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Boeing Dreamliner Safety Concerns Are Specious
SoyChemist writes in to note his article at Wired Science on the uproar Dan Rather has stirred up with his claim that Boeing's new 787 Dreamliner aircraft may be unsafe. "Dozens of news agencies have jumped on the bandwagon. Most of them are reporting that the carbon fiber frame may not be as sturdy as aluminum. Few have bothered to question Rather's claims that the composite materials are brittle, more likely to shatter on impact, and prone to emit poisonous chemicals when ignited. While there is a lot of weight behind the argument that composite materials are not as well-studied as aircraft aluminum, the reasoning behind the flurry of recent articles may be faulty. The very title of Rather's story, Plastic Planes, indicates a lack of grounding in science. Perhaps the greatest concern should be how well the plane will hold up to water. Because they are vulnerable to slow and steady degradation by moisture, the new materials may not last as long as aluminum. Testing them for wear and tear will be more difficult too."
And it was built in the early 1980's. You would think that in a plane whose computers limit turns to 9g's -- not because of the airframe, but because of the stresses on the pilot -- they would have concerns over strength. But that is not so.
One concern the USAF had with the F-16 was that in the event of a crash, a cloud of electrically conductive carbon fibers would settle over the base, shorting out anything electrical. Judging by the F-16 we had burn on the taxiway at Hahn AB in 1985, that wasn't the case.
Chip H.
It only works that way in different load directions. You can take a sheet of CF in a typical layer configuration (say a 45/90/135) and bend it 45 degrees or more and it won't break or even look like it was bent when you return it to its former shape. But if you pull on it it doesn't stretch like aluminum. What people misunderstand is that because it doesn't stretch, they think it is more prone to failure which just isn't true. It is absorbing the same (or more) energy but it doesn't exhibit the same behavior while doing so. Aluminum will fail and snap also, but people are more comfortable with it stretching first because that's what they are used to seeing. It doesn't make it better, just different.
The types of CF composite that degrade faster are the ones where the resin doesn't have a UV inhibitor in it. UV degrades the resin just like it does to any plastic but with proper protection that isn't a problem. Once this was understood companies developed UV inhibitors for the resins to make them resistant to UV degradation. And you can bet the farm on a $150+ million dollar plane being adequately protected. There is no reason to think that they won't last just as long as an aluminum plane. Never mind that the resin only carries a tiny fraction of the load, in the directions the fibers aren't laid up for. Meaning the resin is mainly there to keep the material from delaminating.
Though some may not know it, but as aluminum oxidizes over time it becomes aluminum oxide which is more brittle and prone to fracture. So you face the same problem with aluminum, but it is adequately protected and hasn't been a problem for the many many years that commercial aircraft have been flying. Just like fiberglass boats, adequately protected and maintained they last a long time.
But what do I know, I'm just an aerospace engineer with some composite materials training. I should leave the science to Dan Rather.
BS - the FAA does not examine the plane and "decide" if it is airworthy.
The FAA has set some tests that must be completed by all aircraft manufacturers - and the tests have extremely simple, impossible to fake criteria. For example, the fully loaded plane must go at full throttle on the runway up to the no return line, and slam on the brakes. The plane must stop before the end of the runway, sit for 5 minutes (worst case overheating of the brakes), and then taxi to the terminal. The tires are expected to blow, and the brakes may catch on fire, but other than that no damage is allowed.
There are many tests like this. They have to pass them all. If you build a plane from glass and it passes these tests, it is just as safe as a solid steel one - it would just be a lot harder to design.
Materials do not give a plane safety. Engineering is what gives a plane safety.
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