Editing Airship (section)

==Classification==
Airships are classified according to their method of construction into rigid, semi-rigid and non-rigid types.<ref name="ege" />

===Rigid===
{{Main|Rigid airship}}
A rigid airship has a rigid framework covered by an outer skin or envelope. The interior contains one or more gasbags, cells or balloons to provide lift. Rigid airships are typically unpressurised and can be made to virtually any size. Most, but not all, of the German [[Zeppelin]] airships have been of this type.

===Semi-rigid===
{{Main|Semi-rigid airship}}
A semi-rigid airship has some kind of supporting structure but the main envelope is held in shape by the internal pressure of the lifting gas. Typically the airship has an extended, usually articulated keel running along the bottom of the envelope to stop it kinking in the middle by distributing suspension loads into the envelope, while also allowing lower envelope pressures.

===Non-rigid===
{{Main|Blimp}}
Non-rigid airships are often called "blimps". Most, but not all, of the American [[Goodyear blimp|Goodyear airship]]s have been blimps.

A non-rigid airship relies entirely on internal gas pressure to retain its shape during flight. Unlike the rigid design, the non-rigid airship's gas envelope has no compartments. However, it still typically has smaller internal bags containing air ([[ballonet]]s). As altitude is increased, the lifting gas expands and air from the ballonets is expelled through valves to maintain the hull's shape. To return to sea level, the process is reversed: air is forced back into the ballonets by scooping air from the engine exhaust and using auxiliary blowers.