THEORETICAL AND EXPERIMENTAL INVESTIGATIONS INTO HELICOPTER AIR RESONANCE

The validation of theoretical predictions for the characteristics of the aeromechanical instability known as air resonance has been obtained by the use of a 2m diameter Froude scaled model of the Lynx helicopter. The theoretical and experimental models are described and a simple explanation of the mechanism involved in air resonance is given. The results of an investigation into the effect of rotor in-plane stiffness, fuselage roll inertia, rotor speed and blade incidence on the regressing lead-lag mode stability are presented. A theoretical study of the importance of coning angle and forward flight on air resonance stability is also discussed. In general good agreement has been obtained; sufficient to give confidence in the use of the theory as a design tool.