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Author Topic: FAQ: Electra bouyancy, Ditching at sea  (Read 79470 times)

Ric Gillespie

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Re: FAQ: Electra bouyancy, Ditching at sea
« Reply #1 on: October 15, 2011, 09:12:44 AM »

Thanks Gary.  Very interesting.  The pilot did a beautiful job. 
So a low wing, twin engined airplane with empty long-range ferry tanks in the cabin (safe assumption) remained afloat for 15 minutes after a well-executed ditching.

A Lockheed 10E with standard in-the-wings tanks ditched off Cape Cod in 1967 and remained afloat for 8 minutes.  In each case we're probably looking at the amount of time it took for the tanks to loose their buoyancy.

The Cessna 310, although smaller than an Electra, should be roughly proportional in terms of weight versus buoyancy.  I think 15 minutes is a pretty good estimate for how long NR16020 would float.
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Gary LaPook

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Re: FAQ: Electra bouyancy, Ditching at sea
« Reply #2 on: October 18, 2011, 01:03:41 AM »

Thanks Gary.  Very interesting.  The pilot did a beautiful job. 
So a low wing, twin engined airplane with empty long-range ferry tanks in the cabin (safe assumption) remained afloat for 15 minutes after a well-executed ditching.

A Lockheed 10E with standard in-the-wings tanks ditched off Cape Cod in 1967 and remained afloat for 8 minutes.  In each case we're probably looking at the amount of time it took for the tanks to loose their buoyancy.

The Cessna 310, although smaller than an Electra, should be roughly proportional in terms of weight versus buoyancy. I think 15 minutes is a pretty good estimate for how long NR16020 would float.
----------------------------------------

Well actually, no.

Let's do the computation. It is 2015 NM from Monterey to Hilo. A Cessna 310 gets 8.6 NAM (Nautical Air Miles) per gallon at best range speed and power so it would take 234 gallons to make the flight. Add to this a 25% reserve and you end up with 293 gallons, let's call it 300 gallons. Sea water weighs 8.5 pounds per gallon so empty 300 gallon tanks provide 2550 pounds of buoyancy. The standard empty weight of a Cessna 310 is 3170 pounds though almost all weigh quite a bit more. Since aluminum weighs 169 pounds per cubic foot, the airplane consisted of 18.8 cubic feet of aluminum so displaced 18.8 cubic feet of seawater which weighs 64 pounds per cubic foot so the empty airplane also experienced a buoyancy of 1203 pounds. Putting all of this together, we have buoyancy of 2550 + 1203 = 3753 pounds of buoyancy. Subtract the empty weight of 3170 pounds makes the plane have 583 pounds of buoyancy which would have kept the plane afloat. Since it sank after the cabin flooded we know the total weight in the plane must have exceeded 3753 pounds. This is explained by the empty weight being more than standard, which is the usual case, plus the pilot's equipment and the weight of the ferry tanks made the weight exceed the buoyancy. And, if they only tanked the plane for a 20% reserve then the tankage would have only been 280 gallons so 170 pounds less buoyancy than the above computation assumed with 300 gallons of tankage.

---------------------------------------
We can do the same computation for the Electra. The empty weight was (in round numbers) 7,000 pounds meaning it consisted of 41.33 cubic feet of aluminum which displaced 41.33 cubic feet of sea water providing 2645 pounds of buoyancy. Add to this the buoyancy provided by 1151 gallon empty fuel tanks, 9783 pounds, makes the total buoyancy of 12,428 pounds. Subtract the empty weight of 7,000 pounds leaves 5,428 pounds of positive buoyancy. Based on this, assuming no damage to the fuel tanks during a ditching or landing, the plane should have floated almost indefinitely. The fuel caps are airtight as are the fuel lines so the only way for water to enter the fuel tanks was through the vent lines which are very small, say 3/8th of an inch, so water could not enter at any great rate through them. In addition, depending on the attitude of the plane and the routing of the vent lines, it is also likely that no water could enter the tanks at all through the vent lines. So if the plane was washed off the reef at Niku, there is no reason to think that it sank anywhere near that island, so your ROV search, just offshore of the reef, is probably a waste of money.

--------------------------------------------------

Addition:

I did not allow for the buoyancy of the oil tanks that had a volume of 75 gallons. Assuming that two-thirds of the oil had been burned, 50 gallons, then the empty space in the oil tanks would provide an additional 425 pounds of buoyancy, bringing the total up to 5853 pounds of buoyancy.


gl
« Last Edit: October 21, 2011, 12:23:12 AM by Gary LaPook »
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Gary LaPook

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Re: FAQ: Electra bouyancy, Ditching at sea
« Reply #3 on: October 18, 2011, 01:35:12 AM »

Thanks Gary.  Very interesting.  The pilot did a beautiful job. 
So a low wing, twin engined airplane with empty long-range ferry tanks in the cabin (safe assumption) remained afloat for 15 minutes after a well-executed ditching.

A Lockheed 10E with standard in-the-wings tanks ditched off Cape Cod in 1967 and remained afloat for 8 minutes.  In each case we're probably looking at the amount of time it took for the tanks to loose their buoyancy.

The Cessna 310, although smaller than an Electra, should be roughly proportional in terms of weight versus buoyancy.  I think 15 minutes is a pretty good estimate for how long NR16020 would float.
----------------------------------------------

BTW, I worked on a case in which a Navajo ditched just off shore of Hilo, it sank in about one minute taking one passenger to the bottom of the ocean. One engine had failed and the plane wouldn't maintain altitude on the remaining engine although it should have been able to, since the single engine service ceiling was about 8,000 feet at the weight of 7,000 pounds, so this did not make any sense. We found out the reason when we took the deposition of the mechanic. It turned out he had not used the proper procedure in adjusting the wastegate controller which then prevented the good engine from actually producing full power.

See:
http://dms.ntsb.gov/aviation/AccidentReports/gsoirwf4xfbwxlflxz02foj21/O10182011120000.pdf

gl
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Ric Gillespie

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Re: FAQ: Electra bouyancy, Ditching at sea
« Reply #4 on: October 18, 2011, 04:44:39 AM »

BTW, I worked on a case in which a Navajo ditched just off shore of Hilo, it sank in about one minute taking one passenger to the bottom of the ocean.

Any explanation for why it sank so quickly?
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Gary LaPook

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Re: FAQ: Electra bouyancy, Ditching at sea
« Reply #5 on: October 18, 2011, 05:58:56 PM »

BTW, I worked on a case in which a Navajo ditched just off shore of Hilo, it sank in about one minute taking one passenger to the bottom of the ocean.

Any explanation for why it sank so quickly?

------------------------------------
Contrary to the Cessna 310 and the Electra, it didn't have any extra fuel tanks to provide positive buoyancy and the standard fuel tanks that were there had fuel in them (duh) so didn't provide much buoyancy,  and the exit was open to allow the passengers to get out so the cabin flooded quickly.
gl
« Last Edit: October 18, 2011, 06:28:13 PM by Gary LaPook »
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John Ousterhout

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Re: FAQ: Electra bouyancy, Ditching at sea
« Reply #6 on: October 20, 2011, 08:42:35 PM »

Please forgive a newbee, but wouldn't rectangular tanks collapse pretty easily from seawater pressure?  They're designed to withstand pressure from the inside, not from the outside.  Are there drawings of the internal tank structures?

JohnO
Cheers,
JohnO
 
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Ric Gillespie

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Re: FAQ: Electra bouyancy, Ditching at sea
« Reply #7 on: October 20, 2011, 09:06:40 PM »

Please forgive a newbee, but wouldn't rectangular tanks collapse pretty easily from seawater pressure?  They're designed to withstand pressure from the inside, not from the outside.

Interesting thought. The tanks were lightly built.  Would water pressure cause them to collapse, forcing the air out through the vents?

  Are there drawings of the internal tank structures?

Unfortunately, no.

JohnO
[/quote]
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Gary LaPook

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Re: FAQ: Electra bouyancy, Ditching at sea
« Reply #8 on: October 21, 2011, 12:44:37 AM »

Please forgive a newbee, but wouldn't rectangular tanks collapse pretty easily from seawater pressure?  They're designed to withstand pressure from the inside, not from the outside.

Interesting thought. The tanks were lightly built.  Would water pressure cause them to collapse, forcing the air out through the vents?

  Are there drawings of the internal tank structures?

Unfortunately, no.

JohnO
[/quote]
------------------------------------

Assuming that the vent lines led out the bottom of the wings (a certainty for the wing tanks) and out the bottom of the fuselage for the extra tanks (which seems most probable so that any expansion of the fuel would result in the fuel being ported overboard out the bottom rather than running over the skin of the fuselage) then pressure on the tanks could not squeeze the air out of the tanks nor could water enter the tanks through the vent lines. And this is true even if the tanks were made out of rubber.

Federal Aviation Regulation, FAR 23.975 states in part:

"(6) No vent may terminate at a point where the discharge of fuel from the vent outlet will constitute a fire hazard or from which fumes may enter personnel compartments;"

(FAR part 23 controls the design of aircraft. In the '30 this was controlled by CAR part 3 but the two sets of regulations are almost identical.)

You can prove to yourself that the air won't be squeezed out of the tank through a vent line that comes out the bottom of the fuselage  by making a simple model of the system. Fill the kitchen sink with water, turn a glass upside down and immerse it in the water. The bottom edge of the glass represents the end of the vent line coming out the bottom of the plane. Notice that the air can't get out.

Looking at the size and placement of the fuselage tanks, as long as they and their plumbing were not damaged, it is impossible that the plane would sink so far as to allow the water in the flooded cabin to reach the tops of the tanks. At this position the roof of the plane would not be immersed so the buoyancy that would have been produced by the immersion of the roof would not be available but this is probably not more than 400 pounds of buoyancy. Since the fuselage tanks appear to be less than three feet tall, even if they were made out of rubber and squeezed by the water pressure of that depth, then only about 4.5% of the tanks' buoyancy would be lost so causing a loss of about 450 pounds, still leaving  more than 5000 pounds of buoyancy.

gl
« Last Edit: October 24, 2011, 09:09:06 PM by Gary LaPook »
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John Ousterhout

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Re: FAQ: Electra bouyancy, Ditching at sea
« Reply #9 on: October 21, 2011, 08:06:47 AM »

Good point about the vents.  The tanks would therefore provide very significant buoyancy until something happened to let the trapped air out.  There's a photo of AE kneeling on top of the tanks that clearly shows the vent lines and fill ports.  The filler tubes are very large diameter and lead to the port side exterior.  I have no knowledge of the sort of caps used, but I'll assume they would hold air in the tanks against modest pressure.  The location of the vent lines in the photo is interesting - they are routed to a pair of "header tanks" (my term) on either side of AE.  The vent lines appear to be about 1/2 inch diameter, making a significant restriction for escaping air if the tanks were submerged, and if the exit end(s) of the vent lines were above the tanks.  It would take a while for the tanks to collapse if the only outlet for trapped air were through those small diameter lines - long enough that the plane would sink slowly at first, so it could drift a long ways before heading to the bottom. If the vent lines terminated at the bottom of the aircraft, then the tanks would provide long-term buoyancy as long as there was no other outlet for trapped air.
What is known about surface and deep currents around Niku?  A sinking aircraft would probably descend in a spiral, rather than a long, straight, flat glide, especially if there is any significant damage.  If it started sinking as soon as it slipped off of the edge of the reef, it would tend to return to the cliff face as it spiralled down.  If it drifted away first, it could be somewhere in a broad wedge-shaped region "down-stream".
Cheers,
JohnO
 
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Bob Brandenburg

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Re: FAQ: Electra bouyancy, Ditching at sea
« Reply #10 on: October 22, 2011, 11:03:27 AM »

Gary,

Some observations on your analysis of the Electra's buoyancy:

Your airframe displacement buoyancy calculation uses the total empty weight of the  aircraft to find the volume of seawater displaced, assuming everything in the plane was aluminum.   

Since the aircraft was not watertight, it is correct to assume that it would flood.  However, in order for the combined volume of all the material in the aircraft to contribute to displacement buoyancy, it would be necessary for the aircraft to be fully submerged, in which case it would have sunk.

As for the assumption that everything was aluminum (169 lbs per cubic foot), it's worth noting that there was steel (491 lbs per cubic foot)in the aircraft -- notably in the landing gear and the pinion gears driven by various motors, etc.  There was copper (550 lbs per cubic foot)in power distribution wiring, generator and dynamotor armatures and field coils, etc.  And then there were two storage batteries at 78 pounds each, mostly lead (709 lbs per cubic foot), the radio equipment, navigator's table and equipment, etc. 

Correctly calculating the displacement requires accounting for the densities and amounts of the various materials in the aircraft.  But if the aircraft is floating, any parts not submerged do not contribute to displacement buoyancy. If the plane is afloat, and all fuel has been expended, it will float in a nose down attitude, with much of the airframe aft of the wing out of the water.  The weight of that section would be supported by the buoyant section, but would not contribute to total buoyancy.

You assume that all fuel tanks are intact and dry when the plane is floating.  That's possible but not a sure thing.  There was a spring tide on July 9, 1937, and swells  running on the reef flat from the northeast could have pushed the plane southwestward to and over the reef edge.  During that process, a landing gear assembly -- possibly both -- could have collapsed.  Nessie seems to suggest one got stuck in a crevice, but we know from the Luke Field crash that when one gear collapsed under lateral loading, the other also can fail.  Such an event could deform the gear support structure, directly above which on each side was a 102 gallon fuel tank which could be punctured. 

And swells on the reef impacting the aircraft could deliver considerable jolts, loosening or breaking tank connections.  For example, a 2-foot swell has 32 foot-pounds of energy per square foot of the swell face.  Such a swell impacting a 20-foot section of the aircraft would deliver 1280 foot-pounds.  For a swell period of ten seconds, such a jolt would be delivered 6 times per minute.  A 3-foot swell would deliver a 4320 foot-pound impact.  So it's possible that at least some of the tank connections permitted flooding, reducing buoyancy.

Another consideration is that with the plane floating nose down, a considerable weight is suspended from the cabin tanks, which are held in place by thin metal tie-down straps.  This could result in deforming or tearing of the thin tank walls, reducing buoyancy due to decreased volume, or even allowing flooding through the tears.  If tie-down straps fail, the tanks would be free to float in the cabin, allowing the plane to sink lower in the water.  If the freed tanks are ruptured by objects in the cabin, they could flood.  And, depending on the waterline location, the tank vents on the top of the fuselage could be submerged, allowing flooding.

So, it's by no means clear that the plane would simply flaot away from the island, never to be seen again.  While that's a possibility, it's also possible that whatever buoyancy the plane had was compromised during the chain of events leading to its departure from the reef, and the plane sank in the vicinity of the island.

Bob     

   

   
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Gary LaPook

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Re: FAQ: Electra bouyancy, Ditching at sea
« Reply #11 on: October 22, 2011, 01:11:18 PM »

Gary,

Some observations on your analysis of the Electra's buoyancy:

Your airframe displacement buoyancy calculation uses the total empty weight of the  aircraft to find the volume of seawater displaced, assuming everything in the plane was aluminum.   

...So, it's by no means clear that the plane would simply flaot away from the island, never to be seen again.  While that's a possibility, it's also possible that whatever buoyancy the plane had was compromised during the chain of events leading to its departure from the reef, and the plane sank in the vicinity of the island.

Bob

----------------------------------------

All good points, Bob.

Responding in the same order.

1. I assumed that the cabin and the wings were flooded and provided no buoyancy, the only buoyancy being provided by the empty 1151 gallon fuel tanks plus 2/3rds empty 75 gallon oil tanks (50 gallons of air in the oil tanks) plus the buoyancy of the aircraft structure itself. The empty tanks total 1201 gallons so produce a buoyancy, in seawater, of 10,208 pounds equal to the weight of 1201 gallons of seawater. So, without even considering the contribution of the structure, there would be excess buoyancy of 3,208 pounds and approximately one-half of the plane, whatever its attitude, would be floating above the waterline.

2. I used the simplifying assumption that the structure was all aluminum but, obviously, some parts were made of steel and other denser materials. Steel is more than twice as dense as aluminum but there was a lot more aluminum in the structure than steel so the average density would have been closer to aluminum than to steel. Had the plane been entirely of aluminum, then 7,000 pounds of aluminum immersed in seawater would have produced an additional 2,676 pounds of buoyancy added to that of the empty tanks for a total 5,884 pounds, almost the entire weight of the plane, so the plane would have floated with most of it above the waterline. But, as you point out, the portion out of the water would not contribute to the total buoyancy (I did subtract 400 pounds for this factor in my prior post) so the plane would actually float lower in the water but no lower than approximately half way since that much buoyancy was provided by the empty tanks alone. Even if the entire plane had been made of steel, then the structure would still have provided 918 pounds of buoyancy for a total of 4,126 pounds so the plane would have ridden lower in the water but most of it would still be above the waterline. To take this to extremes, even if the plane had been made entirely out of lead, 7,000 pounds of lead immersed in seawater still provides 636 pounds of buoyancy so the total buoyancy would have been 3,844 pounds causing the plane to float quite nicely.

3. I do assume that the tanks were intact but this seems quite reasonable since the landing on the reef was gentle enough to end up with the plane still standing on its landing gear so that the engine could be operated. According to FAR 23.303 and FAR 23.337 and the parallel 1937 regulations, aircraft structures were required to be much stronger than needed and the Electra's structure, and its components, had to be strong enough to support 3.8 times its weight plus a 50% margin or 5.7 times its designed gross weight of about 10,000 pounds so the structure could support 57,000 pounds before suffering permanent deformation. The tanks structures had to be designed to deal with the loads imposed with them full of fuel and with them empty the forces developed by the tanks in a sudden deceleration would be trivial and easily contained by the structure. And this applies to jolts from swells too.

4. Still using the simplification that the structure was entirely aluminum providing 2,676 pounds of buoyancy, to keep the 7,000 pound plane afloat would only require an additional 4,324 pounds of buoyancy provided by empty fuel tanks meaning that it would take only 509 gallons total of intact fuel tanks to keep it afloat. This means that it would take damaging many of the tanks to make the plane sink. There were 10 fuel tanks total so if even only the smallest 6 held air the plane would float and this does not take into consideration the oil tanks. If the oil tanks were intact then it would take only the 5 smallest fuel tanks to keep the plane afloat. If only the four largest fuselage tanks held air then the plane would float, again without taking into consideration the oil tanks. Taking into consideration the oil tanks, then even the 4 smallest fuselage tanks would keep the plane afloat.

5. Once the tanks were submerged there would be an upward strain on the tiedowns equal to the buoyancy being created by the air in the tanks, they act like inflatable life vests. The very minimum load that must be designed for is in an upward direction and is 1.52 times the weight of the tank itself plus the fuel contained in the fuel tank. To this must be added the 50% safety factor making the tank tiedowns capable of holding 2.28 times the weight of the full fuel tanks. Aviation gas has a density of 6 pounds per gallon and seawater has a density of 8.5 pounds per gallon, only 1.41 times that of gas. Thus the buoyancy exerted by empty fuel tanks immersed in seawater can never exceed the 1.52 minimum structural design limit without even taking into consideration the required 50% safety margin. An example will make this clear. The 148 gallon fuselage tanks hold 888 pounds of gas so the tiedowns must be designed to restrain 1.52 times this weight (plus the weight of the tanks themselves) so must be strong enough to hold down at least 1,350 pounds. Add the 50% safety factor and the minimum strength must have been 2,025 pounds. Since seawater has a density of 8.5 pounds per gallon, the maximum amount of buoyancy that could be produced if this empty tank was entirely submerged is 1,258 pounds, equal to the weight of 888 gallons of seawater, well within the design requirements of the structure.

6. So if the plane were swept off the reef it is unlikely that it sank rapidly so a search limited to the sea bottom in close proximity to the edge of the reef is likely to prove fruitless.

gl

« Last Edit: July 20, 2012, 12:31:36 PM by J. Nevill »
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John Ousterhout

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Re: FAQ: Electra bouyancy, Ditching at sea
« Reply #12 on: October 23, 2011, 02:10:33 PM »

Since the photos of the tanks appear to show all of the vent lines manifolded together, an air leak in any one tank would allow air to escape from all of the tanks, through the vent lines to the damaged tank.  This also assumes the external vent is line is routed to the bottom of the aircraft.  If it's out the top, then nothing will prevent the tanks from filling or crushing.

Gary wrote"...This means that it would take damaging many of the tanks to make the plane sink.", to which I would add "...to sink quickly", but even a single damaged tank would eventually result in sinking, if the tank vents are indeed all manifolded together.

Assuming any initial submersion does not generate any significant pressure in the the tanks, and assuming one vent line is open to the atmosphere, and assuming 1/2 inch ID vent line, how long would the tanks provide net positive buoyancy?  At a modest 125 ft/sec velocity of escaping air (a bit faster than the maximum recommended velocity in compressed-air systems), through a single 1/2 inch diameter tube, it would take about 17 minutes for 1251 gallons/167 cu.ft of air to escape.  To just reach zero net buoyancy only needs the loss of 393 gallons/53cu.ft, which would take just 5 minutes.

It seems unlikely that a tank could be ruptured by any successful landing, so there would be no obvious way for the tanks to lose their buoyancy unless the vent(s) were open to atmosphere somehow.  If the vents were in the top of the aircraft, and if the tanks could flood or crush, then the a/c might be expected to lose buoyancy and sink within a very short time/distance.  If the vents were in the bottom, or otherwise not open to the atmosphere, then the tanks might provide buoyancy indefinitely.

Knowing where the vent was located might narrow the search area significantly.

Where are the best photos to study that might show vent locations?
Cheers,
JohnO
 
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Gary LaPook

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Re: FAQ: Electra bouyancy, Ditching at sea
« Reply #13 on: October 23, 2011, 05:01:31 PM »

Since the photos of the tanks appear to show all of the vent lines manifolded together, an air leak in any one tank would allow air to escape...If it's out the top, then nothing will prevent the tanks from filling or crushing.

Gary wrote"...This means ...how long would the tanks provide net positive buoyancy?  At a modest 125 ft/sec velocity of escaping air (a bit faster than the maximum recommended velocity in compressed-air systems), through a single 1/2 inch diameter tube, it would take about 17 minutes for 1251 gallons/167 cu.ft of air to escape.  To just reach zero net buoyancy only needs the loss of 393 gallons/53cu.ft, which would take just 5 minutes.

It seems unlikely that a tank could be ruptured by any successful landing, ...Knowing where the vent was located might narrow the search area significantly.

Where are the best photos to study that might show vent locations?
------------------------------
All interesting points.
1. To get the tanks to fill with water there needs to be two openings, one to let the water in and another to let the air out. So even if the vent line led upward so that the air could get out you still need an opening into each tank to allow water to enter each tank. Suppose one tank was holed then water would enter that tank and fill it up but after  that one tank was full the water would not travel back through the vent line to flood the other tanks so you would only lose the buoyancy of that one tank. So it would take damaging many tanks individually to lose all of their buoyancy.

2. If a tank was pierced near the top so that the opening acted like a vent then the other tanks still will not fill unless each of them have their own opening to allow the water to enter. Depending upon which of the tanks had the vent like opening it would only allow the other tanks to vent until the holed tank sank below the water line of the other tanks (even if they were holed also) at which point no more air could come out through that hole. For example, if the forward 118 gallon tank sustained damage then it would provide a vent for the other tanks only until the nose tipped down, submerging the hole below the level of the other cabin tanks.

3. The rate of air loss through the 1/2 line would not be nearly as fast as the rate you mentioned for compressed air. The air pressure in a holed tank would only be about 1 & 1/2 or 2 psi, not the normal 100 psi found in your compressed air tank so the air would flow out much more slowly.

4. I don't understand how you computed that it would take losing only 393 gallons of buoyancy to allow the plane to sink. This number means that you figured that the plane had only 3340 pounds of positive buoyancy which is about the amount of buoyancy provided by the tanks alone, I figured 3208 pounds from that source. Did you forget to allow for the buoyancy of the aircraft structure itself? If the plane had been made entirely out of aluminum then the structure would have provided an additional 2676 pounds of buoyancy making the total buoyancy 5,884 pounds. To lose this much buoyancy would take losing 692 gallons of air trapped in the tanks, not the 393 gallons that you stated. Since the plane was not entirely aluminum it would take slightly less than this. Even if the plane was entirely steel it would still have 4,126 pounds of buoyancy so would have to lose 485 gallons of air from the tanks. Since there was a lot more aluminum in the structure than steel we can expect the correct value to be much nearer the 692 gallons than to the 485 gallons figure.

5. You are correct in noting that if the tanks crushed then there would be no need for a hole in each tank to admit water. However, assuming the plane was floating near level, the water pressure on the outside of the tanks would only be about 2 psi so it seems very unlikely that this would be sufficient to crush the tanks. The tanks have to be strong enough to contain the fuel  even in a crash with partial tanks allowing the fuel to exert a great deal of impact force due to its sloshing in a crash. Although they are designed to withstand this force from within, not from without, it seems highly likely that the use of materials strong enough for this purpose would also be strong enough to withstand the unexpected pressure of only 2 psi from the outside.

gl
« Last Edit: July 20, 2012, 12:33:29 PM by J. Nevill »
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Ric Gillespie

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Re: FAQ: Electra bouyancy, Ditching at sea
« Reply #14 on: October 23, 2011, 09:25:33 PM »

Gary,

This is all reminding me of your learned recitation of all the reasons that Noonan could not possibly have missed Howland Island.   And yet he did.
You have also maintained that it was not possible for AE and FN to dead reckon a few hundred miles down the LOP to Gardner.
Now you have offered computations and cited regulations to explain why the Electra would float indefinitely. If the airplane could truly float indefinitely it should still be bobbing around out there somewhere.  Perhaps we should be looking for it on Google Earth. I hasten to say that I'm kidding. I don't think you really mean that the Lockheed has remained afloat for 74 years, but if it did, in fact, eventually sink - what happened?  Once what you describe as a reliably buoyant aircraft was away from the island and removed from the possibility of collision with hard objects, what would make it sink?  When a hurricane is coming, the Navy puts its ships to sea for that very reason - so they don't bump into things. What part or parts of the incredibly robust flotation system you describe failed?  Why did those components fail then and not earlier?  Did some crucial part deteriorate over time?  What part?  How long did it take to deteriorate?  Hours?  Days?  Weeks?  Months?  If the airplane ditched anywhere near Howland and floated indefinitely, why didn't Itasca spot it?  If Itasca somehow missed it, why didn't the planes from the Lexington find it? 

If the intact and indestructible plane you describe floated far away from Gardner (or was never there) why was there such a strong and consistent tradition among the islanders that there was airplane wreckage on the reef when the first settlers arrived in 1938?  As we've often said, anecdotal recollections (old stories) are not evidence unless corroborated by archival records, photographs and/or artifacts.  In this case, we have found no archival records to corroborate the old stories.  Apparently the British authorities were never aware of the wreckage.   We do, however, have 1953 aerial mapping photos that appear to show a debris field of light-colored metal on the reef and an October 1937 photo that shows unexplained debris on the reef in the same spot where a former-resident described seeing wreckage from an aircraft.  Stories of airplane parts being found on the reef or shoreline are corroborated by aircraft artifacts found in the abandoned village that are consistent with a Lockheed 10.

Theoretical calculations suggesting that the intact airplane could have floated far away from the island and sunk in very deep water are trumped by the abundant evidence that it sank in the near-shore environment in water shallow enough for it to be, to some degree, broken up in later storms with some lighter components being cast up onto the reef and shoreline.
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