NACA 4412

NACA 4412 is a NACA four-digit airfoil with maximum airfoil camber $m=0.04$ of the airfoil chord, its maximum at $p=0.4$ chord, and nominal maximum airfoil thickness-to-chord ratio $\eta =0.12$. Thus the first two digits specify a mean-line shape, while the last two specify a thickness-envelope parameter. The designation is geometric rather than a universal measured lift coefficient.^[ref]

For an original $c=0.50\mathrm{m}$ section, the maximum mean-line displacement is 20 mm at a station 200 mm aft of the mean-line origin. The nominal twelve-percent thickness is 60 mm. That thickness does not occur at every station and is not the same quantity as maximum camber.

A calculation away from the maximum-camber station makes the airfoil thickness convention visible. At the mean-line parameter $\xi =x/c=0.2$, the standard construction givesUsing the finite-trailing-edge thickness polynomial and normal offsets, the upper and lower points areTheir different horizontal coordinates are part of the construction. Adding and subtracting the same half-thickness vertically would create a different profile at this station.

Compared with NACA 2412, the mean-line amplitude is doubled while $p$ and the prescribed thickness envelope are unchanged. Thin airfoil theory therefore doubles the camber contribution to its modeled zero-lift angle of attack; direct evaluation gives about $-4.1545{}^{\circ }$ for this ideal mean line. That number follows from the ideal model and is not a wind-tunnel measurement. It does not establish a universal aerodynamic stall angle or drag curve.

The physical motivation for a related family was to vary thickness and mean-line form systematically, then measure the resulting aerodynamic behavior under controlled conditions. The original NACA report describes such a comparison in a variable-density wind tunnel at large Reynolds number.^[ref] A performance statement about NACA 4412 must still identify flow conditions, surface condition and the measured quantity.