Sim - arthurbenemann/ardupilot GitHub Wiki
http://ardupilot-mega.googlecode.com/svn/ArduPilotMegaImages/flightgear.jpg
It's highly recommended to test your autopilot on the ground with a simulator before flying. Doing so is easy, requiring no more than a configuration setting in your APM software and a standard flight simulator program on your PC.
!ArduPilot Mega currently supports two different flight simulators: