Aerostat
[1][2] With airships, which need to be able to fly against wind, the lifting gas capsules are often protected by a more rigid outer envelope or an airframe, with other gasbags such as ballonets to help modulate buoyancy.
This contrasts with the heavier-than-air aerodynes that primarily use aerodynamic lift, which must have consistent airflow over an aerofoil (wing) surface to stay airborne.
These powered aerostats later came to be called airships, with the term "balloon" reserved for unpowered types, whether tethered (which means attached to the ground) or free-floating.
[6][7] More recently, the US Government Accountability Office has used the term "aerostat" in a different sense, to distinguish the statically tethered balloon from the free-flying airship.
[8] A balloon is an unpowered aerostat which has no means of propulsion and must be either tethered on a long cable or allowed to drift freely with the wind.
The dynamic movement may be created either using propulsive power as a hybrid airship or by tethering in the wind like a kite, as a Helikite or kytoon.
Tiny Helikites will fly in all weathers, so these sizes are popular as they are very reliable but still easy to handle and do not require large expensive winches.
Helikites can be small enough to fit fully inflated in a car but they can also be made large if heavy payloads are required to be flown to high altitudes.
Helikites are one of the most popular aerostat designs and are widely used by the scientific community, military, photographers, geographers, police, first responders.
Interest in the sport of hot air ballooning reawoke in the second half of the twentieth century and even some hot-air airships have been flown.
[10] Some works were able to produce a special mix for ballooning events, incorporating a higher proportion of hydrogen and less carbon monoxide, to improve its lifting power.
This would allow the object to float above the ground without any heat or special lifting gas, but the structural challenges of building a rigid vacuum chamber lighter than air are quite significant.
The buoyancy control of an aerostat relies on the principles of buoyant force and the manipulation of the gas inside its envelope.
The basic mechanism involves adjusting the volume and pressure of the gas within the aerostat’s envelope, often through a system of valves and compartments.
This is controlled either through heating (in the case of hot air balloons) or by adjusting the valves that manage the flow of gas between different compartments or the outside atmosphere.
Helium-based aerostats, such as blimps, rely on maintaining the integrity and volume of the helium within their envelope to achieve a stable lift.
Venting gas allows the envelope to lose volume, making the aerostat denser than the surrounding air and causing it to descend.
Sophisticated systems might use automatic valves and sensors to monitor atmospheric pressure, gas volume, and temperature, ensuring that the aerostat remains stable without manual intervention.
This constant regulation allows aerostats to hover at a fixed altitude for extended periods, making them useful for applications such as surveillance, communication relays, or scientific observations, where maintaining a consistent position in the atmosphere is crucial.
