Interior noise levels of two propeller driven light aircraft

A test program is described with the objective of determining the relationship between aircraft operating conditions and interior noise and of determining the degree to which ground testing can be used in lieu of flight testing for performing interior noise research. Measurements are presented for single and twin engine aircraft for 2 or 4 passengers. It was found that noise levels are strongly influenced by the rotational speed of the engine and propeller. Both the overall noise and low frequency spectra levels were observed to decrease with increasing high speed rpm operation during flight. Comparison of spectra obtained in flight with spectra obtained on the ground suggests that identification of frequency components and relative amplitude of propeller and engine noise sources may be evaluated on stationary aircraft.