Noise Tests on a General Aviation Aeroplane 4-stroke Piston Engine.

The overall noise from propeller driven General Aviation aeroplanes is due in part to piston-engine noise. Therefore engine noise cannot be neglected when developing corresponding noise reduction measures for such aeroplanes in trying to meet future - possibly rather stringent - noise limits. An engine noise test facility was developed and initial tests were performed on a Lycoming IO-360 engine. The engine exhaust, rather than direct engine-housing vibration caused radiation, was identified as the prime source of engine noise. Spectral characteristics and radiation directivities were determined for different operational conditions as well as the dependence of the overall noise on full and part throttle engine power. The transmission loss of a typical commercially available exhaust muffler was determined to be sufficiently high (in terms of overall A-weighted levels) essentially because the test engine's noise