Propeller Acoustics
As drones become increasingly integrated into commercial and urban environments, their acoustic signatures has emerged as a barrier to public acceptance and regulatory approval. Propeller noise, often tonal and high-pitched, reaches high psychoacoustic annoyance factors and has proven difficult to mitigate without compromising aerodynamic performance. This report compares two promising blade geometries—blade sweep and toroidal (looped) designs—for reducing propeller noise while maintaining efficiency. To enable fair comparisons, acoustic metrics are scaled to fixed reference thrust and torque coefficients using an effective radius and tip speed. Experiments were conducted in an anechoic chamber using custom-built rigs to measure thrust, torque, and far-field sound pressure levels for a range of 3D printed propeller geometries. Strong agreement was found between measured aerodynamic performance and theoretical power-law scaling with speed. Similarly, acoustic measurements followed expected scaling with distance and tip speed Among the tested designs, both swept and certain looped blades achieved reduction in overall noise; however, these were offset by reductions in aerodynamic efficiency. The quietest propeller overall was the largest tested, despite the dimensionless analysis.
