Lecture 9 – Locomotion: Flight
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Transcript of Lecture 9 – Locomotion: Flight
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Lecture 9 – Locomotion: FlightPowered flight has evolved several times:
Insects
Pterosaurs
Birds
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Powered Flight : Bats
Skin - patagium
Supported by digits 2-5
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Generation of Lift
Turbulent Flow
Laminar Flow
Laminar flow – parallel movement of air streams
Bernoulli’s Theorem
P is air pressure.C is a constant.d is the density of air, and V is velocity.
Lift = P(Lower) – P(Upper)
Velocity across top is higher than bottom.
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Myotis lucifugus (little brown bat)- 20 MPH
Eptesicus fuscus (big brown bat)- 40 MPHTadarida brasiliensis (Brazilian free-tailed
bat) – up to 60 MPH
Bats tend to be slow fliers.
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Generation of lift at low flight speeds.
1. Increase camber, or curvature of the wing.
2. Increase angle of attack (even a symmetric airfoil can generate lift this way)
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Generation of lift at low flight speeds.
3. Alter wing size and shape.
a. Wing loading: Body weight /surface area.
Body Weight Surface Area Wing LoadHouse wren 11.0 g 48.4 cm2 0.24 g/ cm2
Glossophaga 10.6 g 99.3 cm2 0.11 g/ cm2
Myotis 4.2 g 67.6 cm2 0.06 g/ cm2
b. Aspect ratio - length / width
Artibeus – low aspect ratio Tadarida – high aspect ratio
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Eumops perotiswestern bonneted bat
Mollossids
Stopping the up-stroke: Shoulder-locking mechanism
Greater tuberosity of humerus
Vespertilionids also.
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*Situation similar in phyllostomids
Moderately well-developed shoulder locking.
Modest greater tuberosity
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Poorly developed shoulder locking mechanism: entirely muscular.
Sac-winged bats – Emballonuridae.
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Other Adaptations for Flight
1. Compressed thoracic vertebrae - not fused, but very tightly interconnecting2. Fused sacral vertebrae and fused lumbar vertebrae
Some (Natalidae) have rigid axial skeleton.
Keeled manubrium of sternum.