복합소재 기체 구조

Overview

Composite airframe structures represent one of the most significant shifts in aerospace manufacturing since the transition from wood to metal. A composite airframe uses layers of carbon-fiber reinforced polymer (CFRP) — woven carbon fiber embedded in an epoxy resin matrix — instead of traditional aluminum alloys. The resulting material is both lighter and stronger than the metals it replaces, enabling aircraft designers to achieve payload and range targets that would be impossible with conventional construction.

The Boeing 787 Dreamliner and Airbus A350 XWB are the defining examples of composite airframe design, with approximately 50% and 53% of their structural weight comprised of CFRP, respectively. For both programmes, the shift to composites delivered a roughly 20% reduction in operating empty weight compared with an equivalent aluminium design, translating directly into lower fuel burn, reduced emissions, and better economics for operators.

How It Works

CFRP components are manufactured by laying up pre-impregnated carbon-fiber sheets (prepreg) in precise orientations inside temperature-controlled autoclaves. The fibers in each ply are oriented to carry the specific loads expected in that structural zone — spanwise for bending loads in wings, circumferential and axial for pressure and bending loads in the fuselage. Automated fiber placement (AFP) machines lay thousands of tows with sub-millimeter accuracy, replacing the labor-intensive hand-layup used in early composite structures.

One of the landmark innovations on the 787 was the construction of the fuselage as large barrel sections — up to 24 feet in diameter — manufactured in a single continuous piece. This eliminated tens of thousands of fasteners and splice joints required by aluminum panel construction, reducing weight and potential leak paths. The A350 uses a similar large-panel approach, with each fuselage shell spanning the full length of a section.

Key Components

• Fuselage barrels: Major structural sections forming the pressure vessel, manufactured as single large-diameter CFRP cylinders.
• Wing skins and spars: Primary load-carrying elements that resist bending, torsion, and internal fuel pressure.
• Frames and stringers: Internal stiffening members that distribute concentrated loads and maintain cross-sectional shape.
• Floor beams: Composite cross-members supporting cabin floor panels and transferring passenger loads to the fuselage.
• Fairings and access panels: Secondary structure using lighter woven or braided composite forms.
• Automated fiber placement tooling: Large mandrels and AFP machines used during manufacture.

Aircraft Applications

The Boeing 787 family introduced composite fuselage barrels to commercial aviation at scale, with the mid-body section produced by Alenia (now Leonardo) in Italy and forward fuselage by Spirit AeroSystems in the US. Airbus adopted a similar approach for the A350, with fuselage shells produced at the Aerolia facility in Saint-Nazaire. Lockheed Martin's C-130J and Embraer's E2 family use significant composite content in secondary structures, while next-generation designs such as the potential Boeing NMA and Airbus successor programmes are expected to push composite content even higher.

Military aircraft have used high-composite content even longer — the B-2 Spirit bomber is nearly entirely composite, and the F-35 uses composite for over 35% of its structural weight to meet stealth and performance requirements.

Advantages and Limitations

Advantages: Weight savings of 15–25% versus equivalent aluminum structures; superior fatigue resistance (composites do not propagate cracks the same way metals do); excellent corrosion resistance eliminating much of the surface treatment required for aluminum; design flexibility allowing complex aerofoil and fuselage contours not feasible in sheet metal; and potential for large single-piece manufacture reducing part count and assembly labor.

Limitations: Higher raw material and manufacturing cost; sensitivity to out-of-plane impact (delamination can occur from tool drops or bird strikes without visible surface damage, requiring non-destructive inspection); repair procedures are more complex than metal patch repairs and require trained technicians; thermal expansion mismatch with metallic fittings must be managed; and quality control demands tightly controlled autoclaving environments. Certification of composite primary structure required extensive new test programmes and regulatory guidance development at both the FAA and EASA.