There are stories of people long ago who tried to imitate the birds by attaching wings to their arms. Of course, none could truly fly this way, but undoubtedly some were able to enjoy a controlled glide over a short distance. The first successful glider flight may have occurred in England about 900 years ago. A monk fastened wings to his hands and feet, jumped off a tower and glided about 600 feet (183 m) before making a rough landing that resulted in two broken legs. In 1498, an Italian learned how to glide with wings attached, but he also suffered a crash that broke a leg. Others down through the years tried to fly, but none gave any serious thought to the mechanics and aerodynamics involved.
The first to write an extensive analysis of the theory of human flight was Leonardo da Vinci. He sketched many ideas for human flight, nearly all involving flapping wings. In some cases the aviator was to lie prone, like the arrangement in today's hang-gliders. In 1500, da Vinci made some intriguing sketches for a large flying machine that got most of its lift from a rigid wing. It was to be powered by flappable, hinged wingtips operated by a person suspended in a harness under the single wing. It was the first powered hang-glider that closely resembled the gliders used by Otto Lilienthal nearly 400 years later.
No one followed up on da Vinci's ideas until George Cayley in the early 1800s. In 1804, he sketched the design of a model glider based upon his ideas concerning lift and propulsion, concepts which laid the foundations of modern aerodynamics. Cayley's model possessed a wing with a semi-circular leading edge, a movable, cruciform tail unit like a modern airplane, and a sliding weight at the nose for altering the center of gravity. Much later, in 1849, he built a triplane glider which carried his coachman 900 feet (274.5 m).
In spite of the advances made by Cayley, gliders were not again actively pursued until Otto Lilienthal who put gliding on a solid theoretical and practical footing. He realized it was important to control the craft before thinking about any propulsion systems. During the 1890s he built eighteen different types of fixed-wing gliders which he flew himself. He controlled the gliders through swinging his body to shift the center of gravity, just as modern hang-gliders today. Lilienthal also kept meticulous records of his work which helped others with their experiments. Unfortunately, he died when his glider stalled during a flight in 1898.
One American living at the same time, Octave Chanute (1832-1910), was responsible for influencing Orville Wright and Wilbur Wright through his advancement of glider design. One of the most important aeronautical experimenters of his time, Chanute refined Lilianthal's designs for better stability in the air. After publishing his findings in his work Progress in Flying Machines, he was contacted by the Wright brothers and began a close relationship with them. They eventually adopted Chanute's excellent braced biplane wings. Gliders played an important role as the Wright brothers systematically prepared for manned flight. From 1900 to 1902 they built three gliders which incorporated their methods of control: wing warping for turning ability, a fixed tailplane to create fore-and-aft stability, and a forward elevator for up-and-down movements.
After powered flight turned into a reality, gliders were largely abandoned. Germany, however, revived interest in them after World War I when the Treaty of Versailles banned the country from building airplanes. In 1928 the variometer was invented, a device that measures the glider's lift in thermals, the vertical currents of air rising from heated areas on the ground. After World War II, low-drag wings were shaped out of fiberglass, which provided a smooth and precise surface. Today gliders are used for recreation or sport. The newest sail planes have flaps, air brakes, and water ballast which can be jettisoned in flight to lower wing loading in flight.
The great expense of these sailplanes has created a new sport: hang-gliding, in which a pilot sits or lies in a harness under a lightweight wing stretched over a simple wire-braced aluminum-tube structure. Experienced hang-glider pilots can stay aloft for hours, traveling a hundred miles or more over the course of a flight. After all these years, it is interesting to note the similarity between modern hang-gliders and the early machines of da Vinci, Cayley and Lilienthal.
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