FLIGHT MEASUREMENTS OF THE VIBRATORY BENDG AND TORSION STRESS ON A SUPERSONIC-TYPE PROPELLER FOR FLIGHT MACH NUMBERS UP TO 0.95

Vibratory stress measurements were obtained. in flight on a supersonic-type propeller for forward Mach numbers up to 0.95. The magnitude of the vibratory bending stress was low throughout the flight range of the test airplane. Vibratory bending stress was almost pure once-per-revolution stress (l.-P) for flight Mach numbers up to approxImately 0.82. Above this Mach number the wave shape broke down until at a Mach number of 0. 90 the shape was rather complex. An electrical frequency analysis of a vibratory bending record. at a Mach number of 0.90 indicated. that the primary response was at 1.-P frequency (59 cps). A relatively large réspone was indicated at 75 cps which was thought to be the first natural bending frequency of the blade. A maximum vibratory bending stress of ±11,500 pounds per square inch was measured during an air start of the engine at 250 miles per hour at an altitude of 5,000 feet. The stress peaked very rapidly at approximately 750 rpm and decreased to ±4-,OOO pounds per square inch in about 3 seconds time, or by the time the rotational speed. was stabi-lized at 1,000 rpm preparatory to firing the engine. The vibratory torsional stress did not exceed ±2,000 pounds per square inch. There was no evidence of flutter throughout the flight investigation