The blades design is striking, but not new. We have seen those before - a similar contraption is being used by Eurocopter engineers to attenuate the noise caused by blade-vortex interaction, the noisy whoop-whoop-whoop swooshing sound made by the helicopter's rotor.
In the stealth Eurocopter prototype there's also another technology called Blue Pulse, which adds piezo-electric flaps that move up and down at 15 to 40 times per second to the blades' edge to help cancelling the blade-vortex interaction.
It's not hard to believe that the Chinook used in the attack - as recently confirmed by off-the-record sources at the Pentagon - would have this technology too, along with others taken from the stealth RAH-66 Comanche, like heat-absorbing paint. After all, the traditional twin-engine CH-47 Chinook is made by Boeing, which participated in the development of the RAH-66. [David Cenciotti via Danger Room]