Sometime in the not-too-distant future, if you look out the window of a brand-new airplane and see the wing flexing oddly, it might not be cause for alarm, but instead the product of nanotechnology research now underway by the National Aeronautics and Space Administration.
Nanotechnology -- the science of manipulating individual atoms or molecules in order to build never-before-seen substances from the bottom up -- will help create aircraft that can sense and respond to the environment in ways more like birds than machines.
Darrel Tenney, director of the Aerospace Vehicle Systems Technology Program Office at NASA's Langley Research Center in Hampton, Va., understands how nanotechnology -- also called nanotech -- can yield the lightweight, strong materials necessary for next-generation airplanes. He leads $100 million worth of basic investigations into advanced research topics, including advanced vehicle concepts, aeromechanics of highly maneuverable vehicles and noise reduction.
Prior to becoming the AVST's director in June 1996, Tenney had headed Langley's Materials Division since August 1987. Nanotechnology first came to his attention there as he developed next-generation metals, alloys, composites and other materials for aircraft and spacecraft applications. He joined NASA in 1974 after five years as a materials engineering professor at Virginia Polytechnic Institute in Blacksburg.
Tenney contributes to national technical organizations such as the Society for the Advancement of Material and Process Engineering and the American Society of Materials, where he formerly chaired the society's Aerospace Technical Division. He spoke to United Press International at the NanoSpace 2002 conference, which was held last week in Galveston, Texas.
"Because of the tremendous potential for strength and stiffness, far exceeding the best graphite fibers we have today, we're obviously interested in (nanotech) from a structural materials application, to see if we can use that to take weight out (of aircraft designs)," Tenney said. "We know it's in its infancy in terms of mechanical properties, and whether or not we ever get there is a big question. It's a high-risk area and that's why it's legitimate for government to be investing in it."
Graphite composite materials have been studied intensively for about 30 years, yet still see only limited use in military aircraft and next to none in today's commercial aircraft. Nanotech materials should have a much faster transition time, Tenney said.
"There's a lot of rationale for saying it will be shorter," he said. "When we went from aluminum to composites, we went from an isotropic material, basically the same in all directions, to an anisotropic material. We understood how to deal with (aluminum) very well. When we went to composites, we were suddenly talking about materials that were tailorable. We had to invent a whole new mechanics discipline to understand how these fiber-reinforced materials behave under compression, shear and tension."
In the case of going to nanotech-reinforced materials, Tenney said, "we already have in place a lot of that (mechanical) understanding -- we're not plowing new ground. One reason you can say the timetable (with nanotech) will be much shorter is because of all those already-developed supporting things. The other rationale for saying that is because this is an international effort. The pace of technology development maturation will be much, much faster. It won't be 30 years before you see nanotechnology mature, it will probably happen within the next decade."
Some nanotech-related developments already are on the verge of regular use, Tenney said. The ability of a minuscule amount of carbon nanotubes to alter the electrical qualities of a material, for example, soon will be a part of space exploration. Satellites and spacecraft both need to shed electrical charges imparted by the solar wind safely, and nanocomposite polymers fill that niche, Tenney said. Similar qualities make nanoparticles useful in radar-absorbing stealth technology.
"The other place you're likely to see nanotech is in devices, the ability to make miniature sensors," he continued. "If you can put mechanical linkages on the end of nanotubes to make sensors, that's going to be important in a number of areas. We see tomorrow's aircraft having a structure a lot like circuit boards, in the sense of having electronics and sensors embedded everywhere."
The sensors will be able to monitor stress loads on an aircraft's structure both continuously and cumulatively. "Every time you (put stress) on it, it's going to know how much load you put on it, for how long, and factor that into the life expectancy of that structure," Tenney said. "It will know, 'You just used up X number of hours of your useful life.' We're going to know (useful lifetimes) ahead of time."
This ability could transform the Federal Aviation Administration's current time-based inspection schedules into more of a usage-based checkup scheme, he said. The wealth of structural information, combined with the precise location data from Global Positioning System satellites and other sources, should yield next-generation aircraft that "refuse" to crash under regular operating conditions.
Perhaps the biggest advancement will result as soon as researchers understand how to build nanostructures that perform mechanical actions. Aircraft built of such materials will become even more responsive, Tenney said. Thousands of such devices, incorporated into a wing, would provide a highly redundant control surface that would replace today's flaps, slats and rudders.
"You could have ten of (the nanodevices) fail, and the rest will land you safely. If you happen to have suffered damage in one part, the system can reconfigure itself," he said.
Conventional aircraft use rigid control surfaces, Tenney explained. "If you want to change the airflow over it, you deflect a piece of that structure." Nanotech, however, can use materials called piezoelectrics, which can alter their shape instantly in response to changes in electrical current. "You can flex a membrane and 'puff' an air pocket through (the wing's airflow) boundary layer. If you separate the flow, you lose lift and a wing moves."
The mechanics of bird flight provide the key to the concept. "Birds can activate individual feathers, they can dump (excess lift). We're paying a lot more attention to bird flight again. In the past, we couldn't do anything that was the equivalent of a feather, now we can. With the emergence of this adaptive structure, the ability to have feather-like control is now in the realm of possibility."