Aircraft Lift Explained: Bernoulli vs. Newton's Equations | Fly with Magnar

Summary

In 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

00:00

🌀 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.

05:01

🔄 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.

10:03

🌬️ 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.

15:03

✈️ 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.

Keywords

💡Bernoulli's Principle

Bernoulli's Principle states that an increase in the speed of a fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy. In the context of the video, this principle is often incorrectly used to explain lift on airplane wings. The video clarifies that while Bernoulli's Principle is correct in stating that static air pressure drops and velocity increases, it's not the sole explanation for lift. The script uses this principle to discuss the relationship between air velocity and pressure on the wing's surface.

💡Static Pressure

Static pressure is the pressure exerted by a fluid which is not in motion. In the video, it is explained as the pressure when the fluid is at rest. The script mentions that static pressure plays a crucial role in the generation of lift, as the difference in static pressure above and below the wing creates lift. The video uses the concept to explain how airfoils work, with higher static pressure below the wing pushing it upwards.

💡Dynamic Pressure

Dynamic pressure is the pressure generated by a fluid in motion. The video script explains that dynamic pressure is the kinetic energy in a fluid when it's in motion. It is used to discuss how the faster-moving air over the top of the wing (higher dynamic pressure) contributes to the creation of lift, in accordance with Bernoulli's Principle.

💡Equal Transit Time Hypothesis

The Equal Transit Time Hypothesis suggests that air molecules traveling over and under a wing should meet at the same point at the wing's trailing edge if they started from the same point at the leading edge. The video refutes this hypothesis, stating that it's impossible for air particles to know the position of other particles on the opposite side of the wing, thus it cannot be used to explain lift.

💡Angle of Attack

Angle of attack is the angle between the oncoming airflow and a reference line aligned with the wing's or aircraft's longitudinal axis. The script highlights that the angle of attack is crucial for lift generation. It explains how the lift is created when a wing pushes air down, in accordance with Newton's Third Law of Motion, and how the angle of attack affects the pressure distribution over the wing.

💡Newton's Third Law of Motion

Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction. The video uses this law to explain how lift is generated. When a wing deflects air downwards, an equal and opposite force pushes the wing up, creating lift. This law is essential in understanding the direct cause-and-effect relationship in lift generation.

💡Lift

Lift is the force that opposes the weight of an aircraft and allows it to become airborne. The video script explains lift through both Bernoulli's Principle and Newton's Third Law, emphasizing that lift is the result of pressure differences and the wing's action on the air. Lift is a central concept in the video, as it is the primary force that enables flight.

💡Camber

Camber refers to the curvature of an airfoil. The video script uses the term to describe how the shape of a wing, specifically the curved leading edge, allows air to accelerate and create lift. Camber is an important aspect of wing design, as it contributes to the wing's efficiency in generating lift.

💡Ground Effect

Ground Effect is a phenomenon where the presence of a surface near the aircraft (like the ground) affects the airflow and increases lift. The video mentions ground effect in the context of aircraft using propellers or engines to blow air over the wings, enhancing lift for takeoff and landing. This effect is particularly relevant for aircraft with high lift devices like flaps.

💡Stagnation Point

The stagnation point is the point on an airfoil where the airflow is brought to rest due to the airfoil's shape. The video script explains that the location of the stagnation point changes with the angle of attack, affecting the pressure distribution and lift. It is a critical point in understanding how airflow interacts with the wing.

💡Venturi Effect

The Venturi Effect is the reduction in fluid pressure that occurs when a fluid flows through a constricted section of a pipe or channel. The video uses this concept to explain how air accelerates over the leading edge of a wing, causing a decrease in static pressure and an increase in dynamic pressure, which in turn contributes to lift.

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