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Alive & KickingBirds Do Have Propellers |
The neighbor's black cat just sent 20-plus birds into the air from our backyard feeding station.
I have a soft spot for hungry birds: I never tire of watching them fly.
No wonder that theme, "If birds can fly, why can't I?" fit so well when man began to conduct test flights for himself.
Pull up a stump, and let's consider flight. It seems to have three major components: lift , forward motion and steering.
Simply said, lift is accomplished by airflow across a wing's curved upper surface, lowering air pressure above the wing, causing the pressure below the wing to be the greater force supporting the bird.
Stop the airflow across the wing, and gravity will win: the bird is on its way down.
Likewise, of course, aircraft wings provide lift . A convex upper surface, airfl ow and greater pressure below the wing lift the plane.
What causes the bird to move forward? Birds are experts at propulsion. They use air currents (wind), change in altitude, gliding, wing movements, tail twists, wing twists, tail flaps, feather rotation, and many more natural techniques in concert or singularly in ways we likely don't even recognize to get forward motion accomplished with efficiency and beauty.
In order to move forward, a duck in water pushes water backward. In order to run, we push against the earth. Similarly, the bird in flight pushes air backward to propel itself forward.
The primary wing feathers, ten on each wing, are found on the outer wing segments. If you examine a primary feather by its central support you will notice the feather veins on each side differ in width.
Hold the feather gently by its quill and force your hand downward as in a flight power stroke. The feather will rotate, the wider side twisting upward rather like a fan blade or a propeller blade, forcing air behind the bird in flight. The bird's ten primary feathers on each wing act as half-rotation propellers!
As the wing power stroke occurs, the entire wing tends to elevate along the trailing edge, forcing the air backward and the bird forward. Flight is complex; there is a great variety among birds and how they have adapted to propel themselves forward in flight.
Steering is largely controlled by raising a wing or twisting the tail toward one side or the other. A twist to the right results in a right turn. A raised right wing results in a left turn and vice versa. Lower the flaps, and landing is in the works. (Do they fold their tray tables upward?)
I had a young crow once, which fell or was pushed from its nest. A "friend" gave him to me.
The kids and I raised Crow-Magnum until he fledged. On his first flight attempt, he made it to the top of an 80-foot evergreen tree where fear overcame him. He cried all day and spent the night on his high perch.
The second day, fear gave way to gravity, which put him back on the ground.
I'm not surprised that DISTRESS calls went out on his very first flight!
It is difficult to fathom how instinct can completely program that first venture. I suspect observation of other birds may play an important part. The careful observer of birds in flight will detect many flight skills.
Once again, the eyes have it!
Guest columnist John Cooke taught high school biology for 30 years and is pleased to share his insights with our readers.