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JANUARY 7, 2003 SPECIAL REPORT: MILITARY TECHNOLOGY Adaptive Aircraft: No Flight of Fancy? Research into using exotic means of making wings change shape in-flight looks promising, though still a long way from reality
Ronald Barrett, a professor of aerospace engineering at Auburn University in Alabama, is worried. The F-15 and F-16 designs are more than 30 years old, the F-117 more than 20. Not even the most sophisticated jammers can protect them when they fly into radar coverage. "It can pick them up too easily," says Barrett. "It's like wearing a pink and purple jumpsuit into combat." Any battle with Iraq will likely be over long before that changes, but Barrett and other aircraft engineers are nonetheless looking for ways to eliminate flaps and spoilers -- anything with a pronounced shape that radar can pick up -- on wings. The problem is such accoutrements are what make it possible for a plane to take off and land. LIKE MOTHER NATURE. To reconcile the twin needs of stealth and airworthiness, researchers are working to embed adaptive materials into aircraft wings. When exposed to heat or an electromagnetic charge, these materials would morph -- or twist -- wings into the most aerodynamic shape for take-off, cruising, or landing, just as a bird manipulates its wings to lift itself into flight and soar. "Mother Nature has a lead of 3.8 billion years in R&D," says Barrett. "We're working to integrate new muscle-type materials into everything from supersonic guided bullets and missiles to aircraft and helicopters." The quest to create better wings has attracted aerodynamic experts from around the country as well as big guns at the Defense Dept. The Defense Advanced Research Projects Agency (DARPA), best known for inventing the forerunner of the Internet, has dedicated $100 million to "smart materials" research. In December, DARPA launched a new morphing-wing program that aims to create "seamless, aerodynamically efficient aircraft capable of radical shape change," in the agency's words. DARPA also is funding Boeing's smart rotor program, which uses adaptable materials to reduce both the dangerous vibration and noise of helicopter blades. And DARPA supports a research partnership with Northrop Grumman (NOC ) and NASA that has developed and tested a so-called smart wing that uses adaptive materials to alter its shape. Tests in 1998 showed that the Northrop Grumman smart wing improved by 10% a plane's "lift" (the aerodynamic force that keeps it airborne) and "rolling" (the ability to maneuver in mid-flight). A CUE FROM THE PAST. An aircraft that morphs isn't an outlandish goal. The Wright Brothers used a primitive version of "wing warping" to steer their 1903 biplane after observing birds soaring above the North Carolina dunes. To mimic the changing shape of the bird's wings, the Wrights attached lines from the edge of the wings to a harness worn by the pilot, who steered the plane by shifting his weight from side to side. On the centennial of the first human flight, future aircraft design is taking a cue from the past. To give wings the needed adaptability, researchers are experimenting with three kinds of smart materials: piezoelectric materials, which morph in the presence of an electric current; shape-memory alloys, which change shape in the presence of heat; and magnetostrictive materials, which alter themselves in the presence of a magnetic field. The oldest and most commonly used are piezoelectrics, which were discovered in the 1880s by Pierre and Marie Curie and their colleague Paul Langevin. Piezoelectric crystals are widely used in consumer products that beep, such as microwaves, digital watches, and smoke alarms. A small electric charge causes the crystal to change shape, which in turn causes small speakers to sound off. MANY BENEFITS. It wasn't until the late 1970s, however, that engineers began to try to apply piezoelectric power to aircraft. Back then, plane designers were focused on reducing hazardous vibrations that might, for example, cause key pieces of an engine to come loose. Today, designers are more interested in a self-adjusting wing that maintains the most efficient angle relative to the surrounding airflow. Flexible wings would not only allow planes to maneuver better but they could also could reduce the wings' weight, enabling planes to fly longer on less fuel, carry more passengers, or hold more bombs. The Boeing smart rotor program aims to make helicopter blades quieter and smoother by replacing mechanical parts with piezoelectric crystals. This could help eliminate mechanical failure caused by the intense vibrations of the rotor's spinning -- a common cause of helicopter malfunctions and crashes. According to Boeing, which is partnering with researchers at the Massachusetts Institute of Technology, smart actuation systems are too complex for commercialization. Research is continuing, however, and a flight test is planned. Researchers have reasons to believe such a design will work. In a 1997 study at Auburn, Barrett and his students used adaptive materials to reduce the number of components in the helicopter's rotor from 94 to 5, the weight of its flight-control components by 40%, and its gross weight by 8%. A flight test showed improved airspeeds of 18%. WHIZ-BANG TECH. Today, Barrett is working on bringing his ideas to life. He believes that adaptive materials aren't yet strong enough to be used for large, heavy airplane wings, so he prefers to work on smaller vehicles -- unmanned aerial vehicles, cruise missiles, and munitions. One of his most creative projects is designing adaptive materials that can be packed into winged bullets, turning each one into a tiny, self-directed aircraft. "If there's wind, sniper bullets can be blown 15 to 20 feet to the left or right, missing a target or hurting a civilian," points out Barrett. "We're working on a class of bullet that is two orders of magnitude more accurate in any weather. It self-corrects every step of the way." (The details of his work are still under wraps.) Such whiz-bang technology sets curious minds afire, so researchers take great pains not to hype it and turn adaptive materials into the next nanotechnology -- an advance whose performance has fallen far short of the promises that were made about it. Indeed, it may take a decade of research before morphing aircraft take to the skies, says Greg Carman, director of the University of California at Los Angeles' Active Materials Lab. Even the most advanced piezoelectric crystals and shape-memory alloys aren't yet as powerful as the human bicep, which can easily rotate an arm 90 degrees, or a bird's wing, which can arch and flap during flight. "A POWERFUL FORMULA." For the near future, that means adaptable materials will probably be confined to helicopters and small aircraft. "The ideal unmanned vehicle is one that can do things that a human can't tolerate -- sharp swoops and dives," says Richard Aboulafia, vice-president for analysis at aerospace and defense consultancy Teal Group in Fairfax, Va. "If adaptive materials can be used to improve maneuverability and stealth, that's a powerful formula." That's the ultimate goal -- to improve military might without putting lives at risk. "We hope the science fiction of today will be the reality of tomorrow," says UCLA's Carman. With any luck, the work DARPA is funding will bring that one step closer to reality.  By Jane Black in New York Get BusinessWeek directly on your desktop with our RSS feeds.  Add BusinessWeek news to your Web site with our headline feed. Click to buy an e-print or reprint of a BusinessWeek or BusinessWeek Online story or video. To subscribe online to BusinessWeek magazine, please click here. Learn more, go to the BusinessWeekOnline home page  | | JANUARY |
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