Clean Sky 2’s OUTCOME Project demonstrates suitability of PEEK in a safety-critical aircraft structure
OUTCOME has tested and validated the successful use of PEEK thermoplastic in a wingbox – the project represents a boost for energy efficiency in European manufacturing
Use of PEEK thermoplastic material, instead of traditional thermoset, simplifies processing while delivering weight savings which lead to lighter aircraft and reduced fuel-burn
The produced wingbox cover can be recycled at the end of its service life, saving valuable resources and demonstrating European commitment to the circular economy
Clean Sky 2’s OUTCOME project (European Union) announced that it has devised a sustainable manufacturing process for producing a 4m x 1m thermoplastic-stiffened upper skin for the external wingbox (wingbox cover) of a regional/utility (Airbus C-295) aircraft. The project feeds into Clean Sky 2’s Airframe ITD D1-4/6 demonstrator, an advanced composites wingbox (the central structure of an aircraft that connects the wings with the main body/fuselage).
The main premise of Clean Sky 2’s OUTCOME, a consortium of Airbus, FIDAMC(Spain’s Centre of Excellence for research, development and innovation in composites material technologies) and Aernnove (aerostructures design and manufacturing specialists ) was to switch from using thermosetting plastic (1), which requires processing in an autoclave (2) (a high-energy consuming type of industrial oven) to the use of thermoplastics, using an energy-efficient ‘out-of-autoclave’ ‘one-shot process’. This is a production method where sequential production steps are integrated into a unified process involving ‘lamination and consolidation’, a method of combining different parts (in this case the wingbox cover ‘skin’ and reinforcing stiffening structures called stringers (3). This saves time and energy resources – an environmental win. The project aligns with the aeronautics sector’s shift to thermoplastics which are lighter than their metal counterparts.
Recyclability potential
Another key environmental driver of OUTCOME was that “Thermoplastic materials are reversible, and manufactured parts can be reconsolidated, thus reducing the number of non-quality parts that could not be used in a real demonstrator,” explains Mar Zuazo Ruíz, R&D composites specialist at FIDAMC, and project coordinator of OUTCOME. This ‘reversibility’ means that at the end of the component’s operational service life, the material can be recycled for use in future products.
An additional advantage thermoplastics offer is their environmental value in terms of reducing potential contamination. Rubén Tejarina Hernanz, Airframe R&T Manager for Integration at Airbus Defense and Space (ADS), the Topic Manager for OUTCOME, explains the background: ADS has been involved in this technology since around 2010 when we saw that thermoplastics could be an alternative to the thermosets for use on primary and secondary structures. We saw their sustainability potential in addressing not just recyclability of materials but to also help us meet EU REACH (4) contamination regulations.
Around 2007 FIDAMC had also initiated projects using thermoplastics. These mutual interests converged through Clean Sky activities which Airbus, as Airframe ITD demo co-project leader, proposed, launching a call for core partners to explore the potential of thermoplastic technologies. At that point, FIDAMC, along with Aernnova, formed the OUTCOME consortium.
A key sustainability enabler underpinning the project was the consortium’s decision to use a thermoplastic called Polyetheretherketone (PEEK) – a material which matches the performance properties of thermosets, even surpassing them in terms of ageing and damage tolerance, while bringing valuable weight savings. PEEK made it possible to reinforce the wingbox cover using stringers without the need for fasteners (bolts or rivets) which would have added weight and complexity.