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TheLianeonProject t1_iy3cyjz wrote

The problem with hydrogen is the energy density. It is simply far too low. Some planes are already flying with leftover restaurant grease, which seems promising.


jdmgto t1_iy42tj5 wrote

Bingo, getting an engine to run on hydrogen isn’t astounding. The problem is how awful hydrogen is for storage. You’ve got basically two options, absurdly high pressure storage tanks, like 10,000 psi+, or cryogenically. Neither will work with existing aircraft. Commercial aircraft store most of their fuel in the wing structure. You cannot reinforce those structures enough for 10,000 psi storage of gaseous hydrogen, and I know the FAA wouldn’t approve of it. Similarly those structures cannot be retrofitted with adequate insulation to store cryogenic fuels, never mind cryogenic containers which will handle the flex of an aircraft wing without snapping. Which leaves filling up the cargo area with tanks, either high pressure or cryo, which both loses all your cargo space and is inefficient weight wise. And I’m pretty sure if you showed the FAA the plans to turn the entire cargo space of a 737 into a 10,000 psi storage tank they’d retroactively pull the airworthiness certificate of every plane you’ve ever built just on general principle. I’m not even sure if you went full cryo that you could get enough hydrogen onboard an airplane to do much more than short range domestic flights.


FalconX88 t1_iy5490u wrote

> commercial aircraft store most of their fuel in the wing structure.

I wouldn't expect planes to look like they do now. There are a lot of different concepts of planes, look at Airbus Maveric. That blended design would create a lot of volume that can be used.


shwag945 t1_iy5rggt wrote

Commercial passenger planes will probably look the same as they do now because of windows. Windows are important for reducing passenger stress during flight and safety in case of emergencies.

Windowless planes have been a commercial dead end for a long time.


FalconX88 t1_iy7zdsv wrote

Most long haul flights I've been on the past years basically had the windows closed for most of the flight anyway. And in a 10 abreast most people don't have window access right now. However, there are also solutions for that, like fake windows with screens or ceiling windows that let in some sunlight.


jdmgto t1_iy7ucth wrote

MacDonald Douglas/Boeing’s original blended wing body BWB from the late 90’s early 00’s was toyed with but passengers hated it. Most of your passengers wind up in the middle of the plane, far from any windows. You’ve also got issues with trying to get everyone off the plane in an emergency. The FAA has some pretty stringent rules about how long you’ve got to do that. You could, in theory, turn the center of the plane into a giant cryo tank and seat people on the sides near the windows but… well you’re building a huge aircraft and then spending most of the volume on a giant thermos instead of things that make you money.


FalconX88 t1_iy7z38a wrote

> Most of your passengers wind up in the middle of the plane, far from any windows

As they do now, but now we have personal inflight entertainment and on long haul you often got the shades closed almost all flight so not that big of a deal any more.

I agree that there are also challenges, but I wouldn't assume in 50 years planes will look the same


mektel t1_iy6lt3t wrote

Just means the current model for aircraft may need a revamp.

Not that I think hydrogen is the way to go, but we settled on this design based on the fuel we currently use. Future aircraft may very well be of a very different design to support alternative fuel sources or constraints.


westbamm t1_iy3hm00 wrote

Depends on how you look at it I suppose, volume or weight.


JadedIdealist t1_iy3r08e wrote

If you include the weight of the container hydrogen goes back to being abysmal though.


[deleted] t1_iy3s27e wrote



JadedIdealist t1_iy3smq7 wrote

If you store a low density fuel then your container needs to be bigger (and therefore heavier) to hold the same weight of fuel.


[deleted] t1_iy3sspo wrote



dinosaurkiller t1_iy3ugqt wrote

If it’s a bigger tank for the same fuel it’s completely true. The context very much matters and you’re making a lot of assumptions.


[deleted] t1_iy3ux7z wrote



RevolutionaryMove357 t1_iy3x901 wrote

Right? Look at rockets. Destin from Smarter Every Day on YT toured a ULA facility and the tanks for hydrogen and other fuels are insanely, insanely thin.


jdmgto t1_iy44jex wrote

Just… ok… so, no. Rocket fuel tanks do not operate at anything like gaseous hydrogen tank pressures. Every rocket that uses hydrogen fuel is cryogenic, and they are all designed with pressure relief valves specifically so that as the hydrogen boils off the pressure is released. None of them are designed to operate at any significant pressure. Even then, while the actual structural component of the tank is thin, it’s covered in a lot of insulation to prevent the hydrogen from boiling off. Also rockets are designed to be loaded in a single direction, longitudinally and aircraft… aren’t.

Cryogenic hydrogen is just an ungodly pain in the ass to work with which is why every non-rocket utilization of hydrogen as a fuel uses pressurized gaseous hydrogen instead. 


lestofante t1_iy7lxxl wrote

Yes but also that is why Airbus is researching on this.
They think tech may ready to be able to overcome those issues and are gonna try make 3 different demonstrator, one normal frame that burn hydrogen, one lifting body, and one normal frame but fuel cell propeller.
As they are one of the 2 biggest company about planes, I think they know what they can achieve


jdmgto t1_iy7s01s wrote

It's not that you can't make a hydrogen powered aircraft, you can. The problem is that barring the government just straight up banning conventionally powered jets they won't be able to compete. It is just a physical fact that hydrogen’s energy density is awful and working with it is painful. Any aircraft running on hydrogen will either carry less cargo (people or stuff) or have significantly shorter range or some combo of both.


jdmgto t1_iy43exb wrote

>Carbon fibre, kevlar and other materiels are good for the job and weigh less than convential plane fuel tanks.

No, they don’t, because conventional plane fuel tanks are the structure of the wing. Never mind that they aren’t the right shape. Super high pressure storage containers are spheres or cylinders for a reason. Aircraft fuel tanks are long flat rectangles, just about the worst shape to make a pressure vessel out of.


[deleted] t1_iy45do5 wrote



jdmgto t1_iy47q2c wrote

It’s only strange if you have no clue how modern jetliners function, are built, or how hydrogen storage works. Fuel is stored in the wing because fuel is a liquid and can fill odd shapes that are inefficient for anything else. Wings are necessary for aircraft and by their construction have a lot of odd unusable space for cargo. They’re easy to use for fuel storage. Storing fuel in the wing structure is popular because it’s effectively weightless, you had to build the structure regardless. The work to turn them into fuel tanks is pretty trivial and largely what you’d have to do for a single purpose tank. Second, it frees up the fuselage for passengers and cargo, the stuff that makes money. Fuel storage in the fuselage is taking up space that you now can’t sell to make money. And no, there isn’t enough room in the wings for cylinder storage, at least not useful storage. The structure of the wings, the part that holds the fuel is made up of various box girders which are rectangular. The only pressure tanks you could fit in them would be many long, thin, incredibly wasteful tanks that add a lot of points of failure for not a lot of fuel storage.


[deleted] t1_iy48zr3 wrote



jdmgto t1_iy4eywf wrote

It’s condescending because you don’t understand the fundamental reasons why aircraft are built the way they are, how hydrogen storage works, or just basic concepts but you speak authoritatively as if you do. Do you know why the tank in the 737’s wing is that shape? Because the slats and flaps and their equipment take up the leading and trailing edges of the wing. The fuel is contained in the long, rectangular structural box that runs down the center of the wing. That’s what I’m talking about, you don’t understand even the basics of how airplanes work. It’s got nothing to do with balance. 

And no, it couldn’t be used for cargo. Aside from the structural problems of opening that up enough to pack it full of bags which are just horrifying. Do you know how cold that space would be? I doubt passengers would be ok with having their bags frozen solid. Never mind the bag handling issues as you’ve gotta individually Jenga the bags into the wing every time you load it versus chucking it in the hold.

There is a reason about the only place hydrogen is regularly used as a fuel is rockets, and even that’s not universal. Could you build a hydrogen powered aircraft? Sure, but you’ll also see the cost of air travel increase dramatically. Like it or not, baring governments just outlawing conventional jets entirely in favor of hydrogen ones, no ones gonna buy them. 


[deleted] t1_iy3rq6q wrote



jdmgto t1_iy463xm wrote

Cryogenic hydrogen is just an ungodly pain in the ass to work with which is why every non-rocket utilization of hydrogen as a fuel uses pressurized gaseous hydrogen instead. First off the energy usage to create the hydrogen, then chilling it to just a few degrees above absolute zero, then trying to maintain it is just ridiculous.

As far as aircraft, the problem becomes insulation and boil off. The wings of a conventional commercial aircraft aren’t thick enough to store any significant amount of cryogenic hydrogen once you factor in insulation. Never mind trying to keep it chilled in what amounts to a giant radiator. That leaves the body of the aircraft which is, you know, where you put the people and the cargo. You’re losing a lot of your money making space filling it with fuel tank. Never mind the operational problems of cryogenic hydrogen, even the best tanks boil off hydrogen constantly, in flight, everywhere. Rockets can get away with it because they can constantly top off the tanks while they wait to launch then only operate for minutes. An airliner has to operate for hours, and might even be waiting to take off for hours. I’m just imagining a cryogenic airliner stuck on the tarmac in Dubai waiting to take off.


[deleted] t1_iy46qhn wrote



jdmgto t1_iy49rgc wrote

First off, they’re loading those hydrogen tanks into the area the Dash 8 uses for cargo and it looks like a couple rows of seats to boot. They’re gonna lose even more seats because people aren’t going to be ok with a “no luggage” rule on their flight. Second, the normal range of a Dash 8 is two to nearly three times that. I know the three things airlines are always willing to give up on are cargo volume, passenger count, and range. Also, one conspicuous detail I didn’t see in the article is anyone asking the FAA if they’re ok with this idea and I just can’t help but think they might have a little tiny problem loading up six tanks into the back of a passenger plane, the failure of any of which will literally blow the aircraft in half.


[deleted] t1_iy4addj wrote



jdmgto t1_iy4ggr4 wrote

Because when it comes to its use as a fuel that is hydrogen’s only positive. The negatives include the collapse of global air travel back into the domain of the wealthy alone. Global air travel’s piece of the global warming pie is only about 3% which is not insignificant but it’s also not what’s killing our planet. You know what does have tremendous benefits, minimal if no downsides and even some upsides for consumers, and will have dramatically bigger GHG savings? Electrification of railways and vehicles, improving public transit, and transitioning to nuclear power.

Yeah, a 1,200 liter, 10,000 psi tank catastropic failure, I’m absolutely sure you’re right and that flying tin can will tank that like a boss. I'm sure there's absolutely no test footage of much, much smaller tanks turning the back end of cars into so much confetti.


E_Snap t1_iy40400 wrote

Which requires enormous amounts of heavy insulation on aircraft fuel tanks and actively cooled cryogenic plants at airports.


The-Protomolecule t1_iy3k3ro wrote

What you said makes no sense.


merien_nl t1_iy3l31b wrote

It did. Energy density of h2 is 3x that of kerosene, by weight. By volume it is a very different story.


mgt-kuradal t1_iy3ndjq wrote

It does. Energy density of 1 gram of hydrogen vs 1 gram of any other fuel compared to 1 liter of hydrogen vs 1 liter of any other fuel. They are different measures.

Both are valid ways of measuring energy density.


HuckleSmothered t1_iy5odj2 wrote

What weighs more a pound of feathers, or never learning past 5th grade?


syuvial t1_iy3qbi4 wrote

im not really sold on hydrogen either, but weight is actually extremely important when it comes to shipping and transport fuel efficiency. You literally burn less fuel moving less weight.


Philo_T_Farnsworth t1_iy50cx0 wrote

Thank you for flying Tender Air. The only airline where every flight is powered by the very chicken tenders that you, the passengers on this flight, consume. Eat well, travelers. And welcome aboard.