How Bird Wings Work (Compared to Airplane Wings) - Smarter Every Day 62

[Music] Hey, it’s me D, and welcome back to Smarter Every Day. So, some of my favorite things to learn are those things that I've seen for several years, and I've made a lot of observations, and I kind of think I get it, you know? I mean, like really get it, and then I find out I don’t.

So, when I first saw what I'm about to show you, it blew my mind because it was so simple I should have seen it my entire life, but I didn’t. Look at this bird. The muscle that flaps the wing is here toward the center, and he pushes down on the wing. But the feathers going out towards the edge of the wing are overlapping in such a way that they all push together on the downstroke.

But on the backstroke, they delaminate, allowing them to open up like louvers and allowing the wind to pass through them. This means there's a lot less resistance on the backstroke. Basically, this bird wing is a biomechanical check valve. That's amazing! I've never thought about that.

But I saw in the high-speed video in Peru on the macaw for the first time. This is why I've never seen it. Look how fast it happens! There's no way I could have observed that, but watch the malls in high speed, and you can see for yourself. Clearly, the feathers are delaminating on the backstroke.

On the downstroke, you can see that all the feathers are lapped in such a way that they provide a firm boundary layer that air can't pass. But on the upstroke, look what happens. You can see that the wings separate, and the feathers turn so that the air is flowing straight in between them. You can even see straight through the wing! I think that’s amazing!

So, he has a lot less resistance on the backstroke than he does on the downstroke. Another thing he does to decrease this resistance on the backstroke is he's performing more of an elliptical sweep with his wings, instead of just an up and down flap.

So, what he's doing is, on the backstroke, he's pulling that wing in and he's decreasing the length, so he decreases the surface area of the total wing. That’s pretty awesome as well! So, one of the coolest misconceptions I had is pretty clear to see on this red macaw.

I used to think that birds just flap down and they create high pressure underneath them, and they push themselves up. But if you look at this macaw, something else is happening. Look at the back of his wing here; you can see that the feathers are being lifted up on the downstroke. What that means is we have a low-pressure situation there.

It's like in engineering when we use something called computational fluid dynamics. Basically, what we do is we analyze the flow field and we figure out what pressure situations we have at each location. Now, you know that on an airplane wing, we have a low-pressure situation on top—that's exactly what's happening with this red macaw.

So, look at his wing, and you can see that not only does he have a high-pressure situation on the bottom, but the low pressure is so great that it's pulling those feathers off of his wing. That's amazing! So, not only is he pushing down, but he's being pulled up on the same stroke. That's pretty awesome!

Now, this green parrot is doing the last thing that I thought was pretty wild. If you notice, he is angling the tips of his wings on the backstroke and pushing back behind him, so he's providing thrust. But one thing that's happening that I don't really understand, but it looks like it could be true, he's breaking his wing in half between the secondary and primary feathers, and he's angling it.

It looks like he's diverting that flow down, almost like a vertical takeoff Harrier jet. It's pretty cool, and I think it could be happening! But I've never actually thought about a bird being able to provide downward thrust on a backward stroke. That's pretty wild!

So, I thought I knew how flapping flight works, but clearly I didn’t. Send this to any of your buddies that like to think critically, 'cause they'll do what I do now; every time I see a bird against the sky, I watch his wing.

And on the downstroke, right at that point where he's pausing to transition back to an upstroke, if you watch, you can see sunlight pop in between the feathers because he's opening it up for lower air resistance on the backstroke. And I think that's awesome because now I know how bird flight works!

Anyway, I'm Destin; you're getting smarter every day, and I'll leave you with this picture that my daughter made by gluing homing pigeon feathers to a piece of paper to create her own bird. You're getting smarter every day; have a good one!

We are in the middle of a cotton field in Alabama. If you've never seen it, it's a really pretty sight. What are we going to do here, son? Let this bird go!

We're going to let this bird go, but before we let the bird go, we're going to talk about his feathers, aren't we?