So perhaps a better question would be has anyone tested to see how quickly the plane would have sunk?

A Lockheed 10E that ditched off Cape Cod in 1967 floated for eight minutes, but it didn't have the large fuel tanks Earhart's airplane had.  How long NR16020 would float would depend on ow intact it was when it went over the reef edge.  The tanks had drain valves on the bell and vents in the filler ports, so if scraping along the reef on its belly compromised the drain valves the tanks would fill quickly.  When the plane slid on its belly in the Luke Field accident it came to stop in a big puddle of gasoline that, fortunately, was quickly washed down by the fire truck that was following the plane.  Bob Brandenburg calculated that with just the two 102 gallon wing tanks compromised the plane would float for 18 minutes.

To wash the airplane into the ocean there had to be a lot of water running across the reef, so it seems safe to assume there was heavy surf at the reef edge when it happened.  Anything that goes over the edge under those conditions does not peacefully float away.  Even on a calm day, a diver in the water at the reef edge gets slammed against the coral.  Having seen that environment first-hand many times, it's hard for me to imagine that airplane not sinking almost immediately in the relatively shallow water near the reef edge.

Personally I never imagined it "flying" underwater, but instead I had always thought that when folks were referencing the "flying" of the plane they meant on the surface. So the tide takes out the landing gear which puts the belly of the plane on the surface of the water. The wings and fuselage allow it to "fly" along the surface of the water. The plane is carried out to sea where it eventually sinks in the way you suggest. I guess float vs. sink might be a more apt comparison. So perhaps a better question would be has anyone tested to see how quickly the plane would have sunk? I guess the longer it's on the surface the farther it could be carried out to sea before it sank.
Don...
 

The flying-underwater thing has never made sense to me.  Water, like air, is a fluid so the wings of an intact airplane sinking nose-first, so the theory goes, should generate "lift" and the aircraft could "glide" for a considerable distance from where it sank before reaching the bottom. 
Let's try an experiment.  Fire up your airplane and climb to whatever altitude suits you.  Now shut off the engine, take your hands and feet off the controls, and don't touch the trim.  Nothing good will happen.   Flying machines remain under control only through human guidance. The Wrights figured that out a long time ago.

Wondering if anyone has done a scale model test of a properly weighted Electra model to see if it would "float and fly" vs. sink. Given that Ballard didn't find anything near the shore the other hypothesis could be that it's much further off the shore if it "flew".
Don...

Ric, I think this hypothesis is sound. We must persevere.

'Recuit' treatment is justified for a laminated ('écrouissage'), bent and stamped part ( that needs to retain its tear strength.

For the moment, I can't go any further on the subject. I'll try to find more studies on French special steels around 1930.

If I see anything else, I'll let you know. We'll be in touch.  

As for the high silicon content, isn't it possible that the artifact had been contaminated by the sand at the bottom of the pond, which has aggregated with it?  You mentioned that the scan was surface scan only.

I had the same thought, but apparently not.  We have a 1975 breakdown (see below) of the elements in Gull Pond (referred to by its topographic map name Goose Pond).

Interestingly, there is no naturally-occurring:
• Silicon
• Vanadium
• Titanium
• Tin
• Phosphorpus

Alll of which were detected in the XRF scans of the artifact.  The titanium (like the cobalt and lead) is probably from the paint. The silicon and vanadium are apparently part of the alloy. The little bit of copper could be from a tiny pocket of sediment. There shouldn't be any phosphorous in alloyed steel so it's probably an impurity.  Ditto for the trace of tin.

If I’m right, the base metal is steel alloyed with manganese, molybdenum, chromium, silicon, zinc, and vanadium.  That’s a complex, very high-quality “special steel’”.

I couldn't find any mention of L2R among French forges in 1918... But if Levasseur uses it in 1929, it's because it's an established standard, and probably a widespread one.

Agreed.

The 'R' reference could be the metal treatment. Perhaps a reference to the French term 'recuit' which is a heat-tratment of the laminated steel (beteween 500 and 800 °C) to restore his original mécanical properties.

That would make sense.

Ric, a few thoughts.

As for the high silicon content, isn't it possible that the artifact had been contaminated by the sand at the bottom of the pond, which has aggregated with it?  You mentioned that the scan was surface scan only.

I couldn't find any mention of L2R among French forges in 1918... But if Levasseur uses it in 1929, it's because it's an established standard, and probably a widespread one. I will see if i could track any classification around 1930.

The 'R' reference could be the metal treatment. Perhaps a reference to the French term 'recuit' which is a heat-tratment of the laminated steel (beteween 500 and 800 °C) to restore his original mécanical properties.

By the way, i found a source reporting that Le Creusot (Schneider) had won a contract to build parts for the Lorraine 400 hp engine. It is not specified what type, however. Il could be the V12 e 12Db around 1918-1919. So it is likely that Lorraine had established good working trends with Schneider.

But i need more sourcing for all of these.

 

Ric, really bravo, I think you're on to something here... Investigating the composition of the alloy is a good idea. Rather than finding the part, let's find the material!

The L2 standard is, nowodays, American.  In France, we refer to 80CRV2 (Afnor).

Nevertheless, The L standard was already known in France in 1920, and is referred to as “Houille Blanche”. At the time, it was a hard carbon steel alloyed with nickel-chromium to prevent wear, oxidation and deformation. For the time, a standard of tooling. Quite a different acier spécial compared to L2 and the artifact.

Interestingly, the Levasseur spare parts catalog dates from 1929. It's a direct source that categorizes the steel in question according to standards for which an international standardization effort may have been made between 1920 and 1929.

Whatever, it is, possibly, a first direct step and link between the artifact and a first sourced docuement from Levasseur.

Page 35 of the PL4 Parts Manual shows the "Feuilles Metaliques" (sheet metals) used.  There are two steels listed, "Sheet steel No. 12" and "Alloyed sheet L2R".

The latter is presumably the "special steel" referred to in the part descriptions.  I can't find a definition for L2R steel but L2 steel is described on
https://en.wikipedia.org/wiki/Low-alloy_special_purpose_steel
In the attached screen shot, I've compared the element averages found in the XRF scans with the corresponding allowable ranges for L2 steel.
Most of the artifact element averages (shown in green) meet L2 specs. Only the averages for phosphorous and silicon (shown in red) fall outside the limits – both are too high.  Phosphorus showed up in only one scan, so that anomaly can probably be dismissed.  Silicon was detected in 4 scans, so there was probably really some silicon in the alloy.  Our artifact appears to be L2 steel with silicon added.  Maybe that's what the R stands for.

At the very least, our artifact appears to be made of steel very similar to steel known to be used in the PL4.

However, the presence of a preheater is only assumption i am afraid.

True – but it's the only thing we've found so far that seems to really fit the artifact, including a film of oil on the interior surface.