I thought that, rather than look a markings on well-dated Alclad in photos, which are somewhat scarce, I’d take a look at the appearance of the terms ‘24S-T’ and 24S-T3’ in the technical literature. The NACA digital library lists some 8000 papers published between 1917 and 1958. About 30 of these papers have ‘24S-T’ in their titles, the earliest dated 1936 and the latest dated 1949. The earliest ’24S-T3’ title I see is a paper published in 1950, and there are another 6 or so dated between 1950 and 1958. This suggests that the it wasn’t until some time around 1950 that the designation ‘24S-T3’ began to appear.
The fuselage modifications on Electra c/n 1015 that we see in Matching the Markings are marked ‘ALCLAD 24S T3’, so the chronology of appearance of 'T3' in the NACA titles suggests that the modifications to c/n 1015 were made no earlier than about 1950.
Suggests... but far from a definitive answer.
Two points -
- What is known as "T3" (solution heat treated and then cold worked) has been with us since far earlier than "1950", and
- Titles of technical papers hardly define what is likely to be found on production material where such processes were in existance.
There are definitely shifting terms and I believe "T3" did replace an earlier "ST" designation at some point.
As to 2-2-V-1, I am far from satisfied that we as-yet have a fully definitive picture of just what characters are really there; my belief is that more information is 'in there', if it can be teased out by hyperspectral analysis or some other means. So while I could cautiously observe that we have some interesting characters to look at so far, I'm not certain that we're seeing a full definition of the original characters, or that others don't still exist that still evade the human eye. I certainly do not as-yet see "T3" or any characters other than a tell-tale "A" and "D" on the artifact.
So thanks for the research and "suggestion", which I simply find far from conclusive. I hardly see it as grounds to dismiss 2-2-V-1 (which is clearly your intent, no need to bandy words over that).
I agree with Steve - it's worth looking into the history of the 'T3' temper- maybe it will be found on 2-2-V-1...
...and 'T3' does appear to date to around 1950 Jeff, not "far earlier."
Please read again - you've missed my meaning, which was that the actual hardening technique predates the change in designation to "T3", at least in my understanding, i.e. that an aluminum product could be "solution heat treated and then cold worked" has been true much longer, I believe, and therefore the change in designation as would appear in the titles of technical reports is not itself very telling of anything. That is why I asked Steve about whether he had investigated the content of those reports, not just scanned titles.
To this end,
page 148 of the second of the three reports you cited clarifies what I've suggested by a discussion of what "T3" is - it can be seen that not only was 24S-T or whatever form it took (we're speaking of the same material: 2024 sheet) "heat treated", but was necessarily "cold worked" per this discussion, same as 2024 T3 would be -
"T3 temper is especially applicable to 2024 and Alclad 2024 flat sheet which has necessarily been cold-worked to obtain the degree of flatness required commercially." Ergo, "rolling" to give the finished form we observe, whether 24S-T or 2024 T3 provides the "cold working" that clinches the final strength, or temper, if you will.
Now as to 'labels', no argument - "T3" appeared later than the more archaic "S-T", etc. by all I've learned here. Should "T3" surface on 2-2-V-1 as a certainty, then you may have something that puts it out of time-frame due to when the new designation of T3 emerged (and nice if we can pin down more precisely as we still seem to have slightly loose ends on that for now).
The 1941 edition of "Aircraft Materials and Processes" by George Titterton makes no mention of the T3 temper for Alclad sheet. It does cover Alclad 24ST and Alclad 24SRT [...and 'un-clad' 24SO, 24ST and 24SRT.]
There is no mention of T3 in the 1947 edition of the same book-
http://babel.hathitrust.org/cgi/pt?id=wu.89090519661;view=1up;seq=11
The T3 temper is discussed in the 1951 edition, and in the 1956 edition - page 148
http://babel.hathitrust.org/cgi/pt?id=wu.89045771615;view=1up;seq=8
T3 is also described in the 1950 edition of "Alcoa Aluminum and its Alloys." See page 16.
http://babel.hathitrust.org/cgi/pt?id=wu.89083894923;view=1up;seq=24
Oddly, item 6615 on the NACA list cited by Steve is "William H. Colner and Howard T. Francis, Influence of exposed area on stress-corrosion cracking of
24S aluminum alloy, NACA TN 3292, Nov
1954, pp. 23." - not quite the full "24S-T", but not "T3" either - point being, one must dig deeper.
Thanks for providing specific references to data above. That is what we have to get into to learn for one thing, when the actual process changed, not just the designator.
That is for what it is worth. Above all, seems to me we still have to look for signature marks on the artifact in any case, and the more examples we collect - as you've suggested cataloguing, perhaps the better chance of an eventual full match. Just MHO, of course.
Thanks.