Europe has kicked off its latest multi-billion euro public-private research and development programme into low-emission aviation and aims to have demonstrator aircraft taking flight later this decade ahead of possible service entry from 2035.

Building on its two previous Clean Sky programmes, Clean Aviation went live on 30 November as the bloc bids to help the sector achieve climate neutrality by 2050.

EcoPulse c Airbus

Source: Airbus

Clean Aviation could build on previous Clean Sky 2 initiative

A total of €1.7 billion ($1.9 billion) will be contributed by the European Commission to the effort, with participating companies expected to provide a further €2.4 billion.

Clean Aviation foresees service entry of technologies matured under the programme taking place in the mid-2030s at the earliest.

Research efforts will be focussed around “three key thrusts”, it says: hybrid-electric regional aircraft; ultra-efficient short- and medium-range aircraft; and disruptive technologies to enable hydrogen-powered aircraft.

“Each thrust will develop technologies and enablers, leverage essential knowledge and capabilities, and de-risk the identified technologies and solutions, where further maturation, validation and demonstration is required to maximise impact,” says Clean Aviation.

It sees regional aviation – defined as operating flights of up to 560nm (1,000km) – acting as “a laboratory for other domains” within the programme.

“The vision for 2030-plus is to demonstrate innovative and disruptive technologies, enabling new aircraft performance levels, and opening up new business models,” it says.

Different propulsion architectures will be assessed, alongside various fuel sources – including hydrogen fuel cells – and levels of hybridisation.

“In parallel, technologies and solutions that are able to shorten time-to-market and affordability will be pursued,” it adds.

Additional consideration will be given to operating constraints such as short-field lengths and cockpit workload, as well as the broader regulatory environment and infrastructure provision.

Airbus A340 BLADE test aircraft

Source: Airbus

Airbus has researched laminar flow aerodynamic improvements with A340

Clean Aviation says two “interdependent” areas of research are needed to advance the new technologies. In the period to 2025, “building blocks and different integration options will be studied back-to-back” in order to “identify the most promising architectures”.

That will be followed by a second phase to “mature the technologies selected for the demonstrator and deliver suitable final solutions ready for integration”.

However, it will also mature some technologies not suitable for the demonstrator “but valuable for actual aircraft integration in 2030”.

While electric or hybrid-electric designs will be key for climate-neutral regional operations, larger short- and medium-range aircraft, however, will “rely on ultra-efficient thermal energy-based propulsion technologies” burning sustainable fuels, says Clean Sky. The goal is achieve a 30% improvement in “energy efficiency” for next-generation narrowbodies.

“The first phase of the programme will aim to select, mature and qualify ‘best athlete’ technologies to exploit their full potential integrated into an ultra-low-emission single-aisle, short/medium-range aircraft.”

These could build on technologies matured in existing Clean Sky programmes such as EcoPulse – a hybrid-electric demonstrator being developed by Airbus, Daher and Safran – and the Airbus-led Blade laminar flow aircraft.

The 30% goal will be achieved through a combination of airframe improvements alongside ultra-efficient propulsion systems and their integration.

But there is also the option for “for the demonstration and validation” of hydrogen-powered aircraft “subject to a sufficiently mature capability” from Clean Aviation’s H2 workstream.

An initial phase of the programme will identify the desired attributes of a future aircraft and then finalise its conceptual and preliminary design characteristics “by selecting the best configuration”.

That will lead to a validation and integration phase, beginning in 2023 with a two-year period of full-scale integration tests of “ultra-efficient batteries and engines”. For the five years from 2025, Clean Aviation aims to validate the test configuration through ground and flight testing of “20MW-class aircraft technology” using “a large-scale flying demonstrator platform”.

By 2030, the required systems will be at technology readiness level 6, allowing for service entry five years later.

ZEROe concept aircraft -c-Airbus

Source: Airbus

Hydrogen power is seen as promising but with significant technological hurdles

Clean Aviation sees hydrogen power as offering huge potential to achieve true zero-emission flights, but says that significant challenges, such as the requirement to store liquid hydrogen at very low temperatures aboard the aircraft, mean “a high research effort is required to introduce this technology onto the market”.

“Among these topics, some elements are still at a very low maturity level and will need significant development, maturation and demonstration in order to be ready for integration into future aircraft,” it adds.

With this in mind, Clean Aviation aims to mature and demonstrate the relevant systems “ready to be integrated into future aircraft” – including onboard hydrogen storage, fuel distribution systems, fuel cell-based propulsion and direct combustion of hydrogen.

Initial calls for proposals under Clean Aviation are expected in early 2022.

UK-based companies have benefitted from the previous Clean Sky programmes, but at present it is unclear if they will be able to take part in Clean Aviation.

Their participation is dependent on the UK gaining associate membership of Horizon Europe. Although that was agreed in principle as part of the post-Brexit trade agreement struck between London and Brussels, it has been held up by continued political tension between the two.