Linear Analysis of Vibration Reduction Using an Active N-Bladed Helicopter Rotor

In the field of active rotor control, the use of individual blade control (IBC) systems for vibration reduction is a major topic of research. However, as most studies are focused on a specific helicopter rotor, the influence of topological rotor parameters, such as the number of rotor blades, is seldom investigated. The present investigation analyzes vibration reduction using an IBC system in a very general manner with particular focus on the influence of the number of rotor blades. To this end, a model for the quasi-steady transfer behavior of an IBC rotor with an arbitrary number of rotor blades is derived as a function of the blade transfer behavior using only a minimal set of assumptions. Using this model, a minimal set of blade-root load components relevant for the rotor hub loads is determined. Based on this set of components, a coordinate frame of effective blade-root loads is introduced. Subsequently, the vibration reduction potential for the N-bladed rotor is assessed, showing no direct relation between the number of rotor blades and the vibration reduction potential. Finally, the assumptions for the model, as well as the results of the investigation of the vibration reduction potential, are validated using open-loop flight data.