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 \(1400\,N\).

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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 \( 2^{\circ} \).

Answered on 26th July 2021.
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