Some time ago, it was mentioned that a/some drawing/s of the patch installation method may be posted, I have a mechanical background and am interested in such things. I am not questioning the fit, I am mostly interested in the manner of patch installment. In this report;
In the artifact analysis report;
2-2-V-1 Sheet
The sheet was a comparatively large piece (23 inch x 19 inch) of 0.032 inch thick aluminum alloy, shown in figure 1, with a pronounced curvature across the short dimension. ...
0.06 seems to be the maximum stringer/underlying fixture thickness that this artifact could have been attached to; .....stringer thickness from the Idaho wreckage was also measured at 0.06
http://tighar.org/Projects/Earhart/Archives/Research/Bulletins/71_RiddleOf22V1/71_Riddle22V1.html
The procedure outlined below; shows the use of shims ( original skin thickness) to bring the patch flush as to avoid a concave indentation in the center of the panel when the rivets are bucked, and would seemingly eliminate voids near the patch ends making it difficult to buck up the rivets there. It seems by the remaining rivet shank undeformed distance ,along with the Idaho stringer thickness information, that 2-2-V-1 seemingly wouldn't have room to have shims installed .....possibly, there are other repair methods that would allow one to attach the panel directly to the stringer and perform the repair...
The drawing in the attachment shows a typical installation regarding fuselage scab patch installations
A patch installation procedure; page 99 ,.... pg 102 left hand side in this manual
http://www.avialogs.com/list/item/4128-structural-repair-manual-for-the-model-dc-3
Jerry,
Thanks for this, but it actually highlights a problem with calling the nav window covering a "patch" in the first place: we have no idea, other than by conjecture, that the "covering" was a "patch" in the structural sense at all.
It may well have been nothing more than an expedient "cover" that was simply applied over the existing modified structure for the purpose of closing off the window opening.
And for all that has been wondered about the adequacy of the window mod and the "big hole" it created in the overal structure, we really don't have a big obvious reason to question the strength of the bird with that "hole" in it. The primary bending forces in the fuselage with a heavy fuel load, for example, would be absorbed by the upper and lower surfaces - compression above, and tension below. This puts the window (similar to other windows) in something approaching a more neutral zone in terms of stress.
The side skins behave more like diagonal bracing during vertical bending; in those terms it is not clear to me that the missing material, where the window was, is that significant. My personal view is that had some event resulted in damage leading to a last minute alarm and reinforcement of this area, more would be evident. It has been speculated that seam damage can be seen at the lower end of the 293 5/8, but I believe we're only seeing ordinary shadowing at the skin lap there; in any case, were real damage there, I would expect to see some diagonal wrinkles throughout the area, not isolated joint distress as has been suggested about that lap joint shadow.
Consider too just what was - or, if you prefer, what was not removed to create the window opening: approximately a 23x17 inch section of skin, involving a 1x23 inch approximate lap joint with a u channel stiffener, and another 23 inch long section of u channel stiffener. No major structural members like heavy stringers, etc. We can't see what was added behind the outer skin except for the telling rivets near the top of the coaming at the forward end which suggests some internal addition for reinforcement. It is reasonable, however, that given the thought we see in this mod by that one tell-tale feature that the need for some reinforcement may well have been addressed. Finally, the window - although larger than the ordinary cabin windows, is still a similar installation: a look at how those openings were reinforced is not particularly remarkable. It appears to me that the side skins of the L10 were well calculated to tolerate windows without a great deal of fuss.
All of which simply means that trying to rationalize the covering as a structural patch may be an overreach in conjecture; we may simply be seeing a cover with little, if any, features in terms of beef-up. All we can really do is see what the visual record can tell us and should probably use care to avoid forcing an answer to make the artifact fit the picture we might tend to create ourselves.
Merry Christmas to all -