What Is an Airfoil DAT File and How Do You Use It?

Updated

An airfoil .dat file is a plain-text file that lists the x/y coordinates of an airfoil section, usually with a short header line giving the airfoil's name. You use it by downloading it from an airfoil database or pasting its contents into a tool such as Airfoil Tools, where it becomes the geometry that the plotter, comparison, and polar tools operate on. The format is simple enough to check by eye, which is also why most problems with .dat files are formatting problems rather than software problems.

What an airfoil .dat file contains

A .dat file holds nothing but a name and a set of points. The typical structure is:

  • A header line, often the airfoil designation (for example, a NACA number or a named section), sometimes preceded by a comment marker.
  • One coordinate pair per line, x first and y second, separated by whitespace.
  • Points ordered around the contour, normally starting at the trailing edge, running along the upper surface to the leading edge, then back along the lower surface to the trailing edge.

The coordinates are almost always normalized to a chord of 1, so x runs from 0 at the leading edge to 1 at the trailing edge, and y is the thickness or camber offset at that station. Because the file is just text, you can open it in any editor and confirm the point count and ordering before feeding it to a tool.

Where to get airfoil .dat files

Airfoil Tools indexes a large searchable database — the site states it covers 1638 airfoils — and its airfoil search lets you filter by thickness and camber, with preview images of each section. From a search result you can download the dat file data in various formats, or use that data directly in the site's tools, and each airfoil has a details page with polar diagrams across a range of Reynolds numbers. The site also links back to the original data source for each airfoil, which matters if you need to cite or verify the geometry.

If the section you want does not exist yet, the site provides a NACA 4 digit airfoil generator (and a NACA 5 digit generator) to produce sections, and the search index is also browsable by family — symmetrical airfoils, NACA 4/5/6 series, and an A-to-Z list.

Loading a .dat file into a plotter or comparison tool

Once you have the coordinates, the workflow on Airfoil Tools is:

  1. Find the airfoil through the airfoil search, filtering by thickness and camber if you are narrowing down candidates.
  2. Open it in the airfoil plotter to view and plot a full-size plan at your chord width. The camber and thickness can be adjusted, and the pitch can be set to account for wing angle of attack, washout, or wind turbine blade angle.
  3. Print or export the plan. The output is an SVG (Scalar Vector Graphics) plan that can be printed full size, or split over multiple pages for large sections.
  4. Compare sections with the airfoil comparison tool, which plots two or more airfoils on the same plan for shape comparison and can also compare lift and drag polar diagrams across Reynolds numbers. The comparison plan can be downloaded or printed full size for better resolution.

The same dat file data feeds all of these tools, so a section you download for plotting is the same geometry you compare and print.

Adding your own .dat file data

If your airfoil is not in the database, the "My airfoils" feature lets you add it: paste the dat file data into a form and the airfoil becomes available in the tool drop-down menus. Two practical points from the site's own description:

  • The airfoils you add are stored only in your browser session, so they need to be added again when the browser is reopened.
  • You can source the data from other airfoil databases, or generate the section with a generator tool and paste the result.

This is the route to take when you have measured coordinates, a section from a report, or a custom design that no public database carries.

Common .dat file problems and how to fix them

Because the format is minimal, failures are usually visible in the file itself:

Symptom Likely cause Fix
Tool rejects the file or shows nothing Header line missing or malformed Ensure the first line is a name or comment, with coordinates starting on the next line
Airfoil looks distorted or self-intersecting Points out of contour order, or upper and lower surfaces interleaved Reorder: trailing edge → upper surface → leading edge → lower surface → trailing edge
Section is the wrong size Coordinates not normalized to chord 1 Divide x and y by the actual chord before pasting
Only part of the section appears Duplicate or missing points near the leading edge Check for repeated x values and confirm the leading edge point is present
Extra columns cause errors Data pasted with additional fields per line Reduce each line to a single x/y pair

A quick sanity check before using any file: the x values should span roughly 0 to 1, the point count should be consistent with the resolution you expect, and plotting the raw points should trace a closed, smooth contour.

Choosing the right route for your task

  • You just need a standard section — search the database, download the dat file, and plot or compare it directly.
  • You need a NACA section that is not listed — generate it with the NACA 4 or 5 digit generator and use the result in the tools.
  • You have your own coordinates — paste them into "My airfoils" and remember they live only for the browser session.
  • You need a physical template — use the plotter's SVG output, printed full size or tiled across pages, rather than trying to reconstruct the shape from a coordinate table by hand.