A study on the noise characteristics and blade performance of a biplane was conducted to reduce the fluid noise generated by a drone propeller. The effects of the gap (G) and the angle (θ) between the wings of the biplane on thrust were investigated experimentally and numerically. It was found that at θ = 0°, the thrust generated by the lower wing is considerably lower than that of the upper wing, but it was recovered by adjusting G and θ. However, even the biplane with the highest thrust in this study produced only 80% of that of the two monoplanes. Next, the noise and efficiency of the biplane were compared with those of the monoplane under identical thrust condition. For all biplane cases considered, efficiency (FM) and fluid noise were improved compared to those of monoplane. These results are considered to be mainly due to the lower rotational speed. However, since motor noise was highly variable and affected the fluid noise results, improving the accuracy of noise measurements remains an important challenge for future work.
Sawa et al. (Wed,) studied this question.