An airship is a lighter-than-air craft capable of being steered, unlike a balloon, which simply drifts in the wind. In fact, another term for an airship is the word “dirigible” which is derived from the French word meaning “to steer.” A dirigible is not a type of airship, but rather another term for the same thing.
Both blimps and zeppelins are two completely different types of dirigibles. There are three main types of airships; Non-rigid, Semi-rigid, and Rigid.
Non-rigid – Blimps are non-rigid airships, which are typically the smallest of the three types and are defined as non-rigid because their shape is derived from internal gas pressure alone.
Semi-rigid – Sometimes referred to as a hybrid type, these dirigibles are so named because they get their external shape from both gas pressure as well as an internal structure that typically runs the length of the aircraft’s keel. They combine the best of both worlds between non-rigid and rigid! This internal structure may allow for greater size as well as the ability to distribute propulsion systems up along the ship’s hull.
Rigid – Zeppelins are the most well known rigid type airships. The entire shape of a rigid airship is determined solely from its internal structure. The strength of an internal structure can allow for dividing the lifting gas into multiple gas cells while also increasing the size of the airship to very large proportions. In addition to having multiple points of attachment for propulsion and other systems, internal accommodations for passengers/cargo are more easily supported. As the largest type of airship, these craft are the closest to being literal ships of the sky!