On the estimation of time dependent lift of a European Starling during flapping

TL;DR

This study estimates unsteady aerodynamic lift in a flying European Starling by analyzing wingbeat kinematics and wake flow, highlighting the significance of unsteady lift components in bird flight and power estimation.

Contribution

It introduces a method combining kinematic analysis and flow measurements to quantify unsteady lift components in bird flight, emphasizing their importance.

Findings

Unsteady lift varies significantly over wingbeat cycles.

Circulatory lift should not be neglected in lift and power calculations.

Unsteady lift components contribute notably to total lift during flapping.

Abstract

We study the role of unsteady lift in the context of flapping wings in birds' flight. Both aerodynamicists and biologists attempt to address this subject, yet it seems that the contribution of the unsteady lift still holds many open questions. The current study deals with the estimation of unsteady aerodynamic forces on a freely flying bird through analysis of wingbeat kinematics and near wake flow measurements using time resolved particle image velocimetry. The aerodynamic forces are obtained through unsteady thin airfoil theory and lift calculation using the momentum equation for viscous flows. The unsteady lift is comprised of circulatory and non-circulatory components. Both are presented over wingbeat cycles. Using long sampling data, several wingbeat cycles have been analyzed in order to cover the downstroke and upstroke phases. It appears that the lift varies over the wingbeat cycle emphasizing its contribution to the total lift and its role in power estimations. It is suggested that the circulatory lift component cannot assumed to be negligible and should be considered when estimating lift or power of birds in flapping motion.