Which statement about a symmetrical airfoil is true?

Which statement about a symmetrical airfoil is true?

• A. It has a constant center of pressure
• B. It has higher lift at the same AoA than nonsymmetrical
• C. It stalls more readily at low speeds
• D. It has inherently low drag at all angles

Answer: (A)

Symmetry in the airfoil means the pressure distribution on the upper and lower surfaces is mirrored. In subsonic, thin-airfoil theory, this leads to the aerodynamic center being effectively fixed near the quarter-chord, and the overall lift-related moment about that point remains nearly constant as angle of attack changes. Put simply, the single resultant lift force can be treated as acting at a point—the center of pressure—that doesn’t move much with different angles of attack for a symmetric airfoil. That’s why, in typical analysis, a symmetric airfoil has a constant center of pressure, making this statement the best description. Lift at the same angle of attack isn’t higher for a symmetric airfoil compared with a cambered one, because cambered airfoils have a higher lift slope at a given AoA due to their camber, which increases lift without changing the angle of attack. Stall behavior isn’t inherently more favorable or worse for a symmetric airfoil at low speeds; stall characteristics depend on thickness, camber, Reynolds number, and other factors, not symmetry alone. And no airfoil maintains low drag at all angles; drag varies with AoA and flow conditions, so a universal low-drag claim isn’t accurate.

Symmetry in the airfoil means the pressure distribution on the upper and lower surfaces is mirrored. In subsonic, thin-airfoil theory, this leads to the aerodynamic center being effectively fixed near the quarter-chord, and the overall lift-related moment about that point remains nearly constant as angle of attack changes. Put simply, the single resultant lift force can be treated as acting at a point—the center of pressure—that doesn’t move much with different angles of attack for a symmetric airfoil. That’s why, in typical analysis, a symmetric airfoil has a constant center of pressure, making this statement the best description.

Lift at the same angle of attack isn’t higher for a symmetric airfoil compared with a cambered one, because cambered airfoils have a higher lift slope at a given AoA due to their camber, which increases lift without changing the angle of attack. Stall behavior isn’t inherently more favorable or worse for a symmetric airfoil at low speeds; stall characteristics depend on thickness, camber, Reynolds number, and other factors, not symmetry alone. And no airfoil maintains low drag at all angles; drag varies with AoA and flow conditions, so a universal low-drag claim isn’t accurate.