Paul,
It's simple. You take away material and you remove weight. How can that not be understood?
Call it a hole, half ribs, doesn't matter. Weight removal with the building of model airplans, has been going on for ages.
Hollowing out foam wings? Holes in fuselage sides. There's many examples.
I took an incredable amount of weight off The LOSER, A bit more before I planked the fuselage, which, BTW, being egg shapped, added strength.
There's plenty of build sights where the removal of weight, holes or not, is effective in the build.
It all adds up. Or subtracts?
Drope me a note next time your at The LOSER's thread.
Charles