English

Noun

1. one of several small balloons, inside a dirigible, that can be inflated or deflated to control buoyancy during flight

Ballonets are air-filled bags that are located inside the envelope of an airship. An airship has two ballonets, one fore and one aft. The ballonets are similar to the ballast tanks of a submarine. Because air is heavier than helium, the ballonets are deflated or inflated with air to make the blimp ascend or descend, respectively. They are also used to control the trim, or levelness, of the airship.