The most versatile genius of the Renaissance, Leonardo da Vinci, was an artist, musician, engineer and scientist. Leonardo is best known for his paintings The Last Supper and Mona Lisaa. Equally if not more impressive are his studies of flight. Begun in 1486, they are one of the first attempts to scientifically approach the subject. His surviving notebooks contain over 35,000 words and some 150 drawings that illustrate his theories. His sketches indicate advanced ideas regarding the parachute and helicopter, neither of which existed at the time. He also designed the ornithopter, a device with a series of levers and pulleys to supplement the human power of arms and legs that moved the wings of the device. The tail unit was based upon observations of birds and boats, and could be manipulated to cause up-and-down (elevator) and side-to-side (rudder) movement by its attachment to a harness on the pilot's head The flaw in the design of the ornithopter was that da Vinci believed there was enough muscle power in a human to sustain lift. Although no one has yet been able to achieve flight in an ornithopter, Leonardo's technical concepts were phenomenal considering the void in aeronautical knowledge during his lifetime and the centuries that passed before his ideas were applied and improved upon - his notebooks were lost until 1797.

The slight documentation that exists suggests that in 1709 Bartolomeo Gusmao, he who had set fire to the King of Portugal's curtains with the first lighter-than-air device, also demonstrated the first model glider and was granted a patent to build a full-scale man-carrying one. When constructed, however, the Passarola (Great Bird) remained earthbound. It is unknown what the Passarola actually looked like, but a contemporary artist's rendition depicted a tail, movable wings, even the head of a bird. No further accounts of Gusmao's experiments have been discovered.

By coincidence the man who is considered the aeronautical successor to Leonardo da Vinci began to make his contributions just about the time da Vinci's manuscripts were discovered. George Cayley, an English baronet, has been called the "true inventor of the airplane" and the "father of aviation." These claims aside, there is no dispute that Cayley formulated and demonstrated the basic principles on which the modern science of aerodynamics is founded.

Cayley was 10 years old when the Montgolfiers made their first hot air balloons. In 1799 he summarized his studies, which pursued a path entirely different than the highly popular lighter-than-air designs, on a small silver disk. Engraved on one side was a diagram that depicted the interacting forces upon a wing. On the reverse was an aircraft design which in various forms would be used for all his later constructions. Cayley was convinced that humans did not have sufficient muscle power to create lift, nor did he find it necessary. He turned instead to an invention that had been available for observation for over 2000 years: the kite.

An unknown Chinese inventor originated the fixed-wing kite about 500 B.C. Much like a sail filling, the kite attained lift from air currents, with a center of gravity provided by the string held by a "pilot." The kite was used in both China and India to ward off or imitate evil spirits, and to engage in mock battles. Of course any child who has flown one knows the simple pleasure a kite provides, but it took a genius to recognize its potential for manned flight. In 1804 Cayley mounted a kite onto a five foot long stick (fuselage) and adjusted the leading edge so that it was slightly raised (angle of incidence). At the rear of the fuselage he attached a tail unit that combined a rudder and elevator through a universal, movable joint. By adjusting the tail the direction of the flight could be controlled. Unknowingly he had adapted the design of da Vinci. Finally he fitted the model with a moving weight to adjust the center of gravity. The successful flight of his model demonstrated for the first time that fixed wing heavier-than-air designs were a viable alternative to balloons and in fact offered greater opportunities for future development.

Over the next 50 years Cayley added to and refined his principles for controlled gliding flight. He studied air resistance and determined the correct angle of the wing to air flow (angle of attack). He discovered that, by creating a lower pressure above the wing, curved surfaces produced more lift than flat ones. He improved stability by setting the wings at a dihedral angle, by which the tips of the wings are higher than the wing roots and form a flat Vee. He suggested that superimposed wings, such as biplane and triplane designs, would improve lift-to-weight ratio - a maximal lift could be attained with a minimal weight. Approaching the age of 80, Cayley culminated his career with a practical demonstration of his theories. In 1853 he built a full size glider and persuaded his coachman to climb on board, then launched the craft from the top of a hill. The glider made a fast swoop across the valley before coming to a sudden halt. The coachman gave notice immediately upon climbing out that he would no longer be working for his employer in any capacity, but Cayley was thoroughly pleased. He had achieved the first manned heavier-than-air flight in history, and stimulated a great exchange of ideas among those who followed.

Another brilliant theorist, born in 1850, was the Frenchman Alphonse Pinaud. One of his most significant contributions is still successfully used today in model airplanes: propulsion from a twisted rubber band. He independently confirmed Cayley's theory of inherent stability with his planaphore, whose design incorporated raised wings and tail planes. The planophore was tested in Paris in 1871 and flew 131 feet. Five years later, at the age of 26, he patented a man-carrying design with several original features including a glass-enclosed cockpit for the pilot and a single lever to control the rudder and elevators - the first joy stick. These innovations were never realized by Penaud, however, due to lack of financial or emotional support. Severely depressed, Penaud committed suicide at the age of 30.

The first true airman in history was Otto Lilienthal, a German engineer and inventor. He was the first person to repeatedly demonstrate that controlled glider flight was possible. At the age of 14 he attempted to use da Vinci's ornithopter design but eventually determined that flight could not be achieved merely by a flapping of wings. His close study of birds, however, published in 1889 as The Flight of Birds as a Basis of Aviation, contributed many insights as to how they actually fly. He determined, for example, that a bird achieves thrust not simply from the flapping of wings but from the propeller-like action of its so-called primary feathers. He calculated the size a wing must be to sustain the weight of an object - such as a human object. The intent was not to imitate the wings of a bird but to clearly understand and adapt their functionality. In this he was more successful than anyone who had come before.

In 1891 Lilienthal built and flew the first truly successful glider in history. The hang-glider of today is based upon it. Gradually modifying his design, he made over 2000 flights in the next five years. In 1895 he flew a biplane glider that lifted with hardly any running start from the 50 foot hill he had constructed, and carried him distances of a quarter mile at heights of 75 feet. He planned to attach a motor that would drive a mechanism to flap the wing tips and hopefully extend the duration of his flights.

A drawback to Lilienthal's gliders was that a great deal of control was dependent upon movements of his body. To reduce these requirements he devised a movable elevator that was attached to his head, thus freeing his legs. It was while testing this device when something failed. Lilienthal fell fifty feet and died the following day, but his achievements had attracted worldwide attention.

Hiram Maxim, an expatriate American whose invention the machine gun would someday ride on an airplane, emphasized Lilienthal's point that constant wing movement was unnecessary for bird or man. "There is no magic in a bird soaring. Constant interchange of air is taking place, the cold air descending, spreading itself out over the Earth, becoming warm and ascending in other places. Soaring may be accounted for on the hypothesis that the bird seeks out an ascending column of air, and while sustaining itself at the same height as the air, without any muscular exertion, it is in reality falling at considerable velocity through the air that surrounds it."

Meanwhile in Australia Lawrence Hargrave formulated the theory that explains how kites stay airborne. In 1893 he demonstrated the direct relationship between multiple wings and efficient lift when he built a cellular or box kite. His design, influenced by studies of the Lilienthal glider, was quickly adopted throughout the world.

Percy Sinclair Pilcher, a Scottish engineer who had assisted Maxim in aerodynamic tests, visited Lilienthal in Germany and received valuable advice regarding wing design. Combining these ideas with Hargrave's cellular kite principles, Pilcher successfully advanced the progress of the glider. The Hawk, his most successful glider, could be launched with a towline and had a landing gear. His next design was to have incorporated an oil engine that would power a propeller. Before this was accomplished he too, like Lilienthal, died during a glider flight in 1899.

Octave Chanute, an American civil engineer, was in his sixties when he turned his attention to flight. He patterned his glider designs on those of Lilienthal and hoped to eliminate the need for body movement. His knowledge of bridge building led him to increase the strength of the wings by adding braces to them.. To increase lift he designed a triplane. He strongly felt that a thorough understanding of control should precede "the further complications incident to a motor."

Chanute's greatest influence was as an educator and champion of flight. He was a wide reader and compiled all known technical information into a book published in 1894, Progress in Flying Machines . Because of it he began an intense correspondence with two fellow Americans, brothers who ran a successful bicycle repair shop and had more than a passing interest in aviation. Their names: Wilbur and Orville Wright. Their goal: manned, controlled, sustained, fixed-wing, powered flight.

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