But last fall team members observed an unexpected "test" of emergency recovery procedures, the programmed instructions that direct the helicopter to respond to occasionally erroneous sensor data. They were trying out an algorithm, which up until then had been tested only on the simulator. The model was to direct the helicopter to perform two automatic maneuvers in a row, an aileron roll-a corkscrew-like maneuver-followed by a split-S. But when it came time to actually execute the maneuvers, there was a problem: as the chopper was coming out of the roll, it received faulty data about its position, and it responded by going into a spiral dive. Instead of attempting to take over and rescue the helicopter, the team waited to see whether the craft's sensors would receive correct data upon which it could act. To their delight, that is exactly what happened. Unaided, the helicopter recovered from the dive and returned to its starting position.

One of the most dramatic flight moments came when the helicopter first performed a split-S. The researchers had predicted it would drop 36.5 meters in 2.5 seconds as it came out of the split-S, and it did. But the drop-similar to an error-induced free fall-was more nerve-wracking than anticipated. "On a simulator, it doesn't look nearly as dramatic as when you actually see it," Gavrilets says. "It was really wild!"

With its ability to perform tight turns, loops, and rolls, the miniature helicopter is perfectly suited for negotiating urban and natural landscapes, Mettler says. Already it has been used to help film a movie in New York City, although for that, Mr. Chopper operated under human control. A camera attached to its base recorded pigeons in flight for a 2000 Emmy-winning documentary by National Geographic. The helicopter's built-in vibration-isolation system, which cushions the avionics computer during flight, allowed for even filming. The craft's steady-shot capability and its maneuverability are attracting entertainment industry interest because the machine could be used to film stunts inexpensively.

But Feron and his team most often discuss military applications. After all, NASA, the Office of Naval Research, and the Defense Advanced Research Projects Agency fund the project. Last fall the team developed an "air show" program designed to demonstrate that the helicopter can autonomously carry out a planned mission-an ability necessary for such military uses as reconnaissance.

Related work (on larger helicopters) is going on at other universities, including Carnegie Mellon and the Georgia Institute of Technology, but researchers there recognize MIT's advances. Georgia Tech assistant professor Eric Johnson, SM '95, says, "In my view, the impact of Eric Feron and his team's recent results has been to unambiguously show that unmanned aerial vehicles are capable of operating more like manned aircraft."