Acoustic Characteristics of a Model Isolated Tiltrotor in DNW

An aeroacoustic wind tunnel test was conducted using a scaled isolated tiltrotor model. Acoustic data were acquired using an in-flow microphone wing traversed beneath the model to map the directivity of the near-field acoustic radiation of the rotor for a parametric variation of rotor angle-of-attack, tunnel speed, and rotor thrust. Acoustic metric data were examined to show trends of impulsive noise for the parametric variations. BVISPL maximum noise levels were found to increase with a for constant micron and C(Tau), although the maximum BVI levels were found at much higher a than for a typical helicopter. BVISPL levels were found to increase with mu for constant alpha and C(Tau). BVISPL was found to decrease with increasing C(Tau) for constant alpha and mu, although BVISPL increased with thrust for a constant wake geometry. Metric data were also scaled for M(tip) to evaluate how well simple power law scaling could be used to correct metric data for M(tip) effects. Presented at the American Helicopter Society Annual Forum (55th) held in Montreal, Canada on 25-27 May 1999. Published in the Proceedings of the American Helicopter Society Annual Forum (55th), May 1999.