flying animals

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.

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.

insects
click for larger image	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

bats
click here for a diagram of a bat's wing	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

birds
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

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 Here are some experiments with flapping wing models How did animal flight evolve? Click here for some thoughts on this...