Dangers of composite airframes

[hammertime]

I just read this (http://www.newscientist.com/article/mg20327224.400-why-large-carbonfibre-planes-are-still-grounded.html) article and I had to ask something. Will the 787 have to go through a de Havilland Comet phase in order to be perfected? I mean, how do we know the composite airframes won't break apart after, say, six months, or a year, or five years?

[xxChrisxx]

Something like the Comet will never happen again.

Firstly becuase of increased technonlogy, we can run rigourous simulations looking at the behaviour of materials to make sure that its strong enough and wont fatigue.

Secondly becuase the modern society will simply not allow the 'suck it and see' attitude of the previous decades.

When CF airframes fly, they will be safe. As companies in this day and age just cannot afford to put forward something that is inherantly unsafe. This is not saying it will be invincible, there are always accidents and unforseen problems, but you arent going to get multiple failures.


EDIT: Thirdly, there will never be a Comet style disaster again because of the Comet itsself... That plane single handedly killed british aviation for years.

[russ_watters]

I think the comparison is a stretch anyway - the comet failed due to fatigue, a problem that is difficult to predict in advance or test for. Composites don't exhibit fatigue, these failures are essentially design flaws that are found during early testing. They aren't good, but they will be gone by the time the plane goes into production.

Yes, it means there are some growing pains associated with composite planes (though they do already exist....), but that doesn't imply these will lead to in-flight failures.

[FredGarvin]

I just read this (http://www.newscientist.com/article/mg20327224.400-why-large-carbonfibre-planes-are-still-grounded.html) article and I had to ask something. Will the 787 have to go through a de Havilland Comet phase in order to be perfected? I mean, how do we know the composite airframes won't break apart after, say, six months, or a year, or five years?
Composite materials are just like any metallic material in that poor workmanship or unseen flaws will be possible locations for failures. Make no mistake that any material will fall into this scenario. There are a lot of things that are different that make it a completely different ball game then with the Comet. So much that, IMO, it is a stupid comparison. While the article is correct that simulations are not the end all be all because there is no way to theoretically model flaws or something that will degrade the material properties. That is what modern day quality control is for. We also have much more extensive test programs than during the Comet's time. The test bed fuselages will, most likely, get somewhere on the order of 10,000 simulated take offs and landings plus all of the flight testing done prior to certification. The Comet did not have testing like that until after they started crashing (they instituted water tank tests of cabin pressurizations).

[pitts]

I work with composites. I have nothing bad to say about them. There are so many different types of composite and composite process. The technology has come a long way. You have fiberglass kevlar composite and various blends of pure resin with many materials making up it's composition. With any process there are area's for mistake. Resins and epoxies are usually two parts. That should explain it. They also have to be agitated to remove air pockets. Last but not least while in the mold depending on the type there needs to be a nice even vaccum. Composites are an engineering design as well as any structure. They are harder to repair and make look good than standard sheetmetal or wood and steel tube designs. But there strength to weight ratio is uncomparable.