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Fired engineer calls 787's plastic fuselage unsafe

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Fired engineer calls 787's plastic fuselage unsafe

Old 19th Sep 2007, 08:13
  #21 (permalink)  
 
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hey aero junkie

"Well after surviving a crash, you also have to avoid breathing in carbon fibre particles and (if a fire happens) composite material burning in Jet fuel, both not good for the human body."

plane crashes in and of themselves are not very good for the human body, and all the safety devices in the world aren't going to help anyone.

we all know that the sardines in the back of the airplane cant breath un pressurized oxygen at 36000ft. if there is a depressurization, the pilots' job is to land a plane with a whole bunch of either dead or brain-damaged passengers.

also, the life jackets are only intended to help rescuers find the corpses of the passengers in the "unlikely event of an emergency landing on water"... no one is going to survive that...

the fact that no one died in the China Air fire is probably better classed as "miracle" than "luck".
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Old 19th Sep 2007, 08:37
  #22 (permalink)  
 
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A some one who's maintenance engineers licence covers a range of composite aircraft I fail to see how this aircraft will be any more of a problem in terms of risk to passengers involved in an accident that aa aircraft of convetional construction, in fact the ability of composites to absorb energy may well be an advantage keeping the structure intact and allowing more people to escape before the (undoubtedly toxic) fire gets going.

For me the main promlems that I forsee are ones of maintenance. Boeing repair manuals are using "dark ages" methodes that would not be used on any light aircraft or glider and are not fit for primery structure due to the glued contact area between the layers of cloth being so small. these practises may well be satisfactory for floor boards and non critical panels but won't do for a pressure hull.

I have no doubt that Boeing have given this much consideration but will an industry that has for so long been wedded to metal put enough effort into re-traininng staff to repair and inspect these "new " structures that are so much better at hiding defects and dammage than metal ever was!
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Old 19th Sep 2007, 08:43
  #23 (permalink)  
 
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Thabo

The China Air fire evacuation was not a miracle or luck it was due to the correct and speedy actions of the crew putting the safety training that they had receved in to practice.
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Old 19th Sep 2007, 08:46
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Two small observations responding to comments above;

First; I don't understand the use of the word "spectacular" connected to failures of carbon yacht masts; they just break, exactly like aluminium ones do if a stay breaks or the tensions are set up wrongly.

And second; many years ago (late '70's) the FAA and CAA gave a mandatory mod on TPE 331 engines (up to a certain production number) a 4-year compliance period when it should have been 6 months or less, solely to allow the mod to be done on next overhaul, to avoid grounding the large fleet using those engines. Safety gave way to "commercial reality". Maybe things have changed for the better, maybe not. But no-one should assume that any National Aviation Authority will not give way to commercial pressures, and that applies to FAA and EASA.
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Old 19th Sep 2007, 09:14
  #25 (permalink)  
 
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A & C

you are right... i exagerated.

there are safety standards and proreedures which are there to save lives and they do.

I just hate to think what would have happened if that "missing washer" in the slats had started the fire while the plane was still in the air. (that is what I meant by "miracle")
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Old 19th Sep 2007, 10:06
  #26 (permalink)  
 
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It is unlikely that the fuel leak from a flap can would be a problem in the air as the airflow over the wing would keep the fuel away from the hot engine.

The fire started on taxi in because the fuel was running inbd along the underside of the wing and falling onto a hot engine.
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Old 19th Sep 2007, 10:28
  #27 (permalink)  
 
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cwatters

Just a thought, I think you will find as resistence increases, current decreases, Mr Ohm might say E=I x R, and P = V x I.

Cheers

J
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Old 19th Sep 2007, 10:59
  #28 (permalink)  
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The impact survivability of Carbon Fibre structures has been proven to be greater that that of aluminium due to the ability of the composite structure to absorb the impact energy whereas the aluminium deforms.
Eerrr. As the aluminium deforms - it absorbs the impact energy.

In order to ascertain whether one material is better than another, you would need to show us the formal tests of two items constructed to identical dimensions and for the same purpose from different material that were then subjected ... etcetera.

As to CF structures been 'proven' to be better in impacts, there is not as much evidence accumulated to compare with Al, due simply to the length of time that Al has been in use for aircraft. That does not mean that Al is better than CF materials but we do not really know. That question can be answered in another 20 years time.
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Old 19th Sep 2007, 11:53
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Does anybody know if Boeing has incorporated Aramid type upper layers into the stucture to help alleviate the impact resistance problems of CF, I cant recall a composite structure that has to date, only the polyurethane finish on prop blades and the GE90??
I have heard titanium patch plates and splice pieces will be used within repair schemes, the SRM will make an interesting read!
As for impact testing I think we can rely on a few catering trucks for that first!
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Old 19th Sep 2007, 12:51
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How would the composite structure cope with lightning strikes - not knowing much about the science behind them would they be an issue? There are still many metallic components on the aircraft.
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Old 19th Sep 2007, 13:18
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Thabo,

if there is a depressurization, the pilots' job is to land a plane with a whole bunch of either dead or brain-damaged passengers.
Really? You've been watching too many movies.
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Old 19th Sep 2007, 13:50
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A and C & Captain Bloggs

A&C:

youre right, i didnt think of that.


Captain B:

I don't even know what movies are, I have no time to watch them.

at 36000ft with a decent rate of what? 8000ft/min? its going to take you a while to get your passengers back to an altitude where they can breath the oxygen they are being supplied with.

with regard to absorbing impact energy... the vast majority of energy is absorbed during plastic-deformation. cars are designed to have crumple zones which absorb as much energy as possible so that the driver doesn't have to. thats the reason that car accidents look so much worse than they did 20 years ago.

when it comes to designing planes, you take into account maximum flight loads and then add a 5% safety margin or so. you can't design a plane to withstand a crash, the kinetic anergy is just too great and it can not be dissapated.

There is work being done on using composite fittings inside the airplane that produce less toxic fumes when they burn, but you can never produce a plastic for wall panels etc. that is light, sturdy & doesnt burn at all.
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Old 19th Sep 2007, 14:12
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Thabo,

You're talking about 3 minutes to get down to an altitude where people could breathe the outside air. People can go from anywhere between 3 - 10 minutes without oxygen without suffering brain damage. Given that as the plane descends there will be _some_ (ok, not much) oxygen around, people would probably be ok. I assume you're talking about a worst-case scenario where oxygen masks have failed to deploy for some reason.
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Old 19th Sep 2007, 14:54
  #34 (permalink)  
 
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This reminds me of this thread; http://www.pprune.org/forums/showthr...94#post3409994

So after a heavy landing (very rare, I'm sure) how do you check for structural strains in a modern composite construction?

(when I were a lad, composite construction meant metal, wood and fabric)
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Old 19th Sep 2007, 15:04
  #35 (permalink)  
 
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Quite true that aluminium absorbs energy as it deforms. However, to effectively distribute large amounts of impact energy there is normally an energy dissapating structure (crumple zone) behind the aluminium skin which transports the energy around the structure.

Carbon fibre however, due to the complex interwoven nature of its core structure, has the ability to disperse impact energy throughout its own structure in multiple directions therefore dispersing energy and reducing deformation without having to resort to complex energy distribution structures. Whilst this is possibly a good thing in a crash scenario, on the day to day ramp I wonder what will happen when loaders, catering trucks etc get near it. CF is very good at delaminating without it showing on the surface.

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Old 19th Sep 2007, 15:17
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with regard to absorbing impact energy... the vast majority of energy is absorbed during plastic-deformation.
very true and it relates directly to the area under the stress/strain curve taking into account strain rates, and their effect on the area that can be placed under strain in a very short time before the G-loads kill the passenger.
A car has much less velocity so it has time to bring in large crumple zones before the G-loads are exceeded.
With a composite (non-homogenous- metallic) you are dealing in energy absorption by friction between the fibers as they separate from the glue holding them together. Ideally if you had no glue the whole thing would act like a blanket, Unfortunately it wouldn't stay together long enough to fly.
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Old 19th Sep 2007, 16:20
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What concerns me most here is that the FAA position, even if remotely true, seems to be satisfied with safety levels in a new generation aircraft meeting current aircraft saftey levels.

Stop. Rewind. Replay. That's rather like Ford launching a new hybrid vehicle and claiming it matches the safety levels of its 1978 offerings to wit: drum brakes, cross-ply tyres, no ABS, no airbags, no laminated glass, lap-belts.

Let's hope the new Boeing Pinto, sorry 787, doesn't have to be made safer via tombstone technology.
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Old 19th Sep 2007, 17:45
  #38 (permalink)  
 
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My concern is the day to day repair of 'hangar rash'. Water ingress into composite laminates, the subsequent freeze/thaw cycles and weave ruptures would not be as quick to fix as a patch of speedtape.

I reckon it'll very quickly become a pain in the ahhhhs.
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Old 19th Sep 2007, 18:57
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Makes me laugh.
All these armchair couchspuds know more than the Boeing designers. 787 will be as popular as 757 and 320. Both of which were ahead of their time.
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Old 19th Sep 2007, 19:01
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What concerns me most here is that the FAA position, even if remotely true, seems to be satisfied with safety levels in a new generation aircraft meeting current aircraft saftey levels.
Not true. There have been numerous updates of the FAR/JARS since 1969 and each "new" aircraft not grandfathered by acceptable service experience has to meet these new standards. Indeed where the technolgy is new and so novel that doubt exist about where it stands relative to historical experience than "special conditions" are proposed that it has to meet. As I recall there were several special conditions that the B777 had to meet beyond the then current certification standards.

The watchdog for such conditions are not only the Regulators but also include other aviation bodies, NASA and the general public through the petition process. So any of you may endorse the disaffected Boeing engineer and put together a technically sound petition to the FAA to issue special conditions against the A380 and the B787
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