Noise and Vibration Investigation of the PC-12 Aircraft.

Abstract

Uncomfortable noise vibrations and noise occurred during the flight tests of the first production aircraft of the PC 12. This appeared with different intensity in different aircraft despite their equal production. The vibrations were characterized by a frequent low beat which modulates the aircraft's vibration amplitude close to the frequency of the fourth harmonic of the propeller's rotation frequency at 113 Hz. The frequency of the beat could be influenced by the gas generator setting which in turn drives auxiliary units like electrical generators with a fixed transmission ratio. Vibration measurements were performed in order to investigate the noise of the aircraft during flight. The goal of the test was to identify the modes of vibration which are excited by different sources such as the imbalance of rotating components (propeller, gas generator, electrical generator) or their harmonics. Therefore, tests were performed under different flight conditions. The measured time histories were evaluated off line after the flight tests. The test performance and the data evaluation is described in this report.