An aircraft structural member used to give a fuselage its shape. The truss structure of an aircraft fuselage provides the necessary strength, but its cross section is usually square or triangular and does not have the clean aerodynamic shape needed for streamlining.

Formers of wood or light metal are attached to the truss, and stringers (lightweight strips of metal or wood) are placed over the formers to give the fuselage its shape. All of this structure is covered with fabric or thin sheet metal.

A monocoque fuselage carries most of its stresses in its outside skin whose shape is produced by formers to which the skin is attached. Formers that divide a fuselage into compartments are called bulkheads.