How do birds fly?
Well, it mostly has to do with the shape of their wings
and how they move them. When a bird flies, it flies through air,
and the air flows over and under the wing. If we look at a section of a bird’s wing from
the side, we see that it is big up front
and then tapers off toward the back, kind of like an airplane wing.
When talking about flying, this shape is called an air foil.
Now the air flows around the wing like water in a river.
If you’ve ever been on a river, you’ll notice that it moves very slow at the
wide parts but speeds up really fast when the river narrows.
This is because the same amount of water that was in the wide parts
now has to move through a much smaller space at the narrow parts. And so the air is just like several rivers flowing side by side past the bird’s wing.
The shape of the wing, the air foil, makes it so the river of air
that flows over the top of the wing gets squeezed and narrowed.
Just like a river, this air has to speed up.
And the river of air that flows under the wing
actually widens and slows down a little. Just like a real river,
this air has to speed up. and when it does it pushes less on the sides.
Now imagine you are traveling down this river of air
and you have a canon on your boat. The air foil is an island
and you are trying to shoot it with your canon. But you have to reload the canon every time
you fire so you can only shoot it once every few minutes.
If you are going really fast down the river, you will only have time to shoot
a few canon balls at the island. But if you go down the wider part of the river
at a much slower pace, you will be able to hit the island
with more canon balls. This is kind of what happens with a bird’s
wing, but instead of canon balls,
it’s the air that is landing on the wing. Because the air on top is pushing less
on the wing than the air on the bottom, the wing gets moved upward.
This upward push is called lift and it is the main reason birds are able to
fly. But there are other tricks birds use too.
To get more air to pass over their wings birds will flap them,
especially when taking off. When they do, they rotate their wings
forward and down and then lift them back up to start over again.
Rotating the wing forward causes the lift from the air to push the bird,
not only in an upward direction, but forward as well.
This forward push is called thrust. As you can imagine, all this flapping takes a lot of energy,
and so birds have large lungs to help them breathe
and strong muscles to move their wings. Not only that, but their body is shaped
to cut through the air efficiently and their bones are hollow,
which makes them very lightweight to begin with.
So a bird relies on many tools to get through the air –
not just its wings. As for people, we are heavy
and can’t produce the energy needed to fly by ourselves,
so we use aircraft to get through the air. Even though we use machines
to get off the ground, it’s still fun to imagine
that we can fly like the birds.