Airbus announces zero-emission airliner concepts.

By Bjorn Fehrm

September 21, 2020, © Leeham News: Airbus held a webcast today, announcing three zero-emission airliner concepts called the ZEROe line (Figure 1). The two conventional designs, the turbofan airliner and the turboprop use hydrogen as the fuel for their gas turbine engines. The blended wing-body is a more futuristic concept where propulsion technology was not specified.

The idea is to use these concepts as work paths to explore the technologies around them and their aerodynamic characteristics. The concepts “are not products” underlined Airbus EVP development Jean-Brice Dumont. “It’s rather examples of designs around which the technologies can be explored and results compared. After concepts follow demonstrators and then products.”

Figure 1. Airbus ZEROe (e for emission) concepts. Source: Airbus.

Airbus focuses on hydrogen

Airbus CEO Guillame Faury about the announcement:

“This is a historic moment for the commercial aviation sector as a whole and we intend to play a leading role in the most important transition this industry has ever seen. The concepts we unveil today offer the world a glimpse of our ambition to drive a bold vision for the future of zero-emission flight. I strongly believe that the use of  hydrogen – both in synthetic fuels and as a primary power source for commercial aircraft – has the potential to significantly reduce aviation’s climate impact.

We could talk to Airbus CTO, Grazia Vittadini in connection with the announcement. She explained how Airbus has drawn knowledge from all it’s concept projects like E-Fan, Vahanna, City-Airbus, and E-Fan-X. This has lead to an understanding that hydrogen-based propulsion is the solution for today and that electric technologies will come into play as these mature. Vittadini further:

Right now we can integrate electrical starter-generators into the gas turbines, where the generator run as a motor helps the engine with power shifts. The core can then be harder optimized around cruise conditions. The energy source for the motor is a hydrogen fuel cell. There have been several projects around replacing the APU with hydrogen-based fuel cells, but these are not practical when the rest of the aircraft is carbon fuel-based. Now a hydrogen-fueled aircraft opens this avenue as well.”

Three ZEROe concept aircraft

The three concept aircraft released today represent different technologies and challenges. They are all three codenamed ZEROe which stands for a climate-neutral commercial aircraft.

The two concepts closest to what can later emerge as demonstrators and eventually products are the 120-200 seat Turbofan aircraft (Figure 2) and the 100 seat Turboprop (Figure 3).

Figure 2. A 120-200 seat turbofan airliner with a range of 2,000+nm forms one the zero-emission concept. Source: Airbus.

The architecture of the aircraft differs from today’s airliners as the hydrogen fuel tank is not in the wings, it’s placed behind the cabin in the rear of the aircraft, behind the rear pressure bulkhead. For those who want to understand why read my Corner series about the Challenges of Hydrogen.

The Turboprop has the same architecture except here the hydrogen-burning gas turbine engines are a turboprop design. The Hydrogen Corner series also goes through the propulsion alternatives available and why converting today’s Turbofans and Turboprops makes sense.

Figure 3. A 100 seat turboprop airliner with a range of 1,000nm represents a regional zero-emission concept. Source: Airbus.

The most futuristic and perhaps most challenging concept in the Blended Wing-Body (BWB) variant, Figure 4.

Here the BWB shape enables better integration of the cryogenic (cryogenic = extreme low temperature, -253°C) tanks that liquid hydrogen storage requires.

Figure 5. A Blended Wing-Body concept to study tank integration, cabin effect, and aerodynamics. This study could have fuel cell-driven electric propulsion. Source: Airbus.

If the fuselage allows the tanks a better fit, the central cabin now presents challenges to give the passengers a decent cabin ambiance. Here the passengers have the light come in from above in an atrium-style cabin.

It’s about creating an eco-system in cooperation with other industries

Airbus Faury emphasizes that this is as much about building an eco-system as making new aircraft:

These concepts will help us explore and mature the design and layout of the world’s first climate-neutral, zero-emission commercial aircraft, which we aim to put into service by 2035.

The transition to hydrogen, as the primary power source for these concept planes, will require decisive action from the entire aviation ecosystem. Together with the support from government and industrial partners we can rise up to this challenge to scale-up renewable energy and hydrogen for the sustainable future of the aviation industry.

Airbus will use the slump in normal airplane development caused by the pandemic to advance its positions for tomorrow’s technologies. Its bet is on hydrogen as a future energy store and distribution system. It has 200 times the energy-specific weight of batteries and three times that of Jet fuel, making a change to a non-carbon-fueled low emission air transport realistic.

Airbus will kick off several hydrogen demonstrator programs over the coming months. These will test hydrogen fuel cell and hydrogen combustion technologies. A full-scale aircraft demonstrator is expected late in the decade.

64 Comments on “Airbus announces zero-emission airliner concepts.

  1. The “eco-system in cooperation with other industries” comment is pertinent. It is easy to imagine sourcing LH2 at major airports like Heathrow. Not so much at Yellowknife or Dodoma.

    • I don’t see that problem of installing H2 infrastructure at every airport. this reminds me of the discussion about infrastructure for electric cars that we have enjoyed for quite a while. If Airbus applies a similar strategy as Tesla, they will develop, probably install and maybe even run the H2 production, storage and distribution. It would actually be very foolish of the petrol giants not to invest in the future of air transport. A quick check shows that Shell and BP re heading into that direction: https://www.shell.com/energy-and-innovation/new-energies/hydrogen.html and
      https://www.bp.com/en/global/corporate/news-and-insights/reimagining-energy/bp-joins-hydrogen-council.html
      I guess many other will follow. Not sure about Saudi Aramco or Rosneft though.

      • I guess LH2 would have to be created by an energy intensive industrial process (reformed fossil fuel or electrolysis) at or near each airport. I don’t think it can be tankered long distances, unlike jet fuel. That’s a much bigger deal than hooking a charging station into an existing electrical grid.
        And here in rural Kansas, pure electric car owners have to be strategic when planning trips.

        • Re-considering, perhaps high pressure H2 could be transported to distant airports. But it would still have to be cooled, itself an energy intensive process, with probably not inexpensive infrastructure. I still suspect this would be deterrent to the general adoption of LH2

          • LH2 is also a good solution for long haul trucks, so building the infrastructure makes even more sense.

        • There might be trucks delivering compressed H2 to the Airport LH2 plant driven by windmills all around the Airport, so the available volume of LH2 will depend on the last month winds and the capacity of the electrical grid to the Airport. Hence GE Wind could make more money selling Haliade windmills driving the LH2 plants than jet Engines…The US with big natural gas network will probably use it both to make H2 and drive the LH2 plant at smaller Airports. There will be municipal waste to syngas plants built around the US and they can decide how much JET-A and H2 to produce.

        • H2 has been part of different industrial processes for more than 50 years and it is very rarely created on site.

          But, maybe, for this kind of volume, a pipe line is a better option

  2. Very interesting (and ambitious) to see that Airbus hopes to have a demonstrator aircraft flying somewhere in the 2026-2028 timeframe.

    I suppose we’ll have to wait (at least) until then to hear about any (cylindrical) widebody concepts that might be in the pipeline.

      • I used to be involved in wind turbine manufacturing, its an oil based and absolutely filthy business.

        • But you have to start somewhere right.. Chicken or the egg?

          Or do you have convincing arguments why wind turbine manufacturing will never be non oil-based? And if so, what are the net carbon emission effects of a wind turbine vs. a gas powered plant?

          • Yes, some logic to that. I get the Magazine from German Enercon and they seem to be pretty thorough even running their own electrical Railway and develop fast charges for autos. Germany has a need to consume windmill electrical Power where it is produced as the German powergrid is too weak to feed Southern Germany from the North. It is the same problem in many countries where production and consumption is far apart and hence running the powerstations/mills at full Power producing H2 with the excess Power generated that the national grid cannot swallow can be common in the future.

      • Keith may have meant manufacturing aircraft takes energy (all of which is unlikely to be renewable), which is true but relatively small compared to lifecycle emissions.

  3. Airbus looks to have reduced speed and range to cope with the LH2 tank volume and mass. The wings are as slender and with a large span as expected. They will be limited in engine fan size compared to the high wing Boeing SUGAR competitior “Truss brazed aircraft..”with its UDF and tail fan for the boundary layer reenergizing. It looks like Safran put a LH2 version of the LEAP-1A onto it as a minimun cost solution. So history might repeat itself with an advanced Airbus aircraft with “run of the mill” engines onto it. (Not always, the RR T-XWB was new as well as PW1100G, Airbus whished Boeing took the initial problems on that one , but the LEAP-1C for China was designed first, the T700 was designed for the MD-11, the CF6-50/80A/80C2/JT9D/PW4000 for Douglas-Boeing aircraft, the CFM56-series commercial life started on DC-8 and 737). Even the RR Avon on the Caravelle had started commercial life on the Comet 4.
    Airbus might look at RR to partner with SAFRAN for a suitable UDF from its prototype test engine and RR asks “where is the money” approx $7-10bn. France maybe give $1bn to Safran and UK $1-2bn to RR so someone has the ask the banks for $5bn for a high risk 50 years return of the money program that might be killed by a US UDF engine that will not fit under the low wing Airbuis LH2 aircraft design unless you chop 4′ of its fan size…

  4. Very interesting wing treatment on the 120-200 seat turbofan airliner.

    Just from the images what do people think the wingspan would be, and would the tips fold. I.e. what gate would they be targeting ?

  5. Tanks will be at the rear of the fuselage (no more in the wings)
    Mass balance between beginning of the flight (full) and end (empty) will be very funny 😁

    • There might be trim tanks in several places.. The LH2 weights less than JET-A1 so the shift in c.g. will be less severe, still trim tanks even in the wings fwd of the c.g. will probably be used

    • Not so much.
      Empty LH2 tanks might be only little heavier than pax.
      Range is reduced much which helps a lot.
      Still the fuselage might need to be stronger, easier to achieve on small diameter cross sections. The turbofan might be 4-abreast, turboprop 3-abreast.
      This should not take 15 years.

      • I would love to see another part on “The challenges of Hydrogen” from Bjorn, but in this case explaining on detail why working at 1.5 bar on LH2 tanks seems convenient, and what could be the drawbacks if we dont.
        Because I still can not find the answer, I can think in 1 or 3 cases on why that could be true, but I can also can think in examples that would contradict those cases.

        BTW: I dont think that Bob is working with them.

    • Notice how the wings are located way back on the fuselage, just like an aircraft with engines attached to rear fuselage. I presume the design considerations will be similar except that the engine masses remain constant, while the mass of H2 in the rear tank decreases with time and this must be allowed for. Not impossible.

  6. Nice way from Airbus to show that hydrogen is a bad fuel for planes.
    The plain size has to be much larger for the same capacity and than still range is limited. Please cut the crap and stick with hydrocarbon fuel.
    Just use waist gas treatment on a coal plant so you get a flow of high concentration CO2 and water vapor. Run this trough your elektrolyseer with modified anode and cathode materials so you get short hydrocarbons (HxCx) instead of hydrogen. This is one of the methods to make synthetic fuels.
    Another method is to use photosynthesis with algae or plants. You reuse the CO2.
    In my opinion the view must change, CO2 is an asset not a waist/pollutant. It’s essential for photosynthesis, hence in horticulture they increase CO2 levels in the greenhouses to increase yield.
    Besides I want to raise some questions:
    – What is normal; a static climate or a changing climate? (Milankovic cycles)
    – What is the most import UN Sustainable Development Goals? We’ll have to compromise.
    I think with the power densities and reliability required for aviation, there isn’t another method than burning hydrocarbons until beyond the 2050s.

    • Although much of your comment is “out of sync” with consensus opinion, you do raise some valid points.
      I agree that, in the case of aviation, it would be better to stick to hydrocarbon fuels — preferably algal. There are necessary exceptions to every rule. Regardless of what civilian aviation does, the military sector will be in no hurry to switch to LH2 — so why not just extend that situation to commercial aviation also?

      That having been said, I think it’s good that Airbus is trying, at least.

    • Apart of your “out of sync” comments, one thing that you need to keep in mind that you are comparing a mature technologies with a first attempt

      The fact that this 1st attempt is less than one order of magnitude away and that there is lots of room for improvements makes me bullish about the future of H2 in aviation

    • You hit on something important with fuel from algea, some of the high oil content ones grow in salt water, hence one could imagine deserts dotted with salt water ponds growing algea for fuel and food while at the same time the evaporation from these dams could increase rainfall in desired areas making farming possible in earlier dry areas. Still with all the work on producing H2 more and more efficient it might lower the price on “aircraft grade” H2.

  7. Can I ask a question to you? From all your hydrogen parts, and the news from airbus, I still find hard to understand a simple point..
    Why they have an issue with range?? Hydrogen should have the potential to increase range by a lot due his lower weight..
    For example, a 15 hour fly requires around half of the airplane weight on takeoff to be jetfuel.
    If you take the same energy content with hydrogen, it would weight 1/3, this mean your plane at take off would weight 70% from a jetfuel variant.
    But you dont need the same energy content to make the same distance, because you have more efficiency from the engine, your plane weights less this mean less fuel consumption = even less fuel required at take off, an lighter plane also requires less powerful engines or smaller wings that also reduce weight.. so at the end, the weight of the whole aircraft at take off could be 60%.
    This would still require to double the volume of a normal tank.. but we know that just increasing the dimensions of a sphere by a 25%, it doubles the volume.. if you have a center cylinder as tank from head to tail of the plane, placing all the seats around the tank diameter (all seats can be close to windows). Then you may need just to increase the plane diameter by a 10%.. or something like that, the wings does not need to be thick either.
    Not for nothing the phantom eye prototype has choice hydrogen to have a plane able to stay on air by 12 days, not for nothing the skylon that accomplish 1 stage to orbit is only possible using hydrogen..
    SO… WHY you and Airbus said that hydrogen has a RANGE problem??

    • You should read carefully Bjorn gave the answer
      And the answer is dead simple: H2 certainly has a lower weight, but Liquid H2 requires cryogenic tanks (-253°C, 300 bars) which are not only heavy and costly but awfully bulky.
      That is what limits the range.
      no way to put the seats around the tank diameter unless passengers are 3 inches tall!

      • Well, you can choose the Aircraft LH2 tank pressure. The space programs pressurize just a bit with Helium to get a suitable pressure for the LH2 turbopumps.

      • I read it that part, which I disagree, maybe cryo tanks that were designed without weight constraint and trying to maintain cryo temperatures over months are heavy! But vacuum is not needed and the most lightest materials ever created are in fact the best insulators.
        You dont need to keep LH2 over days in the tank.. because your airplane would not be days without reaching an airport anyways..
        Even 50 liters containers for Cryo liquids like Liquid Nitrogen can avoid to lose more than 1 liter by day on LH2.
        And when you increse the volume of a tank, the surface/volume ratio decrease, this mean you lose even less % of LH2 for the same insulation.
        So even with a very bad insulation, you would be able to keep it over days, and if you have boiling, you can use that on the fuel cell that powers all the airplanes controls.
        Tank weight is not an issue if you design a cryo tank for that particular application.

        • There is a very light and extremely isolating material called “solid smoke”, the price is of cause matching its performance but there are companies working hard to produce it much cheaper.

          • Yeah I saw it, but they are not even needed, check my replies to BOB, I even made the calculation that your tanks would weight only 4 tons for two tanks with a combined volume of 400 m3 with enough insulation to last 15 days as minimum, it could be much more taking into account the assumptions that I did.

    • (Liquid) hydrogen has a very low volumetric energy density.
      Lets do the worst and take wiki values. The LHV (lower heat of combustion) values of Specific energy and Energy density.
      Hydrogen (liquid): 119,93 MJ/kg | 8,491 MJ/M3
      Hydrogen (@690bar 25degC): 119,93 MJ/kg | 4.5 MJ/L (DM3)
      LNG [CH4] (@-160deg C): 53,6 MJ/kg | 22,2 MJ/L
      CNG (@250bar): 53,6 MJ/kg | 9 MJ/L
      LPG [C3H8] (Propane): 49.6 MJ/kg | 25.3 MJ/L
      (Jet Fuel) Kerosine: 43 MJ/kg | 35 MJ/L

      The range of hydrogen powered plane is limited by tank volume.
      Sorry but in my opinion hydrogen isn’t a good fuel for all applications. It’s nearly impossible to contain.
      Just bind it with carbon from CO2, to get hydrocarbons, those are fare easier to stow and much more energy dense.

      • Impossible to contain?? What???
        Read my last reply.. or explain why you think it is impossible to contain…
        It does not need 4 times more volume because you only need close to half the energy at equal long range because you save all that energy due how much lightweight your aircraft is.
        So you only need 2 times more volume, and if you know something about volume is that increase by cube, so only a 25% diameter increase is all what you need to double the volume.

  8. This blog and the comments are excellent. Thank you for the high quality work.
    I have a question regarding air pollution. Do you know what kind of air pollution can be caused by burning hydrogen, e.g. like NH3 etc? Is there any synthetic fuel possible instead of hydrogen, which can be handled easier? What kind of air pollution can be expected from synthetic fuels?

  9. Your reasoning is correct except for the empty weight and its effects.

    The tank weight and placement increase the empty weight fraction of a typical single-aisle airliner (737, A320 type) from 53-55% to ~70%. This means you fly the mission with increased average weight and a larger wetted area. The 60% less fuel by weight needed for the mission can’t compensate this.

    • I dont think the tank weight is an issue, check my answer to flying flog, or just clarify why you think the tank placement or structure would increase so much the weight, and how many days you plan to keep that cryo fuel in liquid state.

      • Bjorn has been presenting information on this for awhile and has discussed tank issues in a recent Corner article.

        The gravimetric density values (percentage of fuel weight for fuel + tank combination weight), for H2 storage based on the best available technologies, is on the order of:

        Compressed H2 gas: 5% at 350 to 700 bar, 300 K
        Supercritical H2: 10% at 250 to 500 bar, 120 K
        Cryogenic LH2: 30% at 1 bar, 20 K

        Thus the combined weight of fuel and tank remains greater, and for a single-aisle medium range commercial aircraft, the weight increase is expected to be around 15%. Additionally there is less weight loss due to fuel consumption during the flight, so the aircraft carries a heavier load end-to-end.

        At 20 K in a vented, well-insulated tank, LH2 storage losses are still too high to leave the aircraft fueled overnight. You could use a recovery system to re-liquify the losses, but that adds more weight and energy consumption. You could also have a recovery system on the ground for overnight, but you still have higher energy costs.

        Thus H2 aircraft will probably need fueling immediately before flight and offloading after flight, except for short layovers.

        • I will explain my point in a way super clear:

          Lets start with a real case for liquid hydrogen storage:

          Fact number 1:
          https://www.youtube.com/watch?v=ka1R6EvntuI
          Metavista, 6 liter liquid hydrogen container (320 grams of h2), flight time 12 hours.
          This mean, that the maximum boil off rate from that experiment that we can assume, its 12 hours (probably is less, because that was the energy consumption of the fuel cell).

          Fact number 2:
          Each time you double the dimensions of an sphere for example, the surface area (heat lost) quadruple and the volume (fuel) octupled.
          This mean that if we keep the same thickness of that 6 liter LH2 tank and we increase the volume to 120000 liters (the required for a long range 747 LH2 version), we would need a 6m diameter tank, which surface/volume ratio would reduce the boil off rate with respect the total, in 15 times.. this mean 15 x 12 hours = 180 hours. Of course the plane would consume its fuel much faster than that.
          The weight of the tank vs the fuel would be also 15 times better than the 6 liter tank from metavista.

          So.. considering those fact, is why I am quite skeptical of the range problem that Airbus or Bjorn claims.
          Of course, I dont know what type of safety requirements and boil off rate are being considered in the design of those LH2 tanks. Maybe the problem is that those safety requirements are quite pointless or do not really are designed for the future of the aviation industry.

          • A correction of my last reply:
            sorry, the required volume for a 747 would be around 500000 liters, when I said 120000 liters, I was just taking into account that they carry around 200000 liters of jet fuel, so it would need a 40% less energy for hydrogen. But the point remains, the surface volume ratio would be higher, so even less weight of the tank with respect the hydrogen mass, and less % of boil off compared to the total.

          • The range problem is based on the gravimetric density, resulting in a heavier aircraft. The drone in your video had no payload, it only had to support itself and the weight of the fuel & tank. It was a useful demonstration but would not apply to a commercial airliner.

            As far as boil-off, in very large terrestrial LH2 tanks, the standard is double-walled vacuum insulation surrounded by up to 80 layers of insulation. In that circumstance, the heat gain could be reduced to under 500 watts. That would yield a boil-off loss of about 1 kg/day, so they can store LH2 for months. But those tanks are far heavier than would be possible for an aircraft.

            If we take an LH2 tanker truck, that size is closer to an aircraft tank, but still may be too heavy because they must meet pressure standards (cryo-compressed). Their overall losses are around 4 kg/hr, once venting begins. By allowing the temperature to rise from 20K to 160K (with pressurization), they can store H2 for up to a few days.

            If you have a lightweight, aircraft size, vented tank, you are probably going to have 2 or 3 times that loss, so let’s say 15 kg/hr. That level of loss would likely not be acceptable for long periods of storage. Of course in flight, the loss is consumed by engines so doesn’t matter.

            Another point of reference, the Saturn 5 second stage had an LH2 loss rate of 25 kg/min, being an extremely lightweight tank. The shuttle external tank had 35 kg/min. Interesting that for the shuttle program, NASA bought twice as much LH2 and LO2 than needed, to account for losses. But I’m sure the new emerging infrastructure will be far more efficient than that.

        • Rob:
          1-“The range problem is based on the gravimetric density, resulting in a heavier aircraft”
          What?? no.. LH2 is the dream fuel for any powered flying application. The second point that I already made, is that the weight of the tank is a small % of the total LH2 weight for a long flight.
          https://i.stack.imgur.com/m63vR.png

          2-“The drone in your video had no payload, It was a useful demonstration but would not apply to a commercial airliner.
          Is like you miss the whole point on purpose.”
          That video proved that even an small container like that, it could keep those 6 liters of LH2 from boiling off for more than 12 hours, maybe 24 hours or more.. we dont know.. but surely, for more than 12 hours. Which is a key info to be linked to my second fact, which was that increasing volume, you decrease boiling off rate with respect to the total fuel.
          By the way, that tank does not weight more than than 2 kg.
          There are almost ready to be put on sale:
          https://translate.google.com.ar/translate?sl=auto&tl=en&u=http%3A%2F%2Fwww.usjournal.kr%2Fnews%2Fnewsview.php%3Fncode%3D1065582034093078%26dt%3Dm

          3-“but still may be too heavy because they must meet pressure standards (cryo-compressed).”
          There is no point to have high pressure standards for an airplane specialize LH2, in those truck cases, they use pressure to reduce the boiling off rate, on the case of an airplane, if the pressure rise above 0.1 bar, you can just vent.

          4-“If you have a lightweight, aircraft size, vented tank, you are probably going to have 2 or 3 times that loss, so let’s say 15 kg/hr. That level of loss would likely not be acceptable for long periods of storage. Of course in flight, the loss is consumed by engines so doesn’t matter.”
          As I said, there is no need to have insulation that takes days, but even that could be super lightweight to achieve at those volumes.
          You just need enough insulation to last over 24 hours, once you reach an airport, you can unload the hydrogen on the airport, which would be discounted from the hydrogen you load on departure.

          5-“Another point of reference, the Saturn 5 second stage had an LH2 loss rate of 25 kg/min”
          Even in that case, in which those tanks does not have any insulation at all, all the contrary, aluminum which is really good heat conductor, for the shuttle tank would have take 50 hours to boil off.
          Which makes my point!! Even more than you need for a commercial flight. Because the airplane would consume that liquid hydrogen faster, this without nothing of insulation.

          Now going back to my previous case, lets take a 747-800
          Those had 447 tons of MTOW, which 191 tons are jet fuel, with a volume of 239 m3.

          To achieve the same range with LH2, with need to take into account that LH2 weights 3.3 times less than jet fuel and requires 3.7 times more volume.
          As I explain before, if we reduce the MTOW so much, it means we already need less energy to achieve the same range, which reduce even less the fuel mass needed, a lighter airplane also requires less powerful engines, lighter wings, ligher wheels, lighter reinforcements, etc.
          Lets assume that we need a 60% of the initial energy content on jet fuel to achieve the same range due all weight reductions.
          I imagine that is even less, but ok..
          191 tons jet fuel * 0.6 = 114 / 3.3 (h2 mass) –> 34 tons of H2, this require 400 m3 for the tank.

          Lets calculate metavista drone tank 6 liters and 2 kg estimate weight:
          Capsule shape: Volume: 0.006 m3, surface: 0.19 m2, S/V= 31, 20 cm diameter, 30 cm long, 2kg / 0.19m2 = 10 kg / m2

          747 LH2 double cylinder tanks, tail and head.
          Cylinder shape: Volume 400m3, Total surface for both: 375 m2, S/V= 0.93, each tank has 6 m diameter and 7 m long, 375 m2 * 10 kg = 3.7 tons

          This mean that the tank weights 10 times less than the H2 fuel.
          It also means due the S/V ratio that it has around 30 times less boil off rate than the 6 liter tank with the same insulation.

          So even keeping the same thickness of insulation of the small tank, we can keep the plane fully fuel, that it would take 15 days to boil off as maximun, because clearly the small tank has lower boil off than 12 hours.
          See. is totally possible, the problem is that Boeing and Airbus are very well know by the total lack of innovation, because both rule the business so they dont need to risk any investment to remain the kings.
          Look Boeing on the space program, absolutely no innovation.

          • Ariel, the information we’ve given you is correct for the state of the technology that exists today. You’re welcome to look up the gravimetric density of LH2 tanks yourself. Also you’re welcome to look up the LH2 boil-off rates for common applications yourself. Bjorn has given all that information correctly in his several series and other articles on these topics.

            Your analysis is based on assumptions you’ve made from a Youtube video. So if you know how to actually achieve the things you claim, you should bring those ideas forward as they’d be worth a lot of money. Seek investors, build a demonstration model, etc. The world would embrace them and you, I’m sure.

          • According to Bjorn the tank weight is 2-3 times the weight of LH2.
            If using the tank weight example with 6L=2kg the tank could be 15 times less heavy.
            The basic A321neo tank without ACT has 23490L. An 87595L LH2 tank with 3m diameter and 12.36m length could weight only 1050kg (with 100% load factor which is wrong).
            The weight of an A321ceo ACT is around 610kg for 2992L.
            The weight of an A321neo ACT is around 440kg for 3121L.
            The future RCT with 12900L is announced with 440-610kg.
            So 1050kg for an 87595L tank seems to be too light, but why should 8000kg not be possible.
            8000kg tank with 6202kg LH2 (87595L) is 14202kg,
            23490L jet fuel alone are 18792kg.
            Weight and range (here >3000nm) should not be a problem.
            Also bigger tank diameter makes the tank shorter, bigger cross section will provide wide seats.

          • “”Ariel, the information we’ve given you is correct for the state of the technology that exists today.””

            Who is “we”.
            Do you mean Bjorn and you.

        • I already did a quick read on several papers that talk about LH2 tank design concepts.
          In one of them even Bjorn team is mentioned at the end.
          It looks like they weight a lot because for some reason that I still ignore, the sweet spot for pressure venting should be at 1.5 bar, which neglects all the benefits that we can obtain from the surface/volume ratio at big scales.

          That paper already takes those values as true, which is linked to another huge paper that looks more like a book.

          Maybe that pressure is selected to act as “balloon tank” to provide structural stiffness, or because they need to be strong enough anyway to support aerodynamic forces on the exterior..
          Not sure, 1 hour of lecture was not enough to see the cause, and all graphics that measure the pressure sweet spot start at 1.5 bar.

          Most probably you are right, it must be a “holy reason” why they are heavier, I just hope those reasons are not base on silly regulations that were not made for this type of application on mind.
          Regards.

          PD: I can not reply to Leon, not button.

          • Ariel,

            you can reply everywhere, we read everything 🙂
            Bjorn’s tank might be part of the fuselage. Then of course it would be heavy but also hot on summer days.
            I like the 6L 2kg example. Of course a bigger tank needs to be much stronger.
            Things can’t be apart more. Boeing offers landing with spoilers only as a safety feature and an LH2 tank should weight 10t.

        • I did not specify how much time you would be ok with the Leidenfrost effect, I said “for a short period of time”.
          But you did.. and I guess 1 or 2 seconds is a quite pessimist assumption.
          We are talking about liquid hydrogen, which has much lower boiling point (the effect remain for longer time) and much lower heat capacity due his low density.
          Even liquid nitrogen does not hurt you on 2 seconds.
          This guy (who is death now, but not because this ^_^) spill LN2 on his face, hair and shirt (which we can assume that few droplets remain trapped) and nothing happen.
          https://youtu.be/l1XRspReAvI?t=78
          But if you plan to take a shower under a liquid hydrogen spill, well we can agree that it would be bad.
          But again.. how many situations can you imagine in which you have a tank rupture with massive spill (for both cases, jet fuel and LH2) in which the hydrogen case would be more dangerous?? If you find one… it may not be enough to counter all the cases in which the jet fuel spill would be more dangerous, due aspiration, or ignition (that would happen in most of the cases), or just because it needs 2 tmes more energy for the same range.
          With respect on “the level of risk should be zero”.
          Really? so in order to use Hydrogen first it needs to be much safer than normal jet fuel?
          That’s pretty hypocritical, giving that air pollution caused by airplanes already kill 10000 people by year.
          https://www.nationalgeographic.com/news/2010/10/101005-planes-pollution-deaths-science-environment/
          Then we need to add the economic lost due global warming which also translates into indirect deaths.

          Lets keep searching excuses and old regulations to not make the change, after all… we are great using 30 years old technology.

          • The scenario is a crash with LH2 tank rupture, and cryogenic fluid rushing forward over the passengers from inertia. So pretty easy to imagine. And yes, the risk needs to be near zero. It’s near zero now with the fuel in the wings. So we should expect the same standard for hydrogen in the fuselage.

            The heat of vaporization for LH2 is quite high, so the potential for burns is present even without combustion. The Leidenfrost effect depends on the surface temperature being above the Leidenfrost limit. With LN2, the skin temperatures drops below the limit in a few seconds. With LH2 it would be as fast or faster.

            The YouTube video author you reference also did a video on how long before the skin freezes under LN2. He could only tolerate it for a few seconds, and it was quite painful.

            People will not accept higher personal risk while flying to reduce global warming, or pollution. There is no connection between the two, nor should there be.

            All of this assumes there is no combustion. If ignition occurs with the spilled pool of LH2, the heat release will drive vaporization at a higher rate so there will be an intense upward rushing fire, that lasts only for about 10 seconds or so. But to be caught above that flaming pool could also be lethal. The energy release is more concentrated in time and space, than jet fuel. There would no opportunity to escape.

            You can’t just dismiss these things because you don’t agree. They are fact and will have to be dealt with in the design. It’s more accurate to say the hazards of LH2 are different from jet fuel, but not less.

        • You have a huge imagination… you may also imagine that only a fish tank glass divides the LH2 from the passengers according to the things you are saying..
          Even in a rupture the LH2 would not spill over the passagers, the whole section would split as happen with normal planes.
          The few ways that you can have an spill over people, is with a massive crash (something that you would get ignition anyway or a high death toll just for impact), or there is people outside.
          In any case we are still talking about 70 kg/m3, liquid nitrogen weights 800 kg/m3, not sure if you start to see the difference…
          Heat capacity matters by volume in this case, not weight. 1 watt evaporates 5 times more hydrogen by hour than nitrogen, that means you need less energy to evaporate any droplet of liquid hydrogen over you.
          You know when you burn or frost? when the the heat difference does not instant evaporate the surface layer any more.
          This mean you have more safety range with hydrogen, and I repeat, hydrogen has much lower density and diffuse much faster, gaining temperature and raising.
          Like drop boiling water on a super cold day, it becomes instant froze.
          Maybe you are imaginen Terminator 2 scene, in which a bit of LN2 vapor and some liquid in his shoes is enough to froze the whole body. It does not happen with LN2, even less with LH2.
          It could be dangerous.. of course.. but not at the “movie” level you are imagine.

          “The Leidenfrost effect depends on the surface temperature being above the Leidenfrost limit. With LN2, the skin temperatures drops below the limit in a few seconds. With LH2 it would be as fast or faster”
          How it would drop faster if you have the effect for longer time over a much less dense sample???
          Take that back, or I will understand that you are allergic to logic.

          One more thing, jet fuel is not just in the wings, also in the center of the aircraft and tail. Depending the airplane they also had fuel in the fuselage.. the main purpose to carry fuel in the wings is not safety, is to reduce the wind bending and stress.
          Also, I am not the one saying that Liquid hydrogen is safer than other fuels, NASA and all the people who study Liquid hydrogen is saying that.
          Check the two videos from NASA that I share, or just search your own studies over LH2 safety compared to other fuels.

          -“People will not accept higher personal risk while flying to reduce global warming, or pollution.”
          I never said that Liquid hydrogen airplanes would be more dangerous that today planes, all the contrary, I just added all the other numbers to show how hypocrite was that posture.

          – “The energy release is more concentrated in time and space, than jet fuel. There would no opportunity to escape.”
          Just watch the videos and read the studies!
          Both (as all crashes with ignition) could be lethal, but jet fuel is slightly more dangerous.
          https://history.nasa.gov/SP-4404/ch8-6.htm

          “They are fact and will have to be dealt with in the design”
          The only thing that I still can not grasp, is why the sweep spot pressure is 1.5 bar, I already read several papers and not a clear explanation from where that number is coming. They point as a way to reduce boiling off, but even with 1.5 bar of pressure, the boiling point temperature rise almost nothing.

          How can a jet fuel tank does not require reinforcement giving that has to carry and support a much heavier liquid volume, but an hydrogen tanks needs that? I dont know.. I would bet that are mostly silly regulations with few points of logic.

      • -tons of liquid –> that is what normal jet aicrafts carry.
        -at 300 bar –> liquid hydrogen is kept at slightly higher ambient pressure, something like 0.1 bar of difference.
        -at -250c –> a low emmisivity layers already solves the radiation heat transfer, a good honeycomb structure (super light) of 10 cm thick would solve most of the heat lost by conduction. Techniques to preserve liquid hydrogen are quite old, NASA hydrogen 200m3 sphere tank lost less than 1% due boil off over months.
        -at 16g crashes –> it would not be difference vs normal fuel tanks
        -Next to 150 passengers –> tell me an scenery in which certain accident would not present similar risk with normal jet fuel.
        -for 100 flight hours –> you can unload fuel on arrival, which would be discounted from the fuel you receive on departure.

        -Video: that is a perfect h2-oxygen mixture (no even air mixture I suppose). When we talk about hydrogen tank.. you have just hydrogen… There is no possible way to generate an explossion or air to enter inside the tank. No way.
        Even if it ruptes, the hydrogen would mix slowly with the air generating (if it finds an ignition) a flame, just a flame that it is way less dangerous than a fossil fuel flame.

        • In a massive leak from a light weight isolatoed Aircraft grade LH2 tank the LH2 would boil off into the air and raise/mix very quickly. Boeing has some Point in that certification requirements for LH2 systems on Commercial Aircrafts are not issued yet, hence the requirements and tests Required for certification is not known yet. A bit similar to the hyperloop Technology that also lacks certification regulations.

          • NASA and many others already made several test on liquid hydrogen compared to other fuels, in all spill test or almost any kind of test, LH2 was much safer.
            https://www.youtube.com/watch?v=7bFJK5kU_UQ
            https://www.youtube.com/watch?v=RNzjksIImb8
            Hydrogen public opinion is attached to the Hindenburg meme, which was not an explosion, and if its envelope would have not been flammable, even with a hydrogen lost and ignition, it could have a flame over hours which would not spread because the hole would remain of the same size.
            BTW: if you made a death toll list by mile traveled after world war two, Helium Airships were more dangerous than hydrogen airships by mile. For example in the Hindenburg only 1/3 die from the 90 passengers, meanwhile the US Akron 73 has die.
            Today technology is even much more capable to deal with different types of hazards.
            Even if you have a good h2-air mixture ignition (which is hard, because hydrogen rise so fast that it is hard to accomplish a good mixture because it displace the air), at ambient pressure H2 has low energy in comparison with other fuels:
            https://qph.fs.quoracdn.net/main-qimg-b5c7224815e893981b871a861ef614b1
            Even their flame produce less radiant heat.
            Even if a spill touch you, due the high temperature difference, the Leidenfrost Effect would keep you safe if we are talking for a short time period.
            Yeah.. I agree that we need new certifications for this new type of application..
            Not sure if today LH2 tanks concepts for airplanes are following terrestial regulations for storing cryo liquids and its handling. If that is the case, I hope they evolve.

          • Leidenfrost effect will not protect you for more than a second or two. Studies have shown that a spill from an airliner crash would be about 30 meters in diameter and would vaporize within 25 seconds, leaving the surfaces flash-frozen. The consequences of a person being in that spill would be severe, probably fatal, even with no combustion.

            That will need to be addressed in any H2 aircraft design, the risk of being exposed to LH2 would need to be zero.

  10. How timely the Airbus announcement is, after Bjorn has just done his highly educational series on H2-fueled aircraft and their promises and challenges! Bjorn is prescient! Bravo!
    One minor error: It should say specific energy (which is energy per unit mass) of h2 is 200 times … …

  11. Best readers’ comments that I have in ANY publication. Bjorn could start a new magazine specialising in alternative (carbon neutral) fuelled aircraft.

    • Nothing special, they say it’s challenging and won’t be operational anytime soon. Who could disagree..

  12. Does anybody else find it ironic on the same day LEEHAM claims a lost decade for aviation Airbus launches these concepts _with_ an ambitious timeframe?

    Seems to me an American centric view that extends Boeings miserable medium term prospects to the other side of the atlantic.

    • @Wingman: Umm… 2020-2030 is one decade. 2030-2040 is another decade.

      It’s easy to talk about concepts. Actually launching an airplane program is quite another. No NMA. No Airbus response to NMA. No SpaceJet. Not in this decade. Even if Airbus were to launch a hydrogen program for a 2035 EIS, doing so in 2028, 2029 or 2030 still results in a lost 2020-2030 decade.

    • Also notable that EU governments are putting forth a $15B incentive for these developments. Airbus would be foolish not to get a slice of that. Even if it doesn’t result in a commercial product, it will keep people employed. So it works as a social program as well as a technology program.

      When Airbus paid their $4B criminal penalty, some commenters here said the governments would find a way to give it back as research funding. That would appear to be happening now. But I don’t begrudge this because the research is worthwhile, and it’s effectively the government using their leverage to steer Airbus in the desired direction. If the work spurs greater effort for terrestrial sources as well, and greater worldwide recognition of climate change, that’s a good thing.

      Also it’s important for Airbus and EU airlines because the flight shaming impact is greatest in the EU, where distances are shorter and high-speed rail offers an alternative. So being carbon-free circumvents that issue. There’s less incentive in the US.

      If a commercial product does result, it will end up back in the WTO again, unless Airbus and Boeing can agree to bury the hatchet by then. Hopefully they will.

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