Artifact 2-3-V-2

[Ric Gillespie]

I've benn corresponding with Odile Madden, the primary scientist on the NASM study. She says,
"Raman and XRF are unlikely to give you any useful information about the date of the PMMA. Raman could tell you it's PMMA, and XRF only identifies elements in the periodic table that are heavier than, say, silicon.  PMMA is just carbon, hydrogen, and oxygen.  If you had a sample of window from a contemporaneous 1936/7 Electra to compare with your sample, it might be possible to do some trace element analysis."

So we're back to destructive testing, provided we could get our hands on an original sample to test.  But there's another question to answer.  Were the cabin windows on NR16020 really Plexiglas?  The engineering order calls for "shatterproof" which we always took to mean Plexiglas, but it might also mean laminated safety glass.  How could we know?  If we had a surviving Lockheed 10 built after January 1937 that still had the original windows, Raman could tell us if they are PMMA, but I'm not aware of such an aircraft.  The Electra at the New England Air Museum is only three serial numbers from Earhart's, but its windows were all replaced during restoration.  The same is probably true of all restored Electras.  The old windows tend to yellow and craze so they get replaced.

[Matt Revington]

This google book preview of "Kelly" by Clarence Johnson mentions on page 50/51 that starting in 1937 the Model 14 Super Electra used "a new Plexiglas for windows" .  If we believe this then Lockheed was using it at that time, of course it does not say if it would be put in the 10E.

https://books.google.ca/books?id=S51fBgAAQBAJ&printsec=frontcover&dq=kelly+more+than+my+share&hl=en&sa=X&ved=0ahUKEwjLsfP5qYHnAhWIiOAKHb1ZBKUQ6AEIKTAA#v=onepage&q=kelly%20more%20than%20my%20share&f=false

[Ric Gillespie]

Thanks Matt.  Very interesting.  The Model 14 first flew on 29 July 1937.  Construction of the prototype began "early that year."  (Lockheed Aircraft since 1913, Francillon, Naval Institute Press, 1987) 

[Greg Daspit]

Regarding evidence that suggests the patch was added because of structural problems after the hard landing:
Using the Miami Nilla Putnam photo and the Miami Taxi photo, or the new film he is analyzing.
Do you think Mr. Glickman can do a proportion study to determine if the patch was lapped over an added reinforcing or splice stringer to the top or bottom of the previous opening? This study would use the seam to the upper right of the patch as a reference.
Compare the X to Y proportions in the Nilla photo to the  X to Y proportions in the Taxi photo to see if one edge related to the seam got bigger? Maybe both? See attachment

Edit: Not sure the best place for this post. The removal of the cabin window stringer noted in this discussion is what instigated the question

[Ric Gillespie]

Regarding evidence that suggests the patch was added because of structural problems after the hard landing:

If the window was removed and the patch installed to rectify the weakness caused by cutting stringers to make a hole for the window, I don't think adding stringers in the places you suggest would do anything to strengthen the empennage.  To restore the integrity of the structure it would be necessary restore the continuity the original stringers. If that's what they did, rivet lines on the patch should coincide with rivet lines on the pre-window empennage.  Based on what we can see so far, they don't.  Only the bottom row of large rivets matches up with an original stringer.  The four rows of small rivets don't line up with anything.  In the attached illustration the standard rivet lines/stringers are in blue and the artifact rivet lines are in red.

I think the reason for removing the window was that the window cracked due to the hard landing and flexing of the weakened empennage.  Flexing of the weakened empennage also caused the deformation we see in later photos of the patch.

Do you think Mr. Glickman can do a proportion study to determine if the patch was lapped over an added reinforcing or splice stringer to the top or bottom of the previous opening?

We already know the patch covered a larger area than the window.  Jeff is just now getting to the point where he can start to confirm the lines of small rivets.  It will be interesting to see if we can confirm rivet lines that suggest the presence of the added stringers/stiffeners you propose.