Goshawks help researchers determine critical-speed limits for UAVs

The northern goshawk is one of nature's diehard thrill-seekers. The formidable raptor preys on birds and small mammals, speeding through tree canopies and underbrush to catch its quarry. With reflexes that rival a fighter pilot's, the goshawk zips through a forest at high speeds, constantly adjusting its flight path to keep from colliding with trees and other obstacles.

While speed is a goshawk's greatest asset, researchers at MIT say the bird must observe a theoretical speed limit if it wants to avoid a crash. The researchers found that, given a certain density of obstacles, there exists a speed below which a bird - and any other flying object - has a fair chance of flying collision-free. Any faster, and a bird or aircraft is sure to smack into something, no matter how much information it has about its environment.

 A paper detailing the results has been accepted to the IEEE Conference on Robotics and Automation.

• Video: Watch a hawk fly through a dense forest

These findings may not be news to the avian world, but Emilio Frazzoli, an associate professor of aeronautics and astronautics at MIT, says knowing how fast to fly can help engineers program unmanned aerial vehicles (UAVs) to fly at high speeds through cluttered environments such as forests and urban canyons.

Frazzoli is part of an interdisciplinary team that includes biologists at Harvard University, who are observing flying behaviours in goshawks and other birds, and roboticists at MIT, who are engineering birdlike UAVs. With Frazzoli's mathematical contributions, the team hopes to build fast, agile UAVs that can move through cluttered environments - much like a goshawk streaking through the forest.

Speedy intuition
Most UAVs today fly at relatively slow speeds, particularly if navigating around obstacles. That's mainly by design: Engineers program a drone to fly just fast enough to be able to stop within the field of view of its sensors.