THIS paper presents a brief historical review of the quest for information concerning the mechanism of aircraft noise generation.
It is shown that, after a number of false hypotheses, the noise of propellers was finally traced to the principal aerodynamic loads of the blades. The intensity and characteristics of the noise can now be predicted theoretically from knowledge of the geometry and operating conditions of the propeller.
With regard to jet noise, the picture is not so clear. The actual mechanism of noise generation is still somewhat obscure. Included here is a resume of United States and British work on determining the actual source of noise. Experiments on devices for reducing noise are also discussed.