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In this paper, small-scaled blade prototypes with the flap-driving mechanism, called SNUF (Seoul National University Flap), were manufactured, and tested in order to realize vibratory load reduction in the rotor system. It was achieved by an active trailing-edge flap which is based on piezoelectric actuator. However, it turned out that the target value of the flap deflection angle was not accomplished in the previous designs. Therefore, the flap driving mechanism needs to be amended. Thus, a new piezoelectric actuator was selected to achieve the target deflection by considering the nonlinear relationship between flap deflection angle and the moment arm length. Re-selection of the actuator required increase of the blade inner space and its size. Therefore, it was required to validate the cross-sectional design of the improved blade configuration. So as to verify the structural integrity, crosssectional analysis was conducted by using UM/VABS. After achieving a satisfactory result of the non-rotating static test of the new flap-driving mechanism, a prototype blade will be manufactured and tested in the whirl tower.

Purpose The purpose of this paper is to present the design, analysis and experiments of the active trailing-edge flap (Seoul National University Flap, SNUF) for vibration reduction in the helicopter rotor prior to the small-scale blades planned to test in a whirl tower. Design/methodology/approach The predictions of the hinge moment in both steady and unsteady flows were obtained through computational fluid dynamics calculations. When compared with the results originated from analytical formulations, the proposed method showed improved prediction capabilities. To validate the deflection of the flap under the centrifugal load by rotating, static analysis was conducted using both contact and rotating condition of MSC NASTRAN. The corresponding experiment also was performed using the vertical frame for simulating the effect of the centrifugal force. Findings The hinge moment of the flap is predicted through unsteady analysis in the actuation frequency of 3/rev. The material of the guide in the flap mechanism was selected through static analysis under both contact and rotating condition. Finally, reduction of the deflection occurred because of the load in the axial direction of the hinge like the centrifugal load. Practical implications The important aspects, such as design, analysis, and experiments for the active trailing-edge flap were shown. Originality/value This paper showed the relationship of the displacement, block force and voltage of the piezo-actuator, combined with the hinge moment predicted. The methodology and the experiment were presented for simulating the centrifugal force acting on the flap.

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