A flap stiffener.

Him: “Why is this so expensive? Can it fly me to the moon?” Me: “Yes indeed! It’s the latest aircraft model.”

Some older “aircrafts” have a thin long half-rolled leather piece attached to the inside of the moving flap, which is known as a “flap stiffener.”

Original metal Flap stiffener or flap support was designed for aircraft to reinforce and support the moving panels of its wing flap.

The flap stiffener is located on the moving part of the flap, in the middle, right between the grommets. It provides structure and support to the flap, mainly to its mid-part, helping it maintain its shape, preventing lowering the turnlock over time, and reduce creasing. This feature was added when the turnlock was lower in position than the flap upper edges (which were higher and with no curves, the opposite of now), on single large flaps with light foam cushioning, frameless with no panels, with a higher back, or with an attached snap button pouch.

All larger classics are now double flaps, with higher curved edges and lowered tongue ( lock seat).