Modal Isolation and Damping for Adaptive Aeroservoelastic Suppression

Abstract

Adverse aeroservoelastic interaction is a problem on aircraft of all types causing repeated loading, enhanced fatigue, undesirable oscillations and catastrophic flutter. This adverse response is traditionally suppressed using notch and/or roll off filters in the primary flight control system architecture. This solution has pitfalls; rigid body performance is degraded due to resulting phase penalty and the filter may not be robust to off nominal behavior. An adaptive approach has been developed that determines optimal blends of both multiple outputs and multiple inputs which effectively isolate and suppress problematic lightly damped modes via negative feedback while minimizing adverse effects on the remaining modal response. Additional emphasis is given towards minimizing adverse effects on aircraft rigid body modes so that low frequency behavior is unchanged with minimal phase penalty. A subspace system identification solution has been incorporated to rapidly identify a large order model of the aircraft from multiple measurement sensors. This identified model is used to synthesize the controller, demonstrating the solution to be completely adaptive. Due to successful isolation of problematic modes, this solution can be applied independent of any primary flight control solution. Algorithm validation was performed via real-time piloted simulation of large order aeroelastic F/A-18C aircraft models.