If you thought a single quadrotor with some aggressive flying moves was spooky enough, wait until you see four of them flying in perfect formation.

The GRASP Lab at the University of Pennsylvania is doing some interesting work with UAV quadrotors–tiny four helicopter blade unmanned aerial machines that are as deft as hummingbirds. In the above video they’re demonstrating a new addition to the program, the ability of the quadcopters to fly in formation and maintain formation even when units are removed from the configuration. It’s an impressive display and more than a little unsettling (the hornet like humming of the group certainly doesn’t help matters).

Trajectory Design and Control for Aggressive Formation Flight with Quadrotors [YouTube via IEEE Spectrum]