Silent rotor blades could lead to true stealth helicopters

A European company has invented noise-canceling helicopter blades that virtually eliminate the loud air chopping that gives choppers their nickname.

Can you make a silent stealth helicopter?

The Franco-German-Spanish subsidiary of the European Aeronautic, Defense and Space Company, Eurocopter, has invented noise-canceling rotor blades that do away with the loud air chopping that gives choppers their nickname.

Helicopters are so loud because their blades create turbulence as they pass behind one another in their own wakes. The phenomenon is called a "blade-vortex interaction," and it makes for that thwop-thwop-thwop sound signature to helicopters.

By changing the shape of the rotor blades -- the new product is called "Blue Edge" -- Eurocopter has reduced the blade-vortex interaction enough to allow for a sound reduction of just three to four decibels.

Now that's quiet.

Here's what the company has to say about it:

This revolutionary main rotor blade provides a passive reduction in noise levels, using a double-swept shape that is very different from present-day blades. The aim of this program is to reduce the noise generated by so-called blade-vortex interactions (BVI), which occur when a blade impacts a vortex, created at the tip of the blade of any helicopter.

A five-blade Blue Edge main rotor has been flying since July 2007 on an EC155 testbed, logging 75 flight hours and demonstrating noise reductions of 3 to 4 dB, as well as very good performance of the blade. With this safe and simple means of measureable noise reduction for helicopters now validated, Eurocopter is ready to move Blue Edge into production applications.

Don't believe it? Here's a video of the rotors in action:

[via Autopia]

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