# 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 $$2 ft$$.

Asked on 8th November 2019 in
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.