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In a message dated 2/11/2006 10:35:08 AM Eastern Standard Time, [EMAIL PROTECTED] writes:
This is is word for word right out of the NTSB report: "The collapse of the spar could only occur when enough rivets had corroded to allow the disconnected part of the spar cap to reach its critical buckling strength. " What do you make of that?
Jan,
I'm replying to this and copying the list because I think there are others who will be interested and may offer some more, better educated, opinions.
My background is not in structural analysis, but here's what this sentence says to me:
The spar is basically a truss structure, which depends upon all of the following in order to meet it's designed strength:
1. The strength and physical configuration (size, thickness, shape) of its individual parts,
2. The geometry that the individual parts are assembled into, and
3. The strength of the fasteners that hold the assembly together.
The design strength of the assembly is only achieved when all of these factors meet their designed characteristics. The strength of the assembly is far greater than the strength of the individual parts. It's a case of the whole being greater than the sum of its parts.
I'm reading between the lines a bit here based on the other info in the accident report, but my understanding is that:
1. Enough rivets were corroded that the integrity of the truss structure of the spar assembly was compromised. In other words, rivet heads popped off and the spar cap was allowed to "disconnect" or "come loose" from the spar web. Now the spar cap is no longer part of the truss.
2. Because the spar cap became disconnected from the spar web, the bending force of the wing had to be handled by the spar cap itself. (Remember that the inboard wing attach fittings, or "hinges" are attached directly to the center section spar cap.) The load imposed by the wing was not properly transferred throughout the spar assembly as it should have been. This transferring of forces is critical to the strength of the spar assembly.
3. The spar cap by itself has a buckling strength far less than that of the entire truss assembly. The load implied on the now disconnected spar cap was greater than the critical buckling strength of the spar cap, and the spar cap bent. Once it started to bend, it had no strength at all (relatively speaking) and this allowed a complete failure of the center section.
All of this probably happened almost instantaneously.
So basically I think that sentence in the NTSB report makes perfectly good sense, although it could have been explained in a more detailed, clearer way.
Comments? Corrections?
Best Regards,
Wayne DelRossi
Alon N5618F
Hours logged since restoration: 91.5 (It's raining again!)
Wayne DelRossi
Alon N5618F
Hours logged since restoration: 91.5 (It's raining again!)
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