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[Jerry Germann]

I have been looking for methods of accurate curvature determinations when dealing with fragments,... 7.4 of this article; https://www.fbi.gov/about-us/lab/forensic-science-communications/fsc/jan2005/index.htm/standards/2005standards6.htm    seems interesting ...I believe the determination of 2-3-V-2's curvature was ascertained by placing the fragmented pieces up against an extant Lockheed windowpane, and some may wonder the accuracy of the result, considering the flexibility of plexi, and the test sample used was in fragmented form.
Timeline;.....when did the two fragments found become separated? Do they share the same curvature? If so, that may indicate no additional curvature due to elements after separation, and may narrow the time-frame for warpage to occur. How was the plexi supported after removal from it housing , while on the ground or seas or ??,....If on corral or sand, would the curvature due to heat related bending remain as one would see in standard window design,( a consistent arc shape)... or rather would it take on a non uniform, a twisted bending, cupped shape,if you will, across the artifact, while laying on the scorching sand?

[Ric Gillespie]

I believe the determination of 2-3-V-2's curvature was ascertained by placing the fragmented pieces up against an extant Lockheed windowpane, and some may wonder the accuracy of the result, considering the flexibility of plexi, and the test sample used was in fragmented form.

The curvature was tested by placing the artifact against the cross-section view in the Lockheed engineering drawing and by comparison to an intact Lockheed Model 10 cabin window from c/n 1052 loaned to us by the New England Air Museum.

Timeline;.....when did the two fragments found become separated?

We don't know. They were found together. They fit together, so the saller piece was cut from the larger piece.

Do they share the same curvature?

Yes.

If so, that may indicate no additional curvature due to elements after separation, and may narrow the time-frame for warpage to occur.

If the curvature is due to warpage, the warpage occurred before the small piece was cut from the larger piece.

How was the plexi supported after removal from it housing , while on the ground or seas or ??,....If on corral or sand, would the curvature due to heat related bending remain as one would see in standard window design,( a consistent arc shape)... or rather would it take on a non uniform, a twisted bending, cupped shape,if you will, across the artifact, while laying on the scorching sand?

I take that to be a rhetorical question.

[Jerry Germann]

I take that to be a rhetorical question.

Yes, a bit of food for thought. I believe due to the lack of that evidence, it is supportive of the plexiglass retaining it's original shape. Storage is one way however; that I can see that may allow a sheet good to take on the characteristics of having been originally arc shaped,... if it were stored on edge without adequate, tight supports on either side, for extended periods of time. However; laying on an uneven surface ,and exposed to heat, I don't see the sheet bending in a uniform arc shape manner, rather the surface plane warping unevenly instead.

[Dick Jansen]

Per Ric:

The artifact shows no sign of crazing

This October 1937 research paper says Plexiglas up to at least that point in time had a problem with crazing, even while in storage.  This perhaps suggests a later date of manufacture for the artifact.

http://nvlpubs.nist.gov/nistpubs/jres/19/jresv19n4p367_A1b.pdf


Be forewarned its a 50 something mb file

[Ric Gillespie]

Per Ric:

The artifact shows no sign of crazing

This October 1937 research paper says Plexiglas up to at least that point in time had a problem with crazing, even while in storage.  This perhaps suggests a later date of manufacture for the artifact.

Or perhaps not. If you read the full report and look at the photos on page 379, Fig 5, sample 15 (acrylic resin) you'll see that the "crazing" referred to is a slight clouding, not the white, crackly obscuring I think of as "crazing."  The artifact is not clear and transparent but exhibits considerably cloudiness to the point that it is more translucent than transparent.  In short, the condition of the artifact seems to be entirely in keeping with what would be expected of vintage 1937 Plexiglas that has been exposed to some degree of sunlight for a protracted period.

[Dick Jansen]

I'm not sure that the photos in the report are of sufficient resolution on their own to say much really.  I'm trying to find a 1937 dictionary to see exactly what the definition of the word "crazing" was in 1937...I think we could then, with a good degree of confidence, take that definition to be what the learned authors meant in the report.

Meanwhile,
Per Ric -

The curvature was tested by placing the artifact against the cross-section view in the Lockheed engineering drawing

Note that the Plexiglas remnant measures approximately 4 ¾” in its longest dimension (see first photo below)

The Lockheed drawing defines the cabin window curvature using a straight base line marked with one inch stations and offset measurements to the outside window surface at each station.
http://tighar.org/Publications/TTracks/12_1/PartNumber.html

The copy of the Lockheed drawing shown in the second photo below, was used to demonstrate a curvature match with the artifact, but appears to have been significantly enlarged beyond actual size, evidently by approximately 150%, when compared directly to the known dimension of the artifact (approx. 4.75”).

Since curves are defined by their radii and changing the scale/enlargement of a drawing of a curve also changes its radius, meaningful curvature matching can’t be done by overlaying an actual curved object on a drawing of that object unless the drawing is actual size so the curvature match between the fragment and drawing may need to be confirmed using a life size copy of the drawing.

[Ric Gillespie]

I'm not sure that the photos in the report are of sufficient resolution on their own to say much really.

There was much more to our assessment of the artifact. The curvature of the Electra cabin windows is compound - that is, the plexiglas is not only curved but also slightly bowed.  That's why, as noted that the TIGHAR Tracks article, "To see if it is the same curvature as a Lockheed Electra cabin window we asked our friends at the New England Air Museum in Windsor Locks, Connecticut to send us one from their under-restoration Electra c/n 1052 (Earhart’s was c/n 1055)."
We found that not only did the curve of the artifact match the curve of the window when held edge-to-edge, but when the artifact was laid on the surface of the window the slight "bow" was the same.  I know I took photos at the time.  I'll see if I can dig them out.

The main thing we needed from the engineering drawing was the specified thickness of the material.

[Monty Fowler]

Not to be a wet blanket, but we still can't prove 2-3-V-2 came from Amelia and Fred's plane because there is no surviving paperwork stating it was done. The probabilities are certainly tantalizing, though.

LTM,
Monty Fowler, TIGHAR No. 2189 EC

[Ric Gillespie]

Not to be a wet blanket, but we still can't prove 2-3-V-2 came from Amelia and Fred's plane because there is no surviving paperwork stating it was done.

As I pointed out before, even if we had paperwork stating that 1/8th inch widows were installed on c/n 1055 it wouldn't prove that the plexi found on the island came from one of those windows.  The probability seems to be high, but we'll never get closer than that.

[Frank Hajnal]

Dick or Ric,

Can you provide a link to the Tighar Tracks report that contains the photo with the file name 'curvature.jpg' in Dick's last post?  That photo does not appear in the Tighar Tracks report Dick provided a link to.

Thanks...

[Dave Thaker]

I'm not sure that the photos in the report are of sufficient resolution on their own to say much really.

There was much more to our assessment of the artifact. The curvature of the Electra cabin windows is compound - that is, the plexiglas is not only curved but also slightly bowed.  That's why, as noted that the TIGHAR Tracks article, "To see if it is the same curvature as a Lockheed Electra cabin window we asked our friends at the New England Air Museum in Windsor Locks, Connecticut to send us one from their under-restoration Electra c/n 1052 (Earhart’s was c/n 1055)."
We found that not only did the curve of the artifact match the curve of the window when held edge-to-edge, but when the artifact was laid on the surface of the window the slight "bow" was the same.  I know I took photos at the time.  I'll see if I can dig them out.

The main thing we needed from the engineering drawing was the specified thickness of the material.

Ric, if I understand you, there is measurable curvature to 2-3-v-2 on two perpendicular axes, so it’s not simply a fragment from the a bigger piece shaped like the side wall of right cylinder.  If Electra windows were designed to be curved along two perpendicular axes, then shouldn’t the Lockheed engineering drawing show both of those curves?  Does the Lockheed drawing in fact show both these curves?

What is the radius of curvature of 2-3-v-2, measured along the edge as shown in the curvature.jpg photo?  It should be possible to measure this reasonably well without any fancy tools, shouldn't it?

[Ric Gillespie]

Can you provide a link to the Tighar Tracks report that contains the photo with the file name 'curvature.jpg' in Dick's last post?  That photo does not appear in the Tighar Tracks report Dick provided a link to.

I don't know where he got that photo but that must be my hand.

[Ric Gillespie]

If Electra windows were designed to be curved along two perpendicular axes, then shouldn’t the Lockheed engineering drawing show both of those curves?  Does the Lockheed drawing in fact show both these curves?

You're right.  It should, but it doesn't. I must be remembering it wrong (it was 20 years ago). Apparently the curvature is not compound. I do clearly remember holding the artifact up to the edge of the borrowed window and laying the artifact on the surface of the window and getting a perfect match.

What is the radius of curvature of 2-3-v-2, measured along the edge as shown in the curvature.jpg photo?  It should be possible to measure this reasonably well without any fancy tools, shouldn't it?

I dunno.  How would you do that?

[Steve Treadwell]

What is the radius of curvature of 2-3-v-2, measured along the edge as shown in the curvature.jpg photo?  It should be possible to measure this reasonably well without any fancy tools, shouldn't it?

I dunno.  How would you do that?

One way to do that is to use the old high school geometry method to draw a circle through any three points not in a straight line.  Lay the piece on edge on a large piece of paper and mark three points along the edge - one at each end and one in the middle.  Then connect the points with two straight lines.  Then, using a drawing compass you can bisect each line and draw a perpendicular line at each of the midpoints.  Extend the two perpendiculars until they meet and that is the center of the circle.  The distance from there to any of the three marked points is the radius of curvature.

[Dick Jansen]

Frank asked for the source of the artifact-on-drawing photo...it is included in one of the chapters of this book:
https://books.google.ca/books?id=DDt3AgAAQBAJ&pg=PA12&lpg=PA12&dq=tighar+plexi&source=bl&ots=BxOxnMSDSQ&sig=fpsFjR67BxclDdZ3gmpzskYMUcA&hl=en&sa=X&ved=0ahUKEwjYhIHs443KAhWCWz4KHW6CCpYQ6AEIQzAH#v=onepage&q=tighar%20plexi&f=false


Ric mentioned the artifact nicely matching the curvature of the sample window when laid upon it and this might be a fairly close verification method I guess.  Technically the outer curvature of the window and the inner curvature of the artifact (or vice versa) shouldn't match because their radii differ by 1/8" but I don't know if that difference in radius/curvature would be detectable by eye or feel in practical terms.  The artifact-on-drawing method would seem to be more definitive, as long as the drawing is actual size.