The subject of this call for proposal was support for the development of a number of small scale Feature Demonstrators that enabled down selection of concepts towards a final Integrated Ground Based Demonstrator of the LE region of a Natural Flow Wing. GKN Aerospace, the world's No.1 independent supplier of composite aircraft structures, would welcome the opportunity to collaborate with Airbus, Saab and Aernova in the development of the next generation of wing technologies through the Smart Fixed Wing Programme. The GKN Aerospace Composite Research Centre, a state-of the-art research facility located on the Isle of Wight in the UK, and member of the National Composites Network of the UK, co-ordinated this bid, managed the structural aspect of the programme and worked with partner company, GKN Aerospace Luton, who managed the WIPS aspect of the programme. GKN conducted a trade study that investigated several LOF and ALOF joint concepts for composite LE panels as well as WIPS for metal or CFRP LE components.
Following the trade study, a review and down select of concepts to be manufactured as small scale Feature Demonstrators happened in conjunction with outputs from the Airbus Preliminary Design Review of the Short Range Aircraft concept. An assembled test rig was constructed and the small scale demonstrators subject to testing and evaluation. A final report identified the test outputs against the target requirements delivered at the conclusion of this programme. After the successful conclusion of this bid, GKN Aerospace continued to work in this area as the Natural Laminar Flow Wing was recognised as a potential key technology for the next generation of aircrafts. The UK National Aerospace Technology Strategy (NATS) also identified the Laminar Flow Wing Box Validation Programme therefore giving further opportunities for collaboration in the future.
The following conclusions were reached:
- Top cover attachment: A joggled joint configuration is a viable configuration for the top cover to LE assembly. Joggle spring has been found to occur, but it is considered that this can be compensated in the mould tooling design.
- Metallic LE: The control of the machining or rolling of aluminium LE thickness has been shown to adequately achieve natural laminar flow (NLF) tolerances. If a metallic LE is adopted for GBSSD phase two it is recommended that this joggled mechanical solution is used. A method for post assembly machining or filling of the fasteners heads will need to be fully investigated.
- Composite LE: Two concepts applicable to a composite LE have been shown to completely eliminate any concern regarding step tolerances and fastener head disruption. It is recommended that both concepts are further developed during GBSSD phase two if a composite LE solution is adopted. The post assembly machining concept may be suitable for integration with the erosion shield / protection integration, eliminating the necessary fasteners and ensuring a NLF LE.
- WIPS: Four electrothermal heater mat integration options were examined, namely: bonded to the internal surface of a metallic LE; bonded to the outside surface of a metallic skin; bonded to the outside surface of a composite skin; fastened to the external surface. The relative merits of these systems, in terms of thermal integration, aerodynamic compliance, manufacturability, and maintenance and repair have been summarised.