Comparison of model helicopter rotor primary and secondary blade/vortex interaction blade slap

Abstract

A study of the relative importance of blade/vortex interactions which occur on the retreating side of a model helicopter rotor disk is described Some of the salient characteristics of this phenomenon are presented and discussed It is shown that the resulting secondary blade slap may be of equal or greater intensity than the ad vancing side (primary) blade slap Instrumented model helicopter rotor data are presented which reveal the nature of the retreating blade/vortex interaction The importance of secondary blade slap as it applies to predictive techniques or approaches is discussed When secondary blade slap occurs it acts to enlarge the window of operating conditions for which blade slap exists Nomenclature B = number of blades c =chord CT = thrust coefficient thrust/pIIK2 (ttR)2 CT/a = blade loading R = rotor radius V = tunnel speed x/c = nondimensional chordwise position ots = shaft angle Os = pitch at tip =0T A = vortex/blade interaction angle fj, = advance ratio V/SIR p = density of air a = rotor solidity Bc/HR Q = angular velocity