title: Span efficiency in hawkmoths.
abstract: Flight in animals is the result of aerodynamic forces generated as flight muscles drive the wings through air. Aerial performance is therefore limited by the efficiency with which momentum is imparted to the air, a property that can be measured using modern techniques. We measured the induced flow fields around six hawkmoth species flying tethered in a wind tunnel to assess span efficiency, ei, and from these measurements, determined the morphological and kinematic characters that predict efficient flight. The species were selected to represent a range in wingspan from 40 to 110 mm (2.75 times) and in mass from 0.2 to 1.5 g (7.5 times) but they were similar in their overall shape and their ecology. From high spatio-temporal resolution quantitative wake images, we extracted time-resolved downwash distributions behind the hawkmoths, calculating instantaneous values of ei throughout the wingbeat cycle as well as multi-wingbeat averages. Span efficiency correlated positively with normalized lift and negatively with advance ratio. Average span efficiencies for the moths ranged from 0.31 to 0.60 showing that the standard generic value of 0.83 used in previous studies of animal flight is not a suitable approximation of aerodynamic performance in insects.
authors: Department of Zoology, University of Oxford, Oxford OX1 3PS, UK.
authors: Per
authors: P
authors: Henningsson
authors: Richard J
authors: RJ
authors: Bomphrey
mesh_terms: D000392:Air Movements; D000818:Animals; D001696:Biomechanical Phenomena; D001837:Body Weights and Measures; D005426:Flight, Animal / Q000502:physiology*; D009036:Moths / Q000502:physiology*; D012212:Rheology; D013045:Species Specificity; D014921:Wings, Animal / Q000033:anatomy & histology / Q000502:physiology*
keywords: aerodynamics; hawkmoth; insect; particle image velocimetry; wind tunnel
references: Bioinspir Biomim. 2006 Dec;1(4):S1-9
references: 17671312
references: Science. 2007 May 11;316(5826):894-7
references: 17495171
references: J R Soc Interface. 2006 Apr 22;3(7):311-7
references: 16849240
references: PLoS One. 2012;7(5):e37335
references: 22624018
references: J R Soc Interface. 2012 Feb 7;9(67):292-303
references: 21676971
references: J R Soc Interface. 2012 Oct 7;9(75):2745-8
references: 22593097
references: J R Soc Interface. 2012 Jun 7;9(71):1177-86
references: 22112649
references: J Exp Biol. 2002 Jun;205(Pt 11):1547-64
references: 12000800
references: J R Soc Interface. 2012 Dec 7;9(77):3378-86
references: 22977102
references: J Theor Biol. 2001 Jan 21;208(2):127-39
references: 11162058
references: J Exp Biol. 1997;200(Pt 17):2355-61
references: 9320274
references: J R Soc Interface. 2011 Jun 6;8(59):807-16
references: 21131333
references: J Exp Biol. 2009 Oct;212(Pt 20):3365-76
references: 19801441
references: J Exp Biol. 2011 Feb 1;214(Pt 3):382-93
references: 21228197