This analysis was posted on GLG News October 18th, and is reproduced here for our readers.
Aluminum-Lithium alloys will likely become the material of choice over composites for the fuselages of the next generation of narrow-body aircraft. Lighter than traditional Aluminum, the trade-offs between composites and the new lightweight alloys appear to be favoring Aluminum-Lithium.
Carbon fiber composites have made tremendous inroads on commercial aircraft, primarily due to their light weight and high strength. The Boeing 787 wide body airliner will be the first example of an aircraft fuselage and key structural components being constructed with composites, to be followed by the forthcoming Airbus A350XWB.
But those materials appear to be taking a back seat to new technology metals, particularly Aluminum-Lithium alloys, such as Airware™ from Alcan, a division of Rio Tinto. These new alloys are significantly lighter than traditional Aluminum construction, have significantly improved corrosion resistance, and are lower in cost than composite materials.
Why is Al-Li overtaking composites for narrow-body aircraft? The answer lies in an analysis of the trade-offs between the two materials in airline operations.
Operational Differences
Narrow-body airliners, unlike wide body aircraft, fly short-haul flights and operate many more take-offs and landings each day. This requires a more robust airframe to withstand the stress of multiple daily take-offs and landings, as well as the pressurization cycles and the inherent stresses on the aircraft.
Damage Tolerance
Airframes are subject to ground damage, often from baggage loaders and carts that may inadvertently strike the airframe during routine operations. Carbon fiber composites, while high strength, can incur damage on the inside, rather than the outside, of the airframe from a strike. As a result, non-destructive testing, such as an x-ray device, is necessary to determine whether damage has occurred and if it is significant enough to require a repair process to ensure structural integrity of the airframe.
For Aluminum-Lithium structures, damage can be easily determined through inspection, as with traditional aluminum structures, and straightforward repairs undertaken using “scab patches” of additional material as necessary.
Of course, composite structures can be made stronger and more damage tolerant. One aircraft manufacturer, in evaluating the trade-offs, indicated that an additional ply of composites would be required to those used on the Boeing 787 to provide the level of damage tolerance of Al-Li alloys, and that additional ply would virtually eliminate the weight advantages of the composite material.
Manufacturing Processes
Composite materials require different manufacturing processes than more traditional aluminum construction. Composites require curing in ovens or autoclaves, and significantly different manufacturing processes to manufacture, and attach, components to an aircraft. Aluminum-Lithium alloys utilize the same manufacturing processes as aluminum, which are well known and already established.
Cost and Durability
Tradeoffs also exist between the cost and durability of these materials. The cost of composites is higher than that of aluminum, but is not subject to corrosion. While the new alloys are much more corrosion resistant than traditional materials, corrosion in certain operating environments remains possible. Composites, by contrast, may delaminate should moisture enter a flaw in the surface, as evidenced by delamination around fasteners in some composite tail structures on today’s aircraft. From a durability standpoint, the behavior of Al-Li is well known, while the long-term behavior of composites remains to be proven for aircraft structural applications.
Environmental Concerns
Aluminum-Lithium alloys are a fully recyclable material, and at the end of an aircraft life can be recycles into a new aircraft. Carbon fiber composites include carbon fibers, as well as a metallic mesh to protect against lightning strikes, encased in cured resin. The high strength carbon fibers and metallic mesh are difficult to extract from the material, making recycling difficult if not impossible.
Safety
The behavior of Aluminum-Lithium and Composite components vary significantly in a crash. Aluminum is less rigid than carbon fiber composites, and tends to crush and absorb impact during a crash. Carbon fiber composites, by contrast, tend to shatter on impact, with the high strength carbon fibers separating from the resin upon impact. In a crash scenario, will carbon fiber composite provide an equivalent level of protection for passengers than aluminum alloys, particularly should a fire occur, given the toxicity of the materials and the potential for fire to reach a passenger cabin through a gap? The jury remains out.
Bottom Line:
After examining the trade-offs between carbon fiber and Aluminum-Lithium construction for the next generation of narrow-body aircraft, Bombardier selected Al-Li for the fuselage of its forthcoming CSeries. A senior executive at Airbus has also indicated that their narrow-body replacement would not necessarily utilize composite structures. The aluminum manufacturers are fighting back with innovative materials, and aircraft manufacturers now have a competitive choice.
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As an insight this is not all that new.
Al-Li had strongly rising usage in Airbus craft
and studies indicated an inexplicable lack of gains
from changing over to black materials at least for a
replacement NB design.
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I see the barrelliner as a viral marketing success only.
Boeing had full reign over the introduced meme.
Interesting that better materials understanding does not
cary that much weight in the market.
Must have CFRP, horay, horay.
The final optimum will be much more of a melange than popular opinion previously championed. IMHO barrels will vanish again, CFRP will be prefered for high load bearing parts like
wings, wingbox, tailcone, pressure bulkheads i.e. all constructive elements that allow fastnerless assembly by cocuring.
Jim Albaugh said in a recent interview that he had thought composites would not work for narrow bodies, but that the development of what he called second and third generation composites has changed his mind. I don’t know what Albaugh meant, but certainly CFP mfrs will be improving their products to compete with alternative materials, and airframers will be experimenting with those CFPs. For example, we know Boeing have recently patented a twin-asile, composite fuselage that looks like a 737 replacement. As I understand it, one of its main advances is that the composite thickness can be varied from place to place in the fuselage depending on differing strength needs at differenct places, thus reducing weight.
Also, Airbus have been committed to composites for years, most recently in the A400M, a plane that is likely to see a lot of fuselage damage over its lifetime. And Boeing seem to be reducing the weight of the 788 based upon testing that is revealing in real time how much material they can eliminate from the plane and still have the strength they need. Boeing are now claiming that all of these improvements will be included in the 789 and give it killer economics.
It may recall
The point, IMHO, is that air framers and engine makers can’t decide what advances they should try to make because aviation tech is in the greatest state of flux in its history, from consturction materials to IFE to seats to engines to how construction will be shared globally, on and on. Most importantly these advances are happening at near lighting speed compared to the past, so what seemed like a good new tech investment today may not be so good tomorrow. Add to this uncertainty other variables, such as the availability of materials such as lithium. (I undersand that most of that is located in Bolivia and China.) All this means that we do not know what the future holds; eg Boeing’s and Airbus’ quandries ovaer what to do with their single aassile products.
There is the publicity splash trap too.
The rare earths and lithium have rather even distribution.
China currently has the cheapest refining industry ( by quite a margin ) letting other sources appear unattractive.
apropos A400M:
Afaik the fuselage is Al, Al-Li, Glare, Titan.
A fitting choice for a plane that could have
ramp rash galore by the usage profile.
The Wing, Wingbox, and aerodynamic surfaces are CFRP though.
If one looks at an A380 direct from the FAL the Al/Glare parts are primer green while the plastic parts are white or airline livery already )
Similar observations can be made on the A400M, see:
http://www.a400m-countdown.com/index.php?v=5&spage=3
fuselage is AL ( primer ), rear pressure bulkhead is CFRP ( white ), rear ramp : Al? and rear door : CFRP ?
Too bad that the various Bombardier suppliers weren’t up to speed for the first test flight of the large 110 to 125 seat CS100 jet in December 2012. Now we must wait until first flight in June 2013 to start getting leaked feedback re fuel consumption with its new type P&W, GTF engines and carbon fiber wings, tail and nose along with the aluminum-lithium main fuselage. The whole world is watching this one. By the way, the MTOW for the CS100 is just under 5,000 feet, much shorter than some of Bombardier’s regional jets.