Future flying machines will be faster and more bir

Up, up, and away
Future flying machines will be faster and more birdlike



By Charles W. Petit


While the glory at America's space agency has always gone to heroic astronauts and clever satellites, aircraft engineers are fond of pointing out that the first A in NASA stands for aeronautics. Lately, however, that quip has been more sigh than boast. The aviation research budget has endured the 1999 cancellation of a billion-dollar supersonic airliner project and the axing, as "corporate welfare," of a lot of programs to improve the present fleet of airplanes. This year's budget proposal would nearly eliminate helicopter research. And with the revamped Mars exploration program and a recently revealed $4 billion overrun for the space station gobbling dollars, money for things that merely fly will stay tight.


So why the hopeful smiles in NASA's aeronautics wing? Truly far-out airplane research, of the kind that industry cannot do itself, seems in vogue. NASA's top echelons tipped their hand at a recent briefing on this year's budget. Top billing in a thematic opening video was no spacecraft but a "morphing airplane," a shape-shifting craft that seems more flesh-and-blood bird than machine. In ad***ion, the agency is within a few weeks of testing two extreme aircraft. One is a lightweight but enormous solar-powered flying wing, the other a small, rakish-looking, unpiloted "scramjet" craft set to reach 10 times the speed of sound, making it by far the fastest air-breathing flying machine ever.


The aircraft weirdness prize goes to the morphing airplane, properly the "21st century aerospace vehicle." It is only a computerized animation now. But it represents NASA's vision of airplanes "that fly like eagles," says agency administrator Daniel Goldin. Engineers at NASA's Langley Research Center in Virginia have been working on the basic morphing technologies for years, some in collaboration with the Pentagon.


First applications of the technology may be conventional-looking wings and tails that merely twitch at high frequencies to damp out vibration. But eventually the engineers aim to build airplanes with mechanical muscles under taut, skinlike membranes, forming seamless wings that bend, stretch, fatten, sweep back, and extend featherlike tufts to achieve a level of control far beyond today's aircraft with far less fuel.


"This program is an answer to an aerodynamicist's prayer," says Langley engineer J. Ben Anders. "We want something that flies like a biological creature, not with big hinges and motors and hydraulics." Applying a design tactic called biomimetics-imitation of life-the Langley team has even arranged with a marine lab to study its sea creatures. The animals' fins, tails, and general design-optimized by millions of years of evolution to slip easily through water-could lead to better and more lifelike airplanes.


Shape of the future. Critical to morphing technologies are substances that change shape when stimulated. These include ceramic, piezoelectric crystals that grow or shrink in electric fields, and metallic "shape memory alloys," rich in nickel and titanium, that take new but controllable shapes as they are heated. Sensors and processors will act as nerve networks, feeling the airflow and reshaping the aircraft in response. Such aircraft would be far too complex for pilots to control directly. Instead, crew members or ground controllers would provide the course and let the machine figure how to fly it. The added fuel efficiency of morphing presumably would be useful in all kind of airplanes-but the first applications may well be on small and perhaps unpiloted craft.


While full-fledged morphing planes will take decades to arrive, other NASA aircraft flight tests-one very slow, the other very fast-promise quicker payoffs. In the next month or so, a remote-control NASA-funded plane called Helios is to rev its 14 electric-powered propellers and take off from a runway in Kauai, Hawaii-at the blistering speed of about 25 miles per hour. With 2,000 square feet of solar cells on its top surface providing juice, the 247-foot-wide flying wing is to climb to 100,000 feet, a record altitude for sustained, level flight. The latest of a series of ever larger, solar-electric flying wings, Helios is being called a "near eternal airplane." Within three years, it is to be fitted with fuel cells that, during the day, will store enough extra energy from the solar cells to keep it flying through the night. After this year, NASA will turn it loose to the commercial world. A company called AeroVironment, which built the prototype for NASA, hopes to manufacture dozens of the planes, which it will call SkyTowers, and use them as broadband communication relay stations positioned over major cities. "They are like satellites, but a lot cheaper," says AeroVironment CEO Tim Conver. NASA could use such planes, too. For instance, they would be dandy platforms for scientific instruments studying the atmosphere, oceans, and land.


At about the same time that Helios is to fly in Hawaii, NASA also plans to try flying a scramjet (short for supersonic combustion ramjet) for the first time. A technology in the works for 40 years but unproven outside a wind tunnel, scramjets can work only at high speeds that compress air in the engines without the need of turbine blades. The test vehicle, a 12-foot-long, hydrogen-powered dart, is basically a flying engine that compresses incoming air in a shock wave under its nose, ignites it with fuel in a 20-inch-long chamber in its midsection, and surfs on a fireball erupting under its tail.


Mach ups. The scramjet craft, dubbed the X-43A, is a vastly scaled-down remnant of a stillborn project of the Reagan administration, the National Aero-Space Plane, or NASP. It was aimed at building a full-scale, human-crewed craft able to reach speeds 25 times the speed of sound and convert to rocket power as it left the atmosphere and entered orbit. That project died in the early '90s as costs rose-NASA bit off more than it could chew-but engineers at NASA's Langley center remain convinced that scramjets can be built to operate at hypersonic speeds at least five times the speed of sound. The first flight will take place off the coast of California; the X-43A will be airdropped from a B-52 and initially powered by a rocket booster before the scramjet kicks in. If it works as hoped on the maiden flight, says Vince Rausch, manager of the Hyper-X program at Langley, "We are going to make aviation history. It will be the first aircraft to ever go seven times the speed of sound." Langley has built three X-43A craft, each of which will be lost in the Pacific Ocean after a single flight. The last test could reach 10 times the speed of sound-about 7,000 miles per hour.


All three of these aeronautics projects could someday be useful in space as well. Morphing airplanes could lead to morphing spaceships; a version of Helios could fly in the air of other planets, and scramjet-bolstered booster rockets could economically speed up through the atmosphere toward space. Says Terrence Hertz, chief of aerospace research and technology at NASA: The new aircraft "blur the line between aeronautics and space."

X-43A
Description: The first of three X-43A hypersonic research aircraft and its modified Pegasusđ booster rocket recently underwent combined systems testing while mounted to NASA's NB-52B carrier aircraft at the Dryden Flight Research Center, Edwards, California. The combined systems test was one of the last major milestones in the Hyper-X research program before the first X-43A flight. One of the major goals of the Hyper-X program is flight validation of airframe-integrated, air-breathing propulsion system, which so far have only been tested in ground facilities, such as wind tunnels. The X-43A flights will be the first actual flight tests of an aircraft powered by a revolutionary supersonic-combustion ramjet ("scramjet") engine capable of operating at hypersonic speeds above Mach 5 (five times the speed of sound). The X-43A design uses the underbody of the aircraft to form critical elements of the engine. The forebody shape helps compress the intake airflow, while the aft section acts as a nozzle to direct thrust. The 12-foot, unpiloted research vehicle was developed and built by MicroCraft Inc., Tullahoma, Tenn., under NASA contract. The booster, built by Orbital Sciences Corp., Dulles, Va., will accelerate the X-43A after the X-43A/booster "stack" is air-launched from NASA's venerable NB-52 mothership. The X-43A will separate from the rocket at a predetermined altitude and speed and fly a pre-programmed trajectory, conducting aerodynamic and propulsion experiments until it descends into the Pacific Ocean. Three research flights are planned, two at Mach 7 and one at Mach 10.