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I a modelling an airplane model for FlightGear in Blender. I have a problem with the UV mapping and / or the texture of the LeftElevator. The lower side of that object keeps flickering: Deleting the face leaves a hole, so there is no double face. Also, the lower side is mapped to a wrong place of the texture in the 3D view, but it is mapped to the rightplace in the UV editor.

I've also tried re-unwrapping the object, which did not help either. The weirdest thing is, that when I export the model to an AC3D file an load that in FlightGear, the lower side of the LeftElevator is showing the right texture, but the upper side is now mapped to a wrong place on the UV texture

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    $\begingroup$ Hello and welcome. While files, images, and external videos or links may be helpful additions they should not be the only way to obtain information about your issue. Don't make understanding your question rely on downloading a file, watching a video or visiting an external site. Use the builtin tools to upload images or gifs, along with thoroughly explaining the problem in written form so it can be indexed and searched for thus helping future visitors with similar issues. $\endgroup$
    – Duarte Farrajota Ramos ♦
    Sep 23, 2021 at 21:17
  • $\begingroup$ @DuarteFarrajotaRamos I've added a GIF demonstrating the problem. $\endgroup$
    – TheEagle
    Sep 23, 2021 at 21:31
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    $\begingroup$ If you enable the Face Orientation option from the Viewport Overlays dropdown you will see that the problem is that the Normals of the Left Elevator are facing the wrong way! To fix this : in edit mode select all of the Elevator and open the Mesh menu > Normals > Recalculate outside. Note that you also have the same problem with the LeftTailStabilizer. $\endgroup$
    – 3fingeredfrog
    Sep 23, 2021 at 21:43
  • $\begingroup$ @3fingeredfrog Thank you for the tip. Actually, I had done this before, but for some reason one of the face normals was still pointing inwards ! I flipped only that normal. After that, I still have the flickering in Blender, but at least the UV mapping in FlightGear is now correct, and that's the main thing for me. Anyways, the flickering only happens on the bottom side of the model in Blender, which I seldom look at ! If you want to earn 25 reps, make it an answer ! ;) $\endgroup$
    – TheEagle
    Sep 23, 2021 at 23:02
  • $\begingroup$ Something else I observed is that I only get that flickering in Object Mode, not in Edit Mode. $\endgroup$
    – TheEagle
    Sep 23, 2021 at 23:07

1 Answer 1

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If you enable the Face Orientation option from the Viewport Overlays drop-down you will see that the problem is that the Normals of the Left Elevator are facing the wrong way! Red indicating parts of the model where face normals are inverted, facing inwards.

To fix this : in Edit mode select all of the Elevator and open the Mesh menu > Normals > Recalculate outside. Note that you also have the same problem with the LeftTailStabilizer. : enter image description here

The reason for the flicker and why one of the faces (ngon) needed to be flipped manually is because there is a Duplicate face (ngon) in the mesh. : enter image description here

To remove this extra geometry use the Mesh > Merge > By Distance tool. After this operation the hidden face will be left visible in the UV editor. This UV island will need to be re-mapped manually to the appropriate position on the Image texture. :

enter image description here

When modelling you may find it useful to enable the Backface Culling option from the Viewport Shading drop-down. Enabling this you can see and correct face normals as you go along.

enter image description here

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