We seem to have the elements coming together to make a proper assessment of hydrogen powered aircraft within the next couple of years.

I am not talking about trans-Atlantic, but light and medium class up to 80 seats.

At Bristol airport ground handling equipment running on hydrogen is being tested, to show its safety in a working airport environment.

Meanwhile all sorts of tests are being carried out on cyrogenic storage tanks etc suitable for aircraft:

https://fuelcellsworks.com/news/composite-cryogenic-tanks-tested-with-liquid-hydrogen-by-national-composites-centre/

As for cost, here is one estimate which puts the costs of renewable hydrogen within striking distance of jet fuel by around 2035, about 8% higher they reckon, so with any sort of tax on carbon emissions instead or their present free ride, then it is fine:

https://www.transportenvironment.org/discover/running-a-hydrogen-plane-could-be-cheaper-than-traditional-aircraft-by-2035/

I don't have an opinion on their costings, as I have no information on what assumptions have gone into them, but I would just note that if they are anything like accurate, then for some areas of the world with better renewable resources than Europe hydrogen should be competitive before that, and without worrying about taxation levels. Australia for internal flights?

Maybe RyanAir will continue to be able to lose our baggage across Europe into the future!

What do you folks think?

Gryf, do you still reckon it is a bit of a pipe dream?

I am not handicapped by knowing anything about engineering in general or aircraft in particular! :-0

Hi GdB

I haven't come across ammonia as a candidate for jet fuel replacement, so will have to have a good look at your link tomorrow when I am more awake to learn!

AFAIK though your claim that:

' The H2 storage will be heavier than jet fuel,' is not accurate:

For instance:

https://newatlas.com/aircraft/hypoint-gtl-lightweight-liquid-hydrogen-tank/

' To put this in context, ZeroAvia's Val Miftakhov told us in 2020 that for a typical compressed-gas hydrogen tank, the typical mass fraction (how much the fuel contributes to the weight of a full tank) was only 10-11 percent. Every kilogram of hydrogen, in other words, needs about 9 kg of tank hauling it about.

Liquid hydrogen, said Miftakhov at the time, could conceivably allow hydrogen planes to beat regular kerosene jets on range.

"Even at a 30-percent mass fraction, which is relatively achievable in liquid hydrogen storage, you'd have the utility of a hydrogen system higher than a jet fuel system on a per-kilogram basis," he said.

GTL claims the 2.4-m-long, 1.2-m-diameter (7.9-ft-long, 3.9-ft-diameter) cryotank pictured at the top of this article weighs just 12 kg (26.5 lb). With a skirt and "vacuum dewar shell" added, the total weight is 67 kg (148 lb). And it can hold over 150 kg (331 lb) of hydrogen. That's a mass fraction of nearly 70 percent, leaving plenty of spare weight for cryo-cooling gear, pumps and whatnot even while maintaining a total system mass fraction over 50 percent. '

And GTL and Hypoint are not the only game in town for cyrogenic storage of liquid hydrogen, with Airbus for instance certainly hoping to source very lightweight tanks, I am not sure who from.

The bulk appears to be more of an issue, requiring new aircraft designs, although I am very far from seeking to claim that the cyrogenic tanks and hydrogen in general for aircraft are done and dusted, but there seems to be comfortable headroom at least in the weight of the fuel systems, with it being easier the bigger the target aircraft.

When dealing with hydrogen fuel, you have to consider the volume of the total system as well as the mass. If the plane gets too bulky, it is hard (expensive) to fly it at typical jet speeds.

Hi SJC

I had not thought about how fast a fuel cell configuration can push a plane before, so it is an interesting question.

It does not seem to be a problem for using hydrogen in an engine, here is a rather old link:

https://projects.research-and-innovation.ec.europa.eu/en/horizon-magazine/quiet-and-green-why-hydrogen-planes-could-be-future-aviation

' For a 45-seater aircraft, a hydrogen-powered propeller plane will be capable of speeds of up to 600 kilometres per hour, compared to 850 kilometres per hour for a Boeing 747, according to Dr Kallo. While the focus at the moment is on propellers, there is also work underway to develop hydrogen-powered turbines, which are more efficient at higher speeds. ‘(A parallel) step would be to use turbine-type propulsion, using high-speed motors, which are relatively low noise,’ Dr Kallo added.'

But there again, you never said that that is a problem!

Dunno how fast you can push a plane using fuel cells, I'll continue to dig around and see if anything turns up.

Early days though, and there are a whole bunch of other issues which need solving first!

@GdB

Your link to the use of ammonia in planes is interesting, and it is plain that it has significant advantages.

These include an established supply chain, although not rated as yet for aircraft and airport use.

Practical plans to greatly increase volume without the huge impacts supplying biomass etc for SAF would requre, where they do not even seem to have produced an outline of how to do that in the quantities needed for world supply, since they hope to simply press on regardless increasing airplane outputs of legacy designs regardless of climate impact.

Renewable energy is likely in any case to be exported from the world's most suitable locations as ammonia, so using it in aircraft as is would be dead handy.

The biggest stumbling point would seem to me, aside from dealing with nitrous emissions, the low energy density.

Looking at table 3 the energy density per kg looks great, at 600kg/m3, up there towards the density of jet fuel, until one looks at how much hydrogen that contains, which is down around the 17.8% mark, so giving energy densities broadly comparable to liquid hydrogen, not jet fuel.

As your link very fairly notes on page7:

' While SAF platform integration takes minimal effort, and hydro-
gen integration looks more like a total redesign, ammonia integra-
tion would lie in the middle. Akin to hydrogen, a novel fuel
system (discussed here) would be needed to ensure the ammonia
is properly conditioned and distributed, and changes to the propul-
sor would be required to ensure combustion of the fuel (and possi-
ble NO x reductions). In regard to storage, ammonia can be stored in
the wing and wing center carry-through section of the aircraft, a
large benefit over pure hydrogen, but due to the decrease in LHV
and density of ammonia, additional fuel bladders and storage
space may be needed in other areas of the aircraft to compensate.
It is unclear whether major fuselage modifications and therefore
landing gear changes would be required to handle this increase in
fuel volume. Ammonia also faces the same issue (or benefit) with
contrail avoidance as hydrogen.'

So although the modification requirements are somewhat relaxed compared to liquid hydrogen, for any reasonable range new bodies would still seem to be required.

The speed of the aircraft has nothing to do with the fuel cell it's a propeller driven aircraft the propeller is driven by a motor the motor is powered by electricity from the fuel cells they are not jet engines there is no way they're going to go as fast ...time is money

Here is one take on the trade offs between turbofans, which for the purposes of this discussion I am taking as synonymous with jets, and turboprops ( comment by Tulki Jenkins):

https://www.quora.com/Why-are-turboprop-planes-faster-on-short-routes-even-though-the-turbofan-has-a-faster-cruising-speed

It won't let me copy and paste, just wanting to give me hassle instead, but basically turboprops get up to speed quicker, at lower altitude, airlines are not too hassled about extra time in the air, within limits and he reckons that ground handling is often rather simpler, although whether that would apply to hydrogen fuel cell aircraft is totally unclear at this time, as we have not even one example actually flying currently.

Jim:

Boeing are spending nothing on alternative fuel aircraft design, going SAF which entails only minor engine modifications and nothing but SAF, even though, so far as I can determine, there is zero analysis of SAF production for the fleet size they envisage by 2050, as they propose to ignore the consequences of continuing to pump out GHG, and aircraft designed to use GHG emitting fuels, relying on exemptions, as it is a sector 'difficult to decarbonise'

That is biological sources for SAF, and the other direction they wave their hands at, on the grounds that 'something will turn up' to avoid the consequences of their sociopathic refusal to face facts, is DAC, where the most optimistic, every breakthrough counted in and counted on, results in costs by 2050 several times too high.

Airbus are aware that with the political climate in Europe, they can't get away with so openly peddling fake solutions, and are the ones looking, and it is just that, at the moment at putting billions into real alternatives, although meantime they propose increasing production of legacy aircraft as fast as they can make and sell them, and GHG be damned.

Of course, there is a real, right now alternative, whilst proper alternatives for low carbon flight are developed.

Charge a realistic tax on air travel, and its GHG emissions, instead of the free pass they currently get.

That would stop most of the legacy aircraft being built, and reduce real transition costs.

Jim said:

' Currently there are no good options compared to room temperature liquid fuels, especially if you want to go more than say 1000km.'

Absolutely right.

Both hydrogen and ammonia can be produced in the needed quantities though, even for expanded air travel, from renewable resources, which is very unclear for SAF.

Hydrogen unlike ammonia has the energy density to enable long distance flight, but there is one heck of a way to go to develop it enough to do so.

Meantime the realistic way of reducing GHG emissions from long distance flight is to restrict or reduce it, and certainly the growth of airline fleets.

If SAF is the answer, then it would be good to see plans and money in place to produce it in vast quantity, not simply indefinitely delay such production.

I don't think that they are serious, and certainly not Boeing.

@SJC

Nothing against SAF if produced in a sustainable manner and used to reduce emissions.

Unfortunately the plans of the aircraft industry simply indicate building more and more planes running on present fuels, and indefinitely increasing, not decreasing, emissions, whilst using SAF, someday, and the utterly ludicrous DAC as fig leaves.

This is not capitalism in action, but as Adam Smith put it, a conspiracy against the public interest, 'what is good for GM is good for the country' and via capture of the regulatory system externalising costs.

It is not cost free to pump out GHG, it is just that those responsible are currently imposing the costs on others, and does not reduce the real cost by a dime.

Flying especially intercontinental is very expensive if proper costing were imposed, and far more expensive than at present were taxation levels simply equalised with other forms of transport even without considering carbon taxation.

And transition costs will be increased, not decreased, by enabling through inequitable taxation the expansion of the present 'legacy-from-inception' airfleet.

I agree on taxing aviation fuel.
Why should aviation get off scot free.
This would put serious pressure on them to increase the efficiency of kerosene fueled planes or seek non-carbon dense fuels.
Also things like open rotor engines, and maybe hybrids.

Since I have been swingingly dismissive of DAC, it is incumbent on me to note any progress is that field, which may potentially make it work with acceptable economics.

Here is a new study on DAC converted directly to CO for industrial use, with, it is claimed, very large energy and cost savings:

https://techxplore.com/news/2024-04-approach-reusing-captured-carbon-cheaper.html

Fair enough, and welcome.
However I note that all the comparisons given are against the costs and efficiencies of the massively inefficient and expensive other technologies, with no absolute figures on either.

So for the moment, pending more data, it sounds to me like noting an improvement of the order of the difference between falling off a 200 foot cliff and hitting the ground, improved to falling off a 100 foot cliff and hitting the ground, as you are dead either way.

@Dave trains are OK for intra country travel, but look up Stockholm to Malaga - it takes 44 hours.
+ if you live in Ireland, you more or less have to fly to anywhere, unless you want to bring the car to France or Spain with a loads of kids in it. (Which many people do).
More efficient routing and liquid HC fueled aircraft, like open rotor would help, without throwing the baby out with the bathwater.
You could also make a longer version of the A321, keeping the MTOW of 101 tons, but trading range for 4 or 5 more rows of seats.
(Still get you to Malaga, just not Chicago).