NOISE CHARACTERISTICS OF A MODEL TILTROTOR

Acoustic data have been acquired on a tiltrotor model in the NASA Langley Research Center 14- by 22-Foot Subsonic Tunnel. This isolated rotor model was a 15 percent scale, 3-bladed, JVX rotor, and was tested at forward speeds from 45 to 100 knots, shaft angles corresponding to nacelle tilts from 60 to 95 degrees, and descent glideslopes of 0, 5, and 10 degrees. The acoustic data were acquired in a horizontal plane below the rotor using a traversing microphone array, and are presented in contour maps showing the directivity of the noise generated by the rotor. Selected contour maps, time histories, and narrowband spectra are presented to show the noise reduction potential of varying nacelle tilt and glideslope. In addition, trends of maximum noise generation as a function of operating condition are also presented for a large number of conditions.