Three-Bladed Propeller Design for the Reduction of General Aviation Radiated Noise Characteristics

The purpose of this study was to design a quiet 3-Bladed propeller for general aviation aircraft. A combination of design technique and analytical predictions using the NASA Aircraft Noise Prediction Program - Propeller Analysis System (ANOPP-PAS) was used to achieve this goal. The propellers were designed for an engine power of 200 hp, a rotational speed of 2,400 RPM and a free-stream speed of 160 kts. A straight 76 in. diameter 2-bladed propeller was designed as a reference for the 64 in. diameter 3-bladed propeller. The ANOPP-PAS computer code was used for predicting the aerodynamic performance and radiated noise characteristics for both the 2-bladed and 3-bladed propeller designs. Through blade design modifications and the use of conventional, as well as specifically designed natural-laminar-flow (NLF) airfoils, 3-bladed propeller designs resulted in predicted noise reductions of 3.4 dB in the near-field which corresponds to 5.1 dBA; and a 3.4 dB (7.0 dBA) in the far-field when compared to the 2-bladed propeller. These 3-bladed designs resulted in no appreciable change in aerodynamic performance but an estimated 43% weight increase