Noise from Propellers with Symmetrical Sections at Zero Blade Angle
This is a 1937 NACA Technical Note, issued by the National Advisory Committee for Aeronautics for aeronautical engineers and researchers, reporting measurements of noise from propellers with symmetrical blade sections at zero blade angle. The pictures show a sound analyzer trace, a bench of acoustic measuring equipment, and a motor with a propeller and microphone mounted on a post over water. For designers, they offer period laboratory-technical imagery: oscilloscope-style waveform strips, dense instrument panels with labelled dials, and an outdoor test rig.
