Aircraft manufacturers have been gradually introducing composite materials in their structures. If it has been limited mainly to secondary structure for quite a long time (moving surfaces, body-fairings, …), it appears that composite starts to be heavily implemented into primary structures.
For fuselage structures, research projects such as APRICOS (a European founded project) show that composite technologies can be implemented to improve the performance of the structure (weight reduction). However the cost increases as well, for a similar architecture, due to more expensive materials and assembly procedures (drilling, bolts, lightning strike protection of joints, etc…). One of the APRICOS conclusions was that a reduction of composite manufacturing cost can only be achieved through higher integration leading to a dramatic reduction of number of parts and of assembly steps.
The primary objective of this project was to develop the fibre placement technology which could lead to this required integration thanks to its capability to lay-up typical shapes of fuselage section in all directions and to adapt to non developable surface. The targeted applications for this solutions were reasonably small fuselage sections (pressurised or non pressurised) for business-jets, commuters or tilt-rotor aircraft.
This objective was pursued through the design, manufacture and validation by mechanical test, of a highly integrated forward fuselage section. Geometry and loads of a typical business jet have been used as a reference. This fuselage section included the following key elements: front and rear pressure bulkheads, windshieldframe, window, doorframe and door. The objective of innovative design to achieve highly integrated composite structure has been applied to the major components assembled to the barrel.
Other key objectives of the project were:
- to design and validate affordable large complex composite tool
- to develop in-process monitoring and visualisation techniques and integrate these with the fibre placement machine
- Forward fuselage reference for barrel definition
- General design of barrel
- Detailed design of barrel
- Feasibilities trials and fuselage manufacture
- Design and manufacture of windshieldframe
- Design and manufacture of pressure bulkheads
- Test of composite barrel
Through a planned series of laminate and element trials, the manufacturing methodology to produce a 4.5 metre fully integrated fuselage component by fibre placement was developed within the programme. The majority of processing difficulties experienced within the fuselage manufacturing tasks revolved around the control of the OML surface quality to an acceptable standard and further work would be recommended in this area to develop a production solution for the approach adopted. The fibre placement deposition achieved during part manufacture was as predicted, but it would be anticipated that the make-span be significantly reduced through further optimisation and productionisation. The cured geometry of the fuselage fell within the defined assembly tolerances, which in turn facilitated an efficient assembly process.