| 摘要 |
The noise reduction system uses a second propeller (3) adjacent the main drive propeller (1) operated so that the sound waves emitted by the two propellers cancel each other out over at least part of the frequency spectrum. Pref. the noise frequency spectrum of the main drive propeller (1) is measured using a sensor coupled to a synchronisation device for the second propeller (3) which generates an approximately identical noise spectrum. The noise cancellation effect is obtained by the relative angular offset of the two propellers (1, 3). Pref. both propellers (1, 3) are positioned coaxially and are rotated at the same rate. USE - For reducing noise produced by propeller aircraft or helicopter.
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