How does airfoil camber alter the zero-lift angle and lift-curve slope?

How does airfoil camber alter the zero-lift angle and lift-curve slope?

• A. Camber leaves the zero-lift angle unchanged but increases lift at a given angle of attack.
• B. Camber shifts the zero-lift angle to a negative angle of attack and increases lift at a given angle of attack; the lift-curve slope for thin airfoils remains near 2π per rad.
• C. Camber shifts the zero-lift angle to a positive angle and decreases lift.
• D. Camber only affects drag, not lift.

Answer: (B)

Camber introduces a sustained lift bias: the airfoil’s camber creates lift even when the angle of attack is zero, and the angle at which lift goes to zero shifts to a negative value. We can write the lift coefficient as Cl = Cl0 + Clα α, where Cl0 is the lift produced at zero angle due to the camber, and Clα is the lift-curve slope. For thin airfoils, Clα is about 2π per rad. Because camber adds a positive Cl0, the airfoil generates more lift at a given angle of attack than a symmetric one, and the angle where Cl becomes zero is negative. The lift-curve slope, which is the rate of change of lift with angle of attack, stays roughly the same for thin airfoils—around 2π per rad—so camber mainly shifts the zero-lift angle and raises lift at a given α, rather than dramatically changing how quickly lift increases with α. That’s why camber shifts the zero-lift angle to a negative angle and increases lift at a given angle, while the lift-curve slope remains near its thin-airfoil value. The other statements don’t fit because camber does not leave the zero-lift angle unchanged, does not require a positive zero-lift angle with decreased lift, and it definitely affects lift, not just drag.

Camber introduces a sustained lift bias: the airfoil’s camber creates lift even when the angle of attack is zero, and the angle at which lift goes to zero shifts to a negative value. We can write the lift coefficient as Cl = Cl0 + Clα α, where Cl0 is the lift produced at zero angle due to the camber, and Clα is the lift-curve slope. For thin airfoils, Clα is about 2π per rad. Because camber adds a positive Cl0, the airfoil generates more lift at a given angle of attack than a symmetric one, and the angle where Cl becomes zero is negative. The lift-curve slope, which is the rate of change of lift with angle of attack, stays roughly the same for thin airfoils—around 2π per rad—so camber mainly shifts the zero-lift angle and raises lift at a given α, rather than dramatically changing how quickly lift increases with α. That’s why camber shifts the zero-lift angle to a negative angle and increases lift at a given angle, while the lift-curve slope remains near its thin-airfoil value. The other statements don’t fit because camber does not leave the zero-lift angle unchanged, does not require a positive zero-lift angle with decreased lift, and it definitely affects lift, not just drag.