Longeron

They are primarily responsible for transferring the aerodynamic loads acting on the skin onto the frames and formers.

The primary function here also is to transfer the bending loads acting on the wings onto the ribs and spar.

In the stringer system the longitudinal members are smaller and the frames are spaced further apart (about 15 to 20 in or 38 to 51 cm).

On large modern aircraft the stringer system is more common because it is more weight-efficient, despite being more complex to construct and analyze.

Stringers are usually not attached to anything but the skin, where they carry a portion of the fuselage bending moment through axial loading.