For all the government conspiracy militia nuts out there, I’ve got some good news and some bad news. The good news is that there is no such thing as silent, stealth black helicopters. The bad news is that, thanks to Eurocopter’s noise-canceling Blue Edge rotor blades, there soon will be.
The extremely loud noise made by helicopter blades results primarily from the blades chopping through eddies in their own wakes, a phenomenon known as blade-vortex interaction. By changing the shape of the rotor blades, Eurocopter manages to pair down the blade-vortex interaction so thoroughly that the sound only reaches the whisper volume of 3 or 4 decibels.
At least some of the noise associated with helicopters comes from the rotor blades changing pitch twice per rotation. This is a big part of how helicopters fly and isn’t going away any time soon. The 3-4 db lessening of the sound seems much more likely than that the sound is reduced _to_ 3-4 db.
3db is a halving of the noise, which would be really great for people in helicopter intense areas.
Another issue with noise is that the mechanical energy of the noise is quite damaging to the helicopter structure… less noise means longer life and reduced costs.
Of course, the real question is retrofit to Bell and other non-Eurocopter birds.
Statistically speaking rotor blades are harder to find than most elements on the periodic table. That’s just what I heard on MTV.