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[Ric Gillespie]

As we saw in our discussions about the events surrounding the delivery and testing of the Electra in July and August 1936, there was an apparent problem with the seven fuselage tanks which resulted in their removal on July 28, the day after July 27 when Earhart applied (unsuccessfully) for "NR" registration. The tanks were still out on August 7 when the airplane was inspected for its "R" registration.  The application for the "R" registration listed a total fuel capacity of only 394 gallons because the fuselage tanks had been removed.  The problem, whatever it was, was resolved and the fuselage tanks were re-installed, presumably sometime before August 29 when Earhart left for New York to participate in the Bendix race.
While the airplane was at Purdue in October, Bo McKneeley noticed that the R16020 license only approved the airplane for 394 gallons. Thinking it was a clerical error, Putnam complained to the Bureau of Air Commerce but they responded that the 394 gallons was correct according to the paperwork.  To correct the license, the airplane had to be inspected again.  On November 27, 1936 it was inspected at Garden City, Long Island, NY.  Now there were only six fuselage tanks.  To the question, "Has the airplane been altered or repaired since last inspection?" the answer was "Yes."  By whom?  "Lockheed Aircraft Corporation"  When? "July 28, 1936"  Describe details
of repairs or alterations.  "7 fuselage tanks removed as shown in Item 25. False floor installed"  Item 25 lists the weight of the removed tanks and flooring.  No mention of when the tanks went back in.

I'm curious about the nature of the problem because we have long hypothesized that artifacts we found on Niku are "heat shields" that were were installed between the cabin heating ducts and the fuselage tanks to prevent vapor lock caused by heating of the tanks if the cabin heating system was on. see https://tighar.org/Projects/Earhart/Archives/Research/Bulletins/51_HeatShields/51_DetectiveStory.html
As we know from McLeod's logbook, he made several test flights in the airplane prior to delivery on July 24.  That may have been the first time the plane was taken to an altitude where cabin heat was needed.  Maybe the problem showed up then.  The next day, July 25, McLeod made a one-hour, 200 mile, Burbank to Burbank test flight which must have confirmed the problem.  He logged no further flights in X16020 before the tanks came out on July 28.

So what is a "false floor?"  And what problem could its installation fix?   

[Friend Weller]

So what is a "false floor?"   

Sorry for the low-res photo but I think it will show up.....what is that under the fuel tanks?  It appears to be a separate layer of "something", not part of the observable exterior of the tanks themselves.  Some sort of insulating or isolating layer or flooring material between the topside of the 10E's floor and the underside of the tanks? 

Possible materials might include:

• Felt
• Cellulose fiberboard
• Asbestos fabric

And what problem could its installation fix?

• Insulating the tanks from cabin heat conducting through the floor from the cabin heat ducts (not radiating from the cabin heat duct directly)?
• Damping airframe vibration from being transmitted into the fuel tanks to reduce oscillating waves (not sloshing, more like buzzing) involving such large quantities of liquid?

Or am I up in the night?
 

[Ric Gillespie]

And what problem could its installation fix?

• Insulating the tanks from cabin heat conducting through the floor from the cabin heat ducts (not radiating from the cabin heat duct directly)?

The heater ducts ran along the base of the cabin wall.  I don't see how heat would come up through the floor.  Those tanks are bunged right up against the heater ducts.  In the Alaska wreck (which had one fuel tank in the cabin) heavy asbestos felt had been fastened over the heater duct where the tank was.  (See photo attached.) So we know that insulating the tanks from the ducts was necessary - perhaps a lesson learned from c/n 1055. .  In the case of the Alaska plane it was just one small fuselage tank so the heavy asbestos was a reasonable solution, but to insulate NR16020 with asbestos would have meant a huge weight penalty.  Little free-standing aluminum structures insulated with kapok would be more trouble to build but wouldn't add much weight.

[li$i]Damping airframe vibration from being transmitted into the fuel tanks to reduce oscillating waves (not sloshing, more like buzzing) involving such large quantities of liquid?[/li]
[/list]

Maybe, but the Alaska wreck confirms that protecting fuselage fuel tanks from the heater ducts was necessary.

[Friend Weller]

The heater ducts ran along the base of the cabin wall.  I don't see how heat would come up through the floor. 

I suppose I should ask for my own clarification:  was the floor aluminum or wood?  I can understand how the asbestos fabric would insulate well from radiated heat from the heater duct but if the floor was aluminum, then given the consideration that NR16020 would be flying for many more hours at a stretch than the Alaska Electra (and at altitude), would it be a reasonable concern to insulate the underside of the tank from heat conducted from the ductwork into the floor structure and from there back up into the tank, minimizing the effectiveness of the kapok-insulated aluminum panels?  Throwing it out there for what it's worth, perhaps what we see in the photo are some sort of insulating "blankets" placed on top of the floor when the tanks were reinstalled?

Or maybe the "false flooring" refers to the decking placed on top of the tanks as seen in the attached photo?

[Ric Gillespie]

was the floor aluminum or wood?

The flooring in Electras was made of linoleum-covered plywood panels that could be removed for access to the supporting aluminum structures.

Or maybe the "false flooring" refers to the decking placed on top of the tanks as seen in the attached photo?

Perhaps, but it's hard to see how the installation of the decking would require the removal of the tanks.

[Friend Weller]

The flooring in Electras was made of linoleum-covered plywood panels that could be removed for access to the supporting aluminum structures.

That would address/eliminate the possibility of a the need of insulation from conducted heat...

Describe details of repairs or alterations.  "7 fuselage tanks removed as shown in Item 25. False floor installed"  Item 25 lists the weight of the removed tanks and flooring.  No mention of when the tanks went back in.

Perhaps, but it's hard to see how the installation of the decking would require the removal of the tanks.

In that order, true.

Time to put the thinking cap back on....

[Harbert William Davenport]

I'm wondering if the addition of two filler necks for the fuselage tanks might have been done as part of the rebuild of the fuel system that was going on in late July and early August:
https://tighar.org/Projects/Earhart/Archives/Research/Bulletins/61_FuelSystem/61_FuelSystem.htm

But even if so, I can't see any helpful connection with the hypothesis that heat shields were needed and added at that time, which is what we're after just now, because of those artifacts.

The Timeline for Aug 30 shows a Cleveland newsphoto of AE beside the Electra that shows 4 fuel ports, so the 2 new ports had already been added by then.  See the Timeline, I can't get the photo to transfer.
"At Cleveland Municipal Airport, August [31] 1936. Note fuel ports. Source: Cleveland Plain Dealer Historical Archives (cleveland.com)"

In the excerpt from the movie Love on the Run, at 41 seconds, there appear to be only two fuel filler ports on the side of the fuselage, but then at 50 seconds all 4 are there, as we would expect: https://www.youtube.com/watch?v=7dvJFAlPdNM&feature=em-uploademail

[Ric Gillespie]

I'm wondering if the addition of two filler necks for the fuselage tanks might have been done as part of the rebuild of the fuel system that was going on in late July and early August:

I think you're right.  The addition of two more fueling ports happened some time before the Love on the Run scene was filmed.  The movie went into production on August 19.  Purdue president Elliott arrived to see the new airplane the next day, August 20, so the scene for the film was shot sometime in the week between when Elliott left (August 21?) and August 29 when Earhart left for the east coast to participate in the Bendix race.

So the installation of additional fueling ports was part of the late July/early August change in the fuel system.  We know that the tanks came out and something seems to have been done involving the floor ("false floor installed").  Apparently further work on the fuel system was needed.   One of the tasks that McKneeley was supposed to accomplish while the airplane was at Purdue in October was to "cover the fuel lines" but that didn't get done until the plane was back in Burbank.  See attached from the Doris Rich files at NASM. (Item 5  "hatch for refueling if that plan goes through" is in reference to Earhart's proposed inflight refueling.)

[Jim Zanella]

I would think that the floor would be a "Cargo" floor due to the increased weight of the dense fuel tanks. All of the cargo and military derivative airplanes built in the great Northwest have the cargo flooring option which allows greater carrying capacity. Maybe this is some of the confusion regarding the floor.
Jim

[Jerry Germann]

Was wondering if the reference to false flooring may be an additional layer of plywood material that Friend Weller pointed too in his image? It appears that a layer of flooring in place beneath Earhart's feet, is firmly fixed to substructures in the empty cabin image, attachments seem in place at points along the center seam line. The sheets beside Earhart in the empty cabin image may be the false floor, not yet in place. The foil lined image shows floor sheet goods running the opposite direction of the ( true) subfloor, or it seems so looking at the seam. Sometimes a false floor or chase is utilized so utilities ( electric/water/etc) can run beneath undisturbed, but in this case there appears no void between layers. A guess would be strengthening the floor under the tanks, as it seems that the false floor ends at the tanks, where Friend has his pointers.

[Ric Gillespie]

All really good observations.  Great work gentlemen.  Here's what I see.

The first photo below was taken on May 26, 1936 during construction of the aircraft.  The flooring is standard Electra flooring.  The heater ducts and fueling ports have not yet been installed.  The plywood sheets off to the side are not the false flooring that was later installed. That didn't happen until after the airplane was delivered.

The second photo below is really interesting.  It was obviously taken at the same time as the third photo below because the front of the Sperry Gyropilot is open in both photos.  The false flooring has been installed because, as you guys have observed, the plywood now runs horizontally and has no metal edging.  A rivet on the main beam is no longer visible because the false floor has been laid on top of the original floor.  The purpose of the false floor is obvious - to beef up the floor to support the weight of the tanks.  The work is still underway because the fueling ports have not yet been changed.  This photo must have been taken sometime between July 28 (the earliest date for the removal of the tanks) and the week of August 21-28 (the filming of Love on the Run, the earliest photos showing the four fueling ports.

Of special interest (to me anyway) are the wooden strips on the false floor immediately adjacent to the heater ducts.  Why are they there?  The putative heat shields we found on Niku appear to have been free-standing structures that were nailed, not riveted, to an underlying surface., as shown in the fourth illustration below from https://tighar.org/Projects/Earhart/Archives/Research/Bulletins/51_HeatShields/51_DetectiveStory.html

[Jerry Germann]

Interesting , that little wood strip,....will keep looking for more interior images. From a design standpoint, it seems a heat deflector (dado) constructed that way, would indeed help deflect heat from the bottom of the tanks , but doesn't seem that it would prevent heat from being redistributed along the entire sides of the tanks, via the small space between tanks and fuselage walls... ( a sort of duct-work if you will). If the problem was heating of fuel, I don't know that this would remedy the problem, as a rather large amount of tank surface would still receive heat from the cabin piping. Most shields I have experience with are wrap around or partially wrapped around the pipe and the ends are open to allow heat transfer out of the ends of the shield and out to safe areas. The remainder of the cabin piping to the cabin door was covered with aluminum shields it appears. It appears that the wood strip is too far away from the fuselage wall to involve any attaching of the wall board liner material too it. Does anyone know, for curiosity sake,how hot the cabin pipe got soon after passing through the manifold heater and into the cabin piping?

[Jerry Germann]

One thought, is that little strip of wood for attaching an aluminum shield ( similar to the one aft of the tanks)?

[Ric Gillespie]

One thought, is that little strip of wood for attaching an aluminum shield ( similar to the one aft of the tanks)?

Those are not aluminum shields.  Those are the actual heat ducts.  There is no "hot pipe" inside.  It's just ducting for hot air.  The attached photo shows what the heating ducts looked like in the standard airline version.  As you can see, there was a little grilled opening in the ducts beside each passenger. 
The photo is cn 1026, a 10A in the Oakland Air Museum.

[Jerry Germann]

Ingenious,....fabric that matches the wall panel to boot so it looks nice. Cut out grate holes where you want them.....wonder where Earhart placed her grills, as in the few photos I have, I can't see them. Some pondering on my part though, how does the fabric tube stay open, in case someone placed an object upon it, either unintentionally, or perhaps a child seated in back of the passenger in front of him, tires of kicking the backrest and decides to stand on the tube, causing a stoppage of heat flow to the passengers behind him/her trying to freeze them out, and in turn giving the passenger in front a concentrated heat blast?
On a more serious note; what continues the connection located between the heat ducts, where the flap actuator brackets and covers are located? In the photo it is hard to tell if there is a pipe connection running through the bracket , but it seems a hole is provided if it is the case. I don't see a tying of the ends of the fabric ducts around a pipe there, it would seem the transfer of heat between ducts might be interrupted if some transition piece wasn't installed there.I noted on the edited attachment that on the aft end of the Starboard duct, something seems sticking out of the duct, or maybe it is just wallboard material. I don't see the temperature of this type of ducting becoming all that hot, with such easy passenger access to it....maybe some 75-80 degrees?

As far as the piece of wood, I wonder why it would be necessary to use it to mount a dado atop, as there are already two multi-ply sheets of wood to attach it too.