Airbus A380 Mid-air Engine Failure

[Silent_Buddha]

Now certainly you can imagine a very small skin puncture that could be survivable. The problem is that the skin is meant to handle the tensional, hydrostatic stress as one system. puncture even a small hole and you get a localize stress concentrator (from escaping air) that will tear the skin like a hot knife through butter. Lose a bit of that skin and now your fully depressurized but you have an aerodynamic anomaly in the airframe that might be survivable at low speeds, but you're going 700 mph so it starts to rip more skin and frame ribs and the plane literally breaks to pieces.

This is what I always think of everytime I see that one Mythbuster's episode replayed on Discovery channel that dealt with what would happen if the skin of a plane were to be punctured by a bullet or small explosion. It only dealt with potential explosive decompression but didn't deal with the fact the plane might also be moving at extremely high speeds at a very high altitude where compromised aerodynamics may make the situation a whole lot worse.

Regards,
SB

 

[Squilliam]

1. People on everest are wearing slightly warmer clothing
2. People on everest have O2
3. People on everest aren't falling out of the sky surrounded by the shrapnel like remains of an aircraft that just disintegrated around them


3. is obviously the real kicker.

People in planes theoretically have 02 also everest has been climbed without the use of bottled oxygen. I doubt they would freeze to death either if the plane is still capable of making the decent to a safe altitude. As for the plane coming apart? I hear if you inflate a bunch of lifejackets in the toilets you'll probably survive the crash.

Now certainly you can imagine a very small skin puncture that could be survivable. The problem is that the skin is meant to handle the tensional, hydrostatic stress as one system. puncture even a small hole and you get a localize stress concentrator (from escaping air) that will tear the skin like a hot knife through butter. Lose a bit of that skin and now your fully depressurized but you have an aerodynamic anomaly in the airframe that might be survivable at low speeds, but you're going 700 mph so it starts to rip more skin and frame ribs and the plane literally breaks to pieces.

I thought the idea of explosive decompression had been debunked? I think I saw an episode on Myth Busters for what its worth.

 

[KimB]

I hear if you inflate a bunch of lifejackets in the toilets you'll probably survive the crash.

Wait, what? I'm sorry, but if the aircraft loses its skin, it drops like a stone. A few lifejackets in the toilets aren't going to help much when dropping like a stone from 35,000 feet.

I thought the idea of explosive decompression had been debunked? I think I saw an episode on Myth Busters for what its worth.

They did show that decompression itself doesn't do much. A small hole blows the air inside the aircraft out very rapidly, but doesn't lead to significant damage on its own. The problem is, as SB mentioned, that they didn't test the aircraft moving at 700mph (for obvious reasons).

 

[Silent_Buddha]

Wait, what? I'm sorry, but if the aircraft loses its skin, it drops like a stone. A few lifejackets in the toilets aren't going to help much when dropping like a stone from 35,000 feet.

You won't know until you try it!

Regards,
SB

 

[Mize]

Yeah, mythbusters assuming that 700 mph doesn't affect the mechanical impacts of a decompression is just crazy. 700 mph wind (and it can be higher than that as 700 mph is a typical ground speed) will create a huge venturi effect that they can't account for in a static test...then there is the aerodynamics of the peeled skin.

Aloha airlines showed the top can pop off form a hole. Now you might say metal fatigues and corrosion contributed to Aloha, but if you think you're hopping on a 30 year old plane with no microcracking and corrosion, you're simply insane. Newer plane = better for structural integrity.

 

[KimB]

You won't know until you try it!

Regards,
SB

Well, let's go through the list of events:

1. The amazing Steve somehow knows that catastrophic failure is about to occur, and also somehow manages to collect a bunch of life vests from the aircraft, inflating them around himself in the toilet. The flight staff are very confused, but feel it's best not to interfere with a clearly crazy person.
2. Aircraft skin suffers some sort of breach that expands due to friction with the air at 700mph.
3. As the skin breaks apart, some pieces of the aluminum that make up the shell are blown out from the aircraft, others are blown right through the passenger cabin, peppering passengers with aluminum shrapnel moving at hundreds of miles per hour.
4. Once the skin is almost entirely gone, and the shell remains, the passenger cabin itself is exposed to winds near 700mph (by now the aircraft has probably slowed somewhat due to the added friction). Some passengers who are not seatbelted are blown out of the aircraft. Seats are torn from their fastenings and blown out of the plane. Different, rather hard bits of the craft manage to collide with one another and passengers.

And what of Steve in the bathroom? Well, if he isn't peppered by shrapnel, he'll be quickly blown away the moment the high winds tear apart the bathroom enclosure.

So yeah, this post is basically pure speculation, but I doubt it's wildly inaccurate. Either way, I just don't think that failure of the aircraft's skin at hundreds of miles per hour would be even remotely survivable. Rather, it would be a few moments of abject terror followed by death. Not even enough time to whip it out and masturbate, since death is coming anyway (if you don't get the movie reference, I'm so, so sorry...).

 

[Mize]

But they say a bathroom is the safest place in a tornado...?

 

[Sxotty]

So the assumption is the plane structure fails that makes sense, but as you mentioned the aloha thing went pretty well considering. I don't think that the altitude is as problematic as you seem to. I have done a bit of mountaineering and while it is true that to do lots of physical activity at extreme altitudes O2 is handy to sit on your but you would be fine. Actually at higher altitude maybe you would be less likely for the structure to fail since the friction is less, but the delta in pressure is higher so who knows. Well I guess you do since you have actual experience in the area.

 

[KimB]

So the assumption is the plane structure fails that makes sense, but as you mentioned the aloha thing went pretty well considering. I don't think that the altitude is as problematic as you seem to. I have done a bit of mountaineering and while it is true that to do lots of physical activity at extreme altitudes O2 is handy to sit on your but you would be fine. Actually at higher altitude maybe you would be less likely for the structure to fail since the friction is less, but the delta in pressure is higher so who knows. Well I guess you do since you have actual experience in the area.

My naive guess would be that a sudden loss of cabin pressure, assuming nothing else nasty happens, would be more likely to cause a person to pass out than anything. So if, say, somebody shot a bullet through the center of a window, and it didn't cause any structural problems, I'd be willing to bet a large fraction of the people would pass out before they had a chance to put on the oxygen masks.

 

[Sxotty]

Yeah but is it pressure change? 35k isn't that high. If it was just the altitude you could hang out awhile before passing out. I also scuba dive and know pressure changes are a problem but there you are talking atms in 33 feet. So the change can be pretty fast and obviously has ramifications.

 

[Grall]

The air pressure on top of Mt. Everest (less than 9k m at the peak) is so low that regular couch potatoes like me would probably die of asphyxiation if attempting to stay there (much less attempt any physical activity) for a prolonged period. Jet airliners regularly cruise at what, 11k, 12k? Something like that. That's another 25-33% increase in altitude, and air pressure isn't exactly going to go UP... Seems quite likely that you would pass out at the very least.

 

[Squilliam]

What of the composite air frames ala the Dreamliner etc? Would they have different properties to a regular aluminum skin aircraft under adverse conditions as discussed above? Would my little guy in the toilet survive then since it is the safest place to be in a tornado.

 

[Mize]

Composites are great, but the database of material failure modes is sparse and they are incredibly dependent upon the geometry - much more so than metals. The composites used in aerospace tend to perform extremely well in tension but have very poor compressive properties. Depressurization could be more of a problem if compressive stresses were created.

 

[Sxotty]

Mize do you think there is any realistic chance of self healing composites ever being used? They are a kind of neat technology, but I doubt very reliable.

 

[Mize]

Not in the near future, but, yes, eventually "self-healing" will find it's way into real structures, but they're polymer-based so there are limitations on the applications (temperature for example).

 

[aaronspink]

What of the composite air frames ala the Dreamliner etc? Would they have different properties to a regular aluminum skin aircraft under adverse conditions as discussed above? Would my little guy in the toilet survive then since it is the safest place to be in a tornado.

Jury is still largely out on composites. Boeing for instance is using significant margin in the fuselage of the 787 because of some of the long term unknowns.

 

[Simon F]

FWIW the outer shell of the 380 is also a composite material as shown in these chook gun tests: http://www.metacafe.com/watch/1647350/richard_hammonds_engineering_connections_airbus_a380/.

If I remember correctly it is a sandwich of aluminium and glass fibre.


Also, there was an excellent program on the BBC that showed Rolls Royce engine development and it seemed to say that on their recent engines they had real-time telemetry feeding back the behaviour of each engine while in flight. It also gave an overview of manufacture of the fan and rear turbine blades (although much of that appears to be trade secrets).

Unfortunately the clip linked above doesn't have any of the that - this one (and the related set) is more informative : http://www.youtube.com/watch?v=6ZFjKsJIOFo

 

[aaronspink]

FWIW the outer shell of the 380 is also a composite material as shown in these chook gun tests: http://www.metacafe.com/watch/1647350/richard_hammonds_engineering_connections_airbus_a380/.

If I remember correctly it is a sandwich of aluminium and glass fibre.

Its not technically a composite but as you say a laminate. IIRC it is Alum - fiberglass - Alum. Now some people consider laminates to be composites but its a bit of a stretch.

Also, there was an excellent program on the BBC that showed Rolls Royce engine development and it seemed to say that on their recent engines they had real-time telemetry feeding back the behaviour of each engine while in flight. It also gave an overview of manufacture of the fan and rear turbine blades (although much of that appears to be trade secrets).

All modern jet engines utilize realtime monitoring. As far as the blades, in general everyone is using either CFRP or titanium depending on the application.

 

[Mize]

Jury is still largely out on composites. Boeing for instance is using significant margin in the fuselage of the 787 because of some of the long term unknowns.

largely out WRT long-lifetime commercial aircraft...
Heavily used in military aircraft today - that's where the database will grow the fastest.

 

[Mize]

Its not technically a composite but as you say a laminate. IIRC it is Alum - fiberglass - Alum. Now some people consider laminates to be composites but its a bit of a stretch.

Fiberglass alone is a composite. Glass fibers in a polymer matrix.

All modern jet engines utilize realtime monitoring.

Indeed. There are even sensors in the pylons to detect vibrations that could indicate possible rotor burst and shutdown the engine.

As far as the blades, in general everyone is using either CFRP or titanium depending on the application.

Uh, turbine blades? No. Fan blades? Yes. The outer fan blades on the GE90 are indeed carbon-fiber reinforced polymer composite. These materials are not used for turbine blades as the temperatures are far too high. Nickel alloys are the dominant material for turbine blades though there are some military engines in development using ceramic-matrix composite blades. The only polymer-based composite that would hold up to turbine temperatures is carbon-carbon but I've only ever seen it used in braking systems as it tends to burn under the right (wrong) circumstances.