A Comprehensive Study of Active Microflaps for Vibration Reduction in Rotorcraft

Active Gurney flaps, or microflaps, are studied to determine their effectiveness in reducing vibrations in rotorcraft. A CFD based reduced order aerodynamic model (ROM) capable of modeling the unsteady effects of a microflap was incorporated into a comprehensive rotorcraft simulation code AVINOR. The ROM is constructed based on the Rational Function Approximation (RFA) approach, which results in a state-space time domain aerodynamic model suitable for use with comprehensive codes. Vibration reduction studies were conducted on a hingeless rotor configuration resembling MBB BO-105, using the relaxed Higher Harmonic Control (HHC) algorithm. Various spanwise configurations of the microflap, including a single, a dual, and a segmented five-microflap configuration, were considered and compared to conventional trailing edge flaps. The results indicate that the microflap is an effective device for vibration reduction in rotorcraft, capable of achieving substantial reductions in excess of 80%. However, the 1.5%c microflap was found to incur 3.6% performance penalty due to the increased drag. Parametric studies on microflap sizing suggest that a microflap configuration with the height of less than 1%c may be best in achieving substantial vibration reduction while mitigating performance penalty. Finally, the microflap was also found to be effective at various flight conditions including level and descent flight.