Flight

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Flight

• insects were the first organisms to develop
  active flight
• insects were flying c 100My before pterosaurs!

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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

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origins of flight

• selection pressures?
• gliding (or at least righting)
• thermoregulation?
• sexual displays?
• structures?
• paranotal processes
• gills
• leg-base sclerites

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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 ...

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structures?

• paranotal processes
• historical explanation discredited
• cant explain articulations, muscles etc
• gills
• gills arent aerofoils, selection pressures
  wrong
• flight preceeds aquatic larvae
• leg-base sclerites
• currently accepted as best explanation

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Paranotal processes conceptual model
parallels many vertebrate gliders
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Wings derived from larval gills - based on serial
gills of Ephemeroptera larvae
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Wings derived from leg-base sclerites - based on
muscle attachments, nerve circuitry
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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

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mechanisms that drive insect wings

• direct and indirect flight muscles
• innervated and fibrillar muscles
• energy preserving elastic processes

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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

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Direct flight muscles
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Indirect flight muscles
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Weis Foghclick mechanism
How it fitstogether
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innervated and fibrillar muscles

• two totally different ways of operating flight
  muscleinnervated - synchronousfibrillar -
  asynchronous
• synchronous - Lepidoptera, Odonata etcwing beat
  frequency 12 - 30 Hz
• asynchronous - Diptera, Hymenopterawing beat
  frequency 190 - 1100 Hz

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fibrillar muscles

• contract in response to being stretched
• contracting dorso-ventrals stretch longitudinals
• contracting longitudinals stretch dorso-ventrals
• 1 nerve pulse -gt 40 (or more) muscle contraction
  cycles
• nerve pulse can switch off engine

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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
  -resilindistortion of thoracic sclerites- both
  store and return energy to the flight system

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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

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classical aerodynamics

• calculations used to design planes
• steady-state
• aerofoils and Bernoulli's ppl
• critical angle and breakdown of lift

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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

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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)

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Slick air-air interface -reduces friction,
postpones onset of turbulent drag
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Some of the dynamic flexing axes in a dragonfly
wing
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Butterfly wing rigidity caused by discoidal cell
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Stick insect - no transverse bracing
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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)

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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

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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

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unsteady state aerodynamics

• very high lift generated by vortices
• strongly implicated in insect flight
• known mechanismsclap and fling - Weis Fogh
  1973peel - Ellington 1984leading edge
  vortices - Ellington 1996others suspected
• quantitative analysis at front end of computing
  envelope ...

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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)
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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
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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.
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different flight mechanisms

• ref Wootton 1990 Sci Am article
• document dragonfly flight mechanisms
• note capacity to switch physical
  lift-generating processes - animal doesnt care
  about theory selected for results
• many insects are grossly over-equipped for flying

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downdraft
Trailing vortex
Bound vortex
Vortices around a dragonfly wing - X-section
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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

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Flier type dragonfly wing stroke perp to body
Percher type dragonfly note acute angle
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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

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• 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