Here is a chart showing relative nylon bolt strength. As you can see, a single 8X32 screw would hold the wing of an 8 pound model on even with a 10G load.

You guys are really over thinking the "will they break" issue,, the reason to use nylon is so they don't vibrate out vs. metal bolts.

<span>I've seen too many cases of 'How'd that happen?' to trust one bolt. A little redundancy never hurts, for those times when Peter and his p</span><span>rinciple pop up.</span><div><span>
</span></div><div>Had a guy flying his 40-size high-wing trainer with 6 rubber bands. They musta been old because the trainer porpoised a few times, then the wing detached. End of trainer. The rubber bands that were found looked OK, but one or more must have failed. </div>

I have had the bolts shear when a wing clipped something on the ground. Saved me from doing repairs to the fuse, and lessened the damage done to the wing had it been metal bolts.  I also use them for my main landing gears, and one time when I mis judged a landing and hit the dirt, it sheared the LG off and saved the plane from some serious damage. Much easier to replace 4 bolts than the underbelly of a fuse. 

Bolts are just a single part of a multi-faceted protection system. Two bolts will actually shear nicely, IF there is not a square stop behind it. My Giant Super Sportster fell thirty feet straight down and hit on the front corner of a wing last weekend. The wing, held in place by two 1/4-20 bolts, is also held in the saddle by a square stop (the same thickness as the wing's trailing edge) right behind it. It's an ARF. The wing DID NOT separate upon impact, and the fuse snapped in half. I saw how it was mounted, and I didn't change it. Now I'm rebuilding a fuse snapped apart in the center, and a wingtip that was smashed because it didn't break away.

Many of the planes I built through the years have had two of the same bolts holding the wings on, but I did not build stops behind the wing, I ramped it so the wing's force transferred through the bolts, and anytime there was a crash, the force carried the wings away rather than the wing taking the hit full-force. It reduced the stress on all parts of the aircraft.

When there's a crash, SOMETHING is going to carry the force of the impact. When the pieces breakaway, they carry the force away from each other, and minimize it.

I think two bolts are just fine, but make sure you build your plane in such a way that they can shear when they really need to. Your plane will thank you for it.

~ Jim ~

Maybe we should go with 3 bolts in case the first two fail.



How about cotter pins through the incidence pin dowel thingies, if you're really paranoid.

Yeah, and don't forget it's a lever type system where for a simple constant chord symetricral section wing, the front dowls will take ~60% of the g-loading and the wing bolt will take the other 40%.

But the fact the bolt is already under a good couple of pounds load static (you do tighten them up?) probably balances things up a bit?

However 2 bolts would provide peace of mind if you relocate the hardpoints.

Actually, using as small a bolt as necessary for the tension strength is a good thing. You want a weak shear strength so that, should you hit on a wing tip or cartwheel on landing (thinking of the trainer planes here with beginning pilots) the bolts will shear and do minimum structural damage to the plane or wing. When using one or two dowels at the front and one or two nylon bolts at the rear, 6-32 nylon bolts are an excellent choice to hold the wing on. They will never break under flight loads yet can shear under side loads when it is desirable. When you use 1/4-20, you are making removable wing with no chance of minimising damage in a crash . If all you want is the capability to remove the wing, this works well. If you want some crash protection, go to much smaller bolts.

Remembering, of course, that the bolts won't shear anyway if the wing is set into a recess where it can't "slide" on impact and shear them. The fuse - rather than the bolts - will absorb the impact of the crash in that case.

~ Jim ~

My Kadet, yes, my 4* no. I know exactly what you are referring to. I can use metal bolts on the 4* since I already know the nylon wont shear, but they do shear on the Kadet, been there, done that, still have the broken bolt in my box.
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I'm putting my Giant Super Sportster back together, and I'm glad I came across this thread, because thinking about how I used to build mine reminded me to go ahead and shave the little shelf down to a ramp behind the wing, so the bolts can do their job, in the highly unlikely event something should strike the wing again.

The timing was perfect.

~ Jim ~