Download the principles of flight

THE PRINCIPLES OF
FLIGHT
The Air Around You
The 6 properties of air:
• Air takes up space.
• Air has weight.
• Air can be compressed by applying
pressure or squeezing.
• Air can insulate.
• Air can expand and create pressure
when heated.
• Air can contract when cooled.
• Air is a mixture of
78% nitrogen,
21% oxygen and
1% a combination
of carbon dioxide,
helium, water
vapour and other
gases.
• When air is heated, the molecules speed
up and move farther apart. This heated air
takes up more space. As the air is cooled,
the molecules slow down and move closer
together, causing the air to take up less
space. Heated air, which has greater
volume than cooler air with the same
mass (the number of atoms that holds or
clings together in an object), will naturally
rise, since the pull of gravity workers
harder on the denser air.
Gravity
• Gravity is a force.
• For an object to fly, there must be enough lift (a
force that causes something to rise) to overcome
the force of gravity acting on the mass of an
object. In a hot-air balloon, unbalanced forces
work such that the force of lift must overcome the
force of gravity. The lighter the object, the less
lift is required to overcome the force of gravity.
Thus a very light object, such as a dandelion
seed, can use the wind to give it enough lift to be
carried away.
• Gravity is a force that
results from the
masses of objects being
attracted to each other.
Your mass is attracted
to Earth’s surface. It is
important to know that
the force of gravity
does not depend on air,
it depends only on
mass.
Daniel Bernoulli
The work of Swiss mathematician Daniel
Bernoulli was instrumental in the study of
flight. In 1738, he published his first
article explaining his discovery of how
moving fluids exert less pressure than still
fluids. This discovery was found to be true
for moving air as well. Today this
discovery is called Bernoulli’s Principle. It
means that the faster air moves over an
object, the lower the pressure.
Bernoulli’s Principle
• Bernoulli’s Principle states that moving
fluids (air is considered a fluid) creates
less pressure than non-moving fluids. TRY
THIS EXPERIEMENT: To show how to
generate lift, hold one end of a strip of
paper (5 by 20 cm) against your lower lip
so that the strip sags down over your chin.
Blow hard across the top of the paper.
• how was the lift created?
• When you blew air across the strip of
paper, you lowered the air pressure
by making the air above the strip
move faster than the air below the
strip. With lower pressure on top
compared to below, lift was created
and caused the paper to rise.
• Moving air pushes on objects.
• Moving air can move other objects.
• Moving air can cause changes in
pressure.
Aerodynamics
• Bernoulli’s Principle is used to explain
properties of aerodynamics (The study
of air in motion). This same principle
explains how airplanes work. As a jet
plane is thrust through the air by the hot
exhaust gases expelled from its engines
(or air being moved by propeller) the
shape of the wing forces the air traveling
over the top of the wing to move faster.
This lowers the air pressure and gives it
lift to the wing, allowing the plane to take
off from the ground and increase altitude
as it flies through the air.
Airfoil
The curved shape of the wing
of a bird or an airplane is
called an airfoil. It is
important to understand
how Bernoulli’s principle
relates to an airfoil.
1. As an airfoil moves
through the air, the air
hits the front of the
airfoil (leading edge) and
separates.
2. The air flowing over the
curved surface has a
greater distance to travel
than the air flowing over
the flat surface.
Airfoil
3.
4.
5.
For the two streams of air to
reach the back of the airfoil
(trailing edge) at the same
time, the air over the curved
surface must travel at a faster
speed.
This quickens movement of air
over the top of the airfoil. This
creates a low pressure area
above the airfoil and a high air
pressure area below the
airfoil.
The difference in pressure
causes the wing to lift. In
other words, air below the
wing pushes up more than air
above the wing pushes down.
This difference in pressure
results in an upward force
called lift. All winged aircraft,
including gliders and
helicopters, use airfoils to
create lift.
Airplanes and birds fly even though they are
heavier than air. As mentioned,
aerodynamics is the study of air which
examines the forces of lift, weight, thrust,
and drag. These forces affect every
surface that moves through the air. A
bird, for example, is aerodynamically
designed. It’s curved wings create lift,
and the streamlined shape allows it to
move through the air with little resistance.
Aerodynamics engineers try to design
airplanes whose shape will create
maximum speed and lift, while minimizing
the effects of drag.
The Four Forces of Flight
• The four forces of flight are: Lift,
Gravity (weight), Thrust and
Drag. All flying devices must use
thrust and lift to overcome the forces
of drag and gravity (weight). When
there is a balance of the four forces,
a stable flight can occur.
•
Gravity/Weight A real downer, caused by gravity, pulls everything toward the ground.
•
Lift An upbeat kind of force, caused by air moving over the wings, acts upward against weight.
•
Drag A backward force, caused by air resistance, acts in the opposite direction to motion.
•
Thrust A very forward force, caused by an engine, overcomes the force of drag.
• Thrust is the force that moves the
plane forward. Thrust comes from
the propellers or jet engine. And
when you have thrust or moving air
across a surface you get lift. This is
how an airplane can fly. The thrust
moves the plane forward and
generates lift to keep the plane in
the air.
• Drag slows down or prevents the motion
of an object in air or water. It is difficult to
run in water because the water slows you
down. You could say that the water is
creating a drag on your movement. Air
behaves in a similar way. Air creates drag
on a plane and slows it down. The force
has advantages and disadvantages.
Advantage: It helps the pilot to steer the
plane. Disadvantage: It needs more thrust
(energy) than drag to fly.
• Three terms describe the movements
of an airplane. Pitch is the up-anddown movement of the nose of a
plane. Roll is a motion where one
wing tip moves up while the other
wing tip moves down, causing the
body of the plane to roll. Yaw is the
side-to-side movement of the nose
of a plane. Pilots maneuver planes
through the air using combinations of
pitch, roll, and yaw.
The End