A flight investigation of the spanwise lift requirements of a helicopter rotor blade

Abstract

Surface roughness has been applied systematically to portions of the leading edge of the blades of a Wessex helicopter to reduce the local value of the maximum lift coefficient. The extent to which the inner portions of the blade could sustain a reduced maximum lift coefficient without reaching limiting control loads has been investigated. In this way, some measure of the degree to which reflex camber, with the associated small reduction in maximum lift coefficient, might be used inboard to offset the undesirable pitching moments of high performance sections nearer the blade tip, has been obtained. In a similar way, but using local radial bands of roughness in the tip region, those areas of the blade which can provide the largest potential gain from an improved lifting capability have been identified.