Whats the difference between airships?
There are three principal classifications: rigid (having an internal framework, such as the USS Akron), semi-rigid (those having a rigid keel running the envelope length, such as the Norge or Italia or the new Zeppelin NT), and non-rigid (having no internal framework, such as the present Goodyear fleet — Eagle, Stars & Stripes, Spirit of Akron). And, there are hybrids. In non-rigids, the internal pressure of the lifting gas (non-flammable helium) maintains the shape of the envelope. Internal air compartments — ballonets — are inflated or deflated with air to compensate for ambient pressure differences. These airships are commonly referred to as blimps.
