The final shape of the airfoil section is found by adding a specified symmetrical thickness distribution around the Once the shape of the mean camber line is determined, These numbers provide a means to calculate the mean camber line. Using these numbers, the final shape of the airfoil section can be calculated. The last two digits, "12" specify that the maximum thickness of this airfoil section is 0.12 c. The second digit, 4, specifies that the maximum camber of this airfoil section is located 0.4 c behind the leading edge. The first digit, 2, specifies that this airfoil section has a maximum camber of 0.02 c. The last two digits denotes the maximum thickness of the airfoil section, t, as a percent of the chord.Ĭonsider a specific example, the airfoil designated NACA2412. The second digit denotes the chordwise position of the maximum camber, X Cmax, in tenths of the chord The first digit denotes the maximum camber, C max, as a percent of the chord The digits in NACA's four digit numbering system are defined as follows: The shape of the airfoil section at the leading edge is usually circular, with a radius of approximately 0.02 c. Having defined these fundamental characteristics, additional properties are now defined, before proceeding to an explanation of the NACA system.īecause airfoil sections vary in size, the following properties are generally stated in terms of the chord, c. The thickness is the distance between the upper and lower surfaces, also measured perpendicular to the chord line. The maximum camber is the maximum distance between the mean camber line and the chord line, measured perpendicular to the chord line. The actual distance between the leading and trailing edges, measured along the chord line, is the chord, c. The straight line connecting the leading and trailing edges is the chord line of the airfoil. The most rearward point of the mean camber line is the trailing edge. The most forward point of the mean camber line is the leading edge. The mean camber line is the locus of points midway between the upper and lower surfaces as measured perpendicular to the chord line.
Following are some definitions of airfoil sectionĬharacteristics, followed by a description of how the NACA "four-digit" series specifies these characteristics. The first family of NACA airfoil sections, developed in the 1930s, was the "four-digit" series. Most of this material comes from the reference given at the bottom of this page. Refer to the diagram below for the explanation that follows. This page explains how the four digit system describes an airfoil section. They later introduced a five digit numbering system as well as several other systems. The National Advisory Committee for Aeronautics (NACA), NASA's predecessor, used a four digit numbering system to describe a large number of airfoil sections. NACA 4-Digit Numbering System - A Description