Lifting gas

Because of Archimedes' principle, a lifting gas is required for aerostats to create buoyancy, particularly in Lighter-than-air aircraft, which include free balloons, moored balloons, and airships. Only certain lighter than air gases are suitable as lifting gases. Dry air has a density of about 1.29 g/L (gram per liter) at standard conditions for temperature and pressure (STP) and an average molecular mass of 28.97 g/mol, and so lighter than air gases have a density lower than this. Because of Archimedes' principle, a lifting gas is required for aerostats to create buoyancy, particularly in Lighter-than-air aircraft, which include free balloons, moored balloons, and airships. Only certain lighter than air gases are suitable as lifting gases. Dry air has a density of about 1.29 g/L (gram per liter) at standard conditions for temperature and pressure (STP) and an average molecular mass of 28.97 g/mol, and so lighter than air gases have a density lower than this. Heated atmospheric air is frequently used in recreational ballooning. According to the Ideal gas law, an amount of gas (and also a mixture of gases such as air) expands as it is heated. As a result, a certain volume of gas has a lower weight as the temperature is higher. The average temperature of air in a hot air balloon is about 212 °F (100 °C). Hydrogen, being the lightest existing gas (7% the density of air), seems to be the most appropriate gas for lifting. But hydrogen has several disadvantages: Helium is the second lightest gas. For that reason, it is an attractive gas for lifting as well. Small size of helium molecules increases its lifting value.