YASim Development Tools

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YASim Development Tools
Started in 02/2018
Description addon for Flightgear to visualize the internals of a YASim FDM in-sim
Contributor(s) jsb
Status under active development as of 02/2018
Website none
This article is a stub. You can help the wiki by expanding it.


YASim development tools are an addon for Flightgear to visualize the internals of a YASim FDM while running the simulator. Minimum required version is FG 2018.1


YASim development tools are availabel for download on SourceForge

In order to load the add-on, start FlightGear (fgfs) with the option --addon, like this:

 fgfs <your_usual_arguments> --addon=/path/to/the/YASimDevel/folder

then look at the menubar. :)


Select an entry from the YASim development menu. A canvas window will open, use left mouse click to zoom in, right click to zoom out. Left click+hold to drag. You can also use "+" and "-" on the keyboard to zoom, and <Esc> key to close the canvas window.


You will get a canvas window showing the airplane mass points viewed from top with markers for the CG (the diamond), the desired range as given by the cg-min and cg-max attributes in the XML file and the hard limits for the CG (given by the gear positions).


Similar output as for displayMasses. Also displayed are the centerlines of the wings and the MAC. Last but not least a colored chord line is drawn per surface element (yasim generates several surface elements per wing). They will show green for positive lift and magenta for negative lift. The red part indicates drag.

Canvas showing yasim internals

Old models (before FG version 2018.1) often use <wing> + <mstab> to build complex wing geometry. The CG position in %MAC refers to the MAC of the <wing> element and is most likely wrong, when combining <wing> and <mstab> to build the main wing of the airplane.

Canvas showing yasim internals. CG out of range, incorrect MAC due to old model description.

Since FG version 2018.1 you can build the main wing by using multiple <wing> elements (refer to the Yasim main page for details). Now the MAC is calculated for each wing section and then is combinded to a MAC for the wing and CG is expressed relatively to this overall MAC.

Canvas showing yasim internals. CG green, correct MAC calculation using wing sections.