Two-dimensional Fourier transform analysis of helicopter flyover noise

Odilyn L. Santa Maria, F. Farassat, Philip J. Morris

Research output: Contribution to journalConference articlepeer-review

1 Scopus citations

Abstract

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. 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 separate main rotor and tail rotor noise. 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.

Original languageEnglish (US)
Pages (from-to)130-146
Number of pages17
JournalAnnual Forum Proceedings - American Helicopter Society
Volume1
StatePublished - Jan 1 1999
EventProceedings of the 1999 55th Annual Forum of the American Helicopter Society, FORUM 55 - Montreal, Que., Can
Duration: May 25 1999May 27 1999

All Science Journal Classification (ASJC) codes

  • Transportation
  • Aerospace Engineering

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