{'fraction_non_alphanumeric': 0.013818181818181818, 'fraction_numerical': 0.002909090909090909, 'mean_word_length': 5.460093896713615, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
The reduction of quadcopter propeller noise

Fan affinity laws are combined with a simple scaling relationship for fan noise to 
show that truly significant reductions in propeller noise can be achieved by increasing the propeller diameter while reducing its rotational speed, thereby reducing its 
blade tip speed, while maintaining a given level of static thrust. Fan affinity laws 
are also used to show that efficiency improvements accompany the reductions in radiated noise. The significant reductions in noise and increases in efficiency predicted 
from the scaling relationships are verified experimentally by measuring the radiated 
noise and power requirements for both large, slowly rotating propellers and small, 
high-speed propellers, at equivalent static thrusts, where the large propellers serve 
as possible replacements for the small propellers in typical quadcopter applications. 
The bulk of the noise reductions offered by large and slowly rotating propellers compared with small, high-speed propellers are shown to be maintained at equivalent net 
force (thrust minus weight) conditions, as required for practical implementation into 
a quadcopter UAV, even using readily available hobby grade components. Further 
significant noise reductions are possible with lightweight and custom engineered 
components. © 2019 Institute of Noise Control Engineering