Balloons - a background
A balloon is a type of AIRCRAFT that becomes airborne because of the buoyancy, or lift, supplied by a gas that is less dense than the air surrounding the balloon. (See ARCHIMEDES' PRINCIPLE; ATMOSPHERE.) The first public balloon flight was made by the MONTGOLFIER BROTHERS, Joseph and Etienne, at Annonay, France, on June 5, 1783. Made of linen and paper, this unmanned balloon had a volume of 660 cu m (23,308 cu ft) and was buoyed up by heated air. The balloon rose to an altitude of 1,800 m (5,906 ft) and flew 1.6 km (1 mi) from its starting point. On Nov. 21, 1783, Pilatre de Rozier and the marquis d'Arlandes used a Montgolfier balloon to make the first manned flight, from the center of Paris to the city's suburbs.
On Aug. 27, 1783, French chemist J. A. C. CHARLES inflated a balloon with hydrogen and launched it on an unmanned flight from the Champ de Mars in Paris. In December of that year he and an assistant made the first manned flight in a hydrogen balloon, from Paris to the village of Nesle, 104 km (65 mi) to the north. Hydrogen was found to be superior to hot air for filling a balloon because hydrogen has inherent buoyancy, whereas the ability of hot air to supply lift decreases as the air cools. The preference for hydrogen lasted well into the 20th century, although coal gas was popular for a brief time in the 19th century because it was used for streetlights and was readily available.
Helium, discovered in 1895, did not become commercially available until after 1918; it was also expensive and could not supply as much lift as hydrogen. The great advantage of helium, however, is its safety. Hydrogen is highly flammable and potentially explosive, but helium is not. Once launched, a balloon will rise until its average density exactly equals that of the surrounding atmosphere. In order to go higher, the pilot must discard some ballast (bags of sand are often used). To descend, the pilot releases some of the buoyant gas through a valve. When the balloon lands, a ripping panel is opened; this allows the remaining gas to escape so that the balloon will not be dragged over the ground.
Toward the end of the 18th century a balloon craze swept Europe and the United States. On Jan. 9, 1783, at Philadelphia, Jean Pierre BLANCHARD made the first U.S. balloon flight. As late as the 1930s, balloon flights, races, and ascents in tethered balloons anchored by cables were popular events.
MILITARY USE The balloon was used by the military soon after the first flight of the Montgolfiers. In the Battle of Fleurus between France and Austria (June 26, 1794), the French used a tethered balloon to observe the battlefield and direct artillery fire. A balloon corps, the world's first air force, was organized, and more balloons were built. The corps, however, soon fell into disuse and was abolished. When the Austrians besieged Venice in 1849, they used 200 small hot-air balloons to carry bombs that were released by preset controls. Because of unpredictable winds, however, the results of this first aerial bombing were negligible.
Balloons were also used in the American Civil War (1861-65). Again, however, results were negligible. In the five-month-long siege of Paris during the Franco-Prussian War (1870-71), balloons were the only means of communication and transportation between Paris and the rest of France. Balloons launched from Paris carried mail, passengers, and homing pigeons for carrying messages back to Paris.
The spherical balloon was excellent for free flight, but tethered spherical balloons were subject to bucking and rotation about their anchor cables. This made them unsuitable for military operations, for which a steady platform was required. By 1900, sausage-shaped balloons had been developed that combined the aerodynamics of the KITE with the aerostatics of the balloon. They foreshadowed the motorized AIRSHIP. Thousands of these kite balloons were used during World War I as observation posts and as aerial barrages (aprons of cables were suspended between the balloons to create hazards for enemy airplanes). Barrage balloons were also used during World War II. During the war the Japanese launched 9,000 balloons carrying bombs that they hoped would be blown across the Pacific Ocean to North America. Only about 300 are known to have reached North America, their bombs falling mostly in uninhabited areas.
When the cold war developed between the United States and the USSR after 1948, the Central Intelligence Agency (CIA) launched camera-carrying balloons from Western Europe, which were then carried across the USSR, including Siberia, to the Pacific, where the camera packages were retrieved. Because the flight path of the balloons could not be controlled, the operation had little success. After 1956 the CIA's balloon effort was superseded by the deployment of the Lockheed U-2 photo-reconnaissance plane (see U-2) and later by a series of military spy satellites.
TRANSCONTINENTAL CROSSING The great dream of 19th-century balloonists was intercontinental air travel. Because the prevailing wind in the Northern Hemisphere blows from west to east, the Atlantic crossing is easier from North America to Europe; thus most attempts have been eastward. John Wise, a 19th century American balloonist, detected a "constant current of wind" that, he was certain, would carry him across the ocean to Europe; but Wise was killed in a ballooning accident before he could make an attempt. Today, Wise's current of wind is known as the JET STREAM.
In 1978, 1980, and 1981, respectively, the first transatlantic, transcontinental (North America), and transpacific flights were made, in helium balloons. In 1984 the first solo transatlantic flight was made.
SPORT BALLOONING In the 1960s hot-air ballooning was revived as a sport. The Montgolfiers had to place their heat source on the ground; once they took off, the air cooled. Thus their flights were short. The recent development of a small, lightweight, propane burner, however, now allows the balloonist to carry the heat source aloft. New, tough, synthetic balloon fabrics have also been produced; this has lowered the cost and improved handling. The first hot-air-balloon crossing of the Atlantic was achieved in 1987.
SCIENTIFIC USE Since the 1890s the main scientific use of balloons has been in meteorological research. Small pilot balloons are regularly launched and tracked to determine wind direction and velocity; other balloons containing packages of METEOROLOGICAL INSTRUMENTS record data from the upper atmosphere. Until the development in the 1930s of the RADIOSONDE, a small, inexpensive radio transmitter, it was necessary to retrieve these packages in order to obtain their data. Extremely high-altitude balloons are used by astronomers and physicists to detect cosmic rays and gamma rays arriving from outer space. These balloons are sometimes several hundred meters high, and their reusable instrument packages are returned to Earth by parachute. Development of very thin, tough balloon material such as Astrofilm E accelerated such balloon use in the 1980s.
Richard K. Smith
Bibliography: Crouch, T. D., The Eagle Aloft (1983); Kirschner, E. J., Aerospace Balloons (1985); Lawler, B. P., With a Light Heart (1988); Maran, S. P., "Little Missions, Big Returns," Astronomy, January 1989. Rolt, L. T. C., The Aeronauts: A History of Ballooning (1966).
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