Hybrid-electric regional aircraft, new short- and medium-range jets, and hydrogen as an energy carrier: with Clean Aviation, the European Union is bringing together a substantial share of its research activities aimed at making commercial aviation more climate-compatible. The programme brings together aircraft and engine manufacturers, suppliers, research organisations and universities. Its goal is to develop technologies that could be incorporated into new generations of aircraft from the mid-2030s onwards.
Clean Aviation is one of Europe’s central research initiatives for advancing commercial aviation technology. The programme is managed by the Clean Aviation Joint Undertaking (CAJU), a public-private partnership between the European Union and companies and research organisations from the European aviation sector. It forms part of the EU’s Horizon Europe research programme.
The programme is explicitly not about developing a single aircraft or engine. Instead, Clean Aviation provides a common research framework in which different technologies are developed, integrated and tested in increasingly large demonstrators.
Research covers new electric and hybrid-electric propulsion architectures, their energy supply and their integration into new aircraft configurations. This includes batteries, electric propulsion systems, high-voltage architectures and combinations of multiple spatially distributed propulsion units. Fuel cells are also being considered as a possible energy source for more advanced regional aircraft concepts.
The programme has a total budget of around €4.1 billion. Up to €1.7 billion is provided through EU funding, while private partners are expected to contribute at least €2.4 billion.
From research to aircraft from 2035 onwards
Clean Aviation is working towards a comparatively concrete timeframe. The technologies under development are intended to mature sufficiently to support the development of new aircraft that could potentially enter service from around 2035 onwards.
Compared with aircraft based on 2020 technology levels, Clean Aviation is targeting around 30 percent lower CO₂ emissions for regional as well as short- and medium-range aircraft through new aircraft and propulsion technologies alone. When Sustainable Aviation Fuels are included, the programme cites potential net CO₂ reductions of around 86 percent for these concepts.
There is therefore deliberately still a substantial development step between the research programme and potential series production. Clean Aviation is not intended to take technologies all the way to a finished commercial aircraft. Instead, its role is to reduce technical risks, integrate systems and mature relevant technologies to a level at which manufacturers can subsequently launch concrete aircraft programmes.
Three technology areas at the centre of Clean Aviation
Clean Aviation structures its work around three major development areas:
Hybrid-electric regional aircraft
The first focus area concerns hybrid-electric regional aircraft. Research covers new electric and hybrid-electric propulsion architectures, their energy supply and their integration into new aircraft configurations. Technologies under consideration include batteries, fuel cells, electric propulsion systems, high-voltage architectures and distributed propulsion. Clean Aviation is investigating, among other concepts, regional aircraft whose new technologies could be ready for service from around 2035 onwards.
Efficient short- and medium-range aircraft
A second area focuses on highly efficient short- and medium-range aircraft. The work centres on new aircraft architectures and highly efficient thermal propulsion systems. These include new gas-turbine concepts and potentially open-rotor or open-fan architectures. Significantly higher efficiency could also facilitate the use of alternative energy carriers such as SAF, whose production is more complex and whose availability is likely to remain limited initially.
Hydrogen-powered aircraft
The third focus area covers technologies for hydrogen-powered aircraft. Research includes liquid-hydrogen storage, hydrogen supply systems for aircraft, fuel cells and the direct combustion of hydrogen in gas turbines. Determining which solution is best suited to which aircraft category is explicitly part of the research effort.
Projects such as NEWBORN, which is developing megawatt-class fuel-cell systems, and HERA, which is investigating different architectures for future regional aircraft, are concrete building blocks within this broader research programme.
Clean Aviation builds on Clean Sky
The programme was launched at the end of 2021 as the successor to the European Clean Sky and Clean Sky 2 research programmes. Its legal basis is EU Regulation 2021/2085; Clean Aviation officially started on 1 December 2021.
Its history reaches back to 2008, when the first Clean Sky initiative began its work. Clean Sky 2 followed in 2014 and developed numerous technologies for aircraft structures, engines, systems, regional aircraft and new aircraft configurations, testing them in demonstrators. Clean Aviation continues this work, while placing a stronger emphasis on technologies that could enable a fundamental shift in energy supply and propulsion.
The programme itself runs until the end of 2031. Development work is divided into several phases. While the first phase primarily focuses on selecting and maturing different technology approaches, subsequent phases place greater emphasis on integration and demonstration at system and aircraft level.
Airbus, Safran, Rolls-Royce, DLR and numerous other partners
The range of participants is correspondingly broad. Private founding members include Airbus, Dassault Aviation, Leonardo, Safran, Rolls-Royce Deutschland, MTU Aero Engines, Honeywell, Collins Aerospace, GKN Aerospace, Liebherr Aerospace and Lufthansa Technik. Major research organisations and universities such as DLR, Fraunhofer, ONERA, NLR and the University of Patras are also involved. In addition, there are numerous associated members, including ATR, H2FLY, PowerCell, Siemens, ZeroAvia, TU Delft, the University of Stuttgart, TU Braunschweig and the University of Nottingham.
However, the individual research projects are not restricted exclusively to these members. Other companies and research organisations can also participate in Clean Aviation projects awarded through competitive calls.
Demonstrators rather than a single vision of the future
One distinguishing feature of the programme is its strong focus on practical demonstration. New technologies are not intended to be studied only in isolation in laboratories. Depending on the project, components and subsystems are brought together, tested on the ground and, in some cases, later evaluated in large-scale or flying demonstrators.
This is precisely where Clean Aviation’s significance for the European aviation industry lies: the programme is intended to determine which of the technologies currently under discussion can actually achieve the necessary combination of efficiency, weight, safety, technological maturity and industrial feasibility.
Which technologies will ultimately prevail in production aircraft has therefore not yet been decided in every area. For regional aircraft, hybrid-electric concepts using batteries together with highly efficient, SAF-compatible gas turbines are currently moving to the forefront. At the same time, Clean Aviation is investigating fuel cells, hydrogen combustion and other hydrogen technologies for later applications or other aircraft categories. The programme therefore provides a framework in which different approaches can be developed to a level of technological maturity at which their suitability for future aircraft programmes can be assessed on a robust basis.