# Consider the data for the NACA \(2412\) airfoil. Calculate the lift and moment about the quarter chord (per unit span) for this airfoil when the angle of attack is \(4^{\circ}\) and the freestream is at standard sea level conditions with a velocity of \(50 ft/s\). The chord of the airfoil is \(2 ft\).

Dynamic pressure \[q_{\infty}=\frac{1}{2}\rho _{\infty}V_{\infty}^{2}=\frac{1}{2}\times0.002377\times50^{2}=2.97\;lb/ft^{2}\].Fo r NACA 2412 airfoil coefficient of lift \(c_{l}=0.64,c_{m,c/4}=-0.036\).

Lift per unit span \[{L}’=q_{\infty}sc_{l}=2.97\times2\times1\times0.64=3.80\;lb/span\]

Moment about the quarter chord \[{M}’=q_{\infty}scc_{m,c/4}=2.97\times2\times1\times2\times\left ( -0.36 \right )

\\=-0.428\;ft/lb\] per unit span.