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Author Topic: FAQ: Electra bouyancy, Ditching at sea  (Read 83833 times)

Chuck Varney

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Re: FAQ: Electra bouyancy, Ditching at sea
« Reply #30 on: October 26, 2011, 08:30:52 AM »

The amelia-earhart-equipment_tn photo shows what appear to be the port and starboard vent lines routing to the tops of the two tanks on either side of her, but not visibly connecting to any external vent(s) at those ends.  It is not shown whether the filler connections(?) for those two tanks are external through the upper skin, nor whether such fillers had vented caps.

John,

I think you'll be able to see in the larger version of the subject photo that I posted with Reply #30 that the vent lines from the tops of your "header tanks" connect to the forward ends of their respective vent manifolds, and that both tanks have filler necks accessed externally from above.

Chuck
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Ric Gillespie

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Re: FAQ: Electra bouyancy, Ditching at sea
« Reply #31 on: October 26, 2011, 08:49:34 AM »

I think you'll be able to see in the larger version of the subject photo that I posted with Reply #30 that the vent lines from the tops of your "header tanks" connect to the forward ends of their respective vent manifolds, and that both tanks have filler necks accessed externally from above.

Chuck,

I agree.

Next question.  If the manifolds along the cabin walls are vents for the tanks (and I can't imagine what else they would be), why both sides?  Why two vents on each tank?
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Friend Weller

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Re: FAQ: Electra bouyancy, Ditching at sea
« Reply #32 on: October 26, 2011, 08:56:25 AM »

Chuck, Ric:

"Without fabric" preceding "with fabric" makes perfect sense as I initially thought about the need/desire for "under construction" photos during the pre-flight publicity timeframe yet also knowing that various changes and lightening measures took place during the rebuild is what raised the question in my mind.  I was unaware (or had inadvertently overlooked the fact) that no interior photos were taken after the Luke Field accident.  Thanks to both of you for the clarification....and your patience!

LTM,
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Chuck Varney

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Re: FAQ: Electra bouyancy, Ditching at sea
« Reply #33 on: October 26, 2011, 10:45:50 AM »

Next question.  If the manifolds along the cabin walls are vents for the tanks (and I can't imagine what else they would be), why both sides?  Why two vents on each tank?

Ric,

I don't know what drove the designers, but the scheme interconnects all six tanks without running any vent plumbing across the fuselage width, and it (presumably) provides two dump ports to the outside that are separated by about a fuselage width. In the event that one of those ports were obstructed, all six tanks still have a vent path to the outside.

Chuck
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Ric Gillespie

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Re: FAQ: Electra bouyancy, Ditching at sea
« Reply #34 on: October 26, 2011, 11:49:41 AM »

I don't know what drove the designers, but the scheme interconnects all six tanks without running any vent plumbing across the fuselage width, and it (presumably) provides two dump ports to the outside that are separated by about a fuselage width. In the event that one of those ports were obstructed, all six tanks still have a vent path to the outside.

By "dump ports" I assume you mean unobstructed outlets to the outside so that air can flow in to replace the fuel as it is fed to the engines.  If that is the case, it would appear that the dump ports were co-located with the filler ports for the two tall 118 gallon tanks at the forward end of the cabin. 
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Chuck Varney

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Re: FAQ: Electra bouyancy, Ditching at sea
« Reply #35 on: October 26, 2011, 12:41:02 PM »

By "dump ports" I assume you mean unobstructed outlets to the outside so that air can flow in to replace the fuel as it is fed to the engines.

Ric,

Yes--or to allow venting air from the tanks while filling them, or venting fumes from filled tanks, which is the mind set I had when I wrote that. I should have simply called them "ports".

Chuck
« Last Edit: October 26, 2011, 01:01:56 PM by Chuck Varney »
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Ric Gillespie

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Re: FAQ: Electra bouyancy, Ditching at sea
« Reply #36 on: October 26, 2011, 05:19:24 PM »

Nice system redundancy for venting the tanks but if the airplane goes in the drink it's a quick trip to Davey Jones Locker.  The airplane is going to float nose down and the dual vents provide an open hole for water to go in and another open hole for air to get out.
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Gary LaPook

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Re: FAQ: Electra bouyancy, Ditching at sea
« Reply #37 on: October 26, 2011, 05:52:01 PM »

Nice system redundancy for venting the tanks but if the airplane goes in the drink it's a quick trip to Davey Jones Locker.  The airplane is going to float nose down and the dual vents provide an open hole for water to go in and another open hole for air to get out.
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Two problems with that. First, if they came out even with each other then no water would flow through the vent lines. But the biggest problem with that is that the vent lines go up over the tanks, well above the waterline of the nose down illustration in your book so no water is going to flow uphill to get above the fuel tanks.

gl
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Gary LaPook

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Re: FAQ: Electra bouyancy, Ditching at sea
« Reply #38 on: October 26, 2011, 06:13:32 PM »

It looks like possible vent lines along the bottom of the cabin in the attached photo.

Gary,

If you're talking about the two lines in the photo that run along the starboard wall below the pelorus, I think you'll find that they're electrical cables--typically shown as connecting to the auxiliary battery.

See the attached photo for how the cabin tank venting was arranged--at least early on. There are port and starboard vent manifolds, the aft ends of which bend downwards 90 degrees. Each of the four transverse tanks has a pair of vent lines; one connecting to the port manifold, the other to the starboard manifold. The port and starboard tanks forward of the transverse tanks each have a single connection to a manifold.

Chuck
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This is obviously an early picture and the filler neck has not yet been installed for the starboard 118 gallon forward tank. This filler neck is visible in the other pictures.
I suspect that the caps for the filler necks are the type of airplane gas caps that when you turn the center knob the gasket expands radially to seal the filler neck. Ric, do you have any information on the gas caps?

gl
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Gary LaPook

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Re: FAQ: Electra bouyancy, Ditching at sea
« Reply #39 on: October 26, 2011, 06:16:40 PM »

By "dump ports" I assume you mean unobstructed outlets to the outside so that air can flow in to replace the fuel as it is fed to the engines.

Ric,

Yes--or to allow venting air from the tanks while filling them, or venting fumes from filled tanks, which is the mind set I had when I wrote that. I should have simply called them "ports".

Chuck
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And it is not allowable by today's regulations, and presumably not by the 1937 regulations either, to allow any venting inside the cabin.

gl
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Gary LaPook

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Re: FAQ: Electra bouyancy, Ditching at sea
« Reply #40 on: October 26, 2011, 06:24:32 PM »

Gary - thankyou for catching my errors.  I respondeded too quickly and didn't take the time to read your analysis carefully, or to check my own figures - my bad.  You're right that the tanks would need an entry, as well as an exit to fill with water.  I'm not convinced they would withstand crushing, but only because I'm ignorant of the design of their internal bracing.  I've seen many examples of slab-sided tanks that begin to crush at trivial pressures - a foot of water depth is suffiicient in some cases, yet only develops about 1/2 psi.  There are a lot of square inches being pushed upon, and the skin and bracing were not designed with external pressure in mind. Internal baffles for example are simply flat metal sheets spanning the tank width in several places.  Holes in the baffles allow slow liquid flow and reduce weight.  Forces from the action of fuel (sloshing, sudden deceleration, turbulence, etc) are resisted by shear and tension in the baffles.  There are no significant compression loads on the baffles in normal operation.  A flat sheet with holes in it is not capable of withstanding significant compression loads without buckling.  If the baffles have stiffening features, then they can resist buckling and can carry compression loads.  I'm anxious to learn more about the tank design, since it might be important to define the search area. 

I'm inclined to assume the internal bracing of the extra tanks used simple flat sheets with lightning holes, welded or riveted to the skins. Such a design provides almost no resistance to crushing by submersion in water, but the displaced air would still need to escape for the a/c to sink.

As Ric points out, there was a tradition of an airplane wreck on the reef at one time.  What is known about the ways aircraft breakup on reefs over time?  Surely it wouldn't take much wave and wind action to move an aircraft around on the reef - one modest storm would be enough.  What would be damaged first  - the landing gear getting caught in a crack, anchoring it to one spot?  If so, then the aircraft would "weather-vane" about the stuck wheel, damaging the attach points and nearby structure.  At what point are the empty fuel tanks compromised to an extent they can't float the wreckage?  They would seem to be well protected inside the main fuselage. Would it take a year or two of constant saltwater exposure and pounding by waves to break the stuck parts free of the main body, which then floats away?  I'm guessing something like that could happen, implying there might only be a few pieces deposited near the reef - the larger pieces containing the buoyant tanks might have drifted miles away.

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Looking at the rivet pattern  in the rearmost fuel tank visible in the posted photos it appears that there was quite a bit of stuff inside the tanks including baffles that kept the fuel from sloshing side to side. Such baffles would probably resist crushing of the fuel tanks.

gl
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Ric Gillespie

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Re: FAQ: Electra bouyancy, Ditching at sea
« Reply #41 on: October 26, 2011, 06:57:18 PM »

Two problems with that. First, if they came out even with each other then no water would flow through the vent lines. But the biggest problem with that is that the vent lines go up over the tanks, well above the waterline of the nose down illustration in your book so no water is going to flow uphill to get above the fuel tanks.

We're not talking about an airplane in a swimming pool.  We're talking about an airplane being bashed about in the surf at the reef edge, caught between conflicting forces - the waves refracting around the NW tip of the island and driving southwestward (that's what knocked it off its gear and pushed it over the edge) and the swells rolling in from the west, pushing it eastward against the reef edge.  It's an extremely violent environment.
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Ric Gillespie

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Re: FAQ: Electra bouyancy, Ditching at sea
« Reply #42 on: October 26, 2011, 06:58:36 PM »

Ric, do you have any information on the gas caps?

No.  Wish I did.
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Ric Gillespie

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Re: FAQ: Electra bouyancy, Ditching at sea
« Reply #43 on: October 26, 2011, 07:00:11 PM »

By "dump ports" I assume you mean unobstructed outlets to the outside so that air can flow in to replace the fuel as it is fed to the engines.

Ric,

Yes--or to allow venting air from the tanks while filling them, or venting fumes from filled tanks, which is the mind set I had when I wrote that. I should have simply called them "ports".

Chuck
-------------------------
And it is not allowable by today's regulations, and presumably not by the 1937 regulations either, to allow any venting inside the cabin.

gl

I don't think Chuck was implying that the tanks vented into the cabin.
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Gary LaPook

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Re: FAQ: Electra bouyancy, Ditching at sea
« Reply #44 on: October 26, 2011, 08:47:16 PM »

Two problems with that. First, if they came out even with each other then no water would flow through the vent lines. But the biggest problem with that is that the vent lines go up over the tanks, well above the waterline of the nose down illustration in your book so no water is going to flow uphill to get above the fuel tanks.

We're not talking about an airplane in a swimming pool.  We're talking about an airplane being bashed about in the surf at the reef edge, caught between conflicting forces - the waves refracting around the NW tip of the island and driving southwestward (that's what knocked it off its gear and pushed it over the edge) and the swells rolling in from the west, pushing it eastward against the reef edge.  It's an extremely violent environment.
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So, water still ain't going to flow uphill.

gl
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