An airship is a dirigible (steerable) buoyant aircraft, sometimes referred to as a blimp (normally for non-rigid types). Airships get aerostatic lift (buoyancy) from the atmosphere using a large aerostat as a floatation aid (like a child’s water wings) that displaces the surrounding air in the same way that a ship’s hull displaces water for buoyancy to carry the rest of its weight. Aerostats are filled with LTA-gas to hold their form (i.e., puff them up) against atmospheric pressure, enabling the displacement necessary for resulting buoyancy in accordance with Archimedes’ principle. Atmospheric pressure otherwise would squash their aerostat flat – when the displacement (so buoyancy) enabled would be lost.
LTA-gas is used to minimise aerostat weight, where the gas acts as a structural component (like a pit prop) to prevent its collapse. The larger the volume of the aerostat (so displacement) the greater the buoyancy! Airships of old used hydrogen for the purpose. However, hydrogen is combustible when mixed with oxygen in air, so its use largely was stopped and the airworthiness authorities banned it, favouring safer inert (non-combustible) helium, which is heavier. Nonetheless, the logic of this is based on fear rather than good aircraft engineering to mitigate risks involved, which all airborne vehicles must adopt to enable safe flight. It’s a hypocritical attitude when fuel (also combustible) is permitted in huge quantities for other aircraft (although with numerous rules to ensure safe use).
Fuel, power plants and propeller systems are used to motivate airships (enabling airspeed) and they use aerodynamic surfaces for stability and control in similar ways to nonbuoyant aircraft. However, because the aerostat of airships enables flotation in the atmosphere, motors are only needed to move the airship between points against winds, provide power for systems, and to enable minor unbalanced weight to be borne aerodynamically or by vertical thrust.
Nonbuoyant aircraft require powerful engines to get them aloft and then remain airborne, as well as to propel them at high speed between locations plus provide power for their systems. As a result, for a number of uses needing exceptionally long endurance while carrying large volume payloads, airships are able to achieve a considerable reduction in fuel used and thus operating costs compared with nonbuoyant aircraft for the same purpose. Airships thus relatively easily use alternative sustainable low power methods.
