US Hawks Hang Gliding Association

Introduction
http://airfoiltools.com/compare/index?r ... dex/#xfoil

Downloads:
http://web.mit.edu/drela/Public/web/xfoil/

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
limited trailing edge separation
lift and drag predictions just beyond CLmax
Karman-Tsien compressibility correction
fixed or varying Reynolds and/or Mach numbers
Airfoil design and redesign by interactive modification of surface speed distributions, in two methods:
Full-Inverse method, based on a complex-mapping formulation
Mixed-Inverse method, an extension of XFOIL's basic panel method
Airfoil redesign by interactive modification of geometric parameters such as
max thickness and camber, highpoint position
LE radius, TE thickness
camber line via geometry specification
camber line via loading change specification
flap deflection
explicit contour geometry (via screen cursor)
Blending of airfoils
Writing and reading of airfoil coordinates and polar save files
Plotting of geometry, pressure distributions, and multiple polars

More detail
http://web.mit.edu/drela/Public/web/xfoil/xfoil_doc.txt
Release Conditions
XFOIL is released under the GNU General Public License.