I use it for 2D airfoil design and it's great as far as it goes but there are some assumptions in the programming to cut down on processor time that can cause some fairly large errors (minimum drag and maximum lift can be off and it doesn't do post stall at all (errors at the margins)). Another free program I've heard of but not used that may be better than XFLR5 for stability analysis is AVL (athena Vortex Lattice). Both programs were written by aerospace professors at MIT. There are actually a lot of programs for this but most of it is old command line stuff with a very steep learning curve. The problem that makes these programs necessary for most of us is that aerodynamics is the most math intensive field of Newtonian physics. If you're ideas are for a pretty conventional design monkey see monkey do can work but I wouldn't want a guy with a wife and kids to be the test pilot.