Stealth(ier) Helicopter



The aviation company Eurocopter is developing noise-reducing helicopter blades that could minimize the sound that a helicopter makes:

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.


Video at the link.

Link via Popular Science | Photo: Eurocopter

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Actually, a 3 to 4 Db reduction makes quite a difference: because of the way the Db scale works (it's logarithmic, apparently), for every 3 DB reduction, the sound we perceive is halved in intensity. So yes, please bring on the fancy blades for trauma helicopters that operate from inner city hospitals while I'm trying to get some sleep. Please? Thanks.
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So- Don't be impressed.

But if you look and listen at the vid in the lnk, you see that the sounddistribution is changed so much that even if the reduction is only about 3-4 db's, it is mostly a reduction in the high pitch that bothers us humans.

And that means that to the human ear the sound of those blades dissapears far more that only 3-4 db's.

Where I work, I get a lot of choppers circling over my head. Pléáse give me choppers with those new blades any day!!!
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I will grant that once you get past 100dB, a 5dB increase halves the amount of time you can hear it without damage. But I'm still not impressed.
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"We've landed totally undetected, thanks to the my genius in creating the noiseless shush-copter!"

http://www.imdb.com/title/tt0081249/quotes
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