I have serious troubles with mapping.
Hello Dandolo513, nice model, not something I have seen before.

The model when opened in the Stainless tool gives a few issues but if they are ignored we can try and make
a skin map, however, with the Lorna we only see this part and to get it to show I had to select DarkGrey.tga
texture from the drop down, usually we select the Skin1o but if I do that in this case it only shows a white
area so I had to use the grey texture to create this, no other parts show:

If I take a wing part into gmax I have this, obviously you have mapped it but it seems the
faces are facing the wrong way:

If I try and add a random texture I do not see anything applied:

If I grab all the polygons and flip I can then see colour on the mesh:

Not sure if that is a reason the stainless program does not see this part like the front fuselage
but it could be that all the other parts need to be flipped, not sure.
In gmax before I export the meshes I use something called x-form that applies faces the right way
around so you see the under and upper surfaces in game the correct way up for shadows and such
although if you do it with a cloned part you will also need to flip the faces before exporting.
Please check what leperemagloire mentions because in the stainless program it only shows things if
they are structured the correct way usually with naming as it should be.
Likewise if you do not name your parts correctly it can also create issues in the stainless program.
Your aircraft does not load in Sknil either so there could be any of the above wrong that also stops it
loading in that program.
Hope that helps.
Take care and be safe.
Wishing you all the very best, Pete.
