German Modifications to NACA Airfoils


According to Theory of Wing Sections, the airfoil names you've provided are modifications to the NACA four-digit series developed by researchers in Germany. They devised a new naming system that includes some additional adjustments to the airfoil geometry.

NACA airfoil geometrical construction
NACA airfoil geometrical construction

As discussed previously, the basic NACA Four-Digit airfoils are described by four numbers. The first digit specifies the maximum camber in percentage of the chord (airfoil length), the second indicates the position of the maximum camber in tenths of chord, and the last two numbers provide the maximum thickness of the airfoil in percentage of chord. All but one of the examples mentioned above are symmetric airfoils with no camber, so the first two digits are both zero.

We have described the first series of numbers, but what of the remaining values after the dash? These digits describe the modifications made by German researchers. These changes are similar to those used in the modified NACA Four and Five Digit Series, but the Germans went further by specifying even more modifications. Let us first explain the names provided for the A-4 Skyhawk since these are a simplified version of the full designation system.

The first number after the dash specifies a leading-edge radius parameter. This parameter is defined as being equal to the radius of the leading edge divided by the square of the airfoil thickness. The value given after the second dash is the location of the maximum airfoil thickness in percentage of chord aft of the leading edge. For example, the NACA 0008-1.1-25 is thickest 25% back from the leading edge while the NACA 0005-.825-50 reaches maximum thickness halfway (50%) along its length.

The airfoil sections provided for the S-3 Viking demonstrate yet more examples of the modification system devised by the Germans. For this example, we will pick the wing root airfoil and more fully explain the purpose of each set of values.

NACA 0016.3-1.03 32.7/1.00

The meanings of these values are specified below:

Even these examples, however, do not illustrate all of the modifications available under the German system. The following example provided in Theory of Wing Sections explains additional variations that can be made to the airfoil camber.

NACA     1.8     25     14-1.1     30/0.50

The meanings of these values are specified below:

where The relationships described above can be used to decipher the meanings of airfoil designations of this form. Unfortunately, I have so far been unable to find a source describing exactly how to convert these parameters into complete airfoil coordinates. There are a number of programs to generate NACA airfoil coordinates available on the web, but none appear to be capable of handling the variables described by the German modification system. We will continue to investigate this subject and hopefully provide that additional information in the future. In any event, most of these modifications are so minor and subtle that they should have little discernible impact on the final shape.
- answer by Jeff Scott, 25 April 2004

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