Some calculations for air resonance of a helicopter with non-articulated rotor blades

Abstract

This Report describes an analysis of air resonance in the hover, and the solutions obtained for a helicopter with non-articulated blades. It is shown that stability in air resonance depends critically on blade structural and aerodynamic parameters that are not easily estimated with the required accuracy, and that a calculation technique requires careful, positive correlation with experiment before its accuracy can be accepted. The effectiveness of model rotor experiments for checking data is considered, and measurements of rotor impedances show promise of providing a useful basis for comparing with theoretical equivalents. The effect of an autostabiliser designed to counteract the conventional helicopter instabilities in pitch and roll is investigated. It is found that such an autostabiliser destabilises the air resonance mode.