How Do Airplanes Fly? What Neil deGrasse Tyson got wrong about Bernoulli | StarTalk
Summary
TLDRThe 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
🌌 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.
🛫 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.
🌬️ 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.
🕷️ 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.
Mindmap
Keywords
💡Aerodynamics
💡Lift
💡Bernoulli's Principle
💡Equal Transit Time Hypothesis
💡Angle of Attack
💡Stall
💡Airfoil
💡Newton's Third Law
💡Drag
💡Aircraft Carrier
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
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