The Noise from Piston Engine Driven Propellers on General Aviation Airplanes

Kurzfassung

Analysis of extensive flyover noise data from piston engine powered propeller aeroplanes (General Aviation Aeroplanes) revealed the occurrence of - at first sight quite unexplainable - additional noise components which were, however, clearly related to propeller operation. It turns out that such "excess" propeller noise is a direct result of a nonuniform rotation of the piston engine crank- shaft which causes unsteady aerodynamic propeller blade-loadings. Associated propeller noise characteristics were determined in the framework of wind tunnel tests for a number of full-scale piston- engine/propeller combinations. The subject noise type was found most pronounced at low helical blade-tip Mach numbers and in the forward and the rear arc directions. Azimuthal noise directivity was no longer omnidirectional. Moreover, overall A-weighted propeller noise levels were found to increase by more than 5 dB as a result of such RPM-nonuniformity vs. that of a propeller.