dirigible

A dirigible is a steerable, powered airship—an aircraft that remains aloft because of a buoyant gas enclosed in a large envelope and is controlled in flight by engines, propellers, and fins. The term is often used interchangeably with airship, though in some contexts "airship" may imply any lighter-than-air craft, while "dirigible" emphasizes steerability.

Dirigibles are classified by their construction: rigid airships, which have an internal framework supporting the gas envelope; semi-rigid types, with partial structure; and non-rigid blimps, which rely on the gas pressure of the envelope for shape.

The lifting gas provides buoyancy; hydrogen is light and was used in early designs but is highly flammable, while helium is non-flammable and preferred today, though rarer and more costly. Buoyancy can be adjusted by ballast, venting gas, and by controlling envelope pressure.

Propulsion is usually provided by one or more engines driving propellers, with rudders and fins for steering. Modern dirigibles can hover and loiter over a location, ascend and descend, and travel at modest speeds, using a combination of buoyancy control and thrust.

History: The development of steerable airships began in the late 19th and early 20th centuries, culminating in the rigid Zeppelins of Germany. The era of passenger airships ended after the Hindenburg disaster in 1937, which heightened safety concerns and prompted a shift to airplanes.

Today, dirigibles are used for niche applications such as advertising, surveillance, scientific research, and tourism. Modern examples include the Zeppelin NT and several hybrid designs, which aim for longer endurance and lower operating costs, though operations face weather, logistics, and energy challenges.