Effect of Propeller Blade Spacing on Quadcopter’s Aeroacoustic Noise and Sound Quality

quietdrones2026 Tracking Number 30

Previous studies have demonstrated that propeller and blade geometry are primary contributors of aeroacoustic noise in propeller‑driven vehicles. This raises the question: how does the noise signature of an Unmanned Aircraft System (UAS) equipped with two aerodynamically similar, but geometrically different propeller set change? To investigate this, an outdoor measurement campaign was conducted to characterise the acoustic response of the vehicle operating with two aerodynamically equivalent, two-bladed, low-Reynolds-number propeller sets with different blade spacing angles. The acoustic energy distribution across the frequency spectrum induced by propeller geometry is examined for three distinct flight operations: take-off, hovering, and landing. These operations were characterised using a set of acoustic descriptors ( LAmax, LAeq and LAE). By keeping operational conditions (e.g., altitude and speed) and design parameters (e.g., number of blades and motors, and vehicle mass) constant, significant differences in the emitted noise were observed as a function of propeller blade-spacing angle. A shift of acoustic energy toward the low-frequency range and a redistribution of high harmonics were observed when the vehicle operated with the altered blade-spacing-angle propeller compared with the baseline propeller configuration. This spectral modification affected the evaluated sound quality metrics (e.g., loudness, sharpness and tonality). Variations exceeding the just noticeable difference thresholds in the sound quality metrics indicate that modifying propeller design can plausibly alter perceived noise while maintaining aerodynamic performance.