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.

Air Force Research Laboratory

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.

Via New Scientist