Multirotor electric vertical take-off and landing vehicles and small unmanned aircraft systems commonly use distributed electric propulsion. One approach to reducing their noise involves synchronizing rotor phase relationships to control radiated noise directionally. This paper presents a practical electronic phase synchronization method for multirotor aircraft, experimentally evaluates its effectiveness using a hexacopter in an anechoic chamber, and investigates how vehicle configuration influences noise control capability. Harmonic noise reductions of 10 dB are demonstrated over a 20° azimuthal arc, with limited increases in other directions. Noise amplification of 6 dB is also achieved over the same region. Global reductions of 6 dB across nearly all observer angles are obtained using alternative rotor phase offsets. Statistical analysis of phase controller error indicates that maintaining phase accuracy within 5° is necessary for 10 dB attenuation. Simulations across various rotor configurations show consistent noise control performance, with higher rotor counts enabling greater directional control of radiated noise.
Valente et al. (Wed,) studied this question.