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Poitin
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RE: Airbus Sticks With Panels For The A350

Thu Jun 07, 2007 5:12 am

Quoting SEPilot (Reply 199):
I would agree that this is a distinct possibility, but it's not assured. The present tube with wings will endure pretty much as we know it if it doesn't, in which case the new CFRP airliners will not be obsolete for a long time, and if the engines get updated may well stay economic to operate. Change is a funny thing; who would have thought in 1969 that in 38 years the 737 and 747 would still be in production, and most people would have their own computers?

While it is possible that the cost of fuel will force conversion to BWB designs, I wonder just how do you stretch the basic design as we do with the present tube with wings. All we have to do is make the tube longer or shorter for a more optimized size. However to change the size of the BWB, you pretty much have to redesign the whole thing. Will there be a One-Size fits all BWB?
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Dougloid
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RE: Airbus Sticks With Panels For The A350

Thu Jun 07, 2007 5:35 am

Quoting Poitin (Reply 197):
I have not seen anything relating to the A350 panel construction that shows real detail about what they are actually going to do. However, for the skin to take all the pressurization stress much as a balloon does seems very unlikely unless they are building a fairly strong cylinder.

That's because Airbus haven't designed it yet, m'dear fellow.

 Wink  Wink
If you believe in coincidence, you haven't looked close enough-Joe Leaphorn
 
astuteman
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RE: Airbus Sticks With Panels For The A350

Thu Jun 07, 2007 6:39 am

Quoting Poitin (Reply 197):
And CFRP is not that rigid. Better than most materials, but if thin, it flexes. That is why Boeing has the hops and longerons built into the barrel and Airbus has that Aluminum frame.

A pleasure to agree twice in one night, P.  thumbsup 

PS - I hope Boeing recover soon.....  Wink

Regards
 
ha763
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RE: Airbus Sticks With Panels For The A350

Thu Jun 07, 2007 8:51 am

Quoting TeamAmerica (Reply 192):
do such aircraft have more cycles than flight hours logged?

Yes. In order to have so much cycles, the flight times are very short. The average flight between HNL-OGG/LIH is 15-20 min. HNL-KOA is 40 min and HNL-ITO is 45 min. N73711 (the aircraft involved in the AQ accident), had almost 90,000 cycles. In the 19 years the aircraft flew, it accumulated 89,680 cycles but only 35,496 flight hours.
 
pygmalion
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RE: Airbus Sticks With Panels For The A350

Thu Jun 07, 2007 11:30 am

Quoting SEPilot (Reply 183):
Does anyone know why Boeing (and Airbus, apparently) use Al for the wing ribs?

Wing ribs are mostly loaded in compression from wing bending. The top skin wants to move closer to the bottom one and the ribs resist that. For compression, the high tensile strength of Ti is not as much a benefit as the good compression properties, ease of machining and low weight of Aluminum. Aluminum in fuel tanks and corrosion is a known design issue and not that hard to deal with. All that needs to be done is isolate it from the CFRP. CFRP would be good for ribs as well, but forming a complex shape like a rib with CFRP is more difficult and costly than just machining it out of Al. Almost all the water in fuel comes from the fuel itself. During most of the flight the wing is vented to the very dry air at altitude, as the fuel is used dry air goes into the tank from the outside. During takeoff and landing the 787 has a nitrogen inerting system that also prevents moist war from entering the tank. Microbe and algae resistant fuel tank primers are common and very well understood.

Quoting Poitin (Reply 190):
My point was that the fuselage is a far more serious issue because large parts of it are sealed and thus accumulates more water than the wing. I disagree that the frame of the A350 is not tied to the skin because the longitudinal joints need to be supported. (see my comment above).

Most of the fuselage moisture comes from the pax. All those people breathing and exhaling damp air dumps most of the moisture into the airplane. On Aluminum aircraft, moisture is removed from the air mostly to keep the corrosion maintenance costs down. On a CRFP airframe, the moisture content can be higher and less moisture is removed. Al frames is more difficult to design for than CFRP but is doable. Just keep it out of the belly. Even though all aircraft have poppet drains in the belly, they are prone to clogging with dirt etc. Any ramper could tell you how nasty the belly area can get under a cargo bay. Adding an AL-CFRP battery to the mix is just plain nuts. I am sure that if Airbus uses AL frames they will use them above the floor of the cargo at a minimum.

Quoting Poitin (Reply 197):
That is why Boeing has the hops and longerons built into the barrel and Airbus has that Aluminum frame

Both Airbus and Boeing designs are more monocoque than semi. The pressurization loads are carried almost completely in the skins. The only hoop loads the frames carry are the ones resulting from the non-circular shape. As Zeke said, the frames transfer the internal loads of the floor with seats and pax, the stowbins and the cargo floors etc out to the skins. the only places you really see longerons and straps are around the discontinuities in the monocoque... doors, windows, wings, wheel well bays etc. The stiffened window belt also carries the aero side loads from the tail for engine out and taxi side loads from the nose gear.

CFRP allows local strength tailoring to better match loads while fabricating large monolithic structures. Lots less fasteners, but not none. You do still have to connect things together.
 
WingedMigrator
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RE: Airbus Sticks With Panels For The A350

Thu Jun 07, 2007 1:34 pm

Quoting Zeke (Reply 176):
If on the other hand some of this confusion relating to the role of the frames on the 350 comes from people at Boeing because their hoops are being used to carry some of the pressurisation loads, it would indicate a semi-monocoque design, which is not as structurally efficient as a pure monocoque design. I do not believe this is the case, photos I have seen of the construction would to me indicate a pure monocoque design.

First I've heard of this. Are you saying the 787 doesn't have a keel beam, and that its frames are significantly more svelte than an aluminum equivalent? It is my understanding that all current aluminum airliners employ stressed skin construction, i.e. the frames bear little if any pressurization load.

Quoting SEPilot (Reply 183):
Does anyone know why Boeing (and Airbus, apparently) use Al for the wing ribs?

Perhaps because each one is different and it makes no economic sense to maintain tooling for each part? (versus a different CNC program for each aluminum rib...)

Quoting Poitin (Reply 190):
in the panel construction, the frame must supply the hoop strength of the cylinder under pressure. ... I disagree that the frame of the A350 is not tied to the skin because the longitudinal joints need to be supported. (see my comment above).

Can you provide a reference to look this up? One would figure there exists at least one academic paper describing such an architecture where the frames carry pressurization loads. It flies in the face of everything I've ever read about fuselage construction, namely that the skin takes the vast majority of the hoop stress.

Quoting Astuteman (Reply 194):
Hence I don't believe, and no-one's yet persuaded me, the either the 787 or A350 are full monocoque.

 checkmark  seconded... I haven't seen any convincing evidence that the 787 is anything other than the usual stressed-skin semi-monocoque structure.

Quoting Poitin (Reply 197):
And CFRP is not that rigid. Better than most materials, but if thin, it flexes. That is why Boeing has the hops and longerons built into the barrel and Airbus has that Aluminum frame.

Lots of people confuse strength and stiffness.
 
WingedMigrator
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RE: Airbus Sticks With Panels For The A350

Thu Jun 07, 2007 2:00 pm

Quoting Poitin (Reply 197):
That is why Boeing has the hops and longerons built into the barrel and Airbus has that Aluminum frame.

Did a double-take on that one... must correct your notion. Only the stringers (longerons) are co-cured with the skin.

Boeing's subcontractors install the "hoops", also known as frames, inside the barrels *after* they are fully cured in the autoclave. You can see this process in the first photo of fuselage section 41 on page 28 of this presentation by Mike Bair, the 787 General Manager. Besides the frames, notice at the far end the significant green support framing that is fastened inside the nose section, and compare and contrast to the empty (frameless) barrel in the third photo on that same page.

Here's a barrel being laid up on the mandrel:  spin 

Here it is without frames:  bouncy 

Here it is with frames installed:  Smile
 
StressGuy
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RE: Airbus Sticks With Panels For The A350

Thu Jun 07, 2007 2:01 pm

The fuselage on the 787 is absolutely a semi-monocoque fuselage and pure monocoque designs are not more effecient on a structure as large as a airplane or thats how they would be designed. If the 787 had a pure monocoque fuselage it wouldn't need stringers. The stringers stabilize the skin (help resist buckling) and are in turn stabilized by the frames. As noted the frames also "shear" the floor loads into the skin as well as resisting some of the pressurization loads among other things.

As noted a great deal of maintanence on aluminum airplanes takes place in the lower lobe cargo area because that is where all kinds of corrosive liquids collect (take your pick and mix them all together). I believe that CRFP frames will reduce the maintanence costs on the frames a great deal.
 
Poitin
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RE: Airbus Sticks With Panels For The A350

Fri Jun 08, 2007 2:53 am

Quoting WingedMigrator (Reply 206):
Did a double-take on that one... must correct your notion. Only the stringers (longerons) are co-cured with the skin.

Boeing's subcontractors install the "hoops", also known as frames, inside the barrels *after* they are fully cured in the autoclave. You can see this process in the first photo of fuselage section 41 on page 28 of this presentation by Mike Bair, the 787 General Manager. Besides the frames, notice at the far end the significant green support framing that is fastened inside the nose section, and compare and contrast to the empty (frameless) barrel in the third photo on that same page.

Who said they were cured with the skin? Obviously, they would make removing the mandrel impossible. They would be attached, either with fasteners or bonded in after the mandrel is removed. In the case of the Boeing barrels, it really looks to me that they were bonded in. That effectively "glues" the frame to the skin as I gave in my example.

Quoting Pygmalion (Reply 204):
Both Airbus and Boeing designs are more monocoque than semi. The pressurization loads are carried almost completely in the skins. The only hoop loads the frames carry are the ones resulting from the non-circular shape

First of all, I am not sure what you mean by "more monocoque than semi" A pure monocoque structure is all skin, such as a gas cylinder. While most aluminum airframes are called "monocoque" they aren't really, because they depend on matrix of frames and stringers even though the skin does take considerable stress and load forces. It is quite obvious that both Boeing and Airbus are using both frames and stringers in their designs.

Second, either the frames are firmly attached to the skins or they are not. I believe that they are in the case of Boeing and probably in the case of Airbus. If that is that case, then what happens when the skins stretch even slightly from the pressure? If they are not attached firmly to the skin, then your argument is sound. If they are firmly attached, as in the case of bonding, then they have to take part of the load. How much is questionable, and depends on how much they are designed to take and how thick the skin is. The thickness of the skin could be considerably reduced if this was done. Now if you are claiming that the skins are so thick as to not need the frames and stringers, then fine. I just don't believe Boeing or Airbus is going to do that.
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scbriml
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RE: Airbus Sticks With Panels For The A350

Fri Jun 08, 2007 4:58 am

Quoting Poitin (Reply 208):
They would be attached, either with fasteners or bonded in after the mandrel is removed. In the case of the Boeing barrels, it really looks to me that they were bonded in.

Don't the circumferential rows of fasteners suggest otherwise?
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Poitin
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RE: Airbus Sticks With Panels For The A350

Fri Jun 08, 2007 5:25 am

Quoting Scbriml (Reply 209):
Quoting Poitin (Reply 208):
They would be attached, either with fasteners or bonded in after the mandrel is removed. In the case of the Boeing barrels, it really looks to me that they were bonded in.

Don't the circumferential rows of fasteners suggest otherwise?

Can't say, as they may be the barrel joints. All I have to go by is the photographs of the interior of the barrel, which look to me to be bonded. But as you point out there are fasteners on the outside and from the photos Zeke posted, there appear to be bunch of them, which suggests that the skins are tightly connected to whatever is underneath. My point is if the skin is tightly connected or bonded to the "frame" of the 787, that any pressure stresses on the skins will be transmitted to the "frame". I have seen nothing to suggest that the connections have any sort of play in them. That, in my book makes the 787 a semi-monocoque. Since I have no information on the actual design of the A 350, it is possible that the skins are a monocoque as far as pressure loads are concern. That would require some "give" in the connection of the aluminum frame to the CFRP skins. I would share the concern expressed by at least member (SEPilot, reply 113) that the joints would have a heavy shear load on the joints of the skins if that is the case.

However, that is just one of the maintenance issues with the A350. Leahy has repeatedly said that the A350 will have the same higher humidity level as the 787 for passenger comfort. I agree with Pygmalion when he says:

Quoting Pygmalion (Reply 204):
Most of the fuselage moisture comes from the pax. All those people breathing and exhaling damp air dumps most of the moisture into the airplane. On Aluminum aircraft, moisture is removed from the air mostly to keep the corrosion maintenance costs down. On a CRFP airframe, the moisture content can be higher and less moisture is removed. Al frames is more difficult to design for than CFRP but is doable. Just keep it out of the belly. Even though all aircraft have poppet drains in the belly, they are prone to clogging with dirt etc. Any ramper could tell you how nasty the belly area can get under a cargo bay. Adding an AL-CFRP battery to the mix is just plain nuts. I am sure that if Airbus uses AL frames they will use them above the floor of the cargo at a minimum.
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AvObserver
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RE: Airbus Sticks With Panels For The A350

Fri Jun 08, 2007 6:09 am

Lots of amazing technical analysis in this thread and it's really impossible to verify at this point which airframer has taken the better approach but Tim Clark's 2 cents are a clear warning to Airbus that they too should move toward Boeing's thinking on construction, next time around. I agree it doesn't make sense to redesign the A350XWB again for barrels at this point but whatever other advantages the composite panel construction method may have might be overshadowed by its more labor-intensive fabrication, sure to make the A350XWB costlier to build on a unit basis even if cheaper to develop. It also seems probable it could prove costlier to maintain although that won't be clear until its in service along with the 787. I think Airbus can get comparable performance to the 787 with the XWB but I'm concerned they won't be able to price it competively without eating a lot of profits, particularly if the dollar keeps dropping against the Euro. One thing's for sure, though, Airbus can't afford to lose any more time to Boeing so this XWB design must basically stand and we'll see how it goes...
 
astuteman
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RE: Airbus Sticks With Panels For The A350

Fri Jun 08, 2007 6:21 am

Quoting AvObserver (Reply 211):
sure to make the A350XWB costlier to build on a unit basis even if cheaper to develop

I don't necessarily have an issue with the A350WXB's work content being higher.

My question would be "Just how much are 4 longitudinal joints running the length of the fuselage skin as a percentage of the cost of a finished airliner?"
If the answer is more than 1% I'll be very surprised, (I'll be surprised if it IS 1%) particularly as the process may well be semi, or even completely automated.
IMO it's not beyond the realms of possiblity that the capital investment depreciation of the facilities necessary to undertake the 787 programme could have an equal impact, as could other factors such as financing costs, exchange-rate fluctuations, general productivity, unit labour costs, corporate overheads to be carried etc.

To be honest, I'm only guessing, but, using the A358 and B789 as examples, I'd have thought the work content of the A350's 20% bigger area wing would have a greater impact on cost..........
Just my  twocents 

Regards
 
cygnuschicago
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RE: Airbus Sticks With Panels For The A350

Fri Jun 08, 2007 6:40 am

Quoting AvObserver (Reply 211):
One thing's for sure, though, Airbus can't afford to lose any more time to Boeing so this XWB design must basically stand and we'll see how it goes...

I'm with you on that. Everything about the cost is speculation, but one thing is certain: Airbus needs to get this thing built as soon as possible, or they might as well close shop!
If you cannot do the math, your opinion means squat!
 
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SEPilot
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RE: Airbus Sticks With Panels For The A350

Fri Jun 08, 2007 7:05 am

Quoting Astuteman (Reply 212):
My question would be "Just how much are 4 longitudinal joints running the length of the fuselage skin as a percentage of the cost of a finished airliner?"
If the answer is more than 1% I'll be very surprised, (I'll be surprised if it IS 1%) particularly as the process may well be semi, or even completely automated.
IMO it's not beyond the realms of possiblity that the capital investment depreciation of the facilities necessary to undertake the 787 programme could have an equal impact, as could other factors such as financing costs, exchange-rate fluctuations, general productivity, unit labour costs, corporate overheads to be carried etc.

Good points. I suspect that a bigger impact on overall costs is the ability to have the 787 barrels "pre-stuffed", so that final assembly takes so much less time (3 days, depending on which Boeing source you believe) which ties up much less very expensive building space and utilizes many fewer very highly-paid workers. As others have suggested, this approach might cause more problems with Airbus's unions and political supporters than it does with Boeing.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
Areopagus
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RE: Airbus Sticks With Panels For The A350

Fri Jun 08, 2007 8:03 am

Here's what CompositesWorld's 2005 Paris Airshow report had to say on Boeing's use of aluminum ribs for the 787's wing:
Boeing confirmed its commitment to aluminum for the wing ribs. In most other areas on the 787, titanium is used where metal comes into contact with CFRP, but in the wing, Boeing believes that the fuel stored in the wing will inhibit corrosion at the CFRP-to-aluminum interface. Airbus reports that, while leaning toward aluminum, it has not ruled out carbon fiber composite ribs, and has yet to make a decision.

It isn't the quote I have been looking for, though. I recall reading several years ago an article where Gillette (or Bair?) said Boeing was investigating CFRP wing ribs. At that time, it wasn't as cost-effective as aluminum, but they were hoping to make it so. Evidently, aluminum still won out when they had to freeze the design. Now, can anyone else find that quote? I haven't been able to find it.
 
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SEPilot
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RE: Airbus Sticks With Panels For The A350

Fri Jun 08, 2007 9:01 am

Quoting Areopagus (Reply 215):
Boeing believes that the fuel stored in the wing will inhibit corrosion at the CFRP-to-aluminum interface.

This belief is well-founded, IMO. Even with the possibility of galvanic action the fuel should act as a totally sufficient corrosion inhibitor.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
astuteman
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RE: Airbus Sticks With Panels For The A350

Fri Jun 08, 2007 3:33 pm

Quoting SEPilot (Reply 214):
I suspect that a bigger impact on overall costs is the ability to have the 787 barrels "pre-stuffed",

FWIW I totally agree with that.  thumbsup 

Quoting SEPilot (Reply 214):
As others have suggested, this approach might cause more problems with Airbus's unions and political supporters than it does with Boeing.

also FWIW, IMO the A350XWB's sections will almost certainly be "pre-stuffed" prior to final assembly. (They'd be insane not to)
The debate will be "where"...........
Changes in work practice might cause some issues.
At least they've got a fair bit of time to ireon them out......  Wink

Regards
 
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SEPilot
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RE: Airbus Sticks With Panels For The A350

Fri Jun 08, 2007 8:18 pm

Quoting Astuteman (Reply 217):
The debate will be "where"...........

Without a means to transport the barrels they're pretty much forced to do it at the final assembly site. They're not planning to transport them by barge, are they? I don't think they fit into the Beluga.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
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scbriml
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RE: Airbus Sticks With Panels For The A350

Fri Jun 08, 2007 8:26 pm

Quoting SEPilot (Reply 218):
Without a means to transport the barrels they're pretty much forced to do it at the final assembly site.

Which barrels does Airbus need to transport? confused 
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Stitch
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RE: Airbus Sticks With Panels For The A350

Fri Jun 08, 2007 8:38 pm

Quoting Astuteman (Reply 217):
The debate will be "where"...

My money is on TLS and TLS alone.

Quoting Scbriml (Reply 219):
Which barrels does Airbus need to transport?  confused 

The completed and "pre-stuffed" A350 barrels (composed of large CFRP panels attached to a framework), I imagine.
 
bringiton
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RE: Airbus Sticks With Panels For The A350

Fri Jun 08, 2007 8:45 pm

I think in this case reffering to them as SECTIONS would be better and more acurate then using the term BARREL
 
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Stitch
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RE: Airbus Sticks With Panels For The A350

Fri Jun 08, 2007 8:47 pm

Quoting Bringiton (Reply 221):
I think in this case reffering to them as SECTIONS would be better and more acurate then using the term BARREL

Why? It's long and it's cylindrical. A320s and 737s are shipped as barrels, they're just made of Al instead of CFRP or a mix of CFRP and some other material. After all, if the six major fuselage sections of the 787 were made of Al or Al-Li instead of CFRP, they'd still be fuselage barrels.
 
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SEPilot
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RE: Airbus Sticks With Panels For The A350

Fri Jun 08, 2007 8:48 pm

Quoting Scbriml (Reply 219):
Which barrels does Airbus need to transport?

Stitch has it right; that is what Astuteman and I are referring to.

Quoting Bringiton (Reply 221):
I think in this case reffering to them as SECTIONS would be better and more acurate then using the term BARREL

Good point.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
bringiton
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RE: Airbus Sticks With Panels For The A350

Fri Jun 08, 2007 8:51 pm

Quoting Stitch (Reply 222):
Why?

Just because ever since the 787 program , barrels as a term has been used quite often to describe pre made monolithic CFRP structures that boeing's partners have been making and shipping over to seatle .
 
astuteman
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RE: Airbus Sticks With Panels For The A350

Fri Jun 08, 2007 9:34 pm

Quoting SEPilot (Reply 218):
Without a means to transport the barrels they're pretty much forced to do it at the final assembly site

I understood from some information that Zeke published, that an A350XWB fuselage "section" will fit into the Beluga.
He used a sodding great tank as illustration.
I've no idea how a "pre-stuffed section's" weight would compare to the Beluga's payload, but its hard to imagine it would be too heavy.....

Regards
 
art
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RE: Airbus Sticks With Panels For The A350

Fri Jun 08, 2007 10:00 pm

Quoting Teva (Reply 12):
If the A350 meets the expectations, for the price announced, I don't see why airlines wouldn't buy it.

Is there an expectation that maintenance costs will match those of a barrel fuselage aircraft? I thought not. Come to think of it, when you contract to buy 787, are MX costs guaranteed?

Quoting SEPilot (Reply 19):
As an engineer myself I am totally convinced that barrels is a much better way to go, and I believe Airbus will come to regret this decision.

My uninformed guess is that you are probably right.
 
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Stitch
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RE: Airbus Sticks With Panels For The A350

Fri Jun 08, 2007 10:03 pm

Quoting Art (Reply 226):
Come to think of it, when you contract to buy 787, are MX costs guaranteed?

It has been rumored that some 787 orders were secured with such a guarantee...
 
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scbriml
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RE: Airbus Sticks With Panels For The A350

Fri Jun 08, 2007 10:41 pm

Quoting SEPilot (Reply 223):
Stitch has it right; that is what Astuteman and I are referring to.

OK, that's clear. Astuteman never used the term barrel, and my confusion arose when you referred to such. No problem.

There was a thread where this issue was discussed before, and although no firm conclusion was reached, there were plenty who thought an A350-sized barrel would fit inside the Beluga OK. There has also been the unconfirmed report that the width of the A350 has increased, which might have an effect. Hopefully we'll get more info at Paris.
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SEPilot
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RE: Airbus Sticks With Panels For The A350

Fri Jun 08, 2007 10:59 pm

Quoting Astuteman (Reply 225):

I understood from some information that Zeke published, that an A350XWB fuselage "section" will fit into the Beluga.

You may be right; I was under the impression from other discussions we've had on the subject of barrels vs. panels that it wouldn't. But if it will it certainly opens up possibilities; I agree with you that weight probably is not a problem.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
Poitin
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RE: Airbus Sticks With Panels For The A350

Fri Jun 08, 2007 11:21 pm

Quoting Areopagus (Reply 215):
Here's what CompositesWorld's 2005 Paris Airshow report had to say on Boeing's use of aluminum ribs for the 787's wing:

Boeing confirmed its commitment to aluminum for the wing ribs. In most other areas on the 787, titanium is used where metal comes into contact with CFRP, but in the wing, Boeing believes that the fuel stored in the wing will inhibit corrosion at the CFRP-to-aluminum interface. Airbus reports that, while leaning toward aluminum, it has not ruled out carbon fiber composite ribs, and has yet to make a decision.

It isn't the quote I have been looking for, though. I recall reading several years ago an article where Gillette (or Bair?) said Boeing was investigating CFRP wing ribs. At that time, it wasn't as cost-effective as aluminum, but they were hoping to make it so. Evidently, aluminum still won out when they had to freeze the design. Now, can anyone else find that quote? I haven't been able to find it.

Interesting point. Jet fuel would tend to attack the resin in walls of the fuel tank, but there are ways to seal it, such as a rubber bladder. I would like to know more about their reasoning.

Quoting SEPilot (Reply 216):
Quoting Areopagus (Reply 215):
Boeing believes that the fuel stored in the wing will inhibit corrosion at the CFRP-to-aluminum interface.

This belief is well-founded, IMO. Even with the possibility of galvanic action the fuel should act as a totally sufficient corrosion inhibitor.

On the inside of the fuel tank, yes, on the outside of the tank, no. And what about the outer ribs that are not a part of the fuel tank?

Quoting Astuteman (Reply 217):
Quoting SEPilot (Reply 214):
I suspect that a bigger impact on overall costs is the ability to have the 787 barrels "pre-stuffed",

FWIW I totally agree with that.  thumbsup 

I also agree --The 787 construction technique saves a great deal of cost in a number of ways. This is one of the more important. As Zvezda and others have pointed out, the "final assembly" can be as few as 3 days, and with four bays, Boeing could "assemble" as many as 40 airframes a month in Seattle. I have used quotes to indicate the time the airframe spends in the assembly jig, which is certainly not the time to assemble an airframe from start to first flight. It is however the critical path time. Boeing could outfit and inspect the airframe anywhere on PAE they want once the airframe is out of the jig, so Boeing can produce the 787 in large numbers, assuming that they can get the parts.
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SEPilot
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RE: Airbus Sticks With Panels For The A350

Fri Jun 08, 2007 11:35 pm

Quoting Poitin (Reply 230):
On the inside of the fuel tank, yes, on the outside of the tank, no. And what about the outer ribs that are not a part of the fuel tank?

Could the ribs that are not inside the tank be anodized?
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
Wsp
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RE: Airbus Sticks With Panels For The A350

Fri Jun 08, 2007 11:49 pm

Quoting SEPilot (Reply 214):
I suspect that a bigger impact on overall costs is the ability to have the 787 barrels "pre-stuffed", so that final assembly takes so much less time (3 days, depending on which Boeing source you believe) which ties up much less very expensive building space and utilizes many fewer very highly-paid workers.



Quoting Poitin (Reply 230):
I also agree --The 787 construction technique saves a great deal of cost in a number of ways. This is one of the more important.

From http://seattlepi.nwsource.com/business/318978_vought08.html

Quote:
Vought workers are supposed to "stuff" their fuselage sections with wiring, systems and electronics. Workers in the Global Aeronautics building will do the same thing with fuselage sections from Japan and Italy.

I was under the impression that pre-stuffing is done in JP/IT as well. But it seems they just moved the whole pre-stuffing step to a cheaper location (a green field site) inside the US.

Is there any other justification to do the separate pre-stuffing other than that it allows to utilize cheap labor/facilities far away from the FAL?
 
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SEPilot
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RE: Airbus Sticks With Panels For The A350

Fri Jun 08, 2007 11:55 pm

Quoting Wsp (Reply 232):
Is there any other justification to do the separate pre-stuffing other than that it allows to utilize cheap labor/facilities far away from the FAL?

The facilities cost is a big reason, probably much more important than labor. The floor space in Everett is at an absolute premium, and Boeing can only expand it so much. Anything they can do to shift production time elsewhere probably saves them huge amounts of money, since it enables them to push more planes out the door. Everett is the only place they do final assembly of widebodies, so the less time each one spends there means more production. Since they are selling them far faster than they are building them, this is hugely important.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
Wsp
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RE: Airbus Sticks With Panels For The A350

Sat Jun 09, 2007 12:18 am

Quoting SEPilot (Reply 233):
The facilities cost is a big reason, probably much more important than labor. The floor space in Everett is at an absolute premium, and Boeing can only expand it so much. Anything they can do to shift production time elsewhere probably saves them huge amounts of money, since it enables them to push more planes out the door. Everett is the only place they do final assembly of widebodies, so the less time each one spends there means more production. Since they are selling them far faster than they are building them, this is hugely important.

No doubt this splitting of the process has an advantage for Boeing. Now how about Airbus? Of course pre-stuffing is a nice way to outsource work packages to cheaper places. But is it feasible in the context of the A350 project? This work package is huge in total, I don't see that going outside FR/DE/UK/ES. And while these countries have places with cheap labor too, opening up a new plant doesn't seem realistic either.
 
Poitin
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RE: Airbus Sticks With Panels For The A350

Sat Jun 09, 2007 12:39 am

Quoting SEPilot (Reply 231):
Quoting Poitin (Reply 230):
On the inside of the fuel tank, yes, on the outside of the tank, no. And what about the outer ribs that are not a part of the fuel tank?

Could the ribs that are not inside the tank be anodized?

The issue is aluminum anodization isn't all that good in a electrolytic solution. Most people don't know it, but Titanium is about as reactive as Aluminum (its galvanic series) when not coated with its oxide. Aluminum also insulates itself with oxide, but unlike titanium and stainless steel -- which also forms a protective oxide -- the aluminum oxide breaks down in salt solutions. That is why the important galvanic series is the one conducted in sea water:

http://www.corrosionsource.com/handbook/galv_series.htm

Since that site is not easy to understand I would suggest this one instead:

http://www.corrosion-club.com/galvseries.htm

The important thing in reading these graphs is the DISTANCE between the potentials is an indication of just how strong a battery you can make. Note that the Zinc Carbon battery in your flash light uses zinc and carbon (graphite) which are at opposite ends of the scale. Aluminum is nearly as far from graphite as zinc. However, titanium is right next to graphite so it would have a weak current.

However, I am certainly not a metallurgist and there may well be a phosphoric or similar treatment that would protect aluminum in such a harsh condition. I do know that back in WWII zinc chromate was used to protect the hulls of sea planes, and there are a number of ships, including naval vessels, with large amounts of aluminum on them. So obviously, it is possible to protect the metal. Perhaps someone can tell us more about what can be done to aluminum. I just don't know what they do today.

Quoting SEPilot (Reply 233):
Quoting Wsp (Reply 232):
Is there any other justification to do the separate pre-stuffing other than that it allows to utilize cheap labor/facilities far away from the FAL?

The facilities cost is a big reason, probably much more important than labor. The floor space in Everett is at an absolute premium, and Boeing can only expand it so much. Anything they can do to shift production time elsewhere probably saves them huge amounts of money, since it enables them to push more planes out the door. Everett is the only place they do final assembly of widebodies, so the less time each one spends there means more production. Since they are selling them far faster than they are building them, this is hugely important.

Well put, SEPilot.
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SEPilot
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RE: Airbus Sticks With Panels For The A350

Sat Jun 09, 2007 12:47 am

Quoting Poitin (Reply 235):

The issue is aluminum anodization isn't all that good in a electrolytic solution. Most people don't know it, but Titanium is about as reactive as Aluminum (its galvanic series) when not coated with its oxide. Aluminum also insulates itself with oxide, but unlike titanium and stainless steel -- which also forms a protective oxide -- the aluminum oxide breaks down in salt solutions. That is why the important galvanic series is the one conducted in sea water:

Thanks for the info; I have not dealt much with galvanic corrosion-it has not been much of an issue in my field. Glad to improve my education.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
pygmalion
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RE: Airbus Sticks With Panels For The A350

Sat Jun 09, 2007 1:16 am

Both chromic acid and phosphoric acid anodizing is available for aluminum. From the photos of the wing in MHI the ribs are also primed and installed with faying surface sealant. The interior of the CFRP panels and spars also appear to be painted with fuel tank primer. For aluminum wings, I know that Boeing uses a 2 part epoxy based finish in the tanks for corrosion protection. From the photos it looks very similar for the 787 for both CFRP and Al.

Poitin: I do agree with all your comments about the monocoque structure. Engineers would call the 787 a semi-moncoque fuselage. The frames do not take much pressurization load though. The feet on the frames that you see are not bonded but are fastened. The shear transfer is more from the frame to the skin for payload loads going out to the skins than pressurization loads going the other way. The skins are sized such that deformation/strain is small in hoop so load transfer from skin to frame is small especially across the gap between the skin and frame through the shear tie that connect the two. They do work together but pressurization strains are carried mostly in the skins.

My comments were mostly trying to counter act Zeke's comment that the aircraft frame and not the skin carried the loads. Loads are almost all transferred in shear in the skins than by the internal frame members. More Monocoque than not. I was imprecise but most here are not aero structures engineers and the terms are used a bit imprecisely here. Apologies.
 
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Revelation
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RE: Airbus Sticks With Panels For The A350

Sat Jun 09, 2007 1:19 am

Quoting Bringiton (Reply 224):
Just because ever since the 787 program , barrels as a term has been used quite often to describe pre made monolithic CFRP structures that boeing's partners have been making and shipping over to seatle .

Yes, but isn't it true that 767 "barrels" are build in California and barged up to Everett? Granted these "barrels" are made from sheet aluminum and do not come out of the oven as one piece, but never the less, they are barrels.

Quoting SEPilot (Reply 233):
Everett is the only place they do final assembly of widebodies, so the less time each one spends there means more production.

That was a choice Boeing itself made, a few years ago. They accepted bids from many locations to become the 7E7 final assembly point, but ended up excepting the bid from WA state, which knuckled under and coughed up tax relief and infrastructure improvements to keep Boeing from setting up shop elsewhere. Of course few of us could believe that Boeing would locate its factory thousands of miles away from its design and testing facilities, but it was enough to scare the WA state legislature into supplying the corporate welfare that Boeing so happily accepted.
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amicus
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RE: Airbus Sticks With Panels For The A350

Sat Jun 09, 2007 1:49 am

Quoting Poitin (Reply 235):
The issue is aluminum anodization isn't all that good in a electrolytic solution. Most people don't know it, but Titanium is about as reactive as Aluminum (its galvanic series) when not coated with its oxide. Aluminum also insulates itself with oxide, but unlike titanium and stainless steel -- which also forms a protective oxide -- the aluminum oxide breaks down in salt solutions. That is why the important galvanic series is the one conducted in sea water:

http://www.corrosionsource.com/handbook/galv_series.htm

Since that site is not easy to understand I would suggest this one instead:

http://www.corrosion-club.com/galvseries.htm

The important thing in reading these graphs is the DISTANCE between the potentials is an indication of just how strong a battery you can make. Note that the Zinc Carbon battery in your flash light uses zinc and carbon (graphite) which are at opposite ends of the scale. Aluminum is nearly as far from graphite as zinc. However, titanium is right next to graphite so it would have a weak current.

However, I am certainly not a metallurgist and there may well be a phosphoric or similar treatment that would protect aluminum in such a harsh condition. I do know that back in WWII zinc chromate was used to protect the hulls of sea planes, and there are a number of ships, including naval vessels, with large amounts of aluminum on them. So obviously, it is possible to protect the metal. Perhaps someone can tell us more about what can be done to aluminum. I just don't know what they do today.

As Poiton stated, the problem exists and is well known now. I know a bunch of stuff re this as am an aerospace engineer in composites and have been since the sixties. Prior to this problem being so well known and as my people and I were first engineers to use CFRP in primary structures, I ordered a whole series of extensive salt spray and humidity tests and our research people then did lots of testing, particularly on al al honeycomb cores with CFRP face sheets. At that time the best corrosion resistant aluminum honeycomb core was "CR III" We subjected the specimens to thirty day salt spray and high humidity environments, and, just as predicted, the aluminum cores were destroyed. We then inserted fiberglass layers between the CFRP and the honeycomb to try and kill the galvanic couple. The first try with 120 style fiberglass helped, but did not cure the problem. Next we used 181 style glass as this was 2.5 times thicker than 120 glass. This reduced the corrosion to low levels, as was strategic defense system, we were still not totally satisfied and thus decided to kill the problem by using fiberglass phenolic h/c cores known as HRP. This cost us a weight hit re the lower core performance, but we could sleep well at night.
And re the zinc chromate mentioned by Poiton, we specified "wet insert for all fasteners using liberal doses of zinc chromate" and used only stainless and titanium fasteners as close to galvanic properties of CFRP as possible. These research reports were published and shared with Boeing et al, as clearly a major issue, in the early '70's. Now the issue of high differential CTE's between aluminum and CFRP is also a major one and I would like to see further discussion re this situation. Hope this helps you, Poiton, and proves of interest to yourself and others on the forum.
 
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Devilfish
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RE: Airbus Sticks With Panels For The A350

Sat Jun 09, 2007 3:08 am

Since the very fresh thread on Mr. Aboulafia's Advice Re Power8 and the Update on Power8 after just one reply were deleted, I thought of posting this here, being relevant to the topic.....

Flightglobal has this report.....

http://www.flightglobal.com/articles...allois-presents-new-structure.html

Airbus employees walk out as Gallois presents new structure
By Helen Massy-Beresford

Quote:
"Employees down tools after restructuring plans are presented to European Works Council

Airbus employees have once again protested after chief executive Louis Gallois set out radical plans that include giving management a tighter rein over manufacturing centres of excellence and stripping operational responsibilities from national heads. Employees at Laupheim, Nordenham and Varel in Germany downed tools on 6 June."
"Everyone is entitled to my opinion." - Garfield
 
Poitin
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RE: Airbus Sticks With Panels For The A350

Sat Jun 09, 2007 7:00 am

Quoting Pygmalion (Reply 237):
Both chromic acid and phosphoric acid anodizing is available for aluminum. From the photos of the wing in MHI the ribs are also primed and installed with faying surface sealant. The interior of the CFRP panels and spars also appear to be painted with fuel tank primer. For aluminum wings, I know that Boeing uses a 2 part epoxy based finish in the tanks for corrosion protection. From the photos it looks very similar for the 787 for both CFRP and Al.

I appreciate your explaining. I do not have an intimate knowledge of the 787, but at least I understand some about the aluminum ribs.

Quoting Pygmalion (Reply 237):
Poitin: I do agree with all your comments about the monocoque structure. Engineers would call the 787 a semi-moncoque fuselage. The frames do not take much pressurization load though. The feet on the frames that you see are not bonded but are fastened. The shear transfer is more from the frame to the skin for payload loads going out to the skins than pressurization loads going the other way. The skins are sized such that deformation/strain is small in hoop so load transfer from skin to frame is small especially across the gap between the skin and frame through the shear tie that connect the two. They do work together but pressurization strains are carried mostly in the skins.

I agree that the 787 is a semi-monocoque, and that the skins take a sizable portion of the pressurization loads, but to call it a full monocoque would require the skins to take ALL of the load, which it is obviously is not. Since I do not have an intimate knowledge of the 787design, I cannot say how much is on the skin or how much is on the framing. As for being bonded or fasten, that is a non sequitur. Virtually all "monocoque" aluminum airframes such as the 747, 737, etc, are also semi-monocoque with pressure stressed skins, but their frames also absorb part of the load through rivets. Thus the issue is not how the skin is connected to the frames, but how tightly, with how much give. With rivets, there is virtually none, while with other fasteners, there can be quite a lot.

I know that one problem with pressurized skin all aluminum airframes has been that sometimes the skin deforms around the rivets, causing the skin to crack, but that is another issue. However, having looked at the cracks that form over time on the frames of such aircraft, it is clear that there is a direct relationship between cycles as compared to hours and those cracks, which are fatigue cracks. Thus pressurization can and does cause fatiguing of the frame, even though you will more likely find it first on the skins.

My understanding is that like steel, both CFRP and titanium have a "fatigue floor" unlike aluminum, which is going to fatigue sooner or later. I would be much happier if the A 350 had a CFRP or titanium frame, but that is unlikely. The result may well be that the A 350 ends up like the A320 as effectively an only 25,000 cycle airframe. However, we will have to wait many years to find out.
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zeke
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RE: Airbus Sticks With Panels For The A350

Sat Jun 09, 2007 8:16 am

Poltin,

Sorry had to work for a few days...must make such sacrifices a few days a month ....

Quoting Poitin (Reply 165):
That means that the effective life of the A320 is about 25,000 cycles.

Utter B/S as fare as I am concerned. Many A320 series aircraft exceed that in service at the moment, how an airline value their aircraft is not common, and many advantages could present themselves fir doing so......

Quoting Poitin (Reply 190):
In a barrel construction it is true that the skin takes the stress, but in the panel construction, the frame must supply the hoop strength of the cylinder under pressure

Sounds like B/S again to me....

Quoting Poitin (Reply 190):
And in any case, the al frame will flex in flight and fatigue.

The loads on it will be low, who cares...other things will fail first ...........other things will fail first.....

Quoting Poitin (Reply 190):
What you are missing, Zeke, is that Carbon Fiber, Aluminum and water with a little dirt and grit to supply an electrolyte forms a battery, just like in your flashlight. This is a well known phenomenon. Airbus is clearly aware of this, but they do have a serious maintenance problem.

Not missing it at all, nor is A, their structural design manual took care of that issue 15-20 years ago, likewise B does as well, it is NOT a new issue for A or B.

I see you are just guessing with every statement.....

Please note the following ...

The 787 skin will take most if not close to all the loads of the composite fuselage
No requirement for the AL frames from AB to be circular
Lap joints can be designed to improve fuselage stiffness, especially column buckling
Fuselage frames can be attached directly to lap joints and not to the skin
No requirement for frames to be contact with the skin
A barrel can be joined via lap joints and not fail, nor does it require an internal frame.

One reason why B went with the design they did could be with limitations of the mandrel not being able to be sculpted like is can be if you lay up from the inside (to make the outer surface aerodynamically smooth). Still not convinced you know any details about either design, some of it sounds wrong.

Why have you ignored the following :

Quoting WingedMigrator (Reply 205):
Can you provide a reference to look this up? One would figure there exists at least one academic paper describing such an architecture where the frames carry pressurization loads. It flies in the face of everything I've ever read about fuselage construction, namely that the skin takes the vast majority of the hoop stress.

Why ?
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WingedMigrator
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RE: Airbus Sticks With Panels For The A350

Sat Jun 09, 2007 9:43 am

Quoting Poitin (Reply 241):
I agree that the 787 is a semi-monocoque, and that the skins take a sizable portion of the pressurization loads

Hence and thus, the structural architecture of the 787 (a semi-monocoque tube with stressed skin, stringers and frames) is the same as any previous aluminum airliner. CFRP allows the structure to be tailored to the loads, but the load path (where the forces go) is unchanged from prior practice.

By the way, CFRP ribs are already flying... 23 of the 49 A380 wing ribs are made partially or fully of CFRP.

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