Hovering Performance of a Rotor with Slotted Blade Tips

The effect of a slotted blade tip on rotor performance in hovering flight has been investigated. The slotted tip was designed to rapidly diffuse the blade tip vortex and so potentially alleviate vortex induced unsteady airloads and reduce blade vortex interaction noise. Thrust and power measurements were made on a hover whirl tower stand using two- and four-bladed rotors at tip Mach numbers of 0.417 and 0.472. The results for the slotted blade, including the figure of merit, were compared to those of the baseline blade. It was found that the power increases associated with the slotted blade were less than 6% compared to the baseline blade, most of this being a result of increased profile drag associated with the slots. The resulting figure of merit curves showed that the slotted blade was only a few percent less relative to the baseline blade. The work was complemented by further flow visualization studies to examine the effectiveness of the number of slots and the slot positions in terms of diffusing the tip vortex core.