The ability to fly like a bird is an ancient aspiration for mankind. There are many legendary accounts of men flying, the most famous of which is the Greek legend of Daedalus and Icarus, his son. Daedalus was a famous architect and sculptor, working for King Minos of Crete. He displeased the king, and the king imprisoned Daedalus and his son. They wanted freedom, so Daedalus fashioned wings out of wax and feathers. These he put on himself and Icarus so they could fly to freedom. He cautioned Icarus not to fly too close to the sun, but once they were in the air Icarus became enraptured by the flight and flew higher and higher until the sun was close. Too close, because the wax began to melt and the feathers fell out of the wings. Icarus fell to his death in the sea, becoming the first aircraft casualty!
Historical records indicate no one else even came this close to flying until the eighteenth century. Hot air balloons were the first aircraft in history to take men into the air. Balloons are ‘lighter than air’ craft, so called because the bag of the balloon contains hot air, helium, or hydrogen. These substances are lighter than air, and when held captive in the balloon they cause the balloon to rise off the ground. Lighter than air craft include balloons, blimps, and dirigibles.
Hot air balloons are fabric filled bags which have a basket or similar passenger or cargo vessel suspended below them. They have no capacity for directional control, merely drifting with the wind. Dirigibles have a fabric covered frame which gives the craft its shape. A gondola is mounted on the bottom of the frame which houses passengers and a motor and prop. The dirigible has directional control, and more altitude control than a balloon. A blimp has no framework to give the airbag it’s shape. The shape is maintained by the pressure of the gas inside. Directional control and passenger gondola the same as for a dirigible. Hydrogen and hot air were the principal lifting gases for the early balloons. Helium wasn’t available in large quantities until the 1900’s, but saw limited use by early balloonists. Hydrogen is more buoyant than helium, but is more volatile, so it isn’t used much, anymore. Early hot air balloonists burned wool and straw to keep the balloons aloft. Modern balloonists use propane gas burners to fly. Hydrogen was commonly used, but was it dangerous because of its flammability. It is no longer much used because of it’s extreme volatility.
Flying a hot air balloon is simple, in theory. To gain altitude in a helium balloon, you jettison ballast, usually sand bags. In a hot air balloon you turn up the gas heaters feeding exhaust into the balloon. To lose altitude in a helium balloon, you vent gas. In a hot air balloon you turn down the propane burners. Vagaries in wind currents, air density, presence of thermals, and man made or natural barriers such as trees and power lines complicate balloon aviation.
History of Flight and Avaition
No comments:
Post a Comment