The Forces on an Airplane: Aaron Johnson at K12Live! (MIT Museum Second Fridays, 1-10-14) - By MITK12Videos
Transcript
00:03 | But so now we're actually gonna show you , we're | |
00:06 | going to talk about some of the concepts that we | |
00:07 | talked about in the video . We're not really gonna | |
00:10 | be able to talk about weight . Everyone pretty much | |
00:12 | knows what day it is . Perhaps especially after the | |
00:14 | holidays were especially conscious of it . Uh , we're | |
00:18 | not really going to talk about trust , we didn't | |
00:19 | really bring an engine with us . We are going | |
00:22 | to talk able to talk about the other two forces | |
00:24 | lift and drag . So we need to get our | |
00:27 | Minister wind tunnel set up . Oh , so why | |
00:31 | we're doing this is probably a good idea if you | |
00:34 | want a really good view to come up front . | |
00:37 | So maybe you can sit in some of these seats | |
00:39 | up front or just sit on the floor up here | |
00:43 | because you really need to be closer to see what's | |
00:45 | going on . Yeah , I don't know what this | |
00:56 | is . Yeah , It was always going to bring | |
01:01 | an extension cord . Alright , so essentially what this | |
01:06 | is . This is a miniature wind tunnel . So | |
01:09 | in aerospace engineering were both aerospace engineers . Uh We | |
01:12 | use wind tunnels a lot to test airplanes . It | |
01:15 | would be really cost inefficient if you built a giant | |
01:18 | airplane and then fluid in a crash . And we're | |
01:20 | like , oh , the design was really bad , | |
01:21 | we should change things . Uh So instead we test | |
01:24 | models in wind tunnels . Uh We don't do it | |
01:26 | so much anymore because we have computer programs which will | |
01:29 | actually test out the aerodynamics . This is sort of | |
01:31 | the field of research . Uh They'll test out the | |
01:33 | aerodynamics oh and everything on a computer . So we | |
01:36 | don't have to do a lot of wind tunnel testing | |
01:38 | . But there great for student projects and demonstrations like | |
01:41 | this . So this is a mini version that our | |
01:43 | friends made . So what we're gonna do is we're | |
01:46 | gonna put a couple of different things uh in the | |
01:49 | wind tunnel , we're gonna turn on this fan here | |
01:52 | , at the right side , it's gonna suck the | |
01:55 | air through . These straws are just to straighten the | |
01:58 | flow . So it's not all we call turbulent , | |
02:01 | which is when it's swirling and everything actually have these | |
02:04 | on real wind tunnels , there's just a lot bigger | |
02:06 | than this . So , the flow is gonna come | |
02:08 | in here , flow over our square or are doing | |
02:13 | whatever we have in there and then go out the | |
02:14 | back and we're gonna use this dry ice . Uh | |
02:17 | we're just gonna put hot water on it and it's | |
02:20 | going to start to evaporate and create a lot of | |
02:22 | smoke . And so we're gonna put this in here | |
02:25 | , which will allow us to see the flow over | |
02:27 | the square or the wing really help us to see | |
02:30 | what's going on . So we're gonna turn this on | |
02:35 | and so you can hear it start to go . | |
02:36 | So I will turn the object and sort of talk | |
02:41 | about it just that you want to do the , | |
02:48 | so as you can see , it's gonna start to | |
02:51 | smoke a lot . So the first thing we're gonna | |
02:54 | talk about is drag and so you can see , | |
02:57 | so the air is flowing through this way and if | |
02:59 | I have to square like this , you can see | |
03:01 | there's a big area that's perpendicular to the flow , | |
03:05 | so the air is going to come in and it's | |
03:06 | gonna smack on the side of this square and it's | |
03:10 | not really going to have anything anywhere to go . | |
03:12 | You just put it out so there you can see | |
03:15 | the flow coming in and it's coming in and smacking | |
03:18 | into the side of the swear it has to go | |
03:20 | all the way around the corner . So this has | |
03:23 | a really high drag . It's kind of like when | |
03:26 | you put your hand out the window straight up because | |
03:28 | there's a really big area that the wind is smacking | |
03:31 | too if we turn it sideways so that the air | |
03:36 | at this point and it goes over to one of | |
03:38 | the two sides , so that's a lot smoother flow | |
03:42 | over the square . So this has a little bit | |
03:45 | less strength , still a lot of drag because it's | |
03:47 | a really big blocky object . This is why you | |
03:49 | never really , you know , put some more water | |
03:53 | in there , you really never have wings that look | |
03:56 | like squares because they don't help your airplane fly very | |
03:59 | well , They're pretty bad . So square is not | |
04:02 | a shape that we see in aircraft wings . So | |
04:04 | I'm gonna put in a different shape really quickly and | |
04:07 | we're gonna put in a circle , which is another | |
04:11 | shape that airplane wings don't have , but it's a | |
04:13 | lot less drag . It's just been so it's sort | |
04:24 | of spinning out chunks , surprise , You can see | |
04:27 | the you can see that it's coming over and it's | |
04:33 | going around the side , you can move it up | |
04:35 | and down . I want to do that , just | |
04:36 | move it until it goes over the top . I | |
04:42 | don't know , more dries . Well let's try that | |
04:49 | again because this is the coolest where we obviously don't | |
04:52 | have airplane wings that are squares or circles because they | |
04:55 | don't fly very well , they don't lose any of | |
04:58 | that lift force that we talked about . So we're | |
05:02 | gonna put in this airfoil and this airfoil comes in | |
05:04 | its own special box . It's a very nice airfoil | |
05:07 | . I was told not to mess this one up | |
05:08 | , so that's cold . So this airfoil , so | |
05:20 | we're gonna talk about how airfoils produce lift . So | |
05:24 | you can see this is an airfoil . An airfoil | |
05:26 | is essentially just a cross section of wing . If | |
05:28 | you went out to an airplane and chopped part of | |
05:30 | the wing off , they would chase you out of | |
05:32 | the airport and probably be really mad . But if | |
05:35 | you hear anything to that , I think about that | |
05:37 | , what you have is this section here , which | |
05:39 | is an airfoil . So we have a really , | |
05:41 | this is sort of a really exaggerated airfoil and you | |
05:44 | can see how it's really curved on top and really | |
05:48 | flat on bottom . Real airplanes don't look like this | |
05:51 | . This doesn't fly very well either . This is | |
05:53 | sort of the shape that you see . This is | |
05:55 | like the exaggerated version . So one of the things | |
05:57 | that happened that creates lift is the air flows faster | |
06:01 | on top than the bottom . So you have the | |
06:04 | air going over the top and it accelerates and it | |
06:07 | goes slower on bottom . So that causes a lower | |
06:11 | pressure on top . So there's high pressure on the | |
06:13 | bottom of the weight and low pressure on top and | |
06:16 | pressure wants to go from high to low . So | |
06:18 | there's sort of a net pressure difference and it pushes | |
06:21 | the airplane up . Um That's sort of one of | |
06:25 | the mecca . It's not the only mechanism and that's | |
06:26 | one of the ways that lift works . So we're | |
06:29 | gonna put um actually , let's start with this big | |
06:32 | airfoil . So we're gonna put this big airfoil and | |
06:36 | what you should be able to see is , you'll | |
06:38 | see , you know , we'll just turn it like | |
06:39 | this sort of straight into the flow and this is | |
06:42 | zero angle of attack . As we said in the | |
06:44 | video , and you'll see the air going faster over | |
06:47 | the top than the bottom . I should say . | |
06:49 | You should see it just because of the curve design | |
07:00 | just makes the air accelerates . It has a longer | |
07:02 | distance to travel . The air is coming in at | |
07:06 | the same speed . It has a longer distance to | |
07:09 | travel over the top . So Well . All right | |
07:17 | , well , that used to be working all right | |
07:22 | , so you can sort of pull it up so | |
07:26 | you can see you going over the top so you | |
07:27 | can see it going over the top . It's going | |
07:30 | faster than we move into the bottom . It's really | |
07:35 | it's really teetering out there . We're not sure of | |
07:44 | the correct . Yeah , Well that's way way , | |
08:14 | yeah , this is what science is . You can | |
08:16 | just waiting to be like , oh well it's just | |
08:18 | science . We're just trying things until until it works | |
08:22 | , which is sort of doing a PhD is also | |
08:28 | there were there were better ways . I think our | |
08:33 | water wasn't hot enough I think yeah , you can | |
08:36 | see the flow is really coming here and it's really | |
08:38 | accelerating over the top and if you can't see , | |
08:40 | you're welcome to come off a little bit . Our | |
08:44 | smoke screen isn't terribly fast , you're moving up and | |
08:48 | down . You can sort of see the difference between | |
08:51 | the bottom water . Wait , wait , this is | |
09:05 | why we use real wind tunnels and not . Do | |
09:16 | you want to get a little ? So does anyone | |
09:24 | have any questions while we're true ? Alright , this | |
09:28 | work . Any questions about airplanes or anything ? Yeah | |
09:32 | , I always does this usually happen with dry eyes | |
09:40 | for a second time using this one . So I'm | |
09:44 | gonna say yes . So I don't feel that it | |
09:47 | usually happens . It's not just that we're sure . | |
10:04 | Let's just try a little bit . There's more mother | |
10:11 | there . Well this video is funny , right ? | |
10:14 | So yeah , it wasn't going to be lost . | |
10:28 | Okay , so what we're gonna do is we're gonna | |
10:35 | we're gonna start to turn it up and this is | |
10:37 | increasing the angle of the attack . Like we said | |
10:40 | in the video and it's increasing the drag because , | |
10:44 | you know , there's a larger area that's in the | |
10:46 | flow . Does anyone remember what we called it ? | |
10:48 | The video when you get too high of an angle | |
10:50 | of attack and you start to use lift stall . | |
10:53 | Yeah . So what you can see is here , | |
10:57 | we have to turn it up really high . You | |
10:59 | would never if your airplane is ever like this , | |
11:01 | that's bad . Well , you can sort of see | |
11:04 | the flow here is really swirling around and this is | |
11:07 | what we call turbulent flow . This is bad . | |
11:10 | You really want like this here , the flow is | |
11:13 | really , it's attached to the wing is what we | |
11:15 | call glam Inner uh , it's really attached to the | |
11:19 | wing and there's a little turbulence and this is really | |
11:21 | good because it gives us , but when we turn | |
11:23 | it up really high and we get a lot of | |
11:26 | turbulence , we lose lift and we also create more | |
11:29 | drag . So this is bad . So you can | |
11:33 | actually , like if you're flying in a really spicy | |
11:36 | ever been in like a small like 2 to 4 | |
11:38 | person airplane , like a really small Cessna or something | |
11:41 | . Ok . Yeah , a few people . So | |
11:43 | my friend has when he took me out and he | |
11:44 | was like , do you want to see what stall | |
11:46 | feels like ? He's like no , I don't really | |
11:48 | feel like dying . It's just like , you know | |
11:50 | , land uh because if he did this and so | |
11:54 | you sort of pitch up and up and up and | |
11:56 | then eventually the aircraft obviously we're fine . I'm not | |
12:00 | a ghost for anything , but the aircraft just sort | |
12:02 | of starts to go down a little bit , you | |
12:04 | can actually feel that stall and that loss of lift | |
12:07 | . So it's pretty cool when you realize that airplane | |
12:10 | is not going to fall into the sky . So | |
12:13 | we're gonna try this little wing , which is also | |
12:16 | a good song by Jimi Hendrix . What ? That's | |
12:18 | unrelated . Um , I should say so , another | |
12:22 | nice thing about airplanes . So people are always worried | |
12:24 | like you're in an airplane up above , you know | |
12:28 | , and like if the engines quit , everybody's always | |
12:30 | worried like the airplane just gonna fall out of the | |
12:32 | sky . Like Iraq , which actually isn't true . | |
12:34 | Airlines can glide a lot . They can glide pretty | |
12:38 | far because they , the thrust members said when he | |
12:41 | comes from the engine and going fast helps to produce | |
12:44 | lift , but you're still going fast even if the | |
12:47 | engines go out , you still have a little bit | |
12:48 | of lift and you can actually glide to the airport | |
12:51 | . And there happened a couple airplanes that just ran | |
12:53 | out of fuel . There's one in Canada , they | |
12:55 | thought it was gallons and it was leaders and they | |
12:57 | ran out of fuel but they are not blaming . | |
13:00 | Today's . So here it is really an airport back | |
13:05 | a little bit . Yeah , you can really see | |
13:07 | the float . If we turn , see if you | |
13:11 | come up really close , you can see , yeah | |
13:13 | . So if you want to take a look , | |
13:14 | you can see there's really some gorgeous is happening here | |
13:17 | at the back of the wing and that's turbulence and | |
13:19 | that's bad because that's going to cause us to lose | |
13:21 | lift . And also it's going to create more drag | |
13:24 | and that's sort of an airplane starts falling out of | |
13:28 | the sky . So that's not really good . Uh | |
13:32 | Yeah , so commercial airlines are really cool because they | |
13:35 | have these things on the back called flaps , which | |
13:39 | are these like if you're ever landing and you hear | |
13:40 | this mechanical noise , it's not the airplane coming apart | |
13:43 | . Is these things at the back of the wind | |
13:45 | extending , they sort of come off the back of | |
13:47 | the wing like this . And they actually make the | |
13:49 | wings longer and more curve , which lets you have | |
13:52 | more lifted slower speed . So that's what we use | |
13:55 | for takeoff and landing . Uh because when we fly | |
13:58 | and cruise were flying it like what , 455 100 | |
14:02 | miles an hour , but you obviously can't take off | |
14:04 | that fast , You can't drive that fast on the | |
14:06 | ground . Uh Take out speed is about 120 miles | |
14:09 | an hour . So we have these flaps , we | |
14:11 | extend the airport , we get more lifted slower speed | |
14:14 | . So that's how we take off straight once more | |
14:18 | . Let's just put a little more water dry . | |
14:21 | I supposed to do the , if anyone wants to | |
14:23 | come up closer and sort of seeing the laminar flow | |
14:27 | in the turbulent flow . Now be your chance . | |
14:30 | We'll do it once more . I think we need | |
14:33 | some more . Don't the water out in that bucket | |
14:35 | , in this ball in the water . We still | |
14:42 | got a lot of things that didn't work too . | |
14:46 | But I think I just , okay , science , | |
14:52 | everybody just try it and eventually they give you a | |
14:56 | PhD a story of the last four years . It's | |
15:05 | right . So then any more questions about airplanes or | |
15:10 | anything in general , you know , everybody wants to | |
15:13 | go have dinner or are we just answered all your | |
15:16 | questions . That's what I learned so much . No | |
15:19 | further questions . What's happening , the first set of | |
15:25 | airlines from today ? What are the innovations to help | |
15:31 | them make them live ? Yeah , that's essentially it | |
15:37 | . You know , aviation has been uh , here | |
15:40 | . I'll do this demo . We have dry eyes | |
15:43 | question . So as you can see , you know | |
15:44 | , we have the laminar flow and turn it up | |
15:47 | and there'll be a point there were getting it . | |
15:50 | This is a pretty high angle with that . So | |
15:52 | there you can really see , really see the border | |
15:56 | season . It's also hitting the wing here , deflecting | |
15:59 | . So this is , this is not good . | |
16:01 | You're welcome to come up and take a closer look | |
16:05 | . Uh , yes . So what's happened in aviation | |
16:07 | in the past , you know , since the Wright | |
16:09 | Brothers flew about 100 years ago , It's really about | |
16:12 | efficiency . That's the main thing . So do we | |
16:14 | know how to fly airplanes don't fly differently today than | |
16:18 | they didn't like the thirties . Really . The differences | |
16:21 | in efficiency , so working and making engines more efficient | |
16:24 | . Boys , new airplane , the Dreamliner . It's | |
16:27 | made out of all composite material . So it's very | |
16:30 | little metal , so that's lighter and so you can | |
16:32 | carry more passengers of less fuel and make the airlines | |
16:36 | more , but they make the airlines more money , | |
16:38 | um , which I thought the $25 bag fees than | |
16:41 | that . But apparently that's not enough . Uh , | |
16:44 | we have really efficiencies in the wings , efficiencies in | |
16:47 | the engines . Like if you can get a 1% | |
16:49 | increase in efficiency in your engine , you yeah , | |
16:54 | that's incredible . So it's just really minor increments , | |
16:58 | just sort of making bigger airplanes that fly with less | |
17:02 | fuel . Another big increases , sort of the area | |
17:04 | that we study is in the automation . That's , | |
17:07 | you know , back when , you know , you | |
17:08 | had World War Two and those types of airplanes , | |
17:10 | the pilot was doing everything . They used to have | |
17:12 | four people in the cockpit of like a Boeing 7 | |
17:16 | 47 or something that would fly you from here to | |
17:19 | maybe europe or Asia . There was a guy called | |
17:21 | the navigator who would like half a map and would | |
17:24 | say , you know , go straight until you hit | |
17:27 | Portugal and then turn left . Uh , or you | |
17:31 | could have someone called the engineer who would actually look | |
17:33 | at these gauges that says , oh your engine is | |
17:35 | functioning properly or your engine is broken . You should | |
17:37 | probably land . That's generally a bad thing , especially | |
17:41 | when you're on the ocean . But now they have | |
17:43 | automation . Now the computers can take a look at | |
17:46 | that . Uh , so on these long , well | |
17:48 | on domestic flights , we only have two people in | |
17:50 | the cockpit . And for these long oceanic flights we | |
17:53 | generally have three people still just so someone can take | |
17:56 | over . Uh yeah , actually airplanes can pretty much | |
18:00 | take off , take off . The pilot goes down | |
18:02 | the road , but it pulls the yoke back airplane | |
18:04 | goes up into the sky . They can push a | |
18:06 | button that says autopilot on and their blanket land without | |
18:11 | the pilot really doing anything . Uh I was flying | |
18:14 | back , I was flying from Austin to charlotte and | |
18:16 | we landed and we went into these clouds and I | |
18:19 | was like , oh we're in class , break out | |
18:21 | of the bottom and I'll see charlotte below . And | |
18:23 | the land was looking out the window and I saw | |
18:25 | this light that was literally horizontal with the window and | |
18:29 | that was all I saw was off log and there's | |
18:31 | a light . I was like , I really hope | |
18:32 | it's not like a building or something . Uh and | |
18:35 | then I saw some more lights and we were on | |
18:37 | the runway , there was very little visibility . We | |
18:39 | really couldn't see anything . I don't know if it | |
18:42 | was a legal landing was like at the bare minimum | |
18:44 | but that was , you know , when you're trying | |
18:46 | to land in fog or things like that . That's | |
18:48 | when you're really desisted by the autopilot . You know | |
18:51 | , in the early days pilots could really only fly | |
18:53 | when they could see unless they were incredibly gutsy . | |
18:56 | But now we can fly in all sorts of weather | |
18:58 | conditions thanks to the automation . So that's been a | |
19:01 | big sort of advance . Uh not with the aerodynamics | |
19:05 | but more with sort of aviation as a whole . | |
19:07 | And that's sort of the research that we work on | |
19:09 | on human automation interaction . What should the human doing | |
19:13 | ? What should the autopilot yourself ? Yeah , that's | |
19:16 | a great question . Uh any other questions uh what | |
19:21 | I travel from Korea here or here in Korea , | |
19:25 | there is like a quite different and so much better | |
19:30 | . Yeah , thanks to Yeah , I'm not sure | |
19:35 | the specifics but I'm pretty sure it's yeah thanks to | |
19:37 | the win because they're they're like the jet stream is | |
19:40 | over the atlantic and you know just whether you have | |
19:43 | a tailwind or or headwind it helps you to fly | |
19:46 | because if you're flying with the wind it's just give | |
19:48 | you an extra velocity boost . So yeah exactly . | |
19:52 | Even going to the west coast , you'll get about | |
19:55 | our difference in the travel between going west coming . | |
20:00 | It also matters for how much fuel the airlines have | |
20:02 | to burn going into when you can go as fast | |
20:05 | . You can spend a lot more battery with battery | |
20:13 | . Yeah so sometimes the plane , the Boeing 787 | |
20:16 | Dreamliner um they had lithium ion batteries and they caught | |
20:20 | fire . I'm not sure the specifics it was I | |
20:23 | think the contractor's fault . But yeah , I think | |
20:26 | it was a new type of battery , right , | |
20:28 | wasn't it ? They were using the Dreamliner . It | |
20:32 | was newly designed specifically for the type of battery was | |
20:37 | common . I think it wasn't the battery goes like | |
20:41 | this circuitry associated with . Yeah , I'm not sure | |
20:46 | they fixed that . We were supposed to fly on | |
20:48 | the Dreamliner and then they started catching on fire . | |
20:51 | So yeah . Yeah , I think we probably don't | |
20:55 | have at least one more question . How do planes | |
20:58 | return ? Yeah . So how did things turn ? | |
21:00 | So that's really that's actually a question . I like | |
21:03 | a lot . Uh , it's not like evening . | |
21:04 | So like if you're in a boat , like if | |
21:06 | you've been in a boat , boats have runners and | |
21:08 | essentially if you're going in a boat , you just | |
21:10 | sort of turn the runner and the boat goes , | |
21:12 | you know , this one , you turn the other | |
21:14 | the other way as the boat goes . The other | |
21:15 | way planes actually they have runners , but they don't | |
21:19 | really use them to turn like those two . They | |
21:21 | essentially just banks . If you've ever been on a | |
21:24 | plane , you probably experienced this Rihanna plane and it's | |
21:26 | going along the banks and what this does is you're | |
21:30 | just flying straight and level here . Why don't you | |
21:32 | be the airplane to explain ? So Justin is an | |
21:34 | airplane , you could be a you could be a | |
21:36 | 787 that hasn't caught on fire . So Justin's flying | |
21:41 | straight and level the lift for this is sort of | |
21:44 | like you're looking like head on their plane . We | |
21:46 | should hold it horizontally , but we won't do that | |
21:49 | , we're going to do that . So you can | |
21:51 | imagine that here's the nose of the plane that goes | |
21:53 | back like this . So he's flying horizontally . what | |
21:56 | we call steady level flight . The lift vector just | |
21:59 | go straight up , but he banks to the right | |
22:02 | , a little bit of that lift vector is going | |
22:05 | towards the center of the circle . There's still a | |
22:07 | lot going up , but there's a little bit going | |
22:10 | towards the center . And so that's gonna pull him | |
22:12 | if you guys back up a little , that's essentially | |
22:15 | gonna pull him in a circle like this . And | |
22:17 | if he bangs , this is fun , if he | |
22:20 | begs this way he turns like this in a circle | |
22:24 | . So planes have a runner , but that essentially | |
22:26 | just sort of keeps um then flying efficiently , the | |
22:29 | real way they fly is they just bank and then | |
22:32 | they automatically start to turn . So the next time | |
22:34 | you're on an airplane , you'll notice that the airplane | |
22:37 | doesn't start turning and then bag bags and then it | |
22:40 | starts to turn , it naturally follows . Uhh , | |
22:43 | just following a question , how does it bank ? | |
22:46 | Then there are these little things on the outside of | |
22:49 | the wings called ailerons and they sort of , they | |
22:51 | put one up and they put one now and that | |
22:53 | changes the flow over the wing and then that you | |
22:56 | get less with like if you get less lift on | |
22:59 | this swing and more lift on this swing , it | |
23:01 | will naturally bank like that . Or if you switch | |
23:03 | , you get less lift here and more left here | |
23:06 | . It's gonna impart a torque on there . Thank | |
23:09 | you . I think we have to officially end , | |
23:12 | but we can stick around if you have any more | |
23:14 | questions about airplanes . I think I know who they're | |
23:24 | closing . |
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The Forces on an Airplane: Aaron Johnson at K12Live! (MIT Museum Second Fridays, 1-10-14) is a free educational video by MITK12Videos.
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