Basic Aeronautics
Know the principles of basic aeronautics.
1. Describe the theory of flight.
2. Describe airfoils and flight.
3. Describe the effects of relative wind.
4. Describe the effects of angle of attack.
5. Identify the four forces of flight.
Overview
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4.
5.
Theory of Flight
Airfoils and Flight
Relative Wind
Angle of Attack
The Four Forces of Flight
Theory of Flight
• Aerodynamics
• The science relating to the effects produced by
air or other gases.
• The term comes from the Greek words aero
meaning air and dynamics meaning power.
• Ancient Greeks described air as having the
qualities of moisture and heat. It was observed
to shift in response to heating and cooling.
Theory of Flight
• Aerodynamics
• A lifting force is required for heavier-than-air
flying. An object can be pushed upward by
applying muscle power, an explosion, a hoist,
or other means of force.
• It cannot remain aloft without decreasing the air
pressure from above and increasing lift pressure
from below.
• Increasing the speed of the object can increase the
flow of air.
• The flying object must be shaped to form an airfoil.
• Air flows faster over the curved surface of an airfoil.
Theory of Flight
• Aerodynamics
• Bernoulli principle
• “As the air velocity increases, the pressure
decreases; and as the velocity decreases, the
pressure increases.”
• A major part of the knowledge base needed in the
design and development of aircraft.
• Contributed to the work of G.B. Venturi, an Italian
scientist, who first noted the effects of constricted
channels on the flow of fluids. A round tube, such as
a nozzle or jet engine, designed to increase the speed
of flowing gases and liquids is called a venturi.
Theory of Flight
• Aerodynamics
• Aristotle
• The first useful studies of motion are attributed to
Aristotle. He believed there were two kinds of
motion: natural and violent.
• He concluded, and later stated as a natural law, that
the velocity or speed of an object depends entirely
on the force being applied to it and the resistance it
meets. This law was later proven to be inaccurate.
Theory of Flight
• Aerodynamics
• Galileo Galilei
• Observed that an object in horizontal motion would
continue to move at the same speed with no
additional force.
• This truth was accepted by Sir Isaac Newton and
became the first of three laws of motion stated by
Newton.
Theory of Flight
• Newton’s Laws of Motion
• First Law of Motion
• “A body at rest tends to remain at rest, and a body in
motion tends to stay in motion, unless an outside
force acts on the body.” It is sometimes referred to
as the Law of Inertia.
• One of the most common places people feel this law
is in a fast moving vehicle. If you were standing
inside a train and it suddenly stopped, you would
continue to move forward even though the train had
come to a stop.
Theory of Flight
• Newton’s Laws of Motion
• Second Law of Motion
• “The acceleration of an object as produced by a net
force, is directly proportional to the magnitude of
the net force in the same direction as the net force
and inversely proportional to the mass of the
object.”
• Hitting a golf ball is a common example of
Newton’s second law. The golf club is a force that
causes the ball to move (overcoming inertia), and
picks up speed (acceleration) and since the golf ball
is relatively light, it picks up speed rapidly.
Theory of Flight
• Newton’s Laws of Motion
• Third Law of Motion
• “Whenever one body exerts a force upon a second
body, the second exerts an equal and opposite force
upon the first body.” Simply stated, For every
action there is an equal and opposite reaction.”
Theory of Flight
• Newton’s Laws of Motion
• Third Law of Motion
• This law is exemplified by what happens if you step
off a boat onto the shore. As you move forward
toward the shore, the boat tends to move in the
opposite direction.
Theory of Flight
• Acceleration
• The rate of increase in the velocity of
something.
• Represents a change in velocity.
• Velocity
• The rate of motion in a given direction.
• The change of rate of motion in a given
direction per unit of time.
Theory of Flight
• Force
• The power or energy exerted against a
material body in a given direction.
• Force has both magnitude and direction.
• Mass
• The quantity of material (matter) contained
in a body, while weight (which is often
confused with mass) is really the amount of
gravity being exerted on a quantity of matter.
Theory of Flight
• The four forces in balance with one
another hold the plane in the air.
• The four forces are lift, weight, thrust,
and drag.
Airfoils and Flight
• Airfoil Design
• An airfoil is designed to produce lift. An
airfoil has a leading edge, a trailing edge, a
chord, and camber.
Relative Wind
• The movement of the aircraft through the
air creates the relative wind.
• The term relative wind means the wind
that is moving past the airfoil and the
direction of the wind is parallel to the
flight path and relative to the attitude of
position of the airfoil.
• The pilot controls the direction of the
relative wind.
Angle of Attack
• Formed by the cord of the airfoil and the
direction of the relative wind or between
the chord line and the flight path.
• Is not constant during a flight. It changes
as the pilot changes the attitude of the
aircraft.
• One of the factors that determines the
aircraft’s rate of speed through the air.
The Four Forces of Flight
• According to the Bernoulli Principle,
there is an increase in the velocity of air
as the airflow around an airfoil shape;
therefore, there is an increase of the
relative wind as it flows above and below
the surface of the airplane wing.
The Four Forces of Flight
• Lift can be increased in two ways
• Increasing the forward speed of the airplane.
• Increasing the angle of attack.
• The pilot can increase the forward speed
of the aircraft by applying more power.
The Four Forces of Flight
• Lift Variables
• The pilot must have some way to control the
amount of lift the airfoils generate.
• There are variables acting on the amount of
lift generated.
The Four Forces of Flight
• Angle of Attack
The Four Forces of Flight
• Angle of Attack
• The sum of all the tiny forces over the
surface of the wing is called the resultant.
The Four Forces of Flight
• Angle of Attack
• This resultant has magnitude, direction, and
location. The point of intersection of the
resultant with the chord of the wing is called
the center of pressure (C/P).
The Four Forces of Flight
• Angle of Attack
• The angle at which lift stops increasing and
begins to decrease is called the burble point.
The Four Forces of Flight
• Angle of Attack
• The point at which the amount of lift
generated is no longer sufficient to support
the aircraft in air is called the stalling point.
The Four Forces of Flight
• Velocity of Relative Wind
• The velocity of the airfoil through the air is
another important factor in determining the
amount of lift generated.
• If an airfoil is made to travel faster through
the air, greater pressure differences between
the lower and upper surfaces of the airfoil
result.
The Four Forces of Flight
• Lift Variables
• Velocity of Relative Wind
The Four Forces of Flight
• Air Density and Lift
• Lift varies directly with density. If flying at
18,000 feet where the density is about half
that at sea level, an aircraft will need to
travel 1.414 times as fast as it would at sea
level to maintain altitude.
• If something reduces the lift by half, we will
have to increase the speed so that the square
root of the new velocity is twice the square
of the original velocity.
The Four Forces of Flight
• Airfoil Shape
• It is extremely important to preserve the
characteristic curve that the designers built
into the airfoil.
• Dents, mud, and ice are three common things
that can spoil the built-in shape of the airfoil
and interfere with the performance of the
entire aircraft.
The Four Forces of Flight
• Wing Area and Lift
• The greater the surface area of the wing, the
greater the amount of lift that will be
generated.
• Gliders and sailplanes are very good
examples of how a large wing surface
generates lift.
The Four Forces of Flight
• Weight
• There is a point in the relationship of airfoil
to angle of attack where lift is destroyed and
the force of gravity (weight) takes command.
• Some of the most powerful jet fighter types
and aerobatic sport airplanes can, for a short
time and distance, climb straight up without
any significant help from their airfoils.
The Four Forces of Flight
• Weight
• There is another situation where lift can no
longer overcome weight.
• The atmosphere becomes less and less dense
as altitude increases.
• The airplane must be constructed of the
lightest weight materials that can be used.
• The weight of whatever the airplane carries
also receives very careful consideration.
The Four Forces of Flight
• Weight
• Where the weight, or useful load, is placed
in the airplane is another factor that has a
pronounced effect on how well an airplane
will fly.
The Four Forces of Flight
• Thrust and Drag
• Thrust is the force that propels the aircraft
forward.
• An airplane cannot gain altitude or maintain
straight and level flight unless its engine is
producing enough thrust.
• Without the needed thrust, weight has more
influence than lift and pulls the airplane
toward the ground.
The Four Forces of Flight
• Thrust and Drag
• Drag is present all the time and can be
defined as the force that opposes thrust.
• The friction of air particles rubbing against
all parts of the airplane causes part of the
total drag.
• The shape of something may create lowpressure areas and turbulence that retard the
forward movement of the aircraft.
Summary
1.
2.
3.
4.
5.
Theory of Flight
Airfoils and Flight
Relative Wind
Angle of Attack
The Four Forces of Flight