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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."
What they don't mention is that, while the testing schedule is shorter in terms of calendar days, Boeing is logging just as many, if not more, flight hours with the 787 test aircraft as they have with earlier projects. The accelerated schedule is to meet their delivery deadline, but all the requisite tests are still being done.
Boeing knows that the health of the company for the next 10-20 years rests with this aircraft. Airbus, despite its problems with the A380, isn't going to cease being a fierce competitor. If Boeing screws this project up, and gets a lot of bad PR from an aircraft failure, they'll be lucky to survive. With so much at stake, I trust them to do their jobs right.
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.
For the 777, one test Boeing performed was bending the wing to 150% of its maximum rated load to make sure the wing was structurally sound. The all-aluminum wing shattered at 153%, which makes for a great video: Boeing 777 Wing Ultimate Load Test. (The video is from the PBS documentary miniseries Twenty-First Century Jet.)
When I'm flying and I see the wing bobbing up and down outside my window, I try not to think about seeing this video. (Of course, I know the loads are different, but then I have to convince my reptile brain.)
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.
Of course, they also tested it in many other ways - the drop test is simply one of the many tests the FAA requires. They have even done testing not really required by the FAA - for example, they bent the wings back to see how strong they were until they touched over the cabin!
Most of the tests are on youtube, by the way!
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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."
Not at all. Aluminum won't shatter without being super-cooled or absorbing some kind of catastrophic strike...It'll bend, warp, tear, deform. Carbon fiber will bend, hell, there is theory (not yet tested to my knowledge) that carbon fiber wings could bend to the point of touching above or below the plane.
The difference is, if aluminum bent like that it wouldn't return to it's original shape, whereas carbon fiber might. Carbon fiber is very flexible, but when it bends too far it effectively explodes...Shatters into a zillion pieces. So it's brittle.
Put the two materials side by side, and carbon fiber can absorb a hell of a lot more energy without failing than aluminum, but aluminum isn't brittle, so it might be better at dealing with certain types of impacts.
ad logicam Claiming a proposition is false because it was presented as the conclusion of a fallacious argument.
Is that bike shops dont have neutron backscatter machines and x-rays to do non-destructive tests on carbon fiber parts.
Seriously, if you did preventative maintenance and checks on those carbon fiber parts you'd know when they had exceeded their service life long before they snapped.
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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.
A380: 525 seats. Two levels. Frikkin' huge.
B787: 210-330 seats, depending on dash number. 767 replacement.
Boeing is not developing the 787 to compete with the A380. It is a smaller plane with a long, long range. Airbus bet that the industry wanted to focus more on hub-to-hub travel, and developed a plane that carries a whole lot of people from one major airport to another. Boeing took the opposite track, and bet that the industry wanted to focus more on point-to-point travel. This led them to develop a small plane with a long range that can go from minor airport to minor airport without a stop at a hub in between.
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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.
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The FAA has a number of Airworthiness Representatives (ARs) who work for Boeing and report directly to the FAA. Each of the ARs has a different area of specialization, and is in charge of signing off on the designs the engineers release to make sure they conform directly to the Federal Aviation Regulations (FARs). They also witness tests to ensure they are conducted properly, and work with the engineers to make good design decisions and ensure a safe aircraft.
These ARs report directly to the FAA (not Boeing), and they take their jobs very seriously. Their signature is right there on a piece of paper that says "safe to fly", and if there is a failure, their careers are essentially over. An engineer can only become an AR after completing an FAA training period and getting licensed by the FAA.
Once the plane has been built, the FAA collects all the signatures from all the ARs and all the completed test data that has been signed acceptable by the ARs, and when everyone involved is satisfied that the airplane was built in conformance with the FARs, the FAA "tickets" the plane, and certifies it for flight. (Some of those tests are conducted in isolation, like flammability tests of materials or electromagnetic interference tests; others are conducted after rollout, such as your brake test example, or avionics tests).
As a result of this rigorous signoff process, absolutely every single nut, bolt, and part on the airplane satisfies the FARs. Modification and repair shops have similar methods of ensuring compliance with the regulations.
In the case of the 787, the ARs would be signing off against Part 25 of the Federal Aviation Regulations, which governs large commercial passenger aircraft.
IAABE, but I don't work on the 787 program.
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He said: "Carbon fiber is also a lot more flexible than aluminum and it's lighter."
You said: "Flexibility is defined by Young's Modulus, "E". Carbon fiber has a much higher ratio of Young's Modulus to weight, and a higher outright value of Young's Modulus, than aluminum."
Not quite. Young's Modulus is the stiffness of a material. Flexibility is a non-technical term, but it implies amount of strain a material can withstand before beginning to yield. And for an aircraft, the strength to weight ratio should be the most important. For the non-MEs: strain, stress, yield all have very, very specific meanings in mechanical or materials engineering. Also, aluminium has no lower fatigue limit: It will eventually develop cracks no matter how low the cyclic stresses are. And since airplanes constantly vibrate in operation...