An airship or dirigible is a type of aerostat or “lighter-than-air aircraft” that can be steered and propelled through the air using rudders and propellers or other thrust mechanisms. Unlike aerodynamic aircraft such as fixed-wing aircraft and helicopters, which produce lift by moving a wing through the air, aerostatic aircraft, and unlike hot air balloons, stay aloft by filling a large cavity with a lifting gas.
The main types of airship are non rigid (blimps), semi-rigid and rigid. Non rigid airships 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 compartmentalisation. 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 using auxiliary blowers. Lindstrand Technologies Ltd produce non-rigid thermal, helium manned and helium unmanned airships.
Airships are excellent surveillance vehicles and are very useful in scientific research and advertising. Airships are normally built to a specific end use and since the design and manufacture is conducted in-house, airships of almost any size can be built to the client’s exact requirements. Airships can be flown either by remote control or via a pre-programmed flight path.