Aircraft

The first real success experienced by humans in designing aircraft made use of the concept of buoyancy. Buoyancy refers to the fact that an object tends to rise if it is placed in a medium whose density is greater than its own. A cork floats in water, for example, because the cork is less dense than the water. Buoyant aircraft became possible when scientists discovered that certain gases—especially hydrogen and helium—are less dense than air. Air that has been heated is also less dense than cooler air. Thus, a container filled with one of these gases will rise in air of its own accord.

Balloons were the first aircraft to make use of this principle. The fathers of ballooning are sometimes said to be the Montgolfier brothers, Joseph and Jacques. In 1782, the brothers constructed a large balloon which they filled with hot air produced by an ordinary bonfire under the balloon. The balloon rose more than a mile into the air. A year later, the Montgolfiers sent up a second balloon, this one carrying a tub that held a duck, a rooster, and a sheep. Then, only two months later, they constructed yet another balloon, this one large enough to carry a human into the atmosphere.

Balloon transportation suffers from one major drawback: the balloon goes wherever the winds carry it, and passengers have almost no control over the direction or speed of their travel. The additions needed to convert a balloon into a useable aircraft are a motor to propel the balloon in any given direction and a rudder with which to steer the balloon. The modified form of a balloon with these features is known as a dirigible.

The father of the modern dirigible is generally said to be Count Ferdinand von Zeppelin. Zeppelin's dirigible consisted of a rigid aluminum framework supporting a fabric covering and filled with hydrogen gas. On July 2, 1900, Zeppelin's dirigible took its initial flight; his first working ship was 420 ft (125 m) long and 40 ft (12 m) in diameter. It was capable of lifting 27,000 lb (12,000 kg) and traveling at air speeds comparable to those of airplanes then available. At their peak, Zeppelin-styled dirigibles were able to carry a maximum of 72 passengers in an elaborate gondola that also held a dining room, bar, lounge, and walkways.

The end of commercial dirigible travel came in the 1930s as the result of two events. One was the continuing improvement in heavier-than-air travel which made the much slower dirigible obsolete. The other event was the dramatic explosion and destruction of the dirigible Hindenburg as it attempted to moor at Lakehurst, New Jersey, on May 6, 1937. The ever-present danger that the highly flammable hydrogen gas used to inflate dirigibles would ignite and burn had finally come to realization at Lakehurst. Although later dirigibles were designed to fly with non-flammable helium, they never really regained the popularity of the pre-Lakehurst period. Today, dirigibles are widely used for advertising purposes. The "Goodyear blimp" and its cousins have now become familiar sights at outdoor sporting events all over the United States.