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The argument that Hydrogen can't be used for aviation is now in dispute.  This eVTOL plane supposedly does 320 mph and has an 1150 mile range.  It flies at 21,000 feet, slightly under the 30,000 ft for most long flights bur still well above the weather in most cases.

It's Private Jet size for Billionaires, but I see no reason it wouldn't scale up for commercial passenger flights.  Actually, bigger planes have better volume/surface area ratio and can use heavier structural materials than smaller ones.

Calling it a "Jet" is a misnomer, because it uses electrically power fans, not direct propulsion from hot gas as a real jet engine does, but that's really irrelevant.  It flies at a fast enough speed to do NY-St Louis in under 3 hours and St.Louis-Denver in 2.5 hrs and Denver-LA 2.5 also.  So, 8 hrs, plus you don't need a landing strip.  The lack of sufficient range to do transatlantic and transpacific flights though makes its overall commercial viability outlook poor.  Looks like mainly a toy for billionaires.

I find this still to be questionable, because along with a dozen photos of the plane and 2 videos showing engineers in meetings, there was no video of the plane in action.  I also wonder how well all those little fans would work in a heavy rain?  BMW is a reputable companyy though, so that gives it a little extra credibility.

https://newatlas.com/aircraft/global-unveiling-sirius-ceo-jet-hydrogen-electric/

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Now for the opposite argument, which uses basic physics and math to demonstrate why Hydrogen is a EPIC FAILURE as aviation fuel.  It does it well, and definitely with the current aircraft used by the aviation industry, you can kiss off H as direct fuel for keeping the Billionaire Private Jets airborne.

However, this doesn't necessarily mean being grounded for good, if you're rich enough.  I see two possible solutions to the problem.

I mentioned one a while back, which is to switch from Jet engines to Rocket engines utilizing Solid Fuel propellant like the old Space Shuttle.  Ammonium Nitrate, also used for Fertilizer and making Bombs is used for solid rocket fuel.  This can be synthesized by taking Nitrogen and hydrogenating it over a catalyst to make Ammonia, then combining that with Nitrates created by oxidizing Nitrogen.  All these synthetic reactions require the input of gobs of energy, but this (in theory) could be sourced from renewable power generation.

The other is taking biologically sourced carbon compounds, such as Wood Gas or Ethanol, hydrogenating them and polymerizing up the carbon chain to 5-7 atoms and using pentane-hexane-heptane as your jet fuel.  This produces CO₂ when burned, but it's carbon neutral since the carbon comes from plants you grow to make the wood gas or alcohol.

This whole process would be very expensive and the fuel would cost a bundle, but this is irrelevant to Elon's $56B pay package.  Also explains why Elon & Jeff have Rocket companies, they need them to build their Private Rockets.

You however can kiss off your vacations in Hawaii, unless you have time to sail there.

https://cleantechnica.com/2024/07/01/another-day-another-hydrogen-transportation-firm-plummets-to-earth/

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I've been wondering when this type of catalyst would be developed and made economically viable.  This provides a means to make Green Hydrogen useful as an aviation fuel as well as using atmospheric CO₂ as the carbon source, thus making a closed loop with net zero carbon emmisions, as long as the electricity is produced by renewable carbon-free methods.

Developing the right catalyst is just the first step of course, they also need to produce the hydrogen cheap enough and be able to filter the CO₂ from the atmosphere and combine it with the H to make Methane (CH₄), which would also require electrical energy input for the reaction to go forward.  Finally, they would need to use the methane to produce longer carbon chain liquid synthetic fuel, another endothermic reaction.  At the end of this process you get your Jet Fuel.  Very expensive jet fuel.  Still chump change for Elon Musk and other Private Jet owners though.

https://interestingengineering.com/science/catalyst-co2-methane-clean-energy

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