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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."
Actually, Dan Rather is probably not making this up - he's more likely (mis)reporting some allegations made by a now sacked Boeing engineer, Vince Weldon. The Register has a write up based on what was said by the engineer and the rebuttals made by Boeing and the FAA.
UNIX? They're not even circumcised! Savages!
- Buying Madonna's book: Screwing for Virginity.
- Buying MS Vista for it's speed and congeniality.
Seriously folks, Dan Rather has about as much common sense as a Bugby.This is the guy that went on the airwaves with a "memo" supposedly typed in the 1970's, with proportional fonts and different-font sized superscripts! I would not trust someone like that to tell me it's raining.
Carbon-fiber composite construction has been around for going on forty years now. It's been accellerator tested in hot humid ovens and passed with darn good results. Boeing doesn't make junk. And airframes are warranted for tens of thousands of Hobbs clock hours, so the airlines are not at risk, they're voting with their checkbooks.
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.
I hate articles like this...doesn't anyone actually use, you know, MATH to quantify terms like "safe" and "unsafe", without just throwing around FUD like this? BY FAR, the most dangerous thing we all do everyday is drive our cars around, which account for 44.3% of all accidental deaths in this country. This is followed by "Unspecified non-transport accidents" at 17.6%, and Falls at 13.6%.
Death stats found here http://www.the-eggman.com/writings/death_stats.html.
Aircraft deaths do not even make the list. How can something that accounts for less then 0.1% of all accidental deaths be called "unsafe"?
never bring a twinkie to a food fight.
Oh Dear, here we go again ...
Carbon fibre, Aramid and glass fiber are the predominant construction materials in sailplanes. They all have a long, proven track record of reliability and endurance.
When a plane crashes, toxic fumes (emitted mostly by the material's matrix, usually epoxy raisin) will probably be the least of your problems.
Carbon fibre will burn to C02, because, as the name implies, it consists of carbon.
PS: I know what I'm talking about, because we build sailplane prototypes at the University of Darmstadt (the kind where you can actually sit in and fly).
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.
The comments in this thread are just more evidence for why we should leave the aircraft construction up to the engineers and not try to figure things out here.
Carbon fiber is a VERY active area of research, and it is definitely true that more is known about aluminum than CF structures, but this is for the simple fact that aluminum is about 10x simpler to understand and model than CF. You are talking about a metal that is isotropic (material properties the same no matter what direction you measure them) versus two different polymers, bonded together. Composite mechanics are incredibly complex, but that doesn't mean we don't understand them enough to make them safe. It only means that we have to use larger safety margins in our designs. As research continues, you will not see airplanes get safer, only cheaper and lighter. Safety is driven by FAA regs, and performance that is driven by material knowledge.
In general, carbon fiber is stiffer and stronger than aluminum. This means that you can make the plane weigh less and flex more. Good, right? It also will have better fatigue properties than Aluminum, since it does not have to deal with crack propagation. Aluminum will fail catastrophically, while CF will go gradually. Chances are that you will detect a CF failure long before it becomes a safety problem, as long as you use those fancy infrared/X-ray/gamma ray inspection devices. For those concerned about "water fatigue", there are a number of industry standard tests to measure this degredation, and it is included with every roll of CF that you order. It's definitely not something they haven't thought of.
The FAA has some of the most stringent regulations of any government agency when it comes to airplanes. The chances of an unsafe product making it to market are very low, simply because of the maintenance required and number of test hours needed. If you remember scandals of the past, they all come from companies either cheating the regulations or the regs failing to be applied. Please don't get riled up unless one of these two things is happening.
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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General Electric's GEnx is going to be used on the Dreamliner. It has a composite fan case and composite fan blades with a titanium leading edge. As part of the FAA certification for the engine to be certified to fly, it must withstand several tests: endurance, icing, foreign object ingestion, crosswind, and blade-out. -Endurance runs the engine at take-off power for over a week straight. -Icing involves shooting ice into the engine until it stalls or until you can't shoot a larger amount of ice. This is also done with water. The GEnx did not stall on this test. -Foreign Object Ingestion is where organic objects are shot into the engine (birds of various sizes). Think meat grinder. -Crosswind involves applying winds from non-standard directions. Fairly straight forward. -Blade-out is where an explosive charge is placed in the forward fan and detonated causing a blade to shoot out and get sucked into the engine. By FAA regulations the forward fan case and engine must completely contain the failure. The end result is a destroyed engine. For the GEnx, I have personally seen the fan case from the blade-out, and the carbon-fibre fan case withstood the blade-out on its first run. This truly attests to the strength of composites. Just my 2 cents.
IAAME (I am a mechanical engineer) I hate to be pedantic, but if you're going to give people technical words like tensile strength, give it to them correctly. Tensile strength refers to the amount of stress a material can handle, before failure, when loaded in axial tension. While bending does involve loading that is 50% tensile, it also contains an equal, compressive, component. In fact, many materials have a different compressive strength, and may fail at a loading that does not exceed tensile strength due to buckling or other problems on the compressive side.
"I must not fear. Fear is the mind killer." -Bene Gesserit Litany Against Fear