News that China is looking hard at using aluminium rather than composites for much of its proposed Comac C919 airliner raises the question as to whether ‘plastic fantastics’ like the Boeing 787 Dreamliner and Airbus A350 are mistakes.
Both high composite projects make ambitious claims for the use of non-metallic materials. And the first, the 787, is in diabolical strife. Overweight, hard to build, late, and quite possibly incorrectly modelled in relation to the behaviour of oven baked sheets of laminated reinforced carbon fibre.
Which of course, is what Airbus was warning concerning the risks of plastic airliners right up to losing the contest for the big Qantas 300 seat twin jet order to Boeing in December 2005.
After that Airbus back pedalled and went down the fashionable plastic road in hot pursuit of Boeing with a revised A350, albeit a redesign using composites in a more conventional manner than is the case in the 787s.
The news from China comes soon after Mitsubishi Heavy Industries, which makes the plastic wing for the 787 Dreamliner abruptly decided to go for tin not composites in the wing and most of the fuselage of its own MRJ or regional jet project.
Mitsubishi bailed on plastic wings after the one it is building for Boeing broke during a stress test at the wing-body join earlier this year.
2 Comments
This is a very interesting development. Perhaps Comac have been reading Hans van der Zanden’s online book at lonelyscientist.com
And the ‘planetalking’ blogs.
The infrastructure and knowledge base required to produce composite aircraft is immense.
Another good reason for using aluminum is the manufacturing flexibility this affords. (acknowledged by Mitsubishi)
And as about 17 of the 20% improvement in fuel efficiency claimed by Boeing for the 787 really comes from improved engines & systems (if they had met their target weight for the structure) then the case for composites on the grounds of increased fuel efficiency by virtue of weight reduction looks very shakey.
IMHO there is more to this issue than is obvious for the naive viewer.
Boeings barrel approach is certainly “duhh” obvious as a sales argument.
The technical and process side is a lot more involved.
The barrel process is derived from sail boat main spar manufacture.
Spars can have inside stringers, are long thin, tapered and have
no internal ribs while the B-barrels are short, large in diameter ( the
long closed ~100feet loop really counts for quite a bit of expansion
when you bake it late in processing) untapered and need ribs.
Note that one would not be able to extract the mandrel with co-cured CFRP ribs.
Themal expansion makes keeping fibers under tension over the mandrel a difficult to manage problem.
( Loss of tension while heating for a bake goes up linear with temperature _and_ circumference of the mandrel )
Thus Boeings barrel approach may be seen as the first large step towards
simplified manufacture reclaiming for Boeing the industry leadership in
innovation by a very large margin.
But imho it is an absolute Dead End preventing any further progress.
If you look at european published research efforts there are other path to take.
further progress and simplification can only be gained by integrating
not only the skin with co-cured stringers (B787) but must include frames and a lot
of other items like integrated door and window framing, attachments points
for flooring and other airplane infrastructure.
thus an Airbus “New Panel” will in the long run be a complete fuselage segment
reaching over quite some length and a significant radial segment 90°..180° that
is structurally and “stuffing”wise complete. A section that can be worked on
from both sides with large machinery, easily inspected and cut to minimal
tolerances at connecting borders. ( remember diameter missmatch cannot be fixed
with the barrel approach ). Sections to that design will only have fasteners
at the section borders, nowhere else, and those might go too if in the next
step sections are glued together.
Airbus is known for cool calm and collected going foward with innovations
they each integrate carefully into their workflow. New processes and materials
will not enter the workflow until after they have been understood and mastered.
compare that to the diletante effort we see at Boeing these days.
Thus it may still be open if CFRP fuselages win over metal or not. But Boeing won’t
decide.
uwe