AEROSPACE The requirement for a European civil X-plane

Creative construction​

ALAIN GARCIA past VP AAE, HonFRAeS, membre Emerite 3AF, JURGEN KLENNER, VP AAE, Member of the DGLR Senate, and RAeS Past-President DAVID MARSHALL FRAeS, present the findings of a joint Académie de l’Air et de l’Espace study into the pressing need for a European civil airliner technology demonstrator.

Airbus

Commercial transport aviation is having to cope simultaneously with:

  • huge economic shortfalls in the aviation industry and services operations resulting from the Covid-19 crisis
  • an absolute need to deliver much ‘greener’ aviation to the market as soon as possible
  • a global lack of financial resources to prepare on-time development of the corresponding products

Additionally, since the Airbus A350 was launched in 2007, no entirely new aircraft has been launched in Europe and there exists a widespread concern in the European aeronautical community as to the progressive loss of experience for the successful development of a brand new large civil transport aircraft. This affects particularly the critical areas of architects and integrators. In a few years, in the absence of any demanding new programme launch, almost an entire generation of aeronautical engineers in Europe will have had no chance of applying and sharpening their skills.

An original path for securing these hurdles is being proposed to Europe. It has been laid out in a joint study prepared by members of the Academy of Air and Space based in Toulouse and the German Society for Aeronautics and Astronautics, the DGLR, in the AAE Opinion N°11DGLR Opinion 2020-01. Combining smartly, the needs of selecting the radically new but matured technological solutions for the ‘greener’ aircraft to be put into service in 2035 with maintaining the European aeronautical sector know-how, the proposed solution that came naturally is to launch, very soon, a new architectural-technological ambitious flying demonstrator. A new paradigm for Europe.

What is missing for reaching the ambitious ‘decarbonisation’ goal?

It is a common understanding that very low emissions in aviation can only be approached by applying disruptive technologies to the airframe and propulsion system. This objective is likely to significantly change the way this ‘green’ aircraft is designed, and what it will look like compared to what we have seen up to now.

Airbus has flown a BWB technology sub-scale demonstrator in the form of its Maveric – but if it were to decide on a hydrogen-powered blended wing airliner, will a larger piloted X-plane be needed?

A holistic approach will be necessary, not only continuing incremental developments to the airframe design, featuring more advanced materials and improving the engine, but also challenging all development steps with an unprecedented level of global integration. This could be the case for applying advanced engine cycles including variable pitch blades, some appropriate level of electrical hybridisation, optimised combustion processes, sophisticated gust and manoeuvre loads alleviation systems, changing over to a natural or hybrid laminar flow design, entering a completely new configuration featuring reduced flight mechanic stability and providing the necessary fuel volume for hydrogen fuel (if applicable), to name but a few. Propulsion and engine/airframe integration will of course play a major role. Only by applying breakthrough technologies, daring to deviate from what we know and have achieved so far and ‘thinking out of the box’, can an aircraft be created that features very low emissions and meets the environmental goals set for the middle of this century.

How can such a ‘revolutionary’ aircraft be developed?

Safety is paramount in aviation. No aircraft developer or operator can accept undue risks in order to achieve higher performance or greatly reduced emissions. Risk assessment and risk mitigation are essential when developing a new aircraft. Thus, a technology for which the risk of failure is considered to be too high will not be applied to a new product. Due to these facts, aviation is sometimes considered to be ‘conservative’ compared to other ‘avant-garde’ businesses.

The BAC 221 was a sub-scale but piloted demonstrator to de-risk Concorde’s wing. RAeS/NAL

However, this time the typical ‘conservative’ approach will not result in the needed ‘step change’. So what is the solution? The only way the aviation industry can dare to make this ‘step change’ is by maturing and validating new technologies thoroughly enough before applying/ integrating them into a brand new aircraft that meets both market expectations and environmental needs. In aviation, development programmes are common in research activities that assess, further mature and validate technologies. However, these are individual technologies that – especially if publicly supported – do not go beyond a technology readiness level of 6. Past experience shows that the demonstration needs to go well beyond TRL 6 and new technologies have to be tested and proven in an integrated manner in order to mitigate the risks.

These steps, up to the appropriate levels of progressive integration (eg engine-level demonstrator, flight controls demonstrator, etc.) are necessary. But if a whole bunch of new technologies needs to be validated in an integrated way, in addition to partial conventional validations such as analyses or partial testbeds, the only solution will be a global flying technology demonstrator, which would raise the chances for subsequent application in a new aircraft programme meeting environmental needs, market expectations and competitiveness goals, while mitigating risks. Concerning large civil transport aircraft this has, so far, not been the approach of the aircraft manufacturers (neither in Europe nor in the US). For Airbus, this would be a real paradigm change. 

Why an airborne technology demonstrator?

Partial flying and ground-based demonstrators can be sufficient for sets of technologies applied to one equipment (including the engine) but not for the significant step changes required for a ‘green’ aircraft, for which an unprecedented level of integration is expected, whatever the still-to-be-made technological choices. If we want to achieve this in the envisaged timeframe, a flying technology demonstrator is a must, capable of integrating all essential, interacting technologies.

A large enough ambition for the demonstrator will therefore require the experience and know-how currently at risk and motivate the next generation of young engineers demanding step-change solutions.

Of course, it is up to the aircraft manufacturer and its partners to define the demonstrator and the technologies that will need to be incorporated, bearing in mind that the future product will have to meet both market requirements and environmental demands. However, in order to achieve maximum risk mitigation and the best chance of application, the technology demonstrator should be close enough to this future product in terms of size, configuration and critical technologies (including the airframe/engine integration).

The Airbus/Rolls-Royce E-Fan X hybrid-electric technology demonstrator was cancelled in 2020 before it even took flight. Airbus

How to define the technology demonstrator

The definition of the flying technology demonstrator needs to combine a ‘top-down’ with a ‘bottom-up’ approach. The airframe and engine manufacturers that need to meet both market and environmental requirements must define the technology demonstrator in a top-down way – derived from the requirements – in terms of configuration and technologies to be integrated. This includes a roadmap setting the need date and required maturity level for individual technologies and for each step of integration as well. It is then up to the major manufacturers, internally, but also the supply chain members (including system suppliers) and research establishments (RE), to work on these technologies (up to the concept of pre-industrial modular demonstrators) within publicly supported research programmes and up to the engine manufacturers for integration first into the engine and then into the airframe. In addition bottom-up proposals of suitable technologies will come from REs, the supply chain, the systems companies and engine manufacturers – the latter will be very important since propulsion will very likely contribute significantly to emissions reduction itself (hydrogen use is a big challenge in particular) and optimal integration into the airframe will be challenging but a key success factor.

Concerning timely availability of the technology demonstrators, the integrated in-flight demonstrator and their results, it will be mandatory to properly orchestrate the various technology development activities of the different players, independently of the funding sources, whether Clean Sky, national or even regional research programmes, as long as those activities are focused on stepwise demonstration and later application in a new large civil transport aircraft. An adequate management organisation needs to be set up.

With these properly managed approaches on technology solutions demonstrators and the integrated flying demonstrator, risks and development timing will be reduced for both.

At the airframe side the definition phase of the demonstrator will mainly draw on architectural and integration skills, whereas in the demonstrator development phase the complete spectrum of engineering skills, be it non-specific and specific design work (at the aircraft and engine manufacturers, the supply chain, REs and universities) will be needed.

No less important is the need for a ‘living’ research network driven by the requirement to elaborate concrete applications with the necessary pressure from industry. Academics have a big role to play, particularly in establishing/validating radical new solutions as yet unknown. Theoretical studies at academic level with subsequent studies and testing at the level of the research establishments (such as the DLR in Germany, INTA in Spain, ONERA in France and ATI in UK). The academics’ role is broad: from educational aspects to solution-finding. Their survival at the top world level depends on regularly launching new challenging programmes, essentially in Europe.

Costs, timeframe and financing of a flying technology demonstrator

There will be two cost elements of a flying technology demonstrator: The demonstrator itself (developing, building and flying/testing, analysis of results) and the development and validation of sets of technologies that will be integrated in the demonstrator – provided they are suitable for integration and matured enough to ensure reliable and safe operations of the demonstrator.

THIS PROGRAMME – WITH THE NECESSARY STEPS – NEEDS TO BE LAUNCHED SHORTLY IN ORDER TO DELIVER RESULTS BY THE END OF THE PRESENT DECADE

Depending on the size and the closeness to future product configuration, the flying demonstrator will be at a cost level of €4-5bn (including the definition phase), and will take six to eight years to be developed and tested. The pre-definition phase at the start of the programme, resulting in a suitable configuration of the demonstrator and a ‘top-down’ established list of required technologies, will take some two years. Overlapping with the pre-definition phase and continuing over another three to four years, the detail technologies will be developed and validated already with some level of integration (eg engine) (up to TRL 6) in the course of various research programmes (Clean Sky 3/Clean Aviation, national research programmes such as LuFo in Germany, CORAC in France and ATI in the UK) and even regional research programmes), as long as they are on the short list of the demonstrator programme and aiming at a ‘green’ or ‘climate neutral’ commercial transport aircraft. Additional funding has to be ensured within these programmes if not all needed technologies are covered.

Overall – and taking reasonable overlapping into account – the airborne technology demonstrator programme will take between eight to ten years.

Whereas the technology development research programmes can be funded in the usual way, considering the difficult financial situation due to the coronavirus crisis, the airframer, engine manufacturers, systems manufacturers and the involved suppliers will not be capable of financing the activities at the above-mentioned level in the indicated timescale. Consequently, the flying technology demonstrator will require special public funding that has to go well beyond the usual 50% public funding rate, spread over its lifetime.

Why start now?

The EU is committed to reaching the ambitious goal of significant emissions reduction in aviation by the middle of this century. In order to achieve that goal, the entry into service (EIS) of a first ‘green’ aircraft has to be in the 2030s. For that, the development of such an aircraft needs to start in the late 2020s. Taking the total programme time of eight to ten years for the demonstrator programme into account, this programme – with the necessary steps – needs to be launched shortly in order to deliver results by the end of the present decade. Thus no time should be lost in order to meet the 2050 target.

Whereas the development of technologies is quite well under way, it is mainly the four Airbus nations – France, Germany, Spain and the UK – that will have to initiate the principle of complementary and timely investment in order to finance the required flying technology demonstrator (similarly to what is done in the US). On the basis of a total cost of €5bn, the yearly contribution, over eight years, for a partner assuming a share of 35% (eg France or Germany) would be of €220m and of €125m for a share of 20% (eg for the UK).

This investment will be beneficial not just for Airbus but also for the engine manufacturers, the entire supply chain including systems companies, as well as research establishments, universities and associated testing facilities contributing to the demonstrator.

By doing so, Europe will prepare the ground for green aviation while preserving its know-how for commercial transport aircraft development, thus maintaining its global leadership.

At this stage the article authors want to stress the point that the UK contribution is being assumed as a natural follow-on from its past historical major role in the European aeronautical sector. No one should miss such an opportunity without inducing major risks for its future. 

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