UAS Propeller/Rotor Sound Pressure Level Reduction Through LeadingEdge Modification

Manned aviation is regulated by the Federal Aviation Administration (FAA) to provide for safe, secure, efficient, and environmentally responsible aviation in the United States. 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) per 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 that operate 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 propellers/rotors. The combination of proximity to the ground, high SPL, and increasing UAS density will most certainly result in a negative public reaction. To minimize the audible impact of UAS, the author sought to minimize the SPL of small UAS propellers/rotors via leading edge modifications. The modification consisting of a leading edge comb was inspired by one of the three characteristics found on the flight feathers of certain owls: leading edge comb, trailing edge tuft, and upper surface porosity. The modifications could successfully reduce SPL while maintaining constant levels of thrust over a wide range of rpm.