I am BuildsJets now, but 20 years ago I was BuildsCryoFuelsystems.
Go look at the cross section of an actual hydrogen-powered aircraft that has flown actual missions under it's own power, such as the Boeing Phantom Eye. The USSR's TU-155 flying testbed aircraft does not count, it did not fly under hydrogen power or fly an actual mission, it just ran an engine in the air.
Observe how much of the airframe's space is used by fuel storage, compared to payload. Now do the same thing for a commercial airliner, and realize that commercial aircraft are just barely profitable with their current payload:fuel weight ratio.
Also, did you know that when you refuel a liquid hydrogen tank, a significant portion of the fuel is vented off to the atmosphere? In the case of the Space Shuttle, LH2 filling losses are around 20% of total fuel load. Then there are boil-off significant losses while the vehicle sits around warming up. So to be most efficient, you would need to either fuel up IMMEDIATELY before loading passengers, or hot-loading propellant with passengers on-board, like SpaceX does, and the FAA prohibits for commercial passenger operation. There are also boil-off losses in the transportation and storage equipment to consider, and boil-off losses everytime you transfer to a different storage or transportation medium.
Just a few months ago, Universal Hydrogen did a 200-mile flight of their Dash-8 which has been converted with one hydrogen engine. I’m not going to make any predictions about the future price of hydrogen vs. other fuels, but it doesn’t seem like there are any insurmountable technical barriers to mid-range hydrogen airliners.
Storage of large quantities of hydrogen is a pain and also heavy (which matters a lot on a plane), so if you really want clean fuel, then synthetic hydrocarbons make more sense on a plane than hydrogen.
Storage of LH2 is not, in fact, heavy. Rockets are even launched carrying it.
Management of bulk LH2 is a chore, but is mature technology. The value proposition of LH2 as aircraft fuel is such that, in any market where LH2 airframes come into service, kerosene craft will be immediately wholly unable to compete.
Ah, I was thinking more about hydrogen fuel cells and gaseous hydrogen (which I've seen discussed for the plane replacements) not cryogenic liquid hydrogen.
Hydrogen has great energy density by mass. But creating a very lightweight container to store either liquid hydrogen or highly pressurized hydrogen is challenging. More feasible than powering planes with lithium batteries, though.
Lightweight containers for LH2 have proven so trivial as to have already been in use for many decades aboard space launch systems, which are even more sensitive to weight than aircraft. Aircraft LH2 tanks would want insulation usually omitted from rockets, but insulation is mature tech.
Weight of LH2 is so enormously less than kerosene that, once LH2 aircraft enter a market, no kerosene airframe could continue competing. Given the low volumetric density, such that LH2 tanks would not fit in the wings, they will probably instead be removable nacelles slung under wings alongside the engines. This has the further advantages of eliminating need for mobile hoses and for complicated onboard plumbing. I doubt anybody would want to fly with inboard hydrogen tankage, anyway.
Probably cargo craft will be first to use LH2, because carriers cannot load on another 40% more passengers just because the fuel weighs so much less.
Yet, millions of tons of H2 is produced, stored and transported annually, today.
It needs adequate ventilation to ensure that any leakage doesn't accumulate to exceed a 25% mix with air. That is done where H2 is used now. You are not hearing about hydrogen detonations.
