Sir George Cayley was one of the inventors who believed strongly
in man's ability to fly. Cayley was a brilliant aeronautical pioneer of
the 19th century. He realized that trying to copy the flapping wings of
birds was a waste of time. He thought a better and more simple idea
would be to look at the steady, outstretched gliding wings of a soaring
bird such as a gull or an albatross.
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 referred to the glider 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.
A German man named Otto Lilienthal became fascinated with
Cayley's discoveries and decided to set out to learn how to control a
flying machine, and thus how to fly. Lilienthal designed and constructed
hang gliders. Starting in 1891 he flew the gliders from a hill that he
had built near his home in Berlin. The first of his hang gliders were
monoplanes. Each glider had a hole in the middle of the single wing
where Lilienthal would hold on while he ran down the hill and jumped 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.
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 3 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 oncoming 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. It is
unable to join the air stream at the trailing edge and the wing loses its
lifting power. It was due to this stall that Lilienthal fell to his
death in 1896.