NACA (National Advisory Committee for Aeronautics) airfoil.
A method of indicating characteristics of an airfoil. This can be done by describing the airfoil using 4, 5, 6, 7, or 8 digits. In a NACA 4-digit airfoil, the first digit expresses the camber in the percentage of chord, the second digit gives the location of the maximum camber point in tenths of a chord, and the last two digits give the thickness in the percentage of arc. The illustration shows a NACA 2412 airfoil. In a NACA 5-digit series (NACA 23012), the first digit (2) means the approximate camber in the percentage of chord, the second digit (3) indicates twice the position of the maximum camber in tenths of a chord, the third digit is either 0 or 1 and distinguishes the type of mean camber line, and the last two digits (12) give the thickness in the percentage of chord. That means that this airfoil has a maximum camber of about 20% of the chord located at 15% of the chord from the leading edge (3/10 divided by 2) and is 12% thick. The illustration shows a NACA airfoil—NACA 652
—415 a NACA 6-digit airfoil. In this airfoil, the first digit (6) indicates the series for which the minimum pressure's position in tenths of a chord is indicated by the second digit (5), the subscript (2) indicates the range of lift coefficient of 0.2 above and below the design lift coefficient where a low drag can be maintained, in this case, 2. The next number, 4, indicates the design lift coefficient of 0.4, and the last two digits (12) again mean the maximum thickness in the percentage of chord. NACA 7 and 8 airfoils can be described in similar fashion. NACA 6, 7, and 8 series have been designed to highlight some aerodynamic characteristics.