# The BD-5J is equipped with plain flaps. The airfoil section at the wing root is an NACA 64-212, and interestingly enough, it has a thicker section at the tip, an NACA 64-218.

The BD-5J is equipped with plain flaps. The airfoil section at the wing root is an NACA 64-212, and interestingly enough, it has a thicker section at the tip, an NACA 64-218 (Reference: Jane’s All the World’s Aircraft, 1975-76). Estimate the stalling speed of the BD-5J at sea level.

\[\left ( C_{L} \right )_{max} = 1.55\,\rightarrow \mathrm{NACA}\,64-212\]\[\left ( C_{L} \right )_{max} = 1.52\,\rightarrow \mathrm{NACA}\,64-218\]

With plain flap deflection, \[\left ( C_{L} \right )_{max} = 1.72005\]

\(W = 960\,lb; S = 37.8\,ft^{2}\) \[ V_{stall} = \sqrt{\frac{2}{\rho _{\infty }}\left ( \frac{W}{S} \right )\frac{1}{\left ( C_{L} \right )_{max}}}=\sqrt{\frac{2}{0.002377}\left ( \frac{960}{37.8} \right )\frac{1}{1.72005}}=111.4601\,ft/s\]

\[\Rightarrow V_{stall} = 75.99552\,mph\]