For a symmetrical airfoil, the lift coefficient at zero angle of attack is

• A. Undefined
• B. Positive
• C. Negative
• D. Zero

Answer: (D)

Lift results from a pressure difference across the wing, which depends on the angle of attack and the wing’s camber. A symmetrical airfoil has no camber, so when the angle of attack is zero the pressure distribution on the top and bottom surfaces is symmetric. That symmetry means there’s no net aerodynamic force lifting the wing, so the lift coefficient is zero. In other words, zero lift at zero angle of attack is expected for a symmetric shape because there’s no camber to create an inherent pressure difference. The lift coefficient is defined as Cl = L / (½ρV²S), and with no lift, Cl is zero. A cambered airfoil would need a nonzero angle of attack (or intrinsic camber) to produce lift, and other options like undefined or negative would not apply here.