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Xfoil is a powerful tool for designing airfoils and is freely available for download. While the xfoil community is very supportive, I recently had a hard time properly formatting an airfoil data file in such a way that xfoil would load it. After many hours of working through it I decided to document what I found here. The main xfoil website is here:
This site contains basic usage instructions, downloads and history.
XFOIL is an interactive program for the design and analysis of subsonic isolated airfoils. It consists of a collection of menu-driven routines which perform various useful functions such as: Viscous (or inviscid) analysis of an existing airfoil, allowing forced or free transition transitional separation bubbles. Free Airfoil Design and Plotting software. 3D wing analysis and design softwares and Softwares for RC Airplane wing and airfoil design. Roncz Eppler Airfoil Program. Roncz is a free Eppler Airfoil Program with compressibility Corrections. Foilgen is a software program which allows the user to construct NACA 4 digit and 5 digit aifoil.
Questions I had and answers I found:
What filename does the airfoil data need to be in?
As you may have seen, most airfoil files are .dat files, but are read with a text reader. you can read in a .txt file.
What is the working directory of xfoil?
This is implied in many of the instructions as the local directory where you are keeping the .exe file, and this is correct. In your defense after many hours of seeing
Manual fiat punto 2016 service manual. ‘File OPEN error. Linux binary diff gui. Nonexistant File: filethatactuallyexists.txt
Airfoil Design Program
*** LOAD NOT COMPLETED ***’
anyone will be second guessing themselves. To state this as plainly as possible: drop the airfoil data file into the folder with ‘xfoil 6.99’ in it, open xfoil, type ‘load’ enter, and enter your filename with file extension. If you get the above error it is not due to the directory it is due to the file. See below.
Steps to create an airfoil:
I created my airfoil in excel, it is not a typical airfoil, and I am not using xfoil for its typical application, but I ran into the same problems I’m sure others have had. Below is my ‘airfoil’ plotted out in excel. The more points you have in the data file will not effect computational time, the number of panels are controlled in xfoil. Note I did not upload it as a normalized airfoil. The ‘NORM’ function in xfoil will do this for you.
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Don’t use this geometry and expect to get good results, right now this will not converge, and I suspect it may never. Once you are at this stage take the leading edge point as your first data point. Subsequent data points are the next point up and around the trailing edge and back along the bottom until your last point is your first point. I listed these as an x and y column in excel and copied them into a .txt file thinking I was done, but there is some formatting to be done. Excel delineates the data with a tab, xfoil wants spaces. I did not study exactly what Xfoil wanted, I copied the format of a data file I knew to work. It was five spaces to the first column of data, and four spaces from the first to the second. This was done to every row in the .txt file. Once this is done it should load. A sample of what I had is here:
0.07474 0.017263246
0.07865 0.016782408
0.08256 0.016267853
0.08647 0.015719468
0.09038 0.015137132
0.09429 0.014520715
0.0982 0.01387008
0.07865 0.016782408
0.08256 0.016267853
0.08647 0.015719468
0.09038 0.015137132
0.09429 0.014520715
0.0982 0.01387008
Free Airfoil Design Software
If you do not have text on line 1 xfoil will ask you to name it when you load the data. Then be sure to normalize, and check the airfoil visually as well. The ‘PPAR’ function shows the airfoil you uploaded and allows you to modify.
Airfoil Design Tool
Hope this is helpful! Xfoil is a great tool.