The photography of airscrew sound waves

The detail of the problem of airscrew noise has received little attention in the past, and the present research was undertaken to investigate pressure waves in the neighbourhood of an airscrew. It appears that airscrew noise may be considerably reduced by decreasing the tip speed, but the method involves an increase of airscrew- diameter which conflicts with other aspects of efficient design. The effects now considered are those due to the passage of an aerofoil through air, and the fundamental problem examined has wider application than the consideration of noise production. The primary observations are photographs of the pressure wave system caused by an airscrew blade in motion at high speeds; from the wave shape so found, and measurements of the width of the image a method is developed for estimating the pressure amplitude of the wave.