Final Conclusions

The aluminum sheet with the “ALCLAD” marking, allegedly from Amelia Earhart’s Electra aircraft, is actually from a 1940s aircraft — precisely as the aluminum markings predicted. The artifact’s unique rivet pattern matches exactly the top of the wing of a surviving Douglas C-47B Skytrain built in the 1940s. (This is especially significant since a C-47 crashed on Sydney Island in the Phoenix Group.)

Case closed.

Even More ALC Markings

ALC24ST — ca. 1935. Alcoa Aluminum advertisement, Aviation, May 1935, pg. 9. (Image also reproduced in Aero Digest article below.) Link: http://archive.org/stream/Aviation_Week_1935-05-01#page/n42/mode/1up

ALC24ST — ca. 1936. Douglas fuselage frame in “Development of Aluminum for Aircraft,” C.F. Nagel, Jr., Aluminum Company of America, Aero Digest, Feb. 1936, pg. 27. Link: http://archive.org/stream/aerodigest2819unse#page/n148/mode/1up

ALC 24ST — ca. 1936. “Spot Welding vs. Riveting,” Aviation, Oct. 1936, pg. 29. Link: http://archive.org/stream/Aviation_Week_1936-10-01#page/n14/mode/1up

ALC24ST — ca. 1937. “Thrills of the Navy Test Pilots,” Popular Mechanics, Aug. 1937, pg. 227. Link: http://archive.org/stream/bub_gb_79oDAAAAMBAJ#page/n123/mode/2up

ALC24ST — ca. 1937. Alcoa Aluminum advertisement, Aviation, Nov. 1937, pg. 9. Link: http://archive.org/stream/Aviation_Week_1937-11-01#page/n4/mode/1up

ALC24ST — ca. 1938. Rear cover, Curtiss Fly Leaf, December 1938. Link: http://p40hawksnest.co.nf/Curtiss/CFL/CFL38Dec.html

ALC24ST — ca. 1939. “Slots Are Here to Stay,” Kurt Rand, Popular Aviation, Oct. 1939. Link: http://books.google.com/books?id=NR6fckxHa4UC&pg=PA51#v=onepage

ALC24ST — ca. 1940. “Are You Qualified?”, Hurd Barrett, Flying Magazine, Oct. 1940. pg. 32. Link: http://books.google.com/books?id=CJVLeVu8dxMC&lpg=PA1&pg=PA32#v=onepage

ALC24SRT — ca. 1940. “Assembling of a DC-3 / C-47 aircraft, ca.1940,” California Historical Society Collection. Link: http://digitallibrary.usc.edu/cdm/ref/collection/p15799coll65/id/10435

ALC24ST — ca. 1940. “A man working on fuselage in the factory,” George Strock/The LIFE Picture Collection/Getty Images. Link: http://www.gettyimages.com/license/50452689 (Another source: http://www.google.com/culturalinstitute/beta/asset/-/7gHD1-EtIoRKOA.)

ALC24SO — ca. 1940. “29th March 1940: At the Lockheed Aircraft Corporation at Burbank, California, large numbers of high-speed twin-engined planes, part of a previous British order, are being produced,” Photo by Fox Photos/Getty Images. Link: http://www.gettyimages.com/license/3293948

ALC24SO — ca. 1940. HPM Fastraverse Presses advertisement, Aviation, June 1940, pg. 67. Link: http://archive.org/stream/Aviation_Week_1940-06-01#page/n34/mode/1up

ALC24ST — ca. 1941. “Curtis Wright,” Dmitri Kessel, April 1941. Link: http://www.google.com/culturalinstitute/beta/asset/curtis-wright/CQF4HZsxtsB_9Q

ALC24ST — ca. 1941. Multiple photographs, “Glenn Martin Plane Factory,” George Strock, January 1941. Links: 1, 2, 3, 4, 5, 6, 7, 8

ALC24ST — ca. 1941. “B-17E Flying Fortress Camera Pit Below Radio Compartment.” Link: http://www.boeingimages.com/archive/B-17E%20Flying%20Fortress%20Camera%20Pit%20Below%20Radio%20Compartment-2F3XC569VIN.html and http://www.boeingimages.com/archive/B-17E%20Flying%20Fortress%20Camera%20Pit%20Below%20Radio%20Compartment-2F3XC56983J.html

ALC24ST — ca. 1942. Although other aluminum markings were introduced in the early 1940s, the leading edge of this wing still shows faded “ALC24ST” markings. Link: http://www.loc.gov/resource/fsa.8b05338/

ALC24ST — unknown [DC-3]. Handbook of Instructions for the Transport Model DC3-277B for American Airlines, Inc., Douglas Aircraft Company, Inc., pgs. 11, 34, 64, 89, 106A, 145. Link: http://www.avialogs.com/viewer/avialogs-documentviewer.php?id=3248

ALC24ST — unknown [P-36]. P-40 Warhawk in Detail, Part 1: Y1P-36 through P-40C, Bert Kinzey, pg. 26.

1942 Alclad Marking Documentation: “The Aircraft Apprentice”

Further documentation of ALCLAD aluminum markings was published in the 1942 publication, The Aircraft Apprentice, Leslie MacGregor, Pitman Publishing Corp., 1942 (http://hdl.handle.net/2027/mdp.39015003323030).

From page 100 illustrated below: “It may be noticed that some codes are preceded by the letters ALC which signify that the alloy is covered on both sides with a coating of pure aluminum, and is known as Alclad. This coating prevents corrosion and amounts to approximately 10 per cent of the thickness of the sheet.”

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1943 Alclad Marking Documentation: “Aircraft Production Standards”

Additional documentation of ALCLAD aluminum markings from the 1943 publication Aircraft Production Standards, Stuart Leavell and Stanley Bungay, McGraw-Hill, 1943. (http://catalog.hathitrust.org/Record/001040026)

The entire text is not currently available online, but Google Books allows viewing of snippets of the work including the following: “A typical identifying code such as 24ST ALC may be used for an example. This group of numbers and letters will be found stamped repeatedly across the surface of sheet metal. Here the numerals 24 indicate a specific alloy. By referring to the table on page 253, it is possible to find the materials and their percentages used in the composition of this alloy.”

(Source: http://www.google.com/search?amp;channel=sb&tbm=bks&q=%22A+typical+identifying+code+such+as+24ST+ALC+may+be+used+for+an+example.%22)

1942 Alclad Marking Documentation: “How to Do Aircraft Sheetmetal Work”

Another example of documentation of ALCLAD aluminum markings are provided in the 1942 publication How to Do Aircraft Sheetmetal Work, Carl Norcross and James D. Quinn, McGraw-Hill Book Co., Inc., 1942. (http://catalog.hathitrust.org/Record/001039989)

The entire text is not currently available online, but Google Books allows viewing of snippets of the work including the following from page 50: “Alclad is used to a great extent on all-metal airplanes. Usually the sheets forming the fuselage and the wings are of Alclad. Sheets are easily identified because they are stamped “ALC” preceding the identification of the metal, for example, ALC24S-T.”

(Source: http://www.google.com/search?tbm=bks&hl=en&q=Sheets+are+easily+identified+because+they+are+stamped+%22ALC%22+preceding+the+identification+of+the+metal%2C+for+example%2C+ALC24S-T&gws_rd=ssl)

1941 Alclad Marking Documentation: “Aircraft Sheet Metal Work”

Written documentation of ALCLAD aluminum markings in 1941 is provided in Aircraft Sheet Metal Work: Bench and Repair Work, H. Edward Boggess, New York, Pitman Publ. Corp., 1941. (http://hdl.handle.net/2027/mdp.39015018277460).

From page 13 included below: “The letters AL or ALC preceding the alloy designation indicate that the material is Alclad, which means that it has been surfaced on both sides with pure aluminum.” And further on the following page, “Thus a piece of metal labeled AL-17ST-ANA would be heat-treated, Alclad dural which conforms to the Army and Navy specifications and comes from the mill at Alcoa, Tenn.”

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Numerous photographs show the “ANA” mill/plant marking, but this photograph is the only example discovered to date showing the “ANK” mill/plant marking. (Source: National Archives, http://research.archives.gov/description/535581)

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1930s and Early 1940s ALCOA Aluminum Markings

Documented examples of 1930s and early 1940s aluminum markings. Click each image to enlarge.

All known photographs of aluminum markings from the 1930s show Alcoa Alclad aluminum was marked “ALC24ST” and “ALC24SRT”.

Photographs show “ALC24ST” and “ALC24SRT” markings on aluminum in aircraft from:

Boeing
Douglas
Lockheed
Severski
Glenn L. Martin Co.

Boeing XB-17 (Model 299):

Marking: ALC24SRT
Font: serif
Aircraft: XB-17 (Model 299)
Company / Factory: Boeing
Date: N/A
Source: http://www.nationalmuseum.af.mil/factsheets/factsheet.asp?id=2488
Notes: Additional examples of markings visible in image: http://www.nationalmuseum.af.mil/shared/media/photodb/photos/060706-F-1234S-009.jpg

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Douglas DC-3:

Marking: ALC24ST
Font: serif
Aircraft: Douglas DC-3
Company / Factory: Douglas
Date: N/A
Source: Airplane Maintenance, Hubert G. Lesley, 1940. http://babel.hathitrust.org/cgi/pt?id=mdp.39015009844682;view=2up;seq=324
Notes:

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Seversky P-35:

Marking: ALC24ST
Font: serif
Aircraft: P-35
Company / Factory: Seversky
Date: N/A
Source: http://warbirdinformationexchange.org/phpBB3/viewtopic.php?p=186428
Notes:

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Unknown Glenn L. Martin Co. Aircraft:

Marking: ALC24ST
Font: serif
Aircraft: N/A
Company / Factory: Glenn L. Martin Co.
Date: N/A
Source: http://www.amazon.com/Elevator-Aircraft-Lockheed-Assembly-Airplane/dp/B005F13THK
Notes: 1939 half-tone print.

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Unknown Douglas Aircraft:

Marking: Either ALC24ST or ALC24SRT
Font: serif
Aircraft: N/A
Company / Factory: Douglas
Date: N/A
Source: Airplane Maintenance, Hubert G. Lesley, 1940. http://babel.hathitrust.org/cgi/pt?id=mdp.39015009844682;view=2up;seq=500
Notes:

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Caltech Thesis:

Marking: ALC24ST
Font: serif
Aircraft: N/A
Company / Factory: N/A (Caltech research thesis, thesis acknowledges Douglas and North American Aviation assistance with the specimen)
Date: 1938
Source: http://thesis.library.caltech.edu/2706/1/Dunn_lg_1938.pdf

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Earhart’s Electra:

Marking: ALC24ST
Font: serif
Aircraft: Earhart’s Electra
Company / Factory: Lockheed
Date: ca. 1936
Source: http://earchives.lib.purdue.edu/cdm4/item_viewer.php?CISOROOT=/earhart&CISOPTR=344&CISOBOX=1&REC=3 (URI: ark:/34231/c6n014h4) and http://earchives.lib.purdue.edu/cdm4/item_viewer.php?CISOROOT=/earhart&CISOPTR=529&CISOBOX=1&REC=3 (URI: ark:/34231/c6p26w46)

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Lockheed Electra:

Marking: ALC24ST
Font: serif
Aircraft: Electra
Company / Factory: Lockheed
Date: N/A
Source: “Lockheed Aircraft Corp. Report No. 421”. (Internal pages include dates from 1934 to 1936.)
Notes: Via private communication. No online source at this time.

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Aircraft Template Development (1942):

Marking: ALC24ST
Font: serif
Aircraft: N/A
Company / Factory: N/A
Publication Date: 1942
Source: Aircraft Template Development, Ernest J. Gentle, 1942. (http://babel.hathitrust.org/cgi/pt?id=wu.89090515669;view=2up;seq=38 and http://babel.hathitrust.org/cgi/pt?id=wu.89090515669;view=2up;seq=40)

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NACA TN No. 752, Investigation of Sheet-Stiffener Panels (1940):

Marking: ALC24ST
Font: serif
Aircraft: N/A
Company / Factory: N/A
Publication Date: Feb. 1940
Source: NACA TN No. 752: An Investigation of Sheet-Stiffener Panels Subjected to Compression Loads, Louis G. Dunn, Feb. 1940. (http://babel.hathitrust.org/cgi/pt?id=mdp.39015069157462;view=2up;seq=60)

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George Arnold Photo:

Marking: ALC24SRT
Font: serif
Aircraft: N/A
Company / Factory: N/A
Date: ca. 1934 – 1939
Source: http://www.flickr.com/photos/sdasmarchives/12002881944/in/photostream/ (SDASM Archives)
Notes: According to SDASM Archives: “Photograph dates range from 1934-1939. In 1937, George Arnold was in Shien Chaio, China to build the aircraft factory.”

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NACA TN 883 (1943):

Marking: ALC24ST
Font: serif
Aircraft: N/A
Company / Factory: Alcoa
Publication Date: 1943
Source: “TESTS OF ALUMINUM ALLOY STIFFENED SHEET SPECIMENS CUT FROM AN AIRPLANE WING”, Marshall Holt, TECHNICAL NOTES, NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS No. 883, Aluminum Company of America, Washington, January 1943. (http://hdl.handle.net/2060/19930081583)
Notes:

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OTHER FRAGMENTARY OR NON-ALCLAD EXAMPLES WITH SIMILAR MARKINGS SIZE AND MARKINGS FONT:

TBD Devastator:

Marking: 24SO
Font: serif
Aircraft: TBD Devastator
Company / Factory: Douglas
Date: N/A
Source: http://tailhooktopics.blogspot.com/2012_02_01_archive.html

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Boeing 314 Clipper:

Marking: 24ST
Font: serif
Aircraft: Boeing 314 Clipper
Company / Factory: Boeing
Date: 1938 (approx. February 28, 1938)
Source: http://digitalcollections.lib.washington.edu/cdm/singleitem/collection/imlsmohai/id/4509/rec/99

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Airplane Metal Work, Vol. 2 (1941):

Marking: Unknown
Font: serif
Aircraft: N/A
Company / Factory: N/A
Publication Date: 1941
Source: Airplane Metal Work, Vol. 2, Alex M. Robson, 1941. (http://babel.hathitrust.org/cgi/pt?id=mdp.39015019904690;view=2up;seq=50 and http://babel.hathitrust.org/cgi/pt?id=mdp.39015019904690;view=2up;seq=76)

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F-10-G Fleet:

Marking: 17ST
Font: serif
Aircraft: N/A
Company / Factory: Consolidated
Date: 1934 (approx. September 12, 1934)
Source: http://www.flickr.com/photos/sdasmarchives/14067179107/sizes/o/ (SDASM Archives)
Notes:

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Mech. Prop. of Flush-Riveted Joints (1940):

Marking: N/A
Font: serif
Aircraft: N/A
Company / Factory: N/A
Publication Date: 1940
Source: Bruggeman, Wm. C. & Roop, Frederick C., “Mechanical Properties of Flush-Riveted Joints”. UNT Digital Library. http://digital.library.unt.edu/ark:/67531/metadc65026/.
Notes:

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To Do:
– Add Lockheed Electra
– Add DC-2 example
– Add examples from the Alcoa Aluminum book
– To add: http://www.edcoatescollection.com/ac3/Airline/TWA%20Douglas%20DC-2.html

Aluminum Markings Online

Online photographs showing examples of ALC24ST and ALCLAD markings, primarily dating from the WWII-era:

http://s982.photobucket.com/user/GunnerySgtJackson/media/B24crashsite020.jpg.html?sort=3&o=76
http://www.airforums.com/forums/f381/can-aluminum-skin-be-welded-92625.html
http://colesaircraft.blogspot.com/2012/11/anatomy-of-p-51-mustang-loss.html
http://vanislesecret.blogspot.com/2007/09/historic-64-year-old-dakota-crash-site.html
http://aluminiumidler.blogspot.com/2010/04/endcapitus.html
[repro] http://www.vulturesrowaviation.com/helldiver10_2010.html
[black ink? maybe not alclad] http://746project.wordpress.com/parts/right-wing/right-wing/dsc01995/
http://746project.wordpress.com/parts/right-wing/left-wing/ (http://746project.files.wordpress.com/2012/11/dsc02016.jpg?w=1200&h=&crop=1)
http://www.network54.com/Forum/149674/thread/1266421967/1266668813/HELP+NEEDED-WW2+wreck+parts+identification-B-17–
http://www.questmasters.us/B-24_Page_8.html
http://i.imgur.com/OdDawew.jpg
http://i.imgur.com/kEvPkaN.jpg
http://i.imgur.com/rwZcVZq.jpg
http://www.pacificwrecks.com/douglas/wrecks/mavis/mavis.html
http://www.pacificwrecks.com/aircraft/c-47/43-16261/index.html

http://www.ilmasotakoulunkilta.fi/IlmaSK/ilmaskmma.nsf/sp?open&cid=Content6685E&screen=blogentryscreen&blogid=Content6685E
http://www.flickr.com/photos/sdasmarchives/12528711784/
http://www.flickr.com/photos/sdasmarchives/12528352113/
http://www.flickr.com/photos/sdasmarchives/12528346613/
http://www.flickr.com/photos/sdasmarchives/12002811563/
http://www.flickr.com/photos/sdasmarchives/10317525683/
http://www.flickr.com/photos/sdasmarchives/10317388326/
http://www.p-35.com/new_page_3.htm
http://warbirdinformationexchange.org/phpBB3/viewtopic.php?p=186428

NEW!

//www.nationalmuseum.af.mil/shared/media/photodb/photos/060720-F-1234P-007.jpg

//commons.wikimedia.org/wiki/File:Production_aids-Ruby_Reed_and_Merle_Judd_of_Grumman_Aircraft_Engineering_Corporation._-_NARA_-_535581.tif
//commons.wikimedia.org/wiki/File:Sheet_metal_parts_are_numbered_with_this_pneumatic_numbering_machine_in_North_American%27s_sheet_metal_department,_North_American_Aviation,_Inc,_Inglewood,_Calif.jpg
//commons.wikimedia.org/wiki/File:American_workers_give_up_holiday_to_speed_Victory._The_Blackwelder_family_celebrated_Thanksgiving_at_their_benches_in…_-_NARA_-_196459.jpg

[24ST-PC?] //www.airpages.ru/book/b24d_112.jpg
//www.airpages.ru/book/b24d_110.jpg

[ANA] //legendsintheirowntime.com/Content/1945/B24_Av_4507_DA_attach_p124_W.png
//legendsintheirowntime.com/Content/1945/B24_Av_4507_DA_interior_p125_W.png
//legendsintheirowntime.com/Content/1945/B24_Av_4507_DA_top_p125_W.png

Stencilling and sheets, not necessarily ALCLAD:
http://www.loc.gov/pictures/resource/fsa.8b00608/
http://www.loc.gov/pictures/resource/fsa.8d07130/
http://www.loc.gov/pictures/resource/fsa.8b05105/
http://www.loc.gov/pictures/resource/fsa.8d42808/
http://www.loc.gov/pictures/resource/fsa.8b06275/

Combination of plate markings and thicker piece markings:
http://babel.hathitrust.org/cgi/pt?id=mdp.39015009844682;q1=alclad%20surface%20scratch;page=root;view=image;size=125;seq=501;num=483

(Credit: Thanks to many other researchers for helping discover these images and links.)