I closely watched these threads and found following consent:
The Barrel approach (B787) is generally considered superior versus the Panel approach (A350).
Among the many advantages following are mentioned often:
- Cheaper and fully automated production
- High integration from the beginning
- Lighter (because of the following two points)
- Less fasteners
- Fewer joints
In this thread I want to discuss why Airbus is on the Panel track. I will support this by substantial sources and ideas. Among the most heard reasons why Airbus plans to use Panels we often heard so far:
- Airbus has not the composite know how
- Airbus can not use Barrels because of intellectual property issues
- Airbus needs to go the fast approach therefore has not the time to make it 'right'
- Airbus has not the logistics to transport Barrels
These all imply that Airbus needs to choose a technologically inferior solution because of surrounding requirements. I don't want to add much comment on these but want to raise the question: could there also be technological advantages that we just don't know?
I just mention in short the possible advantages that were listed so far:
- Easier logistics when transporting panels instead of barrels
- Longer panels than barrels possible
When seeking for other advantages quite often there were gentle hints by WingedMigrator but usualy he only earned ingorance or even opposition ( Airbus A350 Cfrp Panel Construction (by WingedMigrator Jun 22 2007 in Tech Ops) ). First I want to share what I gathered around of what he suggested. Let's develop a line of reasoning:
- With Panels the outside of the fuselage lay in the Mandrel. Therefore you will get the smother surface on the aerodynamically important side of the wall (or at least better control on the outcome during manufacturing). Kaneporta1 once raised this point.
- With barrels on the inside you can only vary the thickness to some degree and have limited possibilities to built 3D structures (for the B787 only stringers)
- Having the outside in the form you are free to control the structure complexity on the inside and built 3D structures.
- Thus you could have the idea to integrate and co cure various inner construction elements from the beginning. This could be:
- Window Frames
- Door frames
- Reinforcements that can not be built only by thickness change
- Crash absorbing construction elements
- I made a graphic that shows a panel with fully integrated stringers and frames:
It would come as one piece out of the oven. The number of fasteners is greatly reduced. The splice plate on one side could be made from the panel itself thus eliminating further rows of fasteners.
- The built process to produce such panels would be fully automated. For final assembly the four panels just need to be connected with long rows of fasteners, and that's it (moderate handwork to get a complete fuselage barrel made out of 4 parts). In contrast with the barrel approach you get little more than the skin and you need to put in a large number of frames (more handwork to get a complete fuselage barrel consisting of many more than 4 parts).
- On the B787 only the stringers are integrated into the barrels. As a result a fastener orgy lead to pictures as these:
If we compare the required number of fasteners the panel approach IS the winner. See this picture: http://www.vought.com/gallery/locati.../southCarolina/sc_production18.jpg -> All the white little spots are fasteners that could be left away with the co-cured panel approach.
- The next picture shows a segment of a fuselage with one barrel joint. Red dots are fasteners.
Picture 1: Barrel approach
Picture 2: Panel approach light (only frames and stringers co cured with the panel)
Picture 3: Panel approach max (Stringers, frames, doorframes, window-frames, reinforcements all co cured with the panel)
In the light of these ideas the picture changes dramatically. From the listed advantages for the barrel approach (easier production, Lighter, Less fasteners, Fewer joints) each one can be disposed. The panel approach leads to higher integrated parts allowing cheaper (more automated) production and final assembly. There are fewer fasteners and joints (if you count the joint between each frame and the barrel too).
You see the panel has the clear potential to be technically superior. The question remains whether today composite technology is mature enough to produce such a thing (how complex can structures be built up on the panel inside?). If one day the industry succeeds to realize the "Panel approach max" as outlined above you will for sure see Boeing change to the panel approach!
Now how much of this technology is at hand for Airbus to produce such structures?
So far in this post I summarized what A-Net has brought up so far and what the advantages of panels could be. In the second part of the post I want to share all the sources I have found around this topic. A few google-searches yield a lot of interesting stuff regarding this question. I have found some treasuries of links that shed a lot of light on these questions. A general review of public information available on the internet allows following statements:
- There is a huge amount of know how for composite fuselages available in Europe
- Also crash worthiness is covered well with studies
The first link reveals about a crash worthiness study made in Holland in 2001:
Very similarly to the Boeing 787 crash-tests a composite fuselage section was crashed to verify the accuracy of computer simulations. The report shows that the predictions were not top but still the tests showed principles to make the results predictable.
Remarkable is following structural concept: "The ring-frame configuration as commonly used in fixed-wing aircraft, is a difficult component for crashworthiness. NASA studies have shown, that the "point-load" applied by the ground leads to immediate fracture at this point, followed by severe bending, and further breakages of the frame higher up . This may result in an early disintegration of the structure, and the bypassing of the dedicated energy-absorbing measures. The recommendations followed from these studies were, to separate the livable volume "on top" from the energy absorbing components "below". Hence, a sufficiently strong, closed ring-frame, meant to survive the impact, should be positioned on top of an expandable energy absorbing structure...."
In summary: Having a separated upper and lower structure in fuselage allows in theory a better design regarding crash-worthiness. And regarding the panel-advantage-discussion: By using panels instead of a barrel this concept can be implemented better.
The second link gives deep insight into European composite fuselage research:
Page 5 below: Sidenote about new metal technologies: they promise to have the same potential as today composites regarding cost and weight. But, future composites promise to be unbeatable. Therefore second generation composite fuselages will have a clear advantage over what is top today.
Page 6 below: Possible concepts to make composites conductive (hint: improved lightning protection)
Page 8 below: As above a separation of lower and upper fuselage functions.
Page 9 Top: Shell concept with integrated stringers. Design with co cured stringers and frames is achieved.
Page 11+12: Superior crash worthiness of Gondola concept
Page 12 below: Innovative and cheaper manufacturing, reduced number of bolts
Page 13 below: Summary of various European composite fuselage research programs
General: Work seems more concrete for an A320 sized fuselage, even a mixed demonstrator is mentioned on A320 basis. Building an A320 with a composite fuselage is therefore not impossible.
Now what do you think? Will the panels for the A350 already be superior to any barrel approach?
Based on all of this and to stir up the discussion I want to make some forecasts. These are only personal opinions and I will freely admit my wrong guess if the opposite turns to be the truth:
Forecast 1: CFRP Barrel fuselages will turn out to be inferior regarding crash worthiness
Forecast 2: CFRP Barrel fuselages will turn out to be more expensive in production
Forecast 3: CFRP Barrel fuselages will turn out to be heavier
Forecast 4: The B787 will be the last airliner using CFRP barrel fuselages
Forecast 5: The NG Narrowbodies from Boeing and Airbus will use CFRP panels
Forecast 6: The first 787 write off will be after an incident smaller than BA038 because of unrepairable fuselage damage (something like this:
Photo © Jarett Sirko
, such a hole can not be patched)
Forecast 7: After the first comparing incident with an A350 the plane will not be written off
Forecast 8: CFRP Panel fuselages will allow replacement of single panels for repair of heavy damage (how?: Put the plane in a corset to fix the shape while part of the skin is missing, remove the fasteners for the panel, skin with stringers and frames is replaced as one piece).