Where does the lift coefficient versus angle of attack curve intersect the vertical axis for a symmetrical airfoil?

• A. The origin
• B. Cl = 1
• C. Angle of attack = 90 degrees
• D. Cl = -0.5

Answer: (A)

For a symmetrical airfoil, there is no lift when the angle of attack is zero because there is no camber to create an asymmetric pressure distribution. On a lift-curve plot, angle of attack is on the horizontal axis and lift coefficient on the vertical axis, so the intercept with the vertical axis occurs where angle of attack is zero. Since Cl = 0 at α = 0 for a symmetric airfoil, the curve crosses the vertical axis at the origin. The other options would imply lift at zero angle or require extreme, non-typical flight attitudes, which isn’t where the lift-curve for a symmetric airfoil meets the vertical axis.