"Airliner would have survived xmas day bomb" |
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VulcanB2
Chief Pilot Joined: 02 Apr 2008 Points: 13365 |
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Posted: 05 Mar 2010 at 1:52am |
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http://news.bbc.co.uk/1/hi/world/8547329.stm
When the test was run, did they pressurize the hull to have the same pressure differential as at altitude? Makes a massive difference to the over-pressure, and thus the damage caused by the explosion. If the hull was depressurized, then the test is invalid. EDIT: I just watched the video in the link - what a load of junk! The doors are missing, and it is not pressurized. The test is totally invalid. If they detonated the bomb in a sealed, pressurized hull, you can bet it would split it in half. As it is, the majority of the blast went out the open doors, and the damage to the fuselage is as a result of fragments and local over-pressure from the bomb, but it is nothing compared to what it would have been. Best regards, Vulcan. |
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TomA320
Chief Pilot Joined: 02 Apr 2008 Location: Perth Scotland Points: 10235 |
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Anyone see the docomentery on BBC2 yesterday about this? Quite interesting.
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TomA320
Chief Pilot Joined: 02 Apr 2008 Location: Perth Scotland Points: 10235 |
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I just watched the video in the link - what a load of junk! The doors are missing, and it is not pressurized. The test is totally invalid.
According to the program I watched yesterday, the test is not invalid because the aircraft was below 10000ft so open doors in the test would have no effect.
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Martyn
Just Flight Staff Development Manager Joined: 31 Mar 2008 Location: Huntingdon, UK Points: 7615 |
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Vulcan, watch the entire program and they explain how the test is completely valid. This test was carried out by a UN explosives expert and air accident investigator. I suspect that they understand the basic principles of the subject
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Martyn
Just Flight Ltd |
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MartinW
Moderator in Command Joined: 31 Mar 2008 Location: United Kingdom Points: 26722 |
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Reminds me of many other discussions I've had with Pointy. |
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VulcanB2
Chief Pilot Joined: 02 Apr 2008 Points: 13365 |
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OK - to explode a plastic bag, you seal the top do you not?
Try exploding a plastic bag without sealing the top. You can't.............. Even if the aircraft is below 10,000 ft it is still pressurized (you should know that!), and with the doors closed, it still results in an inability for the pressure to easily escape, so the effect upon the fuselage would still be greater. Another point - when blast mining, why are the explosives buried in the ground and not merely sat on top? Because it concentrates the blast. etc....... The test is flawed. Even if the guy is from the UN, maybe he is not so good as is made out. I do plan to watch the program anyway. Best regards, Vulcan. |
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Rich
Just Flight Staff Joined: 31 Mar 2008 Location: Planet Earth Points: 8543 |
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It’s a real shame that the UN do not currently have a vacancy for a "Consultant expert of experts in absolutely everything" open at the moment. It’s a travesty that such people only reside on internet forums.
These people who waste their entire working lives conducting hands-on practical tests and studying the theory behind their subjects of expertise are just a drain on our taxes. |
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VulcanB2
Chief Pilot Joined: 02 Apr 2008 Points: 13365 |
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It is simple physics!
If you blow up a sealed balloon it takes more effort to get a given volume of air into it, than if you cut a hole in the balloon! You can blow, but the balloon will not inflate; viz a viz if you explode a bomb in a pressurized, sealed space it does far more damage than if you detonate the same bomb in an depressurized, open structure. In short, the pressurization and sealed space of a fuselage would amplify the blast. Best regards, Vulcan. |
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Martyn
Just Flight Staff Development Manager Joined: 31 Mar 2008 Location: Huntingdon, UK Points: 7615 |
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If its simple physics, then I'm sure the explosives expert will have taken that into account |
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Martyn
Just Flight Ltd |
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MartinW
Moderator in Command Joined: 31 Mar 2008 Location: United Kingdom Points: 26722 |
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Sometimes I love this forum.
I do see Pointy's point, but as said, it's doubtful the experts are idiots. I hardly think they would miss something so obvious.
Was there a partition, closed, between the bomb position and the door by any chance?
They may have sealed off that section, so not requiring the door to be shut. Any number of possibilities for the test.
You shouldn't right them off as morons just yet Pointy, along with all the climate scientists.
It's also true that the inside of a 747 is a pretty large space, so the explosion hardly tightly contained, there's a very large volume of empty space in that big boy.
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Odai
Chief Pilot Joined: 05 Apr 2008 Location: NW England Points: 3731 |
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Vulcan is almost completely right. You might all talk down to him for not taking into account the fact that experts ran this test, but everything he said is valid.
He might just have overlooked the fact that the experts would have taken all that into account.
Exactly what I was thinking actually. I assumed the bomb was simply placed in the cargo hold somewhere. If that was the case though, it would produce different results than if the bomb went off in the passenger space.
Actually, the force of the explosion would make that completely irrelevant. |
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allardjd
Moderator in Command Joined: 02 Apr 2008 Location: Florida - USA Points: 4506 |
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I don't know if Vulcan's right or not. I believe that an important point is whether the AC was still pressurized or not, and if the test accurately took into account that fact. I've never seen data on that, but in the actual event, it must at least have been in descent, given the time frame of 20 minutes before landing. It might still have been fully pressurized, but probably not. In an AC at altitude, at or near maximum cabin differential pressure, an additional pressure spike from an explosion would almost certainly cause a breech and the great volume of air bottled up in the cabin would probably have done the rest of the job. Once the eggshell is breached, the internal pressure does the rest. Maximum cabin differential pressure would have represented a "worst case", in my opinion. If fully depressurized or even partly so, the mechanical stress (pre-load would be a good way to characterize it) on the AC structure from the pressurization would have been less, and the volume of bottled up air available to compound the damage would also have been less. If the explosive force were marginal, that single factor, i.e. the cabin differential pressure at the moment of the explosion, might very well be the difference between a casualty and a catastrophe. In any event, the BVD Bomb was a dud and succeeded only in inflicting on the jihadist a little of what he richly deserved - instead of the expected dozens of virgins he got toasted testicles. Good deal - sometimes things just work out! He may even qualify for a Darwin Award by having removed himself from the gene pool - I hope so. Whether his underwear ordnance would or would not have brought down the plane is pretty much academic in this case. Far more important than whether the bomb was large enough to bring down the AC is the matter of how it ever made it through the security at two airports and got aboard in the first place. Arguments about whether it was large enough or whether the recent test was valid are pretty much moot. What was the point of the test exactly - to decide if we need to build stronger AC cabins? |
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John Allard
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MartinW
Moderator in Command Joined: 31 Mar 2008 Location: United Kingdom Points: 26722 |
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Vulcan is almost completely right. You might all talk down to him for not taking into account the fact that experts ran this test, but everything he said is valid.
Yes, we know, no one said his physics was wrong.
He might just have overlooked the fact that the experts would have taken all that into account.
Excatly, that was why he got the response he did.
Actually, the force of the explosion would make that completely irrelevant.
No, I would disagree with that. An explosion that takes place in a capacious environment has more chance of dissipating, through a larger volume of air. The shock front also hits a greater percentage of the aircrafts skin. Therefore more energy is dissipated through the skin to the outside air.
A very large vessel with a small explosive device inside would be unlikely to burst open the container and shower all with shrapnel. However, a same sized explosive, tightly crammed into a very small container would explode with great force.
Put a hand grenade in a footbal stadium sized space and you get a far diferant effect than if you stick it in a aluminium beer barrel.
Throw a hand grenade into a room 3 metres metres square, and all inside die, throw it into a massive auditorium and those further away from the explosion survive, becuse the shackwave has more chance to disipate, desite the fact it's a closed space. Just as the walls of a very large container [an aircraft] are less affected by the shockwave.
The more tightly contained a detonation, the more chance there is of bursting open that container. It's the basic principle behind any explosive weapon. From a hand grenade, to a bullet.
In essence, the energy of a shock wave dissipates quickly with distance. Also, the accompanying expansion wave approaches and eventually merges with the shock wave, partially cancelling it out.
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hurricanemk1c
First Officer Joined: 04 Apr 2008 Location: Portlaoise, ROI Points: 441 |
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I agree with Vulcan here. Experts aren't always right
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737Chris
Chief Pilot Joined: 04 Apr 2009 Location: The Abyss Points: 2247 |
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Only sometimes Martin ? |
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allardjd
Moderator in Command Joined: 02 Apr 2008 Location: Florida - USA Points: 4506 |
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There are at least three things about this "test" that bother me. 1) The aircraft involved in the real incident was an A330 and the test was done on a 747. Different AC from different manufacturers - only very general conclusions could be drawn. 2) A ground level test with doors open is another source of disparity from the real event. Even if internal partitions were used to isolate the section where the test explosion occurred, the bottled up test volume would have been quite different from a full A330 cabin and would certainly have affected the results. 3) If the cabin of the real aircraft were fully depressurized at 10,000 feet, resulting in a cabin differential pressure of 0, then the postulated explosion would have been in that environment, i.e. at a density altitude of about 10,000 feet. That lower air pressure would have affected the explosive force. If, on the other hand, the cabin was still partially pressurized, that was not simulated in the test. In either case, the test conditions were not the same as they were in the event being simulated. What in the world was the purpose of the test, other than a media inspired publicity stunt? Regardless of the result, what is the value of this "stunt"? It has no bearing on anything. - Is it a possible defense strategy for the BVD Bomber? - "Your honor, tests have proven that the device was too small to have brought down the plane, therefore, I move to have my client's charge reduced to misdemeanor disorderly conduct." - Should security regulations be relaxed so that people can bring explosive devices aboard as long as they aren't large enough to bring the AC down? - Are aircraft certification requirements going to be changed to require the cabins to be able to survive the detonation of explosive devices small enough to be concealed in underwear? - Will existing aircraft hulls have to be strengthened to withstand a certain sized blast? Whether the test was valid or not, there's nothing important to be learned from it. |
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John Allard
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hurricanemk1c
First Officer Joined: 04 Apr 2008 Location: Portlaoise, ROI Points: 441 |
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Good points John - I've also noticed one of the windows is open!
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MartinW
Moderator in Command Joined: 31 Mar 2008 Location: United Kingdom Points: 26722 |
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Good post John, many variables indeed.
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Aircraft Aviation
Chief Pilot Joined: 15 Mar 2009 Points: 2149 |
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As per John...
Surely, regardless of the strength and power of the explosive - Wouldn't it be better to have no explosion at all rather than a small one that may not have downed the airliner?
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Odai
Chief Pilot Joined: 05 Apr 2008 Location: NW England Points: 3731 |
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No, I understood your reasoning. I just think it's rubbish.
There's no agree or disagree.
You cannot possibly make such statements without either proper mathematical proof, or extensive experimental data (hollywood movies don't count) - neither of which you have there. Otherwise, it is entirely guesswork. You need to do the maths to find out how much energy is dissipated, absorbed etc etc. And as I don't have access to any relevant figures I can't work it out myself.
And besides - the width of the aircraft is quite small. So there isn't much air between the explosive and the wall.
Plus, this is all irrelevant. The people who conducted the test did so as they wanted to understand how the plane's structure would react in the case of a bomb attack. In a real life situation, the bomber is going to be sitting in an ordinary cabin full of people. He isn't going to be sealed off in a container/partioned from the rest of the cabin. So the conditions they used would have been as close as possible to those in a flying airliner - which is what matters.
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