WEBVTT - Why do planes fly? 0:00:05.920 --> 0:00:11.479 They say that any technology sufficiently advanced is indistinguishable from magic. Well, 0:00:11.520 --> 0:00:15.400 there's one technology that people have lusted after for thousands 0:00:15.440 --> 0:00:18.920 of years that we now rely on even find routine. 0:00:19.400 --> 0:00:22.560 I'm talking, of course, about flight. It's been only one 0:00:22.640 --> 0:00:25.639 hundred years since people were able to leave the ground 0:00:25.680 --> 0:00:29.120 and fly through the air and return safely. Now it's 0:00:29.160 --> 0:00:32.440 so routine that people sleep through it. But imagine what 0:00:32.479 --> 0:00:34.879 that would seem like someone from a thousand or ten 0:00:34.920 --> 0:00:38.879 thousand years ago. It's essentially like magic. Of course, we 0:00:39.040 --> 0:00:42.720 know it's actually not. It's science because we can understand it, 0:00:42.760 --> 0:00:44.800 and we can break it down. We can explain it. 0:00:45.040 --> 0:00:49.199 We understand why planes fly, right, do we could we 0:00:49.240 --> 0:00:52.400 actually explain it to visiting ancestors from the deep past? 0:00:52.960 --> 0:00:55.320 Or is it still some kind of black magic even 0:00:55.360 --> 0:00:59.920 for modern humans and the best aeronautical engineers. So today 0:01:00.080 --> 0:01:03.400 on Daniel and Kelly's Extraordinary Universe, we'll be asking an 0:01:03.440 --> 0:01:06.360 old question, why do planes fly? 0:01:20.280 --> 0:01:20.480 Hi? 0:01:20.760 --> 0:01:23.280 I'm Kelly Wiener Smith and my favorite way to travel 0:01:23.400 --> 0:01:23.959 is by train. 0:01:24.520 --> 0:01:27.640 Hi. I'm Daniel Whitson. I'm a particle physicist, which means 0:01:27.680 --> 0:01:29.200 I have to fly around the world to get to 0:01:29.240 --> 0:01:31.320 the biggest particle accelerator. 0:01:31.080 --> 0:01:33.399 And what is your worst flight experience? 0:01:35.680 --> 0:01:39.399 My worst flight experience is traveling with my own six 0:01:39.480 --> 0:01:42.319 month old baby. We had a bascinet and we got 0:01:42.319 --> 0:01:44.360 her to sleep in the basinet and we thought, oh, 0:01:44.400 --> 0:01:47.040 this is going to be great. Then the stewardess came 0:01:47.080 --> 0:01:48.920 by and said, oh, there's some turbulence. You have to 0:01:48.960 --> 0:01:50.920 take her out and put her in a seat and 0:01:50.960 --> 0:01:54.640 buckle her in. And he said, no, she's sleeping, and 0:01:54.720 --> 0:01:57.800 she said sorry, it's the rules. And everyone around us went, 0:01:58.160 --> 0:02:01.120 oh no, and they were right, because she screamed for 0:02:01.160 --> 0:02:02.400 the rest of the eight hour flight. 0:02:02.800 --> 0:02:06.360 Oh no, that's horrible. I'm so sorry. When you finally 0:02:06.360 --> 0:02:08.320 get your kid asleep and something wakes them up on 0:02:08.360 --> 0:02:09.440 a plane, it's the worst. 0:02:09.880 --> 0:02:12.160 It's the worst. And everybody knew it was the worst, 0:02:12.200 --> 0:02:14.480 and we all knew there's nothing we could do, but hey, 0:02:14.560 --> 0:02:17.320 you know, them's the rules. How about you, what's your 0:02:17.360 --> 0:02:18.720 worst traveled experience? 0:02:18.880 --> 0:02:22.120 It also involves plane with my child. She was probably 0:02:22.160 --> 0:02:25.400 about six months old around there also, and I brought 0:02:25.440 --> 0:02:27.600 a change of clothes for her. I was totally prepared 0:02:27.639 --> 0:02:29.720 for her. She was sitting on my lap and we 0:02:29.720 --> 0:02:32.320 were about to take off, and right as the plane 0:02:32.320 --> 0:02:35.280 started moving forward, she had a blowout poop on my 0:02:35.360 --> 0:02:39.760 leg and so it smelled horrible. But you can't get 0:02:39.800 --> 0:02:43.280 out of your seat until you rechruising altitude. So everybody 0:02:43.320 --> 0:02:45.880 was like giving me dirty looks and covering their noses, 0:02:46.240 --> 0:02:48.519 and it took like twenty minutes before we were allowed 0:02:48.560 --> 0:02:50.320 to get out of our seats. And then you know, 0:02:50.360 --> 0:02:53.239 I had to change her in the airplane changing room, 0:02:53.280 --> 0:02:55.800 which is like so tiny, I thought she was gonna 0:02:55.800 --> 0:02:57.959 fall off the little tray. And anyway, I brought a 0:02:58.040 --> 0:02:59.760 change of clothes for her, but I didn't assume i'd 0:02:59.760 --> 0:03:01.000 have on my pants. 0:03:01.000 --> 0:03:04.280 Oops. Classic parenting mistake exactly. 0:03:04.360 --> 0:03:06.760 So I smelled horrible the whole flight, and people kept 0:03:06.760 --> 0:03:08.600 looking at me, and it wasn't a lot of fun. 0:03:08.639 --> 0:03:11.480 But them's the breaks you got to leave the house 0:03:11.520 --> 0:03:11.920 with kids. 0:03:11.919 --> 0:03:13.840 Sometimes you just got to look back at those people 0:03:13.840 --> 0:03:17.000 and say, hey, who's going to pay for your social security? Right? 0:03:17.280 --> 0:03:21.120 Somebody's got to make the next generation. And to me, 0:03:21.440 --> 0:03:25.440 Madame poopy Pants, I'll get a. 0:03:25.360 --> 0:03:26.800 Little like badge that says that. 0:03:27.840 --> 0:03:29.960 Now, whenever I see a parent with a kid, I'm like, 0:03:30.160 --> 0:03:31.959 what can I carry for you. How can I help 0:03:32.000 --> 0:03:33.720 like I offer to help all the time. 0:03:34.240 --> 0:03:37.160 Yeah, exactly. And the big lesson I learned is never judge, 0:03:37.280 --> 0:03:39.120 and you never in somebody else's family. You don't know 0:03:39.120 --> 0:03:41.760 what they're going through or what they're struggling with or 0:03:41.760 --> 0:03:44.880 how much they slept last night. Just help and smile. Yep. 0:03:44.920 --> 0:03:47.120 And kids are always at their worst because they're always 0:03:47.120 --> 0:03:49.160 the tiredest and they're not used to it, and so 0:03:49.440 --> 0:03:52.800 like anyway, yes, don't judge. But planes are wonderful. I 0:03:52.880 --> 0:03:54.720 needed to get from place to place, and I needed 0:03:54.720 --> 0:03:56.800 to get there quickly. And actually I wouldn't have wanted 0:03:56.840 --> 0:03:58.600 to take my daughter on a long train ride for 0:03:58.640 --> 0:04:00.280 the journey that we were going on, because it would 0:04:00.280 --> 0:04:03.480 have been days. But I was flying to London the 0:04:03.520 --> 0:04:06.040 other day and we had kind of talked about why 0:04:06.040 --> 0:04:08.680 do planes fly? And you said it's complicated, And while 0:04:08.720 --> 0:04:12.120 I was, you know, above the Atlantic, I thought, how complicated? 0:04:13.240 --> 0:04:14.720 How well do we understand this? 0:04:14.840 --> 0:04:17.160 I hope the answer is really well, So I'm looking 0:04:17.160 --> 0:04:18.360 forward to today's conversation. 0:04:18.680 --> 0:04:21.440 Good Well. This question actually came to me from a listener. 0:04:21.520 --> 0:04:25.000 Tom Johnson from Ohio wrote to me and asked if 0:04:25.040 --> 0:04:28.520 we could explain why planes fly because he looked into 0:04:28.560 --> 0:04:31.120 a little bit and he was kind of confused. So 0:04:31.160 --> 0:04:34.279 he wanted a clear explanation for why it is that 0:04:34.360 --> 0:04:35.720 planes stay in the air. 0:04:36.200 --> 0:04:38.080 And if you have a question that you want to 0:04:38.080 --> 0:04:40.160 ask us, we would be happy to answer them. So 0:04:40.240 --> 0:04:43.359 send us an email at questions at Daniel and Kelly 0:04:43.480 --> 0:04:44.080 dot org. 0:04:44.400 --> 0:04:45.760 When I told Tom that we were going to answer 0:04:45.839 --> 0:04:48.040 his question on the pod, he said, quote, my wife 0:04:48.080 --> 0:04:50.240 is absolutely going to roll her eyes tonight when I 0:04:50.279 --> 0:04:53.760 tell her over sushi, which made me wonder. Tom is 0:04:53.800 --> 0:04:56.520 in Ohio. Where is he getting a sushi? Probably they 0:04:56.520 --> 0:04:59.560 have it flown in so even his sushi relies on 0:04:59.600 --> 0:05:00.520 airplane in wings. 0:05:01.040 --> 0:05:03.680 Yeah, and you know, I lived in Ohio for a 0:05:03.720 --> 0:05:05.960 decade or more, and I can tell you that when 0:05:06.000 --> 0:05:07.919 sushi has to fly that far, it's not great. 0:05:10.040 --> 0:05:11.239 You're too far from the ocean. 0:05:11.279 --> 0:05:13.880 At that point, you're saying nobody should fly to Ohio 0:05:13.920 --> 0:05:14.440 for sushi. 0:05:14.640 --> 0:05:15.280 No, I'd say that. 0:05:15.320 --> 0:05:17.039 I'm going to go on the record saying you shouldn't 0:05:17.040 --> 0:05:18.520 fly just to Ohio for sushi. 0:05:18.520 --> 0:05:20.120 Ohio has got other things going for it. 0:05:20.440 --> 0:05:22.800 You should have Ohio pride. You know, I know you're 0:05:22.800 --> 0:05:25.680 a transplanted Virginian, but like you come from Ohio. A 0:05:25.720 --> 0:05:28.640 good thing about Ohio, for example, is it made you You. 0:05:28.600 --> 0:05:30.560 Know, I was actually born in New Jersey, which is 0:05:30.600 --> 0:05:35.480 an even harder state to defend, but I do actually 0:05:35.480 --> 0:05:38.080 love New Jersey and I will defend New Jersey. But 0:05:38.160 --> 0:05:40.440 you know, Ohio was a very safe place to grow 0:05:40.520 --> 0:05:42.359 up where I grew up, and so that's fine. And 0:05:42.400 --> 0:05:45.840 I think Ohio has made the most astronauts, and so 0:05:45.920 --> 0:05:47.760 you know, we all would make jokes about you know, 0:05:47.800 --> 0:05:49.520 what is it about Ohio that makes you want to 0:05:49.520 --> 0:05:52.360 get as far as possible away from this planet? And 0:05:52.960 --> 0:05:55.600 I'm not sure if Ohio is still winning an astronaut production, 0:05:55.720 --> 0:05:57.440 but it was at some point. 0:05:57.600 --> 0:06:00.440 All right, well, let's stop flying around the issue and 0:06:00.560 --> 0:06:02.880 get to the question. I was wondering what people out 0:06:02.920 --> 0:06:05.640 there thought about how planes stay in the air, how 0:06:05.680 --> 0:06:08.440 wings work, what stories they had been told, and what 0:06:08.520 --> 0:06:11.800 they understood about this question. So, as usual, I went 0:06:11.880 --> 0:06:14.720 to our bank of volunteers to ask them why do 0:06:14.800 --> 0:06:17.040 planes fly? If you would like to play for a 0:06:17.080 --> 0:06:19.080 future episodes, please don't be shy right to us to 0:06:19.240 --> 0:06:23.479 questions at Danielankelly dot org. In the meantime, think about 0:06:23.520 --> 0:06:25.960 it for a moment. Why do you think planes fly? 0:06:26.520 --> 0:06:28.520 Here's what a bunch of listeners had to say. 0:06:29.160 --> 0:06:32.120 I believe nobody really knows. I would be glad to 0:06:32.240 --> 0:06:36.039 learn otherwise. I know that I've read in my school 0:06:36.040 --> 0:06:38.359 book that the air takes a longer way on the 0:06:38.360 --> 0:06:40.240 top of the wing than on the bottom of the wing, 0:06:40.360 --> 0:06:43.080 and therefore we have a sort of suction going on 0:06:43.120 --> 0:06:44.120 that pulls the wing up. 0:06:44.360 --> 0:06:48.240 Planes fly because they want to, and because of the 0:06:48.480 --> 0:06:49.760 differential air. 0:06:49.600 --> 0:06:55.039 Pressure forces the air to take a longer path to 0:06:55.160 --> 0:06:59.000 go over the wing versus under the wing, and this 0:06:59.240 --> 0:07:04.719 differential in the path length reduces the pressure on the 0:07:04.800 --> 0:07:08.720 upper surface of the wing, and that provides lift. 0:07:09.400 --> 0:07:14.920 There's some confusion surrounding the Bernoulli effect and the airflow 0:07:15.280 --> 0:07:18.520 speed over the top and bottom of the wings. There's lift, 0:07:19.080 --> 0:07:22.240 which means that the air going over the curved part 0:07:22.240 --> 0:07:24.720 of the wing takes longer than the air going underneath 0:07:24.760 --> 0:07:26.680 the wing, so the lift is created there. 0:07:26.960 --> 0:07:29.120 It takes longer for the air to go over the 0:07:29.160 --> 0:07:29.800 top of the wing. 0:07:30.120 --> 0:07:34.280 The aerodynamics of that wing shape causes low pressure to 0:07:34.320 --> 0:07:37.960 form over the top of the wing and high pressure 0:07:38.200 --> 0:07:39.720 to form under the wing. 0:07:40.240 --> 0:07:44.160 So wasn't it to do with Leonardo da Vinci came 0:07:44.240 --> 0:07:48.800 up with the original idea to base planes on the 0:07:48.840 --> 0:07:50.880 optron from wings of beds. 0:07:51.320 --> 0:07:53.880 Planes fly because they can't swim. 0:07:56.040 --> 0:07:59.760 I think that light blanes such as paper planes can 0:08:00.200 --> 0:08:05.360 fly just because of hierodynamics, but heavy planes need engines 0:08:05.400 --> 0:08:08.640 to generate pressure difference. But I am not entirely sure 0:08:08.680 --> 0:08:09.720 how this works. 0:08:10.280 --> 0:08:12.880 So you have to have thrust greater than drug and 0:08:13.080 --> 0:08:17.800 lift greater than gravity, a higher pressure below and the 0:08:17.880 --> 0:08:21.200 lower pressure above the top of the wing is curved, 0:08:21.640 --> 0:08:23.400 so the air has to travel further. 0:08:24.440 --> 0:08:28.800 I thought the planes flew because the Russian forts caused 0:08:29.160 --> 0:08:32.560 air to flow over their wings and created a force 0:08:32.800 --> 0:08:34.679 that pushes up on the wings. 0:08:35.559 --> 0:08:40.400 So I think planes fly because of the way that 0:08:40.440 --> 0:08:42.520 the wind dends around the wing. 0:08:43.440 --> 0:08:48.520 Planes fly because the lift that they generate is greater 0:08:48.679 --> 0:08:50.160 than the gravitational pull. 0:08:50.520 --> 0:08:51.800 The air has. 0:08:51.640 --> 0:08:54.960 A longer way over the wing than under the wing. 0:08:55.440 --> 0:08:58.320 The top of the wing, because of its shape, it 0:08:58.440 --> 0:09:00.880 makes a suction, so it's the plane up. 0:09:01.280 --> 0:09:04.920 I'm not actually completely sure why plane flies, but I 0:09:04.960 --> 0:09:07.000 know I've been in them and they tend to do that, 0:09:07.040 --> 0:09:08.480 and I hope they continue to do so. 0:09:09.760 --> 0:09:12.440 I love that the answers were a combination of people 0:09:12.480 --> 0:09:15.120 who clearly sort of know what the answer is and 0:09:15.160 --> 0:09:18.640 like gave good answers, and then people who are hilarious. 0:09:21.080 --> 0:09:24.559 Because they can't swim. Made me laugh out loud. So bravo. 0:09:25.760 --> 0:09:27.520 You know. I love that approach. You don't know the answer, 0:09:27.720 --> 0:09:28.720 tell us a good joke. 0:09:29.000 --> 0:09:31.679 Yeah, absolutely, I think that might be one of the 0:09:31.760 --> 0:09:32.400 keys to life. 0:09:32.400 --> 0:09:34.240 I think I. 0:09:34.200 --> 0:09:36.160 Want to see that more of my physics exams. You know, 0:09:36.480 --> 0:09:39.000 when somebody doesn't know how to solve this quantum mechanical 0:09:39.000 --> 0:09:41.360 problemly write me a good joke. I'll give you some 0:09:41.400 --> 0:09:42.040 points anyway. 0:09:42.280 --> 0:09:44.120 You will give points for human sure. 0:09:44.200 --> 0:09:47.080 Absolutely. I used to regularly have a question on exams 0:09:47.320 --> 0:09:49.679 that was just a random New Yorker cartoon, and then 0:09:49.720 --> 0:09:52.720 the question was, write a physics related caption for this cartoon. 0:09:53.440 --> 0:09:56.000 Oh nice. I love that you're encouraging creativity. 0:09:56.640 --> 0:09:58.320 I had an exam where I could get five extra 0:09:58.360 --> 0:10:00.400 credit points if I drew a parasite, and you'd think 0:10:00.440 --> 0:10:02.640 that that would be great, but I was like, I 0:10:02.679 --> 0:10:04.840 hate this because I don't even do nice stick figures. 0:10:04.880 --> 0:10:06.960 That's why I married an artist. He takes care of 0:10:07.000 --> 0:10:08.640 all of it. But the good thing is there's a 0:10:08.679 --> 0:10:11.120 stage of parasites where they essentially just look like a circle. 0:10:11.679 --> 0:10:15.959 And so I just I said, oh, there's a medicinariosist done, 0:10:16.160 --> 0:10:17.360 and I. 0:10:17.320 --> 0:10:20.400 Didn't get full credit. All right, So where do we start? 0:10:20.760 --> 0:10:23.560 So the beginning of the question of why planes fly 0:10:23.840 --> 0:10:26.320 goes all the way back to the Right Brothers in 0:10:26.400 --> 0:10:30.000 nineteen oh three. You know, the Right brothers. They were engineers, 0:10:30.040 --> 0:10:33.080 they were not physicists. And so while the Right Brothers 0:10:33.400 --> 0:10:37.079 made a plane fly, they actually didn't understand it at 0:10:37.120 --> 0:10:40.400 the time. Like, they had no principles, they had no theory, 0:10:40.440 --> 0:10:43.000 they had no real reason to think their plane was 0:10:43.080 --> 0:10:46.200 gonna fly. They just kind of made it work. And 0:10:46.240 --> 0:10:49.120 then they were showered, of course, with awards and fame 0:10:49.200 --> 0:10:51.400 and all sorts of stuff, which led some people in 0:10:51.440 --> 0:10:53.720 the physics community to get a little bit resentful. 0:10:53.920 --> 0:10:56.520 So if they had no idea, why did they pick 0:10:56.640 --> 0:10:58.520 the design they picked? Is it because they were building 0:10:58.520 --> 0:11:01.280 on things that other people had made that maybe they 0:11:01.360 --> 0:11:03.280 understood what they were doing, and so they just sort 0:11:03.280 --> 0:11:03.960 of tinkered with that. 0:11:04.280 --> 0:11:06.720 Yeah, engineering is a lot of tinkering, right, So let's 0:11:06.720 --> 0:11:09.280 try this let's try that, and sometimes things work and 0:11:09.280 --> 0:11:12.280 then later you figure out why that thing floats or 0:11:12.320 --> 0:11:15.319 why does this thing fly? And that's essentially what happened 0:11:15.320 --> 0:11:18.360 with the Wright brothers. And they won this fancy award 0:11:18.360 --> 0:11:21.640 from the Aeronautical Society, and one physicist, Colonel Fullerton, wrote 0:11:21.679 --> 0:11:23.760 it and said, quote, I think it was a mistake 0:11:23.800 --> 0:11:26.040 of the Aeronautical Society giving the rights of metal for 0:11:26.080 --> 0:11:29.320 their contribution to aeronautical science. I agree with they're having 0:11:29.360 --> 0:11:31.280 the medal, but it should have been for what they 0:11:31.320 --> 0:11:34.200 have done. In other words, they didn't understand it. They 0:11:34.200 --> 0:11:37.360 didn't actually advance aeronautical science. They just sort of like 0:11:37.679 --> 0:11:39.880 made it work, and they left open the question of 0:11:39.920 --> 0:11:41.559 like why does this work. 0:11:41.640 --> 0:11:43.280 I still feel like there should be a medal for 0:11:43.360 --> 0:11:45.880 the moment when you're about to push your plane off 0:11:45.880 --> 0:11:49.520 the cliff and you're like, we don't understand what's going on. 0:11:49.679 --> 0:11:53.280 But he the Wiley Coyote Award or something. 0:11:53.559 --> 0:11:55.320 Maybe it's a subset of the Darwin Award. 0:11:55.400 --> 0:11:58.840 Yeah. And this turned out to be really important politically 0:11:58.960 --> 0:12:03.000 because this is just before World War One, right, and 0:12:03.040 --> 0:12:06.319 so World War one is beginning and we have nations 0:12:06.360 --> 0:12:08.800 trying to figure out like how to make planes fly, 0:12:09.200 --> 0:12:12.280 how to make them stable, and nobody really understood like 0:12:12.400 --> 0:12:15.199 why some things work, how to make them better. And 0:12:15.320 --> 0:12:17.600 if you don't have like a model for why planes fly, 0:12:17.679 --> 0:12:21.280 it's pretty hard to improve their performance. And so just 0:12:21.280 --> 0:12:23.800 before World War One you had all these folks in 0:12:23.840 --> 0:12:26.719 Britain and then also on the continent trying to understand 0:12:26.760 --> 0:12:28.960 the theory of flight so they could take advantage of 0:12:28.960 --> 0:12:29.720 it militarily. 0:12:30.320 --> 0:12:33.560 Okay, So the Right Brothers didn't have a theory, and 0:12:33.600 --> 0:12:35.880 nobody else had a theory either, so everyone was just 0:12:35.920 --> 0:12:38.280 tinkering to see how it worked and that it worked 0:12:38.280 --> 0:12:40.880 for the Right Brothers. Did the fact that it worked 0:12:40.920 --> 0:12:44.080 for the Right Brothers give insights into why it would work, 0:12:44.200 --> 0:12:47.520 Like did their design work because it took advantages of 0:12:47.559 --> 0:12:50.599 some physics principle that became obvious after the facts to 0:12:50.640 --> 0:12:51.440 the physicists. 0:12:52.480 --> 0:12:55.120 It certainly isn't obvious after the fact, because people are 0:12:55.160 --> 0:12:59.439 still to this day arguing why planes fly. And it's 0:12:59.480 --> 0:13:01.800 fascinating that the divide in the field we're going to 0:13:01.840 --> 0:13:04.160 dig into this really goes back to the split that 0:13:04.240 --> 0:13:06.480 happened in World War One, where you had the sort 0:13:06.480 --> 0:13:09.840 of like mathematical battle between the scientists. You had the 0:13:09.840 --> 0:13:11.520 British trying to figure it out and you had the 0:13:11.520 --> 0:13:14.400 Germans trying to figure it out, and they took different approaches, 0:13:14.720 --> 0:13:17.560 and those approaches still live on and do battle in 0:13:17.600 --> 0:13:21.080 science today. In modern aeronautical engineering, the Germans took this 0:13:21.120 --> 0:13:23.520 approach of thinking about airs a fluid flowing over the 0:13:23.520 --> 0:13:26.319 wing and analyzing the velocity and thinking about the pressure. 0:13:26.480 --> 0:13:28.160 But the British didn't like that approach. It made some 0:13:28.200 --> 0:13:31.880 approximations that made them uncomfortable, and they like using Newton's forces, Newton, 0:13:31.960 --> 0:13:34.360 of course being British, And so to this day we 0:13:34.400 --> 0:13:38.440 have two competing theories for why planes fly and how 0:13:38.480 --> 0:13:40.480 they work. It's fascinating to me that we still haven't 0:13:40.480 --> 0:13:42.679 figured this out. You're right, we had a working example 0:13:42.679 --> 0:13:45.439 about one hundred years ago, and that definitely helps, right, 0:13:45.480 --> 0:13:49.200 It rules some things out, it inspires experiments, So having 0:13:49.200 --> 0:13:52.199 a working example is useful, but it doesn't always tell 0:13:52.280 --> 0:13:54.160 you exactly why something happens. 0:13:54.520 --> 0:13:56.520 So are these theories, which I'm sure we'll get into 0:13:56.520 --> 0:13:59.839 the details of in a second, are they different enough 0:14:00.320 --> 0:14:03.080 that that resulted in the British and the Germans having 0:14:03.200 --> 0:14:06.200 planes that had different shapes during World War One? Or 0:14:06.240 --> 0:14:09.600 do both theories sort of predict that the same plane 0:14:09.679 --> 0:14:11.240 shape is good. 0:14:11.800 --> 0:14:14.960 Yeah, they make different predictions about what's important in the 0:14:15.040 --> 0:14:17.440 shape of the wing, which is fascinating. And I found 0:14:17.480 --> 0:14:20.040 this quote from a historian David Bloor who said, on 0:14:20.120 --> 0:14:22.360 the eve of the Great War, none of the British 0:14:22.440 --> 0:14:25.320 workers in the field of aero dynamics had any workable 0:14:25.320 --> 0:14:27.760 account of how an airplane could get off the ground, 0:14:28.480 --> 0:14:30.960 which you know, makes it pretty hard to optimize the 0:14:31.000 --> 0:14:33.360 performance of your warplanes. 0:14:32.920 --> 0:14:35.400 And pretty scary to get into a warplane on top 0:14:35.440 --> 0:14:37.280 of all the reasons that it's scary to get into 0:14:37.320 --> 0:14:38.720 a warplane exactly. 0:14:38.800 --> 0:14:42.080 And later on we'll hear about Albert Einstein's personal design 0:14:42.240 --> 0:14:45.040 for an airplane, which really didn't work very well. 0:14:46.520 --> 0:14:48.640 So let's dig Should we start with the Germans or 0:14:48.680 --> 0:14:50.040 should we start with the British. 0:14:50.080 --> 0:14:52.480 So the German story is the one that most people 0:14:52.480 --> 0:14:55.240 have heard about. It's this theory of fluids and flow 0:14:55.280 --> 0:14:58.040 and Bernoulli's equations and all this kind of stuff. So 0:14:58.080 --> 0:14:59.680 we should start with there to make contact with what 0:15:00.160 --> 0:15:02.000 people think about when they think about flight. 0:15:02.520 --> 0:15:03.440 All right, let's do that. 0:15:03.840 --> 0:15:06.520 So the usual story for why plane flies has to 0:15:06.520 --> 0:15:09.800 do with the shape of the wing, and so aeronautical 0:15:09.800 --> 0:15:12.800 engineers call this an airfoil. It's round y in the 0:15:12.800 --> 0:15:14.680 front and it's point d in the back. It's sort 0:15:14.680 --> 0:15:18.280 of like a long, thin tear drop. Right. The idea 0:15:18.640 --> 0:15:21.120 that you're usually told is that the shape of this 0:15:21.280 --> 0:15:24.720 wing creates a pressure difference, that you have lower pressure 0:15:24.760 --> 0:15:27.520 above the wing and higher pressure below the wing, and 0:15:27.560 --> 0:15:30.760 that creates lyft because higher pressure below and lower pressure 0:15:30.760 --> 0:15:34.440 above basically pushes up on the wing. And it's the 0:15:34.480 --> 0:15:37.800 shape of the wing that's crucial in creating these pressure differences, 0:15:38.000 --> 0:15:41.160 which is what creates lyft. So that's the usual story 0:15:41.400 --> 0:15:44.120 for why planes fly. That comes down to this particular 0:15:44.200 --> 0:15:45.080 shape of the wing. 0:15:45.520 --> 0:15:49.160 So you've got this curved edge moving towards the air quickly. 0:15:50.160 --> 0:15:54.160 Why does that shape not create the same amount of 0:15:54.160 --> 0:15:55.840 pressure on the top as it does on the bottom. 0:15:55.840 --> 0:15:58.320 Because that shape is like symmetrical, right is it? Because 0:15:58.320 --> 0:16:00.520 when it goes over, it has more space to sort 0:16:00.520 --> 0:16:01.240 of spread out. 0:16:01.440 --> 0:16:04.400 So the shape is not actually symmetrical. Right. Typically it's 0:16:04.440 --> 0:16:07.520 like flat on the bottom and more curved on the top, 0:16:08.160 --> 0:16:10.680 and so the shape is not actually symmetrical. Which is 0:16:10.680 --> 0:16:13.080 why the Bernoulli story tells you that it pushes up. 0:16:13.240 --> 0:16:15.400 Bernoulli is a guy in the seventeen hundreds who is 0:16:15.400 --> 0:16:18.920 thinking about fluid flow and mostly about like water through 0:16:18.960 --> 0:16:22.000 pipes and pressure and volume and like, fluids are still 0:16:22.080 --> 0:16:25.600 something we're struggling to understand. But Bernoulli had a simplified 0:16:25.800 --> 0:16:28.200 view of it, which oiler actually came through later and 0:16:28.320 --> 0:16:31.160 proved all of his equations for him. But Bernoulli's principle 0:16:31.160 --> 0:16:34.440 tells us that faster moving fluids have lower pressure and 0:16:34.520 --> 0:16:37.680 slower moving fluids have higher pressure. So if the shape 0:16:37.680 --> 0:16:39.760 of the wing as it moves through the air makes 0:16:39.800 --> 0:16:43.120 the air go slower under the wing and faster above 0:16:43.160 --> 0:16:46.200 the wing on this curved shape, then that'll generate lower 0:16:46.200 --> 0:16:48.800 pressure above the wing and higher pressure below the wing, 0:16:49.200 --> 0:16:50.480 and that gives you lift. 0:16:50.920 --> 0:16:53.240 And that feels easy to test, right because you just 0:16:53.240 --> 0:16:56.960 flip the wing over and it should do the opposite, right, 0:16:57.160 --> 0:16:59.120 like it should send you plummeting downwards. 0:17:00.440 --> 0:17:03.440 Yes, already you're identifying a problem with this, But before 0:17:03.480 --> 0:17:06.040 we take this explanation apart, let's do a little bit 0:17:06.040 --> 0:17:08.119 more to support it. Because you're right, it kind of 0:17:08.200 --> 0:17:09.959 is easy to test and you can do a simple 0:17:10.000 --> 0:17:12.160 test at home. You can just like take a piece 0:17:12.200 --> 0:17:15.159 of paper and blow air above the piece of paper, 0:17:15.480 --> 0:17:17.080 and what you see is the paper goes from being 0:17:17.160 --> 0:17:19.080 sort of droopy to being flat, so it sort of 0:17:19.080 --> 0:17:21.879 like lifts up. And so it's like a classic symbol 0:17:21.920 --> 0:17:24.920 at home demonstration. Which you're doing is you're increasing the 0:17:25.000 --> 0:17:27.720 velocity of the air above the paper, which in theory 0:17:28.040 --> 0:17:31.400 lowers the air pressure above the paper, which provides lift 0:17:31.400 --> 0:17:33.679 because now the pressure is higher below the paper and 0:17:33.760 --> 0:17:36.600 lower above the paper. And you know, the story of 0:17:36.760 --> 0:17:39.880 like the air moves faster over the wing and slower 0:17:39.920 --> 0:17:43.320 below the wing is also verified in lots of other experiments, 0:17:43.359 --> 0:17:46.520 Like you can do these smoke tests where essentially you 0:17:46.520 --> 0:17:48.800 put a wing in a wind tunnel. Instead of just 0:17:48.840 --> 0:17:51.720 blowing air over it, you blow smoke over it. Smoke 0:17:51.840 --> 0:17:53.760 just being like a bunch of particles. You can track 0:17:53.800 --> 0:17:56.880 those particles and you can measure the velocity. So basically 0:17:57.119 --> 0:17:59.359 measure the velocity of the air around the wing. See 0:17:59.359 --> 0:18:02.359 what happened, right, don't just like talk about it, you know, 0:18:02.440 --> 0:18:05.160 in your salons while you're smoking cigarettes or whatever. Actually 0:18:05.200 --> 0:18:08.040 figure it out. And this is verified, like wind tunnels 0:18:08.040 --> 0:18:10.240 and smoke tests tell us that the air does move 0:18:10.320 --> 0:18:13.360 faster over the top of the wing than below the wing, 0:18:13.480 --> 0:18:16.000 And so this seems like it all sort of comes together, 0:18:16.480 --> 0:18:20.399 but as you identify, there are some important limitations to 0:18:20.600 --> 0:18:22.680 this explanation of why planes fly. 0:18:23.400 --> 0:18:26.040 So when you get a window seat near the wing 0:18:26.520 --> 0:18:28.920 and you look out, it's easier to see like it's 0:18:28.960 --> 0:18:30.840 bunching up and it gets a little bit like kind 0:18:30.840 --> 0:18:34.159 of white ish. Is that pressure forming? Like are you 0:18:34.200 --> 0:18:36.000 sort of bunching up the air molecules to the point 0:18:36.000 --> 0:18:39.480 where they're visible or something else happening there? Or am 0:18:39.480 --> 0:18:41.200 I imagining it? And this is like an episode of 0:18:41.240 --> 0:18:42.680 the Twilight Zone. 0:18:43.480 --> 0:18:46.159 Nobody else sees that, Kelly, Yeah, exactly, it's just you. 0:18:46.520 --> 0:18:47.920 That was such a great episode. 0:18:48.280 --> 0:18:48.800