Balloon (aeronautics)

In aeronautics, a balloon is an unpowered aerostat, which remains aloft or floats due to its buoyancy. A balloon may be free, moving with the wind, or tethered to a fixed point. It is distinct from an airship, which is a powered aerostat that can propel itself through the air in a controlled manner. Many balloons have a basket, gondola, or capsule suspended beneath the main envelope for carrying people or equipment (including cameras and telescopes, and flight-control mechanisms). Aerostation is an obsolete term referring to ballooning and the construction, operation, and navigation of lighter-than-air vehicles. Tiberius Cavallo's The History and Practice of Aerostation was published in 1785. Other books were published on the subject including by Monck Mason. Dramatist Frederick Pilon wrote a play with aerostation as its title. 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 basket, attached underneath, which carries passengers or payload. Although a balloon has no propulsion system, a degree of directional control is possible by making the balloon rise or sink in altitude to find favorable wind directions. There are three main types of balloons: The hot air balloon or Montgolfière obtains its buoyancy by heating the air inside the balloon; it has become the most common type. The gas balloon or Charlière is inflated with a gas of lower molecular weight than the ambient atmosphere; most gas balloons operate with the internal pressure of the gas the same as the pressure of the surrounding atmosphere; a superpressure balloon can operate with the lifting gas at pressure that exceeds that of the surrounding air, with the objective of limiting or eliminating the loss of gas from day-time heating; gas balloons are filled with gases such as: hydrogen – originally used extensively but, since the Hindenburg disaster, is now seldom used due to its high flammability; coal gas – although giving around half the lift of hydrogen, extensively used during the nineteenth and early twentieth century, since it was cheaper than hydrogen and readily available; helium – used today for all airships and most manned gas balloons; other gases have included ammonia and methane, but these have poor lifting capacity and other safety defects and have never been widely used.