Model helicopter rotor impulsive noise

An investigation of helicopter rotor blade slap was performed on a 1·27 m diameter model rotor. The rotor blades were a NACA 0012 section with a −8° linear twist. The experiments were conducted in the M.I.T. Anechoic Wind Tunnel. The effects of number of blades, blade pitch, advance ratio, and shaft angle on the generation and intensity of blade slap have been investigated. The effect of each parameter was determined by varying the parameter of interest while keeping the other constant. The rotor tip speeds of the tests performed in this study were limited to approximately Mach 0·4. The directivity associated with the blade slap signature was measured. The results of this investigation are based on a subjective definition of blade slap.