Why do planes fly?

Daniel and Kelly dig into the surprisingly controversial question of why airplanes stay in the air. See omnystudio.com/listener https://omnystudio.com/listener for privacy information.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Daniel Whiteson?

  This is an iHeart Podcast. Guaranteed Human.

• 0:05Speaker 01

  If you're a custodial supervisor at a local high school, you know that cleanliness is key and that the best place to get cleaning supplies is from Grainger. Grainger helps you stay fully stocked on the products you trust, from paper towels and disinfectants to floor scrubbers. Plus, you can rely on Grainger for easy reordering, so you never run out of what you need. Call 1-800-GRAINGER, click Grainger.com, or just stop by. Grainger, for the ones who get it done.

• 0:35Speaker 02

  Hey, I'm Niall Rogers. This fall, I'll be driving across the country, meeting some of today's coolest and most fascinating artists. We'll explore the stories before the moments that changed everything, because every musician remembers the moment where it all began. Experience Before the Moment, a Lincoln original series on the iHeart Radio app, YouTube, or wherever you get your podcasts.

• 1:12Daniel Whiteson?

  They say that any technology sufficiently advanced is indistinguishable from magic. Well, there's one technology that people have lusted after for thousands of years that we now rely on, even find routine. I'm talking, of course, about flight. It's been only 100 years since people were able to leave the ground and fly through the air and return safely. Now, it's so routine that people sleep through it. But imagine what that would seem like to someone from 1,000 or 10,000 years ago. It's essentially like magic. Of course, we know it's actually not. It's science, because we can understand it and we can break it down. We can explain it. We understand why planes fly, right?

• 1:55Daniel Whiteson?

  Do we? Could we actually explain it to visiting ancestors from the deep past? Or is it still some kind of black magic, even for modern humans and the best aeronautical engineers? So today, on Daniel and Kelly's Extraordinary Universe, we'll be asking an old question: Why do planes fly?

• 2:27Kelly Weinersmith?

  Hi, I'm Kelly Weiner-Smith and my favorite way to travel is by train.

• 2:31Daniel Whiteson?

  Hi, I'm Dana White, and I'm a particle physicist, which means I have to fly around the world to get to the biggest particle accelerator.

• 2:37Kelly Weinersmith?

  And what is your worst flight experience?

• 2:42Daniel Whiteson?

  My worst flight experience is traveling with my own six-month-old baby. We had a bassinet and we got her to sleep in the bassinet and we thought, oh, this is gonna be great. Then the stewardess came by and said, oh, there's some turbulence. You have to take her out and put her in a seat and buckle her in. And we said, no, she's sleeping. And she said, sorry, it's the rules. And everyone around us went, oh, no. And they were right because she screamed for the rest of the eight-hour flight.

• 3:09Kelly Weinersmith?

  Oh, no, that's horrible. I'm so sorry. When you finally get your kid asleep and something wakes them up on a plane, it's the worst.

• 3:16Daniel Whiteson?

  It's the worst. And everybody knew it was the worst and we all knew there's nothing we could do. But hey, you know, them's the rules. How about you? What's your worst traveled experience?

• 3:25Kelly Weinersmith?

  It also involves flying with my child. She was probably about six months old, around there also. And I brought a change of clothes for her. I was totally prepared for her. She was sitting on my lap and we were about to take off. And right as the plane started moving forward, she had a blowout poop on my lap. And so it smelled horrible, but you can't get out of your seat until you're retrusing altitude. So everybody was like giving me dirty looks and covering their noses. And it took like 20 minutes before we were allowed to get out of our seats. And then, you know, I had to change her in the airplane changing room, which is like so tiny. I thought she was gonna fall off the little tray. And anyway, I brought a change of clothes for her, but I didn't assume I'd have poop on my pants.

• 4:07Daniel Whiteson?

  Oops. Classic parenting mistake.

• 4:10Kelly Weinersmith?

  Exactly. So I smelled horrible the whole flight and people kept looking at me and it wasn't a lot of fun, but them's the breaks. You gotta leave the house with kids sometimes.

• 4:19Daniel Whiteson?

  You just gotta look back at those people and say, hey, who's gonna pay for your social security, right? Somebody's gotta make the next generation. And it's me, Madame Poopy Pants.

• 4:31Kelly Weinersmith?

  I'll get a little like badge that says that uh now whenever I see a parent with a kid, I'm like, what can I carry for you? How can I help? Like I offer to help out all the time.

• 4:41Daniel Whiteson?

  Yeah, exactly. And the big lesson I learned is never judge. You never in somebody else's family, you don't know what they're going through or what they're struggling with or how much they slept last night. Just help and smile.

• 4:51Kelly Weinersmith?

  Yep. And kids are always at their worst because they're always the tiredest and they're not used to it. And so like, anyway, yes, don't judge. But planes are wonderful. I needed to get from place to place and I needed to get there quickly. And actually, I wouldn't have wanted to take my daughter on a long train ride for the journey that we were going on because it would have been days. But I was flying to London the other day and we had kind of talked about, why do planes fly? And you said it's complicated. And while I was, you know, above the Atlantic, I thought, how complicated? How well do we understand this? I hope the answer is really well. So I'm looking forward to today's conversation.

• 5:25Daniel Whiteson?

  Good. Well, this question actually came to me from a listener, Tom Johnson from Ohio, wrote to me and asked if we could explain why planes fly? Because he looked into it a little bit and he was kind of confused. So he wanted a clear explanation for why it is that planes stay in the air.

• 5:43Kelly Weinersmith?

  And if you have a question that you want to ask us, we would be happy to answer them. So send us an email at [email protected].

• 5:51Daniel Whiteson?

  When I told Tom that we were going to answer his question on the pod, he said, quote, "My wife is absolutely going to roll her eyes tonight when I tell her over sushi." Which made me wonder, Tom is in Ohio, where is he getting his sushi? Probably they have it flown in. So even his sushi relies on airplane wings.

• 6:07Kelly Weinersmith?

  Yeah. And you know, I lived in Ohio for a decade or more. And I can tell you that when sushi has to fly that far, it's not great. You're too far from the ocean at that point.

• 6:19Daniel Whiteson?

  You're saying nobody should fly to Ohio for sushi?

• 6:21Kelly Weinersmith?

  No, I'd say that. I'm going to go on the record saying you shouldn't fly just to Ohio for sushi. Ohio's got other things going for it.

• 6:27Daniel Whiteson?

  You should have Ohio pride, you know? I know you're a transplanted Virginian, but like you come from Ohio. A good thing about Ohio, for example, is it made you.

• 6:35Kelly Weinersmith?

  You know, I was actually born in New Jersey, which is an even harder state to defend.

• 6:41Kelly Weinersmith?

  But I do actually love New Jersey and I will defend New Jersey. But you know, Ohio was a very safe place to grow up where I grew up. And so that's fine. And I think Ohio has made the most astronauts. And so, you know, we all would make jokes about, you know, what is it about Ohio that makes you want to get as far as possible away from this planet? And I'm not sure if Ohio is still winning in astronaut production, but it was at some point.

• 7:04Daniel Whiteson?

  All right, well, let's stop flying around the issue and get to the question. I was wondering what people out there thought about how planes stay in the air, how wings work, what stories they had been told and what they understood about this question. So as usual, I went to our bank of volunteers to ask them, why do planes fly? If you would like to play for future episodes, please don't be shy. Write to us to [email protected]. In the meantime, think about it for a moment. Why do you think planes fly? Here's what a bunch of listeners had to say.

• 7:36Speaker 04

  I believe nobody really knows. I would be glad to learn otherwise. I know that I've read in my school book that the air takes a longer way on the top of the wing than on the bottom of the wing. And therefore we have a sort of suction going on that pulls the wing up.

• 7:51Speaker 05

  Planes fly because they want to and because of the differential air pressure.

• 7:57Speaker 06

  Forces the air to take a longer path to go over the wing versus under the wing. And this differential in the path length reduces the pressure on the upper surface of the wing. And that provides lift.

• 8:16Speaker 07

  There's some confusion surrounding the Bernoulli effect and the airflow speed over the top and bottom of the wings.

• 8:24Speaker 05

  There's lift, which means that the air going over the curved part of the wing takes longer than the air. Going underneath the wing, so the lift is created there. Takes longer for the air to go over the top of the wing.

• 8:36Speaker 02

  The aerodynamics of that wing shape causes low pressure to form over the top of the wing and high pressure to form under the wing. So wasn't it to do with Leonardo da Vinci came up with the the original idea to base planes on the updraft from wings of birds? Planes fly because they can't swim. I think that light planes such as paper planes can't fly just because of aerodynamics. But heavy planes need engines to generate pressure difference, but I am not entirely sure how this works.

• 9:17Speaker 02

  So you have to have thrust greater than drag and lift greater than gravity. A higher pressure below and a lower pressure above. Top of the wing is curved, so the air has to travel further.

• 9:31Kelly Weinersmith?

  I thought that planes flew because their motion forwards caused air to flow over their wings and created a a force that pushes up on the wings. So I think planes fly because of the way that the wind bends around the wing? Planes fly because the lift that they generate is greater than the gravitational pull. The air has a longer way over the wing than under the wing. The top of the wing, because of its shape, it makes a suction, so it sucks the plane up. I'm not actually completely sure why a plane flies, but I know I've been in them and they tend to do that, and I hope they continue to do so.

• 10:16Kelly Weinersmith?

  I love that the answers were a combination of people who clearly sort of know what the answer is and like gave good answers and then people who are hilarious.

• 10:27Kelly Weinersmith?

  Because they can't swim made me laugh out loud, so bravo.

• 10:32Daniel Whiteson?

  You know, I love that approach. You don't know the answer? Tell us a good joke. Yeah, absolutely.

• 10:37Kelly Weinersmith?

  That might be one of the keys to life, I think.

• 10:41Daniel Whiteson?

  I want to see that more in my physics exams, you know, when somebody doesn't know how to solve this quantum mechanical problem, hey, write me a good joke. I'll give you some points anyway.

• 10:49Kelly Weinersmith?

  You will give points for humor.

• 10:50Daniel Whiteson?

  Sure, absolutely. I used to regularly have a question on exams that was just a random New Yorker cartoon. And then the question was, write a physics related caption for this cartoon.

• 11:00Kelly Weinersmith?

  Oh, nice. I love that you're encouraging creativity. I had an exam where I could get five extra credit points if I drew a parasite. And you'd think that that would be great. But I was like, I hate this because I don't even do nice stick figures. That's why I'm married an artist. He takes care of all of it. But the good thing is there's a stage of parasites where they essentially just look like a circle. And so I just said, oh, there's a metasuchariocist. Done. And I didn't get full credit. All right. So where do we start?

• 11:27Daniel Whiteson?

  So the beginning of the question of why planes fly goes all the way back to the Wright Brothers in 1903. You know, the Wright Brothers, they were engineers. They were not physicists. And so while the Wright Brothers made a plane fly, they actually didn't understand it at the time. Like, they had no principles. They had no theory. They had no real reason to think their plane was going to fly. They just kind of made it work. And then they were showered, of course, with awards and fame and all sorts of stuff, which led some people in the physics community to get a little bit resentful.

• 12:00Kelly Weinersmith?

  So if they had no idea, why did they pick the design they picked? Is it because they were building on things that other people had made that maybe they understood what they were doing? And so they just sort of tinkered with that?

• 12:11Daniel Whiteson?

  Yeah, engineering is a lot of tinkering, right? It's like, let's try this, let's try that. And sometimes things work. And then later, you figure out why that thing floats, or why does this thing fly? And that's essentially what happened with the Wright Brothers. And they won this fancy award from the aeronautical society. And one physicist, Colonel Fullerton, wrote in and said, quote, I think it was a mistake of the aeronautical society giving the rights and medal for their contribution to aeronautical science. I agree with their having the medal, but it should have been for what they have done. In other words, they didn't understand it. They didn't actually advance aeronautical science. They just sort of like, made it work. And they left open the question of like, why does this work?

• 12:48Kelly Weinersmith?

  I still feel like there should be a medal for the moment when you're about to like, push your plane off the cliff. And you're like, we don't understand what's going on, but hee haw.

• 12:58Daniel Whiteson?

  The Wile E. Coyote Award or something.

• 13:00Kelly Weinersmith?

  Maybe it's a subset of the Darwin Award. Yeah.

• 13:03Daniel Whiteson?

  And this turns out to be really important politically because this is just before World War I, right? And so World War I is beginning and we have nations trying to figure out like how to make planes fly, how to make them stable. And nobody really understood like why some things work, how to make them better. And if you don't have like a model for why planes fly, it's pretty hard to improve their performance. And so just before World War I, you had all these folks in Britain and then also on the continent trying to understand the theory of flight so they could take advantage of it militarily.

• 13:37Kelly Weinersmith?

  Okay, so the Wright brothers didn't have a theory and nobody else had a theory either. So everyone was just tinkering to see how it worked and that it worked for the Wright brothers. Did the fact that it worked for the Wright brothers give insights into why it would work? Like, did their design work because it took advantage of some physics principle that became obvious after the fact to the physicists?

• 13:59Daniel Whiteson?

  It certainly isn't obvious after the fact because people are still to this day arguing why planes fly. And it's fascinating that the divide in the field, we're going to dig into this, really goes back to the split that happened in World War I, where you had this sort of like mathematical battle between the scientists. You had the British trying to figure it out and you had the Germans trying to figure it out and they took different approaches. And those approaches still live on and do battle in science today, in modern aeronautical engineering. The Germans took this approach of thinking about air as a fluid flowing over the wing and analyzing the velocity and thinking about the pressure. But the British didn't like that approach. It made some approximations that made them uncomfortable and they liked using Newton's forces, Newton, of course, being British. And so to this day, we have two competing theories

• 14:43Daniel Whiteson?

  for why planes fly and how they work. It's fascinating to me that we still haven't figured this out. You're right, we had a working example about 100 years ago and that definitely helps, right? It rules some things out, it inspires experiments. So having a working example is useful, but it doesn't always tell you exactly why something happens.

• 15:01Kelly Weinersmith?

  So are these theories, which I'm sure we'll get into the details of in a second, are they different enough that that resulted in the British and the Germans having planes that had different shapes during World War I? Or do both theories sort of predict that the same plane shape? Is good.

• 15:18Daniel Whiteson?

  Yeah, they make different predictions about what's important in the shape of the wing, which is fascinating. And I found this quote from a historian, David Blor, who said, "On the eve of the Great War, none of the British workers in the field of aerodynamics had any workable account of how an airplane could get off the ground," which, you know, makes it pretty hard to optimize the performance of your warplanes.

• 15:39Kelly Weinersmith?

  And pretty scary to get into a warplane, on top of all the reasons that it's scary to get into a warplane.

• 15:45Daniel Whiteson?

  Exactly. And later on, we'll hear about Albert Einstein's personal design for an airplane, which really didn't work very well.

• 15:53Kelly Weinersmith?

  So let's dig in. Should we start with the Germans or should we start with the British?

• 15:56Daniel Whiteson?

  So the German story is the one that most people have heard about. It's this theory of fluids and flow and Bernoulli's equations and all this kind of stuff. So we should start with air to make contact with what most people think about when they think about flight.

• 16:09Kelly Weinersmith?

  All right, let's do that.

• 16:10Daniel Whiteson?

  So the usual story for why a plane flies has to do with the shape of the wing. And so aeronautical engineers call this an airfoil. It's roundy in the front and it's pointy in the back. It's sort of like a long, thin teardrop, right? The idea that you're usually told is that the shape of this wing creates a pressure difference, that you have lower pressure above the wing and higher pressure below the wing, and that creates lift, because higher pressure below and lower pressure above basically pushes up on the wing. And it's the shape of the wing that's crucial in creating these pressure differences, which is what creates lift. So that's the usual story for why planes fly. That comes down to this particular shape of the wing.

• 16:52Kelly Weinersmith?

  So you've got this curved edge moving towards the air quickly. Why does that shape not create the same amount of pressure on the top as it does on the bottom? Because that shape is like symmetrical, right? Is it because when it goes over, it has more space to sort of spread out?

• 17:08Daniel Whiteson?

  So the shape is not actually symmetrical, right? Typically, it's like flat on the bottom and more curved on the top. And so the shape is not actually symmetrical, which is why the Bernoulli story tells you that it pushes up. Bernoulli is a guy in the 1700s who was thinking about fluid flow and mostly about like water through pipes and pressure and volume. And like fluids are still something we're struggling to understand. But Bernoulli had a simplified view of it, which Euler actually came through later and proved all of his equations for him. But Bernoulli's principle tells us that faster moving fluids have lower pressure and slower moving fluids have higher pressure. So if the shape of the wing as it moves through the air makes the air go slower under the wing and faster above the wing on this curved shape,

• 17:51Daniel Whiteson?

  then that'll generate lower pressure above the wing and higher pressure below the wing, and that gives you lift.

• 17:57Kelly Weinersmith?

  And that feels easy to test, right? Because you just flip the wing over and it should do the opposite, right? Like it should send you plummeting downwards?

• 18:07Daniel Whiteson?

  Yes, already you're identifying a problem with this, but before we take this explanation apart, let's do a little bit more to support it because you're right, it kind of is easy to test and you can do a simple test at home. You can just like take a piece of paper and blow air above the piece of paper. And what you see is the paper goes from being sort of droopy to being flat. So it's sort of like lifts up. And so it's like a classic simple at home demonstration. What you're doing is you're increasing the velocity of the air above the paper, which in theory lowers the air pressure above the paper, which provides lift because now the pressure is higher below the paper and lower above the paper. And you know, this story of like the air moves faster over the wing and slower below the wing

• 18:48Daniel Whiteson?

  is also verified in lots of other experiments, like you can do these smoke tests where essentially you put a wing in a wind tunnel. And instead of just blowing air over it, you blow smoke over it, smoke just being like a bunch of particles. And you can track those particles and you can measure the velocity. So basically measure the velocity of the air around the wing, see what happens, right? Don't just like talk about it, you know, in your salons while you're smoking cigarettes or whatever, actually figure it out. And this is verified, like wind tunnels and smoke tests tell us that the air does move faster over the top of the wing than below the wing. And so this seems like it all sort of comes together, but as you identified, there are some important limitations to this explanation of why planes fly.

• 19:30Kelly Weinersmith?

  So when you get a window seat near the wing and you look out, it's easier to see, like it's bunching up and it gets a little bit like kind of white-ish. Is that pressure forming? Like, are you sort of bunching up the air molecules to the point where they're visible? Or is something else happening there? Or am I imagining it? And this is like an episode of the Twilight Zone.

• 19:50Daniel Whiteson?

  Nobody else sees that, Kelly. Yeah, exactly. It's just you.

• 19:53Kelly Weinersmith?

  That was such a great episode.

• 19:55Daniel Whiteson?

  Love that. No, I think what's happening there is you're seeing more water vapor. There are definitely changes in the air pressure below and above the wing. And as you know, water is very sensitive to pressure, what the vapor point and all this kind of stuff. So what you're seeing there is not the air itself, but water vapor forming, which can show you, just like in these smoke tests, can show you where the air is flowing. So that is pretty cool.

• 20:15Kelly Weinersmith?

  That sounds obvious now that you say it, but why did I ask that? But whatever, that's fine. Okay, so we decided now we're going to talk about the limitations. Has anybody flipped the wing the other way and then saw what happened? Did that plane still fly?

• 20:31Daniel Whiteson?

  So planes fly upside down all the time, right? A big problem with this explanation is that it predicts that the asymmetry of the wing is crucial, right? That the curvy bit on the top compared to the flat bottom is really important for making lift. And so it predicts if you flip that over, planes should like crash to the ground, right? That an upside down wing should have anti lift or should have a net force downwards. But we don't see that, you know? You can fly planes upside down all the time. Everybody who's been to like an aeronautics show has seen old fashioned planes or new planes. They can fly upside down. So Bernoulli's equation doesn't answer this question. This can't be the complete story of why wings provide lift, because it gives the wrong explanation for upside down planes.

• 21:16Kelly Weinersmith?

  So you mentioned that Euler figured out all of these equations to support Bernoulli. Does it turn out that Euler's equations were missing some important factor? Because the equation said it should work, but then it doesn't work. So what was missing in the equations?

• 21:30Daniel Whiteson?

  Oh, yeah. Great question. And this really goes to the heart of what's going on here. There's nothing wrong with Bernoulli's equations. And I'm giving Euler credit only because Euler came along and like did all the math. Bernoulli had like these leaps of insight and like, oh, I think this and that and the other thing. And then Euler came along and actually like dotted all the i's and crossed all the t's. And I think Euler would have gotten credit for these equations if he hadn't already gotten credit for like 80% of everything in mathematics. So much of stuff in mathematics that like Euler just let somebody else take credit for. He's already got everything else named after him, which is amazing. So there's no problem with Bernoulli's equations, but they're always a simplified description. Like Bernoulli's equations describe fluid flow and they make some assumptions like they're talking about a fluid as if it's incompressible.

• 22:14Daniel Whiteson?

  For example, or you're talking about it as if it's not made of microscopic particles. That's not true, right? Air is made of microscopic particles. It is compressible. That doesn't mean that the equations don't apply. It means that they apply in some limited sense. It also might just be the wrong story. It might not provide the answer, the explanation. You know, what we're looking for is an answer to a question which is macroscopic. Like we see the wind go through the air, the wind goes up. We want to know why. That's sort of like a human question, right? It's not a mathematical question. It's not like there's a prediction, a number we're trying to calculate. We want like a story that tells us why this is happening. And that's a little bit more slippery than just mathematics. It's something to do with cause and effect and understanding.

• 22:58Daniel Whiteson?

  And you know, it's at the heart of science is coming up with these stories, but it's not always easy. Especially when we're zooming out from a microscopic universe to try to tell a story macroscopically. It's like economics, you know, you can ask like, why do prices go down? Well, I have this theory of inflation. I have a theory that involves prices and supply chains, whatever. And like the theory can be correct, but it doesn't always apply because the conditions it assumes aren't always relevant. And it doesn't always answer the question that you're asking.

• 23:26Kelly Weinersmith?

  I feel like the next time I get on a plane, I'm going to think to myself, I wish it were simple. I wish we've really understood this, but planes tend to stay up, so that's good. So we've established that the Germans got everything wrong in World War One. Oh, wait, was that World War One or World War Two?

• 23:43Daniel Whiteson?

  This is World War One we're talking about.

• 23:45Kelly Weinersmith?

  Well, they got it wrong both times. Sorry, guys.

• 23:56Speaker 02

  Hey, it's Nile Rodgers, host of Before the Moment, a Lincoln original series. I'm driving across the country, meeting some of today's most fascinating artists. We're exploring the stories before the moment that changed everything. This week, I'm joined by my friend, John Legend. What still makes you just sit down at the piano? If you sat down at nine AM and then at noon, you had a full song that you recorded and put

• 24:25Speaker 06

  Your voice recorder or you record it at your studio. You've just created something brand new that didn't exist when you woke up. What a beautiful feeling it is. I'm always excited to write something new. I've been writing for Broadway, which has been a new challenge with new collaborators and amazing performers who are triple threats, who can sing and dance and act and do all these amazing things. And I want to keep feeling that. And so that means not resting on my laurels, going out there and continuing to create something new.

• 24:54Speaker 02

  Experience before the moment. A Lincoln original series on the iHeart Radio app, YouTube, or wherever you get your podcasts.

• 25:03Speaker 01

  OnDeck is built to back small businesses like yours. Whether you're buying equipment, expanding your team, or bridging cash flow gaps, OnDeck's loans up to $400,000 help make it happen fast. Rated A+ by the Better Business Bureau and earning thousands of five-star TrustPilot reviews, OnDeck delivers funding you can count on. Apply in minutes at ondeck.com. Depending on certain loan attributes, your business loan may be issued by OnDeck or Celtic Bank. OnDeck does not lend in North Dakota. All loans and amounts subject to lender approval.

• 25:32Speaker 06

  This is Shirley Strawberry from the Steve Harvey Morning Show. Buy smart, drive for less, and trade for more. That's Toyota affordability. And it starts with a great deal on an all-wheel-drive Camry, Corolla Cross, or a Corolla Sedan with the latest features and tech. Or test drive a spacious Grand Highlander or adventure-ready RAV4. And with so many hybrid models available, you can enjoy longer trips without all the stops. While Toyota's legendary resale value means you could get more at trade-in, get a great deal today and a great value tomorrow. Shop toyota.com for deals and details. Toyota, let's go places.

• 26:22Kelly Weinersmith?

  Okay, so we know that when a plane flips over, it doesn't go crash into the ground. What was he getting wrong, Bernoulli?

• 26:30Daniel Whiteson?

  So Bernoulli's story is very nice and it's very simple, and there's lots of it that's correct. But as you say, it doesn't explain some things. It doesn't explain why planes can fly upside down. And it also doesn't explain something really crucial at the heart of the story, which is, why is the air moving faster over the top of the wing than the bottom of the wing? Like we said, the wing is asymmetric. It's curvy in the top and it's flat on the bottom. But why does that make the air go faster over the top? And you often hear this popsye explanation, which is completely wrong, which is that it's a longer trip over the top of the wing. So the air has to go faster in order to like, meet its air particle partners at the back end of the wing.

• 27:11Kelly Weinersmith?

  Why would it have to?

• 27:12Daniel Whiteson?

  Exactly. Why would it have to? It doesn't have to. It's nonsense. But you hear this all the time. I was taught this myself. You know, that like when air particles hit the front of the wing, if one goes above and one goes below, then to meet up again at the back of the wing, the one that takes the longer route would have to go faster. And it's an example of like, it's a compelling story, but it doesn't actually make any sense because they don't have to take the same time. It's fine. The universe doesn't like crash or implode or hit a seg fault or something if the air particles don't meet up again.

• 27:44Kelly Weinersmith?

  Yeah, right. They're not like buddies. They don't have to get to the same spot at the same time.

• 27:48Daniel Whiteson?

  Yeah.

• 27:48Kelly Weinersmith?

  All right, so that doesn't have to happen.

• 27:50Daniel Whiteson?

  So that doesn't have to happen. That's not the explanation for why air moves faster over the top. And so the Bernoulli story is sort of lacking that explanation, like why is there this pressure difference? And it opens this door to this question of like, well, do the speed differences cause the pressure differences? Or is it the pressure differences that are causing the speed differences? Because Bernoulli's equation doesn't give us causality. It just says lower pressure, higher speed. It doesn't say that lower pressure is caused by the higher speed. It could also be the higher speed is caused by the lower pressure. So that tells us that we need more to the story. Bernoulli's story can't describe completely why planes fly, because it doesn't tell us why planes fly upside down. And it doesn't explain why we see air going faster over the top of the wing, which is something we definitely see happening.

• 28:36Kelly Weinersmith?

  Alright, so I know we're about to talk about another explanation, but does looking at birds help at all? Because they have, you know, different kinds of wing shapes, and they've kind of figured it out over evolutionary time. This isn't going to give us the pressure answer, but does it give us some insights into like, how these wings should be shaped? I'm getting off track, but I just looked at a picture of a bird in my office, and now I have to ask.

• 28:58Daniel Whiteson?

  It does, and bird wings work with similar principles to airplane wings, except of course, for the flapping part. But for gliding, they do. Fascinatingly, insect wings are even more complicated, and insect flight is not something we understand like at all. It's really kind of incredible. We should do a whole nother episode about why insects fly.

• 29:16Kelly Weinersmith?

  And if you're ever feeling depressed, there are some slow-mo videos of insects trying to take off, and it is the most clumsy, amazing thing I've ever seen. It blows my mind that they ever get off the ground, and it makes my daughter laugh so hard she pukes a little. So.

• 29:30Daniel Whiteson?

  I knew a guy who did these experiments where they put an insect on a pin, and like glued it to a pin, and then they showed it videos. So it was like, thought it was flying, and they would like try to take videos of its wings moving to understand it. It's kind of incredible.

• 29:43Kelly Weinersmith?

  Alright, this has been an amazing tangent. I've had a lot of fun. Let's go back to World War I, which is less fun. So I think we've talked about the shortfalls in Bernoulli's explanation. Are we ready to move on to what the British folks were thinking?

• 29:56Daniel Whiteson?

  Yeah, so across the English Channel, we had folks that are working on a completely different theory. And not a completely different theory just because they disagreed scientifically with the best approach. Remember, there's a war here, and so they're not going to collaborate. They're not going to be like going to the same conferences and sharing their ideas. It's sort of like when evolution splits. You know, you get all these weird animals off on an island, and they diverge into their own crazy direction and get weird pouches for their babies or whatever. It's what happens when you work in isolation. You get competing explanations. And so we have this fascinating sort of social experiment where you like isolated two groups of scientists and asked them to solve the same problem, and they took very different approaches.

• 30:33Kelly Weinersmith?

  So was it like allopatrick speciation where they weren't encountering each other at all anymore? And that's why they come up with different theories because there was no crosstalk? Or was it some Patrick speciation where the ideas could have flowed between each other, but they were still deciding to stay segregated? Was it nationalism? Or did they just not know is what I'm wondering?

• 30:52Daniel Whiteson?

  I think it started with nationalism, but then it developed into sort of tribal camps. And the Germans criticized the British and the British criticized the Germans, you know, even after the first war, when these guys could have gotten together and had like a global unified theory of flight, they continued working in their own direction because they were invested in, you know, this guy's advisor told him that the German approach was nonsense. And the German guy's advisor told him the British approach was scheisse, you know, or whatever. And so

• 31:18Kelly Weinersmith?

  Do you speak German?

• 31:21Daniel Whiteson?

  I do not speak German. I speak Danish, which is sort of Germanic a little bit.

• 31:25Kelly Weinersmith?

  Oh, cool.

• 31:26Daniel Whiteson?

  Do not speak German. Anyway, so the British across the English Channel didn't like the German approach. They didn't like thinking about air as a fluid, because they were like, this is too idealized. You can't explain what's really happening. The Germans thought, you know, ideal fluids are a fine approximation, but the British didn't like it. And, you know, anytime you're making an explanation in science, you're going to be making approximations. It's just a question of what approximations you make. There are always shortcuts. Nobody can completely describe the full complexity of the universe in their equations. It's always a simplification. And there's an art to that. Choosing the simplification that captures the essential details of what's happening in reality. So you can provide a useful explanation while dismissing all the irrelevant complexities

• 32:08Daniel Whiteson?

  that you don't need to worry about. Which is why, for example, we can talk about how a ball flies through the air and often ignore air resistance and ignore the quantum effects and ignore everything else that's happening, the tug of Jupiter on that ball, because we judiciously choose what approximations to make. So that's what's happening here is two subjective approaches. And the British were focused not on this ideal fluid approach, but instead on using just a simple approach with Newton's law. They were just thinking about the forces.

• 32:36Kelly Weinersmith?

  How do forces act differently on the top and the bottom based on that teardrop shape?

• 32:40Daniel Whiteson?

  Yeah, so the Newton's approach basically ignores the teardrop shape and it says, "The shape of the wing isn't actually important. What's crucial is the angle of the wing into the wind." So they're thinking, "Hey, the wing is tilted a little bit, and so as the wing is moving through the air, the wind gets bounced basically off the wind and goes down." So you have wind flowing onto the wing, and you have an angle, and then it bounces down, and so the wing goes up. And like anybody who's ridden in a car and put their hand out at an angle knows that you can feel lift, right? Your hand basically flies. And your hand is not a teardrop. It's not an airfoil. It's not like carefully, germanically engineered to get lift. It's just your hand, you know? But still, you can get lift. This is a simple

• 33:23Daniel Whiteson?

  application of Newton's theory, like action-reaction. The wind gets pushed down by the angle of the wing. The aeronautical engineers call it the angle of attack. And so the wing gets pushed up. Very simple.

• 33:35Kelly Weinersmith?

  So if that's true, then you could adjust wing shape to be even better at flying by making it bend even more so that you're stopping even more air as you go? Did the British try that to prove how much better they were?

• 33:49Daniel Whiteson?

  I wish you'd been around in the aeronautical society. So clear with your questions. So what you're describing is actually what you see in an airplane when you take off. If you're paying attention to the wing, modern airplanes actually have a changeable shape, right? They have these flaps and these levers, right? So they can change the shape of the wing. And during takeoff, they do just that. They push down the back of the wing, so it's more of a curvy shape. It like grabs the air a little bit more, so you get more lift during takeoff. And then when you're flying, they make it flatter. So while you're cruising, you get less lift, but you also get less drag. Drag is the force that pushes the wing backwards. So you want upwards force lift without as much backwards force drag. So

• 34:31Daniel Whiteson?

  what you're seeing is exactly what modern airplanes do, is they make it curvier when you take off to get more lift.

• 34:37Kelly Weinersmith?

  Very cool. I was reading about programmable matter and I think one of the proposals was to have matter that responds to the environment and makes those changes on its own without you needing to do anything. But I am glad we have more control over the process right now. I'm not ready to have us let go of that control yet.

• 34:54Daniel Whiteson?

  And the nice thing about this explanation is it explains why planes can fly upside down. They fly upside down because they have the right angle of attack. It doesn't matter the shape of the wing at all. It just matters that the airplane wing is at the correct angle. So if you fly your airplane upside down, you can do it as long as the wing is angled into the air at the right angle.

• 35:15Kelly Weinersmith?

  So does this completely explain everything? That's never how our podcast episodes end. So what is it missing?

• 35:23Daniel Whiteson?

  So this is a beautiful story of the limitations of science because both explanations explain something, but neither of them tell the complete story. So for example, there's a couple of things that the British Newton's theory force explanation doesn't describe. Number one is what's going on on the top of the wing, right? This just focuses on the bottom of the wing, but we see that the pressure is lower on the top of the wing. The Newton's theory approach says all the lift comes from below, that you're getting this force from the wind that's hitting it from below. But we see this lower pressure above, and it turns out, as we'll talk about later, that contributes maybe even more to the lift, the low pressure above the wing than the high pressure does below the wing. And the Newton's theory cannot explain this. That's number one.

• 36:07Kelly Weinersmith?

  And it can't explain why there's low pressure above the wing, right? Just like the other one?

• 36:10Daniel Whiteson?

  Yeah, exactly. Number two is that if you do these smoke studies, we see that the wing affects the flow of the air, not just below the wing. It's like the influence of the wing on the air is larger than just the wing. Like the air begins to flow up above the wing before it hits the wing. There's this upwash in advance of the wing and this downwash after the wing. So it's not just like you have a paddle and it's being hit by molecules and it's getting pushed up. There's a complicated interplay here between the wing and the flow around it and the air itself applying pressure on itself. So you can't ignore the sort of fluid effects of the air if you want to completely describe what's happening.

• 36:51Kelly Weinersmith?

  Yeah. So while you were describing all of that, I thought, oh man, it really feels like fluid dynamics should have explained that. So maybe the German example should have worked. Why does the fluid example not work then with all of that complicated stuff happening?

• 37:03Daniel Whiteson?

  So the fluid example does explain some parts of it. And so where we're going to go in the end is this like weird hybrid of the British German theory in order to have the most complete explanation of why it happens. But what we're doing right now is sort of examining like the failure of the individual ones. So the German explanation, the fluidic approach can describe the flow of the fluid around the wing. But the British approach, though it's simple and satisfying, can't describe all of this stuff.

• 37:28Kelly Weinersmith?

  Okay, spoiler alert.

• 37:30Daniel Whiteson?

  Yeah, so one thing it fails to describe is this sort of holistic flow of the air around the wing. The other is stalling. In the Newton's force approach, the only reason you're flying is the angle of attack. And the greater the angle, the greater the force, right? But anybody who flies knows that if you have too great an angle, you're going to stall. Like if your plane is pointed too far upwards, you're not going to get lift anymore. And what happens technically, what we see in wind tunnels, is that if the angle of attack is too great, then as the air flows over the top of the wing, it doesn't merge smoothly with the air flowing below the wing. And you get this like weird turbulence. They call it a separation region, because the air doesn't nicely reconnect. And you

• 38:13Daniel Whiteson?

  know, when you're going through a fluid, turbulence is a problem. You want to minimize turbulence. And so if the angle is too large, this is like gap between the airflow as they come off the back of the wing, and they don't merge nicely. That's called the separation region between these flows, and that creates the stall and you lose your lift. So you can't explain that also with the Newton's explanation. You need some fluid theory to explain that.

• 38:37Kelly Weinersmith?

  Slightly tangential. We haven't discussed propellers. Do propellers and jet engines play any role here? Or is that just in like, that moves us forward and all of the uppieness comes from the wings?

• 38:50Daniel Whiteson?

  Yeah, so basically, engines just provide forward velocity so that the wings attack the air. Although propellers are a subtle point, because propellers have a particular shape which is related to the shape of a wing, right? Because it's converting motion in one direction to air velocity in the other direction. So the shape of a propeller is related to the shape of a wing. But for the question of why planes fly, you can think of it just like something pushy, right? The pushy bit that gets the plane moving through the air. Yeah.

• 39:18Kelly Weinersmith?

  Okay, so you got the pushy bit, but we don't understand what's happening around the wings yet. So how do you move from figuring out that both the German and the British explanation are failing in some way to figuring out the answer to what's going on? Is this like where we are? We just don't know? Or are there more experiments you can do to figure it out?

• 39:36Daniel Whiteson?

  So what you shouldn't do is ask the world's smartest physicist, Einstein, to weigh in on this very practical engineering question.

• 39:43Kelly Weinersmith?

  Well, let's find out what he had to say after the break.

• 39:55Speaker 02

  Hey, it's Niall Rogers, host of Before the Moment, a Lincoln original series. I'm driving across the country, meeting some of today's most fascinating artists. We're exploring the stories before the moment that changed everything. This week, I'm joined by my friend, John Ledge. What still makes you just sit down at the piano?

• 40:17Speaker 05

  If you sat down at 9:00 AM, and then at noon, you had a full song that you recorded and putting your voice recorder or you recorded at your studio, you just created something brand new that didn't exist when you woke up. What a beautiful feeling it is. I'm always excited to write something new. I've been writing for Broadway, which has been a new challenge with new collaborators and amazing performers who are triple threats, who can sing and dance and act and do all these amazing things. And I want to keep feeling that. And so that means not resting on my laurels, going out there and continuing to create something new.

• 40:53Speaker 02

  Experience Before the Moment, a Lincoln original series on the iHeartRadio app, YouTube, or wherever you get your podcasts. OnDeck is built to back small businesses like yours. Whether you're buying equipment, expanding your team, or bridging cash flow gaps, OnDeck's loans up to $400,000 make it happen fast. Rated A+ by the Better Business Bureau and earning thousands of five-star trust

• 41:16Speaker 06

  Pilot reviews on deck delivers funding you can count on apply in minutes at on deck com depending on certain loan attributes your business loan may be issued by on deck or Celtic bank on deck does not lend in North Dakota all loans and amounts subject to lender approval. I just Mario Lopez from all Mario Lopez daily podcast by smart drive for less and trade for more that Toyota affordability and it starts with a great deal and an all wheel drive Camry Corolla cross or a Corolla sedan with the latest features in tech or test drive a spacious Grand Highlander or adventure ready RAV4 and with so many hybrid models available you can enjoy longer trips without all the stops while Toyota's legendary resale value means you could get more at traded so get a great

• 41:59Speaker 06

  deal today and great value tomorrow shop Toyota.com for deals and details Toyota let's go places.

• 42:14Kelly Weinersmith?

  Alright, so for most of the Daniel led episodes, we have to walk through a what did Einstein think because he just provided so many good insights into so many things. So let's figure out what did Einstein think about this?

• 42:27Daniel Whiteson?

  Yeah, so Einstein, he's a smart guy. He developed relativity. He struggled and failed to integrate quantum mechanics into it. So it's not like he solved every problem he attacked, but he was a smart guy and you know, he was German and this is a relevant question for the Germans at the time and he was interested in this and he wrote, quote, there's a lot of obscurity surrounding these questions and open puzzles like this, you know, they attract smart people like, oh, maybe I can figure this out. Maybe there's an insight, a moment of clarity that will just untangle this whole mess. And so he thought about flight from the German point of view and he actually designed his own wing shape, sort of a weird variation on the airfoil. So Einstein, remember he was not just a clever

• 43:10Daniel Whiteson?

  physicist, he worked in the patent office. And so he had seen lots of inventions, he had a practical mind also. So he designed his own wing and he took it to a German aircraft company and you know, he was an esteemed famous scientist at this point. So they thought, okay, sure. So they worked with him, they collaborated with him, they built the plane and they sent it on a test flight and the pilot came back and said he would never fly the thing again because it quote flew like a pregnant duck.

• 43:37Kelly Weinersmith?

  I feel like whenever a question sort of tiptoes into biology and Einstein is involved, you want to back away. So, you know, I think maybe most of us know that ducks can't get pregnant. They carry eggs, but they don't get pregnant the way we do. And also, like, you know, he married his cousin, which I think is a bad idea, also from a biological perspective. But anyway, okay, so Einstein was great at everything, but not at designing wings.

• 44:00Daniel Whiteson?

  Yeah, exactly. And so, fast forward 50 years or so, what are people talking about today in terms of why planes fly? I went across campus here to a colleague at UC Irvine, Hetham Taha. He's a professor of aeronautical engineering here, and he studies lift. He works on this problem. I asked him, what is a simple explanation for lift? And he said, quote, "This is not settled in the aeronautical engineering community. Please don't laugh."

• 44:28Daniel Whiteson?

  So here we are laughing. It's hilarious, you know, like, these guys still haven't figured this out more than 100 years after the Wright brothers.

• 44:34Kelly Weinersmith?

  But yet, still so much money is made on flight. So it's nice to know you don't have to have everything worked out before you commercialize something.

• 44:40Daniel Whiteson?

  But let's not oversell it. It's not that we don't understand why planes fly. It's that we don't have a compelling, simple explanation at the sort of zoomed out level. And again, there's always a difference between like the microphysics. Can you model what's happening with individual air molecules and the shape of the wing and come up with a simulation in which planes fly? Absolutely, we can. And we do. This is why, for example, Boeing can design their airplanes on the computer and be confident that they will fly. They don't need to use wing tests anymore and build a bunch of models to experiment because we have accurate simulations for what's going on in the microphysics level. It's just that when you zoom out and now you want to tell a simple story about what's happening, there

• 45:23Daniel Whiteson?

  are competing ways to do that. And all of them ignore some details, and so none of them are completely satisfactory. So when he says, "This is not settled," he doesn't mean we don't know why planes fly in a sort of microphysics point of view. He means we don't have a nice, compelling, one-sentence explanation for why this happens. The way we can, for example, like a ball flying through the air. Why does a baseball fly in a parabola? We know the answer is, when you have constant acceleration, you get parabolic motion. Simple one-sentence answer. That's what we're lacking for flight. We have a very complex thing that's happening with microphysics, and it's when we're struggling to come up with a simplified explanation at the macroscopic level.

• 46:03Kelly Weinersmith?

  Do engineers care? So if you can make a simulation on a computer that tells you everything you need to know, like are engineers still interested in this question? Or has this completely moved to the realm of like physicists who never see the light, who are studying it in their offices? Like, yeah, do they care what the answer is anymore? Or do physicists care only?

• 46:22Daniel Whiteson?

  Absolutely, they care because engineers want simple working models. You know, when they want to model how a plane is going to fly, they don't want to have to go back to describing every single particle. They want simple sets of equations that let them work quickly and easily. The same way, for example, we'd love to be able to predict a hurricane without modeling every single raindrop. Currently, we have the technology and we're building these incredibly powerful computers just to model wind and pressure and predict the weather. We'd love simple equations to be able to do that, right? Rather than having to use incredibly detailed computation. And so anytime we can summarize complexity with simple math, we definitely win. So people are definitely working on this and trying to find a complete holistic approach

• 47:06Daniel Whiteson?

  that captures all this behavior that lets us do important engineering without simulating all of the tiny microphysical details. Absolutely. Yeah, people care.

• 47:15Kelly Weinersmith?

  And I want to go on record that I apologize for implying that physicists don't go outside.

• 47:21Daniel Whiteson?

  What is this outside thing you're talking about? I was going to ask you about that. I have heard about this, but I've been too shy to ask.

• 47:26Kelly Weinersmith?

  You told me you've been hiking. I know that you're maybe even more extreme than I am in terms of outdoor adventures.

• 47:33Daniel Whiteson?

  No, I do love going outside. That's why I live in California. It's so amazing here.

• 47:36Kelly Weinersmith?

  Oh, the fall right now is absolutely incredible.

• 47:41Kelly Weinersmith?

  Okay, so we've talked about a lot of different ideas, a lot of things we know and we don't know. I know the answer at the end is that it's complicated, but is there a simple-ish kind of way to summarize where we are right now in our understanding?

• 47:53Daniel Whiteson?

  Yeah, so I think the simplest way to describe it is that both a Bernoulli and Newton's stories help, but they're both limited. And the limitation is that they're trying to tell a story in terms of like, simple causes and simple effects. The air flows and it bounces off the wing, or the pressure is lower above the wing because the velocity is higher. And the real story is that the cause and effect are not so simple. There's lots of things happening here, and they're all interplaying together. So it's not so easy to disentangle the cause and the effect. There's a lot of things at work here, pressure and velocity and forces, all in this fantastic harmony that's making the wing go up, which is why none of these simple stories are satisfactory. We can weave a slightly more complex story

• 48:35Daniel Whiteson?

  to explain why planes fly that involves all of these aspects sort of working together. But you know, humans like simple stories. Ball goes down because of gravity, this kind of thing. We don't have that simple a cause and effect.

• 48:48Kelly Weinersmith?

  I'm always amazed by things that work so well, where when you scratch the surface, we really don't understand. Like, I was talking to someone who uses deep brain stimulation to treat epilepsy. So like, when somebody has a seizure, they're having like, an electrical storm in their brain. And sometimes they have electrodes implanted into the center of their brain, and they essentially just get their brain zapped. And that helps. And so I reached out to an expert, and I was like, why does zapping someone's brain with electricity stop the epileptic seizure? And they're like, we don't know. Just like, I am a little nervous getting onto a plane here, and why does the plane go up? We don't know. I also would not want to hear, why are you shocking my brain? We don't know. But in both cases, it works, and it seems to work reliably. So, uh, we get by.

• 49:32Daniel Whiteson?

  Also true, I think, for most pharmaceuticals, right? We're like, well, it does have this effect. We don't really understand the biochemistry of it, but hey, keep taking it, you know?

• 49:40Kelly Weinersmith?

  That's right. Yes. We all muddle along.

• 49:42Daniel Whiteson?

  And I'm not an anti-vaxxer at all. I just mean, this is sort of the way science is. You always understand science at some level. You don't always need to understand the microphysical explanation in order to make it work. And that's actually a huge gift. Otherwise, we couldn't do anything. If we needed to understand like, the nature of quantum gravity before we made a bowl of chicken soup, we'd never have chicken soup. We'd never understand the world. It's lucky that- The world can be understood without knowing all the details or science would be impossible.

• 50:08Kelly Weinersmith?

  It's lucky you can tinker with the world without understanding it.

• 50:11Daniel Whiteson?

  Yes, that too. So we do have a story we can tell about why planes fly. And I think the best way to think about why a wing goes up is to focus on pressure. Pressure above the wing and pressure below the wing. Fundamentally, a wing goes up because pressure grows below the wing and pressure falls above the wing. And both of these are contributed to by the Bernoulli and the Newton story.

• 50:32Kelly Weinersmith?

  Got it. Okay, we managed to summarize something in like three or four sentences.

• 50:37Daniel Whiteson?

  But we can also dig into it in a little bit more detail, you know, like, why does pressure grow below the wing? Well, Newton tells us to focus on the angle of attack, right? And that's correct. The wing goes through the air and the angle of attack pushes down on the air and the air pushes back and this is pressure. Just like if you're scooping up snow with a snow shovel, right? There's going to be increased pressure, the snow is going to get compacted. So why does pressure form below the wing? Not that controversial, it's the angle of attack that's crucial.

• 51:03Kelly Weinersmith?

  And as long as you go like this and you just don't look at the top part of the wing. And so I'm covering the top part of my eyes and you don't think about the top part of the wing, then everything is good. But we don't understand what's happening above. Is that right?

• 51:13Daniel Whiteson?

  Well, above the wing, we can also think about the pressure. The Newton story can't explain what's happening, but if you think about it in terms of fluid, you can, right? So what's happening above the wing? Initially, if you just like shoot air above the wing, then it wants to flow straight back, which effectively creates like a vacuum underneath. The angle of attack working together with the shape of the wing creates this low pressure zone above the wing because the air needs to go down to flow onto that, right? So that's exactly what happens is you create this low pressure zone, which is like a vacuum. It pulls the air into it and that's pulling the wing up. So you have low pressure above the wing created by the shape of the wing and the angle of attack, which creates low pressure above it. And so these two effects work in harmony.

• 51:55Daniel Whiteson?

  You have a force from below and you have like suction from above. So wings go up not just because the air below them is pushing them up, but the air above them is sucking them up into the sky.

• 52:06Kelly Weinersmith?

  So the Germans got the top right and the British got the bottom right?

• 52:11Kelly Weinersmith?

  I feel like there's so many times where I hear that there's a debate and there's people on this side and people on that side. And five years later, the answer is almost always, oh, they were both right and some combination of things. But okay, cool.

• 52:22Daniel Whiteson?

  Yeah. And so mostly this comes from the shape of the front of the wing. Right now, the shape of the wing is important because you want to minimize drag. Right. The Newton folks tell you the shape doesn't matter. All that matters is you get the force from the bottom. But what you want is to create low pressure on the top without creating a lot of drag and without creating this turbulent zone, which gives you a stall. So that's why you have this shape. You have this shape in the front of the wing to give you this uneven pressure distribution. So you get low pressure, but not so much that you get a stall. And then you have this smooth ending. So the flow comes together nicely without creating turbulence at the end. So the shape of an airfoil and the angle of the attack is optimized to give you smooth flow, low pressure above the wing and to minimize drag, which is important if you want to take off.

• 53:08Kelly Weinersmith?

  I feel like the next time I get on a flight, I'm going to appreciate it all much more, having a better sense of how this all works.

• 53:14Daniel Whiteson?

  But you know, in terms of coming to this explanation, the experts still are arguing about like, how to summarize this. I've given you sort of a summary version of it, but I'm sure there are aeronautical engineers out there who have differing opinions and are going to write into us with their theory for why planes fly, or at least for how to describe it. Our original listener, Tom Johnson, wrote in because he saw this video from the Smithsonian Air and Space Museum that explained it in terms of just Bernoulli, right? The Bernoulli explanation of low pressure on top. And he wasn't satisfied with this. And he wrote to me and he said, quote, "I contacted the Smithsonian about this video voicing my concerns and I was told unequivocally that it's their policy that Bernoulli makes planes fly.

• 53:58Daniel Whiteson?

  I wasn't aware that physics cared about policies, but I guess I'm mistaken."

• 54:03Kelly Weinersmith?

  That's amazing. Institutions are fantastic.

• 54:08Daniel Whiteson?

  Exactly. And so again, you know, while the microphysics is clear about what's happening around the wing and you can track these individual particles, we still do struggle a little bit coming up with a simple explanation. It turns out pressure is important and velocity is important and the forces are important. So none of the sort of classic, simple explanations can describe everything that's happening around a wing. You need a more complex, a fuller description of what's happening to explain all the phenomena, why planes can fly upside down, why the pressure goes down above the wing, all this kind of stuff. So in the end, the British and the Germans have to work together.

• 54:43Kelly Weinersmith?

  Oh, I mean, that's better in the end. So those plane wing shapes. So I'm thinking of other instances where you've got like things moving through the air. So we've got like wind turbines and then you've got racing cars. They don't want to go up. They want to go down. So they do the whole shape in reverse. Like, how has this information been used in other contexts?

• 55:02Daniel Whiteson?

  Yeah, exactly. So Formula One cars, they have a wing in the back, but that wing pushes the car down so that it maintains friction because they need friction in order to go forward, right? The wheels have to get pushed onto the ground so the wheels can grab. And then when they turn the wheels, the car goes forward. If the car lifts up above the ground, then it can't move forward anymore. So they designed it in order to generate downward pressure. So they have crucially a different angle, right? But they also think about the foil and they do really complex modeling because, you know, millions of dollars mean microseconds and that's the difference between winning and losing. So yeah, absolutely. They invert all of this theory in order to get a wing that can push down. And the crucial thing there is the angle of attack, right?

• 55:43Kelly Weinersmith?

  And then wind turbines, they don't want the wind turbine to go airborne, but they want it to spin as fast as it can, which feels like maybe some of the principles we talked about today could help that happen. Yeah. How does this play into wind turbines?

• 55:57Daniel Whiteson?

  Yeah, exactly. Well, it's the same principle. Essentially, you have airflow across the propeller and you want to convert that to a sideways force, right? So you want to force up relative to the propeller. You don't want the whole propeller to fly off the ground, right? But you want it to spin around the axis. And so again, the angle of attack and the shape of it ensures a force that turns it and smooth flow around it because you don't want turbulence in the back of your propeller blade. So each one of those is essentially just a little wing.

• 56:28Kelly Weinersmith?

  Very cool. I'm guessing that we weren't racing cars before we had planes. So probably the plane stuff came first.

• 56:35Daniel Whiteson?

  Yeah, the plane stuff came first. Cars were pretty slow until kind of recently. Like you could win big car races by driving at like 45 miles an hour.

• 56:44Kelly Weinersmith?

  That sounds so cute now. But it's much harder to die at that speed. Why would you watch that?

• 56:49Daniel Whiteson?

  Exactly. But it's really fun to think about how we explain the world around us and how Challenging it can be to explain some things. It makes me really grateful for the times that we can find a very simple explanation. And wonder like why that's possible sometimes and not other times. Is it because of the way that we think about the world? Or is it just something about the way the world works? You know, alien scientists have a better theory for why wings work. Because they started off from a completely different point of view mathematically or scientifically? Or is everybody struggling to describe some complex behaviors? Are these things just inherently complex? Or is it just our language that's making them a challenge?

• 57:29Kelly Weinersmith?

  I wonder if part of that is there's some percent of explanations that we have that we feel good about that are actually wrong if you look at them more closely. But the stuff works anyway.

• 57:38Daniel Whiteson?

  Yeah.

• 57:39Kelly Weinersmith?

  And then I wonder if some other stuff, just there happens to be a metaphor that we're familiar with that makes it easier to understand. And there's just not like a ready metaphor for some of the more complicated things, but.

• 57:48Daniel Whiteson?

  Yeah, and sometimes we accept an explanation, even though it's nonsense. Like the air has to go faster over the top of the wing to meet its partners. Like a lot of people go, oh, yeah, that makes sense, but it doesn't actually make sense.

• 58:00Kelly Weinersmith?

  Yeah.

• 58:02Daniel Whiteson?

  And fundamentally, all of science is quote unquote, wrong if you zoom in far enough. You know, everything is just an approximate description. Not like scientists are lying to us or we're promoting nonsense. But everything is an approximation, even like describe an electron as a fundamental particle. Yeah, probably it's not, probably it's made of something smaller. We just haven't seen it yet, but our theory works so far. We've never been able to make an experiment where it breaks. And so all of science is a work in progress in that sense. Not just like, do we have the best explanation for it? But you know, how far can we push this until we see it break? And seeing it break is an opportunity, right? It's not a disaster. It's a chance to learn something deeper about the universe, to come up with a more accurate description

• 58:46Daniel Whiteson?

  or to poke through reality to another level and see how it works underneath it all. So it's just part of the journey of science.

• 58:53Kelly Weinersmith?

  I feel like it's a great time to be in science. There's still so many fundamental things left to understand. At the same time as we're gaining all this new technology that allows us to address questions in different ways. We have all these new tools. Can't wait to see what we learn in the next couple of decades.

• 59:08Daniel Whiteson?

  Yeah, and it's not just like what's inside an electron, like weird, abstract, fundamental stuff that you'll ever see. It's stuff right in front of you, stuff you can see with your eyes, you know? Tornadoes and hurricanes and airplanes and fluid flow. All this stuff is complex and unsolved. So, smart young people with energy out there, go out there, figure it out. Lots left to do. So, thank you very much to Tom Johnson for sending us this question. If you have questions about the way the world works or why you can't understand it, please write to us, to [email protected]. We love to hear from you.

• 59:41Kelly Weinersmith?

  Thanks, Tom.

• 59:49Kelly Weinersmith?

  Daniel and Kelly's Extraordinary Universe is produced by iHeartRadio. We would love to hear from you.

• 59:54Daniel Whiteson?

  We really would. We want to know what questions you have about this extraordinary universe.

• 1:00:00Kelly Weinersmith?

  We want to know your thoughts on recent shows, suggestions for future shows. If you contact us, we will get back to you.

• 1:00:07Daniel Whiteson?

  We really mean it. We answer every message. Email us at [email protected].

• 1:00:14Kelly Weinersmith?

  Or you can find us on social media. We have accounts on X, Instagram, Blue Sky, and on all of those platforms, you can find us at D and K Universe.

• 1:00:23Daniel Whiteson?

  Don't be shy. Write to us.

• 1:00:28Speaker 04

  Wait, I came in for two things. How is this $47? All right, we're gonna need a plan here. Just start simple with Bank of America Advantage Safe Balance Banking. No overdraft item fees, no monthly maintenance fee if you're under 25. Oh, that's actually really simple. Safe balance banking, one less thing to figure out. Learn more at bofa.com/simplebanking. Terms and conditions apply. Bank of America and a member FDIC. This is Shirley Strawberry from the Steve Harvey.

• 1:01:00Speaker 06

  Every morning show, buy smart, drive for less and trade for more. That's Toyota affordability. And it starts with a great deal on an all-wheel-drive Camry, Corolla Cross, or a Corolla Sedan with the latest features and tech. Or test drive a spacious Grand Highlander or adventure-ready RAV4. And with so many hybrid models available, you can enjoy longer trips without all the stops. While Toyota's legendary resale value means you could get more at trade-in, get a great deal today and a great value tomorrow. Shop toyota.com for deals and details. Toyota, let's go places. Cash flow crunch? OnDeck's small business line of credit gives your business immediate access to funds,

• 1:01:44Speaker 06

  up to $200,000, right when you need it. Cover, seasonal dips, manage payroll, restock inventory, or tackle unexpected expenses without missing a beat.

• 1:01:53Kelly Weinersmith?

  With flexible draws, transparent pricing, and control over repayment, get funded quickly and confidently. Apply today at ondeck.com. Funds could be available as soon as tomorrow. Depending on certain loan attributes, your business loan may be issued by OnDeck or Celtic Bank. OnDeck does not lend in North Dakota. All loans and amounts subject to lender approval. Morning, Carmen. Good morning. Quick question. Just one second.

• 1:02:11Daniel Whiteson?

  Sorry. Carmen's worked at this office for 20 years. She knows everything, which is why Carmen has to help with, well, everything. Hey, Carmen, what did Faye pitch in 2023? Who owns the Nordic account? Oh, uh, where's the printer? But Carmen's revenue report is due in five minutes, so she shows them work IQ.

• 1:02:28Kelly Weinersmith?

  Hey, co-pilot. Who owns the Nordic account? And what did we pitch them in 2023?

• 1:02:34Daniel Whiteson?

  Get the context you need with Microsoft Co-Pilot. Work lives on.

• 1:02:39Speaker 02

  Hey, I'm Niall Rogers. This fall, I'll be driving across the country, meeting some of today's coolest and most fascinating artists. We'll explore the stories before the moments that changed everything. Because every musician remembers the moment where it all began. Experience before the moment. A Lincoln Original Series on the iHeartRadio app, YouTube, or wherever you get your podcasts.

• 1:03:11Speaker 02

  This is an iHeart Podcast. Guaranteed human.