- Have you ever had an experience where if eight year old you could see you now, they wouldn't believe your life was real?

Well, that just happened to me.

(upbeat music) I got invited to fly along with the Blue Angels, the US Navy's elite flight demonstration team.

To say that this was a bucket list, core memory, pinch me, dream come true experience, that would be the understatement of the millennium.

Every single second of this flight was the coolest thing I've ever done.

And Lieutenant Commander Ronnie put me through some seriously hardcore maneuvers, including 7 1/2 sustained Gs.

I know what you're thinking.

Did I pass out?

Did I throw up?

Don't worry, I'll give you plenty of opportunity to watch me suffer and answer those questions.

But there was one specific moment in the flight that I haven't been able to get out of my head, and I'm making this entire video to try and figure it out.

And that moment is right here.

We were inverted.

This is exactly the moment that I realized I don't really know how lift works So I set out to figure out just that.

And I did it the way that you'd expect a big nerd like me to do it, by building my very own wind tunnel so I could see it for myself.

Here's the problem.

I've heard lots of explanations of lift before, but every one of them seem to fail or be incomplete in some way.

So this video is my attempt to create the ultimate explanation for what keeps planes in the air.

One that's not only right, but also doesn't oversimplify or skip over anything, and that you don't have to be an aerospace engineer to understand because most of us aren't.

(playful music) Thank you to Anydesk for supporting PBS.

Hey smart people, Joe here.

I promised you the best explanation of lift that you've ever heard.

We're gonna get to the science in a minute, but let's be honest about why you're really here.

Before you learn how a plane stays in the air, you wanna see what it's like for a normal person to fly with the absolute best of the best pilots in the entire world, and see a fighter jet do some sick stuff.

So let's do that.

(upbeat music) Earlier this year, I took a trip to Pensacola, Florida, home base of the US Navy's elite flight demonstration team known as the Blue Angels.

What was immediately clear to me is that these men and women are seriously elite human beings who exemplify the absolute top class of skill and determination.

And they're really good at making an FAA team go zoom.

But first I should probably come clean that my friends at Blue Angels HQ apparently forgot to plug in the audio cable into the cockpit GoPro before we took off.

So you don't get to hear all the super interesting and cool stuff I'm saying.

- Can't hear you.

- But before you go getting mad at the Navy, look on the bright side.

This is my chance to add some sick 80s hair metal and homemade sound effects.

(upbeat music) And honestly, I think that makes it even more enjoyable than the real thing, which is really just half an hour of me saying, "Whoa, dude, that was awesome," like a hundred times.

No fighter plane ride along experience would be complete without watching a civilian like me try to maintain consciousness while having all the blood sucked out of their brain during seven plus G maneuvers.

This is suddenly real.

It's go time.

My seat for the morning.

Wish me luck.

So without further ado, enjoy watching me sit upon the throne of suffering.

In order to keep the extra weight of seven times the pull of gravity from sucking all the blood and oxygen from my brain and into my feet, I learned what's known as the anti-gravity straining maneuver, which is basically flexing every muscle in your lower body and squeezing your core in a futile attempt to keep enough blood pressure up top to maintain consciousness.

Right about here, you can see what it feels like to suddenly have your head weigh 50 pounds as your vision narrows to the diameter of a straw and everything goes black and white.

It was freaking awesome, and I wish I could do it again.

Now you might say that that means there's something broken deep inside of me, but remember, I did it for science, so it's all good.

I definitely don't have a problem.

Now with all the awesome highlights out of the way, let's get back to the question of what makes that plane fly.

Here's the problem.

Planes are heavier than air, so they need some kind of upward force to stay in the sky.

If you believe certain headlines out there, you might be led to believe that engineers and physicists don't actually understand what keeps planes in the air, which of course is a ridiculous thing to say because scientists understand flight super well.

We've made sick flying machines like the SR-71, the F-22, and the space shuttle.

What?

Did you think they were winging it?

If you're new here, you can expect a lot more of that, and no, I will not be apologizing.

Anyway, I think it's safe to say they know what they're doing and why it works.

The problem is why it works looks like this.

These equations, or so I'm told, because I certainly don't understand them, perfectly describe how fluids, and yes, areas of fluid, move when they encounter things like wings and how that produces lift.

But these hieroglyphics aren't a very satisfying explanation for, well, the rest of us.

So the challenge isn't that scientists don't understand what keeps planes in the air, it's that we need an explanation that ordinary people can understand.

I spent a lot of time looking at other explanations and I have yet to find one without some critical error or blind spot, but I think I've solved that.

and By the end of the video, you can tell me if I was right.

So here's our goal.

We need an explanation for lift.

Doesn't involve any scary math or going to college to get an engineering degree, is deep enough to capture the real complexity.

It feels satisfying and easy to understand, and most importantly, that isn't wrong.

Now, according to all of those hot and heavy arguments about what's happening to make flying work, you've got to pick a side.

either this guy's team or this guy's.

Big lift.

They're always trying to divide us, but I'm here to tell you that you don't have to choose a side because it turns out that neither of these fellas can give us the satisfying explanation that we're looking for, at least not on their own.

Let's start by looking at some of the other explanations that are out there so we can see where they fail.

Now, according to Team Newton, a wing works basically the same way as holding your hand out the car window.

Stick your palm at an angle and you can feel the air pushing it up.

Tilt it more, you get a bigger push.

And according to old Isaac, if the wing is pushing air down, the air knocks the wing upward in an equal and opposite reaction.

Okay, that sounds great.

Thanks, Newton.

Everybody can go home.

Except for two major problems.

This explanation has air behaving like a shotgun blast of tiny bullets bouncing off the bottom of the wing, and that, that's wrong.

Air acts like a continuous stream, not a bunch of little particles bouncing off of stuff.

On the other hand, the wing pushing the air down and the equal and opposite reaction pushing the wing up, well, that's logical.

It's simple.

It's pretty intuitive.

And it's not technically wrong, it just isn't enough.

A good explanation can't just be simple and correct.

It has to explain everything that we see, and that's where this one fails big because while it does a good job of creating the force we need to push a plane against gravity, it doesn't explain what happens up here.

And what happens up here is that we see an area of much lower pressure compared to the bottom of the wing.

Team Newton's answer doesn't have an explanation for any of that, so we need something else.

The next explanation you'll see of why lift works relies on some version of a wing that's longer on the top and has a shorter path on the bottom, and that makes the air move faster and have lower pressure on top versus the bottom for reasons.

This is team Bernoulli's answer, named after this Swiss scientist, Daniel Bernoulli.

Now, in the early 1700s, old Dan figured out his principle about how fast the fluid is moving and how that relates to its pressure.

And Bernoulli's principle is true.

I mean, faster air does have lower pressure, but it also can't give us a complete explanation of lift.

Often, the team Bernoulli explanation relies on saying that the air on top moves faster to catch up to the air on the bottom that it got separated from, and that gets a big fat L for a couple reasons.

Reason one, nobody can tell you why the air would do that.

There is no law of physics that says two bits of air that were next to each other have to meet up again later.

They aren't a couple.

They didn't carpool together.

Just like your middle school crush, the air on top has no idea the air on the bottom even exists.

Reason two is that when we actually test this idea, it turns out that the air on top doesn't catch up with the air on the bottom.

If we look at two blobs of air above and below the wing, the one that went over the top actually gets to the back first.

Equal transit time is a myth.

Even if all of this were true, it can't explain why planes can fly upside down, which I know they can because I've been in one, and it was awesome.

It also can't explain why an air foil shaped like this creates lift or why even a flat plate can create lift.

So we need a new explanation.

Above the wing, the air is getting squeezed into a narrower path like water through a nozzle.

Now, squeezing a fluid through a narrower space does speed it up.

That's true.

It's why putting your thumb over a hose makes the water shoot farther.

Problem is air above a wing isn't in a nozzle.

There's nothing up here for it to push against.

It's just more sky all the way up.

So we can toss that one too.

And then there's the one that your teacher or some other video creators might have done in front of you.

Hold up a piece of paper, blow across the top, and the paper rises.

Boom.

Bernoulli.

Cue the applause.

(audience applauding) Except this isn't what happens over a wing at all.

One stream of fast air in a room full of still air?

Well, over an actual wing, all of the air is moving.

And here's the kicker.

The air coming out of your mouth might be moving faster, but it's actually at the same pressure as the rest of the air in the room.

If this trick really did explain lift, then it should also work when I blow on a piece of paper pointing straight down and it doesn't.

Everyone who says this explains lift is lying to you.

The reason that every science teacher's favorite trick works is thanks to a thin little layer of lower pressure on top of that curved piece of paper, but the reason it's happening is the same reason that this ball gets held inside of a jet of air.

It's not because of lift.

Now it's time for the actual answer, and it uses exactly one simple idea.

A wing makes lift by turning the air.

Let's start underneath because that one's easy.

Air comes at the bottom of the wing, hits something that's in its way and gets bent downward.

This is that hand out the car window idea, but think about what it takes to turn something.

If you swing something on a string around your head, it desperately wants to fly off in a straight line.

And the only reason it goes in a circle is the string pulling it inward.

Let go, and it leaves in a straight line instantly.

Same thing in a car.

Turn left and it feels like you're getting thrown right, but what's really happening is the seatbelt seat and the rest of the car are pushing you left to drag you around the curve.

Anything that turns is getting pushed towards the inside of the curve.

There are no exceptions to this.

So what's pushing the air?

There's no string.

There's no seatbelt.

There's only one thing that can shove a chunk of air sideways, and that's more air, AKA- ♪ Pressure ♪ - This means wherever air turns, the pressure has to be lower on the inside of the turn.

Down here, further from the wing, we're closer to the inside of that turn, so the pressure has to be lower than up next to the wing.

Turning air is why the inside of a tornado sucks things in, and we see this in other fluids too.

If you stir a liquid, the lower pressure near the center gets pushed down into a vortex.

We're unlocking all kinds of secrets around here, aren't we?

Now, it's not hard to see why the bottom of a wing forces air to turn.

I mean, air can't go through the wing, but on top of the wing is where things get weird.

Now the air up here is curving too, and the inside of that curve points down toward the wing.

So let's start way up high, way above the airplane where the air is running in a straight line at totally normal pressure.

As we walk downward toward the wing, every step we take, the air is curving a little harder and the pressure drops a little further the closer we get to the inside of the turn.

By the time you get to the top of the wing, we're well below normal pressure.

From underneath, you get the exact opposite, pressure climbing the whole way up until it's at higher than normal, right at the surface of the wing, pushing up on the bottom.

And up on top, it's lower than normal, pulling it up.

That's lift.

That's the whole thing.

If you wanna put it in one sentence that you can carry around in your pocket, lift happens because wings turn the air.

(upbeat music) We never had to compare the speed on top to the speed on the bottom.

We never even needed the wing to be curved on top at all, which is why a flat shape can produce lift too.

And it's also why a sail works and why I could roll upside down in a fighter jet and not fall out of the sky.

So what is actually keeping a plane in the air when it's upside down?

(upbeat music) Fighter jets use wings that are symmetrical.

If we look at their cross section, they don't have a longer top than the bottom like an airliner wing does.

And when the pilot flips the plane on its back, they actually push forward on the stick, forcing the upside down nose up above the horizon and it turns the air just like it would happen right side up.

Of course, lift isn't unique to aircraft.

It also applies to race cars, sailboats, spinny wind turbines, and a whole bunch of other things.

And all of these create the forces they need by turning the air.

So we've got a pretty complete explanation put together now.

We can explain why the air on either side of an air foil creates low or high pressure thanks to the turning of the air, and we haven't fallen for any of those common misconceptions.

So we're ready to land this thing, right?

There's one more thing that we haven't quite accounted for, and I'm curious how many of you noticed it.

(gentle music) So what's missing from our explanation?

Well, we haven't explained why the air up here follows the shape of the wing at all.

The truth is it doesn't actually always do that.

If the angle of the wing gets too steep, there actually isn't enough pressure pushing the air down to follow the air foil, and this happens.

The result of this is a loss of lift called a stall, and you don't wanna be in an airplane when that happens.

But under normal circumstances, the air over the top really does follow the curve of the wing, and it joins back with the air from the bottom right here at the trailing edge of the wing.

And to learn why that happens, why don't we ask what else could hypothetically happen and see if we could eliminate any of those possibilities?

First, let's say the air does separate from the top of the wing.

That would create some sort of a void of low pressure here near the back or maybe even a vacuum.

And if that happened, the air up here would just push the stream back down to fill that void, ending up with the air following the wing.

Maybe the top and bottom air flows could meet back up somewhere else besides the trailing edge, like if the air took a ridiculously sharp turn and met up somewhere around here.

This is actually possible, mathematically speaking, but in real life, there just isn't enough pressure to make the air take that sharp turn.

So just by the process of elimination, we've gotten rid of basically every other place that these air streams could join back up, and we're only left with one, the place where it actually does happen, at the trailing edge after the air on both sides has followed the shape of the wing.

(upbeat music) So now you know more about what keeps planes in the air than at least 99.9% of people on earth, and you will no longer fall for any of those logical, intuitive, but ultimately wrong explanations ever again.

Lift happens because wings turn the air.

We don't have to pick a side because it turns out the real friends were the pressure gradients we made along the way.

Stay curious.

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Now I'm gonna keep playing with this thing.

I stayed awake.

- Best day ever?

- You did?

- You stayed awake.

- Best day ever.

- You stayed awake?

- Yeah, the world got about that big.

- [Speaker] He didn't pass out.

Wow.

- I don't know how he does.