Showing papers by "James E. Hubbard published in 1979"

Parametric Studies of Model Helicopter Blade Slap and Rotational Noise

Abstract: : A parametric study of model helicopter rotor blade slap due to blade/ vortex interaction was studied in an anechoic wind tunnel. The parameters studied were blade number, advance ratio, pitch, and shaft angle. The separate effect of each parameter was studied with other parameters held fixed. The intensity of blade slap was found to decrease with an increase in the number of blades. As the advance ratio was increased to a maximum and then decreased with higher advance ratios indicating a blade slap envelope. The intensity of blade slap was observed to be directly proportional to pitch. The intensity increased with increasing pitch until unsteady lift was encountered, at which time the intensity rapidly diminished. As the rotor shaft angle was increased, the intensity of blade slap was found to decrease to a condition of no blade slap. Directivity measurements were made of blade slap due to blade/vortex interaction in the plane normal to the tunnel wind axis. No blade slap was encountered at the intersection of the rotor disc plane and the plane normal to the tunnel wind axis. The first indication of blade slap occurred at 30 deg below the rotor disc plane and increased in intensity, reaching a maximum intensity at 90 deg below the rotor. In all studies the presence of blade slap was determined subjectively by observing and listening to the transient acoustic signature.