AERODYNAMICS
The principle of flight is made up of four
fundamental forces: lift, weight, drag,
and thrust. These forces work together
in a delicate balance to determine an
aircraft’s trajectory, with lift and
weight opposing each other and thrust
and drag doing the same.
GEORGE CAYLEY
Cayley founded the science of aerodynamics
and is generally credited with the invention of
the airplane. He has also been called the world's
first aeronautical engineer.
GEORGE CAYLEY
Born in 1773, Sir George Cayley essentially created
the science of flight. Using scientific methods and
keeping careful and detailed notes, Cayley became
the first to identify the basic problems of heavierthan-air flight, the first to carry out basic
aerodynamic research, and the first to discover that
curved surfaces produce more lift than flat ones
AERODYNAMICS
What Are the Four Forces of Flight?
The four forces of flight are lift, weight, thrust
and drag. These forces make an object move up and
down, and faster or slower. The amount of each
force compared to its opposing force determines
how an object moves through the air.
AERODYNAMICS
AERODYNAMICS
What Is Lift?
Lift is the push that lets something move up. It is the force that is the
opposite of weight. Everything that flies must have lift. For an aircraft
to move upward, it must have more lift than weight. A hot air balloon
has lift because the hot air inside is lighter than the air around it. Hot
air rises and carries the balloon with it. A helicopter’s lift comes from
the rotor blades. Their motion through the air moves the helicopter
upward. Lift for an airplane comes from its wings.
LIFT
LIFT is the man made force which
counteracts gravity. Special
shapes, or airfoils produce the
force called LIFT and allow an
airplane to rise in the air.
AERODYNAMICS
How Do an Airplane’s Wings Provide Lift?
The shape of an airplane’s wings is what makes it possible for
the airplane to fly. Airplanes’ wings are curved on top and
flatter on the bottom. That shape makes air flow over the top
faster than under the bottom. As a result, less air pressure is
on top of the wing. This lower pressure makes the wing, and the
airplane it’s attached to, move up. Using curves to affect air
pressure is a trick used on many aircraft. Helicopter rotor
blades use this curved shape. Lift for kites also comes from a
curved shape. Even sailboats use this curved shape. A boat’s sail
is like a wing. That’s what makes the sailboat move.
AERODYNAMICS
Subsonic speeds—slower than
the speed of
sound.
Supersonic speeds—faster than
the speed
of sound.
WHAT IS THRUST?
Thrust is the force that is the opposite of drag. It is
the push that moves something forward. For an
aircraft to keep moving forward, it must have more
thrust than drag. A small airplane might get its thrust
from a propeller. A larger airplane might get its thrust
from jet engines. A glider does not have thrust. It can
only fly until the drag causes it to slow down and land.
THRUST
Thrust is the man-made force, which counteracts drag.
Thrust is produced by an engine or power plant, which pulls
the airplane forward through the air.
DRAG
WHAT IS DRAG?
Drag is a force that pulls back on something trying to move.
Drag provides resistance, making it hard to move. For
example, it is more difficult to walk or run through water
than through air. Water causes more drag than air. The
shape of an object also affects the amount of drag. Round
surfaces usually have less drag than flat ones. Narrow
surfaces usually have less drag than wide ones. The more air
that hits a surface, the more the drag the air produces.
Drag is the force exerted on a moving body, which
tends to reduce its forward motion.
WHAT IS WEIGHT?
WEIGHT
Gravity is a force that pulls everything down to
Earth. Weight is the amount of gravity multiplied by
the mass of an object. Weight is also the downward
force that an aircraft must overcome to fly. A kite
has less mass and therefore less weight to
overcome than a jumbo jet, but they both need the
same thing in order to fly — lift.
Gravity is the force of attraction by
which all objects tend to fall towards
the center of gravity.
In straight and level flight, at a constant speed, LIFT exactly equals
GRAVITY and THRUST exactly equals DRAG.
If we alter or change any of the man-made forces, a change will take
place in the movement of the airplane.
If LIFT is increased to be greater than GRAVITY, the airplane will climb and
theoretically keep on climbing.
If the LIFT is reduced, the airplane will descend or go down and also keep
on going down.
When THRUST is increased, the airplane will start
to go faster, but since DRAG will also increase,
the airplane will only increase it’s speed until
THRUST will again equal DRAG.
The reverse will take place when THRUST is
decreased. The airplane will slow down until
THRUST again equals DRAG .
WHO IS DANIEL BERNOULLI?
Daniel Bernoulli was an 18th-century Swiss mathematician and
physicist known for his contributions to fluid dynamics, studying
how fluids move and behave. He is particularly famous for his
principle, which explains how a fluid’s pressure and velocity are
related.
DANIEL
BERNOULLI
This principle is vital for understanding how air moves around
objects, including airplane wings. It is crucial for understanding
the principles of flight.
HOW LIFT IS PRODUCED
Bernoulli’s Theorem
At least 50% of the lift created by an airfoil is due to Bernoulli’s
theorem of physics, which states “as the velocity of a fluid(air)
increases, its internal pressure decreases”.
Air, as we know, is a fluid. Air will try to flow from high to low. Since
the air travels faster over the airfoil, a low pressure area is created.
“as the velocity of a fluid(air) increases, its internal pressure decreases”.
AIRFOIL
An airfoil (American English) or aerofoil (British English) is a
streamlined body designed to produce lift when moving through the
air. Airfoils are used in the design of aircraft wings, helicopter
rotor blades, propellers, and other applications where lift is
required.
HOW LIFT IS PRODUCED
Any object moving through the air will not
produce lift. The object must be of a special
shape.
Only then will it have the capability of producing
lift. This special shape is called an “airfoil”.
Leading Edge
camber
Trailing Edge
chord
HOW LIFT IS PRODUCED
■ Leading Edge - Most airfoils have a rounded leading edge which the
oncoming air can move smoothly around.
■ Trailing Edge - Most airfoils have a very pointed, sharp trailing edge,
behind which the two air streams (above and below the wing) can rejoin
smoothly.
■ Chord - The imaginary line that connects from the leading edge of the wing
to the trailing edge, and is usually discussed in terms of chord length.
Generally, a longer chord length produces more lift.
■ Camber - The curvature of the airfoil. Generally, the upper surface of an
airfoil is more curved than the lower surface, however this is not required.
Airfoils with more camber generally stall at higher angles of attack.
HOW LIFT IS PRODUCED
The curved surface of the airfoil is called “camber”. A
line, an imaginary straight line from the leading edge
to the trailing edge of the airfoil, is called the “chord”.
As you can see, the upper curve or camber of the
airfoil is greater than the bottom, which is almost a
straight line.
upper camber
upper camber
lower camber
lower camber
HOW LIFT IS PRODUCED
Bernoulli's Principle: This principle states that as the
speed of a fluid (like air) increases, its pressure
decreases
Airfoil: Wings are designed with a specific cross-sectional
shape called an airfoil.
Now, let us imagine a piece or block of air
striking the leading edge of the airfoil.
The piece of air will split in half, one half
will go over the top of the airfoil and the
other half will go under it.
Since that piece of air must come exactly
together again when the two halves meet at
the back of the airfoil.
The pressure on the bottom of the airfoil will be higher. As
a result, the air will push on the bottom of the airfoil
trying to flow to the low pressure area on top.
You will see that the top piece of air must travel
farther, therefore, faster, than the piece of air, which
travels under the airfoil (above).
The pressure on the bottom of the airfoil
will be higher. As a result, the air will push
on the bottom of the airfoil trying to flow
to the low pressure area on top.
HOW LIFT IS PRODUCED
How it works:
When air flows over an airfoil, the curved upper surface
forces the air to travel a longer distance compared to the air
flowing under the flatter lower surface. To meet at the
trailing edge of the wing, the air over the top must travel
faster. According to Bernoulli's principle, this faster-moving
air has lower pressure than the slower-moving air below. This
pressure difference creates an upward force, known as lift.
HOW LIFT IS PRODUCED
HOW LIFT IS PRODUCED
LIFT
LOW PRESSURE
HIGH PRESSURE
HOW LIFT IS PRODUCED
LIFT
LOW PRESSURE
HIGH PRESSURE
FACTORS AFFECTING LIFT
Shape of the airfoil
Speed of the relative wind
Angle of attack
ANGLE OF ATTACK
Relative wind – air
which passes the
airfoil.
FACTORS AFFECTING LIFT
ANGLE OF ATTACK:
This is the angle between the wing's chord
line (an imaginary line from the leading
edge to the trailing edge) and the
oncoming airflow.
FACTORS AFFECTING LIFT
ANGLE OF ATTACK:
This is the angle between the wing's chord
line (an imaginary line from the leading
edge to the trailing edge) and the
oncoming airflow.
STALLS
A stall is what happens when an airfoil can
not make enough lift to keep the aircraft in
level flight. Stalling is risky and can be
dangerous during low-level flying.
An airplane stall is a dangerous situation
that occurs when the wing's angle of
attack exceeds a critical point, causing a
reduction in lift and potentially leading
to a loss of control. Here's a breakdown
of what happens during a stall:
CAUSE OF STALL
Critical Angle of Attack: Every wing has a critical angle of
attack, typically around 15 degrees, though this can vary.
Beyond this angle, the airflow over the wing's upper
surface separates, becoming turbulent and causing a
dramatic decrease in lift
In fluid dynamics, a stall is a reduction in the lift
coefficient generated by a foil as angle of attack
increases. This occurs when the critical angle of
attack of the foil is exceeded. The critical angle of
attack is typically about 15 degrees, but it may vary
significantly depending on the design of the wing.
CAUSE OF STALL
The amount of lift produced by an airfoil is increased
when we increase the angle of attack.
If we increase the angle of attack more than 12-20
degrees, the airflow over the wing will break away and
“burble”, then the wind will fill in the low pressure area
and lift is destroyed. This condition is called a “stall”.
The stall is a condition of excessive
angle of attack. When the wings of an
aircraft stall, the nose of the airplane
will drop and a loss of altitude or
height results until the airplane is
brought out of the stall.
BURBLE
Smooth Airflow: Under normal flight conditions, air
flows smoothly over the curved upper surface of a
wing (airfoil). This smooth airflow is crucial for
generating lift.
Increasing Angle of Attack:As the wing's angle of
attack (the angle between the wing and the oncoming
wind) increases, the airflow over the top surface
starts to become disrupted.
Burbling: At a certain point (the critical angle of attack),
the airflow can no longer adhere to the wing's curved
surface. It separates, becoming turbulent and chaotic. This
turbulent, separated airflow is what we call a "burble."
RECOVERY:
To recover from a stall, the pilot must
decrease the angle of attack to re-establish
smooth airflow and regain lift.
STALL WARNER
An aircraft Stall Warning System is that
system which provides the pilot with advance
warning of an impending stall.
STALLS
This type of sensor uses a small opening on
the wing's leading edge. As the angle of
attack increases, a low-pressure area forms,
drawing air through a tube to a reed in the
cockpit. The vibrating reed creates a sound,
alerting the pilot.
HE IS NOT KISSING THEIR AIRCRAFT FOR GOOD
LUCK, MERELY TESTING THE STALL WARN AS
PART OF PRE-FLIGHT CHECKS!
First, let’s talk about what is meant by “wing.” Yes, those big
rectangular things jutting out from a fuselage are wings of
course, but when talking about stalls, we are looking
specifically at the chord line of the wing. If you draw a side
profile of a wing and extend a line from the leading edge to the
trailing edge, you’ve just drawn the chord line. Why bother
with a chord line, why not just say “the wing”? Watch what
happens to the chord line of the wing as you add flaps, or
aileron inputs. The chord line changes as you manipulate
control surfaces!
The only thing that causes a stall is exceeding the critical angle of
attack. The airplane still produces lift, but it gets really inefficient.
The airplane does not fall out of the sky. You are still flying.
The only way to correct a stall is then to reduce the angle of attack.
Spoilers:
Primarily designed to reduce lift.
They do this by disrupting the airflow over the wing's upper surface.
Their main purpose is to slow the aircraft down.