Originally Posted by
vikingivesterled
But what if in the confusion of bolt definition they used an available fully threaded bolt (called set screw (with no head they are called grub screw)) instead of one only partially threaded (just called bolt). How much would that reduce the shear strength. And in this case it's bending and hitting/pushing on the middle by the roller pins strength we are talking about, not pull strength.
(Definitions on bolt type names are from the website of the supplier of stainless steel hardware inox.ie)
This could also have been done by a Spirit employee and especially if they thoght Boeing routinely would replace them later.
They could even have used non hardened bolts.
That Alaska plane needs to be taken apart to see if not at least one bolt have fallen into a gap and down into the belly of the plane. If they did fail its unlikely they all failed at the same time.
And I wouldn't worry to much about lose bolts on other planes. It's the precense of the bolt that is important. Not its thightness. And a castellated nut with a split pin would stop it coming out altoghether, unless it was broken in two.
The bolts used here would never be full threaded bolts. The bolts used would have unthreaded shanks and are clearly drilled for split (cotter) pins. To be drilled for split pins they aren't #6 and most likely aren't #10's (although they could be but I highly doubt it). It's far more likely that these are 1/4 inch AN bolts with an ultimate strength of 125ksi. They could even be A286 material as that is more corrosion resistant. A286 bolts have an ultimate strength of 160 ksi. A quarter inch bolt in double shear is good for about 5500 pounds of force each. That would apply to the lower bolts. You're looking at it requiring 11000 pounds of force to shear just the lower bolts, never mind that you have to get past the upper bolts too. The upper bolts are in bending since they are loaded by the roller, The person who designed this was very smart. In this design the upper bolts can bend some and thus share the load with the lower bolts. If the upper bolts were in pure shear then all of the bolts need to be in contact at the same time to make sure they share the load. With this design it's going to take significantly more load to get past the bolts if they are in place. The amount of vertical force to move the door off of the pads is likely well over 15,000 pounds. That is the lower bolts require bout 11000 pounds to fail in shear, and the upper botls are likely about half that and they fail in a combination of shear and bending since they're essentially a simply supported beam with a center loading. The bottom line is that if the bolts are in there the door isn't moving since there are no appreciable loads in that direction and it will require more than 7 TONS of load to move the door up with the bolts in palce.