A dirigible is a buoyant craft that is powered by an engine and propellers. It has rudders for steering. They are normally filled with a lighter-than-air gas such as helium. They are also known as airships or blimps. The most common type of dirigible still in operation is the Goodyear Blimp, or other advertising blimps.
Three types of airships have been built over the years. A rigid airship has an internal metal frame that helps maintain the ship's shape. A semi-rigid airship has a keel that runs down the length of the airship to help it maintain its shape. The most basic, a non-rigid airship uses a lifting gas such as helium to maintain its shape.
Airship envelopes are normally made from Dacron, Mylar and polyester. They are sometimes made of Tedlar, which is bonded with Hytrel. These fabrics help protect the envelope from ultraviolet light. The bladder, or gas bag, is normally made from leak-resistant polyurethane plastic.
In semi-rigid and rigid airships, the frame is typically made of aircraft-grade aluminum that is riveted. The nose cone is usually made of wood, plastic or metal and is then laced to the airship's envelope. The gondola is manufactured with metal.
