Abstract
An experimental quiet aircraft has been developed by LMSC for research in quiet aircraft technology. This company-owned aircraft, designated the Q/Star, had minimum acoustic signature as its principal design goal. To achieve this goal several significant noise-reduction features were employed. A relatively clean aerodynamic design reduced aerodynamic noise. A “Wankel”-type rotary combustion water-cooled engine was selected to avoid noise-reduction problems associated with air-cooled engines. The muffler system was designed to be most efficient at cruise flight conditions and the system was “tweaked” in the field for maximum performance. The propeller is driven through a 5.34:1 reduction system to provide propeller tip speeds less than Mach 0.2. Over all, these design features have produced an exceptionally quiet airplane. A series of flight tests have been conducted using a variety of propellers including one designed specifically for acoustic noise performance. Data are presented to show aircraft flyover acoustic noise signature as functions of propeller configuration, engine rpm, and air speed.
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