Findings: Breakthrough in heli-science

The tiny unmanned helicopter smoothly corkscrewed through 360 degrees, prompting the small crowd gathered below in a field on the outskirts of Boston to burst into applause, writes Steve Farrar.

The manoeuvre may have been mundane compared with the stunts expert fliers are capable of, but the watching engineers were elated nonetheless.

That flight, on November 28 2001, marked the first time that an onboard computer had been able to guide a helicopter through an acrobatic trick without help from a human.

The success brings closer the possibility of long-range automated military drones that could venture into complex urban or mountainous landscapes, emergency probes that could hunt for survivors amid hazardous disaster scenes or camera platforms capable of capturing stunning aerial photography for the entertainment industry.

Eric Feron, associate professor of aeronautics and astronautics at the Massachusetts Institute of Technology in the United States, has been working with Vlad Gavrilets, Ioannis Martinos and Kara Sprague for two years to conquer the control engineering challenges involved in guiding helicopter flight.

Helicopters are inherently unstable, and even experienced pilots find them difficult to control.

Professor Feron rigged up an off-the-shelf X-Cell 60 model with an array of sensors to record its every movement as it was taken through a roll by an expert.

His team created one of the most realistic computer helicopter simulators to help them use the data to devise the control software for the onboard computer.

This had to correct instabilities rapidly while responding to high-level commands sent from its human operators.

The 8kg model helicopter carried a small box containing an array of sensors, including an altimeter, global positioning system receiver and inertial measurement unit, its radio link and the computer.

The sensors enabled the computer to know exactly how the machine was moving. It then relayed signals to servo mechanisms to control the motion.

The findings have been reported to the American Helicopter Society.