spar lightening holes

[EthanP]

The outboard bay between rib locations 9 and 10 is longer and has enough room for four lighting holes in the web.  From my research is sounds like the XL uses tapered spar caps in this area to reduce weight.  Seems like a good low load area of the spar to save a bit of weight.  Thoughts, opinions, or preferably some math?

[Vince Carucci]

I drilled increasingly larger holes as I moved away from the center of the wing. The LE drawing show 3" holes in all bays. I did 3" next to the strut bracket and increased hole size as I moved inboard and outboard. What I don't remember at the moment, are the exact sizes. It could be: 3.0", 3.5", 4.0", 4.5". Or it could be 3.0", 3.5", 3.5", 4.0"

The shear forces in the wing drop to almost zero at the ends of the wings, with the greatest shear being felt at the strut bracket. Since the web bears the shear load, it seemed like a reasonable idea.

[EthanP]

Thanks, I like the idea of 3 larger holes vs 4 smaller, it leaves a bit more web between holes while removing more material overall.