Helicopter rotor noise and airloads in hovering cases are calculated for various tip sweep angles and angles between the blades to obtain geometric conditions of the blades having low noise without the penalty of the performance. The thickness and loading noise are calculated in the frequency domain by using a modified Hanson method especially for a asymmetric rotor having unequal angles between the blades. A NACA 0012 airfoil is used in calculating the strength of the thickness noise. Steady airloadings are calculated to obtain the strength of the loading noise and the performance of the rotor. Nonlinear vortex lattice method is used to represent the rotor blade and Landgrebe's empirical tip vortex and vortex sheet models are used to represent the rotor wake. To calculate the induced velocities due to the vortex system on the blades, a semi-infinite wake integral is employed for the far wake. Good agreements are obtained between the experimental data and the calculated results for both thrust coefficients and circulations along the blade span. For the cases of varying the sweep angles, the lift coefficients near the tip increase as the tip sweep angles increase whereas the lift coefficients in the inborad of the blade decrease. The rotor noises decrease as the sweep angles increase especially at the rotor disk plane, which is explained by using noise vector plots. For the cases of varying the angles between the blades, the lift coefficients on the preceding blades increase as the angles decrease from the 90.deg for the case of the 4 blade rotor whereas those on the following blades decrease. Significant noise reductions are made on the rotor disk plane as the angles decrease. However, it depends on the observer positions."
