History

XFOIL 1.0 was written by Mark Drela in 1986. The main goal was to combine the speed and accuracy of high-order panel methods with the new fully-coupled viscous/inviscid interaction method used in the ISES code developed by Drela and Giles. A fully interactive interface was employed from the beginning to make it much easier to use than the traditional batch-type CFD codes. Several inverse modes and a geometry manipulator were also incorporated early in XFOIL’s development, making it a fairly general airfoil development system.

Since version 1.0, XFOIL has undergone numerous revisions, upgrades, hacks, and enhancements. These changes mainly originated from perceived shortcomings during actual design use, so XFOIL is now strongly geared to practical airfoil development. Harold Youngren provided the Xplot11 plot package which is a vast improvement over the grim Versaplot-type package used initially. Enhancements and suggestions from Youngren and other people were also incorporated into XFOIL itself along the way.

Over the past few years, bug reports and enhancement suggestions have slowed to practically nil, and so after a final few enhancements from version 6.8, XFOIL 6.9 is officially “frozen” and being made public. Although any bugs will likely be fixed, no further development is planned at this point. Method extensions are being planned, but these will be incorporated in a completely new next-generation code.

Note to code developers and code enhancers… XFOIL does not exactly have the cleanest implementation, but it isn’t too bad considering its vast modification history. Feel free to muck with the code as you like, provided everything is done under the GPL agreement. Drela and Youngren will not be inclined to assist with any code modifications at this point, however, since we each have a dozen other projects waiting. So proceed at your own risk.