four star 60 doesnt have a sheeted LE and the TE only has a couple of inches of sheeting but it does have an upper and lower main spar with a piece glued between them making an I-beam, two upper and two lower LE spars then of course the leading edge it self and behind the main spar it has diagonal bracing, and center sheeting. the wing is very stiff. so sheeting is not needed if designed and built right but sheeting is easier and faster.