The next generation Multifunctional Fuselage Demonstrator — leveraging thermoplastics for cleaner skies

In order to leverage the full potential of thermoplastic composites in aviation, the Next Generation Multifunctional Fuselage Demonstration (MFFD) project is progressing towards the integration of innovative Clean Sky technologies which will help to enable the future of European airliner production to become faster, greener, and more competitive. With greater integration between fuselage, systems, cargo and cabin elements at an earlier design stage using a holistic and modular approach, Europe's aircraft assembly lines will be better placed to respond to the 5% growth rate of the global air transport market.

"Modularity, integration and creating common platforms are key" says Ralf Herrmann, Airframe Research & Technology Typical Fuselage at Airbus Operations GmbH. "We've known for a long time that the benefits of weight reduction and the lowering of recurring costs in aircraft production — when using thermoplastic composites — can only be achieved by the integration of several disciplines. This means that focusing on the structure alone cannot achieve the full benefit of composite technology, we need to collaborate from the start on several levels with systems experts and cabin experts, and we need to apply new disruptive ideas and integrate them across the functions. Doing so will enable us to really leverage the opportunities of these several disciplines into one combined technology".

The MFFD project — which seeks to validate high potential combinations of airframe structures, cabin, cargo and system elements using composite thermoplastics, innovative design principles and advanced system architecture in combination with the next generation cabin — has a formidable checklist of quantifiable goals: 

It aims to enable production rates of at least 60 large passenger aircraft per month, while reducing fuselage weight by 1 ton with a reduction of recurring costs. This in turn would bring significant fuel-burn reductions — and therefore reduction in the CO2 and NOx footprint — by substantially reducing the overall aircraft energy consumption due to lower weight systems and improved system architecture integration. Underpinning all this is the application of Industry 4.0 opportunities including design for manufacturing and automation, sensorization, and data analysis to demonstrate desired manufacturing cost effects.

Led by Airbus and incorporating the expertise of Fokker GKN, DLR, TU Delft, NLR, Fraunhofer-Gesellschaft and other partners, the project runs until 2023 with one of the major 'deliverables' being a thermoplastic composite 8 metre long fuselage barrel that will be manufactured by 2022. This ground demonstrator will be supported by various smaller test rigs and component demonstrators in the preparatory phase of the program, aiming to reach TRL 6 in respect of new materials, manufacturing and assembly concepts. 

Pivotal to the project's success is the extent to which composite thermoplastics can be demonstrated to be appropriate for unifying the functionality of systems, cabin and fuselage.

"Fibre composites are very flexible for contour design and shaping and so on. What we’re doing now in terms of processing is evaluating thermoplastics which are easy to model by pressing or stamping using high-production processes that are already employed in the automotive and metallic industries" says Herrmann. "We have been reshaping flat sheets of material into more complex shaped parts using a kind of casting injection moulding. We have complex moulds where the thermoplastic material together with the fibres is injected in so that we can produce really intricate parts, particularly brackets and other types of components that connect the fuselage structure with the systems and the cabin monuments. And we can do this with very low manufacturing costs".

Saving weight and simplifying the aircraft assembly and installation processes is only part of the story — there are compelling environmental benefits too, says Herrmann: 

"Beyond optimising the weight savings, the production processes we're developing are less time consuming which means using less energy, and these efficiencies will eventually translate into CO2 and NOx reductions. Another important aspect is that by using thermoplastic material, components at the end of their service life can be recycled".

The versatility of thermoplastics needs to be applied in combination with a design approach, according to Paolo Trinchieri, Project Officer at Clean Sky: "It is necessary to remove the artificial separation of functions at the aircraft pre-design stage and to plan for a high production rate of aircraft manufacturing, assembly and installation right at the start. It is not only a question of the thermoplastic materials but also a question of how to design systems that are more efficient in order to increase the rate of aircraft, reduce cost and lower the aircraft weight. This is one of the key factors of the Multifunctional Fuselage Demonstrator project — to devise new solutions to design the fuselage structure and to integrate the systems and the cabin elements in a better way". 

The project is also strategically important for European aeronautical manufacture. To keep pace with the growth rate of air travel — currently at around five percent — airframers need to ramp up production levels. But current methods of aircraft manufacture involve a sequential approach whereby the fuselage needs to be at an advanced state of completion before systems and, subsequently, cabin and cargo features can be installed. That's where Clean Sky's MFFD project is a gamechanger:

"The sequential approach to manufacture is time consuming and 'failure sensitive' and for this reason we really want to have pre-equipped structural elements and system modules that are highly integrated which can be installed into the structure quite early, before the final assembly has taken place" explains Herrmann. 

"By having greater integration of structure, systems and interior elements too it becomes viable to reduce the amount of successive steps. Using new thermoplastic joining technologies that enable moulded elements to be combined into larger components is also part of the plan. What we are doing now is investigating and testing the joining, by use of welding, of larger thermoplastic structures, leading up to the production of a full fuselage barrel. Thermoplastics are a more expensive material than what is currently used for structures and their connecting brackets and anchor points, but due to the fact that we can automate and be more efficient we can reduce the overall manufacturing costs as well as the recurring costs" says Herrmann. "Airframers outside Europe are also looking at similar opportunities, but if we are successful this will be a big step forward for European aeronautics". 

This is quite novel in aeronautics. The project is now working towards generating and progressing the 'techno-bricks' and 'design allowables' that are applicable to the welding of large composite thermoplastic structures, to ensure that welded thermoplastics on this unprecedented scale can bear the loads over the duration of an airframe's service life. In terms of process and parameters, it's a question of adapting what is already known regarding smaller thermoplastics parts and seeing what is required to scale up to make it possible to manufacture big fuselage parts. The plan is to start production of the actual fuselage barrel in 2020, having the first big components ready in 2021 and to have the final barrel ready by the end of 2022. 

What this potentially means for the aircraft's operators is that with a more modular form of design it will be possible to adapt and modify the cabin interiors if airlines wish to change the cabin elements such as new monuments, seating, cabin partitions, galleys and so on, during the course of the aircraft's lifespan. Cabin interior upgrades are essential for airline branding and inflight passenger experience differentiation, and a thermoplastic fuselage could be designed with integrated anchor points that would make future cabin furnishing changes easier to implement.

"We are doing coupon testing and small component testing currently together with our partners and exploring the possibilities of how we use welding of large structural elements to reduce the overall weight and promote flexibility to the operators for reconfiguring the cabins in the future" concludes Herrmann. "For Europe this could be a stand-alone capability in terms of competition. Clean Sky has been, and continues to be, essential in bringing together all the partners in this project. Although we are sometimes competitors in other projects, this particular Clean Sky project demonstrates the power of collaboration and its value for the future of European aeronautics".

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