Hawks, eagles, and other birds of prey have been known to stay aloft for hours on end using a strategic mix of flapping and gliding. Robotic birds can do the same, except that they can't replenish their batteries by snatching a mid-flight snack. However, researchers at the University of Maryland are perfecting a set of flexible solar cell wings that could allow flying bots to stay aloft indefinitely, as long as they get a peek at the sun every so often.

What's particularly clever about integrating solar panels into the bird's wings is that they add minimal weight—at least compared to just tacking them onto its body—and less weight means the Robo Raven needs less energy to stay airborne. That's important moving forward since the researchers still haven't quite bridged the gap between the robot's energy needs and what the solar wings produce.

In its current form the Robo Raven's motors draw about 30 watts of power, while the solar cells in its wings only produce about 3.6 watts, which is a fairly large discrepancy. But as the energy output from its wings is increased in future generations, while the efficiency of its motors is improved, eventually it will break even and the bird will—at least in theory—be able to fly forever once it's launched. And in the world of autonomous drones, that's the brass ring. [University of Maryland via Pursuit of Unorthodox Ideas via IEEE Spectrum]