Ease of repair is reportedly one of the main reasons the Canadian airplane maker Bombardier Aerospace has chosen not to use carbon- or glass-fiber composites in the main fuselage of its composite-heavy CSeries aircraft. The high-cycle aircraft, due to enter service in 2013, is expected to sustain a lot of impact damage from ground support equipment. Since repair and maintenance standards are often based on the performance of metal-based planes, damage is easier to identify and repair in metal portions of aircraft using current techniques.
Unlike the Boeing 787 Dreamliner and the Airbus A350 XWB, the fuselage of the two CSeries models is constructed primarily of aluminum-lithium. Composites are used in the empennage, rear fuselage, nacelle, and wings. Altogether, the advanced materials give the plane a 2,000-pound weight savings.
Problems surrounding the repair and maintenance of composite aircraft have become much more visible since a GAO report questioned the safety of repair and maintenance procedures for Boeing 787 Dreamliner composites. That report said impact damage to composite structures may be difficult to detect, since that type of damage isn't as easy to see as impact damage to metals.
The Canadian CSeries CS100 commercial aircraft uses aluminum-lithium, not carbon-fiber composites, in its fuselage to save weight.
Photo courtesy of Bombardier Aerospace
In addition, the nondestructive inspection techniques commonly used on in-service aircraft for detecting and characterizing composite damage vary with each composite's construction methods and with the particular type of damage done. For example, the 787 uses at least two different types of carbon-fiber composites: carbon laminate and carbon sandwich. So repair and maintenance technicians aren't as likely to find damage in the first place if they don't use the correct technique for finding it in a given material.
Compounding that problem is the fact that composite repair itself deploys up to 60 unique materials, while traditional metal repairs require only a dozen or so, according to one study cited by the GAO report. In addition, technicians are less likely to repair a composite correctly, since the quality of repairs depends primarily on which process they use. The scale of knowledge and supplies that must be kept on hand is thus multiplied several times. Though there's a certain degree of standardization for the repair and maintenance of metals in aircraft, the same is not yet true for composites.
I would think it goes without saying that there should be new standards and certifications for technicians charged with the responsibility for vetting out and orchestrating the fix of composite structures in need of repair. Composite materials are very different that what's required to repair metal and steel structures. I don't know why we need a government report to tell us an heavy investment in training and skills building is necessary!
@Beth.The government gets involved because the private sector tends to gloss over problems in order to maintain market share. That being said too much government involvement stifles progress. The Bombardier decision is more likely based around deHavilland's experience over the years where their tough aircraft stood up to some primitive operating conditions...dings and dents being the standard operating experience. Also the flight cycle time for the Dash 8 on the west coast averages 58 minutes which is rough on a structure where fatigue is concerned. Aluminum-Lithium is a difficult material to work with but (again) Fleet Industries in Ontario has had long experience in building (and repairing) such structures.It will be interesting to see where Bombardier goes with this since the C series is a big change from the smaller aircraft built previously.
@Ann: The title of this article seems to be out of step with its contents, to say the least. Obviously Bombardier doesn't think composite aircraft repair is advancing enough to justify using composites in the CSeries fuselage.
Which aluminum-lithium alloys is Bombardier using? There was an article on this website a few months ago about Alcoa's new third-generation aluminum-lithium alloys, which were developed cooperatively with Bombardier.
I'm curious as to whether this is a transition time for composite materials or whether there is something intrinsic to composites that makes detection of problems and repair more difficult for composites than it is for more conventional materials.
I think the answer is a bit of both. Beth, the industry apparently has been working on solving this problem along with the FAA. At least, that's what they all tell us. But it's quite difficult to find out any details. And that's where ScotCan's point comes in. As the report delineates, industry has been extremely secretive regarding the details about their materials--the type of details which must be well known for determining when and how to repair--in the name of trade secrets.
Rob, that's the $64,000 question. I think the answer here is also 'both." Composites are definitely moving forward in aerospace, as shown by all the aircraft makers using them in greater amounts. And detection of at least certain types of damage is difficult, but apparently not impossible.
I'm impressed by the breadth of your recent coverage on composites, Ann. I'm wondering if you see new standards emerging out of the FAA as regards composites repair, or will we see industry-standard practices come into play first, which will become de facto methodologies for both repair and recycling?
This is a classic example of the need to beware that what looks good on paper may not always be so. As design engineers, we are often trained to consider matters of stress and strain -- bending, shear, torsional capacity, etc. But here we have a situation where the composite is apparently appropriate in matters of material strength, but not in matters of maintenance. Obviously, maintenance is a huge consideration for aircraft. In 1979, an American Airlines flight leaving Chicago O'Hare crashed, killing 271 people, after a design flaw left the engine pylon vulnerable to maintenance damage.
@Charles: You're absolutely right; materials selection involves many considerations besides the material's response to stress and strain -- which can be complicated enough, since the material may respond very differently at different temperatures and strain rates, and its properties may be different in different directions. But how a given material will perform in your application also depends on its location in the galvanic series, among other things. Cost and manufacturability are always major concerns, too. Then there are externalities such as recyclability and end-of-life issues, sustainability and lifecycle emissions, etc. And -- although I may be somewhat biased in this regard! -- this is why having a good materials engineer is a necessity.
Thanks, Alex. The news just keeps coming out on this subject. Regarding standards, that's a really good question. One of the key critiques in the GAO report was the point that you can't base repair standards and best practices for composites on the same ones that were created for metal. There are too many differences across the board, and making the same assumptions or using the same templates would be ineffective and dangerous. That may be another reason why we're not hearing much yet about the details of repair whens and hows. I suspect it's a WIP.
We looked at a number of sources to determine this year's greenest cars, from KBB to automotive trade magazines to environmental organizations. These 14 cars emerged as being great at either stretching fuel or reducing carbon footprint.
Researchers at MIT and Sandia National Labs have observed a reaction in lithium-air batteries that could help improve the design of these cells for electric vehicles and other applications.
Healthcare might seem to be an unlikely target application for the Internet of Things technology, but recent developments show small ways that big-data is going to make an impact on patient care moving into the future.
As energy efficiency becomes more and more a concern for makers of electronics devices, researchers are coming up with new ways to harvest energy from sound vibration, footsteps, and even electromagnetic fields in the air.
From Dell / Intel® New Paradigms in Design Work Scott Hamilton, vertical market strategist for Dell Precision workstations, 5/2/2013 3
Early in my career, I worked as a draftsman and remember the days of drawing on vellum with numbered pencils and Mylar with plastic lead. This was a fun experience in the sense that I ...
I've been using workstations for more than 10 years and love finding ways to get more performance from my system. With demanding professional applications that require more power each ...
A lasting memory from my first job as an engineer in an auto assembly plant is standing on hard concrete at six in the morning, vending-machine coffee clutched in hand, listening to ...
A quick look into the merger of two powerhouse 3D printing OEMs and the new leader in rapid prototyping solutions, Stratasys. The industrial revolution is now led by 3D printing and engineers are given the opportunity to fully maximize their design capabilities, reduce their time-to-market and functionally test prototypes cheaper, faster and easier. Bruce Bradshaw, Director of Marketing in North America, will explore the large product offering and variety of materials that will help CAD designers articulate their product design with actual, physical prototypes. This broadcast will dive deep into technical information including application specific stories from real world customers and their experiences with 3D printing. 3D Printing is
To save this item to your list of favorite Design News content so you can find it later in your Profile page, click the "Save It" button next to the item.
If you found this interesting or useful, please use the links to the services below to share it with other readers. You will need a free account with each service to share an item via that service.
Tweet This
4 
