A long-time TIGHAR observer who read my post pointed me to a document on the TIGHAR web site that does provide an actual thickness measurement for 2-2-V-1. In 2015, Lehigh Testing Laboratories in New Castle, Delaware performed chemical and mechanical tests on several specimens of aluminum sheet submitted by TIGHAR, including a specimen cut from 2-2-V-1 [5]. A table on page five of the report listing the measured dimensions of each specimen reports that the 2-2-V-1 specimen was found to be .030 inches thick.
This measurement result raises the possibility that 2-2-V-1 is not a piece of .032 inch 24ST aluminum sheet as TIGHAR has long supposed it to be, but instead that it is a piece of .028 inch 24ST aluminum sheet. Note that I’m talking here about nominal thicknesses, not actual thicknesses, of aluminum sheeting. As discussed in my last post, at the time that artifact 2-2-V-1 was produced the thickness tolerances for Alclad 24ST sheet were .0025 inches for both nominal thicknesses, .028 and .032 inches. This means that nominal .028 inch 24ST aluminum sheet manufactured back then might actually be as much as .0305 inches thick, and nominal .032 inch 24ST aluminum sheet might be as little as .0295 inches thick. A thickness of .030 inches falls within the acceptable ranges for both nominal thicknesses and so it isn’t possible to know from this one measurement whether 2-2-V-1 was fabricated from a piece of .028 inch or .032 inch aluminum sheet.
The same person who pointed me to the Lehigh Laboratories thickness measurement pointed me to a thread on TIGHAR’s online discussion forum, excerpted below, in which Ric Gillespie reported his own thickness measurement results for 2-2-V-1 [6]. This part of the discussion was prompted by TIGHAR’s announcement that Lehigh Testing Laboratories would be analyzing specimens from 2-2-V-1.
++++++++++++
TIGHAR announcement quoted by forum member: Lehigh Testing Laboratories, Inc. was recommended to TIGHAR by Prof. Eager at MIT as the best lab for trying to learn more about 2-2-V-1 (and other aluminum artifacts) through materials analysis. By pure coincidence, LTL is located in Wilmington Delaware about 45 minutes from TIGHAR HQ. I contacted LTL and dropped Tom Eagar's name. They responded with enthusiasm and today we set out a program of testing that should give us the answers to a number of important questions. Those answers could confirm our fondest conclusions about 2-2-V-1 or they could blow them out of the water... I won't try to list the alphabet soup of technologies LTL will be using to do this work. They're doing this pro bono because such is TIGHAR's reputation in the scientific community that they consider it an honor to be asked to help with our investigation. What they'll be doing represents thousands, perhaps tens of thousands, of dollars worth of work if hired at commercial rates. The results we'll get will be scientifically sound, whether or not they're what we want to hear.
Forum Member: Would it be possible to have LTL confirm the gauge of the aluminum? I believe the NTSB is the only one that measured it at .032, and I think at least one of their other measurements was slightly off (the convergence of the rivet rows?). It would be helpful to know for sure what the gauge is. Just a suggestion.
Gillespie: Your belief is in error. The thickness of the sheet has been checked many times by many people. All it takes is a micrometer.
Forum Member: Alas I have no micrometer at my disposal at the moment nor access to the piece and am therefore dependent upon the written reports of others in this regard. Could you please direct me to a source(s) that describes and documents any of the many gauge measurements that were made (other than the NTSB report already mentioned), preferably one that includes a description of the tolerance levels involved. Thank you.
Gillespie: Okay. Here's a written report especially for you. I have a micrometer and I have access to the piece and I have measured it numerous times. It's .032". You can choose not to believe me and wait for the LTL report which will include much more detail.
++++++++++++
Gillespie’s answer may be flippant, but it nevertheless contains some useful information. His belief that 2-2-V-1 is a piece of .032 inch 24ST aluminum sheet is based at least in part on multiple thickness measurements that he himself made using a micrometer. But remember what Gillespie said in questioning Tom Palshaw's micrometer skin thickness measurements on the NEAM C-47 wing [7]:
“I know from experience that measuring skin thickness with a digital micrometer is difficult and frustrating. Measure three times and get three different answers. With a little confirmation bias you can get any result you want.”
Tom’s follow-up measurements made using an ultrasonic thickness gauge show that Tom’s original micrometer measurements were correct. I think it’s fair to ask whether Gillespie’s own thickness measurements on 2-2-V-1 might have suffered from confirmation bias. When Gillespie made his measurements, what sheet thicknesses did he think 2-2-V-1 might have been manufactured from? Current aluminum product catalogs like the one reproduced below don't list a sheet thickness between .025 and .032 inches for 2024-T3 Clad aluminum, the modern designation for 24ST Alclad. As discussed in my last post, Alcoa product literature from the early 1940s list .028 inches as an available thickness for Alclad 24ST sheet. Did Gillespie know that when he made his measurements? I wonder if Gillespie arrived at his firmly stated .032 inch thickness for 2-2-V-1 through the following process:
1. Gillespie measures 2-2-V-1’s thickness several times with a micrometer; his measurement results cluster around some value between .032 inches and .025 inches, but closer to the former value;
2. Gillespie knows that Alclad 2024 aluminum sheet is currently produced in nominal thicknesses of .025 and .032 inches but is unaware that decades earlier it was produced in a nominal sheet thickness of .028 inches;
3. Since Gillespie’s micrometer measurement results for 2-2-V-1 are closer to .032 inches than to .025 inches, he concludes that 2-2-V-1 is a piece of 24ST Alclad sheet of .032 inch nominal thickness.
 |
| Thyssennkrupp Aluminum Stock Guide [8] |
If any readers out there know of TIGHAR data that convincingly settles the matter of whether 2-2-V-1 is a piece of nominal .028 inch of .032 inch aluminum sheet, please let me know where to find it. If there is no such data — and I suspect that there isn’t — TIGHAR needs to arrange to have quality measurements made to try to settle this question. Tom Palshaw noted in his most recent report update that factors such as corrosion, shape, installed fastener effects, and stress induced changes to original dimensions would need to be carefully considered in making thickness measurements on a beaten up, weathered piece of aluminum sheet like 2-2-V-1, and so this is not a job for an amateur wielding a micrometer, with all due respect to Ric Gillespie.
Why is it important to accurately characterize 2-2-V-1’s thickness? Tom Palshaw has shown that 2-2-V-1’s rivet pattern matches the rivet pattern on the upper wing of a C-47 at the New England Air Museum (NEAM). It is reasonable to think that the rivet pattern match would extend to many other C-47s, including the C-47 that crashed on Sydney Island. Tom has confirmed through ultrasonic thickness gauge measurements that NEAM C-47 wing skin is .032 inches thick at the location of interest, the same thickness that TIGHAR has long reported for 2-2-V-1. C-47 repair manuals indicate that the skin of a C-47 should be .028 inches thick at the location of the rivet pattern match, and so it is not a sure thing that the Sydney Island C-47 would also have a seemingly non-standard .032 inch skin thickness at the matching location. On this basis Ric Gillespie can say that the rivet pattern match to the NEAM C-47 wing is a “crazy coincidence”, and TIGHAR’s claim that 2-2-V-1 is a piece of Amelia Earhart’s Electra can perhaps limp along, badly wounded but not dead. But the .030 inch thickness value measured by Lehigh Testing Labs suggests that if 2-2-V-1 might really a piece of nominal .028 inch 24ST Alclad. If careful thickness measurements show this to be true, there would be no reason left to think that 2-2-V-1 wasn’t a piece of the wing of the Sydney C-47 wreck. The match in rivet patterns between 2-2-V-1 and the NEAM C-47 wing makes it reasonable to think that the Sydney C-47 wing matched 2-2-V-1’s rivet pattern at the location of interest. If 2-2-V-1 is nominal .028 inch aluminum sheet then it matches the thickness for a C-47 wing at the matching location given in repair manuals. There would be no physical attribute of 2-2-V-1 that can't be matched to a C-47 wing. The claim that 2-2-V-1 is a piece of Amelia Earhart’s Electra would truly be dead.
Comments, corrections, additional relevant facts, differing viewpoints, etc., are welcome. Send to gardnersghost@gmail.com
+~+~+~
Footnotes/References
[1] https://tighar.org/smf/index.php/topic,2074.msg43572.html#msg43572
[2] (NTSB) https://tighar.org/Projects/Earhart/Archives/Documents/NTSB_Report/ntsbreport.html
[3] (MMR) https://tighar.org/Projects/Earhart/Archives/Research/ResearchPapers/Artifact2-2-V-1/MMR%20Project%20No.%20128927%20Report.pdf
[4] Letter from MIT Professor Thomas Eagar to Ric Gillespie https://tighar.org/wiki/2-2-V-1#cite_note-3
[5] The Lehigh Testing Laboratories Report can be downloaded at: https://tighar.org/Projects/Earhart/Archives/Research/Bulletins/75_Findings2-2-V-1/75_Report_of_Findings_2-2-V-1.html
[6] https://tighar.org/smf/index.php/topic,1490.msg35664.html#msg35664
[7] https://tighar.org/smf/index.php/topic,2074.msg43575.html#msg43575
[8] http://www.tkmna.com/wcm/idc/groups/internet/documents/web_content/mdaw/mdiy/~edisp/d_004646.pdf
