Synthesized propfan interior noise

Abstract

Recent fuel‐conservation measures have led to increased interest in propeller‐driven aircraft for commuter as well as long‐haul applications. The increased fuel efficiency of these vehicles could be offset, however, if passenger acceptance necessitates increased aircraft weight for purposes of noise reduction. Thus, a laboratory investigation was conducted to describe passenger acceptance criteria for the interior noise environment of these vehicles, and as a corollary, to assess the validity of various noise descriptors or metrics for quantifying the interior noise environment. The investigation was conducted in the passenger ride‐quality simulator located at the NASA‐Langley Research Center. The tests involved a total of 96 subjects which evaluated synthesized propeller noises using a nine‐point discomfort category scale. The sounds consisted of a turbulent boundary‐layer noise with a factorial combination of blade passage frequencies (50, 80, 100, 125, and 200 Hz), harmonic rolloffs (0 and 10 dB harmonic), tone/noise ratios (0, 10, and 20 dB), and noise levels (85, 90, 95, and 100 dB). The results indicate that noise‐level and blade‐passage frequency are the primary noise characteristics that determine passenger reaction. Although A‐weighted noise level was determined to be the most accurate predictor, additions of up to 8 dB (Corrections) were required in some cases to fully account for passenger reactions.