March 31, 2023, ©. Leeham News: This is a summary of the article New aircraft technologies. Part 6P. Fuselage manufacturing. The article discusses how a non-circular cross-section drives material use towards composites and the difficulties of manufacturing aeronautical composite structures in high volumes.
In last week’s article, we saw that to make a dual aisle aircraft drag and weight competitive with a single aisle alternative for a 250-seat airliner, we need to use an elliptical cross-section, Figure 1.
Such forms introduce bending moments in the skin when the fuselage is pressure cycled during flight. It can only be allowed if we use CFRP (Carbon Fiber Reinforced Polymer) materials, as they are less fatigue sensitive.
CFRP is extensively used in widebody production, including for fuselages. The established thermoset production method, where the CFRP resin is irreversibly hardened under high temperature, forces a tooling and labor-intensive manufacture of the parts (skins, stringers/longerons, frames) before they can be joined to larger assemblies. Joining is by “drill and fill” methods, i.e., bolting/fastening the parts together.
The whole process is labor and cost intensive and has stopped CFRP from being used for high-volume fuselage production. New developments aim to address the cost problem.
Production methods that don’t require expensive autoclaves (Figure 2) for curing are trailed, and the epoxy thermoset polymer is changed for thermoplastic polymers.
A thermoplastic polymer gets soft at high temperatures, above the temperatures experienced in a fuselage structure. It allows the welding of parts into larger assemblies, reducing labor-intensive “drill and fill” operations.
Thermoplastic composites started with small parts a decade ago (brackets, hatches) and have now advanced to research with fuselage sections and horizontal tail parts.
We can expect that the weldable thermoplastic composite will change the dynamics in aircraft manufacture over the next decades.