History of Flight  billowing heap of cloth capable of no more than a one-way,  downwind journey.  Balloons solved the problem of lift, but that was only one of  the problems of human flight. The ability to control speed and  direction eluded balloonists. The solution to that problem lay  in a child’s toy familiar to the East for 2,000 years, but not  introduced to the West until the 13th century—the kite. The  kites used by the Chinese for aerial observation, to test winds  for sailing, as a signaling device, and as a toy, held many of  the answers to lifting a heavier-than-air device into the air.  From prehistoric times, humans have watched the flight of  birds, and longed to imitate them, but lacked the power to do  so. Logic dictated that if the small muscles of birds can lift  them into the air and sustain them, then the larger muscles  of humans should be able to duplicate the feat. No one knew  about the intricate mesh of muscles, sinew, heart, breathing  system, and devices not unlike wing flaps, variable-camber  and spoilers of the modern airplane that enabled a bird to  fly. Still, thousands of years and countless lives were lost in  attempts to fly like birds.  The identity of the first “bird-men” who fitted themselves  with wings and leapt off of cliffs in an effort to fly are lost in  time, but each failure gave those who wished to fly questions  that needed to be answered. Where had the wing flappers  gone wrong? Philosophers, scientists, and inventors offered  solutions, but no one could add wings to the human body  and soar like a bird. During the 1500s, Leonardo da Vinci  filled pages of his notebooks with sketches of proposed  flying machines, but most of his ideas were flawed because  he clung to the idea of birdlike wings.  [Figure 1-1 ] By  1655, mathematician, physicist, and inventor Robert Hooke  concluded that the human body does not possess the strength  to power artificial wings. He believed human flight would  require some form of artificial propulsion.  One of the men who believed the study of kites unlocked  the secrets of winged flight was Sir George Cayley. Born  in England 10 years before the Mongolfier balloon flight,  Cayley spent his 84 years seeking to develop a heavier-than­ air vehicle supported by kite-shaped wings.  [Figure 1-2]  The  “Father of Aerial Navigation,” Cayley discovered the basic  principles on which the modern science of aeronautics is  founded; built what is recognized as the first successful flying  model; and tested the first full-size man-carrying airplane.  The quest for human flight led some practitioners in another  direction. In 1783, the first manned hot air balloon, crafted  by Joseph and Etienne Montgolfier, flew for 23 minutes.  Ten days later, Professor Jacques Charles flew the first gas  balloon. A madness for balloon flight captivated the public’s  imagination and for a time flying enthusiasts turned their  expertise to the promise of lighter-than-air flight. But for  all its majesty in the air, the balloon was little more than a  Figure 1-2.  Glider from 1852 by Sir George Cayley, British aviator  (1773–1857). Figure 1-1.  Leonardo da Vinci’s ornithopter wings.  1-2 