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Author Topic: Grand Rapids trip (2-2-V-1)  (Read 135795 times)

Ric Gillespie

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Re: Grand Rapids trip
« Reply #45 on: January 27, 2014, 05:47:00 PM »

Were the wheel wells lined?  I couldn't find any photos with an appropriate view.  (I'm also sure that you've already looked into it.)

No, the wheel wells in a Model 10 are not lined and, of course, there are no gear doors.
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John Ousterhout

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Re: Grand Rapids trip
« Reply #46 on: January 27, 2014, 06:06:43 PM »

Thanks, that's what I expected to hear.
The object appears to have encountered something else during it's life, beyond a simple hydraulic blow. There appears to me to be a large witness mark across it's narrow dimension near the "bottom" end as viewed in the picture.  The deformation appears to me to have been caused by impact with a generally curved surface.  The aluminum is bellied-out above the witness mark on the right, and bellied-out below the witness mark on the left.  There is also what appears to be a second impact mark above the primary one on the right, and angled from it, as though the piece encountered the same impactor a second time at a different angle.  This make it look a bit "funnel" shaped at the bottom end.
Am I just seeing things, or are these clues to the dynamic event that failed this piece of metal?
Cheers,
JohnO
 
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Jeff Victor Hayden

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Re: Grand Rapids trip
« Reply #47 on: January 27, 2014, 06:24:58 PM »

A link to aircraft rivets/fasteners and their use in repairs to aircraft structures and skin to maintain integrity and strength.

http://aviation.spenner.org/AircraftRivetsandSpecialFastners.pdf



This must be the place
 
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Dave McDaniel

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Re: Grand Rapids trip
« Reply #48 on: January 27, 2014, 10:55:59 PM »

My guess is that it was more than just one hydraulic event that caused the delamination of the artifact piece (2-2-V-1 Sheet). The repeated cyclic torsional stress (twisting) applied to the airframe by wave action most likely caused a failure of the structural panel it was attached to. This might account for some of the plastic deformation of the artifact piece that was discussed in the NTSB report. Oil canning of the structural panel, and its movement under load, would be more than enough over a relatively short period of time to cause failure of the rivets holding 2-2-V-1 in place. Having one landing gear fixed in place (stuck in reef) would certainly aggravate the torsional forces applied to the airframe by wave action. In concert with this, the tension and compression forces acting on various parts of the airframe due to the lifting effect of the waves acting under (and maybe over) the wings, and more particularly the empennage. Due to its position relative to the reef it was most likely the part of the airframe that was subjected to most movement due to its surface area, configuration, light weight and long arm/moment. And then there was that one last wave. It's a wonder that the airframe held together as long as it did. Just my 2cents worth. They'll get it figured out!

LTM,
Dave
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Tim Collins

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Re: Grand Rapids trip
« Reply #49 on: January 28, 2014, 05:47:40 AM »

The rivets did not pull through.  The rivets apparently fractured at the base of the head.  The force of the water on the interior surface of the skin literally blew the heads off the rivets.  There is one surviving rivet that pulled through the stringer because it was improperly bucked.

Has this been tested in any way - that so many rivets could have their heads blown off all at once with seemingly little or no external evidence of stress?
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JNev

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Re: Grand Rapids trip
« Reply #50 on: January 28, 2014, 06:40:41 AM »

I happen to have my own notion of that possibilty (merely a different area of the same airplane) as many have seen I'm sure.

I'm certainly open to other suggestions.  The tricky thing is finding a span of .032 skin that long (24 inches) with no crossing line of rivets.

Anything is possible - including any number of source locations on the Electra, of course.  But what you've pointed out, actually seeing the artifact in person and the Harney drawings are all what got me looking at the lavatory window covering that was installed as a field effort in Miami. 

That window was very large - at least 24 inches in fact fore-aft (from just aft of Station 293 5/8 to roughly Station 320 - a bit over).  As evidenced in the pictures of the window in its open condition, there was no intermediate bracing - the outer frame was substantial.  To cover that would not require crossing rows / intermediate bracing (across the rows we see).  But some form of bracing to offset oil-canning / timpanic effect would be advisable, hence the rows of small rivets, IMO, as a possibility.

Prior to seeing Harney's drawings at the symposium in June 2012 I had not realized that this window had been cut into the Electra, then covered over later as decided unnecessary by Earhart and Noonan, apparently.  It would not take much in the way of 'structure' to effect such a cover - just light guage metal, as we see (which also happens to be consistent with skins aft of Station 293 5/8 I'm told).  The use of 3/32" rivets for light stiffening would be ideal, especially if the owner was fretting over weight concerns; there would be no primary structural challenge - the outer frame for the previously installed window would continue to bear those loads quite effectively.

See pictures here of the window prior to covering, then covered as done prior to departing Miami.  Finally, I've illustrated the conjectured use of light stiffeners spanning the panel fore-to-aft, which would reasonably fit what we see - light (3/32") rivets in slightly irregular rows, as if hand-drilled in field as after-thought or perhaps just an improvised / expedited effort to stiffen the rather large tempanic covering. 

This is all just an idea of course, but it made a lot of sense to me as a possible source for such a large, light-guage panel with evidence of light stiffening having been attached in the past (my read of the rows of 3/32" rivets). 

One other aspect of the cover being in this area is that it might be particularly vulnerable to any explosive force (water?) that was trying to escape the cabin / lav / tail area of the bird.  The large surface area covering a fairly large compartment with little baffle effect to stifle the force could leave the cover easy prey to overt force like that; it could be largely knocked out, and any remaining fasteners / seams then subject to rapid fatigue as the panel might shift to and fro with nature's forces (or someone salvaging an opportune piece of metal).  That may fit what you've described as forceful removal of this item from the craft.  A belly skin might be problematic in that way, considering that the flooring might serve as a baffle against the offending forces, just a thought.

Is there more information on the window covering effort that was done in Miami?  That might be an additional area of study to see what can be learned.  It is entirely possible that the photos are the only evidence we have - as a minor alteration done in haste, it is possible that no record was made of this effort.  But, with the artifact in-hand, that area of an existing Electra might be studied for similarity to rivet patterns along the edges - realzing Earhart's was altered with a substantial window frame, of course.  But maybe there is some additional information somewhere on that mod as well. 

In my mind, the lav window covering could be a real link to this mysterious large, thin piece of metal - that sort of thing would not turn up too many places, certainly not as a sister member in primary structure IMO.
- Jeff Neville

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« Last Edit: January 28, 2014, 06:50:33 AM by Jeffrey Neville »
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Albert Durrell

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Re: Grand Rapids trip
« Reply #51 on: January 28, 2014, 07:25:01 AM »

Could this part have come off the plane as part of a bigger piece, then have the rivets removed by human hands so as to not have any damage to the skin?
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John Ousterhout

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Re: Grand Rapids trip
« Reply #52 on: January 28, 2014, 07:38:54 AM »

Jeff - your "L10E Lav Window..." photo includes an excellent view of the antenna lead pass-through (likely a white ceramic insulator) and connection point to the Ventral V antenna.
Albert - anything is possible, but it is unlikely that hand-removal of individual rivets would leave the deformation seen in the artifact.  The sheet metal is ballooned-out a little bit between the lines of rivets, and each rivet location has a small dimple where the rivet heads resisted the force that  caused them to fail, essentially in a single event rather like a zipper unzipping.  If each had been drilled out or sheared off, there would be no reason for the dimpled deformation.  If each had been chiseled off, there would likely be tool marks and no similar deformation.  If a person had intentionally removed the rivets, so as to obtain a workable piece of sheet metal for a project, why leave one rivet that appears to have been improperly upset during assembly?  The removal process did damage the skin.
Something implied by the deformation is that the structure the sheet was riveted to was quite strong (0.060 is pretty thick, implying a structural shape, such as stringers) and obviously supported by some additional structure that resisted the pressure applied to the large area of the sheet (like a window frame or other substantial structure).  The necessary pressure to fail the rivets could be calculated, and the resulting force resisted by the underlying structure would likewise be estimated, giving a rough idea of the sizes of structural elements (and a hand full of additional assumptions).
Cheers,
JohnO
 
« Last Edit: January 29, 2014, 07:55:38 AM by John Ousterhout »
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Tim Collins

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Re: Grand Rapids trip
« Reply #53 on: January 28, 2014, 08:39:43 AM »

...and each rivet location has a small dimple where the rivet heads resisted the force that  caused them to fail, essentially in a single event rather like a zipper unzipping.  If each had been drilled out or sheared off, there would be no reason for the dimpled deformation.  ...

Before making that conclusion spend a few moments with the link that Jeff gave above, in particular p.p. 19ff:

A link to aircraft rivets/fasteners and their use in repairs to aircraft structures and skin to maintain integrity and strength.

http://aviation.spenner.org/AircraftRivetsandSpecialFastners.pdf
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JNev

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Re: Grand Rapids trip
« Reply #54 on: January 28, 2014, 10:33:52 AM »

...and each rivet location has a small dimple where the rivet heads resisted the force that  caused them to fail, essentially in a single event rather like a zipper unzipping.  If each had been drilled out or sheared off, there would be no reason for the dimpled deformation.  ...

Before making that conclusion spend a few moments with the link that Jeff gave above, in particular p.p. 19ff:

A link to aircraft rivets/fasteners and their use in repairs to aircraft structures and skin to maintain integrity and strength.

http://aviation.spenner.org/AircraftRivetsandSpecialFastners.pdf

It is tempting to simplify the failure mode (or removal mode) of whatever was attached via the small rivets, but in fact that could have been a separate event from the intial web failure / separation from the mother structure.  Note I didn't say "was", but could have been separate events.

The panel as a whole (with intermediate light bracing) could have been 'blown off', i.e. mechanically or hydraulically expressed from the parent structure in some manner so as to leave the bulging effect, etc. that is observed; were simple, light stringers still attached, a secondary action could have removed those - deliberately or not.  Or, the 'skin' could have blown away in some fashion from ALL attachments - provided the underlying bracing was more substantially attached to the parent structure than to the skin.  I have doubts about the latter, mainly because intuition suggests to me (OPINION, CONJECTURE) that the 'underlying' attachments were very possibly very light structure.  My bias rests on the size of the rivets, and the slightly irregular alignment of the holes suggesting a somewhat impromptu arrangement.  I could be wrong - the skin could have been fully attached to heavier stringers in some way yet.

Point being that while the more defined the failure mode might be made and thereby more telling of the possibilities, what really matters is that we appreciate how much this panel might tell us, especially as to what 'mother ship' this item came from. 
- Are we looking at something that experienced an initial, partial separation due to brutal natural forces, e.g. crashing surf against an open structure that was pinned against a reef, and then failed and fully separated due to subsequent cyclic fatigue?  Or -
- Are we looking at something that was manually removed by man's hand from a wreck? 
- What were the opportunities for each of those events (where was the bird and when)?

The artifact was found in the village at Niku - does that mean it was originally harvested there on the island?  I'd like to think so, but a sniff test must include where else might Gardner Islanders might have gotten their hands on pre-war dural and perhaps imported it, if they were given to such as that sort of activity?  At face value it is easy to suppose they must have found it there - especially coupled with anecdotal material regarding an old wreck.

Then we have other odd pieces that TIGHAR has been able to rule out, I believe, such as the navigator's bookcase.  So we have some evidence, I believe, of some imported stuff.  It leaves us with a challenge - but finding a pre-war piece such as this artifact on that island does make for a pretty hot trail marker IMO.
- Jeff Neville

Former Member 3074R
 
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Walter Runck

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Re: Grand Rapids trip
« Reply #55 on: January 28, 2014, 12:00:57 PM »

I'm having a hard time accepting the theory that the rivet heads were blown off without putting a lot of "belly" in the material between the rivet lines, so I went back to the original reports and started modeling the skin, rivets and possible stiffeners.  I'm not sure how far I'll go with this, but it helps me to sort through my ideas and the others posted here.  I have a couple of questions and comments for the Forum.

1.  It looks like there is a typo in the original FAA report regarding the hole/rivet sizes.  The small holes are for 3/32 diameter rivets, not 3/16 as stated in the second sentence of the paragraph describing 2-2-V-1.  This allows the top row of 5/32" holes to be the "big" ones.

2.  The FAA analysis of the surviving rivet claims an indicated thickness of the member it was attached to of .060 inches, roughly 1/16".  This is just twice the nominal thickness of the skin itself.  I'm not an airframe mechanic, so I'm wondering what the likely shape and size of the siffener would be?  How would it have been attached to the existing airframe?

3. I like Jeff's idea about 2-2-V-1 coming from the window skin.  If we wanted to recreate the modification electronically, do we know how the original window and surrounding structure was configured?  Could some of our resident aviation tinknockers offer thoughts on how the job is likely to have been done in Miami?

4.  Would the covering over of the window have required FAA approval?  I'm guessing so, but I haven't seen anything here regarding a Miami FAA records search.

Now it's time to go watch snow in the Deep South.  Always worth the price of admission.
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Tim Collins

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Re: Grand Rapids trip
« Reply #56 on: January 28, 2014, 01:46:29 PM »

- for an aircraft "skin" to have flush mounted rivets, that skin would need to be dimpled to begin with wouldn't it? See the above link re: rivets.
 
- to remove said "skin" from stiffeners to which it is mounted wouldn't the butt end of the rivet need to be removed/chiseled off?  In which case tool marks would be on the [missing] stiffeners not the skin wouldn't they?  Otherwise the external side would show evidence of forceful removal or resistance.

I just can't see how the rivets could all pop off without leaving signs of force to the holes, beyond mere dimpling, than observable (at least as I can see) on the item. Unless of course the rivets were made of something ridiculously soft.  Has anyone done any experiments on similar materials?   

I am of the opinion that suggesting that all the rivets just popped of as a result of some focused force, be it water or air, is akin to pulling a table cloth off a table set with fine china and crystal and expecting nothing to move. 
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Chuck Lynch

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Re: Grand Rapids trip
« Reply #57 on: January 28, 2014, 02:19:48 PM »

In addition to any common rivet pattern alignments, could there be any photographic similarities between the artifact and the 1937 image? Maybe bends or shadows that appear in both photos?  The window "patch" in the photo seems to look less flat and less contoured than the rest of the plane's skin. And if it is a window "patch," then possibly it was not fastened as secure as the original airplane structure, allowing it to be blown off or removed easier..

Just a thought.
« Last Edit: January 28, 2014, 02:22:51 PM by Chuck Lynch »
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John Ousterhout

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Re: Grand Rapids trip
« Reply #58 on: January 28, 2014, 05:24:45 PM »

I think I can answer a couple of the points presented above, but not all:
For Tim - the rivets weren't flush, they had shallow domed heads, that wouldn't cause much drag in designs of the era. The heads of the installed rivets looked rather like the heads of modern-day thumbtacks, but smaller - a low rounded profile with a wide contact area. There was no dimple or countersink involved in the process.  The rivets were made of soft aluminum.  3/32" is the shank diameter, which is quite small.
For Walter - the underlying structural shape might have been in the shape of an "L" or "Z", with 90-degree bends, perhaps only 1/2 inch tall, although I've seen them more commonly about an inch tall. Using material twice as thick as the skin is about right for most stiffeners - the skin provides stiffness at a right angle to the stiffness of the structure, but the combination is still flexible across the structure (the 3rd angle),which would be consistent with a non-load-bearing piece that spanned a relatively narrow space.  The small diameter (3/32") also indicates non-load-bearing use.
The Van's Aircraft Site has lots of very nice photos and descriptions of modern riveting.  Note that they use lots of flush rivets and "pop" rivets, not the domed rivets used on the artifact.
Attaching the stiffeners to surrounding structure could have been done in a variety of ways.  I think Ric or others might be able to offer insight into the methods used in the 1930's.  Otherwise there are a variety of examples to be seen in the Van's aircraft photos.
Jeff's conjectures and caveats are appropriate and well put.  We don't know the sequence of events that resulted in this artifact becoming separated from its aircraft.  I understood that it wasn't found "in the village", but "near the village" on the beach (quotes mine).  It hadn't been seen the previous expedition that looked quite thoroughly in that area, and there were clear indications of wave damage to village structures, leading to the idea that it got washed up there in the recent past.  From where?  An intriguing question.
Also for Tim - the "dimpling" I mentioned was described in the NTSB report:"The skin around these holes was, in general, dimpled inward toward the concave side of the sheet suggesting that the sheet had been area loaded from the concave side while the rivets and underlying structure were intact."
More later...
(added later: the photos of another Lockheed show that the common stringer shapes were C-shape channels]
Cheers,
JohnO
 
« Last Edit: January 29, 2014, 08:00:44 AM by John Ousterhout »
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Ted G Campbell

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Re: Grand Rapids trip
« Reply #59 on: January 28, 2014, 07:19:19 PM »

Jeff Neville,
Do you have any diagrams/pictures that you can share with the forum on how we rivet two sheets of aluminum together?

For example, on a flush rivet we have to countersink the hole before the rivet is put into place and then bucked.  Whereas a brazier head rivet is put into an uncountersunked hole and then bucked into place.
 
When you remove a flush riveted piece of skin there are the countersink marks left behind but when you remove a piece of brazier head riveted skin there is not a noticeable indentation on the skin of the panel – maybe a little depression, which is dependent on the force of the bucking process.

I am thinking that basis the pictures of 2-2-V-1 that I have seen it is suggested there was some type of explosion that caused the panel to come lose i.e. was there a battery in the area were we suspect the panel was installed e.g. subject a lead acid battery to submersion in sea water and what do you get?

I agree with you Jeff, there was something there that caused them (AE/FN) to block out the lavatory window, what could it have been?  Is this where the panel came from I don’t know.

Ted Campbell
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