We Need More Than Just Lightweight Design | Exploring Circular Aviation with NLR

Rising to the challenge of reducing aviation’s environmental impacts while remaining economically viable is naturally a complicated task, filled with potential paradoxes and pitfalls. It’s also, however, the core challenge facing the SUSTAINair project on its quest for circular aviation.

Decreasing the weight of aircraft in the name of reducing emissions might sound like a simple win for the environment – but what if lighter aircraft prove difficult to reuse? What if we inadvertently promote a shift towards wasteful ‘single use’ aircraft rather than pushing the dream of nimble, modular, and above all ‘circular’ aircraft designs.

Ligeia Paletti is an expert on structural engineering and circular economy in aviation and innovation at the Royal Netherlands Aerospace Centre, a key technical partners on the SUSTAINair project. With years of aeronautical engineering experience and a specific focus on the topic of sustainability, she’s very well-positioned to discuss how we should address some of the possible conflicting outcomes in the battle to bring circular design to aviation.

Circular Aviation Trends in Engineering

Current trends have been seeing airframe structures move towards increased levels of integration, i.e., being manufactured as one large frame rather than being assembled from a variety of constituent components. “Now of course this is beneficial in terms of saving both manufacturing costs, and the weight of joining elements (fasteners, bolts) – and also in terms of having one part carrying out multiple functions (like structural batteries),” explains Paletti. “But this could limit the possibilities to replace or repair smaller parts of such integrated part, in case of damage or failure. It is like the example of certain mobile phone batteries being glued to the frame of the product: in that way, the battery itself contributes to the structural need of the product, but then when anything happens to the battery, it cannot be replaced easily and the entire product needs to be disposed of. And once the product is disposed, it is also not easy to disassemble it or dismantle it for recycling.”

Ligeia Paletti​ © NLR

Putting more ‘circular’ design methods into practice for aviation would inherently rely on repairs, maintenance, and disassembly to be not only the norm, but even worked into designs themselves. An emphasis would be placed on the possibility to replace components and reassemble aircraft from various joined components rather than lighter, yet less repairable, single frames. Paletti assures us that maintenance and repairs can be performed on certain integrated structures – such as in the case of repairs made to structures built from composites – but it can be complicated and time- (and energy-) consuming task, with some further development still required to be considered truly viable.

."When it comes to design, being lightweight isn’t necessarily synonymous with sustainability."
Ligeia Paletti, NLR
SUSTAINair presenting at the RTDS EU Green Week Event The Market-driven Circular & Bioeconomy in June 2021 towards zero pollution and zero waste
Circular Aviation Diagram © SUSTAINair 2022

“Just thinking of lightweight design may not be enough,” says Paletti. When it comes to design, being lightweight isn’t necessarily synonymous with sustainability. It means using less material and thus generating fewer emissions, yes, but this is all only during the ‘use-phase’. As Paletti questions, “what if the material extraction causes a high impact at mining? Or during material production? Steel production, for example, is highly polluting. What if the lightweight material comes from a conflict country? Or is extracted by child labour? What about using additive manufacturing, which is a high energy process? And lastly, what about end-of-life? What if the material cannot be recycled or, even worse scenario, it releases hazardous substances when landfilled or burned?” While LCA (Life-Cycle Assessment) can offer some answers as to the level of circularity we can attribute to an aircraft, it’s still not quite enough to give us the full picture. “The results of LCA and Circularity indicators need to be included in design and optimisation tools,” suggests Paletti.

Aviation's Supply Chain: A Holistic Overview

While eliminating in-flight emissions is paramount, it’s important to ensure the problem is not simply displaced somewhere else, and in ways which will be difficult to solve later on. SUSTAINair will form a vital step in the development of truly holistic LCA in aircraft production that will monitor all phases of the lifecycle for aircraft components and bring as many elements as possible into a circular economy. For example, it is clearer than ever before how much the energy transition is going to rely on critical raw materials (CRMs). “Such materials are of limited availability in a high-risk supply chain, and demanded by other sectors, some more essential than aviation,” explains Paletti. “What if a government needs to decide to use 1kg of nickel for building batteries for aircraft or for domestic heating? Designing the energy transition of aviation by including the recovery of CRMs and by retaining them in the aviation industry may become an essential design requirement sooner than expected.”

"Circularity indicators need to be included in design and optimisation tools."
Ligeia Paletti, NLR

So how would Ms. Paletti advise we address this at scale, across the entire aviation industry? “A good way forward from which the aviation sector could learn is the EU directive on end-of-life vehicles applied to the automotive sector. In that EU directive, the focus is on recycling and reuse. For aviation I would change it to reuse and remanufacturing respectively.”

One key bit of supporting legislation will be the EU’s Critical Raw Materials Act due to get adopted this year. Even so, there’s some visionary reassessment to be done with how we think about the entire aeronautical manufacturing supply chain, and the ways in which we not only integrate everything into a “self-reliant supply chain” as Paletti puts it, but how we integrate this thinking at the design stage specifically. Solutions are needed for both future designs, and currently existing components – all of which could be flying in the aircraft of tomorrow. In this sense, Paletti aptly summarises the knowledge with which projects like SUSTAINair are aiming to provide us: “we need to know how recycled materials behave”.

Find out more about NLR's research with SUSTAINair

The Royal Netherlands Aerospace Centre (NLR) is the independent knowledge enterprise in the Dutch aerospace sector. Its multidisciplinary approach covers the whole RDT&E (Research Development Test & Evaluation) range, and it focuses on developing new and cost-effective technologies for aviation and space.

Leave a Reply

Your email address will not be published. Required fields are marked *