I've been playing around with Kerbal Space Program for the last couple months and am actually quite amazed (I'm easily impressed) at what it can simulate. Granted it's mostly a rocket sim, but with some free addons, it actually simulates aircraft pretty well too. Rather than trying to shape a gray blob like in X-Plane, here you attach parts to other parts. Your design failing is denoted by same said parts detaching from other parts (structural failure) and accompanied by the odd explosion (such as impacting something like the ground). One of them, "Ferram Aerospace Research" actually calculates the stability derivatives of your creation, which is a pretty involved process to compute by hand. I'm not saying use this as design analysis, but it's always fun to see how numbers corellate to actual handling. That and how well designs that you think "look cool" perform. Take for example this thing, which has a negative static stability (thereby negative dynamic stability). It flips out into an uncontrolled tumble at transonic speeds at certain altitudes, glides like a brick, and has a landing of speed of around 250 knots. And this thing has the directional stability of a frisbee, given it's tendency to go into irrecoverable flat spins. But this boring design apparently does fine. Given this is foremost a game about getting into orbit I haven't done any lower speed stuff, but some of the addons that support prop engines. But all in all, a great program for getting a feel for aerodynamics and for people who like to tinker...and for people who like explosions. Thoughts? And if others have found something like this?