Propeller blade vibration nature and severity of vibration at edgewise resonance as influenced by coupling effects due to blade twist

Abstract

Information was required as to the stress distribution in propeller blades occurring at edgewise resonance, and the importance of this vibration relative to the other modes. Tests were carried out on a duralumin-bladed propeller so mounted that the dynamical system was equivalent to an engine and propeller subjected to engine torsional oscillation. The fundamental edgewise vibration and its interaction with the adjacent second overtone flapping vibration was investigated for non-rotating conditions. Edgewise resonance is important in so far as the twist of the blade causes unsymmetrical bending on the blade sections. In normal blades this twist results in large deflection in the plane of greatest flexibility, the accompanying stresses being of the order of 70 per cent. of those occurring at the second overtone flapping resonance for the same excitation. The effects of blade twist on the vibration of rotating propellers will be examined as opportunity affords.