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Balloon (aircraft)

Balloons are aircraft that remain aloft due to the effect of buoyancy. They are a type of lighter than air aircraft. Balloons move through the sky by being carried along by the wind. They are distinct from airships which are buoyant aircraft which can be propelled through the air in a controlled manner.

Balloons as flying machines

A balloon is conceptually the simplest of all flying machines. The balloon is a fabric "envelope" filled with a gas that is lighter than the surrounding atmosphere. As the entire balloon is less dense than its surroundings, it rises, taking along with it a "gondola" attached underneath that carries passengers or payload.

The first balloon, launched in 1783 by two Parisian brothers named Montgolfier, used hot air to obtain buoyancy. Balloons using the light gas hydrogen for buoyancy were also developed at the same time. Jean Pierre Blanchard made the first piloted balloon flight in North America on January 9, 1793. Although a balloon has no propulsion system, a degree of directional control is possible through making the balloon rise or sink in altitude to find favorable wind directions.

Both the hot-air, or Montgolfière, balloon and the gas balloon are still in common use. Montgolfière balloons are relatively inexpensive as they do not require high-grade materials for their envelopes, and they are popular for balloonist sport activity.

Light gas balloons are predominant in scientific applications, as they are capable of reaching much higher altitudes for much longer periods of time. They are generally filled with helium. Although hydrogen has more lifting power, it is explosive in an atmosphere full of oxygen. With a few exceptions, scientific balloon missions are unmanned.

There are two types of light-gas balloons: zero-pressure and superpressure. Zero-pressure balloons are the traditional form of light-gas balloon. They are partially inflated with the light gas before launch, with the gas pressure the same both inside and outside the balloon. As the zero-pressure balloon rises, its gas expands to maintain the zero pressure difference, and the balloon's envelope swells.

At night, the gas in a zero-pressure balloon cools and contracts, causing the balloon to sink. A zero-pressure balloon can only maintain altitude by releasing gas when it goes too high, where the expanding gas can threaten to rupture the envelope, or releasing ballast when it sinks too low. Loss of gas and ballast limits the endurance of zero-pressure balloons to a few days.

A superpressure balloon, in contrast, has a tough and inelastic envelope that is filled with light gas to pressure higher than that of the external atmosphere, and then sealed. The superpressure balloon cannot change size greatly, and so maintains a generally constant volume. The superpressure balloon maintains an altitude of constant density in the atmosphere, and can maintain flight until gas leakage gradually brings it down.

Superpressure balloons offer flight endurance of months, rather than days. In fact, in typical operation a Earth-based superpressure balloon mission is ended by a command from ground control to open the envelope, rather than by natural leakage of gas.

For air transport balloons must contain a gas lighter than the surrounding air. There are two types:

• hot air balloons: filled simply with hot air, which by heating becomes lighter than the surrounding air; they have been used to carry human passengers since the 1790s;
• balloons filled with:
  • hydrogen -- no longer used because of the high flammability. See Hindenburg disaster
  • helium

Large helium balloons are used as high flying vessels to carry scientific instruments (as do weather balloons), or even human passengers. See: Montgolfiere, Zeppelin, Blimp, Airship, QinetiQ 1.

Balloons in the military

Some military use of balloons is discussed in hot air balloons.

Hot air balloons were used by military observers in the American Civil War (1861-65) and the Franco-Prussian War (1870-71). However, hydrogen-filled ballons were widely used during World War I (1914-1918) to detect enemy troop movements and to direct artillery fire. Observers phoned their reports to officers on the ground who then relayed the information to appropriate destinations. Because artillery was such an important factor in WW I, balloons were frequent targets of opposing aircraft. Though balloon companies of all combatants were protected by antiaircraft guns and patrolling fighters, casualties frequently were heavy.

Observation balloons were retained well after the Great War, being used in the Russo-Finnish conflicts (1939-40 and 1941-45).

In World War II, gas-filled barrage balloons with cables hanging from them were used to intercept low-flying aircraft in the Battle of Britain. Also, the Japanese launched thousands of balloon bombs to the US and Canada, carried in the jet stream; see fire balloons.

Surveillance balloons, or, more correctly, aerostats, have also been used in the 2004 American occupation of Iraq. Utilizing a high-tech optics system to detect and observe enemies from miles away, balloons have been used, accompanying foot patrols in Baghdad.

Types of balloon aircraft

There are three types of balloons:

• hot air balloons: obtain their buoyancy by means of heating air above the ambient temperature. They are by far the most common type of balloon aircraft today.
• hydrogen -- no longer used because of the high flammability, rarely used since the Hindenburg disaster
  • helium -- the most common gas used today
  • ammonia -- infrequently used due to its caustic qualities
  • coal gas -- used in the early days of ballooning, high flammability
• dirigible) balloons started to be developed in

the 1800s.

Ed Yost refined the design of hot air balloons in the 1950s using rip-stop nylon fabrics and high powered propane burners to create the modern hot air balloon.

See also: Montgolfiere, Airship