AIRFOIL FAMILIES

t

NACA Four-Digit Series

Around 1932, NACA tested a series of airfoil shapes known as the four-digit sections. The camber and thickness distributions for these sections are given by equations to be found in Reference 3.1. These distributions were not selected on any theoretical basis, but were formulated to approximate efficient wing sections in use at that time, such as the well-known Clark-Y section.

The four-digit airfoil geometry is defined, as the name implies, by four digits; the first gives the maximum camber in percent of chord, the second the location of the maximum camber in tenths of chord, and the last two the maximum thickness in percent of chord. For example, the 2412 airfoil is a 12% thick airfoil having a 2% camber located 0.4c from the leading edge. The 2412 airfoil is pictured in Figure 3.7 along with other airfoils yet to be described.

NACA Five-Digit Series

The NACA five-digit series developed around 1935 uses the s ness distribution as the four-digit series. The mean camber line differently, however, in order to move the position of maximum camber

Whitcomb—type supercritical airfoil

C

NASA GA(W)—1

Figure 3.7 Comparison of various airfoil shapes.

forward in an effort to increase Indeed, for comparable thicknesses and cambers, the Qma values for the five-digit series are 0.1 to 0.2 higher than those for the four-digit airfoils. The numbering system for the five-digit series is not as straightforward as for the four-digit series. The first digit multiplied by 3/2 gives the design lift coefficient in tenths of the airfoil. The next two digits are twice the position of maximum camber in percent of chord. The last two digits give the percent thickness. For example, the 23012 airfoil is a 12% thick airfoil having a design Ct of 0.3 and a maximum camber located 15% of c back from the leading edge. This airfoil is also pictured in Figure 3.7.