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 The human species has been able to fly for about a century - with
the help of aircraft of various kinds, that is! So we have quite a good understanding of
aerodynamics.
However, although the flapping wings of
animals served as an inspiration to the pioneers of human flight, I think it is fair
to say that to this day we don't really understand how they work. Animal wings provide
both lift and propulsion, whereas our creations tend to separate those roles with engines
attached to quite rigid airframes (the helicopter is of course an exception). Conventional
aerodynamic theory is based upon fixed wings in a steady airflow, while the airflow around
flapping wings is anything but steady and challenges our understanding. |
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animals that fly
There are many variations on the theme of animal flight -
parachuting, gliding, and powered flight. Many species routinely use flight in some form
or another - flying frogs, gliding lizards, flying squirrels, flying lemurs and so on -
but the three classes of present-day animals who excel in this skill are the insects, bats and birds.
In the fossil record we also have evidence of flying dinosaurs called
pterosaurs, some of which attained a remarkable size.
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 | insects |
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click for larger image
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Insect wings come in a huge variety of
shapes, sizes, and appearance. However, they resemble each other (and many sails) in that
they are passive membranous foils that depend largely on the arrangement of their
supporting framework for many of their aerodynamic properties. So, during flapping flight,
the wings become distorted by the changing forces acting on them, but in an effective and
efficient way. The leading edge of the wing has a much stronger and stiffer structure than
the other regions of the wing which are more flexible and capable of twisting.
Energy is put into the wings from the root by the powerful muscles within the insect's
thorax. The joints between wing and body are remarkable for the complex movements they
allow and their ability to store and release energy appropriately at different stages in
the flapping cycle. insect flight |
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| bats |
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click here for a diagram of a bat's wing
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Bats' wings have a much more dynamic geometry
than those of insects. The slender bony framework is jointed and the relative positions of bones
are controlled by numerous muscles within the wing and attaching to it from the body. Thus
the repertoire of movements is much greater than for insects, both during flapping flight
and when the wings are folded at rest. However, like insects the main area of the foil is
composed of membrane, although in this case it is an elastic and adaptable membrane rather
than relatively non-stretchable as in the insect's wing. Bats are mammals
and belong to the family Chiroptera, which means 'hand-wing'. The
family is divided into two taxa, the Microchiroptera or microbats
and the Megachiroptera which includes the much larger fruit bats
and flying foxes. There are nearly 1000 species of bat in the world
today. Bat flight |
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| birds |
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click here for a diagram of a bird's wing |
Birds (Aves) go one step further than bats - instead
of a membrane stretched elastically between the skeletal elements, they have numerous
feathers, each shaped and equipped for a number of functions. This greatly increases the
range of geometries over which an aerodynamically effective foil can be maintained.
Although birds' wing share similar structures and composition, different species have
emerged with sophisticated adaptations for different modes of flight: long range or high
speed or hovering or short take-off to give just a few examples. Bird flight |
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| how do flapping wings work?
 | Well, we are not sure yet, but some things we do know!
Follow this link to find out... flapping flight
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| Here are some experiments with flapping
wing models
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| How did animal flight evolve? Click here for some thoughts on this...
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