Dynamics of a High-Authority Active Flap Rotor

A demonstration rotor with integral trailing edge active control flaps was designed, built, whirl and wind tunnel tested as part of a multi-year program to develop technology capable of providing high authority on-blade controls and evaluating its impact on noise, vibration and aerodynamic performance. During testing a linear, frequency domain, active rotor controller (ARC) was used to perform closed-loop trim and vibration control that resulted in vibration suppression of the hub in several hub load axes while maintaining rotor trim. The controller included an actuator equalization method that eliminated differences between commanded and actual actuator responses. The demonstration rotor was designed to operate with two different values of the 1st torsion mode frequency, achieved by changing the root restraint. The structural dynamics of the rotor were characterized via test and analysis to determine its ground resonance and aeroelastic stability margins. Ground resonance tests were performed at the beginning of the wind tunnel test, and the rotor was found to be stable for all testing conditions. During wind tunnel testing the rotor was verified to be stable when configured to be torsionally stiff but encountered a flutter instability when the blades were configured to be torsionally soft. This instability was investigated and the results are presented in this paper.