Wanted to demonstrate something. This is the way I made the holes in the fuselage side sheeting.
After the stab tube and wing tube supports are glued on, then the truss is sheeted, the two holes need to be made.
I did this using a circular saw, in reverse, and backing it with another scrap balsa sheet.
this is the stab tube hole, after using the circular saw.
For the wing tube, I used the 1.5" diameter circular saw, with no pilot bit. The actual hole is bigger than this, but at least enough to open in up.
this is after going thru it, but not thru the balsa back up sheet.
here is the hole before sanding it round.
I then used a drum sander, that is 1 & 5/8" diameter, and was able to finish it off, so that the tube fits thru.