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Buoyant Flight
There are two basic ways to fly. An airplane relies on air moving past its wings to generate lift. A balloon or airship relies on buoyancy, the upward force that occurs when an object weighs less than the amount of fluid (air) it displaces.
One way to make a flying machine buoyant is to heat the air inside a large, lightweight balloon envelope, which causes the air to expand and become less dense, and the balloon to rise until it reaches an equilibrium altitude. The other approach is to fill an airship envelope with a gas much lighter than air, such as hydrogen or helium.
The basic principles and technology of buoyant flight are much simpler than those of heavier-than-air flight. As a result, human beings took to the sky in lighter-than-air craft long before the invention of the airplane. |