Solving Complex Engineering Challenges of Large Composite Aerostructures

Large-scale composite parts present unique design and manufacturing challenges in aerospace.

Composites are becoming the material of choice for the manufacture of large, complex aerostructures. The aft section of the jumbo Airbus A380 and the wings of the military transport Airbus A400, for example, are all made of carbon-fiber composites. Boeing, for the first time, is building an all-composite airframe and wings for its groundbreaking 787 airliner. Because of these and other recent manufacturing achievements, there is little doubt that composite materials will be used extensively in many future aircraft programs — from wide-body jets and commercial airliners to regional, business, and “very light” airplanes.

Aerospace manufacturers plan to increase their use of composites because these materials offer proven benefits over aluminum and steel, such as weight reduction, improved strength, and corrosion resistance. Composites exhibit better impact response. They improve product performance, efficiency, and comfort for passengers. Composites enable part consolidation and low-cost tooling to reduce production cost and time. They also give engineers more design flexibility to customize materials based on demanding specifications, and more freedom to design unique and innovative products.

Despite the many benefits of composites, however, large aircraft structures such as wings and fuselage sections present tremendous design and manufacturing challenges. Creating a carbon fiber wing box nearly 100 feet long or a fuselage section 20 feet in diameter and 40 feet long is a complex undertaking. Aerospace engineers traditionally have used composites for relatively simple, smaller, and non-critical components. These parts were made of flat or mildly curved monolithic laminates or sandwich panels. Today, developing an entire composite fuselage from nose to tail involves the combination of multiple sets of design and structural specifications utilizing many manufacturing methods, from manual lay-up to automated fiber placement, and possibly resin infusion/injection processes for some parts.

As composite subassemblies become more complex, aerospace engineers are realizing they need to explore new, innovative design and manufacturing processes and predict part manufacturability early in development. To do so, they must more efficiently collaborate on large amounts of highly complex and interrelated data that define requirements for materials, structures, methods, and processes. This data readily affects all critical aspects of a composite part, including weight, shape, strength, cost, and producibility.

A large carbon-fiber fuselage is made up of many components such as skin panels, stringers, frames, and bonds. It is designed with numerous openings for doors and windows, local reinforcements for point loads and stress concentrations, and varying skin thicknesses that are tailored to resist aerodynamic loading, internal pressure, or bird strikes. The assembly of composite components requires accurate control of laminate thickness, ply orientation, layer boundaries, and drop-off placement so that each part meets stringent producibility requirements. In order to achieve timely design, several groups of engineers must work concurrently on all the various components. Therefore, it is critical for engineers to subsequently merge individual component designs accurately, incorporating necessary knowledge and design data in the final composite aerostructure (see Figure 1).