HELICOPTER ROTOR NOISE GENERATION AND PROPAGATION
Final rept., 28 May 1964-31 Aug 1965
UNITED TECHNOLOGIES CORP STRATFORD CT SIKORSKY AIRCRAFT DIV
Pagination or Media Count:
An improved method is presented for calculating rotor system overall vortex noise and frequency spectra for stalled and unstalled rotors. Correlation of measured and predicted vortex noise was evaluated using two rotor systems operating over a wide range of speeds and thrusts. Correlation was found to be excellent. Blade tip planform studies revealed significant vortex noise reductions with tapered tips. A new procedure is also derived for calculating near and far field rotor rotational noise with nonuniform inflow. The method extends the standard steady load method by including the effects of harmonic airloads. Correlation studies were conducted using an H-34 helicopter. Agreement between low frequency measured and predicted noise was good. However, correlation with high harmonic rotational noise was poor. This is probably due to inadequate definition of high harmonic airloads. The study was performed for single rotor systems only, and in its present form is not directly applicable to systems with multiple rotors in juxtaposition.