A380 cracking wings?

[rattlsnak]

BBC News - A380 wings to be checked for cracks, EASA says

[Flieger]

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.

[J P Stein]

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.

[Flieger]

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

[J P Stein]

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. Either way, somebody screwed the pooch.

[Flieger]

Originally Posted by J P Stein

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. 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).

[slodave]

Airbus traces A380 wing cracks to manufacturing process

[Jeff Higgins]

Originally Posted by Flieger

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.

Simply untrue in every regard.

Originally Posted by Flieger

appears that they may have miscalculated the stresses the wings would see and so they may be fatiguing early?

That's it in a nutshell.

Originally Posted by Flieger

Or maybe they are just checking to confirm the cracks are progressing as expected.

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.

Originally Posted by J P Stein

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.

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.

[Flieger]

Originally Posted by slodave

Airbus traces A380 wing cracks to manufacturing process

Interesting.

[Flieger]

Originally Posted by Jeff Higgins

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.

Sorry Jeff, but this is :

Simply untrue in every regard.

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?

[slodave]

And here we go....

I'll be right back with some popcorn.

[Flieger]

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.

[Jeff Higgins]

Originally Posted by Flieger

Are you an Engineer?

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?

[J P Stein]

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?

[450knotOffice]

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.

[Jeff Higgins]

Originally Posted by 450knotOffice

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

Maybe a little...

Originally Posted by 450knotOffice

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.

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.

[sc_rufctr]

So how do you fix cracked wings?

[slodave]

Originally Posted by sc_rufctr

So how do you fix cracked wings?

A little bondo and buffing should do the trick.

[Bob Goding]

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

[Flieger]

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.