Hi All
I was looking through photo's and upon looking at following image, i noticed faint lines either side of rivet line obviously the edges of stringer or structure this skin was attached, Do we know the width of the stringers/structure of Electra and do they match these faint lines ?
Thanks Richie
Into the Waves
We now see that the aircraft's skin had been distorted by a force acting from the exterior, so that the skin "registers" the stringers in a way that is still visible.
I have two questions for those more knowledgeable about aircraft construction and maintenance than I:
1. Is it normal for .032 aluminum skin to become distorted like this over time simply due to the action of air passing over the skin?
2. Does a skin get visibly distorted like this during the normal process of assembly and riveting?
For the rest of this post I will assume the answers are no.
If simply flying or assembly won't do this, then there must have been some force acting upon the exterior of the patch while the patch was attached to the stringers, and the stringers were attached to some larger body to resist the force. This is entirely consistent with the aircraft being battered by waves before the patch was removed. In fact it is hard to imagine any other situation that would cause this.
Note that this requires the patch to still be in place when the aircraft was in the waves. Short of a truly calamitous landing which is not well supported by the post-loss signals, the patch was in place for some time after the landing and most likely until at least July 8 (I assume, reasonably I think, that the height of waves required to batter the patch would disable the radio).
Thus the speculation that FN or AE kicked out the patch, either immediately after landing to escape or later for ventilation, is not supported by this logic. The surf had to distort the patch before it was removed from the aircraft.
Jon
What you describe, Jon, is the evidence that Richie saw where stiffeners were riveted to the skin, not the unfastened vertical 'mystery member' that left traces, mostly on the exterior.
It is not unusual for traces of stringer or stiffener contact to be evident where so-fastened; likewise, minor distortions can easily happen during ordinary ground handling just by people leaning their bodies against the contour of the airplane, etc. Ordinary vibrations and repetitive air loads can also create such evidence where contact is firm within a structure, yes. Then, if assembled for any reasonable length of time in an outdoor environment - especially the tropics, there may corrosive effects - even if minor, that leave traces.
I've seen the artifact in person and my impression is that all such marks are very subtle - there is no major 'distortion' from stiffener contact (nor from the veritcal member as I understand it) that I've been able to discern.
What I've also understood is that some unknown 'hydraulic' force, i.e. by wind, waves, explosive gasses, tootsies or other blunt object(s), seem to have worked from the inside surface, not outside, to lend the characteristic convex shape the part generally displays. It lacks the micro-porosity, pitting and pocking that would indicate the application of conventional explosives.
It could have been worried-loose by AE and Fred in some attempt for whatever reason, removed by another opportunistic harvester, or by mother nature - by any combination of these over time, or in one swift event by some singular effort. The failures on the part appear chaotic to me - as if there was a partial failure imparted by mishap or mother nature, and a finishing off by additional force(s) being applied.
Possibililities that come to mind include perhaps, considering for a moment that this IS a part from NR16020, an initial tearing away of the bottom seam from the double row of fasteners where the angular 'saw tooth' failure pattern exhibits: that appears to be a failure in tension by a singular event; it seems consistent with diagonally-applied forces that could impart enough tension to the skin to cause a failure roughly along that staggered line of rivets. Later might follow some 'worrying' failure elsewhere by repetitive wind or tidal forces - or someone seeing the partially-failed skin as an easy grab and cutting at it with something as crude as a machete along the aft and upper lap joints. Then the prize might have been taken by bending inward and outward until the rather neat cyclic fatigue failure occurred along the surviving lower leading edge of the part. All conjecture, but I'm trying to give a reasonable illustration of how the things I see in 2-2-V-1 might have occurred - IMHO.
I don't believe that the overall gross distortions that we see are inconsistent with what I've described.
At some point the rivets attaching the stiffeners, later I think, must have been removed with considerable care; the holes don't bear evidence of failure by force - unless failure in fastener tension: there is some slight dimpling effect around some rivet holes, as I recall. That might not be too mean a task with reasonable tools once in a modest shop environment. I don't know what tools there were at Gardner, but if combs and ornaments were being crafted from aircraft skins, then they had some capability.
Just thoughts, hope this helps answer some of your own.
