2 The Vibration and Acoustic Effects of Prop Design and Unbalance on Small Unmanned Aircraft 11 Fig. 2.2 Damaged propeller (left) and undamaged propeller (right) for the Standard 9450S and Low Noise 9455S Table 2.2 Summary of Acceleration Testing of the DJI Phantom 4 Pro with Various Propeller Configurations BladeType Amplitude: pk-pk (m/s2) Increase % Standard Deviation (m/s2) Increase% DJI OEM Standard 72 12 DJI OEM Standard Damaged 127 76 21 75 BTG Standard 67 11 BTG Standard Damaged 160 139 26 136 DJI OEM Low-Noise 70 11 DJI OEM Low-Noise Damaged 93 33 17 55 Helistar Low-Noise 138 22 Helistar Low-Noise Damaged 197 43 30 36 of the propeller, was removed to emulate damage. Figure 2.2 shows the damaged and undamaged props for the 4 types of props studied. 2.3 Vibration Testing To measure vibrations, a PCB Model 333B30 single-axis accelerometer (10.5 mV/m/s2) was attached to the base of the aircraft and the data was collected using a Data Physics Abacus 901 at a rate of 1536 Hz. The data was collected while the aircraft was in a hovering configuration approximately 1–2 meters above ground level. The peak-to-peak amplitude and the standard deviation for the recorded accelerations are shown in Table 2.2. Table 2.2 illustrates several interesting findings observed from the accelerometer data. First, damage had a more dramatic impact on standard prop designs than it did with the low noise prop configurations. In the undamaged state, all props showed similar peak-to-peak and standard deviation amplitudes, except for the Helistar low noise prop. This prop design had significantly higher peak-to-peak and standard deviation amplitudes compared to all other undamaged prop formats. The highest increase in vibration amplitudes due to prop damage was observed in the BTG standard prop model. The lowest increased in vibration amplitudes due to prop damage was observed in the DJI OEM low noise prop model. The Fast Fourier Transform (FFT) of each of the propeller configurations tests are shown in Figs. 2.3, 2.4, 2.5 and 2.6. The FFT plots show the frequency response of the aircraft for frequencies up to 600 Hz.
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