Definition
A thin, symmetrical airfoil whose upper and lower surfaces are formed from arcs of circles, producing a curved, lens-like cross-section. It is used primarily on high-speed and supersonic aircraft, where a thin, low-drag profile matters more than the lifting efficiency of a thicker, conventional shape.
Plain English
A wing cross-section shaped like a thin lens, with both the top and bottom curved as parts of circles. It is chosen for very fast aircraft because it cuts through the air with less drag at high speeds.
Context Anchor
Seen in airfoil design diagrams when comparing different wing-section shapes and how they affect lift and drag.
Derivation
Circular arc means a section of a circle, and airfoil refers to a shape designed to produce useful aerodynamic force when air flows over it. So the name is literal: an airfoil whose surfaces are pieces of circles.
Why Pilots Care
Recognizing this simple shape helps explain lift and drag behavior in basic trainers and early propeller designs.
Analogy
Think of the side view of a thin strip bent into a smooth, even curve. A circular arc airfoil is shaped in that same simple curved way.
Intuition Check
Do not read “circular arc” as meaning the whole wing is round or that the airplane flies in a circle. Here it refers only to the curved shape of the airfoil cross-section.
Example Sentence 1
The textbook showed a circular arc airfoil next to a conventional airfoil to illustrate why high-speed aircraft often use thinner wing sections.
Example Sentence 2
Early propellers often used a circular arc airfoil because it was easy to manufacture while still generating thrust.