March 24, 2023, ©. Leeham News: This is a summary of the article New aircraft technologies. Part 5P. Optimal fuselage. The article discusses different cross-sections and how these drive drag and weight. The cross-section chosen depends on the container type employed for the area below the floor.
In last week’s article, we realized we might end up designing the next volume model airliner as a dual aisle aircraft instead of a single aisle.
What cross section gets chosen depends much on the cargo container that shall go with the concept. Figure 1 shows that for anything other than an LD3-45 container, a full dual aisle cross section is the result, either a 767 cross-section if the LD2 is used or the eight abreast A330 cross-section if the LD3 is used (Figure 2).
The original Airbus A300 was designed for 300 passengers intra-Europe flights. Eventually, it was scaled down to 250 passengers, then called A300B. The fuselage was designed around the ubiquitous LD3 container, creating the successful A330/300 eight-abreast cross-section, Figure 2.
But an eight-abreast fuselage builds more circumference length per seat abreast than a single aisle cross-section or a dual aisle elliptical fuselage. In fact, the only dual aisle cross-section that can compete with an A320 single aisle is the elliptical dual aisle, Figure 1. But such shapes have not been produced as they introduce fatigue-inducing bending moments in the structure.
The result of such forces results in fatigue failures, as in Figure 3.
The only way to handle such bending forces is to change from an aluminum to a carbon fiber fuselage, which is largely agnostic to fatigue stresses.
Then the caveat becomes how to produce 60 to 80 carbon fiber fuselages per month when we struggle to produce 10 to 15. This is the subject of the next Corner.