We’re pushing to get a stable X-Plane 11.30 beta 3 right now, and I think we’re making progress: Chris has fixed the crash when using the radio stack audio (this Windows-only crash was very frequent) and I have found at least one case of collapsing landing gear.
The bug report was the landing gear collapsing when taxiing on orthophoto-based scenery. It turns out that the custom DSF meshes have triangles that are duplicated and then flipped. In other words, a few of the triangles have twins that are upside down.
Here’s a pair of pictures to illustrate.
The image on the left is the “tops” of the orthophoto mesh triangles – this is what you expect to see. The image on the right is the bottoms!
Now normally the “bottom” view should show nothing – we should see only the light blue background, because the camera is above the mesh, so all of the triangle backs are facing away from us. Those extra triangles you see are copies of parts of the orthophoto mesh that have been duplicated and flipped over, so that their fronts face down and their backs face up.
This DSF violates the DSF specification, which requires all triangles to be wound counter-clockwise when viewed from above. But as of X-Plane 11.26, this wasn’t a huge problem; X-Plane blissfully ignored the flipped triangles. X-Plane 11.30 is intermittently detecting the upside-down triangles and the resulting upside-down normal vectors are making the collision physics go crazy. We should have a fix for this in X-Plane 11.30 where we filter out these flipped triangles.
One last bit of the mystery: the creation agent on both bad DSFs I have looked at is “X-Plane Scenery Creator 0.9a”. Does anyone have a link to this tool or know who the author might be?
Post script: there is a separate bug where the new physics code is reacting to DSF boundary cracks more severely than X-Plane 11.26. I had hoped this would all be one big bug but it’s not, so mesh cracks will be next on my todo list.