Lesson 2-2a
Principles of Flight
The Forces of Flight
How many forces are present when an aircraft is
cruising at constant speed and altitude?
Chapter 1, Lesson 2
Lift is produced almost entirely by moving air
over and under the wings
The profile of a wing is called an airfoil
Changing the airflow on the surface of the
airfoil (or wing) will increase or decrease the
amount of lift
Bernoulli’s Principle
Faster airflow causes a decrease in air pressure
Air flowing over the curved upper surface of a wing
speeds up
Increase in speed reduces pressure above the wing
and produces the upward lifting force
Can be wings or propeller blades
 Parts of airfoil Include leading and trailing
edges, camber and chord line
Wind Tunnels, cont.
The Wright Brothers tested more than 200
wing shapes in a tunnel before the successful
1902 glider
 Researchers can carefully control airflow
conditions and measure the forces on an
aircraft model
Bernoulli’s Principle in Action
 Let’s
do a quick experiment to demonstrate
Bernoulli’s Principle in action using a funnel
and a ping-pong ball
Effect of Angle of
Attack on Flight
If a plane alters pitch—the up and down movement
of the plane’s nose—the angle of attack on its wings
will change
As angle of attack increases, wings generate more
lifting force
Critical Angle of Attack
 Point
at which a plane stalls—around 15⁰
Chapter 1, Lesson 1
Reproduced from NASA/Glenn Research Center
How Lift is Generated
Air flows over top of wing reducing
pressure on top surface relative to
bottom surface of wing
Lift depends on aircraft’s shape,
size, and velocity
To increase lift:
Increase aircraft’s forward speed
Increase airfoil’s angle of attack (up to
stall angle)
Increase surface area of airfoil
Chapter 1, Lesson 2
Reproduced from NASA/Glenn Research Center
Airfoil Camber
The curve in an airfoil is the camber
In most airfoils the upper surface curves more than the
lower surface
Airfoil’s thickness is the maximum distance between the
upper and lower wing surfaces
Airfoil Types,
Purpose, and Function
Aircraft weight, speed, and
purpose determine wing’s shape
Streamlined airfoils don’t create
enough lift
Teardrop shaped airfoils have
no lift at zero angle of attack
Airfoil Types,
Purpose, and Function
 See
handout of conventional airfoils
The Fuselage
The fuselage is the aircraft body
Fuselage vary in shape to fit the mission
Fuselage must be strong enough to withstand torque
Chapter 1, Lesson 3
Courtesy of USAF/CMSgt Gary Emery
Wing Position and Parts
Wing position
depends on aircraft’s
 Main internal parts
are spars, ribs and
 Fuel tanks usually
part of wing
Chapter 1, Lesson 3
Reproduced from US Department of
Transportation/Federal Aviation Administration
Wing Angles
Dihedral angles give
aircraft roll stability and
level flight
 Large commercial
airliner wings have
dihedral angles
 Fighter aircraft have
anhedral angles
Chapter 1, Lesson 3
Modified from NASA/Glenn Research Center
The Role of Stabilizers
and Rudders
Stabilizers are on the aircraft’s tail
Stabilizers keep aircraft stable so it
can maintain straight flight path
Vertical stabilizer prevents the nose
of plane from roving side to size
Horizontal stabilizer keeps plane
from bobbing up and down
The Role of Stabilizers
and Rudders, cont.
Rudder is the hinged piece on the vertical
Lets pilot steer the aircraft by moving the tail left
or right
Elevators are the hinged flaps on the
horizontal stabilizer
Lets pilot steer the aircraft by moving the tail up or
The Positions of Flaps,
Spoilers, and Slats on Aircraft
Flaps are hinged device at
wing’s trailing edge that
produces lift
 Spoiler is small, flat plate that
attaches the tops of wings; it
increases drag
 Slat is moveable, hinged
parts that pivot down to
generate more force
Primary and Secondary Controls
Primary Controls make aircraft controllable and
safe to fly
 Rudders, elevators, and ailerons
Secondary controls let the pilot maintain more
control over aircraft’s performance
 Flaps, slats, and spoilers
Primary Flight Controls
Pilot uses primary flight controls to control aircraft
yaw, pitch, and roll
 Rudders control yaw or side-to-side motion of
 Elevators control pitch or up and down motion
of aircraft
 Ailerons control roll or banking of the wings
How Ailerons Work
Aileron is a small hinged section on the outboard portion of
each wing
Ailerons operate in opposite direction on the wings, causing
one to increase lift (point aileron down), one to decrease lift
(point aileron up)
Secondary Flight Controls
Used primarily in more challenging flight
conditions where low speeds are required
(take-off and landing)
Flaps are on trailing edge of wings and
increase/decrease lift and drag on both
wings at the same time
Slats are on the leading edge of the wings
and also increase/decrease lift and drag on
both wings at the same time
Spoilers reduce lift and increase drag and
can be used on both wings at same time or
on one wing and not the other
Spoilers are small, flat
plates that attach to the
tops of the wings with
 Raising spoilers on both
wings slows aircraft in any
phase of flight
 Raising spoilers on only
one wing causes a rolling
Airplane Parts and Functions
 Label
the airplane parts
 Define
their function in flight