Longerons

Longerons are longitudinal structural members that run along the length of a vehicle’s fuselage or wing, forming the main frame to which skin, frames, and other components are attached. In traditional aircraft, they serve as the principal load-bearing elements and help keep the structure in shape under bending, compression, and torsion.

Functionally, longerons carry bending and axial loads from the wing or fuselage and transfer them to the rest of the structure. They provide attachment points for ribs or frames and for the exterior skin, helping to maintain the geometry of the shell under aerodynamic and pressurization loads. Along with frames and stringers, longerons determine the load path and stiffness of the structure, and designs may use truss-like or shell-like arrangements depending on the approach.

Materials and construction vary by era and design. Wooden aircraft historically used sawn or laminated longerons. Metal aircraft employ extruded or built-up aluminum longerons, often in box or I-sections to maximize stiffness. Modern aircraft may use composite longerons made from carbon fiber or fiberglass, sometimes integrated with the skin. They are typically tapered along their length to match changing load distribution.

Relation to other components: Longitudinals run along the inside of the skin and cooperate with transverse frames (ribs) to resist loads. Stringers are smaller stiffeners along the skin; in semi-monocoque designs, the skin carries part of the load while longerons contribute to overall stiffness.

Other applications: The term longeron is also used in shipbuilding for longitudinal hull members that support plating and frames, performing a similar structural role.