Yes, I understand, but the MSFS models don't have towbars. I'm actually more interested in understanding how the SimVar is "hooked in" to a model to trigger an animation.
The plain "hookup" of variables to animation is explained in the SDK, and it should be clear by just looking at the vehicle XML behavior. We might have used another variable, it just that one is available for writing without any systems interfering with it, because that vehicle is not really a "wagon" and when it's created by GSX, is not used as a default MSFS ground vehicle, so the variable is free to use.
But that still won't tell you anything about how the Towbar really works, because what makes it work is in the underlying GSX code, that calculates how a Towbar should work.
I don't doubt that's true. But, I'm setting the WAGON simvar with the same data definition I'm setting lat/lon, and I'm able to move the tug model around without issue. But changing the WAGON simvar doesn't move the towbar. I've tried various "degrees" values, from -90.0 to 90.0 with no movement.
Assuming you are not trying to change it while GSX is using it (you would end up fighting with it to do the same thing), the variable works by setting it to a numeric value in degrees, otherwise the Towbar pushback couldn't possibly work in GSX.
But again, I cannot say why it doesn't work for you, without looking at your code.
