I was kinda incorrect about the .obj n-gon thing. I had another look at your fan blade and found that it wasn't the n-gons causeing problems, it was the fact that the surface was not closed.
I found this when I deleted the large faces, and tried to re-make them, the object only half filled, broken where the outside loop wass broken.
I fixed the outside loop, remade the large faces, and it renders OK.
see attached.
