A340-600 wrinkles

[flightmedic]

Flew on one of these beasties with Lufthansa to Vancouver and back. Not bad at all; wide body, comfortable and attractive design inside. However,
the attention to detail and finish isn't as good as it might be. I was quite surprised to see a very rough-finished panel on the wall of the loo - not cut straight and still with the pencil marks!

However, the point of this posting is more to raise a concern - seen from a punter's POV. On the out flight, we were sitting inboard of the port wing, and could see the whole wing clearly out of the window. Towards the
end of the flight, the flexibility of the wing increased - probably because the fuel load was low, of course. However, unlike Boeing wings, which seem to flex equally throughout their length, there seemed to be a
specific pivot point at the mounting of the far engine, so that just the far end of the wing flapped, and the rest flapped far less. Even worse, there was a noticeable crease in the upper surface of the wing, suggesting
that this point was being distorted beyond the recovery of the skin. Now I completely understand that this is just the skin, and there are spars underneath which are doing the work, but this is a brand-new aircraft. I
remember the early Comet fatigue problems, and would hate to have spotted something that crew members and technicians may not see. I realised that I had taken a picture of the wing, and I have put this up at
http://www.cix.co.uk/~rowleys-host/webpages/A340-600%20wing.jpg where the rippling of the reflection of the canard (or whatever those wingtip flip-ups are called) is quite evident. I didn't get such a good look at
the wing on the return leg on a different aircraft as it was dark but my impression was it didn't look so creased.

Would any of the professionals like to comment? Am I being paranoid or is this worth passing on to Airbus, Lufthansa or someone?

[747FOCAL]

flightmedic,

I can't see the "crease" that you refer to in the attached picture. In fact the flex in the outer wing looks quite normal to me. Have you ever seen a 747s wings on takeoff? They look like a wet noodle bending and flexing all over the place in different directions.

I can tell you that the windows in aircraft cause funny distortions sometimes. Maybe that is what you saw.

As a comforting note, that part of the wing outboard of the engine could come off and the plane would still fly. The landing would have to be made a bit faster and there would be some assymetry, but I don't think it would always cause a crash and certainly the wing is not going to open up like a zipper all the way to the root.:ok:

[Paracab]

I remember the early Comet fatigue problems, and would hate to have spotted something that crew members and technicians may not see.

Don't worry, You haven't - this has all been covered in flight testing. As yet an A340 has not been lost due to the reasons that you are concerned about, and I suspect, never will be.

Relax and enjoy the flight.

[Lu Zuckerman]

If you expand the picture you can see a distortion of the reflection of the wing tip sail which may be attributed to the “wrinkles”. If you look even closer you can see lines that pass through the distortion running from the leading edge towards the trailing edge. I vote for wrinkles.

:E :E

[Paracab]

I vote for wrinkles.

Do you think that the designers are not aware of them ? The important thing is do they affect flying and flight safety, not whether they are present or not.

And they do not affect flight safety, therefore it shouldn't matter if they are there or not.

[flightmedic]

I accept that the technical testing looks at these things, and that people are acutely aware of the risks of major structural loss/damage. Equally, if you take a sheet of aluminium and repeatedly flex the same point it will fracture.

747focal, the effect is visible on the reflection of the wing tip sail (thanks for the correct term) in the wing itself, with distortion of the smooth image across the axis of the wing at two specific points. It isn't a window effect - I have been flying (correction - mostly flown by others) extensively over the last 25 years and know what these distortions look like. You can see the distortion on the trailing edge.

It would still fly, although it would also lose the flaps on that side, I suspect. I know what you mean about 747 wings - the striking difference in this case was the flexing beyond the outboard engine mount rather than the whole wing.

My entire posting was directed towards the safety issue - the wrinkles are there, it is whether they matter or not as paracab rightly points out. I have never seen them before in any of the dozens of aircraft I have flown in, hence the query.

[Lu Zuckerman]

To: Paracab

Do you think that the designers are not aware of them ?

The designers may very well be aware of them but do they do something about it.

I was the senior Reliability Engineer on the A-310 wing (secondary flight controls) and I found two significant problems involving design flaws. I made this information known to several levels of the design consortium including BAe and I was told that they did not want to notify Airbus about these problems because they did not want to have to absorb the redesign costs. BAe offered their synmpathies to me relative to the design flaws but they stated that they could not help me. I also made the FAA, CAA, DGCA, and the LBA aware of the problems. It took the FAA several months to take action and when they did two high ranking individuals were fired. The design however was never changed. So don’t jump to the conclusion that there may not be a design defect in the flexing of the outer wing on an A340-600.

Remember the Reindeer. (No highway in the sky).


:E :E

[aviate1138]

Lu Zuckerman said........


"Remember the Reindeer. (No highway in the sky)."

Aviate 1138 says....

Film was based on a Novel by Neville Shute [Norway] who used to design aircraft between the two World Wars. Not reality really, was it? Typical hyped Movie sensationalism. Remember the "Sound Barrier"? Another in the same ilk.

As for the wing deformation judging by the reflected distortion it must be pretty small and I bow to your superior engineering skills but surely there is a test wing being subjected to higher stress levels many hours ahead of any Airbus 340 actually flying?
If you look at any sheet of glass that looks flat isn't it amazing how a reflected image is seen as distorted unless the glass is absolutely Optically Flat. Not neccessary in sheets of metal bent over a high aspect ratio flexible wing.
I personally would not lose one wink of sleep over seeing that wing out of my window.
BTW, does the same effect happen on the 330 wing?

Aviate 1138

[Paracab]

I was the senior Reliability Engineer on the A-310 wing (secondary flight controls)

And ? Whats your point then ?

I appreciate the fact that you identified a problem but fail to see the relevance as far as I as I know you did not work on the A340. At the end of the day the alleged problem is irrelevant, because is doesn't exist

[Lu Zuckerman]

To: aviate1138

In my reference to the Reindeer I was alluding to the fact that no matter how well an aircraft is designed and how well it was tested their are problems that can manifest themselves that were not even considered by the engineers. In my voting for wrinkles I was just agreeing with the original post. I did not say that the wing would break off or anything related to wing failure.

To: Paracab

In my reference to the A-310 I was just showing the culture within the consortium that existed at that time. Since the same companies that are involved with the A-340 wings are those same companies that designed and built the A-310 wing then there is an excellent possibility that this same consortium culture still exists.

If they turned a blind eye to the problems then it can be assumed that they would do the same thing all over again.

:E :E

[Felix Lighter]

I fly the 333, 343 and 346.......this "crease" is commom across all types (it coincides with the chordline running fwd from the inner edge of the inner aileron)

Im flying the 346 in a week, I'll have another look!

[747FOCAL]

For the life of me, I can still not see these "wrinkles". :{

[jrs2-benson]

I will stand corrected but,

Background info.
the skin on the under/bottom surface is in tension, and the skin on the upper surface is in compression. the axis of the second moment of area (point about which the wing bends) is somewhere near the middle of the wing. The skin in compression (and on the wing in general)has a very low buckling coefficient, it is very thin, designed to cofrom to the aerodynamic shape and to enclose the upper wing box. The skin on the lower surface can stretch more (not exceeding its elastic limit) more than the skin can compress when the wing is bent. So with the excess length on the upper surface and the low buckiling coefficient the skin buckles on the upper surface (instead of getting fatter).

Rippled effect.
the rippling effect is cased by the skin buckling in between the ribs which it is attached to when it is in compression. when aircraft are fully fuelled and on the ground, this can also be observed on the lower surface.

Problems.
If the skin buckles the stringers as well(skin stiffeners in line with the spar but not as strong (Z section) attached by glue or rivets to the wing skin but not the ribs), that is when probems can arise in terms of how the wing and its properties change, possibly for the worse!

As I said, if any of the above is incorrect, I'll stand corrected.

JRSB

http://www.airliners.net/open.file?id=218872

Now thats winkles....

[Volume]

Hi flightmedic,

if you are still around, please send me a PM.
I´d like to have some more detailed Information on this topic.

Volume

[swh]

Hello,

What you have described is normal design practice for aircraft, and is called buckling or post buckling.

You will see this on most semi-monocoque aluminium aircraft especially on the top skin, my most notable recollection of seeing this effect was in a PA38 tomahawk in a steep turn.

I was fortunately involved some years back with designing composite parts using semi-monocoque design techniques for Boeing, ribs, stringers etc, and still had post buckling in the composite panels, we were able to photograph the buckling using special techniques.

Its nothing to be concerned about, the buckling is designed for, and is used by the engineers as a means of achieving a minimum weight for the component.


:ok:

[OverRun]

This bit about "No Highway".

Lu Zuckerman said........
"Remember the Reindeer. (No highway in the sky)."

and Aviate 1138 said....
Film was based on a Novel by Neville Shute [Norway] who used to design aircraft between the two World Wars. Not reality really, was it? Typical hyped Movie sensationalism. Remember the "Sound Barrier"? Another in the same ilk.

Actually I'm in the middle of a high-level design biffo right now, and when I re-read No Highway the other day, I was flabbergasted to see the similarities between the novel and my reality. I could even pick most of the characters, from 'Dennis' (hope that's me) to Captain Bill Samuelson (that's B), Mr Honey (that's N), Prendergast (probably C). I rather think that Lu's comment was appropriate here, and will no doubt be appropriate elsewhere in aviation.