Aerodynamic Efficiency Explains Flapping Strategies Used by Birds

Overview

Journal Proc Natl Acad Sci U S A

Specialty Science

Date 2024 Nov 6

PMID 39503894

Authors

L Christoffer Johansson

Affiliations

Soon will be listed here.

Abstract

A faster cruising speed increases drag and thereby the thrust () needed to fly, while weight and lift () requirement remains constant. Birds can adjust their wingbeat in multiple ways to accommodate this change in aerodynamic force, but the relative costs of different strategies remain largely unknown. To evaluate the efficiency of several kinematic strategies, I used a robotic wing [E. Ajanic, A. Paolini, C. Coster, D. Floreano, C. Johansson, , 2200148 (2023)] and quantitative flow measurements. I found that, among the tested strategies, changing the mean wingbeat elevation provides the most efficient solution to changing thrust-to-lift ratio (/, offering insight into why birds tend to beat their wings with a greater ventral than dorsal excursion. I also found that although propulsive efficiency (η) may peak at a Strouhal number (, measure of relative flapping speed) near 0.3, the overall efficiency of generating force decreases with . This challenges the expectance of a specific optimal for flapping flight and instead suggest the chosen depends on /. This may explain variation in preferred among birds and why bats prefer flying at higher than birds [G. K. Taylor, R. L. Nudds, A. L. Thomas, , 707-711 (2003)], since their body shape imposes relatively higher thrust requirements [F. T. Muijres, L. C. Johansson, M. S. Bowlin, Y. Winter, A. Hedenström, , e37335 (2012)]. In addition to explaining flapping strategies used by birds, my results suggest alternative, efficient, flapping motions for drones to explore aiming to extend their flight range.

References

Hubel T, Riskin D, Swartz S, Breuer K . Wake structure and wing kinematics: the flight of the lesser dog-faced fruit bat, Cynopterus brachyotis. J Exp Biol. 2010; 213(Pt 20):3427-40. DOI: 10.1242/jeb.043257. View

Johansson L, Henningsson P . Butterflies fly using efficient propulsive clap mechanism owing to flexible wings. J R Soc Interface. 2021; 18(174):20200854. PMC: 7879755. DOI: 10.1098/rsif.2020.0854. View

Muijres F, Johansson L, Bowlin M, Winter Y, Hedenstrom A . Comparing aerodynamic efficiency in birds and bats suggests better flight performance in birds. PLoS One. 2012; 7(5):e37335. PMC: 3356262. DOI: 10.1371/journal.pone.0037335. View

Stowers A, Lentink D . Folding in and out: passive morphing in flapping wings. Bioinspir Biomim. 2015; 10(2):025001. DOI: 10.1088/1748-3190/10/2/025001. View

Taylor G, Nudds R, Thomas A . Flying and swimming animals cruise at a Strouhal number tuned for high power efficiency. Nature. 2003; 425(6959):707-11. DOI: 10.1038/nature02000. View

Muijres F, Bowlin M, Johansson L, Hedenstrom A . Vortex wake, downwash distribution, aerodynamic performance and wingbeat kinematics in slow-flying pied flycatchers. J R Soc Interface. 2011; 9(67):292-303. PMC: 3243385. DOI: 10.1098/rsif.2011.0238. View

Henningsson P, Spedding G, Hedenstrom A . Vortex wake and flight kinematics of a swift in cruising flight in a wind tunnel. J Exp Biol. 2008; 211(Pt 5):717-30. DOI: 10.1242/jeb.012146. View

Hedrick T, Tobalske B, Biewener A . How cockatiels (Nymphicus hollandicus) modulate pectoralis power output across flight speeds. J Exp Biol. 2003; 206(Pt 8):1363-78. DOI: 10.1242/jeb.00272. View

Heerenbrink M, Johansson L, Hedenstrom A . Power of the wingbeat: modelling the effects of flapping wings in vertebrate flight. Proc Math Phys Eng Sci. 2016; 471(2177):20140952. PMC: 4985036. DOI: 10.1098/rspa.2014.0952. View

10.

Salehipour H, Willis D . A coupled kinematics-energetics model for predicting energy efficient flapping flight. J Theor Biol. 2012; 318:173-96. DOI: 10.1016/j.jtbi.2012.10.008. View

11.

Rosen M, Spedding G, Hedenstrom A . The relationship between wingbeat kinematics and vortex wake of a thrush nightingale. J Exp Biol. 2004; 207(Pt 24):4255-68. DOI: 10.1242/jeb.01283. View

12.

Hubel T, Hristov N, Swartz S, Breuer K . Changes in kinematics and aerodynamics over a range of speeds in Tadarida brasiliensis, the Brazilian free-tailed bat. J R Soc Interface. 2012; 9(71):1120-30. PMC: 3350744. DOI: 10.1098/rsif.2011.0838. View

13.

Park K, Rosen M, Hedenstrom A . Flight kinematics of the barn swallow (Hirundo rustica) over a wide range of speeds in a wind tunnel. J Exp Biol. 2001; 204(Pt 15):2741-50. DOI: 10.1242/jeb.204.15.2741. View

14.

Wolf M, Johansson L, von Busse R, Winter Y, Hedenstrom A . Kinematics of flight and the relationship to the vortex wake of a Pallas' long tongued bat (Glossophaga soricina). J Exp Biol. 2010; 213(Pt 12):2142-53. DOI: 10.1242/jeb.029777. View

15.

Johansson L, Jakobsen L, Hedenstrom A . Flight in Ground Effect Dramatically Reduces Aerodynamic Costs in Bats. Curr Biol. 2018; 28(21):3502-3507.e4. DOI: 10.1016/j.cub.2018.09.011. View

16.

Tobalske B, Warrick D, Clark C, Powers D, Hedrick T, Hyder G . Three-dimensional kinematics of hummingbird flight. J Exp Biol. 2007; 210(Pt 13):2368-82. DOI: 10.1242/jeb.005686. View

17.

von Busse R, Waldman R, Swartz S, Voigt C, Breuer K . The aerodynamic cost of flight in the short-tailed fruit bat (Carollia perspicillata): comparing theory with measurement. J R Soc Interface. 2014; 11(95):20140147. PMC: 4006254. DOI: 10.1098/rsif.2014.0147. View

18.

Pennycuick , Alerstam , HedenstrOumlM . A new low-turbulence wind tunnel for bird flight experiments at Lund University, Sweden. J Exp Biol. 1997; 200(Pt 10):1441-9. DOI: 10.1242/jeb.200.10.1441. View

19.

Chin D, Lentink D . Birds repurpose the role of drag and lift to take off and land. Nat Commun. 2019; 10(1):5354. PMC: 6877630. DOI: 10.1038/s41467-019-13347-3. View

20.

Hakansson J, Jakobsen L, Hedenstrom A, Johansson L . Body lift, drag and power are relatively higher in large-eared than in small-eared bat species. J R Soc Interface. 2017; 14(135). PMC: 5665827. DOI: 10.1098/rsif.2017.0455. View