State-space aerodynamic model reveals high force control authority and predictability in flapping flight

TL;DR

This study introduces a data-driven state-space model that efficiently predicts aerodynamic forces in flapping flight, revealing high control authority and predictability of wing kinematics for agile aerial maneuvering.

Contribution

A novel, computationally efficient state-space model trained on extensive data that outperforms existing models in predicting unsteady aerodynamic forces in flapping flight.

Findings

Model surpasses quasi-steady models in accuracy and generality.

Aerodynamic forces are largely predictable within a half-stroke cycle.

Key wing kinematic variables like angle of attack and pitching motion strongly influence force generation.

Abstract

Flying animals resort to fast, large-degree-of-freedom motion of flapping wings, a key feature that distinguishes them from rotary or fixed-winged robotic fliers with limited motion of aerodynamic surfaces. However, flapping-wing aerodynamics are characterised by highly unsteady and three-dimensional flows difficult to model or control, and accurate aerodynamic force predictions often rely on expensive computational or experimental methods. Here, we developed a computationally efficient and data-driven state-space model to dynamically map wing kinematics to aerodynamic forces/moments. This model was trained and tested with a total of 548 different flapping-wing motions and surpassed the accuracy and generality of the existing quasi-steady models. This model used 12 states to capture the unsteady and nonlinear fluid effects pertinent to force generation without explicit information of fluid flows. We also provided a comprehensive assessment of the control authority of key wing kinematic variables and found that instantaneous aerodynamic forces/moments were largely predictable by the wing motion history within a half-stroke cycle. Furthermore, the angle of attack, normal acceleration, and pitching motion had the strongest effects on the aerodynamic force/moment generation. Our results show that flapping flight inherently offers high force control authority and predictability, which can be key to developing agile and stable aerial fliers.