Bjorn’s Corner: The challenges of Hydrogen. Part 16. A Hydrogen airliner

December 4, 2020, ©. Leeham News: To dig a level deeper into the challenges of hydrogen airliners, as a next step we design such a plane (on a high level), now that we have covered the basics.

It will make us traverse the fundamental design tradeoffs of such a design. Reflecting on what we discussed in Part 3, “The Application Space for a Hydrogen Airliner,” we focus on the single-aisle short-haul domestic market, Figure 1.

Figure 1. CO2 emissions per aircraft type and range flown. Source: EU Hydrogen Powered Aviation report.

A hydrogen airliner

To gain a deeper understanding of a hydrogen airliner’s challenges, we spend the next Fridays designing one. We will discuss the critical decisions, like size, payload-range capability, type of operation, main systems, general configuration, and the operational economics of the design we have chosen.

We use our airliner performance and cost model to work out parameters like the size of the fuselage, aerodynamic surfaces needed, weights, and what size powerplant we need. From the overall performance, we can then extrapolate probable operations economics.

The market segment

We must first define the target market for such an airplane. There are many considerations, not least we are designing for the first wave of such airliners.

The fundamental change from carbon to hydrogen fuel will give us enough technical problems to solve; we shouldn’t seek additional ones.

Therefore, we stay with conventional solutions for other areas as far as possible to reduce the number of unknown unknowns.

The first problem is which market segment to address with a hydrogen airliner. We know from the development of carbon-fueled airliners over the last 50 years:

  • The segment below 150 seats is a magnitude smaller than the 150 to 200 seat market. This was the state before the COVID-19 Pandemic.
  • The so-called heart of the market, the segment with the highest sales and deliveries, was 165 to 180 seats in 2019. It moved up-market with about 1 to 2 seats per year before the Pandemic.
  • We can assume the upmarket move to be zero for the next years and that the heart of the market could have retracted a few seats.
  • The payload-range for this market segment is the next question. The average stage length for domestic flights in the US and West Europe is around 800nm, converting to about two-hour flights.
  • We have in Part 3 said we limit the range of a hydrogen airliner to 2,000nm. With the problems of the placement of a hydrogen tank, we need to keep fuel consumption within a limited range. Consumed fuel results in a displacement of the center of gravity of the aircraft, unless we have a tank placed at the center of gravity. As we’ve seen, this isn’t easy.
  • Therefore, it’s essential to not overdo the range required to limit the change of fuel mass and, by it, the shift in the center of gravity.
  • In most other aspects, we will follow the present trends for the heart of the market airliners Airbus A320neo and Boeing 737-8.
The design rules

As argued above, we will avoid exotic design solutions for problem areas outside the change from carbon fuels to liquid hydrogen fuel, LH2.

But we design for the 2030s and 2040s. Our development time will be around seven years. So we need to embrace technologies that are relevant between 2025 and 2050.

Production-wise there will be a ramp-up that spans at least five years, if not longer. The typical increase in production year by year is double the rate for the first couple of years, then it slows to 50% per year.

The market size

The market size for the first hydrogen airliner projects will be decided by politics. There will be technical risks to operate the aircraft and what we know so far is the cost of the hydrogen fuel will be higher at least the first part of the airplane’s life.

It means a hydrogen airliner can’t penetrate a market ruled by carbon-fueled airliners unless these pay for the environmental problems they contribute to. This can be constructed as tax relief for the hydrogen airliner or emission taxes on the carbon fueled ones.

The dynamics of the market with production rates of the single-aisles at 40 to 60 aircraft per month, means the hydrogen ones will operate side by side with today’s and tomorrow’s single-aisle airliners in the 160 to 180 seat segment for decades.

Given the production capacity for the first generation of hydrogen airliners (with a reasonable investment), we can postulate an initial market penetration of a maximum of 10%.

Later, with more variants developed from the first model (a stretch is plausible) and the entry of more participants in the market, the addressed market share can expand.

11 Comments on “Bjorn’s Corner: The challenges of Hydrogen. Part 16. A Hydrogen airliner

  1. In theory you could have the tank in the middle of the fuselage with zero shift in c.g. and biz class in front and economy in the rear with separate doors, galleys and toilets. Before Airports will have double gates the encomy class then have to enter from the tarmac and climb up the stairs like in the old days.
    It might be allowed an intermediate step with twin tanks using LH2 at T-O and landing and LNG outside teminal areas, the emission effect will be substantial but not as good as pure LH2. To be successful I think versions with Trans US range will be needed. Just look at the A321 when it came with winglets and a bit more range, the 757 was almost done, then the A321neo was the final blow. There is a big chance the US will approve at least one Covid-19 vaccine before New Year and that will effect fwd bookings.

  2. I’ll admit to not being overly scientific but has anyone studied the effects of all that water vapor being deposited into the atmosphere? Could it affect climate patterns or itself cause greenhouse effect, or would it not be significant?

    • There’s lots of water in the atmosphere already, but not so much at the altitude airliners cruise at. Fly the Atlantic and look at the cloud cover down below and you’ll see what I mean.

      Last I heard the jury was out on whether high altitude water vapour deposition causes net warming or net cooling. As I understood it, a contrail causes warming during the night as it reflects infra-red back to earth, but causes cooling in the day because of the albedo effect, reflecting sunlight away from the planet before it enters the lower atmosphere and warms it.

      I can’t source this info, but I understand that 9/11 – when flights in the continental US were stopped suddenly – highlighted this effect and that it was measured. Of course, this would include high altitude CO2 emissions as well as water vapor. I stand ready to be corrected.

      I think the consensus is it’s less harmful than CO2.

      • Chris is right, the contrail contribution to climate change is a small percentage overall, about equivalent to CO2 contribution from flight.

        Also right about the mechanism, the contrails exist as ice crystals rather than the water vapor in lower clouds, so have different spectral properties.

        Research is underway to adjust flight profiles to minimize contrail formation, which occurs at specific altitudes and conditions. So that may offset any enhancement from hydrogen fuels.

  3. Is LH2 miscible and/or soluble in (say)LNG or bioethanol? If so, could that alter and perhaps simplify the storage properties favourably?

    • LNG freezes at about 90 K, and LH2 exists within a range of about 15K to 33 K (20 K at 1 atmosphere). So either the LNG would become solid in the mixture, or the LNG would boil off the LH2. Not sure about ethanol but I imagine even worse.

      LH2 is just a difficult storage problem overall. It can liquefy and solidify atmospheric gases as well. That can be a problem if the fuel becomes contaminated, but the problem is well studied from rocketry.

    • Germany is working to have H2 och Natural gas mixed in the Natural Gas grid and design filters to extract either. Then you can convert H2 to LH2 where you need it.

  4. Bjorn, for some time I have been wondering if you could come up with a realistic LH2 airliner concept base on your knowledge and analysis capacity.
    I really look forward reading your next’s Friday’s publications!

  5. One of the key issues is range.

    Averaging can be useful or misleading. If one flight is 4 x 250 KM and the one is 4828 KM (3000 miles) then the average is 2539.

    That allows your 2000km bird but does not accommodate the 4828 mission.

    I don’t have the data to even begin, but the 737-100 (first of the true Single Aisles) was lower range.

    Range has been growing ever since. Is it truly that much excess or is it used enough to make it a base?

    So, is there enough ability to adjust inside the pretty anemic 1300 KM range?

    • Some runs are short, such as among the Hawaiian islands, early Southwest Airlines, and AirCal, with only a few airports.

      Some airlines needed versatility, such as Pacific Western whose average flight was short but needed to fly longer segments and do milk runs through AB and BC (where refuelling infrastructure could be limited).

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