# Calculate the lift and moment about the quarter chord (per unit span) for this airfoil.

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.