Imagine an Apache or a Cobra equipped with one of these rotor blades. Silent and Deadly comes to mind. blade-vortex interaction is the physical phenomenon that causes the ear piercing noise you hear when a helicopter is near. Eurocopter engineers have developed a new kind of rotor blade called Blue Edge that reduces the noise. The blades are beautiful one of those things where function follows form and not the other way around as it usually does.

Photo: Eurocopter

Eurocopter video showing the reduction in rotor noise acheived in flight tests of its Blue Edge blade on an EC155 helicopter. Compared with a conventional blade, the Blue Edge has a tip with both forward and rearward sweep. Eurocopter says this gives the blade more time to interact with the vortex shed by the rotor, reducing the characteristic impulsive (slap-slap) blade-vortex interaction noise generated by a helicopter.