Transcript Flight
Flight • insects were the first organisms to develop active flight • insects were flying c 100My before pterosaurs! importance of flight • flight was the breakthrough underlying the evolutionary success of insects • about 99% of insect species belong to the ‘Pterygota’ – the winged insects • flight has enabled these relatively small animals to overcome the effects of distance • can use ‘rare’ or dilute resources, therefore can specialise, can find mates over large distances origins of flight • selection pressures? – gliding (or at least righting) – thermoregulation? – sexual displays? • structures? – paranotal processes – gills – leg-base sclerites selection pressures? • gliding (or at least righting) – insects as herbivores - hitting fruiting bodies – long way down … – presence of (large numbers) of chelicerate predators • thermoregulation? – … Kingsolver … temp. control IS important • sexual displays? – ? can justify anything ... structures? • paranotal processes – historical explanation … discredited – can’t explain articulations, muscles etc • gills – gills aren’t aerofoils, selection pressures ‘wrong’ – flight preceeds aquatic larvae • leg-base sclerites – currently accepted as best explanation Paranotal processes – conceptual model: parallels many vertebrate gliders Wings derived from larval gills - based on serial gills of Ephemeroptera larvae Wings derived from leg-base sclerites - based on muscle attachments, nerve circuitry flight capabilities • Prodigous flight capacity of insects – Common eggfly, Painted Lady, Meadow Argus: regularly fly from Australia to N.Z – NZ Red Admiral to near Palmer Pen. – Pantala flavescens - circumtropical migrant … Australia/Pacific Is to NZ – Aphids, other 'aerial plankton’, cross oceans mechanisms that drive insect wings • direct and indirect flight muscles • innervated and fibrillar muscles • energy preserving elastic processes direct and indirect flight muscles • 2 totally different forms of flight muscle organisation – direct … Odonata, Orthoptera, etc. etc – indirect … Diptera, Hymenoptera etc. etc • direct flight muscles work the wing bases • indirect flight muscles distort the thorax as an elastic box Direct flight muscles Indirect flight muscles Weis Fogh ‘click’ mechanism How it fits together innervated and fibrillar muscles • two totally different ways of operating flight muscle innervated - synchronous fibrillar - asynchronous • synchronous - Lepidoptera, Odonata etc wing beat frequency ~ 12 - 30 Hz • asynchronous - Diptera, Hymenoptera wing beat frequency 190 - 1100 Hz fibrillar muscles • contract in response to being stretched • contracting dorso-ventrals stretch longitudinals • contracting longitudinals stretch dorsoventrals • 1 nerve pulse -> 40 (or more) muscle contraction cycles • nerve pulse can switch off ‘engine’ energy preserving elastic processes • Insect muscles are supposed to be about 8% efficient cf 15% in homeotherms … how do they do it? • energy-preserving elastic processes resilin distortion of thoracic sclerites - both store and return energy to the flight system how? • … 'scientists have proved that the bumblebee can't fly' - refers to some 'back of an envelope' calculations done by an aerodynamicist in the 1930s • classical ‘steady-state’ aerodynamics classical aerodynamics • calculations used to design planes • ‘steady-state’ • aerofoils and Bernoulli's ppl … • critical angle and breakdown of lift insect wings as aerofoils • traditional method of analysis • supination/pronation • arc of wing movement • under steady-state aerodynamics an insect wing can provide lift for ~85% of the stroke cycle insect wings as dynamic structures • • • • • turbles forming aerofoil effects of setae/scales flexing of wing dragonfly ... nodus, pterostigma changing aerofoil shape through stroke or along wing (or both) Slick air-air interface reduces friction, postpones onset of turbulent drag Some of the dynamic flexing axes in a dragonfly wing Butterfly wing rigidity caused by discoidal cell Stick insect - no transverse bracing problems • 'spoiling' of second aerofoil … – link with hooks (Hymenoptera, Lepidoptera) – flap out of phase (Orthoptera) – one functional pair of wings (Diptera, Strepsiptera, some Ephemeroptera, some Hymenoptera, Coleoptera) scale effects • insects are flying in a different physical environment to (say) aircraft, or even birds • scale effects • Reynolds’ number: length * speed * density / viscosity • can visualise flow by operating at same Reynolds’ number different ways of flying • above critical angle turbulence doesn't destroy lift until aerofoil has travelled several chord lengths • unsteady flows can generate rotational flows (vortices) which generate very great lift unsteady state aerodynamics • very high lift generated by vortices • strongly implicated in insect flight • known mechanisms: ‘clap and fling’ - Weis Fogh 1973 ‘peel’ - Ellington 1984 leading edge vortices - Ellington 1996 others suspected • quantitative analysis at front end of computing envelope ... ANTERIOR VIEW … Clap-and-fling, wings clap together at top of stroke, then fling apart … this generates strong circulation about wing. Originally proposed for small wasps, now widely recognised (e.g. pigeons taking off) DORSAL VIEW Peel – wings peel apart from front edge (peel maintains a constant angle). Like the ‘fling’ this generates air circulation around the wing. Easiest place to see: Big greasy butterfly Leading edge vortex – vortex established over front edge of wing, part of toroidal vortex. Generates very significant lift. Can also recover energy from vortex of preceding stroke. different flight mechanisms • … ref Wootton 1990 Sci Am article • … document dragonfly flight mechanisms • note capacity to ‘switch’ physical liftgenerating processes - animal doesn’t care about theory … selected for results • many insects are grossly over-equipped for flying downdraft Bound vortex Trailing vortex Vortices around a dragonfly wing - X-section flight envelope • a dragonfly can switch from forward flight at 100 body-lengths/s to backwards at 3 body-lengths/s within a few body lengths • dragonflies can hover with their wings beating vertically • dragonflies are unstable in all axes allows enormous manoeuvrability Flier type dragonfly – wing stroke perp to body Percher type dragonfly – note acute angle References • Ellington C.P. 1984 The aerodynamics of hovering insect flight. (parts I - VI) Phil. Trans. R. Soc. Lond. B. 305 • Ellington, C.P., van den Berg, C., Willmott, A.P. and Thomas, A.L.R. (1996). Leading-edge vortices in insect flight. Nature 384: 626-630. • Somps, C. Luttges, M. 1985 Dragonfly flight: novel uses of unsteady separated flows. Science 228: 1326-1329 • Wootton, R.J. 1990. The mechanical design of insect wings. Sci. Am. 263(5): 66-72 • Dickinson papers 2000, 2001, 2002 and web site (hovering flight of Drosophila) • Srygley + coauthor – free flight in a butterfly (Nature, Dec 2002) … but see also German work 1986 on free flying hawk moths • Rüppell dragonfly flight – analysis of high-speed film