ORIGINAL: Rcpilet
I think foam is always going to be heavier than built up.
Whats all that space between the ribs in a built up wing? Air
Whats air weigh? Nothing
Whats foam weigh? Solid foam wing?
Even using 1 pound density foam--compared to 8 pound balsa. I still think balsa built up is lighter than foam. There is very little of that balsa in a built up wing.
Thats my totally biased opinion because I prefer a built up wing over foam sheeted. IMO--sheeting foam wings is a pain in the butt. I can frame up a wing pretty quick.
Uh, air has weight to it just as any other fluid. What's in a built up wing is alot of stuff not found in a foam core wing: ribs, spars, shear webs, etc.
This brings the weight of the two types of wings very close to each other, particularly when speaking of larger sized airplanes.
I find foam core wings much quicker to build up but they do require some aquired experience, particularly when cutting out control surfaces, planning for retracts, etc......