Textron subsidiary Pipistrel Aircraft flew the first piloted liquid hydrogen-powered electric aircraft last Friday. The HEAVEN project HY4 demonstrator took off from Maribor, Slovenia, with two pilots onboard and “demonstrated safe and efficient operation throughout multiple flight tests,” the company said. The hydrogen is used by a fuel cell that creates electricity for the electric motor. Pipistrel claims the use of liquid hydrogen instead of compressed hydrogen gas doubles the range of the aircraft to about 800 nautical miles.

Pipistrel Chief Engineer Tine Tomažič said the flight is a milestone in making emissions-free flight practical. “At Pipistrel, our aim is to be the pioneer of future flight and playing a role on the liquid hydrogen tank integration, we, along with all the other partners involved, are able to demonstrate the success of alternative sustainable fuels, ready to power the aircraft of tomorrow.”

Russ Niles
Russ Niles is Editor-in-Chief of AVweb. He has been a pilot for 30 years and joined AVweb 22 years ago. He and his wife Marni live in southern British Columbia where they also operate a small winery.


  1. Bending the English language to the point of calling this an “emissions-free” flight or calling H2 a “sustainable fuel” is a lie by omission.

    • Emmission-free. Yes, that’s the real question. True, it doesn’t have direct emissions. Emphasis is on DIRECT. Emissions in all these ”eco”- and ”sustainable” are usually just off-set. Clear of view, clear of mind.
      H2 is mostly produced from fossil fuel. Shocking discovery, right? Just a small portion is produced by electrolysis.
      Untill we have surplus of sustainably produced electricity H2 will not be a viable source. To be more precise, it will ectually never be a source, just an intermediary.

    • Dear Mr. Foyt,

      Apparently you missed this bit of information about the flight’s use of green-hydrogen:

      “Fuelled with green hydrogen produced by Air Liquide at its French liquefaction facility, […]”

      Green hydrogen is hydrogen produced by the electrolysis of water, using renewable electricity such as photovoltaics (solar).

      Best regards,
      Larry Dighera

    • The emissions from a fuel cell is water vapor, a much more powerful ‘green house’ gas than CO2. So, what are they ‘saving’ ?
      These ‘renewable’ fuels are hardly emissions free. They all require fossil fueled equipment to produce the machinery to that produces the solar/wind hardware.!

      CO2 is not a problem since there is no ‘climate crisis’.

      • Implicit in your thesis is the notion that it is not possible to recover the pure H2O produced by fuel-cells. Or, did I miss something?

        • Since fuel cells operate at elevated temperatures of up to 200 degC, the H2O is a vapor when emitted.
          It could certainly be condensed back to a liquid state.

    • Hydrogen is not an energy source, it’s an energy storage medium. The energy ultimately has to come from somewhere else.

      • You are correct. The storage of electricity has been a fundimental issue since its discovery, that has yet to be satisfactorially resolved in a general way.

        It was the attempt to store electricity that lead to Dutch scientist Pieter van Musschenbroek of Leiden (Leyden), Netherlands to develop the “Leyden Jar” in 1745. He was attempting to “pour” high-voltage static charge into a glass vessle …

      • Sort of getting “semanticky” here. Is oil from the ground an energy source? You can go up a level or two and say “sun!” … or ultimately, “big bang!”

    • That completely depend on the source of H2. Solar power is now the cheapest source of electricity to the point where others (Toyota) have determined that it may be better to use H2 made from same in IC engines vs Batteries to power autos.
      Current Cost at the site in California w/o tax subsidies for Electricity is 3 cent per KWH. the factors to $ 1.50 used for a one Kg which is a one gallon of gasoline energy Eq. 127 Mj for gasoline 1 gallon vs 141 Mj for 1 kg of H2. so it is actually closer tio 1.25 a gallon for energy neede to make the theoretical gallon of fuel equivalent.

      • Where do I sign up for that 3 ct per kWhr ? PG&E is charging $0.36 per kWhr, and $0.40+ over the baseline of 360 kWhr ?
        20 years ago, before CA installed huge amounts of solar pv and wind, PG&E was charging me $0.13 per kWhr.

        utility scale solar pv and wind is a huge boondoggle for the mfgr and installers. !!!

  2. Just saw a lengthy documentary last night on the hydrogen powered Hindenburg. Didn’t work out too well for them. Probably different hydrogen……….. Ready for incoming

  3. That is great! We can just head over to the Hydrogen store and buy some liquid that is cheaper than gas. Airports are just going to love storing that stuff for pilots who may never show up!

    • Not quite yet, but Air Liquide is working on the infrastructure. Note that Air Liquide is not a niche company focused on iffy technology but a major player in gas production and supply.

      Universal Hydrogen takes a similar approach. From their website:

      “We are building a flexible, scalable, and capital-light approach to hydrogen logistics by transporting it in modular capsules over the existing freight network from green production sites to airports around the world. At the airport, the modules are loaded directly into the aircraft using existing cargo handling equipment. No new infrastructure is needed. Starting with regional airplanes, we are also developing conversion kits to retrofit the existing fleet with a hydrogen fuel cell powertrain.”

      I wonder if A.L. is using a similar approach. I saw one shot of the A.L. supplied aluminum tank in the Pipistrel – it looked like it could be readily swapped out.

      • Air Liquide does not have a very good corporate reputation in Houston, where they have a major presence. Employees and customers generally don’t have much good things to say. As a former vendor, I found them unusually hard to deal with.

  4. This is pretty cool. The challenge with green energy (solar, wind, tidal, and (to some extent) nuclear) is that the operator loses direct control over the amount of power being generated. Hydrogen production is one way to absorb excess energy and save it for later. While there is clearly a lot of development left to go (that’s an awfully big two-place airplane) and cryogenics aren’t going to be at the self serve pump anytime soon. But this could be significant step towards bringing the energy density of hydrogen into a usable range… something batteries have yet to achieve.

    To the naysayers, I can see you sitting on the sand at Kitty Hawk in October of 1902 complaining that “Those two boys are idiots. That stupid thing doesn’t even have an engine. They should go back to building bicycles. What are they going to do… pedal that thing?”

    • These alternative energy paths strike me as being much like the WW-I & -II era efforts in Sweden and other petrol-starved countries to operate vehicles on wood or charcoal. The “gasifiers” used to do this produced carbon monoxide gas which could power an internal combustion engine and allow operations to continue, albeit with major downsides comparable to those being faced today. They were “usable” in the sense that they worked, but…

    • If history serves, the challenge will likely be the politics of the petroleum industry losing control of energy production, much as is beginning with domestic solar electricity generation.

      I can foresee a future in which each home has a rooftop photovoltaic generation system, and ultimately a H2 liquefaction and storage system, and a bank of fuel-cells.

      The redundancy inherent in such a decentralized system would be very much appreciated in the event of a disaster ….

      • Your future better include nuclear plants to provide energy to make the panels as well as some serious battery innovations.

      • I live in a comfortable 2000 sqft suburban home on a 1/5 acre plot, in a very quiet neighborhood. Sure, I can get a second mortgage to pay for my power generation & storage equipment, not sure if a second basement would be an option to build it.

  5. Any thoughtful reply to this article requires a meme *. Since we can’t post graphics here I shall refrain.

    * The meme would be directed at the subject of the article not the author.

    • I apologize for posting in this message thread, but are you able to provide information on how to upload an avatar. I couldn’t find it in my Account Details page, nor the FAQ. I was also unable to find a way to contact you directly.

      • Yes, I see one appear from time to time. If one of those who has found a path to doing this could post the info, it would a nice public service for the group.

  6. “Pipistrel claims the use of liquid hydrogen instead of compressed hydrogen gas doubles the range of the aircraft to about 800 nautical miles.” Looking forward to Pipistrel developing this technology further towards a future 800 NM flight. That’s roughly the range of a C172; and if we can scale petroleum from C172 range and speed to long haul range and speed perhaps the same will be possible with the hydrogen burning jet engines currently being researched. As to how hydrogen fuel can be produced with little emissions, electrolysis powered by any number of energy sources (wind, solar, hydro [to take advantage of the storage of surplus power a la Rob’s comment], or likely the cheapest option, nuclear) are available today. What I’m not aware of (and what would make for a great avweb article) is what the potential economics of a hydrogen based airplane might be.

  7. Liquid hydrogen may be viable – in many years to come. Currently, it is riddled with so many issues that yes, you can make it work (as seen here) but it is so far from practicality that it borders on absurd. It takes a lot of energy to produce it and much more to liquefy it and store it, not to mention the hazards of handling. Researchers at (I think) Michigan State have been experimenting with using liquid ammonia as a fuel. Rich in hydrogen (NH4), simple to produce, store, and handle, it has promises. Never rule one out, but be practical.

    • Well, I hate to “rain on your parade”, but ammonia probably isn’t the fuel of the future.
      Yes, ammonia will burn, and it is easier to liquefy (requiring only -40 degrees of refrigeration, versus -420 degrees), but there are a few little problems. First, it is highly toxic to humans. Second, it produces large volumes of oxides of nitrogen when burned. Combined with the water from the combustion, it will create nitric acid and other corrosive compounds that would likely eat engine and exhaust system materials. Third, forget trying to use it in a fuel cell to make electricity. But at least, it will be easy to detect a leak, given its very pungent odor.

  8. The potential of LH2 powered flight is awesome, given this fact:

    The gravimetric energy density of a fuel is the amount of energy that can be released by a given mass of
    fuel. It is typically measured in megajoules per kilogram (MJ/kg) 12.

    Liquid hydrogen has a gravimetric energy density of 141.8 MJ/kg 3. In comparison, gasoline has a
    gravimetric energy density of 46 MJ/kg 13. Therefore, liquid hydrogen has a 300%+ higher gravimetric
    energy density than gasoline.

    However, at this point in development, the efficiency of electrolysis is ~70-80%, and the efficiency of fuel-cells is about ~60%.

    What makes electric motive power of automobiles and aircraft viable today is the dismal ~20% efficiency of internal-combustion engines.

    • Well, you have to expend 4x the energy to create liquid H2 and then practical use means you waste half of that to venting; Gasoline looks to be at least 3x better as far as a practical fuel. Again the “lie of omission” is that liquid H2 is a terrible liquid fuel for practical use.

      • I’m not being intentionally obtuse, but “4x the energy” of what?

        Are you implying it requires four times the energy contained within the LH2 liquified from solar-powered H2O electrolysis and liquified with cryocooler technology, to produce it? If so, please cite empirical research that supports such an assertion.

        With regard to LH2 venting, vented H2 is easily recaptured for re-liquefaction with a simple hood above the containment vessel, as H2 is significantly lighter than air, or perhaps a cryocooler within the Dewer.

        As has been discussed elsewhere in these comments, when gasoline was at the stage LH2 is currently, it too was thought impracticable. It takes time for technology to develop.

        I’ll grant you there are many technological challenges to address concerning the practicality of LH2, but I see evidence they are slowly being overcome.

        Thank you for providing your viewpoint.

  9. Bit disappointed in the lack of history and technology in some of the comments. In 1912 30% of the automobiles were electric. Gasoline was combustible, explosive under the right conditions and considered dangerous. There were no gas stations (infrastructure) and electric battery powered automobiles were considered the future. The problem with both systems was distance. Automobiles were good for around town but not between cities. Then along came this guy named Rockefeller and he had all these oil wells and he got together with this other guy named Ford and then the two of them talked to Vanderbilt who controlled the railroads and they built the infrastructure for petroleum powered automobiles. They paid farmers and such to store gasoline drums along dirt roads and sell it to drivers. These men created the infrastructure we have today, it just didn’t happen! I did a study for a client on this historical process a few years back. One of the biggest concerns was that the safety of pumping a flammable product would require people to be trained for safety, just such things as we do today when we ground our airplanes. Think Hydrogen is this nasty explosive fuel and 100LL is a safe non-flammable fuel? Really? If we were switching our automobile fuel from electric to gasoline presently, people would not be allowed to fuel their vehicles. Some attendant in a fireproof suit would saunder out, ground your vehicle after you got out and pump the gasoline for you. You can read all about the creation of the gasoline infrastructure and the demise of electric cars. I found it very interesting including the creation of our national highway system. There are many interesting historical articles about this. Keep an open mind.

    • Interesting comment; thanks for the post.

      With respect to how we’d treat gasoline pumping if it had just been introduced: Imagine proposing an infrastructure which would allow cars to legally travel on the same road, in opposite directions, with a closing speed of over 100mph, only yards (or feet!) between them, and with nothing to protect them except a dotted line on the highway and a driver who’s supposed to know the rules…

      Maybe a quarter mile between opposed carlanes, with GTC (Ground Traffic control) controlling the on-ramps?

      • I know. One rocket fueler from Vandenberg commented to me that the gas station attendant would have a haz mat degree and a SCAPE suit. 🙂

        • The Vandenberg fueler’s commant was obviously meant tongue-in-cheek, as today there exist H2 fueling stations at which motorists refueling their Toyotas require no special apparel.

  10. Hydrogen fuel cells are superior to batteries and the only current viable way to make electric airplanes practical and functional as the weight of batteries is a non-starter in aviation.

    BUT its still unnecessary.

    Jet A remains cheap and plentiful and has existing infrastructure. We have generations of oil left in the ground. Drill, pump, refine, repeat. Problem solved.

  11. Battery powered electric aircraft will always be limited to small short haul planes unless somebody changes the laws of physics.

    Hydrogen seems to be the only viable path to larger, longer ranged electric aircraft. I doubt I will ever fly on one in my lifetime but I am sure the technology will eventually become commercially viable.

  12. All these ‘sustainable energy’ schemes are little more than diversions from reality. There is no free lunch no matter what you do. If something is moving, energy was used in one way or another to build it and fuel it. No one ever talks about the real problem. There are too many humans clomping around the earth. It can be calculated how much energy it takes to feed, clothe, house, move and even bury each. Anyone trying to tell me that a hydrogen powered airplane is gonna “save” the planet is full of … well … beans … aka bravo sierra.

      • That’s the first comment with the all truth I’ve read in this space related to topic. If (and only if) there’s a change in climate caused by humans that will, soon or later, cause the death to all of them, earth, as a planet containing forms of life will survive and those form will survive too and a new reality will appear. In that virtualization, humans are spared and they deserve that.

  13. Food for thought: If we keep reducing the amount of CO2 currently being produced by everything; will the Trees, plants and phytoplankton still be able to produce enough oxygen to keep 8+ billion people alive and well?

    • That’s precisely the issue, J B. Small percentage (relative) of increased levels of co2 help plants to produce MORE food for what is essentially becoming a population too big for the earth to sustain. Trying to build vehicles to move humans around without producing co2 is like a cat chasing its tail in a circle. Ridiculous. Reduction in so called greenhouse gases or decarbonization of the planet is nothing more than a scam by governments and politicians trying to control the masses.

      • I agree with Larry!

        Every “thing” that damages the environment is a function of humans. More humans equals more demand on the environment. No way around that. Unless and until “environmentalists” go back to working on “Zero Population Growth” they have no credibility.

        In this case the issue isn’t that hydrogen has worked, but that the folks working on it and supporting it are touting it as “the answer.” If you think it’s the answer you’re not looking deeply enough.

        I’m glad it’s been done and I’d like to see them keep working on it, but depending what changes and how it changes (because everything changes sometime) this may be pointless in the end. But it is worth exploring.

        But y’all go easy on those of us who fail to jump on the “Rah-Rah! This is the answer!” bandwagon right now. We’re just seeing things y’all aren’t – or are ignoring.

          • Here ya go, LDig … if ya want to save the planet, don’t build a H2 powered airplane … just stop mowing your lawn:


  14. I want to congratulate pipistrel for once again finding an excellent use for an airplane, the Taurus, which seems to be able to do everything. Different variations of this plane have won all sorts of contests and set all sorts of records.

    Just none of them sales records. Maybe they should figure out if they can make a version that people will buy to fly around in.

    • Pipistrel has sold around 100 Velis Electro electric planes since its launch in 2020.
      Pipistrel had delivered 100 aircraft of the microlight glider Taurus family by 2011.

      Given the niche market, I’d say Pipistrel’s sales record is stellar. Their mere continued existence is a testament to their sustainability, in the face of a difficult market.

      • I’m not knocking anything here except lack of sales for what seems to be an excellent design. 100 isn’t a lot.
        I was not happy they sold to Textron, and not surprised that hasn’t resulted in better sales.
        I’ve not sat in any of their aircraft, but I suspect they are missing something in the marketing department.

  15. LDighera said:
    “and you use sunlight to power the cryocooler to liquefy H2”
    —–Nope. Solar is already being used on the grid. If you take it away for this project then you back-fill with traditional oil/gas/coal to make up for it for this. That’s another lie by omission.

    “With regard to H2 venting, given the fact that the Space Shuttle was powered with LH2, its use has a proven record of feasibility.”
    —–Nope, it’s venting so much that ice builds up on the structure before launch. Shuttle launches are a poster boy of waste when it comes to H2. Just because it’s feasible does not make it sane to use.

    • “ it’s venting so much that ice builds up on the structure “

      I don’t disagree with your premise, but it’s a strange use of ‘so much’. It doesn’t take much to get moisture and even ice out of the Florida atmosphere.

      • Point is main tank is open to the atmosphere and has to be connected full time to an LH source until liftoff. H2 cars in Europe are banned from parking garages for this same reason! Any airplane will need to be completely UNFILLED before you can put it in a hangar.

  16. Video total of 1:28. Of that, 1:14 is the airplane turning around on the ramp and taxiing in the direction of the runway. Then 14 seconds of footage of the airplane flying away from the traffic pattern. No footage of the actual takeoff, none of the landing. Lame video.