Transcript Lecture 11

Recall: Lift
As a fish or a bird
moves through the water
fins/wings create lift forces -forces that tend to raise or lower
the animal. These forces
“originate from [fluid] viscosity
and are caused by asymmetries
in the flow. As fluid moves past
an object [such as a fin or a
wing], the pattern of flow may
be such that the pressure on one
…side is greater than on the
opposite. Lift is then exerted on
the object in a direction
perpendicularto the flow
direction” (Sfakiotakis 1999).
Lift decreases, drag increases with increasing tilt of
hydrofoil or aerofoil relative to the direction of flow.
Hydrofoils and aerofoils: the fluid flowing faster has lower pressure; faster flow occurs on
the upper surface of an aerofoil or hydrofoil and so lower pressure generates lift.
Hydrofoils more robust than aerofoils: due to fluid density; water is more dense than air
Ladybird beetle
Diversity in aerofoil shape
Linden Gledhill
Animal wings must not just
generate lift they need to
move through a cycle of
propulsion: bird flight
involves dips, cardinal.
Harris’ Hawk
Some wings don’t look like aerofoils
Feathers are themselves aerofoils
Primary feathers
Feduccia, A. & Tordoff, H.B. 1979. Feathers of Archaeopteryx:
asymmetric vanes indicate aerodynamic function. Science 203:
1021-1022
• Rachis: tapering central
support of a feather: to
either side is the vane
• Body feathers have vanes
symmetrical about the
rachis, but bird primaries are
not symmetrical in this way:
in primaries the rachis is
closer to the edge that leads
in flight. In strong fliers the
leading primary vane is
sometimes almost
obliterated. This asymmetry
gives each feather an aerofoil
transverse section, i.e., the
primaries of most birds
function as aerofoils in their
own right.
•
* [ mod. from Wikki] Keratin a fibrous structural protein. Keratin is the key material in the outer
layer of human skin; also in hair, nails and bird feathers. Keratin monomers assemble into bundles to
form intermediate filaments, which are tough and insoluble…. The only other [material] known to
approximate the toughness of keratinized tissue is [the polysaccharide] chitin.
Figure 4. The structure of the trailing edge vane of a pigeon primary feather. The barbs are inclined from the vertical and
cambered in cross section and the proximal barbules curve near their tip. This structure facilitates distal and ventral movement of
the blade (arrows) and helps prevent proximal movement and detachment of the barbules. Distance between barbs is
approximately 0.5mm
Katayoon Taghizade et al. Designing a Mobile Facade Using Bionic Approach. American Journal of Materials Engineering and
Technology, 2013, Vol. 1, No. 2, 22-29. doi:10.12691/materials-1-2-2
© The Author(s) 2013. Published by Science and Education Publishing.
Another function of feathers besides promoting smooth flow of air and lift: thermal
insulation
Thermal insultation: reduction of heat transfer between objects of differing
temperature. ‘Low thermal conductivity materials reduce heat fluxes’. Gases
are poor thermal conductors compared to solids and liquids Trapping air in
small surface pockets that stop transfer of heat by natural convection.
Birds in winter: fluffed at the bird feeder.
Riding a bike at low temperatures without gloves is not a good idea. Windchill will soon make your hands uncomfortable. Flying makes low
temperatures a larger problem and the feathers are an adaptation for this.
Taghizade K. & Taraz M. 2013. Designing a mobile facade using bionic
approach. Doi: 10.12691/materials-1-2-2
Feathers as insulators; feather movements on the skin – puffing out or
sleeking down…bionics “explains the relation between nature and product
design” “innovative designing and engineering based on the systems present
in nature” outside of buildings
“This arrangement produces a light structure which …may be easily mended
by the bird drawing the vane through its bill.”
Supracoracoideus muscle is wing elevator; it originates on the sternum and lies
beneath its antagonist, the wing levator.
Load of wing is
taken up by the
tendon of the
supracoracoideus.
Stress (force) is
created by the
contracting muscle
and tension
develops in the
tendon which
stretches,
i.e., shows strain.
Direction of muscle
pull is changed by
the rope-like nature
of the tendon, i.e., it
is a pulley.
Why are the muscles that power bird flight located below the wing?
Flight muscles are 1/5 of the body mass. Keeping the centre of gravity
low keeps the bird from out-of-control rolling.
Class 3 lever both up and
down: effort is always
applied between the
fulcrum and the load in
birds.
Costal suction pump
Intercostal muscles run between
ribs and contract to move
ribs forward and downward
during inspiration; this coincides
with downstroke: sternum
moves forward and down.
Forward and down the volume
of thoracic cavity is greatly
increased giving reduced internal
pressure and
causing an air inrush.
Reverse happens on upstroke.
Sternum moved down (and up) by supracoracoideus and pectoralis major operating
during flight: flight power movement integrated with ventilation.
Birds have pneumatic bones (air-filled) and air sacs
•
•
Lungs of human occupy about 5% body volume. Lungs of bird only occupy 2% of body volume. But
lungs plus air sacs of a duck occupy about 20% of its body volume. Nevertheless bird air sacs are not
involved in gas exchange: they are not vacularized (no blood vessels): but they are involved in air
circulation. Air sacs are reconnected to the mesobronchi by recurrent bronchi.
Multiple functions of air sacs: cooling system: flying produces heat and air sacs are well placed to
remove this excess heat (bird has an air-cooled engine). Shock absorber: gannets, pelicans diving into
the ocean from a great height. Resonance: sound box areas in bird sound production. Egg laying:
abdominal air sacs help in egg laying (and in defecation?).
Tiny air capillaries within the parabronchi walls, in
the (fixed-volume) lungs, are the site of actual gas
exchange.
Tracheae, which
conduct the low
density fluid (air)
into the body need
cartilaginous rings to
support their lumen
against the denser
tissues (waterbased) that
surround.
Convergence of a
sort with the
tracheae of insects.
Bird lung section
Bird air sacs are how a bird can inhale and exhale with lungs that don’t
change volume.
Posterior thoracic sac
Syrinx is located at junction of trachea and bronchi
and is an organ for sound generation: developed
elaborately in songbirds. Modulation of air flow to
create sounds: respiratory system serves also in
communication.
There are 9 air sacs. An anterior group:
interclavicular (1), cervical (2), anterior
thoracic (2). Then there is a posterior
group: abdominal (2), posterior thoracic
(2). Unpaired interclavicular air sac in
anterior midline sends diverticulae into
some of larger bones (sternum, pectoral
girdle): called pneumatic bones: these
serve to lighten the bird for flight.
Diagram to right is simplified bird
lung, ‘it ‘groups’ anterior and
posterior air sacs in order to
more easily visualize the air
circulation. The lungs cannot
change their volume, but the airsacs do. Two cycles of inspiration
and expiration (powered by the
muscles of flight , including the
intercostal muscles between the
ribs of the thorax) are required
for one breath to make its way
through the system, in and out
again; it is a true circulation and
not a tidal system such as in
mammals.
Follow one breath through the
system: remember, on inhalations
sacs expand, on exhalations they are
compressed, this being accomplished
by thoracic volume changes linked to
flight muscles & rib cage [costal
pump].
Inhalation 1, posterior air sacs
expand & draw breath into
themselves: draw this air via primary
bronchus>mesobronchus.
Exhalation 1, breath air displaced
from squeezed posterior air sacs into
posterior secondary bronchi and
parabronchi; in latter the gas
exchange occurs.
Inhalation 2, expanding anterior air
sacs draw ‘breath’ from the
parabronchi into themselves.
Exhalation 3, the anterior air sacs
expel the air breath to the outside.
‘Ontogenetic transitional wing hypothesis’ of how birds evolved flight.
•
•
•
•
•
To select forelimbs for flight -- to alter the neuromuscular system and forelimb
form to create a powering aerofoil -- involves many complex body changes. A
‘protobird’ ancestor had to change gradually from a ground-walking reptile to a
bird capable of “level flapping flight” (i.e., from a lizard to a soaring eagle).
Needed is a plausible hypothesis of locomotion-related selection pressures: one
that envisages gradual changes to forelimbs that are adaptive throughout the
evolutionary process, i.e., are adaptive at each stage in the historical process.
The authors of a recent paper propose an hypothesis based upon study of the
development (ontogeny) of young partridge, the ontogenetic-transitional wing
hypothesis. They studied ‘wing-stroke dynamics’ of maturing partridges and
traced a developmental pattern of forelimb movement that is consistent with
‘incline flap running’.
Dial, K.P. et al. 2008. Nature. A fundamental avian wing-stroke provides a new
perspective on the evolution of flight. Nature 451: 985-989.
Read this paper to understand their hypothesis, how they arrived at it and what
experimental evidence they present that tests the hypothesis.
“…we propose that explorations of the ontogeny of post-natal behaviour and
morphology among extant taxa provide insight into ecological and evolutionary
locomotor transitional stages” (jargon destroys interest)
Chukar: Alectoris chukar
As newly hatched young
birds move about, they use
their developing wings as
well as their legs. The
wingstroke goes through
changes as young bird
matures. The ontogeny of
wing movement
‘recapitulates’ phylogenetic
change. The wingstroke
referenced to gravity rather
than the longitudinal axis of
the bird is very conservative
and useful at each stage.
Backyard chickens
“Our data suggest a default or basal
wing-stroke is used by young and
adults and may exist in all birds….
At hatching, chicks can ascend
inclines as steep as 60° by crawling
on all four limbs. From day 8 through
adulthood, birds use a consistently
orientated stroke-plane angle over
all substrate inclines during wingassisted incline running (red arcs) as
well as during descending and level
flight (blue arcs). Estimated force
orientations from this conserved
wing-stroke are limited to a narrow
wedge (see Fig. 3b).
When the wing
movement is
considered relative to
the body’s
longitudinal axis it
seems to vary a lot for
locomotory learning
behaviour, but
considered relative to
gravity it is actually
the same relatively
simple wingstroke for
both up-incline and
fluttering down
incline.
“Blue and black outlines represent the positions of the bird and wing at the start and end
of downstroke, respectively. a, In the vertebral space, the mean wing-stroke plane angle
shifts more than 30° from a more antero-posterior orientation during flap-running to
dorso-ventrally in flight, implying different wing-strokes are used to execute different
locomotor modes. The wing-stroke path is consistently oriented, however, in both the (b)
global and (c) gravitational coordinate spaces over diverse locomotor behaviours,
illustrating a simplified wing-stroke that is multi-functional. Data for juveniles are presented
from 8- to 10-day olds.”
“a, When wing-stroke plane angles are viewed
side-by-side in both the vertebral and
gravitational frames of reference, the wingstroke is nearly invariant relative to gravity
whereas the body axis re-orients among
different modes of locomotion. Red lines
represent the wing-tip trace in WAIR (flaprunning) and blue lines represent the wing-tip
trace in level flight. b, Wing-strokes are
estimated to produce similar aerodynamic forces
oriented about 40° above the horizon during
WAIR, level flight and descending flight. Error
bars are s.e.m. c, Representative traces of AOA
through a wing-beat for an animal flap-running
vertically (red) and in horizontal flight (blue)
demonstrate the similarities of AOA among
behaviours. The similarities are further clarified
by examining wing cross-sections and mean
global stroke-planes in the first, middle and last
thirds of downstroke. Here, the orientation of
the aerodynamic force (Faero) is estimated from
the middle third.”
Conclusions about flight evolution
•
•
“Our experimental observations show that proto-wings moving through a stereotypic and conserved wing-stroke
have immediate aerodynamic function, and that transitioning to powered flapping flight is limited by the relative
size of the wing and muscle power, rather than development of a complex repertoire of wing-beat kinematics.”
In other words, wingstrokes were useful to protobirds even before they could take to the air. Wing beats (at the
particular narrow range of angles the authors discovered) could help a non-flying bird ancestor to run faster, up
or down inclines – faster than ‘birds’ that were not modifying and using their forelimbs in this way. Flapping
with forelimbs and running on hindlimbs was a better, faster means of escape from a predator than running on
all four limbs at the same time.
Turning now to flight in insects: some anatomy is necessary: tergum, sternum, pleuron
are ‘top’ ‘side’ and ‘bottom’ of each insect cuticular metamere.
•
•
•
•
•
Insects are descended from metameric, i.e., segmented animals and the thorax is a
locomotory tagma comprised of three metameres.
Segments of the abdomen contrast with those of the thorax. The thorax is a
tagma functioning as a locomotory ‘box’, giving a firm base on which muscles can
originate and pull, muscles for walking (legs below) and for flying (wings above).
The mesothorax + metathorax: the two segments specialized for bearing the wings
and for flight are together called the pterothorax.
Muscles involved in flight in insects (with exceptions, e.g., in Odonata) insert on
the exoskeleton of the thoracic box and NOT on the wings directly; they move the
wings by distorting pterothorax shape and are referred to as indirect flight
muscles.
LONGITUDINALS DOWNSTROKE; TERGOSTERNALS UPSTROKE
Attitude of the wings (pronation, supination) is achieved by the elastic interplay of
the veins and membranes with the air flow. The wings don’t just go up and down
and maintain elevation they must scull through the fluid (air) just like fish fins.
Locust flight {Source: R.E. Snodgrass The thoracic mechanism of a
grasshopper, and its antecedents. Smithsonian Miscellaneous Collections 82,
pp. 111. } [This reference is given just for completeness; it is not something you
should try to obtain and read, but it is the source of much of the information
given here and in the lab.]
Locusts are strong fliers. The flight-powering muscles of the locust are indirect and
have their effect upon the wings by distorting the pterothorax and by tergal tipping of
the second axillary. (The pterothorax is the flight tagma (just segments 2 & 3, not the
prothorax.) There are two antagonistic muscle sets: longitudinals (downstroke), and
tergosternals (upstroke).
contraction of the longitudinals wings go down
contraction of the tergosternals wings go up
Sct2 is the scutum of the
second segment of the
thorax; scutum is a region
of the ‘top’ sclerite
(tergum) as is Scl2 which is
a tergal region called the
scutellum.
Muscle 81 is an indirect
longitudinal flight muscle
pulling between phragma 1
and 2; 112 is another,
pulling between phragma 2
not labelled, and 3Ph,
pharagma 3). These
increase the arching of
their respective terga,
creating forces at the wing
bases (PWP & 2nd axillary
sclerite, see next slide).
•
Apodemes
are Inflections
of cuticle,
phragma are
a kind of
apodeme.
The longitudinals are situated high up in the pterothorax. Partially obscured behind
them, arrayed against the pleuron, are the many tergosternals (83, 84, 89 etc.), running
between the sterna (S2,S3) and the terga (Sct2, Sct3). The axes of the tergosternals all
lean headward (the insect’s anterior is to the left). Notice how the upper end of the
tergosternals insert on the terga where their contraction can reduce the convexity of
this region. Reducing tergal convexity is associated with elevation of the wings.
More diagramatic views: Snodgrass drew the phragmata (Aph anterior phragma, Pph posterior phragma) of Fig. 129 purposely
distorted, so as to show their interconnecting longitudinal muscles both ahead and behind: notice the critical placing of the second
axillary, 2Ax, atop the pleural wing process, WP.
Euler buckling
dorsal
Function of the pleural ridge
ventral
“The addition of flanges stabilizes
against buckling since it increases
the effective thickness of the plate
in selected areas effectively
dividing the plate into shorter
lengths.”
Tergosternals contract and forces would tend to buckle the pleuron; the
pleural ridge stiffens the side between the wing base and the coxa.
Function of the pleurosternal muscles: even more stiffness
Imparted to the thoracic sides (pleura): and VARIABLE.