"Rotary wings." . . "Noise measurement." . . "Wind tunnel tests." . . . . . . . . . . . . . "Acoustic measurements of a full-scale rotor with four tip shapes"@en . . . "Helicopter design." . . . . "Ames Research Center." . . "Blade tips." . . "Aerodynamic configurations." . . "Helicopters." . . "Acoustic measurement." . .