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Airfoil data information

Dat file parsing

The dat files is parsed using the rules below. Any warnings are displayed in red to the right of the dat file data in the airfoil plotter form

  1. The file is read a line at a time starting from the top. Blank lines are discarded.
  2. The first line is the name or description of the airfoil
  3. All subsequent lines must have 2 numeric values separated by white space characters
  4. If the first numeric values are greater than 1 the file is assumed to be in Lednicer format and these indicate the number of coordinates on the top and bottom surfaces. Otherwise the format is assumed to be selig. See University of Illinois, Airfoil format page for more information on the dat file formats. All subsequent lines are treated as data points.
  5. The X coordinate should be in the range 0.0 to 1.0. In practice some files contain values slightly out of this range. so any X value in the range -0.01 to 1.01 is included in the data with a warning shown if the values are outside the range 0.0 to 1.0.
  6. The Y coordinate must be in the range -1.0 to +1.0. This is an arbitrary cut off but should flag bad values, missing decimal points, etc.

Dat file download

There are options to download the dat files in either Selig or Lednicer format. These are generated from the parsed data so any information that failed parsing will have been removed. Most airfoils also have a link to the original source dat file if required.

Calculating the camber and thickness

The camber and thickness are calculated in the Y direction. Some airfoil formulae, like the NACA series, calculate maximum thickness perpendicular to the camber line so there can be some small discrepancies. During parsing the top and bottom surfaces of the airfoil are stored separately. The surface with the larger number of points is used as the master. The the points on the master surface are scanned and the Y value on the opposite surface is determined by finding the 2 points that are either side of the X value, and triangulating between them to determine the intermediate Y value. This is the equivalent of drawing a straight line between all the points and measuring the distance between them.

Having found the Y values of the top and bottom surfaces the thickness is the difference between the two values. The camber line is the average of the two Y values. The maximum camber and thickness (Y) and the position (X) is determined by iterating along these values. The following should be noted.

  • The location of the maximum values will always be at a point in the dat file. The more points the more accurate the data will be.
  • Some symmetrical airfoils will have a very small camber value and non zero X position. To overcome this the data in the database was rounded to 3 places so these values should appear as zero.