GATE 2026 AE – Question 56
Consider a finite wing of aspect ratio 10 with span effectiveness factor 0.95. Its airfoil section has a lift slope of 0.106 per degree and a zero-lift angle of attack of $-1.5^\circ$. The lift coefficient of the wing at an angle of attack of $3.5^\circ$ is ________ (rounded off to 2 decimal places).
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Correct answer: 0.43 to 0.45
Explanation
The section lift slope is $a_0 = 0.106 \times 57.3 = 6.074$ per radian. The wing lift slope is $a = \frac{a_0}{1 + \frac{a_0}{\pi e AR}} = \frac{6.074}{1 + \frac{6.074}{\pi \times 0.95 \times 10}} = 5.046$ per radian, or 0.0881 per degree. Then $C_L = a(\alpha - \alpha_{L=0}) = 0.0881 \times (3.5 + 1.5) = 0.44$.