The construction of aircraft fuselages has evolved from early wood truss structures, to monocoque shell structures, to the current semimonocoque shell structures.
The main drawback of a truss structure is its lack of a streamlined shape. In this construction method, lengths of tubing, called longerons, are welded in place to form a well-braced frame.
Vertical and horizontal struts are welded to the longerons and give the structure a square or rectangular shape when viewed from the end.
Additional struts are needed to increase strength and handle stresses that may occur from any direction. Stringers and bulkheads, or formers, are added to shape the fuselage and support the covering.
As technology progressed, aircraft designers began to enclose the truss members to streamline the airplane and improve performance. This was originally accomplished with cloth fabric, and then evolved to lightweight metals such as aluminum.
In some cases, the outside skin can support all or a major portion of the flight loads. Most modern aircraft use a form of this stressed skin structure known as monocoque or semimonocoque construction.
Monocoque construction uses stressed skin to support almost all aerodynamic loads.
Although very strong, monocoque construction is not highly tolerant to deformation of the surface. For example, an aluminum beverage can supports considerable forces at the ends of the can, but if the side of the can is deformed slightly while supporting a load, it collapses easily.
Because most twisting and bending stresses are handled by the external skin rather than by an internal framework, the need for internal bracing was eliminated or reduced, saving weight and maximizing space.
Although employed in the early years of aircraft design, monocoque construction would not reemerge for several decades due to the complexities involved in its use.
Semimonocoque construction, partial or one-half, uses a substructure to which the airplane’s skin is attached. The substructure, which consists of bulkheads or formers of various sizes and stringers, reinforces the skin by supporting some of the bending stress from the fuselage.
A new emerging process of construction is the integration of composites or aircraft made entirely of composites.
Composite is a broad term and can mean materials such as fiberglass, carbon fiber cloth, Kevlar cloth, and mixtures of all of the above.
Composite construction offers two advantages: extremely smooth skins and the ability to easily form complex curved or streamlined structures.
Many manufacturers are now incorporating composite materials into their aircraft designs.
-Lesson derived from the Pilot’s Handbook of Aeronautical Knowledge-
Post time: Jun-19-2017