Slashdot Mirror
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."
Rather didn't single-source this. He has confirmation from a number of other, currently-employed Boeing engineers of doubts about the composite materials. And if you look at the resume of his main source, it's impressive - the man was one of the top engineers at Boeing, and had done high-level work on NASA projects. Does that mean he's perfect? No engineer is. Does that mean his doubts should be considered seriously? Of course, especially when other engineers do agree about them.
... from 15 feet up.
There' also the very plain fact that Boeing is rushing this plane to market with far less testing than was used for recent generations of more conventional passenger jets. That gives Boeing every incentive not to listen to doubts. Boeing is betting that this can finally allow them to pull decisively ahead of Airbus, who has caused Boeing serious hurt over the last decade. Maybe it can, in the short run. Orders are coming in. But what happens if there's a spectacular crash or three? Will Boeing take the reputation hit that, say, Ford took about the Pinto? Maybe not. The public expects there to be no survivors from jetliner crashes. On the other hand, the sheer number of people these things will carry means the first such crash will be the most fatal - not counting people in buildings crashed into - ever. There will be weeks of international media scrutiny.
Boeing, we should be relieved to know, has tested the fuselage by dropping a section of it
"with their freedom lost all virtue lose" - Milton
Carbon fiber will burn in air around 500-600F. Air has oxygen which attacks the carbon...this is why almost all composites on an airplane undergo TOS (thermal oxidative stability) studies. If the plane has crash landed and is on fire the fumes are from the resin used not the carbon. The FAA requires rigorous fire testing of materials. Usually, flame retardant additives are used on structures that could burn or they use a phenolic resin.
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.
The story is about a former Boeing engineer who has serious concerns with the new plane's safety.
Nope, it's about a guy who got canned for making racist remarks on the job, looking for some way to lash out at Boeing and get some revenge. Fuck him.
-jcr
The only title of honor that a tyrant can grant is "Enemy of the State."
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
You have several things confused.
... if it breaks too far beyond the design limit, it means you made it too heavy).
The 787 has not yet had wing tests conducted. The "touch over the cabin" part of your statement comes from the fact that many of the engineers at Boeing believe that to be possible; carbon fiber is so much more flexible than aluminum that it is, in theory, possible to bend the wings up over the fuselage until the two wingtips touch. Boeing will not perform the stress test to that extreme, however. Boeing will test the wings to the design maximum and then stop. They will not test to failure.
The reason for this is twofold: first, it doesn't matter after the design max. If the plane actually experienced design max stresses in flight, several other components (like the fuselage, or the vertical stabilizer) would fail first, so as long as the wing reaches that maximum without a problem, there's no need to test further. It doesn't matter how strong your wings are if your fuselage snaps in half first. Second, carbon fiber does not have a plastic strain region; it's all elastic strain before failure. That means that it will just continue to bend farther and farther without damage to the wing right up until failure (contrast with metal... when you bend far enough, it doesn't return to it's original shape anymore, but it has not yet failed). But, when it does finally fail, it doesn't snap, it shatters. That means clouds of hazardous carbon fiber dust and shards would be sent flying around in the factory. Not good.
The video on YouTube is of the 777 wing stress test conducted in the 90s. It was designed to reach 150% of max in-flight loading before snapping. It actually snapped at 154% (which is impressive
IAABE, but I don't work on the 787.
For security, the MD5 hash of this message and sig is 09f911029d74e35bd84156c5635688c0.