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In-Flight Rotorcraft Acoustics Program

S-76 Flight Tests

Photo of S-76 and YO-3A

The S-76C in formation with the YO-3A.

Measurements of S-76C BVI Noise

Acoustic measurements of a Sikorsky S-76C helicopter in flight were compared with acoustic measurements of a full-scale S-76 rotor tested in the 80- by 120-Foot Wind Tunnel at NASA Ames Research Center (Yamauchi, et al., 1993). The flight data were acquired using the NASA Ames YO-3A Acoustics Research Aircraft. Flight and wind tunnel data were compared for three conditions. For the low and moderate advance ratio conditions (figs. 1 and 2, respectively), the BVI pulse widths of the flight and wind tunnel data were very similar, indicating the conditions were well-matched. Comparisons between the flight and wind-tunnel data waveforms for the high advance ratio case (ยต near 0.25) were poor (see fig. 3). For this condition, the wind tunnel data showed greater blade-to-blade and revolution-to-revolution variability than the flight data.

Effects of tip-path-plane angle and advance ratio on the BVI flight data were also analyzed. The flight data showed the BVI peaks increased with increasing tip-path-plane angle until reaching a maximum angle, which varied with flight condition. Further increases in the tip-path-plane angle resulted in reduced BVI peaks. Increasing advance ratio increased the magnitude of the BVI noise for the flight conditions tested.

S-76 data fig.1 Fig1 conditions S-76 data fig.2 Fig2 conditions S-76 data fig.3 Fig3 conditions

Related Publications:

Yamauchi, G. K., Signor, D. B., Watts, M. E., Hernandez, F. J., LeMasurier, P., "Flight Measurements of Blade-Vortex Interaction Noise Including Comparisons with Full-Scale Wind Tunnel Data." 49th Annual Forum of the American Helicopter Society, Stl Louis, MO, May 1993.

See also the references page.

Point of Contact:

C. W. Acree
NASA Ames Research Center
Moffett Field CA 94035-1000