Tiltrotor Whirl Flutter Mitigation Through Active Mini-tab Control

Tiltrotor aircraft offer a versatile flight envelope for the commercial, civil, and military domains, and are a leading platform for the emerging urban air mobility market. However, these configurations are vulnerable to safety-critical aeroelastic behaviors - such as whirl flutter - that must be addressed by new technologies. Whirl flutter instabilities can arise in tiltrotors due to the combination of the large rotor mass, flexible wing, and high advance ratio, placing significant constraints on design and operation. To address the limitations of passive design mitigations, active control strategies have been explored previously using flaperon and swashplate control. Using primary controls such as these in vibration control is undesirable from a reliability and certifiability standpoint, so a stand-alone active mini-tab device is proposed here as a novel method of improving the stability of tiltrotor whirl modes without affecting the primary controls. This paper presents a novel methodology for deriving empirical mini-tab models coupled to an expanded XV-15 tiltrotor model modified using finite element techniques. The proposed active mini-tab concept is demonstrated successfully with linear quadratic regulators, increasing the flutter advance ratio by up to 21%. This is the first time whirl flutter control has been demonstrated using a mini-tab.