Friday, February 14, 2020

Is 2-2-V-1 Piece of the Sydney Island C-47 Wreck? Update #4

Since my last post on the topic of Tom Palshaw’s report, there have been new developments that are worth discussing. In a recent post on TIGHAR’s online discussion forum [1], Ric Gillespie rejected the report’s conclusion that TIGHAR Artifact 2-2-V-1 is a piece of the wing of a C-47 transport plane that crashed on Sydney Island. Gillespie writes:

TIGHAR Artifact 2-2-V-1 did not come from a C-47.  The Wing Plating diagram in the C-47 structural repair manual shows the skin thickness in the entire area where the rivet pattern allegedly matches 2-2-V-1 is .028".  The artifact's skin thickness is .032”

Tom Palshaw measured the skin thickness on the C-47B wing at the New England Air Museum as .032 using a micrometer at the edge of the skin.  .004" is an easy error to make. It's a small but important discrepancy.  The NTSB lab, Professor Eager at MIT, and the Massachusetts Materials Research metallurgical lab all measured 2-2-V-1 as .032”.

The C-47 manual dates from September 1942 and was updated in 1945.  There is no indication that the basic structural components of the wing were changed. With this new information, the rivet pattern on the C-47 wing, although remarkably similar to the artifact, becomes another of the crazy coincidences we sometimes encounter.

In response to this critique, Tom Palshaw has updated his report with new skin thickness measurements on the NEAM C-47 wing at the location of interest. These measurements were made by a level 2 nondestructive testing technician from Bombardier Business Aircraft Service Center using an ultrasonic thickness gauge. I take it that this technique is not prone to sort of errors that Ric Gillespie suggests might have afflicted Tom’s original measurements.  Five ultrasonic thickness gauge measurements yielded skin thicknesses of 0.032, 0.031, 0.032, 0.031, and 0.032 inches. These new measurements confirm that the skin of the NEAM C-47 wing at the location of interest is the same thickness that TIGHAR has reported for 2-2-V-1.

 Wing location matching 2-2-V-1 is marked in yellow (Markup by Palshaw of a DC-3 repair manual; See Ref. 8)

As Ric Gillespie points out, C-47 repair manuals indicate that the skin of the NEAM C-47 wing should be .028 inches thick at the location of interest. It isn’t clear why the NEAM C-47 wing’s skin at the location of interest is thicker than repair manuals indicate it should be. Damaged aircraft skin is often replaced with sheeting in the next higher thickness produced by manufacturers, which in this case would be .032 inches thick. Tom tells me he’s sure that at the location of interest the C-47 wing skin is original factory-installed Alclad 24ST aluminum alloy sheeting, not a later repair. For what it’s worth, I’ll note that .028 inch 24ST aluminum alloy sheeting is not listed as a standard size normally carried in stock in 48 inch widths in the Alcoa's Aluminum in Aircraft published in 1941.  Would sheeting of that width be needed for fabricating the skin at the location of interest on the C-47 wing? If so, perhaps this is a clue that should be pursued in understanding why the NEAM C-47 wing skin is .032 inches thick at the location of interest. Something else that suggests .028 inches is not your typical aluminum alloy sheet thickness: the 1943 version of Aluminum in Aircraft has only one mention of .028 inch aluminum -- in a table of sheer strengths of spot welds for various metal thicknesses

Aircraft sheet metal thickness table, Aluminum in Aircraft, Published by Alcoa in 1941

Spot weld shear strength table, Aluminum in Aircraft, Alcoa 1943

As things now stand, Tom Palshaw has shown that a location on the wing of the NEAM C-47 closely matches 2-2-V-1 in terms of rivet line spacing, rivet pitch, irregularities in pitch of its -5 rivets, and that it has the same .032 inch thickness that TIGHAR has reported for 2-2-V-1. The NEAM C-47 wing and 2-2-V-1 match in every physical attribute determined so far.  From the standpoint of physical dimensions the match between 2-2-V-1 and the NEAM C-47 wing has been better established than the match between 2-2-V-1 and Amelia Earhart’s Electra. As discussed in my last post, past TIGHAR efforts have failed to demonstrate that 2-2-V-1 fits within the boundaries TIGHAR defined for the putative source location on Earhart’s airplane, the window patch installed at Miami in 1937.

The letters ‘AD’ that are faintly visible on the artifact’s surface are another feature that is consistent with the idea that 2-2-V-1 is a piece of the Sydney Island C-47. To help factory workers identify aluminum sheet stock, Alcoa applied material markings to the aluminum sheeting it produced. The Aluminum Markings web site documents a clear trend in how Alcoa’s material markings for Alclad 24ST aluminum sheeting that aircraft skins are made of changed over time.  Photos of aircraft manufactured before 1942, including Amelia Earhart’s Lockheed Electra, consistently show the marking to be  ‘ALC 24ST’.  Photos of aircraft manufactured from 1942 onward predominantly show the marking to be  ‘ALCLAD 24 ST’, though some photos show aluminum aircraft parts marked ‘ALC 24ST’.  So the photographic evidence —a lot of it— indicates that by early 1942,  had Alcoa started to mark 24ST Alclad sheeting it manufactured with a new material marking, ‘ALCLAD 24ST’. This line of evidence therefore tells us that the window patch attached to Earhart’s Electra in Miami in 1937 could not have the letters ‘AD’ seen on 2-2-V-1 because because Alcoa didn’t start using the ‘ALCLAD 24 ST’ material marking for several more years.

Remnant of 'AD' on Artifact 2-2-V-1. See reference [5] for source

B-25 factory photo, circa 1942. Note 'ALCLAD 24S-T' markings to left of female worker

Underside of Earhart's Electra, circa 1937. The material marking reads 'ALC 24ST'. Full photo at upper right

The similarities between the NEAM C-47 wing and 2-2-V-1 are just too great to be dismissed as a ‘crazy coincidence’.  The problem with the assertion that the wing of the Sydney Island C-47’s can’t be the source of 2-2-V-1 because repair manuals indicate that skin at the location of interest shouldn’t be .032 inch thick is that an actual C-47 wing, the one at NEAM, shows that C-47 wings were not always manufactured with the skin thicknesses indicated in repair manuals.

The right thing for TIGHAR to do, given the evidence Tom Palshaw has produced, is gather evidence that might shed further light on the Tom’s conclusion that 2-2-V-1 is a piece of wreckage scavenged from the Sydney C-47. To misrepresent a piece of the Sydney C-47 wreck site as a piece of Amelia Earhart’s Lockheed Electra would be a disservice to those who died in the Sydney C-47 crash and to the crew of the Electra. Surely TIGHAR would want no part of such an abomination.

TIGHAR should carefully document how well the rivet pattern on the NEAM C-47 wing matches 2-2-V-1. Laying 2-2-V-1 over the NEAM wing at the location of interest and documenting the match with photographs would take no more than ten or fifteen minutes to do. While at NEAM to conduct this comparison, TIGHAR can also demonstrate whether or not 2-2-V-1 fits within the boundaries defined for the dimensions of the Miami window patch in a previous TIGHAR study [2]. This too would be a simple exercise that would only take minutes to carry out. These comparisons should be done with the full cooperation of Tom Palshaw. I find it odd that Ric Gillespie visited NEAM only a few weeks ago to conduct measurements on the NEAM Electra but gave Tom Palshaw no advanced notice of his visit.

Another basic piece of information that needs to be better documented is 2-2-V-1's thickness. Although TIGHAR has repeatedly stated that 2-2-V-1 is .032 inches thick, I can find no clear information about how 2-2-V-1’s thickness was determined. A few posts further along the discussion thread in which Ric Gillespie dismisses Sydney Island C-47 as the source of 2-2-V-1, he comments that “The NTSB lab, Professor Eager at MIT, and the Massachusetts Materials Research metallurgical lab all measured 2-2-V-1 as .032” [3]. I’ve reviewed all three of these sources [4,5,6] and as best I can tell, 2-2-V-1’s thickness was not actually measured by NTSB, MIT or the metallurgical lab. Where the thickness of 2-2-V-1 is stated in these sources the authors appear to simply be stating the artifact thickness reported to them by TIGHAR. There certainly is no description in any of these sources of a measurement method or a presentation of actual measurement data.

Surely the 0.32 inch thickness TIGHAR has reported is based on an actual measurement, but how that measurement was made and what the actual measurement result was has never been reported, as far as I know. Did Ric Gillespie make these measurements using a micrometer? If so, then the claim that 2-2-V-1 is .032 inches thick is based on the same measurement technique that Ric Gillespie has said could easily be in error by .004 inches. Gillespie in a later post on the same TIGHAR discussion forum states: “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” [7]. Here it is worth quoting something Tom wrote in his latest update on the NEAM C-47 skin thickness measurements:

Measuring the thickness of a new sheet of ALCLAD is as simple as using a standard 1" micrometer. The metal is smooth, flat, and clean. Once the metal has been installed, or exposed to the elements, several factors can affect the accuracy of the measurement. These include a paint coating, corrosion, shape, installed fastener effects and stress induced changes to its original dimensions.

2-2-V-1 is not a fresh new sheet of aluminum alloy, it is a beaten up sheet of aluminum alloy that undoubtedly has been exposed to the elements for many years. The Massachusetts Materials Research Laboratory report on 2-2-V-1 describes it thusly:

Overall, the artifact presented a grey, oxidized aluminum appearance with isolated regions of buff-colored calcareous deposits and thin, green discolorations. Both the buff and green deposits were reported to have been previously tested and found to be consistent with coral and algal growths

Note that before making his new measurements on the C-47 wing, Tom gently removed accumulated surface coatings from his measurement locations using a Scotchbrite pad. Were surface deposits accumulated in the years of exposure of 2-2-V-1 to the elements removed before its thickness was measured? Tom points out that at the time artifact 2-2-V-1 was produced, the thickness tolerances for Alclad 24ST sheet was .0025 inches for manufactured sheeting in either the .028 or .032 inch thickness. For all we know, 2-2-V-1’s actual thickness falls within the range falls within the range for nominal .028 inch sheeting, but TIGHAR has erroneously reported it to be .032 inches thick. For example, if 2-2-V-1 was nominal .028 inch sheeting whose actual manufactured thickness was .029 (well within the manufacturing tolerance) with a .001 inch thick coating of weathering/coral/algal residue, and a .001 inch micrometer measurement error was made, the measured thickness would have been .031 inches (.029+.001+.001=.031). The individual making the measurement might have  concluded that 2-2-V-1 was .032 inch thick since this was the closest nominal Alclad 24ST sheet thickness to the measurement result.

Clearly then another thing TIGHAR must do is document what 2-2-V-1’s thickness was when manufactured. Given the .0025 inch manufacturing tolerance, it may not be possible to definitively exclude that 2-2-V-1 was either nominal product thickness, .028 or .032 inches. The determination of 2-2-V-1’s original manufactured thickness is yet another activity that TIGHAR could and should carry out in collaboration with Tom Palshaw. The effects of factors Tom mentions in his update such as shape, installed fastener effects, and stress induced changes to original dimensions would need to be carefully considered.

It would also be useful to accumulate more information about rivet patterns and skin thicknesses of surviving C-47s and DC-3s in museum and private collections. Tom’s update includes ultrasonic measurements of the thickness of the skin of the NEAM DC-3 at the location of interest [8], and there the measurements indicated a skin made of .028 inch nominal sheeting. Accurate skin thickness measurements made on other C-47s and DC-3s might reveal a pattern relevant to the question of whether the Sydney C-47 is the source of 2-2-V-1.

Comments, corrections, additional relevant facts, differing viewpoints, etc., are always welcome.  Send to

[2] Earhart Project Research Bulletin #73, The Window, the Patch, and the Artifact.
[3] See the TIGHAR discussion forum post at reference 1
[6] Links to the MIT emails can be found at
[7] [,2074.msg43575.html#msg43575]
[8] DC-3s and C-47s are to a great extent the same airplane, the former manufactured for use as a civilian airliner while the latter was made to be a military transport. The wing diagram above comes from a 1940s-vintage DC-3 repair manual