In vivo recording of aerodynamic force with an aerodynamic force platform

TL;DR

This paper introduces a novel aerodynamic force platform that enables direct, nonintrusive measurement of aerodynamic forces in freely flying animals and robots, validated through experiments with a quadcopter and a bird.

Contribution

The paper presents a new aerodynamic force platform capable of in vivo force measurement during free flight, filling a critical gap in aerodynamic research methods.

Findings

The AFP accurately measures aerodynamic forces in free flight.

Validation with a quadcopter confirms measurement accuracy.

Application to a bird reveals insights into wing activity during flight.

Abstract

Flapping wings enable flying animals and biomimetic robots to generate elevated aerodynamic forces. Measurements that demonstrate this capability are based on tethered experiments with robots and animals, and indirect force calculations based on measured kinematics or airflow during free flight. Remarkably, there exists no method to measure these forces directly during free flight. Such in vivo recordings in freely behaving animals are essential to better understand the precise aerodynamic function of their flapping wings, in particular during the downstroke versus upstroke. Here we demonstrate a new aerodynamic force platform (AFP) for nonintrusive aerodynamic force measurement in freely flying animals and robots. The platform encloses the animal or object that generates fluid force with a physical control surface, which mechanically integrates the net aerodynamic force that is transferred to the earth. Using a straightforward analytical solution of the Navier-Stokes equation, we verified that the method is accurate. We subsequently validated the method with a quadcopter that is suspended in the AFP and generates unsteady thrust profiles. These independent measurements confirm that the AFP is indeed accurate. We demonstrate the effectiveness of the AFP by studying aerodynamic weight support of a freely flying bird in vivo, which demonstrates that its upstroke is inactive.