How Do Airplanes Fly? What Neil deGrasse Tyson got wrong about Bernoulli | StarTalk

Summary

The video script features a critique of astrophysicist Neil deGrasse Tyson's explanation of aerodynamics on his popular podcast, StarTalk. It argues that Tyson's description of lift based on the equal transit time hypothesis is incorrect. Instead, the video presents NASA's view that lift is a result of the flow of air being turned by the wing, following Newton's third law of motion. The script debunks the common myth that lift is solely due to airspeed differences over the wing's curved surface, emphasizing the importance of understanding both Bernoulli's principle and Newton's laws to fully grasp how airplanes achieve lift.

Takeaways

• 😀 Neil deGrasse Tyson is an astrophysicist, writer, and science communicator who has studied at Harvard University, the University of Texas, and Columbia University.
• 👨‍🏫 Tyson served on government commissions regarding the future of the US airspace industry and space exploration, and was awarded the NASA Distinguished Public Service Medal.
• 🎙️ Since 2009, Tyson has hosted 'Star Talk', a popular podcast with nearly 3 million subscribers on YouTube, co-hosted by comic co-host Chuck Nice.
• 🚫 The script challenges Tyson's explanation of lift in his podcast, arguing that his understanding is based on a misconception about aerodynamics.
• ✈️ The common explanation of lift, based on the equal transit time hypothesis, is debunked with evidence showing that air does not travel at the same speed over and under the wing.
• 🔍 According to NASA, lift is generated when a moving flow of gas is turned by a solid object, creating an opposite reaction force, aligning with Newton's Third Law of Motion.
• 📚 The Bernoulli principle is not entirely dismissed but is used in conjunction with Newton's laws to explain the pressure differences that contribute to lift.
• 📉 The video by Holger Babinski, a professor of aerodynamics, visually demonstrates the flaw in the equal transit time hypothesis using smoke to track airflow.
• 🛫 During takeoff, pilots use flaps to increase the angle of attack, which increases the pressure difference and lift, allowing the aircraft to ascend.
• 🌬️ The script emphasizes that lift is not solely created by air hitting the underside of the wing, but by the complex interaction of airflow over and under the wing.
• ✋ The idea of comparing wing lift to holding a hand out of a car window is flawed, as most of the force felt is drag, not lift.

Q & A

What is the main topic of the podcast episode featuring Neil deGrasse Tyson?

The main topic of the podcast episode is the explanation of how airplanes fly, specifically addressing the common misconceptions about lift and aerodynamics.

What is the 'equal transit time hypothesis' mentioned in the script?

The 'equal transit time hypothesis' is a previously held belief that the air on the top of an airplane wing travels a longer distance and therefore must move faster to reach the end of the wing at the same time as the air on the bottom, creating lift. However, this hypothesis has been debunked as incorrect.

According to the script, what is the correct explanation for lift on an airplane wing?

The correct explanation for lift, as per the script, is that lift occurs when a moving flow of gas is turned by a solid object, such as an airplane wing. The flow is turned in one direction and the lift is generated in the opposite direction, following Newton's third law of motion.

What role does the Bernoulli's principle play in the generation of lift according to the script?

Bernoulli's principle is still relevant in explaining lift. It helps to calculate the velocity of an airstream when the static pressure is known and is useful for visualizing the pressure distribution above and below the wing. However, it is not the sole explanation for lift.

What does the script suggest about the importance of the angle of attack in flight?

The script suggests that the angle of attack, which is the angle between the airflow and the chord of the wing, is crucial for generating lift. As the angle of attack increases, the static air pressure over the wing decreases, leading to more lift.

Why do pilots increase the flaps on the tail wings during takeoff, as mentioned in the script?

Pilots increase the flaps on the tail wings during takeoff to create extra pressure that pushes the tail down, pivoting the nose upwards. This increases the angle of attack, which in turn increases the lift generated by the wings.

What is the significance of taking off into the wind, as discussed in the script?

Taking off into the wind is significant because it provides a headwind component that increases the airspeed over the wings, which is crucial for generating lift. This allows the aircraft to become airborne more efficiently.

How does the script explain the evolution of aircraft carrier designs, particularly regarding the flight deck?

The script explains that aircraft carriers evolved from having a straight deck to an angled flight deck. This change allowed aircraft to land and take off more safely by enabling missed landings to go around the deck instead of crashing into parked aircraft.

What is the purpose of having multiple runways at different angles in airports and on aircraft carriers, as described in the script?

Having multiple runways at different angles allows for aircraft to take off and land into the wind regardless of its direction. This ensures optimal headwind components for better lift and control during takeoff and landing.

What is the challenge issued to Neil deGrasse Tyson at the end of the script?

The challenge issued to Neil deGrasse Tyson is to make a new video about lift, correcting the misconceptions and incorporating the insights provided in the script, possibly with the guidance of experts like Holger Babinski, D. McEn, and Kristoff Foskett.

Outlines

00:00

🌌 Debunking Misconceptions about Lift

The paragraph introduces Neil deGrasse Tyson, an astrophysicist and science communicator, who is critiqued for his incorrect explanation of aerodynamics, specifically the lift on airplane wings. Tyson's explanation, which relies on the equal transit time hypothesis, is shown to be misleading. The paragraph discusses how the faster-moving air on top of a wing creates lower pressure, but this is not due to air particles meeting at the rear of the wing simultaneously, as Tyson suggests. Instead, the correct understanding involves Bernoulli's principle and the behavior of air around the wing's shape, which is better explained by considering the wing's angle of attack and the force required to change the direction of airflow.

05:01

🛫 Newton's Laws and the Generation of Lift

This section delves into the correct principles behind lift, emphasizing Newton's third law of motion—action and reaction—as the fundamental force generating lift. It clarifies that while Bernoulli's principle is not the sole explanation for lift, it still plays a role in understanding airspeed and pressure relationships. The paragraph explains how the curvature of a wing forces air to follow a curved path, necessitating a change in direction that results in lift. The importance of the angle of attack and how it affects the pressure differential between the top and bottom surfaces of a wing is also discussed. The paragraph concludes by highlighting that lift is a result of both Bernoulli's principle and Newton's laws, working together to create the necessary forces for flight.

10:02

🌬️ Understanding Airflow and Aircraft Design

The paragraph discusses the importance of airflow around an aircraft's wings and how it contributes to lift. It explains that the design of a wing is intended to maximize lift while minimizing drag, which is contrary to the common misconception of air 'hitting' the wing. The text also addresses the concept of aircraft taking off into the wind to ensure the best lift conditions. It further explores the geometry of runways at airports and the strategic orientation of these runways to accommodate varying wind directions. The discussion includes the historical evolution of aircraft carriers and the introduction of angled flight decks to improve safety and efficiency during takeoff and landing.

15:04

🕷️ Encouraging Correct Understanding of Aerodynamics

The final paragraph humorously encourages viewers to seek accurate information and challenge misconceptions, using a playful threat of finding a spider in their bed if they don't. It wraps up the video with a call to action for viewers to like, share, and engage with the content, promoting a culture of learning and curiosity.

Keywords

💡Aerodynamics

Aerodynamics is the study of the motion of air, particularly as it interacts with solid objects like airplane wings. In the video, aerodynamics is central to understanding how airplanes generate lift and overcome gravity. The script discusses the common misconceptions about lift and how aerodynamics principles, such as the Bernoulli's principle and Newton's laws, are incorrectly or correctly applied to explain this phenomenon.

💡Lift

Lift is the force that opposes the weight of an aircraft and allows it to ascend. It is generated by the pressure difference between the upper and lower surfaces of an airplane wing. The video script challenges the common explanation of lift based on equal transit time and instead discusses how lift is a result of the air's momentum change according to Newton's third law. The script uses examples such as the angle of attack and the shape of the wing to illustrate how lift is created.

💡Bernoulli's Principle

Bernoulli's Principle states that an increase in the speed of a fluid occurs simultaneously with a decrease in pressure. The video script mentions this principle in the context of explaining lift, suggesting that while it is often used to explain why fast-moving air over the top of a wing creates lower pressure and thus lift, this explanation is misleading. The script argues for a more nuanced understanding of how pressure differences contribute to lift.

💡Equal Transit Time Hypothesis

The Equal Transit Time Hypothesis is a theory that suggests air moving over the top of an airplane wing has to travel a longer distance and thus moves faster to reach the wing's end at the same time as the air below, creating lower pressure and lift. The video script debunks this hypothesis, showing through a video by Professor Babinski that the air on top does not reach the end of the wing at the same time as the air on the bottom.

💡Angle of Attack

The angle of attack is the angle between the oncoming airflow and the chord line of an airfoil (the wing's imaginary straight line from the leading edge to the trailing edge). The script explains how changing the angle of attack can increase the lift generated by a wing, up to a point where the airflow becomes turbulent and lift decreases, leading to a stall.

💡Stall

A stall occurs when the smooth flow of air over the wing is disrupted, leading to a dramatic loss of lift. This is often associated with an excessive angle of attack. The script uses the example of holding a hand out of a car window to illustrate the turbulent flow and loss of lift, which is similar to what happens during a stall.

💡Airfoil

An airfoil is the cross-sectional shape of an airplane wing, designed to generate lift efficiently. The script discusses how the shape of an airfoil, particularly the curvature of the top surface, influences the airflow and pressure distribution, which in turn affects lift.

💡Newton's Third Law

Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction. The script uses this law to explain how lift is generated: as the wing turns the airflow downward, the air exerts an upward force on the wing, which is the lift. This explanation complements the discussion of pressure differences and provides a different perspective on the generation of lift.

💡Drag

Drag is the resistance that opposes the motion of an object through a fluid, like air. The script contrasts lift with drag, explaining that while lift is the force that allows an airplane to rise, drag is the force that opposes this motion and must be minimized for efficient flight. The script also mentions that a common misconception about lift is that it is created by air 'hitting' the wing, which is more akin to drag.

💡Aircraft Carrier

An aircraft carrier is a large naval vessel designed to serve as a seagoing airbase, equipped with a flat deck for aircraft to take off and land. The script discusses the evolution of aircraft carrier design, particularly the introduction of the angled flight deck, which allows for more efficient and safer takeoff and landing operations, especially in the context of changing wind directions.

Highlights

Neil deGrasse Tyson is challenged on his explanation of aerodynamics and lift.

Tyson's explanation of lift based on the equal transit time hypothesis is critiqued.

The debunking of the equal transit time hypothesis with evidence from a Cambridge professor's video.

Explanation of lift according to NASA, involving the turning of gas flow by a solid object.

The importance of both Bernoulli's principle and Newton's third law of motion in understanding lift.

The role of the wing's curvature and angle of attack in generating lift.

The incorrectness of the common analogy of holding a hand out of a car window to explain lift.

The significance of air flowing around the wing for maximum lift and minimum drag.

The concept of stalling in aerodynamics explained through changes in air flow and angle of attack.

The strategic use of runway orientation for takeoff and landing into the wind.

The historical evolution of aircraft carrier design to improve takeoff and landing efficiency.

The introduction of angled flight decks on aircraft carriers and their operational benefits.

The impact of jet-powered aircraft on the necessity for improved landing procedures.

The detailed explanation of how aircraft carriers manage wind direction for takeoffs and landings.

The recommendation for Tyson to consult specific mentors for a more accurate understanding of lift.

A call to action for Tyson to create a new video correcting his previous explanations of lift.

The humorous conclusion with a playful threat to encourage engagement with the video content.

Transcripts

nearly grass Tyson may I have your

attention please you know everything

about the universe Stars comets planets

galaxies you know it all but when it

comes to basic

aerodynamics I'm sorry to say it but in

your head there is a black hole and

besides my shirt is cooler than

yours hello aviators how you today my

name is m Nal I am an alen captain and

instructor nearly Tyson is an

astrophysic writer and science

Communicator he studied at Harvard

University the University of Texas and

he got his PhD at Columbia

University Tyson served on a 2001

government Commission on the future over

the US airspace

industry and on the 2004 Moon Mars and

beond commission he was awarded the NASA

distinguished public service medal since

2009 Tyson has hosted star talk a weekly

podcast with nearly 3 million

subscribers on YouTube it is very

popular not only because of Tyson but

also because our co-host sh nice who

makes it even more

entertaining when I found Tyson's

podcast about how airplanes fly I was

excited because Neil degrass Tyson is

reaching out to many people finally I

thought here is a podcast that you

debank the most common misconceptions

about lift but but I was

wrong as you can read on the website on

NASA quote there are many explanations

for the generational lift found in

encyclopedias in basic physics textbooks

and of websites unfortunately many of

the explanations are misleading and

incorrect Mr Tyson you have been

fooled all right so uh so the top part

is curved okay and the bottom is uh it's

typically flat okay so you have a pocket

of air that the moving Wing is passing

through and the air wants to stay as one

parcel it wants to okay okay so as you

do this the air on top to go that bigger

distance has to travel faster to keep up

with the air on the bottom so that when

it reconnects it's the same parcel

gotcha all right so you have forced the

air to move faster on the top than on

the bottom and fast moving air has lower

pressure and I've done this it is

correct that fast moving air has lower

static pressure and it is correct that

low static air pressure over the wing

results in lift but this does not happen

because air particles separated at the

front of the wing are forced to meet

behind the wing at the same time this is

called equal Transit time hypothesis

but this is a wrong application of

baruli principle which says that within

a horizontal flow of a fluid points of

higher fluid speed will have less static

pressure than points of slower fluid

speed this works well in

aventuri but the wing divides the air

flow into two individual air flows and

that changes everything think about it

how can two air particles separated at

the front of a wing know where the other

air particle is this is a video produced

by holar Babinski professor of

aerodynamics at the University of

Cambridge it's often said the lift on a

wing is generated because the flow

moving over the top surface has a longer

distance to travel and therefore needs

to go faster this common explanation is

actually wrong this video shows that the

air on the top does move faster but it

doesn't reach the end of the wing at the

same time as the air along the

bottom here we use smoke to visualize

the streamlines around an airfall we can

pause the Smoke by briefly interrupting

the supply this gives us lines that

travel through the flow as we can see

here and if we now slow the video down

you can follow those lines and that

gives you an idea of how fast the flow

is in different parts of the air

flow here you can see it's speed up as

it approaches the air foil and it moves

faster over the top compared to the

bottom you can see that it reaches the

end on the upper surface much earlier

than it does on the lower surface in

fact by the time it reaches the end on

the lower surface the flow's already

gone a long way past on the upper

surface this shows very clearly that the

flow doesn't take the same amount of

time to reach the end of the

wing the eal transit time hypothesis is

hereby debunked Beyond

doubt so how can we explain lift then

according to NASA code lift occurs in a

moving flow of gas is turned by a solid

object the flow is turned in One

Direction and the lift is generated in

the opposite direction according to

Newton's F law of action and

reaction this is the easiest way to

explain

lift but this doesn't mean we shall

throw baruli out the window for example

bari's equation can be used to calculate

the velocity of an Airstream when you

know the static pressure it is also

useful to visualize the pressure

distribution above and below the ring it

is not Peri or Newton both are correct

bar through the preservation of energy

Newton through the preservation of

momentum the reason why air accelerates

over the wing is the curd path the air

is forced to follow around the wing and

especially the Leading Edge at high

angular attack the angle of attack is

the angle between the airflow and the

cord of the wing a changing direction

requires a force and this is where

Newton Second L motion comes into play

and behold Newton Second law can be

rearranged into beris equation you can

freeze the video and read the text for

yourself I have also made a few videos

about lift where this is explained in

more detail and you will find links in

the description

below now back to Tyson and

nice okay so on the runway where you're

ready to take off right and they playing

accelerates the pressure difference

between the top and the bottom is

becoming greater and greater and

greater and the plane saying I'm ready

to do this okay but you don't want to

rely only on that you want to make sure

this happens

So What by the way it continues to

accelerate through this what the pilots

do is they they in they up the flaps on

the tail wings okay right what does that

do that creates extra pressure to push

the tail down pivoting the nose upwards

aha when the nose goes upwards the

upward pressure on the wings is no

longer just this berui effect bernui is

the guy who first uh uh decoded this

phenomenon it's not only that the wing

is now pitched upward towards the moving

air

right it's pitched upward so air is

flying straight into the wing that's

going to also add to the bruli effect

and that plane is going to

pop that's why it doesn't slowly gain

altitude that plane changes its angle to

the air and it

flies when the aircra no is rotated up

the angle of attack is increased as the

angle of attack increases the static air

pressure over the wing decreases while

the pressure under the wing remains near

constant the pressure difference between

the upper and lower surfaces of the wing

is lift and when the lift is greater

than the weight of the aircraft it will

climb the idea that lift is created by

air hitting the under surface of the

wing is flawed many people compare it

with holding the hand out of the window

of a car and feeling the lifting Force

but most of this force is drag

a wing is designed to produce maximum

lift and minimum drag and that means the

air must flow around the wing and not

hit it like a sledgehammer as noasa says

it quote neglecting the upper surfaces

part in turning the floor leads an

incorrect theory of

lift this illustration is from the book

aerodynamics by LJ Clancy it shows the

pressure distribution around the wing at

different angle of attack the green area

about above the wing is low pressure the

Blue Area below the wing is high

pressure at plus 2° the underside and

overside of the wing contributes equally

to lift 50% each when the angle of

attack increases the overside of the

wing produces more and more of total

lift and at 15° it is close to maximum

when the angle of attack increases

further the airf flow over the wing

becomes turbulent and the lift decreases

rapidly this is stall and this is what

you experience when you hold your hand

out the car

window

so every plane if it has the

option is going to take off into the

wind

aha because what matters is not the

speed relative to the ground because a

Tailwind would give you high speeded

relative to the ground but once you're

Airborne you want to stay there and so

what matters is the speed over your

wings that the air has and so you take

that's why every airport and aircraft

carriers have at least two runways at an

angle to each other so that when the

wind direction switches they can change

which Runway you're using so that you

will always take off into the wind nice

always and the two the forgot what the

is it 45 or 30° angle it's not it's not

at a 90° angle to each other okay no

because if you do if you do the math and

the geometry on this you want it to be

about at 30 Dee angle because then all

combinations what you do is you if you

if the wind changes Direction then you

just take off in the opposite direction

of the of the all right and it turns out

many solutions are solved just by having

two runways at that angle and that's why

aircraft carriers you will see um just

take a look at their shape the World War

II class aircraft carriers you could

they had two angles you could land on

their de yeah on it and if you're going

to land from the direction you're coming

they would turn around the aircraft

carrier so that you're coming in Against

the Wind so most airports have only one

Runway or two parallel runways and

regarding aircraft carriers I will come

back to them soon do allow for an

aircraft to take off from an airport

with two runways with maximum heading

component the runway should not cross

each other with 30° but

90° this ensures maximum headwind

component for example an airport has two

runways Runway 36 is oriented towards

360° North and Runway 03 towards 03

0° if the wind is 20 knots from 90° Reno

36 will have pure crosswind and for r 03

the wind will be offset

60° which means the headwind component

is 10

knots then we have an airport where the

runways are crossing each other with 90°

Runway 36 and

09 if the wind is 20 knots from 90° The

Heading component on Runway S9 is uh 20

knots a worst case scenario will be the

wind from 45° giving a hidden component

of 40 knots for both runways

then we have the aircraft

carriers they always steer into the wind

when aircraft are taking off on Landing

NR Tyson since you're living in New York

I'm sure you have visited intered Sea

Air and Space Museum USS ined was

commissioned in 1943 and the Commission

in

1974 in the hangar you see two models of

the aircraft carrier one model shows the

initial configuration with a straight

deck and this was Norman during World

War II but it had a major flaw before

take off aircraft were parked at the

after section of the deck and the rest

served as a Runway no problem with

that when the aircraft were returning

they had to catch one or several wires

stretch across the deck with a tail hook

after landing the aart will TX it to the

forward part of the

deck and a barrier was erected to

protect the parked aircraft from Landing

aircraft that missed the wires but this

Arrangement was not perfect when an

aircraft hit the barrier it could

receive so much damage that it may had

to be scrapped or dumped

overboard this problem increased with

the introduction of jet powered aircraft

which had Higher Learning speed and

therefore less margin for

error the solution came with the

introduction of the angled flight

take USS interpid receiv received this

modification in the middle of the

1950s all aircraft carriers in the US

Navy have this Arrangement today this

allows for learning aircraft to go

around if they miss the wires simple as

that

Tyson I challenge you to make a new

video about lft where you got those

things right for inspiration I recommend

the following mentors olar Babinski

professor of aeronomics University of

Cambridge D mcen retired technical

fellow at boing and Kristoff fski

professor of a a Space Engineering at

the University of

Michigan if you love your mother click

like share and all that or you will find

a spider in your bed tonight thank you

for watching have a wonderful day and

happy learning