The Marvelous Mechanics of Flight
Although airplane wings may be somewhat modeled after the wings of birds, the mechanics of bird flight are far more complex. A number of forces act on the flexible wings of a bird and are very different from those on the fixed wings of an airplane. Birds are highly specialized creatures and adapted for flight. They dominate the skies and occupy a unique niche in the environment.
One factor which has a great effect on flight is the power to mass ratio. In general a bird’s skeleton has a lower mass than that of the feathers. The bones are light and feature an inner honeycomb type structure.
The wings of each bird are aerodynamically designed for effective flight. Well streamlined, the wings are able to move smoothly through the air. The curve of the wing provides the necessary lift to keep the bird floating through the air. Lift is created when air passing over the front edge of the wing and over the convex top moves faster resulting in a lower pressure than that under the concave lower side of the wing. The wing must be held at the correct angle of attack to prevent turbulence, however, this turbulence is sometimes counteracted by a bastard wing on some birds. Wing size and shape varies according the different roles filled by bird species. Some are ideal for short, quick bursts of flight whilst others are well suited for soaring.
Thrust is also important for bird flight. Power is generated on the downward stroke of the wings. As the wings push down, the tips of the primary feathers (those on the wing tip) are pushed up and pull at an angle, acting almost like a propeller. When the wing moves up again, the primary feathers separate to prevent resistance.
Strong flight muscles are needed to operate the bird’s wings in this fashion. The breast bone is deeply keeled to provide necessary surface area for muscle attachment. White muscle is prevalent in ground birds as it is useful for quick bursts of activity. Red muscle is more common in active fliers and migratory bird species. These muscles are filled with blood vessels to keep them well supplied with nutrients and oxygen.
In addition to the lungs, most bird species have air sacs located in chambers in the body. These provide the muscle tissue with extra oxygen. Interestingly, flight generates much heat in the body of the bird which could lead to death if not regulated. This danger is balanced and offset through a unique respiratory system that keeps birds from overheating.
Indeed, flight is a marvelous ability, carrying these remarkable feathered creatures to wherever they please, even on journeys covering hundreds or thousands of miles. So next time you see a bird in flight, consider the amazing design behind its magnificent maneuvering.