XFOIL

XFOIL is a software program, originally developed in 1986 by Mark Drela at MIT, for designing and analyzing 2D airfoils in subsonic flow. It is an interactive tool that calculates lift, drag, and pressure distribution on airfoils based on their shape, Reynolds number, and Mach number. XFOIL is widely used in the aviation industry for airfoil analysis and education.

Key Aspects of XFOIL

Development

XFOIL 1.0 was created by Mark Drela in 1986 for the MIT Daedalus project, combining high-order panel methods with a viscous/inviscid interaction approach. It was further developed with Harold Youngren.

Interactive Design

XFOIL features a fully interactive interface, allowing users to modify airfoil geometry and performance predictions in real time. This differs from traditional batch CFD tools.

Inverse Modes

XFOIL includes full-inverse and mixed-inverse design modes, allowing airfoil redesign by modifying speed distributions or geometric features such as thickness, camber, highpoint, and trailing edge parameters.

Analysis Features

• Viscous and inviscid flow analysis
• Forced or free transition modeling
• Separation bubble and limited trailing edge separation handling
• CLmax prediction and Karman-Tsien compressibility correction
• Mach/Reynolds number variation

Geometric Control

Users can interactively alter airfoil contours using cursor-based tools, and define geometry based on camber line shape or loading.

Additional Capabilities

• Airfoil blending and mixing
• Plotting of geometry, pressure distributions, and polar curves
• Read/write of airfoil coordinates and polar files

Platform Support

• XFOIL is written in FORTRAN
• Supported on Unix, Windows, and Mac systems (including optimized Pentium builds and Mac-specific ports)

Software Tools and Integrations

• MATLAB port: “Xfoil for MATLAB”
• mfoil: Similar airfoil analysis in MATLAB and Python
• JavaFoil: Independent Java-based tool
• QBlade and OpenVSP integrate XFOIL routines via XFLR5

Licensing

XFOIL is released under the GNU General Public License (GPL), allowing free copying, modification, and redistribution under the same license.

Current Version and Maintenance

• The latest stable release is XFOIL 6.99 (as of December 2013)
• While reliable, the interface is considered dated—XFLR5 was developed as a modern GUI alternative incorporating XFOIL's core functionality

Accessibility

The official website, complete with source code, documentation, session files, and announcements: http://web.mit.edu/drela/Public/web/xfoil/

Summary

Despite its age, XFOIL remains a foundational tool for airfoil research, design, and education. Its real-time interactivity, accuracy, and extensibility keep it relevant for engineers, researchers, and hobbyists alike.