A380 cracking wings?
 

Metal fatigue is a well-established phenomenon, particularly in Aluminum. Carbon fiber composites are much better in this regard.

Cracks are nothing new in airplanes. They have a designed lifetime. After they are worn out the cracks can become unstable and cause fracture. Prior to that the cracks are not harmful. If we made them stout enough not to fatigue they would be too heavy to fly. If made from metal.

It appears that they may have miscalculated the stresses the wings would see and so they may be fatiguing early? Or maybe they are just checking to confirm the cracks are progressing as expected.

Odd....ALL formed or machined parts we made at BOP are non-destructive tested.
ANY/ALL parts showing actual cracks are scrapped by engineering without exception....in my experience.

The cracks develop through cyclical loading. They are not present to begin with, as that would shorten the life span even more.

Odd....from what I read the cracking has been blamed, by some, to have occurred during the manufacturing process and the cracks have also been called inconsequential......right.:rolleyes: Either way, somebody screwed the pooch.

OK, but the BBC article supports that these are normal fatigue cracks, but growing at a faster rate than expected it appears.

With this type of fatigue, cracks take a lot of cycles to form, then they start growing a little bit each cycle in a stable crack propagation with little consequence other than a bit of lost rigidity. At a certain point they reach a critical length where the stress concentration is too much and the cracks start growing unstably (fracture).

Simply untrue in every regard.

That's it in a nutshell.

No. There is, essentially, no predicted, much less allowable, cracking in any structural component of an aircraft. These are entirely unexpected, and must be repaired.


Many parts on our aircraft are indeed subject to non-destructive testing or, more accurately, non-destructive inspection. Most are not. Once past initial development and certification, many parts are certified by the process used to make them, rather than checking each and every individual part.

Airbus is facing potentially very, very big problems with this. I won't go into everything, but suffice to say we are keeping a very keen eye on this. It doesn't look good for them.

Interesting.

Sorry Jeff, but this is :
How can you say that there is no cracking expected in a non-ferrous, cyclically-loaded metal part which has minimal safety margins on stress in order to keep the weight down?

Are you an Engineer?

And here we go....

I'll be right back with some popcorn.

One of my professors teaches a whole class on engineering failures, involving fatigue and fracture mechanics. Lots of aviation stuff in there. And not just the easy stuff like the Comet.

Yes. One with 30 years at a large commercial aircraft manufacturer located the in the Puget Sound area. And one who has spent the last ten years of that career on a team charged with the in-field repair and service of of our fleet of large commercial aircraft.

And you?

I'm aware of metal fatigue......I was in NDT for many years and it's all in background studies. A 2 year the life span of parts is not much for an airplane. AB wanted to sluff it off as a manufacturing problem and that also caught my attention. Any design problem would would make the whole aircraft suspect. Much better to blame it on some small subsidiary effin' up the widgets.
Then they tried the old "Oh, no big deal"....the brackets just hold the wing skin to the ribs....no danger there, eh?

And Jeff, that begs the question...are you biased against Airbus?

This from an airline pilot with 27 years experience. Not that it counts in an engineering sense, but I've been in this business long enough to know there are VERY deep rivalries between Boeing and Airbus.

Maybe a little...;)

Let's call it a "friendly rivalry", at least at the engineering level. Deep respect on both sides. We share more than you might think...

The "deep rivalries" are more with the suits in the ivory towers, and the politicians they have in their pockets. In other words, with the money boys. We try to stay out of that. We just want to build airplanes and have fun, on both sides. Part of the fun is building a better one than the other guy.

So how do you fix cracked wings? :(

A little bondo and buffing should do the trick. :D

If it ain't Boeing, I ain't going

Well I know my professors use the example of the wings flexing on taxi and in the air when talking about fatigue. When those are made of Aluminum the life span must be calculated. This requires lots of data to know what stresses and at what frequency the metal is subjected to, then the lifespan is predicted based on high cycle fatigue SN graphs which reflect a curve fitting of experimental data, with modification factors for the type of loading and such that the actual part experiences.

Engineering is partially about acknowledging that nothing is perfect and is about knowing when enough is enough. You can't make money if you are replacing parts all the time for tiny cracks that are not hurting anything.

Even aircraft quality material is known to not have defects above a certain size. They use high powered methods to find tiny defects, but atomic sized cracks and slip planes which are cracks in waiting cannot be detected without even more expensive means such as scanning electron microscopes.

Aluminum and most other non-ferrous engineering metals do not have a fatigue endurance limit and even if steel is used, to design a part for infinite life adds cost of fuel to haul that weight around, so the designers want the lightest aircraft that meets the specs.

Cracks are expected to form and grow. The size of crack that necessitates replacement of a part may be quite small in a structural component and larger on others, but cracks are still expected to form after a certain number of cycles.

Granted, the published life span is more like 20 years for an airframe, with extra safety margin since fatigue is not based so much on first principles and is subject to statistical errors and such. So these failures on the Airbus wing are not normal, but cracks in general are.

Not even Boeings, good as they are, are immune from metal fatigue, unless they are made out of composite like the 787. At which point there are other things to worry about like delamination.

Well, there is really no such thing as a "cracked wing". There may be cracked wing components, and that's what Airbus is faced with.

In retrospect, I think I was too hard on you, Fliegler. Sorry about that, I think I misunderstood your point.

Yes, by all means, parts crack. Every single structural part has a predicted mean time to failure. We more or less "know" when it's going to happen. What we decidedly do not do, however, is allow any given part's service life to extend beyond even any initial cracking, and continue to fly it while proclaiming "yeah, we knew it would do that".

We endeavor to replace or repair cracked parts as soon as possible, especially those that have cracked unexpectedly. It becomes very difficult, if not impossible, to predict the rate of crack propagation when we have well and truly missed on its mean time to failure anyway. In these cases, inspection intervals are severely compressed, and we monitor the situation very closely.

Inspections on parts approaching a certain percentage of their mean time to failure become more vigorous as well. Parts are replaced at some percentage of their predicted lifespan (depending on application and relation to safety of flight). These parts get pretty thoroughly analyzed in an effort to validate our predictions.

So, yes, you are technically quite correct - airplanes do have a designed-in, finite lifespan. Just not at an "entire airplane" level, which is kind of how I read your post. (I don't think that's what you meant.) It's really the individual parts that make them up that do. There are, however, very few we cannot replace, even in the field. So, technically, airframes really do not have a "designed lifetime", but parts of them do.

OK, now you are making sense. :) Yes, by an aircraft lifetime I meant lifetime until something big enough starts cracking such that it is not worth repairing.

By the way, "Are you an Engineer?" was an authentic question. I knew you were with Boeing, but did not know if you were a skilled worker in assembly or an Engineer or both...

I don't think this is true at all. A properly maintained airplane should last a long time no? Perhaps even a hundred years? Or longer?.

/Looks at the BUFF

I am not a engineer. Just a computer tech.

Jeff pointed out my error. I was referring to each part of an airframe having a service life. I did not mean to imply that the whole aircraft was treated as a single piece with one lifetime.

The B-52s are not the same as they were when they rolled off the line. Lots of upgrades.

Airplanes are like some Porsches. All that is left that is original is the vin plate. :)

I don't think this is a big issue at all - isn't most of the Aeroflot fleet held together by cracks?
AM

Again, sorry for the misunderstanding. We're on the same page.

To satisfy your curiosity as to whether I'm "a skilled worker in assembly or and Engineer or both...", I would have to answer "all of the above". At least at one time or another.

A quick "history of me in aerospace": Graduated high school in '78, and went on in pursuit of a degree in mechanical engineering. After a year and a half, dad dies, leaving me as the oldest male at home. I drop out of school and go to work at Boeing in an effort to help support my mom and two younger siblings. I started there at the ripe old age of 19 as an apprentice tool maker. By the time I'm 26, I've been promoted to a lead position over about 70 other tool makers (way, way out of sequence, union seniority wise, thereby pissing off all the old union do-nothings).

By then, my mom was working and two younger siblings were out of the house. So, fulfilling my "obligations" at home, I up and got married and started a family. Just in time to weather a couple of union strikes...

Having had enough of that (and the union in general), I restarted my education after 16 years and two kids, and fulfilled my dream of becoming an engineer. And I've had a ball ever since.

I initially made the "easy" transition at work, from the tooling world I had grown familiar with as a tool maker, into the design end of the tools I had built for so long. Growing bored with that about ten years ago, I made the jump into the world of "AOG" - "Aircraft on Ground", wherein we repair damaged aircraft. Often under "austere" conditions, often in third world shyt holes, often ill-equipped and therefore engineering "on the fly", I've never had more fun.

I'm in the best of both worlds - I get to design the tools and equipment for a unique in-field repair, and then often get to roll my sleeves up and get down and dirty with the mechanics, working side by side to use my equipment and affect the repair. All union boundaries are forgotten, and we go to work.

I'm one of the few "hands on" engineers in a big union company, working with a hand-picked team that transcends all of that union b.s. and just gets it done. Whatever it takes, wherever we need to go. It's great.

You have my respect.

I saw a TV program, I think it was on National Geographic or something about their emergency repair team. If a plane runs off the end of a runway in a far away land they would go with the part and get it ready to fly.

The TV program was them repairing/replacing the aft bulkhead for the pressure cabin. I think it was a tail strike due to over-rotation or something.

That was us. I didn't make that particular trip (it was in Paris, too, dang it), but that's what we do, and that's the crew I do it with. I designed all of the tooling for that job, an aft pressure bulkhead replacement (due to a tail strike). The guy with the white hardhat, running the overhead crane (using the pendant) is my partner Jason, who sits right next to me when we are all home.

First, no...I am not an engineer. But aircraft do fly with known cracks (at least in the military realm). I worked as both a machinist/welder and managed a NDI (Non-Destructive Inspection) Lab and know for a fact that some structural elements on aircraft are allowed to crack. It's quite common to find cracks, schedule hourly inspections and track crack progression. Once the crack gets to the known fatigue limit...parts are replaced or repairs are made.

I will admit that I am biased against Airbus and thats only with 39 years experience in the field.

Again, "if it aint Boeing, I aint going!"

Compared to a DC3 this is funny!
The DC has been around maybe 50 yrs and nothing falling off..LOL

Yes, but their cabins are not pressurized, correct? And the wing loading is not like the A380 I imagine. And they do not fly as high, correct? So that means less stress on the components.

But the big thing is when is the last time you flew in an all original DC-3? I bet most all of the mission critical parts have been replaced or restored on the DC-3s.

I saw a 737 in a Jig in Evertt Wa
Robots were bending the wings every 30 sec. or so about 6' past center !
I thought it would just blow apart.
It did give me confidence in the structure.
True the old DC 3 was a recip....still, it is a old flying dog and they still beat the Hell out of them way up North (Alaska)

Yes, those wing bending destruction tests are pretty spectacular. I have seen them on TV. They sure make a hell of a bang when they finall let go (with the wings bent about 45 degrees!).:eek:

You both are partially correct.

Pressurization does stress the fuselage but how about wings? The wings and tail feathers on most -3's flying today are prolly still original, but inspected as needed.

Ah, sorry. I did not phrase that too well. I meant that the A380 wings seem to have a finer aspect ratio and the plane is meant to carry a large load (to make money), so the wings would flex more on the A380. But I don't have enough facts to back that up.

Legend has it has it that the wing load testing for the 747 used up all the travel on the jig which was 150% of load requirements +. They were supposed to load it to failure....uh, now what? It took 13 saw cuts in the wing to get it to break.....legend has it.

IIRC, the 380's wing failed before the 150% requirement........the excuses flowed hot & heavy. AB said at one point that the structure actually failed at the wing/body joint & all was well.....or some such nonsense. Boeing had a similar problem with the 787.

They DON"T make em' like they used to. Planned obsolescence is now the mantra.

Rumor also has it "They" did not know much about Aluminum in the begaining and over built the design requirements.
Now it has swung the other way..............

That is not really true. I have been in/under many B52s and they are pretty old. They did a wing improvement, I think in the early 70's but that is about it. Avionics/radar are always being upgraded but that is like putting a new radio in your car.

With the latest upgrades they predict the B52 will have been in service 100 years. The last one was made in 1962.

I remember this day well. I'm in that crowd surrounding the airplane. I had just started at the company when we did this to the 767, and was on hand for that. I also witnesses the 787 test.

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Less spectacular, but every bit as important, is the cyclic fatigue test. A similar fixture pulls up and down on the wings to simulate one "cycle", or take off and landing. Pretty boring stuff compared to the spectacular ultimate strength test.

And yes, the 747 damn near touched its wing tips above the fuselage. They couldn't break them. There are plenty of photos of it decorating our offices.