Definition
A structural reinforcement bonded or fastened to a thin sheet of aircraft skin or web to increase its rigidity and resistance to bending, buckling, or vibration without significantly adding weight.
Plain English
A small strip or shape attached to a thin metal panel to keep it from flexing or buckling under load.
Context Anchor
Seen in aircraft structure and sheet-metal maintenance, especially when discussing skins, panels, doors, and repairs.
Derivation
From the verb 'stiffen' — to make rigid or firm. The name describes exactly what the part does: it stiffens an otherwise flexible piece of structure.
Why Pilots Care
Damaged or improperly repaired stiffeners can let a panel buckle in flight, which changes how loads travel through the structure and may signal deeper airframe issues during inspection.
Analogy
Like the cardboard ribs glued behind a thin poster to keep it from flopping — without them, the surface bends easily; with them, it holds its shape.
Intuition Check
A stiffener is not a chemical that makes something hard. In aircraft structure, it is a physical support piece added to help another part resist bending.
Example Sentence 1
During the inspection, the mechanic found a cracked stiffener riveted to the inside of the wing skin.
Example Sentence 2
Longitudinal stiffeners run the length of the wing to keep the upper surface from buckling under flight loads.