Original Posted By: Doug Hunt
Pietenpol List:=0DIn Pietenpol's Corvair/3-Piece-wing supplements, the spars are lami-=0Dnated from 3/4" strips. Utilizing shorter lumber would save me $20-$25 =0D=per spar. I'd don't feel this is worth the trouble of all that scarf =0Djointing and laminating, so I'd like to use solid 3/4" stock.=0D=0DMy question: are there any other reasons for laminating the spar? Lam-=0D=inations are usually superior in strength, only because they allow =0Ddefects to be removed from otherwise unsuitable full sized stock. =0D=0DPoints of attachment are supplemented with plywood plates (1/8" each =0Dside). Is it necessary to use plywood reinforcement along the entire =0Dspar length, or are folks adjusting their rib plans to fit the thin-=0Dner spar?=0D=0DI see some concern over sanding wood before gluing. Plywood MUST be =0Dlightly sanded before gluing. Government tests quoted in the EAA's =0D"Wood Building Techniques" book show an average 40% increase in bond-=0Ding strength for most species. Light sanding removes the crushed =0Dcells from the wood surface, which form a glaze inhibiting good glue =0Dpenetration. It is the hot steel rollers which burnish the surface =0Dduring manufacture, when the plys are compressed. I have the written =0Dinstructions from Ciba-Geigy for their Aerolite 306 glue. I quote, =0D"Surface Preparation: Thoroughly sand the surface to be joined. =0DEnsure that all surfaces are free from dust or other deposits".=0D=0DHope this helps=0D=0DGlenn Robb=0D________________________________________________________________________________