Some how knowing there are cracks in the wings and knowing they aren't on track to be fully fixed until 2013 would make me very reticient to hop on one these babies, even though they are undoubtedly a beautiful example of A&D design.
Interesting that Airbus has suffered its fair share of setbacks on this plane, due mostly to miscommunications and missteps in the design process. To whit: One of the highly publicized delays related to the project was due to problems around the wiring harness system and the structural design--a miscue some attributed to interoperability and incompatibility issues between CAD platforms.
The main problem seems to be where composites interface with metals: and that is a new problem. It happens because a commercial plane is made of both materials: composites have not been designed to replace everything yet and metal can't be used everywhere due to weight/fuel reduction requirements. These problems took about 10 years to show up in in-service planes.
Ann, composites and metals is not a new problem at all. Been dealing with it for 40 yrs. Most aircraft were made from a combo of them.
The problem is the engineers or above can't bring themselves to do composites as they have always worked in alum, etc. So instead of doing it right, glueing, they use a bastard mechanical fasteners because they are scared of doing anything new. Sadly this goes through many industries.
Naperlou just the expansion, contraction of the Composite tubes in the metal joints from the 1000F to -200F of space temps as it comes into and out of sunlight would be enough to destroy it as their rates are so different.
titanium and carbon fiber have similar thermal expansion rates. aluminum is quite different... titanium also does not corrode when placed next to carbon fiber, aluminum must be well insulated with fiberglass or something else...
Jerry, we've reported several times on on the use of composites in aircraft over the last few decades. We've also done features on fasteners and adhesives for structural apps, including aerospace. What I've been told is that composites have been adapted to component designs originally engineered for metal without rethinking those shapes, and that fasteners for composites have not been re-thought thoroughly. This was all in the rush to get composites into commercial aircraft. It's the 50% and greater proportions of composites to metal that are new--as well as all this being somewhat newer in commercial than in military aircraft--which means joints are being made between dissimilar materials where they weren't before. Also, adhesives are simply not strong/durable/reliable/etc enough for the extreme stresses involved and, as kfw2qd points out, it's tough to tell when they've failed.
,Jerry, we've reported several times on on the use of composites in aircraft over the last few decades. We've also done features on fasteners and adhesives for structural apps, including aerospace.
----------How about a link to the tape adheasive one?
What I've been told is that composites have been adapted to component designs originally engineered for metal without rethinking those shapes, and that fasteners for composites have not been re-thought thoroughly. This was all in the rush to get composites into commercial aircraft.
-------- Basically what I just said, they can't change easily because of the way they think. I started in composites 45 yrs ago now so I've alway thought that way and saw others do just as you say. This cuts across almost all industries.
It's the 50% and greater proportions of composites to metal that are new--as well as all this being somewhat newer in commercial than in military aircraft--which means joints are being made between dissimilar materials where they weren't before.
------------- The problem is one material or the other take the main share of the load. Otherwise the weaker one will just be destroyed. It has nothing to do with the materials, it's the designer, engineer who is at fault for not designing within specs, good engineering practice. There is little difference in materials/metals used then and now.
----------------BTW this is the same problem CF has. It has to take all the load because it will. If only 50% on CF and 50% on FG because the FG elongates more, the CF takes the whole load until it breaks which then transfers it to the FG which also breaks then. Had it been in CF or FG it would have been fine.
Also, adhesives are simply not strong/durable/reliable/etc enough for the extreme stresses involved
------------ Again military jets are under far heavier loads and most of the 70's jets had many composite parts including many of mixed metal, composite close to equal amounts and are still flying. And modern adheasives are better we hope. Only time will tell.
and, as kfw2qd points out, it's tough to tell when they've failed.
--------------- Maybe kfw, some others have a problem finding debondings but those who do it for a living don't have a problem. If there was the FAA wouldn't let them fly. It's not easy to get something by the FAA/NTSB like that more than once.
Ann, it would be helpful if commenters would NOT try to draw conclusions from smaller aircraft and military aircraft using composites
DeHavilland in Canada is a past master at glueing aircraft together right from the days of the Mosquito all the way up to the Dash 8 and it's a lot trickier working with composites. Both Boeing and Airbus lost their way going hell bent into composite construction with both of them barging ahead with insufficient testing and arguments around military aircraft experience and smaller aircraft are not valid since neither of them carry large passenger payloads.
In earlier days when Boeing bought DeHavilland it found out very quickly that building smaller aircraft was not the same as Boeing's normal expertise...there is a magical divide when the transition is made from one size of aircraft to the other.
ScotCan, I have also noticed that some commenters draw conclusions for large aircraft from the use of composites in smaller aircraft. My understanding, like yours, is that scale matters and that a divide has been crossed with Airbus and Boeing. That said, the comparisons with the use of composites in military aircraft have been made by nearly everyone involved in using composites on these large aircraft, including the OEMs and the suppliers, such as in this DN article: http://www.designnews.com/document.asp?doc_id=235863
Fair comment, I suppose, except that small aircraft are generally way over designed and military aircaft are more so. Large passenger aircraft are designed for reduced weight and maximum payload and as a result end up with using exotic materials about which there is little history...that's the problem. If the cracks are in AlLi (and the location suggests that they may be) preload and other fit up factors could stress the material. I mentioned fitup factors because nothing fits together perfectly...despite the use of CAD. Most aircraft parts are designed to nominal sizes and when the parts are made tolerances have to be provided...a classic example is a machined part which nests into a formed sheet metal part....sometimes it'll fit other times it won't. Since the machined part carries tighter tolerances, the sheet metal part is deemed to be under or over size as the case may be. On other occasion a wee bit of persuasion gets the undersized sheet metal part to fit albeit with some preload which is OK for 2024-T3, marginal for 7075-T6 and totally unacceptable for ANY AlLi.....as you can see here the rules change quite a bit for AlLi BUT it is not always conveyed explicitly to the shop floor....there will be marginal conditions which the shop floor experience deems it knows how to work around and which work admirably for the above mentioned 2024 and 7075 material.This is liaison engineering talking, and we're the guys that return the aircraft to the design intent...a bellwether indication of how troublesome a new aircraft is is to do a count of the number of liaison engineers a company hires for the production run...the Boeing Dreamliner had one of the highest number ever, so, we'd best stay tuned for upcoming events concerning that aircraft....the A 380 has more flight hours than the Dreamliner and more landings and take-offs...when the Dreamliner matches that number things'll start showing up....it's the name of the game!
ScotCan, thanks for all the detailed feedback. The cracks were stated to be in an aluminum alloy, although it was unnamed. You seem to be implying that the alloy is AlLi--is this true? If so, can you tell us how you know that for a fact?
It wasn't intended to imply that the A 380 problem was related to AlLi, rather experience with the material has shown that it is a tricky material to work with and doesn't like preload. 7449 is the Aluminum Alloy in the A 380 ribs which are cracking and it is susceptible to Stress Corrosion Cracking and it also doesn't like preload.
Beth, I agree with you. I wouldn't fly one yet. If they really could tell if it was safe they would not have had the problem. This is new stuff. They can't really know.
I saw a similar situation on the Landsat spacecraft. The structure was a large space frame made of composite tubes. The joints were of metal (titanium, I think). It was clear that if you put the fastrner holes in the normal position, as for an all metal structure, that there would be problems with cracks. This was becuase of the use of dissimilar materials. This was found by building a test sub-structure. I wonder if Airbus did enough testing of actual materials, or whether they relied on CAE. When using new materials it is important to understand that the CAE tools may not be able correctly predict what is happening.
naperlou, I think the potential gap between existing modeling techniques and assumptions and the new realities of a new material is a good point, and one that the GAO was concerned about in its report addressing repairs to the Boeing 787's composites: http://www.designnews.com/document.asp?doc_id=235037 They focused on the back end of repair and maintenance, not the front end of design, but the concerns were similar.
The fastener problem makes me, too, wonder about safety issues, regardless of what Airbus says. In a previous feature on fasteners, manufacturers told me they were designing new ones to go into new composite materials, which have very different requirements from metal. So what does that say about whatever fasteners or insertion techniques are currently being used? OTOH, composites in aircraft are not at all new and you'd think they'd have figured out that part by now.
I would expect that these type of problems of material incompatibility would be first tested and then applied on smalled jet designs. The stress may be better detected at faster speeds and fuselage deformations under changing Gs.The chance of serious accident with many lives lost is a clear possibility. I would avoid this plane as a plague for now.
What about the liability issues. In some ways, it's pretty amazing that they can admit there are problems that they don't fully understand, yet still keep the fleet in the air. I understand the logistics issues related to retrofitting the fleet, but still ...
The Dreamliner's next in line for complications. Both Boeing and Airbus bit off more than they could chew, both with the use of composites and Aluminum-Lithium (AlLi)
AlLi is great stuff EXCEPT it does not behave like standard Al Alloy material. Generally,percussion rivetting is avoided because AlLi has been known to crack under impact...one project used blind fasteners all over the assembly to avoid cracking AlLi components. The shop couldn't fix mistakes as readily as they could with traditional Al Alloys, and etching AlLi prior to adhesive bonding did not work out at all well.
ScotCan, I also find your comments on AlLi intriguing, since this is being positioned by aluminum makers as the answer to the commercial aircraft OEMs' composite woes. Interestingly, the Airbus wing cracks occurred in the unnamed aluminum alloy. I wonder if it's AlLi?
The EH 101 helicopter Lower Forward Fuselage built as an industrial offset in Canada was almost exclusively AlLi. The shop had a whale of a time working the stuff since it does not behave the same way as even 7075 material. The shop had "tribal knowledge" on how to fix discrepancies in the standard alloys, but came up against all sorts of stumbling blocks with the AlLi. It has an enormous strength and as a consequence the cross sections (and the weight) were correspondingly less than the conventional material. Stringers for example were somewhat forgivable in preload, but could develop large internal stresses unknown to the operator tweaking the fit...all it needed was a glancing blow to crack the stuff. Eventually the shop got used to its eccentricities and we did OK towards the end of the contract. The weight savings with AlLi are remarkable. The lower fuselage slighter larger in planform than the Dash 8 lower flight compartment weighed in at 350 lbs, so as a material it is here to stay.
It has to be considered that EADS is a transnational company with plants in France (final assembly for some types as 380) and Germany. This incompatobility came from the 2 different origins of the softare packs. It was an orrigine error and it unfortunate that it manifested at this project.
I am not affraid of the hair cracks since their evolution is very well monitored and it is NOT the only plane in use which has minute cracks and requires periodically controls and repair. In fact almost all planes have this problem.
What I do not understand is the fastener introduction problem. I know the fatener type and the technology used and I do not see where the "introduction" could harm.
It would be good to have more on this subject.
As for the tests AIRBUS is extremelly careful and one cannot imagine the number and the depth of done tests. It could be possible that the loading combination in flight/landing was in the real world different from the one previewed by desighners.
As far as I know the fasteners do only "clamp" the composite between 2 metallic layers. This can be the reason the cracks did appear in the aluminum and not in the composite.
Nick Name, previous reporting elsewhere has cited Airbus as stating that the fasteners were inserted with too much force for the not-flexible-enough aluminum alloy, which thus formed cracks--but after 10 years. Since the background info also talked about the problem occurring at the aluminum/composites interface, that can make it sound as if it's the composites that failed. In any case, Airbus is not releasing much info, and not releasing any formal statements online.
Hi Beth, the cracks will be monitored for growth vs flight hours and an update would be issued regarding the seriousness or otherwise of the condition. The communication problems with the Europeans reminds me of a helicopter program they once ran where the Germans and the French were partners and since very few Germans spoke French and few French spoke German they settled as English as a common language! So, there were 3 sets of paperwork kicking around to make everything legal one in German, one in French and one in English!
I wouldn't worry about this unless they ground the fleet then AVOID. A year in the life of a airliner is a long time. And during that period it will be monitored normally and I would bet money in a quite paranoid fashion about these cracks. If the customers loose confidence in a design and won't fly it that design can soon be in trouble, witness the MD vs Loughheed. Both looked about the same ie 3 engines but only the MD was seeing issues with floors and controls yet people wouldn't book a flight on either. And other than flying boxes for Fedex there aren't any around in the air.
For the 380 this is just another problem its had. It may turn out to be nothing. For the most part Airbus designs are typically pushed a bit further than what Boeing will do. In the case of the 380 they set goals for performance and weight that forced them to use some semi exotic materials such as the alli alloy. That saves about 20% in weight but as a few guys have mentioned is a "slight" pain to work with. And the company that pioneered its use and has the most experience was bought out by a company called Boing so Airbus was unlikely to get much help in designing a competitor. And this may just require a retraining of the workforce. We had headaches from the floor guys banging stuff together in the same ole usual way which usually meant they ignored what we designed cuz they knew better. We even tried putting written instructions that they comply with all specifications and to contact engineering if there were any questions and hence was born MIL-TDP-41 which we stamped on every drawing for about a month. And of course no one asked about it until a aqap inspector saw it and asked as he was not familiar with it. So we had to explain to him that it meant "Make It Like The Damn Plans For Once"
Considerring the testing that has to be done -subassemblies tested to destruction, tested for some number of cycles... it would seem that the testing procedures were not correct fot this type of assembly.
It sounds like this is a problem with components inside the wing, and may not pose a risk of structural failure, but rather of wear and erosion of both the composite and the aluminum.
The problem with adhesives in some of these applications is that the adhesive may not be flexible enough, or it is extremely dificult to tell is the adhesive bond has failed. What would happen if the bond was failing in the middle of the assembly, but not near the edges? how do you check it for failure other than by damaging the adhesive to look at it?
Some of this is what every engineer has gone through at some point in their carreer - you thought you had everything nailed down, you did all the correct tests, only to find out the one thing that you were very confident in was the problem. The one property that no-one would have considerred was the one property that was the most important.
I think it was the DeHaviland Comet that had an array of holes drilled in the lower wing skin near the landing gear because of cracks that wanted to form there. By drilling the holes that section of wing skin was able to flex and no more cracks. A bigger problem was the failure of several of the comets because of the stresses around the sextant port in the top surface of the aircraft. Was one of the early pressurized aircraft and they didn't properly account for the stresses around that hole in the fuselage - several of them broke at altitude and crashed... They built a huge tank and submerged the fuselage and then presurized it under water to figure out wha tthe failure was.
An interresting aside - Jimmy Stewart played an engineer (Was a B17 Pilot WW2) in the film "No Highway in the Sky" (co-starred Marlena Dietrich ) in which metal fatigue was the cause of a catastophic failure, and crash of the Reindeer. Three years before the crash of the Comet - due to metal fatigue in the fuelage, not the tail as in the movie. They didn't want to believe him - he was a bit of an eccentric... Then as now, engineers have a problem with PR.
You're very welcome!!! 40 years in aerospace Design/Liaison gives a pretty major oversight of what goes on in these human endeavours...methinks the experienced hands should be using this technology (digital communication) to get the word out and keep things from going astray.
So, the airplane built by committee is falling apart? I know this is an exaggeration, but I could see it coming a mile away. I like Boeing and the fact that a private (publicly owned private company) has every control in-house. The European governments spread everything over politically correct avenues. I never like when governments get involved in anything other than what governments were designed to do. And that isn't making airplanes!
As far as the cracks are concerned, mixing materials is a relatively new science and has yet to play itself out. My confidence level is not high, and as a very frequent flyer, I want it nailed down tight before I risk my very precious hiney at 5 miles in the air going 600 MPH! I want the wings, at least, to hold together. The food can be lousy or nonexistent, the service crummy and grumpy, and we can circle while the President gets a haircut, but I want the wings to be just peachy.
Perhaps "we" have rushed into this composite thing too fast. Maybe it is time to step back a generation and take another look at the long-term stresses and the conditions the wings will operate under. Takeoffs and landings, radical changes in temperature and pressure, extreme wind forces, birds and other objects, and expansion and contraction and other phenomena affect the boundaries between the different materials that seem to be separating. Do we need to rush into this thing?
warren, what I'm hearing is that part of the problem that's occurred with composites in aircraft was not completely redesigning components to take fully advantage of this different material, instead of what did happen, which is trying to make the new composite materials fit old processes designed for metals. John Moore of Hexcel explains why this complete redesign did not happen in my aircraft materials feature here: http://www.designnews.com/author.asp?section_id=1392&itc=dn_analysis_element&doc_id=246025&page_number=2 This is not an unusual situation in manufacturing, especially of large, complex systems like aircraft: there's no such thing as a drop-in replacement in materials. OTOH, one would hope there would have been a lot more testing of those metal/composite interfaces, which seems to have be the culprit in the Airbus case.
I think this strengthens my point. Not enough attention was paid to the changes composites would make to old processes. I remember reading your article and thinking how would an old timer used to aluminum and plastics think to modify his old way of doing things for something so space edgy and different. I think the answer is, "He won't." Now maybe he will after this high profile failure.
Too bad. I like the idea of new technologies coming on line. I just like to see them properly thought out before putting my life on the line...
warren, I agree: not enough design controls to anticipate potential problems, not enough "what if" scenarios in both design and testing. I find it interesting that the Airbus CEO came right out and said that the company didn't understand the materials and interfaces as well as they thought they did. That's quite an admission. It's also scary: not knowing what you do and don't know. Of course, I wonder if there weren't some engineers who did know, but weren't listened to, as several commenters have suggested.
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