Plastic Aeroplane Safety Questions?

[Atheist-Lite]

http://www.newscientist.com/article/mg2 ... lanes.html

Report questions long-term safety of composite planes

ON 1 NOVEMBER the first aircraft with a pressurised fuselage and wings made from carbon-fibre reinforced plastic (CFRP) flew its first passengers from Tokyo to Hiroshima. The All Nippon Airways Boeing 787's composite structure makes it around 15 per cent lighter than a typical aluminium-based plane of that size, increasing fuel efficiency and making aviation greener.

But the media hoopla over the flight disguised some worrying questions about the long-term safety of composite aircraft. On 20 October, the US Government Accountability Office (GAO) published a report which, while accepting that the 787 has been certified as airworthy, questions the ability of the US regulator, the Federal Aviation Administration, to ensure that inspectors are capable of assessing and repairing damage to composite structures over the long life of a plane.

"It is too early to fully assess the adequacy of FAA and industry efforts to address safety-related concerns and to build sufficient capacity to handle composite maintenance and repair," says the GAO.

Until now, only smaller, isolated pieces of secondary structure, such as tail fins and wing leading edges, have been made from composites. The GAO reviewed the scientific literature and interviewed engineers about the evidence underpinning the expansion of composite use to incorporate the whole fuselage. On damage and ageing issues it found the science wanting.

The GAO found that engineers don't know how such materials will behave when damaged, what such damage will look like, and how these factors change as the material ages. Because composite damage is hard to detect - indeed it can be effectively invisible - working out what risk a dent poses is difficult. Too few inspectors are being trained to diagnose such damage, the GAO report adds.

(continued)

[klr]

Given that an aircraft could stay in service for, oh, 50 years or more, this is a non-trivial issue.

[JimC]

Duct-tape?

[JacksSmirkingRevenge]

Because composite damage is hard to detect - indeed it can be effectively invisible - working out what risk a dent poses is difficult.

In my experience with carbon fibre bikes, it doesn't dent - it just shatters into fragments. That's why carbon fibre downhill bikes are seldom used - they don't withstand impact well and don't last long.

[JimC]

Because composite damage is hard to detect - indeed it can be effectively invisible - working out what risk a dent poses is difficult.

In my experience with carbon fibre bikes, it doesn't dent - it just shatters into fragments. That's why carbon fibre downhill bikes are seldom used - they don't withstand impact well and don't last long.

Gotta love the forgiving nature of metallic bonding...

[Feck]

Would not the other uses of composites provide suitable information ?

[JacksSmirkingRevenge]

The nearest application I can think of where CF might be used is in gliders - but they don't have pressurised cabins.
Also, I seem to remember a documentary in which a composite glider was struck by lightning and disintegrated into a million pieces.

[klr]

The nearest application I can think of where CF might be used is in gliders - but they don't have pressurised cabins.
Also, I seem to remember a documentary in which a composite glider was struck by lightning and disintegrated into a million pieces.

Nor do they have the enormous stress of taking off/landing at the same speeds as airliners (which are also very heavy). IIRC, the cumulative effect of take-offs/landings (including the climb out and approach in) is the most important factor in airframe stress, not the total distance travelled.

[HomerJay]

All Nippon Airways are simply beta testing, maybe Boeing knew it wouldn't be a good idea for a domestic to do the beta?

I'm surprised they only achieved 15% weight saving, it seems a small gain for unknown consequences, perhaps they've over-engineered to be more cautious?

[Atheist-Lite]

This is gonna be tested by the first guinea pigs, suckers, customers like those who flew in the De Haviland Comet.

[Feck]

DOOOOOOM DOOOOOOOOM it will never work Man's not meant to fly ........ Next you will be saying Iron ships will float !

[Atheist-Lite]

DOOOOOOM DOOOOOOOOM it will never work Man's not meant to fly ........ Next you will be saying Iron ships will float !

You can have my ticket.

[JacksSmirkingRevenge]

All Nippon Airways are simply beta testing, maybe Boeing knew it wouldn't be a good idea for a domestic to do the beta?

I'm surprised they only achieved 15% weight saving, it seems a small gain for unknown consequences, perhaps they've over-engineered to be more cautious?

I think that's a given. CF parts do tend to be bulkier in order to attain the same strengths as the equivalent aluminium/Duralumin parts.

This is gonna be tested by the first guinea pigs, suckers, customers like those who flew in the De Haviland Comet.

It may well be that CF can better withstand the pressure cycling that caused the fatigue in the Comets...Who knows, though? Not me.

[Feck]

This is gonna be tested by the first guinea pigs, suckers, customers like those who flew in the De Haviland Comet.

De Havilland Comets flew until 1997 ,your point ?

[Atheist-Lite]

"Carbon fiber is unsafe to use after a point determined by the possibility of catastrophic failure due to some trigger factors. Infact, very dangerous. Note that you don't need an exceptionally high force to cause carbon fork failure. The ones that cause fatigue are frequently forces of lower magnitude, below those that cause irreversible plastic deformation."

http://cozybeehive.blogspot.com/2008/12 ... ilure.html

With metals the fatigue fractures start out on the surface of the material and then grow inwards until failure occurs. So ultrasonic ndt testing can be used on high stress patches and spot problems before they lead to catastrophic failure. Seems once these novel materials have sustained overloading damage to the carbon strands it won't give a indication until it fails because the damage begins in the middle of the material rather than surface? Even ordinary plastic displays this property of failure from the centre outwards if you've ever tried to bend a plastic spoon repeatedly....very difficult to guess when it will snap compared with a metal spoon.