Propeller acoustic exper iments have been completed on the ground.The experimental results show that the aerodynamic and acoustic performances of 4 bla des ARA D propeller are better than that of the 3 blades NACA64 propeller.The sound field of propellers has directional properties

and i t is dominated by discrete tones

especially the 1～5×BPG tones.So

increase of the blade number and application of the advanced aerofoil w ill be very effective to improve aerodynamic and acoustic performances of the propeller.The best way for propeller noise reduction and aircraft fuselage noise suppression is a try to reduce the propeller discrete tones

especially the 1～5×BPF tones.