THE PRACTICAL IMPLEMENTATION OF AN ACTIVELY CONTROLLED FLAP TO REDUCE VIBRATIONS IN HELICOPTER ROTORS

This paper describes a study of vibration reduction in a four-bladed helicopter rotor using Individual Blade Control (IBC) implemented through an actively controlled trailing edge flap located on each blade. The first stage of this study, utilizing a simple offset-hinged spring restrained blade model, indicated that the actively controlled flap produced vibration level reduction comparable to conventional IBC, in which the entire blade undergoes cyclic pitch change, but required substantially less power for its implementation. This sequel examines the influence of modifying the model, by replacing the previous dynamic model for the blade by a completely flexible blade model. A deterministic controller is implemented to reduce the 4/rev hub loads using both control approaches. The control studies performed using the flexible blade model and the spring restrained blade model are compared. It was found that despite large increases in vibration levels due to the more realistic model, vibration reduction could still be accomplished without excessive power expenditures or control angle inputs. A careful parametric study in which variations of torsional frequency, spanwise location of the control surface, and hinge moment correction factor was conducted. The results demonstrate the feasibility of this approach.