Most airships built since the 1960s have used helium, though some have used hot air. The envelope of an airship may form the gasbag, or it may contain a number of gas-filled cells.

How are airships powered?

The ballonets act like ballast tanks holding "heavy" air. When the blimp takes off, the pilot vents air from the ballonets through the air valves. The helium makes the blimp positively buoyant in the surrounding air, so the blimp rises. ... The cone shape of the blimp also helps to generate lift.

Are airships fuel efficient?

Airships are far more fuel-efficient than planes, which must constantly burn jet fuel to stay aloft. "It's only working half as hard, and as a result you're burning much less gas," Girimaji says.