Spy planes to recharge by clinging to power lines

Paul Marks

The next time you see something flapping in the breeze on an overhead power line, squint a little harder. It may not be a plastic bag or the remnants of a party balloon, but a tiny spy plane stealing power from the line to recharge its batteries.

The idea comes from the US Air Force Research Lab (AFRL) in Dayton, Ohio, US, which wants to operate extended surveillance missions using remote-controlled planes with a wingspan of about a metre, but has been struggling to find a way to refuel to extend the plane's limited flight duration.

So the AFRL is developing an electric motor-powered micro air vehicle (MAV) that can "harvest" energy when needed by attaching itself to a power line. It could even temporarily change its shape to look more like innocuous piece of trash hanging from the cable.

Hanging about
AFRL's initial aim is to work out how to make a MAV flying at 74 kilometres per hour latch onto a power line without destroying itself or the line.

In addition, so as not to arouse suspicion, AFRL says the spy plane will need to collapse its wings and hang limply on the cable like a piece of wind-blown detritus. Much of the "morphing" technology to perform this has already been developed by DARPA, the Pentagon's research division. Technologies developed in that program include carbon composite "sliding skins", which allow fuselages to change shape, and telescopic wings that allow lift to be boosted in seconds by boosting a wing's surface area.

Challenges abound, though. Zac Richardson, a power-line engineer with National Grid in the UK, warns that if the MAV contacts an 11-kilovolt local power line, it could short circuit two conductors, causing an automatic disconnection of the very power the plane seeks.

And, on a 400 kilovolt inter-city power line, it risks discharging sparks. "It will hang there fizzing and banging and giving its position away anyway," says Richardson.

"Even kites falling across power lines cause breakdowns," adds Ian Fells, an expert in electricity transmission based in Newcastle, UK. "It's an utterly bizarre idea to try to land a plane on one."

Regardless of the challenges faced, AFRL plans test flights in 2008.