Aras, your images have no length scale. Here, I measured it for you, it is 6 microns.  Is that a significant dimension?  What is the source of the STL file? Is the STL data computer generated from a model or is it scan data from a physical prototype?  Even if the data is computer generated, when a physical prototype is made, I doubt it will be made to 6 micron tolerances.

In my videos and my replies, I mentioned that the Skin tool is not exact, it does a best fit of a B-spline surface to the STL vertices and faces. I showed you how to use the Deviation plot in SpaceClaim so you can see the magnitude of the error. Here is a plot which shows the deviation between the STL facets and the top tail surface is +0.02 mm to -0.06 mm. This is a small fraction of the 70 mm chord length and these numbers are 10 times larger than the dimension you are showing above.

Here is the bottom surface deviation:

You need to decide what an acceptable tolerance is for deviation from the STL facet to the surface. Maybe while I was making the solid, I did not zoom in carefully to pick the exact last vertex on the STL. You can be more careful to not miss the last vertex at the trailing edge.

As I mentioned before, if you want zero deviation from the STL, then mesh the STL directly as shown in the Fluent video.

I did not record a video while making this solid.

Using SpaceClaim, I created two planes parallel to the XY plane. Move the first plane to Z = 0.1 mm and the second one to Z = 29.9 mm.  Draw a block of air between those planes. Use the Combine tool to subtract the SolidFilledWing from the block of air.

I also tried a block of air that is wider than the wing and SpaceClaim had no problem subtracting the wing from the block of air.