> What's the difference in lift/density of hydrogen vs hot air, like in a balloon? Density data from Wikipedia: Air @ STP: 1.225 kg/m³ Air @ 100°C (typical f

> What's the difference in lift/density of hydrogen vs hot air, like in a balloon? Density data from Wikipedia: Air @ STP: 1.225 kg/m³ Air @ 100°C (typical for a hot air balloon): 0.9486 kg/m³ → lifting force ~0.2764 kg/m³ Hydrogen: 0.0899 kg/m³ → lifting force ~1.1351 kg/m³ Helium: 0.1786 kg/m³ → lifting force ~1.0464 kg/m³ Subtract the density from air and you get the lift force (mass). i.e. hot air can lift about 24% as much as hydrogen, or conversely, you need 4 times the volume. There are hot air airships. See: https://en.wikipedia.org/wiki/Thermal_airship https://en.wikipedia.org/wiki/Thermal_airship