Airbus prepares contrail flight tests

July 21, 2022, © Leeham News at Farnborough Air Show: Airbus is converting two Arcus high-altitude gliders to check if the contrails produced by hydrogen combustion engines create an environmental problem.

The background is that experts can’t agree if the water vapor produced by hydrogen combustion (which merges hydrogen with oxygen to water) can cause global warming or not. The only way to resolve the dispute and gain fundamental knowledge is to fly and measure.

Figure 1. First flight with the Blue Condor program’s test aircraft. Source: Airbus.

Airbus’ Blue Condor program conducts flight trials on the contrail issue

The big question mark for propulsion with hydrogen-burning gas turbines is if these produce troublesome levels of persistent contrails at high altitudes or not. If they do, such contrails will contribute to global warming.

Experts have analyzed the problem for decades but can’t agree on whether it’s a problem or not. One camp says the contrails will definitely contribute to global warming. While the H2-burning jet aircraft will emit no CO2, thus alleviating the CO2 load in the atmosphere, persistent contrails will be equally bad.

Another camp of experts believes it will be no big problem. The ice crystals produced will be larger than the crystals of today’s contrails and, therefore, will not stay airborne for long.

Aircraft and engine manufacturers can’t live with this lack of certainty. The solution is to get a hydrogen-burning aircraft to the altitudes where this problem appears (typical jet altitudes of 30,000ft or more) and fly a measurement aircraft in the emitted contrails.

German DLR (the German NASA) has developed a measurement methodology and aircraft (Figure 2) and is an authority on the subject. What was missing was a hydrogen combusting aircraft. Airbus would get its test A380 airborne with a hydrogen combustion GE Passport engine by 2026.

Figure 2. The Blue Condor test setup. Source: Airbus.

But this is late. The industry needs data now. If this is a problem, there are things that can be done, like the collection of the water by condensation in the engine exhaust nozzle, but this needs development time and, therefore, early warning.

Airbus solved the problem in an innovative way. In its Blue Condor program, it equips two Arcus gliders with jet engines (Figure 1). One has a hydrogen-burning engine; the other burns our usual Jet-A1 kerosene.

By flying these gliders in front of the DLR measurement aircraft, one after the other, the formation process of contrails from the hydrogen combustion can be studied (ice crystal size, amount, etc.) at the same time as reference data from normal combustion is gathered. By virtue of the Jet-A1 reference data, the scaling to actual size engines can be made.

The best part of the story is we don’t have to wait long. The jet-converted glider has already performed its first flight, and test flights with both engine types will be done before the end of the year. The important test will then be done in a cold climate in North Dakota during spring 2023.

Other emissions

Hydrogen combustion also produces NOx emissions. There is plenty of knowledge on how to get this to about one-fifth the level of today’s engines by careful combustor design. The glider tests will also measure these emissions, but knowledge gaps are here less of a problem.

It’s a benefit that the DLR measurement aircraft can also trace these emissions, which will increase the NOx emissions understanding. But it’s questionable if this problem would have motivated such trials on its own. There is not the gaping hole in the knowledge around NOx emissions that we have for H2 combustion contrails.

Why the tests are important and timely

The swift action by Airbus is commendable. Instead of debating, it uses innovative means to get data for the most pressing problem of hydrogen combustion. The aim is to gain first knowledge, so the system decisions that must be made from now to 2026 can be based on knowledge and not assumptions.

Do these trials mean Airbus is leaning towards hydrogen burn instead of fuel cell propulsion? No, there are not enough results and data from the different Airbus research and test activities to point Airbus one way or the other, according to Sabine Klauke, Airbus CTO.

But this knowledge must be gathered over the next years if Airbus shall have an operational airliner by 2035. The glider tests are an essential part of the gathering of such insights.

23 Comments on “Airbus prepares contrail flight tests

  1. I think the action of Airbus is commendable, not condemnable. Anyway, great update as usual from Bjorn,

  2. “The swift action by Airbus is condemnable”.

    It is very “commendable”, before committing to a future strategy that is supposed to improve things, first make sure that you’re not going to make things worse.

    Some really sensible, practical forward thinking by Airbus. Easier to be proactive when you’re not mired in problems like some others!

    • Thanks, spell checker riot! Fixed, and agree, good action by Airbus.

      • Actually I like “condemnable”, there are quite a few places I think it applies sadly.

        I’m just hoping that at some point (sooner rather than later) Boeing gets it’s act together and gets to the point where it’s also looking forwards and providing innovative solutions rather than fire-fighting.

        • I too like condemnable, have to add it to the lexicon!.

          That said its a word so its a context issue – I always did turn the context checker off when writing (mostly out of Word). If you could program good writing we would have no good authors.

          Word was not going to tell me what I intended!

          Maybe ok for a newspaper but not an tech writting

          • > Maybe ok for a newspaper but not an tech writting <

            Superb- thank you.

          • “Superb- thank you.”

            AI who needs AI … 🙂

    • Agreed!
      Airbus is really taking its hydrogen R&D very seriously.
      Also all sorts of JVs with airlines, airports, gas suppliers, etc., to identify and iron out practical problems at an early stage.

  3. Thanks, a very interesting news item. It’s good to hear that Airbus are addressing the issue so thoroughly.

  4. Contrails are only generated in cold enough air. So what is the big deal about flying lower, in warmer air? Going from FL350 to FL250 0r so should cost some 20% in additional cruise fuel burn. Make passengers pay for flying lower, when necessary, and let’s move on with aero H2 combustion.
    Actually, flying lower when facing colder air should be adopted right away. To get rid of aviation macabre contrails.

    • That would create havoc in the aviation industry! 20% lower fuel burn sets you back move than a generation of jets!

  5. It seems that this would have been done sooner before the big Hydro bandwagon took off.

    And how about testing SAF ?

    and H2 produces NOX? Curiouser and curiousor (no, I don’t follow H2 all that close as its like the ever morphing open rotor that keeps getting kicked down the runway)

    • H2 doesn’t produce NOx.
      H2 *combustion* produces NOx, when N2 and O2 in the atmosphere come into contact with regions of very high temperature on/near the combustor.
      H2 fuel cells don’t suffer from this problem.

      • Bryce:

        Well really. I suppose I need to tell you where to put an period at the end of a sentence as well.

        But then H2 does cause NOX as you need a mining truck, dozer, processing etc to get your green energy that you turn into H2 don’t you? If you don’t just use the NOX power grid.

        We get to see how well the fuel cells work when our own illustrious Ravn (to avoid a conflicting with the Raven Bird as its held sacred by the Athabasca Alaska Tribes) fails to pan out (get it, pan out like Gold Mining in Alaska?)

        • Wha ?

          It’s drunk, stoned, or a bot; decide for yourself.

          🙂

        • “But then H2 does cause NOX as you need a mining truck, dozer, processing etc to get your green energy that you turn into H2 don’t you? If you don’t just use the NOX power grid.”

          Drill baby drill … oh my.

      • The interesting result is if the lack of soot particles will delay contrials and if they will form later from small water droplets merging. So measuring this effect is different than measuring at the normal contrail forming distance from regular JET A-1 buring jet.
        NOX formation in turbpfan engines is well known and the combination of hotter and faster combustion with H2 need work. GE and I assume RR/PWA are working and testing in one segment buriner test rigs by now.

  6. The short answer is yes. H2O is a greenhouse gas .
    But unlike CO2 which is present in tiny parts per mill , water vapour is in the air ( depending on location) in massive amounts.
    Human causes adding small amount of CO2 seems to make a measurable increase.
    I would assume ( at a first estimate) that the increase for hydrogen burning to produce H2O isnt measurable above the existing baseline. But the data may be different ?

    • Greenwashing really is the best solution (that’s not snark, or ironizing, by the way).

  7. “leave *my* technology alone; it is not responsible for this mess!” is a recurring refrain, just now.

    No, I don’t have an answer, and I apologize (a tiny bit, anyway) for my snark.

  8. Aside from the potential research benefits..

    So, some guys/galls in Airbus convinced management to buy Arcus gliders (which are awesome), mount a little engine on it, and are now cruising around thoroughly enjoying themselves. While recording real important data naturally. (cough)
    I wish I had thought of it!
    Absolutely brilliant.

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