Sound Pressure Level Measurements with Standard and Low Noise Propellers on a Phantom 4 Pro+

One environmental issue regulated by the FAA is the noise created by aircraft. Federal Aviation Regulation (FAR) Title 14 Part 36 deals specifically with sound pressure levels (SPL) according to aircraft type when the aircraft are in close proximity to the ground. Minimizing aircraft noise helps to maintain positive relationships between the aviation community and the general public. Unmanned aircraft systems (UAS) are a very rapidly growing segment of the aviation industry within the National Airspace System (NAS); however, there is currently no regulation for UAS SPL. The UAS are regulated, as of August 29, 2016, such that they are mandated to be in close proximity to the ground (no higher than 400 ft). As with manned aircraft, UAS produce high levels of SPL, much of which is due to the rotors. The combination of close proximity to the ground, high SPL, and increasing UAS density will most certainly result in a negative public reaction. In order to minimize the audible impact of UAS, the author seeks to minimize the SPL of small UAS propellers/rotors via experimental rotor modifications. These modifications were inspired by the characteristics found on the flight feathers of certain owls. The modifications were evaluated individually and optimized on two-bladed rotors on thrust stands. The most recent phase of the project collected SPL data from a DJI Phantom 4 Pro+ UAS in flight with standard and low noise