Upon seeing your assembly file I saw that you've simply placed those rod parts into the aerofoil part. While slicing this will lead to issues, because the software still acknowledges those parts as different objects and tries to print them that way !!
You don't want that, what you want is a single uniform body for 3d printing with no meshing issues, no trapped volumes.
You can refer Youtube videos regarding videos about merging bodies for 3d printing.
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