Airship - Types

Types

• Non-rigid airships (blimps) use a pressure level in excess of the surrounding air pressure to retain their shape during flight. Unlike the rigid design, the non-rigid airship's gas envelope has no compartments. At sea level, the ballonets (internal flexible cells) are filled with air. As altitude is increased, the lifting gas expands and air from the ballonets is expelled through air valves to maintain the same hull shape. To return to sea level, the process is reversed. Air is forced back into the ballonets by both scooping air from the engine exhaust and using auxiliary blowers.
• Semi-rigid airships, like blimps, require internal pressure to maintain their shape, but have extended, usually articulated keel frames running along the bottom of the envelope to distribute suspension loads into the envelope and allow lower envelope pressures.
• Rigid airships (Zeppelin is almost synonymous with this type) have rigid frames containing multiple, non-pressurized gas cells or balloons to provide lift. Rigid airships do not depend on internal pressure to maintain their shape and can be made to virtually any size.
• Metal-clad airships were of two kinds: rigid and non-rigid. Each kind used a thin gas-tight metal envelope, rather than the usual rubber-coated fabric envelope. Only four metal-clad ships are known to have been built, and only two actually flew: Schwarz's first aluminum rigid airship of 1893 collapsed, while his second flew; the non-rigid ZMC-2 flew 1929 to 1941; while the 1929 non-rigid Slate City of Glendale collapsed on its first flight attempt.
• Thermal airships use a heated lifting gas, usually air, in a fashion similar to hot air balloons.