Propeller Tip Flutter
A 1932 NASA technical report on propeller tip flutter, a research document prepared for aeronautical engineers and aircraft designers studying vibration in propeller blades. Its four pictures are plates of high-speed film frames showing a rotating blade model in sequence, a graph of oscillation traces, and a chart of flexural frequency against revolutions for different chord-to-length ratios, which a designer might take as a record of how rotating blade tips bend and vibrate under load.
