The Basics of Aerodynamics

The Basics of Aerodynamics


Hello and welcome to this video tutorial
on the basics of
Aerodynamics.In tutorial, we will discuss
what makes
an airplane fly, and we’ll learn some
important terms and concepts
along the way.But first
let’s learn about the Bernoulli’s
principal. Daniel Bernoulli,
who is a Swiss mathematician, expanded
on Newton’s ideas and discovered the motion of
fluids.
He described in his 1738 publication,
“Hydrodynamica,” the basic principles
of airflow pressure differential. The
principle
simply states that as the velocity of a fluid, such as air,
increases its pressure decreases.
let’s take a look at the diagram
to understand this concept a little better.
As the air
or fluids in general travel through the
tighter passage of the tube,
the velocity increases since fluids
travel at a faster speed to reach
the end of the curve.What’s interesting,
when he measured the pressure, Bernoulli
discovered that every time the
velocity increased
or decreased the pressure would have the
opposite effect
In this slide
will define a very important force that
will help us
understand the future concepts.That
force is the “Relative
Wind.”The relative Wind is simply the
airflow that is parallel
and opposite to the flight path the airplane. An airfoil
is any surface, such as a wing, that
provides
aerodynamic force when it interacts with a
moving stream
of air.When given a flight path
and an opposite relative wind
it’ s important to remember
that the airflow over the surface of the wing
will have a higher velocity than the airflow
under the wing. it’s also important to note
that the circulation on the airstream
about the
airflow is an important factor in the
generation
of lift. The Camber
it is
the characteristic curve of the airfoil’s upper
and lower surfaces. The Chord line
is an imaginary straight-line
drawn through the airfoil and the
direction of
the relative wind. The chord line
is a very important determinant of
what’s called
the “Angle of Attack.”The angle of attack
is simply the angle between the Chord
line
and airflow at the direction
of the relative wind. In this slide
we will learn that as the angle of attack increases
the lift also increases.
Please note that the lift acts perpendicular
to the relative wind regardless of the
angle
of attack. According to Bernoulli’s Theorem,
the increased speed of the air on top of an airfoil
produces a pressure drop. This lowered
pressure is one component of a total
lift. However,
when the angle of attack is increased
beyond the maximum allowed the lift
is decreased; this causes
what’s called a “Stall.” As we mentioned earlier,
a stall is the result of
a critical angle attack. It is also caused
by the disruption on the airflow
from the upper surface of the wing
or airfoil. The airflow then separates
at what’s called the “Trailing Edge.”
The airflow progresses forward until the wing
is fully stalled
Therefore, a stall is a rapid decrease
of lift caused by separation of
airflow. In this slide,
we will learn about the four very important forces
of flight. The challenge
to understand what makes an airplane fly
starts with learning the four forces of flight.
During a flight, the four forces
acting on the airplane are : Lift,
Weight, Thrust, and Drag
Lift as we discussed earlier is created
by the effect of airflow over and under
the wing. The weight of the airplane
that is the force caused by gravity.
The Thrust: That is the force that propels
the airplane. And finally,
the drag, which is the force that limits
the speed of the aircraft.
By now we have established that lift is the key
aerodynamic force. Please remember
that when
weight and lift are equal
an airplane is said to be in a state of
equilibrium, and that means
Lift=Weight also,
when vertical and horizontal forces are applied
as shown on the left of the slide, the resulting force
acts in a diagonal direction
therefore the resultant of two
opposing forces which are equal in
magnitude
is zero. I hope you enjoyed the tutorial
and thank you for watching 🙂

24 Replies to “The Basics of Aerodynamics”

  1. I am only 14 years old and i plan to do aeronautical engineering to be a pilot. Luckily, I have read many books on this subject and I get that mainly the lift is important as it increases the pressure underneath the wing causing it to lift off into the air. 🙂

  2. This video is wrong in many respects. I am not a student pilot but I am a career pilot and engineer. To start with the explanation of Bernoulli’s theorem is wrong. The fluid does not speed up “to reach the end of the curve”. This explains nothing. The fluid does not make a decision to go faster to reach the end of a curve. The velocity increases due to the physical constraint of the conservation laws. In order for momentum to be conserved the velocity has to increase in order maintain the mass flow rate. You can also explain the Bernoulli effect in terms of conservation of pressure energy. Because the fluid velocity increased the kinetic energy of the fluid increased. The increased kinetic energy of the molecules can be seen as a redirection of the pressure energy hence the fluid has increased dynamic pressure at the expense of reduced static pressure. If you want to reduce the explanation to simple statements such as the “fluid speeds up to reach the end of the curve’ you have not simplified the explanation, you have simply made it wrong.
    Next we have a very poor description of the stall. A wing stalls at its critical angle of attack yes. But the stall is not “the result of a critical angle of attack”. The critical angle of attack is defined as the point at which the wing stalls, so if anything the critical angle of attack results from the inherent individual stall property of any given airfoil. However once the critical angle of attack is known you can say the wing will always stall when it reaches the critical angle of attack. Also you say that in a stall the airflow “separates at the trailing edge”. This is completely false. In a stall the airflow separates well before reaching the trailing edge. That is one of the key points to know. The lift depends upon the streamlines staying attached for as long as possible as the angle of attack is increased. The early separation of the streamlines and resultant increased turbulent wake are the two things that give the loss of lift and increased drag associated with the stall. If you could keep the upper flow attached all the way to the trailing edge, the wing would not be stalled.
    Also, you say that an aircraft is in a state of equilibrium if the lift equals the weight. However, the aircraft can only be in a state of equilibrium if lift equals weight AND thrust equals drag. Otherwise the aircraft will be accelerating or decelerating and therefore the lift will be changing.
    Finally you show two vectors and a resultant by way of explaining “the resultant of two opposing forces which are equal in magnitude is zero”. And yet the two vectors in the diagram are not opposing each other, hence they have a non-zero resultant. The correct explanation would be that the aircraft would be in equilibrium when the resultant of the thrust and weight vectors is equal and opposite to the resultant of the lift and drag vectors.

  3. Hi, I am a practicing Aerospace/Aeronautical Engineer.
    With due respect to you, I found that your presentation can be better if you pay more attention to basic Aerodynamic facts.
    Firstly, the concept of fluids traveling faster does mean nothing to science; its a result of energy balance as per Bernoulli.
    Secondly, Relative Wind is not a force, it is in fact a cause of various Aerodynamic forces on the Airfoil. Relative wind can be best explained by the Relative wind velocity.
    Airfoil is not "a surface such as a wing"; it is at best a cross -section; remember we can have both Two-dimensional and also 3 dimensional airfoils.
    The airflow velocity on the upper surface depends on various factors like up wash, camber,angle of attack etc.
    When you talk of the circulation you must describe in detail what you mean.
    The flow leaving at the down wash is one of the main causes of lift.
    Your definition of Camber is also not correct. Camber is the asymmetry between the upper and lower surfaces.
    Also, chord line is basically the shortest distance (straight line)between the Leading and trailing edges of the Airfoil.
    The stall is not a result of the Critical Angle of attack; in fact we get the max. coefficient of lift corresponding to the Critical angle of attack, beyond which due to progressive separation of air on the upper surface that moves towards the leading edge,along with increased surface drag, we get total loss of lift creating the Stalling condition.In fact if the flow separation occurred just at the trailing edge as you explain, it would have been a very desirable effect!
    Lastly, as XPLAIN has correctly mentioned, a complete equilibrium can be possible only when the Lift = Weight and the Thrust=Drag condition.
    Good Luck!

  4. Thanks your videos and free engineering aerospace I am understand mechanical i need exam both avionics and mechanic this good preparation

  5. Dude, this video sucks! Your drawings are whack, you use terms incorrectly and basically, you are just regurgitating the same old stuff!!! Most of which has already been shown to be incorrect or misleading at best. Sorry homie, it's back to the drawing board for you…

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