Analytical and Experimental Evaluation of an Active Trailing-edge Flap (ATF) for Vibratory Loads Reduction in Rotorcraft

Abstract

This dissertation focuses on improving a Mach-scaled helicopter rotor blade prototype with a flap-driving mechanism termed as Seoul National University Flap (SNUF). The flap-driving mechanism is further improved by considering performance of the piezoelectric actuator and aerodynamic loads acting on the flap. In order to improve its vibratory load reduction capability, blade design optimization is conduced. First, multibody dynamic analysis is performed to determine the influence of the flap dimension and location within the rotor blade upon the hub vibratory load reduction. Second, numerical optimization technique is applied to improve the blade sectional design. The cross sectional optimization framework using the genetic algorithm is established and extracts improved design, such as the decreased first torsional frequency and the reduced blade weight. The structural integrity of the present blade is evaluated in various ways. The strain recovery analysis is conducted and the in-plane stress near the blade root is estimated. Furthermore, the three-dimensional static structural analysis including the hub, blade and detailed flap-driving component is performed by considering the external aerodynamic/centrifugal loading and the practical contact condition among those components. The present flap-driving mechanism is fabricated and its flap deflection is measured by a static bench experiment, however excluding aerodynamic and centrifugal loads. In addition, a virtual centrifugal load is applied on the flap, and the flap deflection under such condition is monitored during the required operation duration. Finally, system identification of the present SNUF rotor system is conducted and a continuous-time higher harmonic control compensator is designed. Stability and the vibratory load reduction capability of the controller are demonstrated analytically.