The Dreamliner tests new ground in areas apart from composites. Specifically, it has a no-bleed systems architecture which replaces most of the pneumatics with electrical pumps. One can make an analogy between the Dreamliner and the first fly-by-wire aircraft, which put computers in charge of the flight control surfaces (and more). Twin-engine overwater is another example of scarily going where avionics hadn't been before. When you think about it, it's amazing that all these disruptive transitions have occurred pretty much within the parameters of acceptable safety. And thank goodness for that.
Here's a link to the full report for anyone who's interested in reading it. Based on some of the comments, I'm not sure if some people even bothered to read the article - it's much easier to simply spout preconcieved ideas.
GAO was asked by Congress to evaluate the certification processes which FAA and EASA followed. This was not a task which GAO took upon itself in order to justify its existance, as some commenters seem to be suggesting; GAO is part of the legislative branch, and works on whatever Congress tells it to work on. In this case, GAO was asked to make sure that the money which taxpapers are giving FAA to certify composite materials in civilian aircraft is being spent effectively.
The GAO report isn't a comprehensive technical review of composites technology, nor is it intended to be. The focus is mainly on the processes which FAA followed for certification. And, basically, it looks like FAA did what taxpayers are paying it to do. They followed their own procedures, and where they thought their procedures might not be adequate, they took additional steps.
I might add that the same people who are complaining about GAO "wasting" money to check FAA's work (something which other people would call oversight or accountability) would probably also be complaining about the lack of a GAO investigation if it turned out that FAA had done anything wrong.
GAO identified some areas which will need continued attention, which mainly center around the fact that using composites at this scale in a civilian aircraft is still a new thing. The issues which GAO identified (lack of information, need for standardization, need for training, etc.) are common whenever anything is new. I don't think anyone could seriously disagree with GAO's conclusion that it's too early to assess whether FAA and Boeing got everything right - the proof will be in the pudding.
I would assume there are scores of tests that have been done over the years and a lot of test day a available that someone could at least point to for reference. Would there be fatigue adn age data for this that shows the degradation over time?
For repairs, I hope someone has a process for fixing cracks in composites or a means to replace the cracked parts.
The aerospace industry, Boeing and Airbus have enough experience on this subject to go forward but it certainly would help for them to join in on this discussion and point to their test data and show us what they know.
Every composite failure resulting in any loss of life should be investigated throughly and the results made public for every one to keep their confidence up.
It's all politics. The US has been building composite components for many years in many Boeing and and the Europeans in many airbus Airbus commercial and military acft.
They have mutually been developing and establishing standards and procedures over the years. Every aircraft Boeing and Airbus builds has numerous critical surfaces built of these materials with accepted and approved procedures for repair and replacement.
The article is a frantic non-involved govt agency busting it's ass to save itself from obsolescence and un-importance in any way it can. Procedures have been in place for years. All they are saying is... "we need some extra fed money to justify our existence."
If composites have been reliable in smaller applications they should also be reliable in the larger ones.
I think that I recall reading that fine wires were being embedded into all of the composite structures to provide warnings, when the strain deformation went beyond allowable limits. It that feature has been included then it would just be a matter of keeping attention to the structural integrity monitoring instrumentation. Of course, if such a feature were not included, there would need to be other monitoring means applied. These methods could include resonant element evaluation and P-wave propogation time measurement. There may also be other evaluation models that I am not aware of.
Of course, none of these methods is as cheap as ignoring the potential problem and hoping that it does not matter.
Actually the military design information is not available, at least in the USA to the commercial design staff, this was brought up before.
Composite materials are not ready to be the main wings of a commercial aircraft.
Hell NASA can't even understand all of a composite materials properties and they have more eggheads than anyone.
The main problem is going to be the overworked low paid ground crews who will miss stress fractures and then one of the 787's is going down.
Composites do not react to stress like metals they don't stretch and bend, they hit their wall and then fracture explosively.
A major wind shear which twists is either gona directly make the plane crash or damage the structure and then the ground crews will miss the damage and the next big twist or bend will take out the wing.
As to the military, they have already lost at least one B2 that I know of.
They paid two billion for them and don't care how much repairs cost.
And then look at the structure of a B2 versus a 787 wing, a B2 is a lifting body blended wing and probably just about the best structure for a composite.
The thin flexy 787 wing is going to be strested threw flexing all the time and will get micro fractures then a big wind shear and its done for.
Yes the mechanism is well known. The plastic resin matrix became embrittled over time and the part failed under a lower load than it was tested for when new. The report on the American Airlines crash faulted the First Officer for using full rudder excursion below the certified Manuvering Speed. Metal rudders have never failed under such operation. Pilots have used full excursion for over 60 years with no failures. Only aged Composite rudders. The last two failed in cruise flight with no excursion at all because they were older. The TIME tensile strength curve is constantly downward until failure. You mentioned Military Aircraft. All military aircraft with structural composite components have not been based in forward air theaters. Too fragile. When a B2 bomber bombs Irag, it must fly from a US base, refuel in the air, bomb, then fly back to the US. The military does not report it's embarassing failures of composite components. My experience includes design engineering with 35 years composite experience and 10 years as an instrument rated pilot. The president of a competing company was klled when he took a demonstration flight in a composite aircraft that failed in flight. The executives of Lancair were killed in a composite company aircraft that suffered structural airframe failure one year returning from Oshkosh. The accident list is endless for composite airframe failures in normal flight. Not so for metal airframes unless they were stressed well beyond design load like the recent Reno disaster.
The materials aging mechanisms of structural composites are well understood by the design community, test community and such in the miltary, the commercial and the general avaition manufacturing, support and service industries. These materials have been in use in high load primary structes in the miltary aircraft industry for over 27 years.
By primary I mean if the part failed the vehicle is not reciverable in flight. In secondary structres (ie if the part fails, safety of flight is NOT compromised) these materials have been in service for over 50 years.
Contrary to prior reports modern structral composites (since at least 1982 from personal experiance) do not use plasticizers in the martix materials. Some material are toughtend with a second pahse elastomeric material which fist was started i belive in Hexels 3501-6 or the follow on 3502 epoxy system.
The rudder failures of the Airbus vehicle in question have been related well in the published information and should be reviewed by those interested for report accuracy. Pleas note the issues at play in that specific desing had little to do with the aging of any material as noted in the reports.
Linear guides are one of the most important components required for the design of automated or computer-controlled equipment. Aluminum profile extrusions, used for these guides, can enable designed-in functional features.
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