Cool stroboscopic effect on a helicopter

If you've seen an old western movie in which a stagecoach rolls into town with its wheels appearing to spin backwards, you're familiar with the stroboscopic effect. It has to do with the movement of something with a consistent pattern (like the spinning spokes on a wagon wheel or the rotors on a helicopter) in relation to the shutter speed of a film or video camera. When the synchronization is just right, you get a cool effect like this...