This is pretty cool:
Wired said:Just about every helicopter operator is quite familiar with noise complaints. Whether it be the local news helicopter or even a medical helicopter, many people on the ground don’t like the sound created by rotary-wing aircraft.
This week Eurocopter unveiled its most recent effort to reduce helicopter noise with the radical-looking Blue Edge rotor blade. The new blade has been tested on one of the company’s EC155 helicopters and was shown to reduce noise 3 to 4 decibels, according to the company.
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.
You can listen to a cockpit recording of Eurocopter’s EC155 with and without the Blue Edge rotor below.
Normally, the entire length of the rotor blade interacts with the vortex of the preceding blade. With the Blue Edge rotors, the double-swept tips of the rotor blade reduce the length of the blade-vortex interaction, and it does it at the tip where the blades are moving the fastest relative to the air. The result is a decrease in the sound produced due of the wake interaction at the tip.
Both the new rotor blade and trailing edge flaps are part of what Eurocopter is calling its “Bluecopter” technology. The company says the goal is to create more environmentally friendly helicopters from both a noise and emissions standpoint. We reported on Eurocopter’s plan for a fuel-efficient diesel helicopter on Wednesday.
No confirmation from Eurocopter, but in avoiding putting the “green” label on their efforts, the company appears to be borrowing from everybody’s favorite movie helicopter legend, Blue Thunder. The 1980s cinematic masterpiece features a helicopter made by what is now Eurocopter, an Aérospatiale Gazelle. And one of the helicopter’s most impressive technologies was its “whisper mode” that allowed it to fly around as quiet as a glider. Could just be a coincidence.
Read More http://www.wired.com/autopia/2010/02/eurocopter-moves-one-step-closer-to-whisper-mode/#ixzz0gg6McDKD