I've run a bunch of calculations on the RV-6 wing structure, which I have decided *not* to publish. As a P.Eng I do have liability to be concerned with. I will say that the limiting factor on loads on the structure is definitely not the spar or wing structure... To say that the spar on the RV-6 is overbuilt is a bit of an understatement... I'll leave it at that.
However, there may be other factors. I looked closely at the wing-fuselage interface and wing and spar construction, but didn't look further into the fuselage structure or loading to see what may be going on in the fuselage. Maybe the limiting factor is the fuselage, and the load of the pilot pushing on the seat pan... It would be interesting to mount a GoPro on the underside of the wing, looking at that overlap, and go do a loop... To see if the gap opens slightly. Or maybe some things you don't want to know.
I'm not going to pursue any further analysis right now... For many reasons. One, my -6 is 17 years old and shows no ill effects. Two, I talked to someone who had to remove the wings from his -6 for a repair, and it soudns like it really wouldn't be that hard to retrofit as per plans: pull the bolts from one wing at a time, separate the wing far enough to gain access, and then install the hardware as specified on the plans. A little more work than putting round-head screws in without removing the wings, but I hate the idea of using round-head screws... I'd rather pull the wings off than add drag.
The third reason is, regardless of any analysis I could do, even if I proved beyond any shadow of a doubt that the screws aren't needed, if I ever wanted to sell the plane, *not* having the screws would likely prove detrimental to my resale value.
So the TL;dr is, it's not that hard to retrofit, and sounds like it might be a fun experience (yeah, my definition of "fun" may be suspect... But I did just spend two nights poring over plans and running calculations for "fun" too...
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