2
$\begingroup$

Airbus recently announced three concept aircraft for commercial use, powered by liquid hydrogen, with an ambition to have the plane in operation by 2035.

https://www.airbus.com/innovation/zero-emission/hydrogen/zeroe.html

https://www.airbus.com/newsroom/stories/these-new-Airbus-concept-aircraft-have-one-thing-in-common.html

From what I can tell, the turbofan variant is in the same segment as the current A320, albeit with somewhat reduced range.

Considering hydrogen powered planes, the challenge is to carry enough fuel to make it compete with kerosene.

There are several options, and from this question it seems 3 options stand out:

  • Cryogenic: storing the fuel as a liquid
  • Compressed: requiring heavy and strong fuel tanks
  • Hydrides: bind hydrogen with another substance and release upon heating

Airbus intends to go with option number 1, that is storing the fuel liquid and cryogenically behind the rear pressure bulkhead.

The unbalanced weight distribution storing not only the fuel, but assuming also heavy tanks and cooling equipment in the far rear of the plane seems like a maneuverability issue to me, with a pitch-up moment from the shifted weight balance.

What measures can be taken to mitigate the (assumed) adverse handling this creates?

$\endgroup$
  • $\begingroup$ Why assume that there will be any adverse handling? It looks to me like the fuel tank will be quite close to the centre of gravity. $\endgroup$ – CatchAsCatchCan Sep 27 at 20:36
  • 1
    $\begingroup$ Behind the rear pressure bulkhead would be pretty much as far back as you can go insida a plane. So pretty much as far as you can go from CoG. $\endgroup$ – Jpe61 Sep 27 at 20:45
  • 1
    $\begingroup$ @jpe61 My bad. I was thinking of the blended wing design where wing and engines are all behind the CG. $\endgroup$ – CatchAsCatchCan Sep 27 at 20:55
  • 1
    $\begingroup$ @Federico Please give questioners more time to refine their question to your taste before closing them next time! $\endgroup$ – Peter Kämpf Sep 28 at 5:31
  • $\begingroup$ Questions should be closed until such changes are made, not left open (attracting answers which will no longer be applicable). Closed questions can be edited; closing and reopening is better than deletion of multiple answers later. $\endgroup$ – Nij Sep 28 at 8:24
3
$\begingroup$

The situation is not as dire as one might think, as the energy content per kilogram of hydrogen is 3.3 times larger than that of kerosene (142 vs 43 MJ/kg): wikipedia, Energy density in fuel Wikipedia: Energy Density - Energy density in energy storage and in fuel

Taking into account a slight weight saving in wings, and a little heavier hydrogen tank and fuel lines (insulation, pressure), the weight of the hydrogen fuel itself and the fuel system should be somewhere between half to third of the weight of a "traditional" fuel & fuel system.

It is true, however, that placing a constantly decreasing weight as far from the center of lift as possible, is a dumb idea. This would lead to very uneconomical trim condition at some point of the flight, unless the plane carries a movable trim weight, which also is kind of dumb idea IMO. Variable geometry wings might also be a solution, but again, would add weight and complexity.

I have to say that I think Airbus is pulling our leg here. It is not uncommon for companies to purposefully mislead their rivals in this way. I bet most of us are familiar with the many weird patents that emerge every now and then, the stupidest I can recall being slicing the headphone plug in half to save space in phones. Duh...

| improve this answer | |
$\endgroup$
  • 1
    $\begingroup$ Yes, these designs are as speculative and fluid as SpaceX's were in 2003. BWB, seriously?! "Airbus will need to launch the ZEROe aircraft programme by 2025." This press release expresses interest in hydrogen, nothing more. We can't reverse engineer something that hasn't been engineered yet. We can only note the obstacles. $\endgroup$ – Camille Goudeseune Sep 27 at 20:51
  • $\begingroup$ I recall reading long ago that the really big obstacle to a hydrogen fuel economy is the existing petroleum distribution system based on steel for tanks and pipelines, which can't be used for hydrogen distribution due to embrittlement. $\endgroup$ – John K Sep 27 at 22:34
  • $\begingroup$ Interesting angle about leg-pulling. There is/was something called "Airbus AlbatrossOne" which looks like it could be done now, as in the next thing after neo. Let's see what comes of it. $\endgroup$ – Abdullah Sep 28 at 9:08
3
$\begingroup$

Airbus will store hydrogen by chemically binding it to carbon for a looong time. This way, it can be put into the wings, a belly tank and the horizontal tail and its gradual disappearance during the flight will not shift the center of gravity much.

What the PR department just published is just for political correctness. It has not been thoroughly checked for practicability by the engineering department. Nobody seriously expects to use hydrogen for airliners. The problems of storage are obviously putting it at a huge disadvantage, and your correctly identified issue of storing fuel far from the center of gravity is one of those problems.

When an Airbus is delivered today, its tanks are filled with a blend containing hydrocarbons from a carbon neutral source. Beluga flights delivering parts between the Airbus plants use this fuel. Virgin Airlines tested a renewable fuel already in 2008 and Lufthansa flights departing from Frankfurt also use it.

Of course, most airlines will refill with regular, mineral oil based kerosene after this fuel has been used up because it is cheaper and availability is much better. But technically there is nothing holding back airlines today to use a carbon-neutral fuel.

Generating hydrogen today is mostly done using natural gas which is not quite as carbon intensive as kerosene but everything but carbon-neutral. Also, the energy source for refining and transporting fuel from renewable sources will make them less than 100% carbon neutral. The current sources for renewable fuels (plant oils and waste materials) are less than optimal and hard to scale up, but work on using direct sequestration from atmospheric carbon dioxide is progressing. Today, we waste excess solar power by shorting it to ground. I know better uses for that excess energy …

| improve this answer | |
$\endgroup$
  • 3
    $\begingroup$ @Erik: In case the joke elided you, all fossil fuels are made out of carbon and hydrogen, typically a chain of 8-12 carbon atoms with hydrogen atoms attached. There's a small part where it's accurate; typically the carbon chains found in nature are a bit longer so some of these long chains are "cracked" in refineries. This involves adding hydrogen atoms at the point where the chains are broken. $\endgroup$ – MSalters Sep 28 at 9:10
  • 1
    $\begingroup$ @MSalters I'm not particularly proficient in chemistry, but what you and Peter are saying about "Airbus will store hydrogen by chemically binding it to carbon for a looong time.", is regular jetfuel? And this announcement from Airbus is nothing more than a dream? $\endgroup$ – Erik Sep 28 at 9:37
  • 1
    $\begingroup$ @Erik: Yes, what I meant to say is that all airliners will continue to use kerosene (a mixture of molecules consisting mainly of carbon and hydrogen). That should not be misunderstood that Airbus personnel will be adding each hydrogen atom to kerosene molecules but that Airbus is working with companies which try to sequester carbon from the atmosphere and add hydrogen, ideally from water. Or leave this process to plants which do the same since maybe 2½ billennia. $\endgroup$ – Peter Kämpf Sep 28 at 10:40
  • 1
    $\begingroup$ @PeterKämpf So taking carbon from the atmosphere and adding hydrogen is to make synthetic kerosene? But then this talk about cryogenics and liquid hydrogen, in the shape Airbus talked about it at their press event, is false? If this is the case, wouldn't this quickly be uncovered by those with knowledge of aircraft design and looked at as a joke? $\endgroup$ – Erik Sep 28 at 10:57
  • 1
    $\begingroup$ @Erik: You have never worked in/with marketing, have you? This is Airbus trying to look politically correct. It is not a blatant lie, more like what you say about controversial topics without getting into hot water. Of course the engineers don't take that seriously. $\endgroup$ – Peter Kämpf Sep 28 at 13:18

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.