- Apr 6, 2020
Hi Dana!1700# at 4g, OK (gross weight 425#?). 4g is your limit load factor, which is the maximum you expect to see in flight. That gets multiplied by a 1.5 safety factor to get the design load, so you're actually designing for 6g or 2550#, or 1275# vertical load per side. The actual tension in the strut is that vertical load divided by the sine of the angle, so if, say, the strut is 30°, 180/sin(30) = 2550# tension. Assuming two bolts per attachment equally loaded, that's 1125# per bolt. "But wait, there's more!" For bolted or riveted connections, an additional 20% safety factor must be applied to allow for things like misdrilled or misaligned holes, so now you're looking at 1350# per bolt.
I was actually going to ask what a recommended safety factor would be so thank you for the 1.5! Thank you for pointing out my mistake, I was assuming all the lift bearing bolts would be counted in to the equation, which was obviously not the way to do it.
I definitely wasn’t thinking of converting between vertical load and tension, so it’s very good to know that there is an equation for this. Thank you for a walk through bearing stress!
We haven’t finished our load distribution or spar placement calculation yet, so to be conservative I’ll assume 23 degrees. With this assumption and the conversion to tensile strength, it would require 3 bolts (Of course, I’ll recalculate this with our actual degree once we calculate it) So I’m very appreciative of the time you put in to helping me through this, or this attachment may have failed!
Sorry, I should have been more specific, but I the thickness I was worried about the distance from the edge of the bolt to the bottom of the spar. So the shear stress on the spar, which I’ve calculated is fine as well. (I used our bearing stress on the attachment and divided it by inches to the bottom* wall thickness).
Thank you again!