An airship, also known as a dirigible, is a powered lighter-than-air craft. In other words, an airship is an aircraft that derives its lift from a lifting gas (usually helium or hot air) while it is propelled forward by an engine. A lighter-than-air craft is any vehicle that flies because it is lighter than air. This includes balloons and airships, also known as dirigibles. What makes a vehicle lighter than air, is the fact that it uses a lifting gas (i.e. helium or hot air) in order to be lighter than the surrounding air. The difference between airships and balloons are the following: Balloons simply follow the direction of the winds. In contrast, airships are powered and have some means of controlling their direction, usually with rudders.
There are four categories of airships, Rigid, Semi-Rigid, Non-Rigid and Hot Air Airships. Rigid airships have an internal frame. Zeppelins are a good example of rigid airships.See the post on Airships in my aerophilately blog
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