Monday, December 17, 2007
Composite Safety Concerns are Red Herrings
Still, composites represent the most important improvement in aircraft construction since the introduction of aluminum in the 1920s. The adoption of these "miracle materials" is sweeping all sectors of aviation, challenging the traditional ways of doing business.
But it is the general aviation manufacturers that have been more aggressive on adopting composites than transport manufacturers, given the fact that Boeing’s soon-to-be-introduced 787 is 50 percent composites and the Beech Starship composite aircraft was introduced to the GA and business aircraft market in 1988.
All-composite aircraft such as the many business jets, especially Very Light Jets (VLJs), are in the vanguard of aviation innovation. Indeed, the General Aviation Manufacturers Association reports that in 2006, 34.7 percent of shipments were “all” composite aircraft and composite shipments equaled that just in the first three quarters of this year. All composite GA aircraft include Adam A500, Raytheon’s Premier 1, the Hawker Beechcraft 4000, the entire families of Cirrus, Diamond and Columbia aircraft along with Liberty Aerospace’s Liberty XL2. In addition, several very light jet manufacturers boast increasing composite content in their aircraft. While not a VLJ, the Cirrus design is based on a NASA program and, those that have adopted the NASA program, specifications and processes, have a far easier certification task, according to TECOP International President Hans Weber, who heads a management firm designed for technology optimization, and was one of the webinar speakers.
While the Eclipse 500 uses composites mostly for fairings and non-load bearing structures, both the A500 and A700 are approximately 90 percent composite. Epic's aircraft are 100 percent composite construction, said Spokesperon Lyn Freeman.
“I think you’ll find the real innovation in aviation design backstream from the airliners,” he said. “It was Burt Rutan who began some real design changes and breakthroughs back in the 1970s and 1980s when he began experimenting with composites and canards and all kinds of other ideas. Because the Experimental Aircraft category allows the most room for growing new ideas and technologies, that's where you saw, and still see, the revolution taking place. Epic is right there at ground zero.”
But, as with Eclipse, Embraer’s Phenom 100 is about 20 percent composite and the Phenom 300 at 16 percent. Embraer, which cut its teeth on manufacturing regional aircraft which used composites for various components, recast those airframes for the business market including its Legacy and Lineage series which are based on the ERJ 145, 170 and 190. It noted that, although many general aviation manufacturers are using composites, it does not share the vision that executive jets use more composites than airliners. “It is true that there are some executive jets made entirely with composites but this does not mean they are more advanced or efficient,” Spokesperson Pedro Ferraz told Aviation Today’s VLJ Report. “We do see a trend of a higher percentage of composites in future products, but a trade-off must be carried out balancing fuel burn according to stage length of each product, the importance of maintenance cost and the benefits in production costs. There are also downsides on the extensive use of composites, like cabin noise. In Embraer's latest airliners, the E-Jets, composites represent 12 percent of structural weight.”
Even so, composites are garnering increasing attention as Boeing launches its 787 at 50 percent composites and Airbus A380 at 25 percent. Composites now make up a $7.3 billion market which is expected to quadruple in the next 20 years. Air transport accounts for $3.3 billion while business aircraft accounts for $0.6 billion and maintenance repair and overhaul $1.8 billion. The balance is in the military sector.
While the leading-edge technology promises major advances in both manufacturing and aircraft operating efficiency, composites also present challenges for operators, inspectors, maintenance technicians, and accident investigators so much so that they likely constitute a “brave new world,” according to Air Safety Week Editor Ramon Lopez, who spoke about their impact on accident investigation. But this new world also faces most other sectors of the industry.
Even so, Weber noted, composites are not exactly new and most sectors already have considerable experience with the new technology. Aviation Maintenance Editor in Chief Joy Finnegan, echoed Weber when she said that the civil industry can look to the vast operational experience of the military which dates back to the B1B bomber for lessons on operating and the life of the material as well as repair and overhaul of the aircraft.
The three panelists also pointed to coming advances, including nanotechnology that will provide a self-healing capability to automatically eliminate defects or flaws to composite airliners, according to Weber, who indicated it would first be used on military aircraft before adaptation to the civil industry. He also said that that structural health monitoring is just around the corner and would completely eliminate unseen impact damage. He noted the technology was not mature enough for the 787 but was not far out.
Of course the advantages of composites include a reduction in fuel, which, said Weber, was four to five percent, to say nothing of any improvements in aerodynamics. In addition, composites do not corrode as aluminum does, meaning corrosion or fatigue cracking concerns will disappear along with the necessity for rebuilding structure as an airframe ages, all of which lead to a significant reduction in costs. In addition, composite airframes can be pressurized to higher loads leading to vastly more comfortable flights.
Weber also predicted, structural health monitoring, which is already being used on bridges, could eliminate unseen impact damage. Weber did not think composite use will rise by much beyond 50 percent of the aircraft structure, largely because engines are still made of metal. But, Finnegan pointed out that the GE 90 has a composite fan and its NextGen engine is taking composites a step further. In addition, nacelles have long been made of composites. Composites also promise to open up new routes and uses for aircraft as they change aircraft economics. She indicated it was the dramatic drop in composite costs over the last 15 years that paved the way for increased usage such as the 787.
Manufacturing differences for composites includes increased design and manufacturing efficiency and accuracy, according to Weber, which promises to dramatically reduce manufacturing costs as well as enhance aircraft performance. He indicated that metal aircraft require aircraft to be over designed to provide more redundancy, while composites allow manufacturers to tailor their designs to specific requirements. This will yield enhanced safety through improved modeling and simulation and new capabilities for composites. Composites will help manufacturers design only what they need, manufacturing in tolerance for defects or flaws. This will further reduce structure in addition to allowing for more daring approaches to design as they learn how to use the medium. Right now, there is still a learning curve since the industry approaches composites from a perspective of metal structures rather than how composites differ and what that difference means. Weber indicated that the biggest push during a recent meeting of the Commercial Aircraft Composite Committee is for standardization of composite material manufacturer. Finnegan echoed that, adding that currently there is a shortage of composites and that once that shortage is over, manufacturing costs could drop further.
As for certification, certification authorities already have vast experience with composites. Regulations require any new technology to have the same or an enhanced level of safety and, for the 787, FAA is requiring additional testing of the 787 fuselage that is not required of aluminum aircraft, said Weber. Finnegan indicated the challenges for the FAA will involve far more than certification, suggesting that training will be key in all sectors of the industry – FAA, MROs and aircraft operators. She noted that inspection techniques are designed for metal aircraft and the question remains as to whether they are sufficient for composite aircraft. “The FAA really needs to address this in the near future,” she said.
Much of the concern are already being addressed, according to Lopez, who pointed out that Sandia National Labs has begun composite flaw detection experiments designed to establish whether inspection techniques must be changed. Weber also pointed out that technology is already available for inspecting aircraft, having been long deployed in the military. What Sandia is doing is validating existing techniques in the civil sector for how accurately they work in real life with real inspectors, he said. Finnegan said the industry would not only be learning from the military experience but from that of the general aviation manufacturers and operators that already have training for inspection and maintenance personnel in place.
Weber noted that composites allow tolerance for damage to be designed in to the point that a 787 will not be stranded at an outstation. As long as the damage is not visible it can be ferried to a maintenance base. However, it is only strong enough to accommodate defect and damage that are not readily detectable. Composites are designed so subsurface damage will not compromise the aircraft. Indeed, manufacturers are already beefing up certain portions of the aircraft – such as around aircraft doors – based on customer reports they are often damaged by service vehicles.
The webinar panel also discussed the unintended hazards of composite use, such as survivability in the event of a crash or fire which would emit toxic fumes. Weber did not give such concerns credibility since certification standards for crashworthiness remain unchanged. “It’s a red herring,” he said. “Composites fail differently but that does not mean they don’t have the same energy absorbancy as metal and manufacturers can allow the shattering to work for them.” He pointed out that interiors are already composite and are subject to the same toxic fumes release and flashover points as conventional aircraft.
Finnegan noted that FAA’s Airport Technology, Research and Development branch recently issued a paper on composite fires which, she described as a paradigm shift in dealing with fires. Composite fires, she said, were more deep seated and, like coal fires, were not always visible. Instead they smolder and could reignite leaving firefighters to learn a new firefighting technique.
In addition, the National Transportation Safety Board already has experience in composite crashes. In addition to the Cirrus crash in New York City, NTSB studied the composite failure of the tail of the American Airlines jet that crashed in New York in November of 2001, which included examining the manufacturing process of the material, just as it does for aluminum. The cause was found to be overloading for the certificated critical load of the tail, said Weber.
In describing his brave new world for accident investigators, Lopez noted that all or a high percentage composite aircraft involve primary structures rather than secondary structures.
Finnegan also said repair shops already have composite capabilities to assess and repair composite structures, which have been certified.
Weber observed that Boeing has traditionally been a highly conservative company and its high use of composites was really borne of its need to redefine its future after its acquisition of McDonnell Douglas and its heavy emphasis on the military sector. Boeing, in trying to redevelop its emphasis on the civil sector, focused on the, now-defunct sonic cruiser, which was, of course a composite aircraft. When the market did not respond to the project it turned its attention to using composites in other commercial projects, not only to take a step in aircraft design but to remain in the commercial business, he said. “They changed their emphasis from high speed to higher efficiency and composites were necessary for that,” he said. “The cost of composites – which have dropped dramatically in the last 15 years – was low enough to make that feasible and, from its military business, it had a fairly good hand on the technology.”
Lopez said that United has already asked Boeing to design a narrow-body replacement for the 737, making it a good decision that it went with composites.
To listen to the entire webinar click here.