Why faces have a dark texture? Already recalculated normals When I imported this model into Unity a few parts of the model seem to be inside out. (the wings and the left engine)



I opened the model in blender, selected the relevant components, and recalculated normals. Now nothing is inside out.



However you can see that those parts are now really dark. And I can't fix this.



The problem itself can be seen in blender as dark faces. Similar to the problem seen when faces are inverted.

I have already tried:


recalculating normals on all components (the rest are unchanged)
checking that the normals actually ARE facing outwards by showing the weights of the normal
checking that both parts share the same material


why are these faces darker? how can I fix it?
Since you can't upload your model, I will try to point out the problems with your plane based on your screenshots. As stated in the comments, your issue is caused by flipped normals. You also have overlaying geometry, that can be caused by


duplication of the object at the exact same spot of the original mesh 
duplication of all faces "inside" (in Editmode) of the objects


One of the objects has normals facing inwards, the other object faces outward. That explains why the normals are consistent, but look inconsistent. Find the Object or faces that point inwards (dark blue) and delete them or move them to another layer.

There were also some additional issues with your model, they are not part of the question but I want to point them out anyways.




faulty mirror modifier: (sorry for the typo in the screenshot)
the mirror axis is off, you have intersecting geometry on your Y-axis  
there are several places with poor topology. I would suggest you to remodel parts of the object with cleaner topology. I hope you didn't pay too much for this model, its quality isn't very good.


if you want me to take a closer look, send the file to ian.smith[ätt]posteo[dott]de