I was playing around with GCS last night and was able to get the flight simulator going without too much trouble. Here are a few tips if people want to try it out themselves:
(I'm using a Ubuntu 16.04 in a VM)
1. I built LibrePilot using the instructions here:
https://librepilot.atlassian.net/wiki/display/LPDOC/Linux+-+Building+and+Packaging --> I pulled code from the 'next' branch as of 16.06.12 in case it matters
2. Once you have LP running, build simposix (FC emulator) by executing 'make simposix' (builds with warnings)
3. Install the FlightGear flight simulator from here:
https://launchpad.net/~saiarcot895/+archive/ubuntu/flightgear --> run it and make sure it runs properly. Use 'fgfs --launcher' to set your aircraft, location etc, then exit the app
--> Note: I had problems getting OpenGL working in my Vmware VM, but setting the Vm to version-9 compatibility solved that
4. Open a new shell window and run simposix.elf (in build/firmware/fw_simposix/)
5. Now run GCS. If simposix is running properly you should be able to go to the Configuration page. Set your vehicle type to Fixed Wing and assign your output channels (motor=channel1, aileron 1=channel2, elevator 1=channel3, rudder=channel4). Save.
6. Go to the HITL page. Select Window / Edit Gagets Mode. Change the top widget to 'FlightGear HITL'.
7. Click Start at the top of the HITL widget. If everything is working properly FlightGear should load and you should be able to use the HITL page Controller widget to take off and fly around.
8. At this point you should be able to use GCS to fly around & navigate normally. I've had issues with getting the default vehicle to navigate properly, but it's probably something in my settings.
This is all from memory, so I probably forgot something... Feel free to post with questions & corrections.
Disclaimer: I deserve absolutely NO credit; actually I'm relatively new to LibrePilot. Kudos to the hard working developers who made all of this a reality! Also, fair warning: There are some rough edges - this stuff is under active development and subject to change. (Still, it's fun to play around with and get familiar with GCS features without risking your hardware!)