Print

[Mark Pearce]

These two fonts look very similar.

Not to me. The D on Helldiver has "serifs." The D on the artifact does not.

It looks as if there is a trace of a serif there, but you have the thing in hand.  On-line images of these stamps tend to show the inking could be very spotty at times- where ink is missing entirely. There are no serifs on the .032 Alcoa Alclad sheet shown in the link at bottom here either - seems to be post-war.

The Alcoa engineer you spoke with was mistaken about the significance of "AN-A-13," so maybe he was wrong about the 'hand-stamping' too.  How did he link the "D" so positively to "AN-A-13"?  Maybe he was right about that.  The font is a key piece of evidence here. 

http://tighar.org/wiki/2-2-V-1
"The unique style (font) of the letters enabled ALCOA to identify the full designation as ALCLAD 24S – T3 AN - A – 13"

[Stamps shown here have no serifs, and no AN-A-13.  Photo is dated to Oct 1942.]
http://commons.wikimedia.org/wiki/File:Production_of_B-24_bombers_and_C-87_transports.jpg

http://www.airstream.com/files/library/ba001792c0a731f5.pdf

[John Ousterhout]

Here's a picture from "ca. 10/1942" that clearly shows crooked ALCLAD stamps in a B-25 assembly plant.  It looks to me as though the sheet metal got run through the printer more than once, and at a bit of an angle.
What is known about the printing machine?  I have the impression (so to speak) that the finished sheets were hand-fed into a machine that had printing rollers that simply stamped as they rolled along the sheet as it passed underneath.  If the sheet was crooked, then the print would appear to be crooked, relative to the finished edges.
I can't tell if the font is sans-serif or not.

[Steve Lee]

.mis-alignment with the grain of the metal

Looks like classic rolled-on with the grain labeling to me.

Ric,

For those of us who don’t know much about grain patterns in aluminum, can you show a photo of 2-2-V-I in which we can see the grain pattern of the aluminum and how it relates to the lettering? I think I see a grain pattern in the photo Mark Pearce’s reply #628 above, but I don’t see a direction to that pattern so maybe what I’m seeing isn’t a grain pattern 

[Mark Pearce]

The rows of rivets appear to taper but does that necessarily mean the underlying structure had to taper, given a poorly aligned rivet job?

Applied an over lay showing one possible fit for 1" parallel stringers on 4" or 4.25" centers.

Very interesting Doug.  Thank you for taking the time to put this together.  Parallel stringers work out very well with the rivet rows. 

[Kevin Weeks]

The rows of rivets appear to taper but does that necessarily mean the underlying structure had to taper, given a poorly aligned rivet job?

Applied an over lay showing one possible fit for 1" parallel stringers on 4" or 4.25" centers.

Doug where did you get that plotting of the panel?? I was thinking how nice it would be for Ric and company to have something like you picture printing full scale on velum paper. It is a clear plastic sheet that is used in drafting. I have a roll of it here at work that is used every once in a while to be used to match up radius' and such against parts in a shadow graph. it would be extremely helpful to just be able to take a clear plastic sheet that is durable and lay it over a rivet patter to see if the rivets line up with the printed dots.

[JNev]

http://commons.wikimedia.org/wiki/File:Joe_Cobb,_former_%22fat_boy%22_in_the_original_%22Our_Gang%22_comedies,_now_helps_build_B-25_bombers_at_the_Inglewood..._-_NARA_-_195480.jpg

alclad labeling shown in this image ( war time) displays a somewhat wave action pattern...mis-alignment with the grain of the metal

Wavy for sure, but appears to be machine rolled-on printing.  I have no idea how that apparatus worked and might have been subject to some variations as we see, but that is suggested visually.

[Doug Ledlie]

Posted by: Kevin Weeks
« on: Today at 05:56:48 AM »

Doug where did you get that plotting of the panel??

Kevin, heres link     http://tighar.org/wiki/2-2-V-1

[JNev]

The rows of rivets appear to taper but does that necessarily mean the underlying structure had to taper, given a poorly aligned rivet job?

Applied an over lay showing one possible fit for 1" parallel stringers on 4" or 4.25" centers.

No, it does not necessarily mean the underlying structure had to taper, it is merely implied.  Had 2-2-V-1 simply been a scab laid over damaged skin, any pattern is possible - including to have even possibly ignored stiffeners and just picked-up skin adjacent to stiffeners (which would largely assume the original skin was left attached in original fashion to the stiffeners).

Or we could be seeing a deviation where damaged stringers were straightened and new skin reattached.  Problem is, 3/4" (original L10 spacing more on order of 3.5" I believe) is significant.  It is not, however, impossible - and your illustration makes a good point of this.

ADDED:

Further to this point, what IS the actual width - outside and inside of flanges - of the stiffeners in the L10?  Reasoning: the keel line makes sense, as does the first line of rivets (3.5" offset, as per L10 original), but the others are fairly uniformly displaced 3/4" - implying a sister member laid in for the next three stiffeners.  Consider that the area we are talking about was subject to 'straighten or replace' on the work description, so a fair question is whether straightening might have happened, with some additional bracing added to keep contours and stiffeness in good order afterward.  This is far from unheard of in repair world and kind of a battleship tough approach. 

It would have surely beat having to rip out a full length of stringer just because a couple of bays were bent up, and faster and perhaps stronger than splicing in a short section as well (more original stiffness retained) - straighten them as best one can, then lay in a sister member next to the original.

Conjecture, of course - but looking at the picture, far from out of the question.

As an aside, when we look at the B-17 we may find more constraint as to row spacing - the corrugated stuff underneath is monolithic as to ridge spacing so I wouldn't expect as much potential for variation like we see here.  But seeing is better proof, so we shall see on that and other types.

[Kevin Weeks]

Posted by: Kevin Weeks
« on: Today at 05:56:48 AM »

Doug where did you get that plotting of the panel??

Kevin, heres link     http://tighar.org/wiki/2-2-V-1

ahh... it's been converted to a graphic file... I was thinking you had the original cad drawing that was done... any print shop should be able to reproduce that panel drawing on velum paper in one sheet.

[JNev]

It would be good to have that on vellum for the inspection effort.  In fact, I'd love to electronically 'hammer 2-2-V-1 flat' - if we knew how.  Problem is, it is so tortured that I'm not sure how to take some of the distortion out of it that we can see, lots of interpolation I'm afraid.

[Kevin Weeks]

It would be good to have that on vellum for the inspection effort.  In fact, I'd love to electronically 'hammer 2-2-V-1 flat' - if we knew how.  Problem is, it is so tortured that I'm not sure how to take some of the distortion out of it that we can see, lots of interpolation I'm afraid.

I thought it would be helpful....

hammering the material flat would be problematic as you say....

 another thought along the lines of distortion. this particular piece was determined to be a T3 heat treat correct?? Based on a quick Wiki search... the failure specs for 2024 T3 allow for 10-15% elongation before failure. any point that has a crack or failure point could be stretched as much as 15%. and due to the explosive forces that popped the rivet heads off we may need to account for that elongation for the remaining piece??

I'm no metallurgist Jeff's post just made me think this may be something to look into??

[Kevin Weeks]

Ric, I was reading the WIKI on 2-2-v-1 and in it you stated that ALCOA said the T3 temper was introduced in 1937?? i have found a PDF from alcoa that states the T3 temper was introduced in 1931..... I didn't like the 1937 date at all for being fitted to the Electra. I'm much more comfortable with the 1931 date.

http://www.alcoa.com/mill_products/catalog/pdf/alloy2024techsheet.pdf

DESCRIPTION
Alloy 2024 was introduced by Alcoa in 1931 as an alclad sheet in the T3 temper. It was the first
Al-Cu-Mg alloy to have a yield strength approaching 50,000-psi and generally replaced 2017-T4
(Duralumin) as the predominant 2XXX series aircraft alloy. With its relatively good fatigue resistance,
especially in thick plate forms, alloy 2024 continues to be specified for many aerospace structural
applications. 2024 varient alloys, such as higher purity 2124 and 2324, with improvements in
strength and other specific characteristics, have also found application in critical aircraft structures.
An improved sheet alloy for fuselage applications was introduced in 1991. Alclad C188 offers
improved fracture toughness and fatigue crack growth while maintaining the strength characteristics
of 2024.

[JNev]

It would be good to have that on vellum for the inspection effort.  In fact, I'd love to electronically 'hammer 2-2-V-1 flat' - if we knew how.  Problem is, it is so tortured that I'm not sure how to take some of the distortion out of it that we can see, lots of interpolation I'm afraid.

I thought it would be helpful....

hammering the material flat would be problematic as you say....

 another thought along the lines of distortion. this particular piece was determined to be a T3 heat treat correct?? Based on a quick Wiki search... the failure specs for 2024 T3 allow for 10-15% elongation before failure. any point that has a crack or failure point could be stretched as much as 15%. and due to the explosive forces that popped the rivet heads off we may need to account for that elongation for the remaining piece??

I'm no metallurgist Jeff's post just made me think this may be something to look into??

That may be a very important consideration, Kevin.  Look at the peculiar cracks WITHIN the boundaries of 2-2-V-1 - given what you've found, it took a lot of elastic range to get to a plastic modus (where cracking occurs) within the sheet that way.  I guess using it over a fire, if that was done, might do it - but so could mechanical / hydraulic forces.

Could we be looking at some spacings that are distorted by as much as 10 percent or so in places?  Not saying it would be uniform throughout the sheet - I can't imagine how that would happen in situ on a real airplane.  But it could mean a normal spacing of 3.5 inches could appear, after deformity, to be in a range approaching 4.25"...

2-2-V-1 remains a very telling piece, about something...

And something did apparently 'blow' this thing off the mothership at least to some degree - still a mystery.  So many 'wrinkles' in this search.

As a footnote, one thing that troubles me a bit about the installation of similar skins on the B-17 - I think we're not as likely to see the kind of failure that we see on 2-2-V-1 with all that waffle plate (corrugated metal) backing the interior side of the skin - whatever forces might have acted on the backside would have had to work through the undersheathing, not directly against the outer skin as would be the case in a structure like the L10 has.

Oh well, slipper in-hand, one says "where art thou, Cinderella?"

[Ted G Campbell]

All,

To get a good approximation of what 2-2-V-1 would look like flat why not use a clear flexible piece of plastic and stretch it over the 2-2-V-1?

Suggested process:

Get a Wal-Mart bag, cut it into a known square (large enough to cover 2-2-V-1), stretch it over the piece and trace the rivet pattern.

Remove the bag (clear plastic), lay the sheet on a flat surface and trace in the outer edges of 2-2-V-1 onto the flat plastic sheet – use the distance from the edges of 2-2-V-1 to the nearest rivet hole as your template master.  The use of the outer edge to rivet hole distance is going to result in minimal deviation due to bulging of the original pattern.

Ted Campbell

[Greg Daspit]

I think we have to be careful in looking at that tracing. That drawing was taken from tracings of a deformed piece of metal and it looks like the dimension strings are off, or the dimension might be to an interpreted guide line estimated for a string.  It may be a paper laid flat and then dimensions taken from that paper, which may not be indicative of what the original curved form was.  You may have to stretch a tape over the metal from each hole to hole to get a better idea of the taper and also determine how much the metal was stretched as well.

Looking at some pictures of the artifact it looks like it tapers different than this drawing would indicate. But that is only looking at a picture.
The taper and deformation is something I wish we had information on. It is hard to see by looking at a picture or a tracing. That computer technology to rebuild a crumpled sheet looks interesting.