# Hybrid LQR-H2 Control of a Kestrel-Based Ornithopter with a Nature-Inspired Flow Control Device for Gust Mitigation

## TL;DR

This paper introduces a hybrid control system for a kestrel-inspired ornithopter that uses a nature-inspired flow control device to stabilize flight during gusty conditions.

## Contribution

The novelty lies in combining a biomimetic flow control device with a hybrid LQR-H2 control strategy to achieve gust mitigation in ornithopters.

## Key findings

- The hybrid control system reduced gust-induced oscillations by up to 70%.
- Gust-mitigation efficiency reached 32% with stabilization under 1.4 seconds in high-intensity gusts.
- Simulated responses closely matched previously reported findings, validating the approach.

## Abstract

Unsteady atmospheric disturbances significantly compromise the stability of ornithopters, necessitating advanced turbulence-mitigation strategies. In contrast, natural flyers display remarkable aerodynamic adaptability through dynamic flow-control mechanisms such as covert feathers, enabling stability across unsteady flow regimes. Drawing inspiration from this biological phenomenon, this study presents the modeling and hybrid control of a kestrel-based ornithopter equipped with a Nature-Inspired Flow Control Device (NFCD) that replicates the adaptive feather deployment mechanism observed in kestrels. A reduced-order multibody bond-graph model (BGM) of the full ornithopter is developed, incorporating the main body, propulsion system, rigid wings, and the NFCD subsystem. The model captures key fluid-structure-interaction (FSI) effects between morphing feathers and surrounding airflow. A Linear Quadratic Regulator (LQR) ensures optimal performance under nominal gust conditions (≤3 m/s), while an H2 controller activates during high-intensity gusts (≥4 m/s) to enhance disturbance rejection through electromechanical feather actuation. A gain-scheduled transition is employed in the intermediate gust range (3–4 m/s) to ensure a smooth transition between controllers. Simulations indicate up to 70% reduction in gust-induced oscillations and 32% gust-mitigation efficiency, achieved through feather actuation in the NFCD combined with hybrid control, stabilizing the ornithopter in less than 1.4 s under higher gust conditions. The close correspondence between simulated responses and previously reported findings validates the proposed approach. Overall, by merging biomimetic aerodynamics, nature-inspired flow control, and advanced control design, the LQR-H2 governed NFCD provides a promising pathway toward gust-tolerant ornithopters capable of resilient and stable flight in unsteady atmospheric environments.