OPTICOMS brings automated composites manufacture to the SAT category
The economic and weight-saving benefits of composite materials have been recognised for decades. However, making airplane structures in composites has proven in the past to usually be labour-intensive and challenging in terms of manufacturing repeatable components of reliable quality.
Investment in automating the manufacture of large composite structural components can significantly lower the costs and improve consistency. But this luxury of large scale automation is experienced mainly by the largest airframe makers with high manufacturing volumes who have had the resources and budgets to pursue automated composite production options.
That could be about to change thanks to Clean Sky's six-year OPTICOMS (Optimised Composite Structures for Small Aircraft) project, which kicked off in July 2016. Funded by the European Commission under Horizon 2020, it aims to bring innovative approaches in automated composite aircraft structure R&D to the Small Air Transport (SAT) category of aviation, enabling smaller airframe companies to justify building up automation infrastructure and realise a return on investment on low volume production.
The project’s ambitious targets include reducing composite design and certification costs by 30%; cutting composite production costs by 40%; lowering structural weight by 20% (relative to use of metals); and trimming lifecycle costs by 20%.
‘OPTICOMS is a very innovative project for the development of more affordable and optimised composites, and tries to eliminate the need for an autoclave which is an expensive and energy-consuming technology,’ says Clean Sky's project officer Sonia de la Cierva. ‘But this is not easily done at the level of the small aircraft sector.’
At the project's inception, coordinator Israel Aerospace Industries (IAI) assembled a consortium comprising three composite materials automation specialists: Coriolis, known for its Automatic Fibre Placement (AFP) technology; Techni-Modul Engineering (TME) which uses ‘robotic pick and place’, a process that applies multiple layers of composite fabric which are then infused with a glue-like resin; and Danobat, a firm which uses a composite material automation process called ADMP (Automatic Dry Material Placement).
A seven-metre long composite wing
The project is in the process of building a seven-metre long composite wing for the Piaggio Aerospace P180 in the form of an ‘integral structure.’ This means that the wing's spars, ribs and skin are simultaneously constructed in a ‘one shot’ process, leveraging the best of the three companies' respective technologies. The idea is to then compare, evaluate and down-select the options in line with the best results in terms of quality, cost, and speed of manufacture.
But the successful outcome of OPTICOMS depends not only on finding the best automated methods of applying and curing the multiple layers of composite materials. It's also about the tooling side of the project. This is facilitated by three complementary projects: FITCoW and ELADINE, both coordinated by the National Institute for Aerospace Research “Elie Carafoli” (INCAS), and WIBOND, coordinated by Metitalia.
The FITCoW project is carrying out the manufacturing tooling for the integral structure, using a novel tooling system which allows a higher rate of work to proceed at lower cost. This reduces manufacturing time, minimises material waste, and saves energy by using an ‘out of autoclave’ process. This is a method whereby the composite material and adhesive-like resin that binds the fibres is ‘cured’ without the use of an autoclave – an oven-like chamber used to ‘bake’ the composite material together.
The other supporting project, WIBOND, is focused on the assembly tooling, from the integral upper wing skin, spar and rib structure to the lower wing skin. WIBOND will produce very innovative tooling which will allow structural bonding of the lower wing skin to the already-produced integral substructure.
‘Very complex tooling is needed,’ explains Arnold Nathan, OPTICOMS coordinator and Director of R&D, Aviation Group, IAI. ‘You want the bond line to be of a consistent thickness, constant pressure and tight location tolerances, which resulted in innovative ancillary equipment such as vacuum cups, pneumatic cylinder and inflatable tools.’
Despite all these preparatory steps throughout the process, one of the lingering questions around composites is always how to ensure that the internal bonds between the elements are of appropriate integrity and dependability. Therefore, to monitor the bond-line between the skin, spars and ribs, optical fibres are embedded within the composites to enable structural health monitoring (SHM). Two years into the project, the expertise of the Italian Aerospace Research Centre (CIRA) was added to the project to develop an algorithm for the SHM.
‘With structural health monitoring using embedded fibres you're checking the signals in the fibre, and when stress, strain or deformations exist – that fibre will elongate. And then we can read the optical fibres and translate the result into stress, a strain, or distortion,’ explains Nathan.
The inclusion of SHM paves an important path towards smarter and more environmentally friendly built-in technology that facilitates future aircraft in the realm of maintenance, explains Clean Sky project officer Sonia de la Cierva: ‘Structural health monitoring is one of the key technologies for next generation aircraft. This is essential to be able to monitor the structure of the materials’ life and this allows us to anticipate wear and damages, so this implies protection of the operational limits and maintenance costs later on.’
Another aspect addressed by OPTICOMS is the tendency of large parts made out of composite material to become distorted when extracted from the tool.
‘One of the biggest fears when you manufacture a seven metre spar, or skin, or skin and spar together, is “spring in” deformation when you take it out of the tooling, due to residual stresses in the structure,’ explains IAI's Nathan. ‘It is possible that a 7m wing section can deform enough to have serious implications on the ability to ensure an effective wing skin bonding interface with the spars.’
To counteract this phenomenon, the ELADINE project was set up to evaluate the distortion of laminate composites in the manufacturing process and instigate approaches to managing deformations using scaled test coupons and numerical simulation approaches.
Currently the OPTICOMS project is heading towards the final phase, which will involve full-scale fatigue and static tests which will be carried out by Piaggio Aerospace. But to get to this point has been no easy feat, especially in pandemic times. Despite the challenges, 2020 has witnessed an impressive checklist of tangible achievements:
- The wing successfully passed its critical design review (CDR) and the full-scale 7m wing demonstrator composite lay-up has been defined.
- Four small scale demonstrators have been manufactured, inspected and assessed.
- Partner TME improved an innovative prepreg gripper and produced full scale demonstrator moulds, while Coriolis improved preforms (shaping, positioning and defects) and developed an innovative ‘raw’ dry fibre preform manufacturing process. Concurrently, Danobat worked on ADMP ‘demo cell’ improvements, and made improvements to its robotic head.
- Additionally, the manufacturing tooling and assembly tooling aspects of the project have both passed their CDRs, and skin assembly has been performed with embedded SHM fibres which have been tested on a small scale demonstrator at Piaggio.
We learned so much from the small scale demonstrators – about defects, wrinkles or ply lay-ups in low radius corners, and instead of making the mistake on a seven metre part we were able to iron out a lot of the problems in advance. An important aspect of the project has been the small scale demonstrators,’ says Nathan.
To get to this stage, the coordinator reports that the project is a case study in collaboration. ‘At the outset of the project, Coriolis, TME and Danobat were competing with different technologies, but over the course of the project competitors have pivoted to becoming collaborators,’ says Nathan. ‘There's been really excellent cooperation, friendliness and an exchange of ideas – it's a really positive environment and the project is progressing really well to get the safest, cheapest, the lowest non-recurring expenses as well as the strongest, the most repeatable, optimised structure.’
This view is mirrored by Clean Sky's de la Cierva, who reports that although the final outcomes of OPTICOMS won't be known until the end of 2021, the project has already proven to be ‘a very good example of how the different partners collaborate with each other.’ She says that the interaction between the various stakeholders and establishment of synergies between IAI, Piaggio, CIRA, Danobat, Coriolis, TME and the three complementary projects has been exemplary: ‘It's due to IAI's excellent coordination skills. They are doing a great job in keeping all the targets aligned and the objectives met and are also keeping a very good relationship between the different members. Thanks to the CS2 programme, OPTICOMS and the three complementary projects are bringing together the expertise and know-how of 15 entities, half of them SMEs, based in 5 different countries. It constitutes a great opportunity to strengthen the productivity and innovation capacity of the European industrial network.’