AT-2820 (RP-266) -- Propeller Fan Dynamics II: Dynamic Vibration Test Procedure

Test procedures and a mounting configuration for the vibration testing of propeller fans have been developed and evaluated. The dynamic testing procedures are discussed in this article. To accurately interpret the acceleration data and properly identify the resonance frequencies, it is necessary to obtain a plot of the blade tip acceleration as a function of frequency over the frequency range of interests. Vibration measurements were made on a three-and four-blade propeller fan in a circular downflow unit heater. A subminiature accelerometer (1 gram) was attached to the leading tip of a specified fan blade. The acceleration signal was passed through a slip ring to a charge amplifier and then to a FFT analyzer. The normal operating condition tests yielded results that were in fair agreement with available theory.