Experimental Effects of Tip Shape on Rotor Control Loads

Experimental results from tests of a 44-ft-diam helicopter rotor in the Ames 40- by 80-Foot Wind Tunnel are presented. The rotor system employed four interchangeable blade tips of 5% radius with rectangular, tapered, swept, and swept-tapered planforms. The effects of blade planform geometry are compared primarily on the basis of one-half peak-to-peak control loads for a range of rotor lifts at advance ratios of 0.2, 0.3, and 0.38. However, at the higher advance ratio, the presence of substantial high-frequency harmonic loading is noted and found to be significantly influenced by blade tip planform. This should be considered in evaluating the relative merits of the various tips. The swept-tapered tip lowers control load for the high advancing tip Mach number condition.