Aircraft Lift Explained: Bernoulli vs. Newton's Equations | Fly with Magnar
Summary
TLDRIn this educational video, Magnanudal, an island captain and instructor, clarifies misconceptions about how wings generate lift. He explains that while Bernoulli's principle is often incorrectly used to describe lift, it's actually the pressure difference above and below the wing that creates it. The video debunks the equal transit time hypothesis and emphasizes Newton's third law of motion as the simplest explanation for lift. It also discusses the importance of wing design, including the role of the leading edge and the impact of angle of attack, and touches on the limitations of flat wings in flight.
Takeaways
- 📚 Bernoulli's Principle states that an increase in fluid velocity leads to a decrease in static pressure and vice versa, with the sum of static and dynamic pressures remaining constant.
- 🌀 The equal transit time hypothesis suggests that air molecules must travel faster over the top of a wing to meet those below, leading to lower pressure and lift.
- 📉 The pressure difference above and below a wing, not the speed of air over the wing alone, creates lift.
- 🔄 Newton's Third Law of Motion explains lift as a reaction to the downward deflection of air by the wing.
- 📐 The Kutta-Joukowski theorem is used by professionals to calculate the lift of a two-dimensional airfoil and the Lanchester-Prandtl equation for three-dimensional wings.
- ✈️ The shape of the leading edge of a wing is crucial for efficient airflow and lift generation.
- 💨 The airflow over the top of a wing is faster than below, contributing to most of the lift.
- 🚫 A flat wing is inefficient for lift generation due to airflow separation at the leading edge.
- 🌬️ The Coanda effect is not the primary reason airflow stays attached to a wing; it's the pressure difference that matters.
- 🔝 Thin wings with sharp leading edges are ideal for supersonic flight but require flaps for efficient low-speed flight.
Q & A
What is Bernoulli's principle as explained in the script?
-Bernoulli's principle states that when the velocity of a fluid increases, its static pressure decreases, and the dynamic pressure increases, and vice versa, with the sum of static and dynamic pressures remaining constant according to the principle of conservation of energy.
What is the relationship between static pressure and dynamic pressure in the context of fluid dynamics?
-Static pressure is the pressure exerted by a fluid that is not moving, while dynamic pressure is the kinetic energy in a fluid when it is in motion. According to Bernoulli's principle, an increase in dynamic pressure leads to a decrease in static pressure and vice versa, maintaining a constant sum of both pressures.
How does the angle of attack affect the lift generated by a wing?
-The angle of attack is crucial for lift generation. As the angle of attack increases, the wing deflects the air downwards more effectively, creating more lift. However, beyond a certain point, the airflow over the wing can separate, leading to a loss of lift, known as a stall.
What is the equal transit time hypothesis mentioned in the script?
-The equal transit time hypothesis is the idea that air molecules or particles separated in front of a wing must meet at the same point behind the wing, leading to higher velocities and lower pressures on the upper surface due to the longer path, according to Bernoulli's principle.
Why is the pressure difference above and below a wing important for lift?
-The pressure difference above and below a wing is essential for lift because it is this difference that creates the net upward force on the wing. The wing's shape and angle of attack cause air to move faster over the top surface, reducing pressure, while the air below moves slower, maintaining higher pressure.
How does Newton's third law of motion relate to the generation of lift?
-Newton's third law of motion states that for every action, there is an equal and opposite reaction. In the context of lift, when a wing pushes air downwards, an equal and opposite force is generated, pushing the wing upwards, which is the lift.
What is the Venturi effect, and how does it relate to lift generation?
-The Venturi effect is the reduction in fluid pressure that occurs when a fluid flows through a constricted section of a pipe or channel. In the context of wings, the air is compressed over the leading edge, causing an acceleration and a decrease in static pressure, which contributes to lift.
Why is the shape of the leading edge of a wing important for lift generation?
-The shape of the leading edge is important because it influences how air flows around the wing. A curved leading edge allows air to follow a curved path, which, according to Newton's second law, results in acceleration and a consequent decrease in static pressure, contributing to lift.
How do flaps on an aircraft wing contribute to lift?
-Flaps on an aircraft wing increase the wing's surface area and camber, which enhances the airflow's adherence to the wing's surface, especially at lower speeds. This increase in curvature over the wing allows for greater lift generation, which is crucial for takeoff and landing.
What is the Coanda effect, and how is it related to lift?
-The Coanda effect is the tendency of a fluid jet to stay attached to a convex surface. While it can be used to increase lift in some applications, it is not the primary mechanism for lift generation on a wing. Lift is primarily due to the pressure difference above and below the wing, not just the attachment of the airflow to the wing's surface.
Outlines
🌀 Understanding Lift with Bernoulli's Principle
The paragraph explains the misconceptions around Bernoulli's principle in explaining lift. It clarifies that while Bernoulli's principle states that an increase in fluid velocity leads to a decrease in static pressure (and vice versa), it is not the sole explanation for lift. The speaker, Magnanudal, points out that many aviation books incorrectly use the equal transit time hypothesis to explain lift, suggesting that air molecules must travel faster over the curved upper surface of a wing to meet those below, creating lower pressure and thus lift. However, this overlooks the fact that air particles cannot 'know' the position of particles on the other side of the wing. The speaker emphasizes that it's the pressure difference above and below the wing, not just the speed of air over the top, that creates lift.
🔄 Newton's Laws and the Role of Angle of Attack
This section delves into how Newton's laws of motion complement Bernoulli's principle in explaining lift. The speaker agrees with viewers that angle of attack is crucial for lift generation, as it aligns with Newton's third law, which states that for every action, there is an equal and opposite reaction. The explanation continues with how the pressure difference is created by the wing's shape and angle, deflecting air downwards and creating an equal and opposite upward force (lift). The discussion also touches on how the air's behavior over and under the wing at different angles of attack affects lift, with maximum lift typically achieved around a 15-degree angle. The paragraph concludes by addressing the common misconceptions in aviation literature regarding the airflow and pressure distribution around a wing.
🌬️ The Coanda Effect and Ground Effect in Aerodynamics
The paragraph discusses the Coanda effect and how it is sometimes mistakenly used to explain lift. The Coanda effect refers to a fluid jet's tendency to stay attached to a convex surface, which is different from the airflow around a wing. The speaker clarifies that while the Coanda effect can increase lift, it is not the primary reason for lift generation. Instead, it is the pressure difference above and below the wing that is crucial. The paragraph also explores other methods used in aircraft to enhance lift, such as blowing air over flaps, and the ground effect utilized by some aircraft with propellers or additional engines to increase lift during takeoff and landing.
✈️ The Importance of Wing Design in Aerodynamics
This section highlights the importance of wing design in creating lift. The speaker explains that while a flat wing or surface can experience some upward force when moved through the air, this is not the same as how an airplane wing works. The discussion points out that a flat wing is inefficient because the airflow tends to separate from the wing's surface, creating a separation bubble that reduces lift and can lead to an early stall. The paragraph contrasts this with the design of efficient wings that use curvature to accelerate air over the top surface, creating lower pressure and thus lift. The speaker also addresses the idea that a wing's underside is more important for lift than the top, concluding that it is the pressure difference between the top and bottom that creates lift. The paragraph ends by emphasizing the importance of airflow over a correctly designed airfoil for efficient lift generation.
Mindmap
Keywords
💡Bernoulli's Principle
💡Static Pressure
💡Dynamic Pressure
💡Equal Transit Time Hypothesis
💡Angle of Attack
💡Newton's Third Law of Motion
💡Lift
💡Camber
💡Ground Effect
💡Stagnation Point
💡Venturi Effect
Highlights
Bernoulli's principle is often incorrectly used to explain wing lift production.
Bernoulli's principle states that an increase in fluid velocity leads to a decrease in static pressure and vice versa.
Static and dynamic pressure sum to a constant value according to the principle of conservation of energy.
The equal transit time hypothesis is debunked as a standalone explanation for lift.
Lift is created by the pressure difference above and below the wing, not solely by the wing's shape.
Angle of attack is crucial for lift generation, aligning with Newton's third law of motion.
Newton's laws of motion are compatible with Bernoulli's principle in explaining lift.
Kutta-Joukowski theorem is used by professionals to calculate lift based on circulation around an airfoil.
Lift is explained through both energy conservation (Bernoulli) and momentum conservation (Newton).
The Venturi effect and Bernoulli's principle are used to explain the acceleration of air over the wing's leading edge.
The pressure distribution around a wing changes with varying angles of attack.
The shape of the leading edge is critical for efficient airflow and lift generation.
The Coanda effect is not the primary reason for lift but can be used to enhance it in certain applications.
Supersonic aircraft wings are designed with thin profiles and sharp leading edges for low drag.
Early aviation pioneers were inspired by bird wings, but the Wright brothers' design was more efficient due to the curved leading edge.
A flat wing is inefficient for lift production due to airflow separation at the leading edge.
Flat surfaces can produce lift when tilted at an angle to an airflow, but this is not how wings work.
Aerodynamic lift is maximized when air flows around an airfoil, creating a pressure difference.
Flat plates are used as air brakes and spoilers to reduce lift during landing, not for lift generation.
Mario Stokes equations are used to model airflow around wings, integrating conservation of mass, momentum, and energy.
Transcripts
most of you have heard about the flat if
Society
but do we also have a flat Wing Society
coming up
hello elevators how are you doing my
name is magnanudal I'm an island captain
and instructor
a few weeks ago I posted a video
explaining how Bernoulli's principle or
equation very often is incorrectly used
to explain how a wing producers lived
there's a link to that video below here
Bernoulli's principle is as following
when you increase the velocity of a
fluid the static pressure will decrease
and the dynamic pressure will increase
and vice versa
and the sum of the static pressure and
the dynamic pressure is constant
this follows the principle of
conservation of energy
static pressure is the pressure when the
fluid is not moving
Dynamic pressure is the kinetic energy
in a fluid when it's in motion
and if you follow me to the end of this
video I will reveal the truth about flat
wings
but first let's recap the essence on my
previous video
many Aviation books and manuals are
telling us that two air molecules or
particles when separated in front of a
wing will meet at the same place behind
the wing
and since the upper part of the wing is
more curved than the other side the
particle must travel a longer distance
therefore it must move at a higher
velocity
according to Bernoulli's equation The
increased velocity causes the air
pressure to decrease
this is called the equal Transit time
hypothesis
and while it's correct at the static air
pressure will drop and the velocity
increases
it's impossible for the air particles
overdoing to know the position of the
particles under the wing
in a winter now we can see that the air
flowing over the wing reached the end of
the wing much earlier than the
airflowing under the wing
this is what I addressed in my previous
video
I also explained that it is the pressure
difference above and below the wig that
creates lift
and this resulted in many reactions
many viewers have rightfully commented
that angle of attack is important for
lift and that lift is created when a
wing pushes the air down in accordance
with Newton's very low emotion for every
action there is an equal and opposite
reaction
I totally agree
Newtons for law of motion is the easiest
way to explain lift
I want to stress out that there is no
contradiction between Bernoulli and
Newton here it's not Bernoulli left or
newton-left it's Bernoulli and Newton
both explain the same lift Bernoulli
explains lift through conservation of
energy
Newton explains lift through
conservational momentum
in fact Bernoulli's equation can be
calculated from Newton's secular motion
professionals are using the code
yokosuki theorem to calculate the lift
of a two-dimensional airfoil
the launches the problem Theory to
predict lift distribution of a
three-dimensional wing and the novice
talks equations for conservational Mass
momentum and energy
and here is a fun fact the Navy stocks
equations are developed from the Euler
equations
leonhard Euler was a student of Daniel
Bernoulli's father Johan
before we continue let's look at
Newton's treelor's emotion the first law
an object at rest remains at rest and an
object in motion remains in motion at
constant speed in a straight line and
less acted on by an unbalanced force
think about an air particle in a
streamline
Newton's Second Law the acceleration of
an object depends on the muscle the
object and the amount of force applied
for example if the static air pressure
head of a particle is less than a static
pressure behind
the particle will accelerate towards the
area with the lower pressure and vice
versa
the arrival of a wing will force the air
particles to change direction there will
be one airflow over the wing and one
airflow below the wing
the two floors are separated at the
stagnation point
when the ring meets the area the low
angle of attack the stagnation point is
at the front of the Leading Edge
when Anglo attack is high the stagnation
point is further behind and below the
Leading Edge
now the air flowing around the Leading
Edge and over the top of the wing
follows a curved path right
according to Newton's second law when
the air particle changes Direction it's
because of an acceleration do you agree
good
therefore there must be a force acting
on a particle and this is the
centripetal force
and it causes the particle to accelerate
and follow a curved path
therefore there must be a pressure
gradient across the Streamline where the
static air pressure is decreasing
towards the center of the curvature
think about the tornado
and when a static air pressure is
reduced the velocity of the air steam
mast in accordance with Bernoulli's
equation be higher
since the airflow on the upper surface
of the wing has a low pressure it is
pushed towards the Wings upper Surface
by the atmospheric pressure from a ball
it's not the condo effect that keeps the
airflow stuck to the wing I will explain
the counter effect later on
when the air steam leaves the out part
of the wing it will continue in the same
direction creating a dawn wash
and that brings us the Newton's fur law
for every action there is an equal and
opposite reaction
and it allows us to explain Nifty in
less than 10 seconds
all you have to say is a ring creates
lift because it's deflecting air
downwards
and in accordance with Newton's Fair law
of motion this creates an equal and
opposite Force pushing the wing up
it's that simple
it's a little more complicated to
explain why the wing deflects the air
downwards
instead of using Newton's Second Law we
can explain the acceleration or the
airflow around the Leading Edge by
observing the distance between the
streamlines
over the Leading Edge there's a Venturi
effect compressing the airstreams
this causes an acceleration which in
accordance with Bernoulli causes static
pressure to decrease
under the wing the streamlines are
further away which means the Airstream
slows down that means the static
pressure increases Bernoulli again
this figure shows the pressure
distribution above and below a wing of
different and low attack
as the angle of attack increases the
upper part of the wing contributes more
and more to the lift
maximum lift is achieved at around 15
degrees and low attack
at higher angle of attack the airflow of
the main separates and there's a certain
loss of lift this is tall
still the underside of the wing produces
some lift but it's not sufficient to
maintain level flight
and we are getting closer to the
flat-wing society
and talking about pressure distribution
this figure shows that the static
pressure is at the highest at the
stagnation point and at the lowest
pressure is over the Leading Edge of the
wing
when you see the rapid change of air
pressure around the Leading Edge it's
easy to understand why the shape of the
Leading Edge is so important
they don't wash happens because air is
heavy and therefore has a momentum
at sea level the air pressure is
slightly more than 10 tons per square
meter
when the air is set in motion we are
talking about serious forces
just see what a hurricane can do or a
tornado
lesser known is that there is an
airbrush ahead of the wing this is
caused by the area with a high air
pressure under the wing sadly many
illustrations in aviation literature are
plain wrong
this is wrong
and this
and this
and this
this is pretty close
finally this is correct
does the Airstream follow the curvature
of the wing because of the colander
effect yes and no yes because the
corunda effect can be used to increase
lift no because when you're talking
about lift we are talking about the
pressure difference above and below the
wing
the corona effect works only on one side
so what is the Quant effect then per
definition the quantum effect is the
tendency of a fluid jet to stay attached
to a convex surface in other words we
are not talking about an air flowing
around the wing but a jet that emerges
from our orifice
here are some examples
you can blow air over the surface of a
paper
when you hold a paper like this the
paper is curved and we lift up
but when the paper is hanging straight
down the paper will not move merge when
you blow along one of the sides
the reason is that the static air
pressure in your lungs is the same as
the atmospheric static pressure
therefore the pressure is the same on
both sides of the paper and this cannot
explain Bernoulli
still it's very tempting to use this
demonstration to explain lift right
this balloon is hanging in the air
because the fan is blowing air upwards
the balloon sticks to the Airstream this
prevents the balloon from falling down
and gravity prevents the balloon from
being blown away
only when the airflow is obstructed the
Ballon Lee fell down
on the Lockheed f104 Starfighter is air
from the engine compressor directed over
the flaps to increase lift
hence reducing the speed attack of an
Landing
other aircraft using blonde flaps I make
21 and black panther can air
propellers blowing air or a ring also
utilizes the ground effect to enhance
lift
this is the shimaiva us1a from Japan in
addition to having four propellers
flowing here all the way the aircraft
has a fifth engine installed in the wing
box this engine blocks compressed air
over the flaps and flight control
surfaces allowing the airplane to take
off and land at Short distances
here is a comment from a viewer
supersonic airplanes are symmetrical
profilings so no Bernoulli effect also
some aerobatic airplanes have
symmetrical profilings so again no
Bernoulli effect
OK let me comment on this when arraying
with a symmetrical profile moves through
the air with zero and no attack the
streamlines above and under the wing are
identical and there is zero lift but
since the streamlines are compressed
over and under the wing the pressure
will decrease and the velocity will
increase in accordance with Bernoulli's
equation
so how can an airplane with a
symmetrical wing profile create lift
them
by flying with a positive angle of
attack
this causes the stagnation point to move
down and under the Leading Edge and the
air steam over the wing will accelerate
more than the air under the wing just
like a wing with an asymmetric profile
all you need is low and a higher angle
of attack
and when you fly upside down in
asymmetrical profile you do the same you
increase the angular attack
airplanes are symmetrical Wing profiles
can also fly upside down you just need a
higher angle of attack
and of course the aircraft must be
designed to fly with a negative G for a
prolonged time
and now what about supersonic airplanes
supersonic airplanes have thin wings
with a sharp Leading Edge
the wind profile doesn't have to be
symmetrical however
search links are perfect for supersonic
flights because they create very low
drag
but they are not good for slow flight
the f104 Starfighter is an extreme
example
the wings are very small and the Leading
Edge is sharp as a knife not razor sharp
but sharper than a better knife for sure
in order to fly slow enough to take off
online the wings are equipped the
Leading Edge flaps called maneuvering
flaps and trailing Edge flaps this
increases the curvature over the wing
and therefore increases lift
on this picture the aircraft is flying
with a maneuvering flaps extended
a modern fighter aircraft like the F-16
the operation of the maneuvering flaps
is automatic and flying at a lower angle
of attack the flaps is attracted
an angler attack increases the flux
extends
early Aviation Pioneers were inspired by
the birds and copied the shape of the
Wings
the Wright brothers took it a step
further and designed the first internet
it was important for them to develop an
efficient Wing because the first engine
produced only 12 horsepower
this is a replica Sonia type G
the wing profile is typical for that era
without the curved Leading Edge the wing
would have been almost flat what makes
the wing efficient at least for its time
is the curd shape of the Leading Edge
this allows for the air to accelerate
and create lift
the sale of a sailboat works in the same
way
when the wind fills the sail it has a
curvature a camber
that means the airflow is following a
curved path and according to Newton's
Second Law we have an acceleration which
reduces the static air pressure of the
curvature Bernoulli and on the other
side the static air pressure along the
cell is increased
and the pressure difference is lift as
you can see a very thin Wing or a cell
can produce lift
the magic happens because of the
curvature
here is another comment the airfall
shape simply Smooths the airflow over
the top of the wing
while this does create a comparatively
low pressure over the top it's the
higher pressure on the bottom of the
wing that pushes the wig up
yes the underside of the wing produces
lift but the oversight is more important
you cannot isolate one part of the wing
from the other its depression difference
between the top and bottom of the wing
that creates lift and since the air is
Flowing faster over the wing than below
the force is stronger contributing to
most of the tone wash
no pilot will take off an upper surface
of the wing is contaminated with snow or
ice it must be removed first
and I have another argument
if the underside of the wing is so
important for Lift why do many military
aircraft and lots of stuff hanging under
the wings but not over them
yes it's more easy to hang in drop tanks
and Ordnance under the wings
but the real reason it's placed there is
aerodynamic lift
according to Leslie G fries the chief
designer at Bristol Aircraft Company
during the second World War even a
kitchen table will fly if you give it a
big enough engine
the fastest kitchen table he designed
was the bullfighter attack aircraft
and the comment section reflects similar
ideas about the flat wings
you can tilt a flat board out of your
car window and it will violently be
pushed upward does not require an
intricate theory on why this happens
yes the flat board is pushed upward but
is that how a wind works
yes but only when it's told
an airflow can be defined as a body
witch when set in a suitable angle to a
given airflow produces much more lift
and drag
a flat Wing doesn't do that this is a
simulation of a flat wing
the Streamline just about the stagnation
Point has to negotiate the sharp corner
of the Leading Edge which causes it to
separate from the surface
this creates a separation bubble behind
the Leading Edge
not only does the bubble reduce the lift
of the airfoil but as the angular attack
increases the separation bubble spreads
Downstream and an early stall occurs
we have to conclude that a flat Wing is
a terrible airfoil
some people are arguing that the model
airplane with a flat Wing will fly sure
but only because model airplanes are
small overpowered with their engine and
they made of very light materials like
Pulsa and foam
a wing like this is nothing more than a
kitchen table
if you scale up a flat wing and install
it on a real airplane it will not be
able to fly I promise you
but the flat plate do have a purpose air
brakes and spoilers are used to create
drag and remove lift from the wing of
the landing and a flat plate is perfect
for this
but when you need lift you make sure the
air is Flowing around the airfoil
creating lift with minimum resistance
in the beginning of the video I
mentioned in Mario Stokes equations for
conservational Mass momentum and energy
the equations are used to model the
airflow around the wing and as I said
Bernoulli explains Lyft through the
conservation of energy and Newton
expense lived through the conservational
momentum
the conclusion is there is no
competition between Newton and Bernoulli
we need them both
and then use correctly they explain the
same lift
therefore next time somebody tell you
about the equal Transit time you know
not to answer right
okay that's all for this time thank you
for watching have a wonderful day and
happy learning
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