Question

For any thin airfoil (symmetrical or cambered), the rate at which lift increases with the angle of attack is

• A. \(6.28\) per radian
• B. \(9.42\) per radian
• C. \(3.14\) per radian
• D. \(5.14\) per radian

Hint:

For a thin airfoil, \[ \boxed{ \frac{dC_L}{d\alpha}=2\pi \approx6.28\ \text{per radian}. } \] This result is independent of whether the airfoil is symmetric or cambered.

Answer 1

The Correct Option is A

Step 1: Recall the Thin Airfoil Theory. According to Thin Airfoil Theory, the lift coefficient is \[ C_L=2\pi\alpha, \] where \[ \alpha \] is measured in radians.

Step 2: Determine the lift curve slope. Differentiating with respect to angle of attack, \[ \frac{dC_L}{d\alpha}=2\pi. \] Since \[ 2\pi\approx6.28, \] the lift increases at the rate of \[ \boxed{6.28\ \text{per radian}.} \] Therefore, \[ \boxed{(A)} \] is the correct answer.