3 ms·

> Putting [a fuel cell] in an aircraft adds extra complications such as safely transporting the liquid hydrogen in fuel tanks, storing the water produced and de

• aaron695 6y ago
  "Blau gas was most famous, however, as the buoyancy compensating fuel for the LZ 127 Graf Zeppelin. It had several advantages over liquid fuels such as gasoline. Because it weighs approximately the same as air, burning it and replacing its volume with air did not lighten the airship, eliminating the need to adjust buoyancy or ballast in-flight" - https://en.wikipedia.org/wiki/Blau_gas https://en.wikipedia.org/wiki/Blau_gas If it was a hydrogen airship you could dump hydrogen to compensate, but helium needs to be reused. I'd guess they have run the numbers on the different ways to change the buoyancy and it's easier to keep the water.
• perilunar 6y ago
  Why does the hydrogen need to be liquid? Airships are weight not volume constrained, so you could probably just store it as gas. You could make it buoyancy neutral by compressing it (at 13 atm it has the same density as air at 1 atm), or carrying oxygen as well (which would also make the fuel cells more efficient that just using hydrogen + air). In some ways hydrogen is an ideal fuel for airships, because although the energy density is very low, the specific energy is very high — much higher than batteries, and 2-3 times hydrocarbon fuels.