Originally Posted by erich weaver
I can assure you that one ply of FG is both easily measured and adds considerable stiffness to the wing tips. I know because I did it. If even more rigidity is desired, add a 2nd ply, but I didn't find it necessary.
Good to know, I only did the bench test. It was with 4 layers 8 oz, then 2-core-2 in the photo. I later did a 2-core-1 test that "seemed" as stiff as the 2-core-2, but only tested it for strength. The 2-C-1 piece was cut to expose the core to see if it would fail in shear, it didn't. Also, the pict was an infused piece. I got the Soric for plenum covers.
It seems the tips may only have a couple of glass layers, at least from my measurements the rest is gel coat. So, if a single layer works excellent! If more stiffness is desired a core will give much greater stiffness per oz, but it also has weight, probably equal to another glass layer. All in the expectations, I suppose.
Edit: Lets add some numbers. Deflection is inversely proportional to the moment of inertia. 2 layers of 8 oz is about .020", 3 is .030" So, one additional layer - Proportionally 1.5X^4 ~5X stiffer. With a 2mm core .020 becomes .070 thick and ~150X stiffer. Conclusion: 5 is pretty good (but not for a plenum)