Dr. Björn Nagel is the director of the Institute of System Architectures in Aeronautics at the German Aerospace Center (DLR).
EASN: The realisation of hydrogen in aviation turns out to require more time than anticipated and SAF appears to be the easier way forwards to sustainable aviation. What is your take on that?
Björn Nagel: Both, the use of hydrogen or the use of Sustainable Aviation Fuels (SAF) in aviation can lead to an almost complete reduction of its climate impact. SAF can be produced using Biomass to Liquid procedures (BtL). However, the availability of biomass is limited, especially with view to the promotion of sustainable agriculture and general efforts to avoid waste. Therefore, in the medium to long term, SAF is likely to be largely of the Power to Liquid (PtL) type.
The production and distribution of PtL is significantly more energy intensive than that of liquid hydrogen (LH2). There are many uncertainties in predicting the future energy supply, but the energy required to produce and to distribute PtL in a global energy system could be in the ballpark of 50% higher than the one required forLH2.
A paramount challenge is imposed by the energy transition of mankind and by providing renewable energy, not only for aviation. There is an urgent need to ramp up the SAF production for the legacy fleet and future aircraft, in order to meet the target of climate-compatible aviation by 2050. But if we can master the technologies to introduce hydrogen into aviation in an economically viable way, we can significantly reduce aviation’s energy demand.
EASN: Increasing competitiveness is the emerging target in Europe. How does this relate to research on hydrogen?
Björn Nagel: Energy demand in flight plays a crucial role when looking at competitiveness, as do topics such as cost-efficient manufacturing and supply chains, as well as maintenance, repair and overhaul (MRO). Digitalization, automation and the seamless use of data offer great potential for probably all aircraft technologies. However, in order for these to unfold, aircraft need to be specifically constructed e.g. for future factories using Industry 4.0 technologies. This is an aerospace revolution in itself.
These technologies can also mitigate the specific challenges of cryogenic LH2 and can substantially enhance the economic performance of LH2 aircraft, which are expected to produce similar Direct Operating Costs (DOC)to those aircraft operated with PtL. Consequently, the resulting costs for the passengers and the airlines’ revenues should not differ significantly from one aircraft concept to the other. Yet there is one strategically important difference: The energy carrier PtL is more energy intense in production and hence more expensive than LH2. On the other hand, LH2 aircraft are more complex, heavy and expensive. Thus, LH2 offers a significantly greater revenue potential for airframers, suppliers and MRO providers than SAF.
Furthermore, a technological step-change like LH2 is hard for competitors to catch up with. Here, in particular China’s ambitious developments towards LH2 aviation are worth observing. Right now, Europe is leading the development. But there is a risk that hydrogen aviation could follow the same market trajectory as electric cars.
EASN: So, we need to consider both sustainability and competitiveness in the design of new aircraft, in the same time comply with an emerging number of certification rules and we need to be fast. How can we approach this?
Björn Nagel: There are great digital engineering methods available such as Model Based Systems Engineering (MBSE) and Multidisciplinary Design Optimization (MDO) that allow multiple targets and constraints to be considered when optimizing the product architecture and characteristics. However, while several tools are commercially available at a high level of maturity, there is little experience available of how to apply them to complex use cases. This is even more critical when many individual engineers working in different companies across the supply chain need to collaborate – and are likely to be using software from different vendors. Interfaces are the key to realizing the digital thread.
Knowledge Based Engineering (KBE) and Artificial Intelligence (AI) techniques are available but need to be deployed properly to support the rapid generation of detailed digital twins. In my view, it is of utmost importance to unleash the potential of widely available software to master complexity and accelerate time to market in a way that puts the human instead of algorithms in the driver’s seat, able to comprehend and interpret the results and who take responsibility for decisions.
A deep understanding is necessary to successfully apply MDO in digital engineering. How can we achieve the same level of understanding for e.g. large language models? Educating new engineers to work collaboratively in such future digital engineering environments is a key investment.
EASN: Is there a new role for academia and research?
Björn Nagel: In order to achieve the sustainability and competitiveness goals, we need to consider revolutionary technologies that are not simply substitutes within the aviation system as we know it, but that require new optimized architectures of aviation. There is no single industrial stakeholder that covers aviation in its entirety - from the supply of green energy, to the design and operations of aircraft and their impact on the climate. Joining forces across research and academia can thus play an important role in identifying the most promising technology pathways.
In particular large-scale research centres in collaboration with academia have many different competences at disposal and hence are predestined to develop processes for using smart design software in large-scale digital engineering campaigns. A strength of academic research on digital engineering processes but also on the future of aviation is the lack of bias in terms of organizational structures, products and supply chains.
Scientific societies, in particular the European Aerospace Science Network (EASN) and the International Council of the Aeronautical Sciences (ICAS), should actively engage not only in knowledge-sharing but also in providing a network for collaboration to address these emerging system-level research questions. The well-established exchange of validated results at congresses remains important. But we also need to foster forums for dialogue where we share our thoughts on the problems we have not yet solved. This is the inspiration and motivation for our next collaborative research initiatives.