The Cross-coupling Problem of Helicopter Rotors - A Review

Abstract

Until recently it was beyond the capability of helicopter rotor models to predict correctly the cross-coupling response. During the mid-nineties it became clear that wake distortion effects are the main contributors to the cross-coupling response. Wake distortion effects can be modeled by using detailed free or prescribed wake models. However, these models require large computer resources and long computing times, thus they are not suitable for various applications. In such cases dynamic-inflow models can be corrected to account for the missing effect, by using the wake distortion coefficient or an aerodynamic phase lag. Recently, a new actuator disk model was developed where the wake distortion effect is obtained as an integral part of the derivation. In the paper all the methods of considering the wake distortion effects are reviewed and compared. The results of the various models are also compared to flight test results. Conclusions are drawn and further necessary research is identified.