Climate-neutral up above the clouds

They will play a key role in making aviation more climate-neutral in the coming decades. A recent study commissioned by Clean Sky shows that system innovations in aviation combined with hydrogen technologies could help reduce aviation’s share in global warming by up to 90%.

However, Prof. Rolf Henke, member of the Executive Board of the German Aerospace Center (DLR) and expert in the field of aeronautics research, says that reaching this goal will by no means be smooth sailing: “We still need to do extensive research and development work for aircraft, further improve fuel cell technology and liquid hydrogen tanks, and make major investments in infrastructure both on the ground and in the air. It will also be important to define regulations and certification standards so we can ensure that safe and reliable operation of hydrogen-powered aircraft is possible.” This means that a number of factors must be clarified before it is possible to reliably use hydrogen-powered aircraft. Nevertheless, various initiatives are already energetically working on the concrete implementation of these promising aircraft engines.

Exhaust gases in the form of water vapor soon to be reality?

Industry experts estimate that hydrogen could be usable for aviation on a large scale in 10 to 15 years. According to the study results, the first short-range hydrogen-powered prototype could be designed and made operational by 2028. This symbolic step would be an important sign that we are moving towards “green aviation.” Aviation is currently known to be the exact opposite of this: In addition to CO₂, emissions of nitrogen oxides (NOx), soot and water vapor, which produce contrails and cirrus clouds, also have a negative impact on the climate. Of course this has nothing to do with “chemtrails,” but to convert these contrails into water vapor would be a welcome improvement.

However, in the case of hydrogen-powered aircraft and with a view to climate-neutral aviation, there are other technological changes that we will also need to consider in the future. For example, there will have to be an increase in overall efficiency with lighter tanks and fuel cell systems, including cooling and innovative distribution systems for liquid hydrogen within the aircraft. We will also need turbines that can burn hydrogen with low NOx emissions and efficient refueling technologies that enable flow rates similar to those of kerosene.

First prototypes take off

Incidentally, there have been various prototypes lifting off into the clouds since the early 2000s. The first ever “passenger plane” flying on pure hydrogen propulsion took off in 2016. Designed by the German Aerospace Center in cooperation with the Slovenian manufacturer Pipistrel, the small aircraft HY4 has four seats and can fly up to 1,500 kilometers.

In October 2020, aircraft manufacturer ZeroAvia, which specializes in environmentally friendly aircraft engines, followed suit and sent a hydrogen aircraft called “HyFlyer” into the air. The “HyFlyer” is a fuel cell aircraft with six seats, which is expected to cover more than 400 kilometers in another test flight before the end of the year. As part of a project supported by the British government, the first commercial operation is planned as early as 2023. After that things should move fast: by the end of this decade, we can expect to see aircraft models that can hold 50 to 100 passengers. The company considers flights with more than 200 seats and a range of more than 5,000 kilometers to be realistic by 2040.

In the medium term, ZeroAvia aims to integrate its technology into aircraft with ten to twenty seats, which will have a range of up to 800 kilometers. These airplanes are to be used for commercial passenger transport on the one hand, and in a converted version also for freight transport. ZeroAvia even expects the hydrogen-electric powertrain to have operating costs lower than comparable kerosene aircraft due to lower fuel and maintenance costs. We are on the edge of our seats!

Big plans at Airbus

Airbus is ambitious, aiming to launch the world’s first zero-emission commercial aircraft by 2035. To this end, the European manufacturer has three different concepts in the pipeline, one of which is will be implemented. The so-called turbofan design is intended to transport 120 to 200 passengers over medium distances of about 3,700 kilometers. The concept here is somewhat smaller than the current baseline A320neo, which is in use by numerous carriers, but at a good 800 km/h it also achieves the same cruising speed they do, using hydrogen propulsion.

The second design is a turboprop aircraft with propeller drive for up to one hundred passengers for short routes. At a good 600 km/h, this would be about one hundred kilometers per hour faster than today’s turboprop aircraft. What’s so special about this? Both of these designs are driven by modified gas turbines, supplemented by a hybrid electric motor powered by fuel cells. So Airbus is not reinventing the wheel, but rather consciously relying on a “conventional” configuration.

Perhaps most spectacular is the hydrogen-powered “Blended Wing Body.” Here, the wings and fuselage form a continuous aerodynamic body for optimum accommodation of the hydrogen tank with advantageous aerodynamics. According to Airbus’ own forecasts, at the moment the turboprop model seems to be the most likely candidate for future implementation. The specified period of 15 years is also ambitious, but – according to numerous experts – absolutely within reach for the European flagship company.

Always two sides to the coin

What we still might want to do is take a closer look at the pros and cons of hydrogen itself. Even if H₂-operated aircraft do not produce any environmentally harmful emissions, there are still a number of factors that need to be considered. The idea of using hydrogen instead of kerosene as an energy source for aircraft engines is not new, but it continues to pose challenges. Hydrogen, for example, has an energy density three times higher than that of kerosene, a common aircraft fuel – a major advantage over batteries – and weighs only a third as much. On the other hand, hydrogen takes up four times more volume than kerosene. In addition, liquid hydrogen requires complex cooling systems, which above all means more weight – a decisive factor in aircraft construction.

At the same time, appropriate measures such as larger tanks and hydrogen depots will also be needed on the ground. No to mention the (well-known) fact that the production of hydrogen itself is also still very complex and expensive, especially if its production is to meet the criteria of sustainability.

In short, there is yet a lot to do before a climate-neutral hydrogen aircraft is ready for the market and for normal operation. Good thing the politicians have already put it on their agenda.