Evaluation of the influence of diameter propeller on the acoustics characteristic of the power plant by the light aircraft

The article presents the results of the performed computational and experimental studies of the influence of the propeller diameter on the acoustic characteristics of the power plant (PP) by the light aircraft to determine the method of community aircraft noise reduction of this class of aircraft by changing the diameter of the propeller while maintaining the aerodynamic and geometric similarity and propellers invariance of the rotation frequency. The experimental method is based on a comparative analysis of the measured under static conditions of acoustic characteristics by the power plants of light propeller aircraft MAI-223M and F30, differing only in the propeller diameter and thus tip speeds at a constant frequency of rotation propellers. Calculated estimate is based on semiempirical method for calculating propellers noise. As a result of the research it has been found that a slight decrease in the diameter of the propellers on the 3.3 % leads to the reduce of the total noise power plant light aircraft by 1.5 dB. At the same time the estimated value of the expected reduction of tonal loading propeller noise is 1.2 dB. The difference between the calculated and experimental data is explained by the fact that the calculation does not take into account the thickness noise. Based on semiempirical model propeller noise ratio is obtained to determine the effect of the propeller diameter on the load propeller noise on the condition of the geometric and aerodynamic similarity propellers, and at a constant rotation frequency. Comparison of sound power levels of high-frequency broadband radiation (1000-5000 Hz) PP aircraft MAI-223M and F30, with aerodynamically similar propellers of different diameters, showed that the difference in the sound power level may be related not only to the difference in the diameter of the propellers but the presence of other sources of noise generation related to the arrangement of the power plant for propeller aircraft (particularly wrap inductive flow from the propeller the inlet oil cooler of the engine).