Definition
An airfoil that has identical curvature on its upper and lower surfaces, so the shape above the chord line is a mirror image of the shape below it. Because of this symmetry, it produces no lift at zero angle of attack and generates lift equally well in upright or inverted flight.
Plain English
A wing or blade shape where the top and bottom are the same. It only makes lift when tilted into the airflow, and it works the same way right-side up or upside down.
Context Anchor
Seen in discussions of wing sections, control surfaces, stabilizers, propeller or rotor blades, and airframe design.
Derivation
From Greek symmetria, meaning 'same measure' — the upper and lower surfaces have the same shape. 'Airfoil' refers to the cross-sectional shape of a wing or blade. Together: a wing-shape with matching halves above and below the centerline.
Why Pilots Care
Symmetrical airfoils allow identical performance upright or inverted, which is why they are used on aerobatic aircraft and many horizontal stabilizers.
Grounding Statement
Picture the side view of a wing shape with the top and bottom drawn as exact mirror images around a center line.
Intuition Check
Symmetrical does not mean “unable to make lift.” It means the airfoil has matching upper and lower surfaces; it can still make lift when it meets the airflow at an angle.
Example Sentence 1
The aerobatic trainer uses a symmetrical airfoil so it performs the same in upright and inverted flight.
Example Sentence 2
Aerobatic aircraft often have symmetrical airfoils in the wings to maintain the same handling characteristics when flying upside down.