A main longitudinal strength member of a fuselage attached to the fuselage formers.

In aircraft construction, a Longeron is a thin strip of wood or metal, to which the skin of the aircraft is fastened. Longerons are attached to formers, in the case of the fuselage, or ribs in the case of a wing, or empennage. In very early aircraft, a fabric covering was sewn to the longerons, and then stretched tight by painting it with dope, which would make the fabric shrink, and become stiff.