At least for fueling airplanes, hydrogen doesn't appear to be non-sense. I initially suspected that Airbus was just putting out some hot air, but now I think th

At least for fueling airplanes, hydrogen doesn't appear to be non-sense. I initially suspected that Airbus was just putting out some hot air, but now I think there's a 50-50 chance they are serious. The basic idea is: hydrogen is by far the chemical fuel with the highest energy density in terms of mass: about 3 times the energy density of gasoline or jet fuel. However, liquid hydrogen has very low (mass) density so in the end the volumetric density of hydrogen is about 3 times lower than that of gasoline. But that works out ok. For example, an Airbus A320 has a max takeoff weight of about 75 tons, out of which about one third is fuel. If you replace that fuel with the liquid hydrogen that has the same caloric content, you need only a third of that in terms of mass (so about 8 tons), but since that occupies pound for pound 3 times as much volume, these 8 tons will fill the same volume as the 25 times of the regular jet fuel. This is great news: you don't need to modify the shape of the airplane, you don't need to make it like a beluga to fit bigger tanks. Moreover, there are reasons to believe hydrogen-fueled engines have higher efficiency, maybe 10-20% higher. On top of that, if you reduce the takeoff weight from 75 tons (which is 25 tons of fuel + 50 non-fuel) to only 58 tons, you end up needing less fuel to carry this airplane around. It's the curse of the rocket equation working in reverse, in other words it's a blessing: using a more dense fuel means you need to carry less fuel, therefore you need to carry less fuel that moves the fuel, etc. In the end you probably get a few percentages of savings right there for free. So, these are the pros. What are the cons? You need cryogenic storage, you probably need tanks with a special interior lining to limit the leakage, you need infrastructure to move the hydrogen around. On top of that, there's a chance you increase the NO2 pollution (and it's not like an airplane can carry with it a catalytic convertor to take care of that). An obvious pro is no CO2 emissions. An obvious con is the cost of producing the H2. All in all, I think there's a fair chance that H2-powered airplanes could be a good idea.