Download or read book Two Dimensional Fourier Transform Applied to Helicopter Flyover Noise written by Odilyn L. Santa Maria and published by . This book was released on 1999 with total page 70 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Two Dimensional Fourier Transform Applied to Helicopter Flyover Noise written by National Aeronautics and Space Adm Nasa and published by Independently Published. This book was released on 2018-09-21 with total page 66 pages. Available in PDF, EPUB and Kindle. Book excerpt: A method to separate main rotor and tail rotor noise from a helicopter in flight is explored. Being the sum of two periodic signals of disproportionate, or incommensurate frequencies, helicopter noise is neither periodic nor stationary, but possibly harmonizable. The single Fourier transform divides signal energy into frequency bins of equal size. Incommensurate frequencies are therefore not adequately represented by any one chosen data block size. A two-dimensional Fourier analysis method is used to show helicopter noise as harmonizable. The two-dimensional spectral analysis method is first applied to simulated signals. This initial analysis gives an idea of the characteristics of the two-dimensional autocorrelations and spectra. Data from a helicopter flight test is analyzed in two dimensions. The test aircraft are a Boeing MD902 Explorer (no tail rotor) and a Sikorsky S-76 (4-bladed tail rotor). The results show that the main rotor and tail rotor signals can indeed be separated in the two-dimensional Fourier transform spectrum. The separation occurs along the diagonals associated with the frequencies of interest. These diagonals are individual spectra containing only information related to one particular frequency.Santa Maria, Odilyn L.Langley Research CenterFOURIER TRANSFORMATION; AIRCRAFT NOISE; FOURIER ANALYSIS; AERODYNAMIC NOISE; AEROACOUSTICS; HELICOPTERS; SPECTRUM ANALYSIS; FLIGHT TESTS; TAIL ROTORS
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Download or read book On the Use of the Noncentral Chi square Density Function for the Distribution of Helicopter Spectral Estimates written by and published by . This book was released on 1993 with total page 46 pages. Available in PDF, EPUB and Kindle. Book excerpt:
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