News from the helicopter world via Wired: Eurocopter is developing technology to reduce the noise generated by helicopters.   The first technology is a different blade design.   Instead of a straight-edge blade, angles are built-in to the blades:


In addition to the Blue Edge rotor blade, the company also introduced something called Blue Pulse technology. Also designed to reduce helicopter noise, the Blue Pulse system uses three flap modules in the trailing edge of each rotor blade. Piezoelectric motors move actuate the flaps 15 to 40 times per second in reduce the “slap noise” often heard when a helicopter is descending.

Both of these technologies are able to reduce noise by minimizing the blade-vortex interaction of the main rotor on a helicopter. Blade-vortex interaction is the source of the pulsating sound most of us are familiar with when helicopters fly overhead. The noise is created when a rotor blade hits the wake vortex left behind from the blade in front of it.

Here’s a demo:

Pretty amazing.   I’d say look for this technology in those unmarked black helicopters, but you won’t hear them coming.