Hot Air Baloon

A hot air balloon is a lighter-than-air aircraft that consists of a bag, called an envelope, which contains heated air. Suspended beneath is a gondola or wicker basket, which carries passengers and a source of heat, in most cases an open flame caused by burning liquid propane. The heated air inside the envelope makes it buoyant, since it has a lower density than the colder air outside the envelope. The top of the balloon usually has a vent of some sort, enabling the pilot to release hot air to slow an ascent, start a descent, or increase the rate of descent, usually for landing.