Balloon

I

Introduction

Balloon, lighter-than-air craft consisting of a large spherical, pliant bag made of varnished silk, rubber, or other suitable non-porous material, and containing either hot air or a gas that is lighter than air. Manned balloons carry one or more people in a suspended gondola; unmanned balloons carry instruments used to measure and record a variety of physical phenomena. The earliest balloons were filled with hot air and often carried a brazier to replenish the supply continuously. Modern balloons are filled with hydrogen or helium, or, in the case of modern hot-air sports ballooning, air heated by a small gas burner. Helium has the great advantage of being non-flammable, but it is twice as heavy as hydrogen and has 7 per cent less lifting power. Hydrogen weighs 1.14 kg/cubic m (0.071 lb/cu ft) less than air at standard atmospheric pressure and temperature, and a hydrogen balloon of 30 cubic m (1,060 cu ft) is able to lift, therefore, about 34 kg (75 lb). See Atmosphere.

II

History

In 1783 two French brothers, Jacques Étienne and Joseph Michel Montgolfier, who were wealthy papermakers in Annonay, sent up a balloon filled with hot air. In the same year the French physicist, chemist, and aeronaut Jacques Alexandre César Charles released one filled with hydrogen, which made a successful two-hour flight, covering 43 km (27 mi). The same year also marked the first balloon ascent by human beings, when the French physicist Jean François Pilâtre de Rozier made flights near Paris, first in a captive balloon and later in one that was free. A year later the first balloon ascent in Britain was made, by a French diplomat. In 1785 the French aeronaut Jean Pierre Blanchard, accompanied by John Jeffries, an American, made the first balloon crossing of the English Channel. The first free balloon ascent in America was made at Philadelphia on January 9, 1793. In 1836 The Great Balloon of Nassau, of 2,410 cubic m (85,000 cu ft) capacity, sailed 800 km (500 mi) from London to Weilburg, Germany, in 18 hours. During the Franco-Prussian War of 1870, balloons were used for military observation by the armies of both nations, and the French minister Léon Gambetta made a dramatic escape from the besieged city of Paris by balloon. A long-standing distance record for the flight of manned balloons was set in 1914, when the balloon Berliner travelled from Bitterfeld in Germany to Perm in Russia, some 3,052 km (1,897 mi). Armies in World War I made extensive use of balloons, especially for military observation. Interest in ballooning as a sport was stimulated by the Gordon Bennett Balloon Trophy Races. The competition was held annually, except during World War I, from 1906, when the American journalist James Gordon Bennett donated the trophy, to the start of World War II, when the races were discontinued.

Sports ballooning has become popular around the world, using hot-air balloons that are kept aloft with butane or propane burners. Such balloons are also ideal for flights over wildlife reserves.

Ascents to great heights have been made by a number of aeronauts in balloons. In 1931 the Swiss physicist Auguste Piccard ascended into the stratosphere in a spherical, airtight, metal cabin suspended from a specially constructed, hydrogen-filled balloon of 14,000 cubic m (46,000 cu ft) capacity, reaching an altitude of 15,781 m (51,793 ft). The following year he reached 16,507 m (54,156 ft). In 1935, two US Army captains, Orvil Anderson and Albert William Stevens, ascended to 22,080 m (72,440 ft).

In August 1957, Major David Simons, a US Air Force surgeon, ascended to about 31,110 m (102,000 ft), remained in the air 32 hours, and drifted 652 km (405 mi) from his take-off point. The flight was designed to chart the reactions of humans at high altitudes. On August 27, 1960, Captain Joseph Kittinger parachuted from a polyethylene plastic balloon at 31,354 m (102,870 ft), setting a new altitude record for balloon flight and a new record for parachute descent. On May 4, 1961, the Americans Malcolm Ross and Victor Prather set a record of 34,679 m (113,775 ft) on a flight launched from a US Navy aircraft carrier.

The first transatlantic balloon flight ended on August 17, 1978, after setting a distance record of 5,000 km (3,108 mi) and an endurance record of 137 hours 6 minutes. The helium-filled Double Eagle II, manned by the American businessmen Ben Abruzzo, Max L. Anderson, and Larry Newman, took off from Presque Isle, Maine, on August 11 and landed in Miserey, France. The first hot-air balloon flight across the Atlantic was made in 1987 by the Virgin Atlantic Flyer, flown by Richard Branson and Per Lundstrand. The endurance record was broken by two Americans, Troy Bradley and Ben Abruzzo's son Richard, who took off from Bangor, Maine, on September 15, 1992. In the world's first transatlantic race, they were blown off course and landed near Fès, Morocco, 146 hours later. Kittinger made the first solo transatlantic crossing when he flew his helium-filled Rosie O'Grady's 5,690 km (3,535 mi) from Caribou, Maine, to the Italian Riviera near Savona, September 14-18, 1984.

In March 1999 Bertrand Piccard and Brian Jones succeeded in circling the globe in their helium/hot air balloon Breitling Orbiter 3. As well as becoming the first balloonists to circumnavigate the Earth, they also set new records for the longest continuous balloon flight measured in both time and distance, at 46,759 km (29,055 mi) travelled in 19 days, 21 hours, and 55 minutes. The Swiss-born Piccard was son of the oceanic explorer Jacques Piccard and grandson of the balloonist Auguste Piccard but was not a professional balloonist; Jones was a balloon flying instructor.

In July 2002 the American millionaire Steve Fossett became, on his sixth attempt, the first solo balloonist to circumnavigate the globe, after spending over 13 days in the air. His helium/hot air balloon, Spirit of Freedom, reached speeds of almost 322 km/h (200 mph) during the 34,000 km (22,100 m) journey. In the same effort Fossett broke his own 1998 world record for the longest distance travelled alone by a balloonist. Another ballooning record was set in November 2005, when the Indian businessman and aviator Vijaypat Singhania ascended 21,290.89 m (69,852 ft) in a specially designed hot air balloon, fitted with a pressurized cabin attached to the 48.8 m (160 ft)-high balloon.

III

Modern Scientific Ballooning

Three types of balloon are in common use for meteorological research.

The rubber or neoprene balloon is used for vertical soundings, either as a radiosonde-carrying balloon that transmits meteorological information, or as a pilot balloon, a small balloon sent aloft to show wind speed and direction. The balloon, inflated with a lifting gas (hydrogen, helium, ammonia, or methane), stretches as it ascends into thinner air. When the diameter of the balloon has stretched by three to six times (that is, when its volume has increased to 30 to 200 times its original amount), the skin ruptures, destroying the balloon.

The zero-pressure plastic (usually polyethylene) balloon is used to carry scientific instruments to a predetermined density level. The plastic balloon is filled only partly with gas while on the ground. As the balloon ascends, the expanding gas fills the envelope. This type of balloon has a valve that automatically discharges excess gas when the balloon has reached its equilibrium altitude, so that the balloon can maintain this altitude. When the Sun sets, the gas cools, the volume decreases, and the balloon descends to the ground, unless ballast is released.

The superpressure balloon is a nonextensible balloon that is sealed to prevent the release of gas. By the time the balloon reaches its equilibrium level, the free-lift gas has become pressurized. Variations in the temperature caused by the heat of the Sun produce changes in the internal gas pressure, but the volume of the balloon remains fixed. So long as the balloon remains under pressure, therefore, it continues to float at its predetermined constant-density level.

The highest unmanned research balloon flight was made from Chico, California, in October 1972, reaching an altitude of 51,850 m (170,100 ft).

Around the world each day radiosonde balloons make over 1,000 soundings of the winds, temperature, pressure, and humidity in the upper atmosphere. These flights are made almost exclusively from land areas. As a result, adequate measurements of the atmosphere are made over less than 20 per cent of the globe. To obtain coverage over ocean areas, Global Horizontal Sounding Technique (GHOST) balloons have been flown experimentally from the southern hemisphere. (See Meteorology: Upper-Air Observations;Airship).