Fantastic thermoplastics

Suspended between discrete skeletal jigs, it wouldn't attract a second glance on an aircraft assembly line. Yet inside an anonymous hangar in northern Germany, a matt-black fuselage section – or barrel, in the jargon – could be the super-efficient shape of things to come.

Clean Sky 2 is an ambitious, EU-backed public-private partnership, whose overarching goal is to help reduce aircraft CO₂, nitrous oxides and noise emissions by up to 30% in line with the European Green Deal. The Deal’s stated aim is to make the EU climate-neutral by 2050. 

Launched in 2014 and falling under Clean Sky 2’s Large Passenger Aircraft platform, that black barrel is the Multifunctional Fuselage Demonstrator (MFFD). Eight metres long and four metres wide, it’s made largely from thermoplastic composites. By examining these polymers’ viability as a structural material, the MFFD has effectively become a springboard for accelerating aircraft production, thereby improving European aerospace’s competitiveness.

Lighter, faster fuselages

A fuselage doesn't just contain passengers and cargo. It carries vital electrical, mechanical, pneumatic and hydraulic systems too. Fitting the systems once the fuselage is complete adds cost and time to production. The systems are also heavy. A lighter, simpler-to-produce fuselage helps counter these penalties.

Thermoplastics can enable this, largely since the weighty fasteners that join conventional metallic fuselage sections together are either no longer needed or the number needed is far lower.

Also known as carbon fibre-reinforced thermoplastic polymer composites (CFRTP, admittedly a mouthful), thermoplastics are moldable at high temperatures. They then solidify on cooling. Their introduction could lead to a structural weight saving of over 10% per aircraft if a typical fuselage section is combined intelligently with cabin and cargo technologies. 

CFRTP composites also offer a more immediate advantage: they are simpler to reuse and recycle than metallic or  carbon fibre components.

Pre-equipped modules

Back to our hangar. The MFFD consists of two half-cylinder shells, or modules, which make up the fuselage barrel. The lower module is pre-equipped with systems and cabling; the upper with some cabin monuments. 

In pure production terms, thermoplastics enable these modules to be assembled using novel methods, each tested on the MFFD. For example, its shells are joined by automated ultrasonic or laser spot-welding, rather than riveted together. This creates a relatively dust-free environment for assembly workers. The floor of the lower fuselage model is then fixed into place by automated conduction welding.

By the project’s conclusion in late 2024, the MFFD had actually overachieved its weight-saving target, at neutral cost compared to a metallic fuselage barrel. Over 40 technology ‘bricks’ had been tested to a high level of readiness, from small-scale micromechanics (the study of composite behaviour) to novel jigs, tools and, as mentioned, advanced welding techniques.

MFFD's disruptive methods could enable a CFRTP composite fuselage build rate of up to 100 units per month, which is the target zone for a future single-aisle aircraft. Besides the economic benefits, the novel fuselage’s advanced architecture, lower weight and greater manufacturing efficiency would contribute to lower lifecycle emissions, in line with Clean Sky 2’s objectives. 

A European success story

Since completion, the demonstrator has resided at the ZAL Centre of Applied Aeronautical Research in Hamburg. It was actually assembled at the Fraunhofer Institute near Stade. Airbus has extensive facilities in both German cities.

The MFFD’s innovations are a wholly European success story. Airbus is one of 13 major partners that made up the consortium, including SAAB, GKN Fokker, the German aerospace lab DLR, the Delft University of Technology, as well as a network of subcontractors. 

“The MFFD is a fantastic example of what can be achieved if academia, research centres and industry players align around a common objective,” says Airbus’ York Roth, leader of the Clean Sky 2 Large Passenger Aircraft platform. “One player alone would never have been able to deliver such a complex large-scale demonstrator.”