Transcript Lecture 6 Fluid for skeletons

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: density
Ladybird beetle
Lecture 12
From swimming
to flight: still in
fluid
Linden Gledhill
Diversity in aerofoil shape
Harris’ Hawk
Some wings don’t look like aerofoils in section
Feathers as aerofoils
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
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.
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* [from Wikkipedia] Keratin refers to a family of fibrous structural proteins. Keratin is the key
structural material making up the outer layer of human skin. It is also the key structural component
of hair and nails [and the feathers of birds]. Keratin monomers assemble into bundles to form
intermediate filaments, which are tough and insoluble and form strong unmineralized tissues found
in [tetrapods]. The only other [material] known to approximate the toughness of keratinized tissue
is [the polysaccharide] chitin.
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.
Drawing can be
criticized for
misleading re
passage of the red
muscle through
the foramen.
Direction of muscle
pull is changed by
the rope-like nature
of the tendon.
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.
The flight of birds is made possible by close integration of the muscle system with their
Respiratory/ventilation system: flight and breathing are linked.
Costal suction pump
Intercostal muscles run between
ribs and contract to move
ribs forward and down during
inspiration which coincides with
downstroke (? Check): sternum
moves forward and down.
Forward and down the volume
of thoracic cavity is greatly
increased giving reduced internal
pressure and
causing air inrush.
Reverse happens on upstroke.
Sternum moved down (and up) by supracoracoideus and pectoralis major operating
during flight: flight directly linked to ventilation.
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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 (bird has shock absorbers). Resonance: sound box areas in
bird sound production (birds have sound boxes). Egg laying: abdominal air
sacs help squeeze egg along the oviduct? 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.
How did birds evolve flight?
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The use of wings in flight would seem to involve quite sophisticated changes in the
in aerofoil form, in musculature in neural motor control. For the protobird
ancestor to change from a scrambling-forelimb terrestrial ‘lizard’ [reptile] to a
soaring eagle requires a plausible hypothesis of change: one that envisages slight
changes to forelimbs that are adaptive all during 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.
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.
“Our data suggest a default or basal
wing-stroke is used by young and
adults and may exist in all birds….
The fundamental wing-stroke
described herein is used days after
hatching and during all ages and over
multiple behaviours (that is, flaprunning, descending and level flight)
and is the foundation of our new
ontogenetic-transitional wing
hypothesis. 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 wing-assisted 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.”
Turning now to flight in insects: some anatomy is necessary: tergum,
sternum, pleuron are ‘top’ ‘side’ and ‘bottom’ of each insect cuticular
metamere.
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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, camber etc.) 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)
in ways rather like some 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).
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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.