Definition
The main upper or lower spanwise member of a wing rib that runs along the top and bottom edges of the rib, forming the surface to which the wing skin or fabric is attached. Cap strips give the rib its airfoil shape and carry the loads transferred between the wing skin and the rib's internal structure.
Plain English
The strips of wood or metal that run along the top and bottom of a wing rib. They shape the curve of the wing and give the covering something to attach to.
Context Anchor
Seen in airframe maintenance when inspecting, building, or repairing wing ribs, especially in fabric-covered or light aircraft structures.
Derivation
Cap' comes from the idea of capping or covering the edge of something. The cap strip caps the top and bottom edges of the rib — it sits on the outer edge and forms the finished surface the skin attaches to.
Why Pilots Care
A damaged cap strip can weaken a wing rib or let the wing covering lose proper support, so it is something a mechanic must inspect and repair correctly.
Intuition Check
A cap strip is not a decorative trim piece or a removable cover. In this context, it is a structural part of a wing rib.
Example Sentence 1
The mechanic inspected each cap strip along the wing rib for cracks before recovering the wing with new fabric.
Example Sentence 2
Cracks in the cap strip can reduce the wing's ability to handle flight loads.