Definition
A thin, flat sheet of metal, often produced by rolling or beating the metal until it is very thin. In aviation, foils are used for tasks such as lining, sealing, shielding, or balancing components.
Plain English
A very thin sheet of metal. Think of it like the thin metal sheets used in everyday life, but made for use on aircraft parts.
Context Anchor
Seen in discussions of wings, propeller blades, rotor blades, and how lift is produced.
Derivation
From the Latin folium, meaning 'leaf.' The word captures the idea of metal worked so thin it resembles a leaf -- flat, light, and flexible.
Why Pilots Care
Understanding what a foil is helps a pilot see why the shape and angle of a wing or blade matter to lift, control, and performance.
Intuition Check
Foil does not mean aluminum foil here. In aviation, a foil is a shaped surface that works with moving air to create force.
Example Sentence 1
The technician applied a strip of lead foil to fine-tune the balance of the control surface.
Example Sentence 2
Propeller blades act as foils that convert engine power into forward thrust.