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December 17, 2001

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   Troy Anderson, (858) 822-3075 or


Researchers at the UC San Diego (UCSD) Jacobs School of Engineering are looking to nature for new ways to reduce airplane fuel consumption and traffic. Birds innately fly in a delta or "V" pattern to conserve energy, and control engineer Miroslav Krstic of the Jacobs School's Mechanical & Aerospace Department predicts that by flying airplanes in a similar pattern, fuel use could be cut by up to 50 percent.

"The white streaks that follow a jet do not originate from the engine like many people think, but from the wingtips as they cut through the air. These swirling vortices are like horizontal tornados," says Krstic. "By getting a lift from the lead planes' turbulent wake, the follower's could cut fuel use and a group of planes could fly twice as far. Even a formation of just two or three planes could achieve a 30 percent fuel savings."

Logistically, Krstic says that in practice, the planes would take off from different airports and safely join together during flight, disbanding as they near their destinations. This flight formation would also decrease air congestion. He says the concept would work especially well for long international or transcontinental flights and be less beneficial for short, commuter trips.

Krstic's research was funded by the Air Force Office of Scientific Research. His predictions are based on computer simulations of the C-5 military transport plane, which is larger than commercial jumbo jets. The sluggish plane posed a significant challenge, but by successfully controlling this plane, he is confident that the control scheme can be applied to any aircraft.

To benefit from turbulent lift, Krstic says a plane's pitch-angle must be just right and the nose must actually be pointed downward. The vertical and the lateral distances between planes must also be precisely adjusted. Such a "sweet spot" is hard to find as it depends on weather, altitude, and speed of the aircraft.

His group has developed an autopilot control system to automatically find and keep the plane in the sweet spot, and to ensure planes in the formation are safely spaced apart. This system is based on their theoretical results on "extremum seeking," previously applied to the optimization of jet engines, power generation turbines, and bioreactors, and extensively used by United Technologies, Pratt and Whittney Aircraft, and Ford Motor Company for various control problems.

Krstic's control system uses sensors that make up the aircrafts' inertial navigation system (INS) and global positioning system (GPS), so no new technology is needed to implement this approach. The gyroscope monitors angular motion, and the 3-axis accelerometers gauge linear motion (forward, vertical, and lateral). Integrating the data provides measurements on pitch angle, velocities and position. "The extremum seeking control system reads the sensors and automatically navigates the plane to the optimal formation," explains Krstic.

"Our computational tests were successfully performed on a dynamic, high-fidelity model. This technique is developed to the extent that it can now be tested experimentally with actual planes," says Krstic.

-- High resolution image file available here.
-- An airplane creates vortices as its wingtips cut through the air. This "wake" can be beneficial in reducing fuel costs.

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