# Find the angle of attack for this airfoil, if the lift per unit span produced is $$1400\,N$$.

A NACA 0012 airfoil having a chord of $$2.3\,m$$ is in an airstream velocity of $$70\,m/s$$ at standard sea level conditions. Find the angle of attack for this airfoil,  if the lift per unit span produced is $$1400\,N$$.

Asked on 22nd July 2021 in
Span is the wingspan of the airplane. It is the distance from one wing tip to other. It is measured in a straight line and is independent of the wing shape and sweep.  Lift per unit span produced by a wing is given as $${L}’ = \frac{1}{2} \rho _{\infty}V_{\infty}^{2} c\left ( 1 \right )c_{l}$$. Here, $$\frac{1}{2} \rho_{\infty}V_{\infty}^{2}$$ is called the dynamic pressure , $$q_{\infty}$$.  Coffeicent of lift, $$c_{l}$$, for this airfoil will be $c_{l} = \frac{{L}’}{q_{\infty}c\left ( 1 \right )}$$\Rightarrow c_{l} = \frac{1400}{\left (\frac{1}{2} \times 1.225 \times 70^{2} \right )\left ( 2.3 \right )\left ( 1 \right )}$$\Rightarrow c_{l} = 0.203$Therefore, coefficient of lift for this airfoil is $$0.203$$. For, NACA $$0012$$ airfoil from the lift curve -slope for this airfoil, the angle of attack is $$2^{\circ}$$.