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.

Longerons are sometimes called "stringers". The primary function of the stringer is to assume longitudinal loads—loads in the fore and aft direction. This may be internal loading from fuselage bending or applied loads from secondary structure that attaches directly to the stringers. Stringers, along with skin, are very effective under tension loading. However, under compression loading the stringers depend on the belt frames for stability.

In modern aircraft, such as Boeing commercial aircraft, stringers are typically made of an extruded aluminum alloy hat-shaped section. There may be 30 or more stringers spaced along the contour of the fuselage.

Aircraft components