Interior Noise and Vibration Measurements on Operational Military Helicopters and Comparisons with Various Ride Quality Criteria

Abstract : This paper presents physical measurements of the interior noise and vibration obtained within eight operational military helicopters. The data were analyzed and are presented in the following forms: noise and vibration spectra, overall root-mean-square acceleration levels in three linear axes, peak accelerations at dominant blade passage frequencies, acceleration exceedance data, and overall and A-weighted sound pressure levels. Peak acceleration levels were compared to the ISO 1-hr reduced comfort boundary, the fatigue decreased proficiency boundary, and the NASA discomfort criteria. The A-weighted noise levels were compared to the NASA annoyance criteria, and the overall noise spectra were compared to MIL-STD-1294 ( Acoustical Noise Limits in Helicopters ) . It is shown that specific vibration components at blade passage frequencies for several aircraft exceeded both the ISO reduced comfort boundary and the NASA passenger discomfort criteria. The A -weighted noise levels, corrected for SPH-4 helmet attenuation characteristics, exceeded the NASA annoyance threshold for several aircraft. The spectral components of the noise at cruise, corrected for helmet attenuation, fell within the limits of MIL-STD-1294 for all aircraft.