Lighter-than-air aircraft

An aircraft supported chiefly by buoyancy from gas less dense than the surrounding air. Its main forms are balloons and airships, which differ in how they are steered and propelled.

Archimedes' principle: A physical principle stating that a body immersed in a fluid experiences an upward force equal to the weight of displaced fluid. The buoyant force that supports the aircraft follows directly from this principle.
Balloon: A flexible or rigid enclosure filled with gas that is less dense than its surroundings. A balloon's buoyant enclosure is the basic form shared by lighter-than-air craft.
Montgolfier brothers: Joseph-Michel and Jacques-Étienne Montgolfier, French inventors associated with the first public hot-air balloon demonstrations in 1783. Their demonstrations began the era of human balloon flight.
Hot-air balloon: A balloon that rises because heated air inside its envelope is less dense than cooler surrounding air. Unlike a powered airship, it generally travels with the wind rather than steering through it.
Buoyancy: The upward force exerted by a fluid on an immersed or floating body. The aircraft's lift comes chiefly from buoyancy rather than aerodynamic lift.
Gondola: A suspended compartment that carries people, equipment, or cargo beneath a balloon or airship envelope. It holds payload below the buoyant volume.
Jacques Charles: French scientist and balloonist who made the first hydrogen balloon flight in 1783. His hydrogen balloon showed an alternative to heated air for buoyant flight.
Heavier-than-air aircraft: An aircraft supported in flight chiefly by aerodynamic lift or thrust rather than buoyancy. Its lift mechanism contrasts with the buoyant support of lighter-than-air craft.
Lifting gas: A gas, such as helium or hydrogen, less dense than air and used to provide buoyant lift. Its density relative to surrounding air determines how much lift the envelope can generate.
Airship envelope: The gas-containing outer structure of an airship, designed to provide buoyant lift. Its shape and volume set the craft's lift and aerodynamic behavior.

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