In an urban setting, the sound level of a drone must be acceptable. This paper compares a stock DJI Phantom 2 propeller to a stock propeller modified with a Trailing Edge (TE) notch. The purpose was to determine the extent of the near and far field noise signature of the propellers. Measurements were taken in an anechoic chamber at measurement distances of 1 ft to 24 ft. Upstream of propeller, the sound decay follows the standard decay rate (6 dB decrease for a doubling of the distance) from a location of approximately 4 ft. Downstream the sound decay does not follow standard decay rates until 22 ft. A comparison of the two propellers shows that the TE notch and stock propellers have similar Sound Pressure Level (SPL) values at all distances measured. Traverse measurements downstream of the two propellers in the wind tunnel confirms that the magnitudes of the SPL values are similar after a distance of one foot, however, there does seem to be an influence of the TE notch on the frequency spectrum, shifting frequencies slightly higher.
In addition to the single propeller tests, a DJI F550 Flame Wheel hexacopter was used to compare the stock and TE notch propellers. While the hexacopter was overall 20 dBA nosier, no discernable difference in SPL between the two propellers was measured.