Definition
A propeller or compressor blade airfoil shape in which both the upper and lower surfaces are formed by arcs of circles, producing a thin, symmetrical or near-symmetrical cross-section. This shape is used on blades that operate at high subsonic or supersonic speeds, where conventional thicker airfoils would generate excessive shock-wave drag.
Plain English
A blade shape where the top and bottom surfaces are each part of a circle, giving the blade a thin, curved profile. It is used on blades that have to slice through the air at very high speeds without building up too much drag.
Context Anchor
Seen in propeller construction, propeller inspection, and aircraft maintenance discussions about blade shape.
Derivation
Circular arc simply means 'a piece of a circle.' The name describes the geometry directly: the blade's surfaces are drawn as arcs taken from circles, rather than the more complex curves of a traditional airfoil.
Why Pilots Care
Knowing that circular arc blades are designed for high-speed flow helps explain why some propellers and compressor stages look unusually thin and sharp-edged. The shape is a deliberate trade-off — less lift efficiency at low speeds in exchange for far better behavior near and above the speed of sound.
Intuition Check
Do not picture a round blade or a spinning disk. “Circular arc” describes the curve of the blade’s cross-section, not the overall outline of the propeller.
Example Sentence 1
The high-speed propeller used circular arc blades to reduce shock losses at the tips.
Example Sentence 2
Early constant-speed propellers often used circular arc blades because the shape was simple to manufacture.