flowing over the top of a curved, fixed wing will create "lift", an upward force that can cause the wing to rise.

He had already decided that using a fixed wing would be the only way man could fly. He knew that copying the wing movements of a bird was not practical.

Man jumping with wings

Cayley also found that the larger the wing, and the faster the flow of air over it, the greater the lift created. He also found that some sort of tail was needed to give the craft stability.

It is believed that Cayley actually built a glider that was flown by an assistant. Cayley wrote down his conclusions and observations. He was the first person to write about the principles of aerodynamics. For the next century anyone seriously interested in the science of flight would refer to Cayley's writings.

The next person to advance the knowledge of flight, through gliding, was Otto Lilienthal. Lilienthal designed and constructed hang gliders. Starting in 1891 he flew the gliders from a hill hear his home in Berlin, Germany. The first of his hang gliders were monoplanes; later he made 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 or more. He made over 2,000 flights in his own gliders. Warm air rising up the hill helped "lift" the glider.

With each flight Lilienthal 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. Adding a tail with a vertical structure helped keep the glider stable and added distance, but the end of the flight was still the same. The glider would pitch forward and down. He knew he was losing lift suddenly, but did not know why. He gradually realized it was the angle of the wing to the wind that caused the problem. Today this motion or problem is called a "stall".

Normally, the air flows across the wing towards the trailing edge causing lift. 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.

Since the upper, forward surface of a wing is two to three inches thicker than the lower, trailing surface, the air molecules that move over the top of the wing must move faster than those on the bottom of the wing to reach the trailing edge. This causes a low pressure area to develop above the wing. This is "lift".

Now, if the wing is angled up too steeply, the air stream is interrupted and lifting power is lost. The pilot may feel a shudder or quiver, then pitch downward. This is a stall. If the vehicle is not high enough to recover it will dive into the ground. It was due to a stall that Lilienthal fell to his death in 1896.

Today, because gliders can be towed to five thousand or more feet, they generally have sufficient height to pull out of a stall. Gliders also have instruments and control surfaces to change the angle of the wing to pull out of a stall.

What began as a curiosity has now become a very poplular sport. Glider events are now worldwide. First came the Otto Lilienthal Meet, an informal gathering of visionary self-launched flying fanatics. Then came a few regional contests and then national and world meets. Competions between individuals, teams, clubs, and nations are held every year.

To participate as an observer or as a competitor all you need to do is contact a local glider club, school or store that carries glider products. There are also several publications: Fellow Feathers Flash, in Daly City, California or Wings of Rogallo Newsletter published in Redwood City, California. Information can be found on the Internet, too.

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