Airfoils, Lift and
Bernoulli’s Principle
History
• Ancient Discoveries
– Chinese and kites
– Early flight explorers Lilienthal and Cayley in
the 1800s
• Camber
– A measure of the curvature of the airfoil
• Airfoil
– a part with a flat or curved surface, such as a
wing or rudder, specifically designed to keep
an aircraft in the air.
Airfoil
Airfoil
Trailing Edge
Leading Edge
Angle
of Attack
Bernoulli’s Principle
The pressure of a fluid decreases as
the speed of the fluid increases
– The principle was first discovered in the
1700s.
– When a fluid moves quickly, its pressure
decreases.
– Since air is considered a fluid, this
principle can be applied to the design of a
wing.
Lift
Bernoulli’s Principle
– When a fluid
moves fast, its
pressure
decreases.
– Since air is
considered a fluid,
this principle can
be applied to the
design of a wing.
Bernoulli’s Principle
• Both streams must meet at the end of
the wing at the same time.
• Stream A has farther to go; therefore, it
must travel faster.
Bernoulli’s Principle
• Bernoulli proved
that as fluids
move faster,
their pressure
decreases.
• This principle
explains why a
plane rises.
Factors that Affect Lift
The Object: Shape and Size
The Motion: Velocity and Angle of Attack
The Air: Mass, Viscosity, Compressibility
Factors that Affect Lift
The Object – Wing geometry
– Airfoil shape
– Wing size
– Aspect ratio: Mathematical relationship
between the wing span (overall length) to the
wing area
Factors that Affect Lift
Motion – Move the object
– Velocity (speed)
– Angle of attack (how the object is tipped
toward the wind)
Factors that Affect Lift
Air – Mass
– Viscosity
• Stickiness
– Compressibility
• Springiness
– Density Altitude
• Density of air molecules at a given altitude
Airfoil Shapes and Lift
Wing or Airfoil?
– Airfoil is a shape
designed to generate
as much lift as
possible while
incurring as little drag
as possible.
– The wing is attached
to a plane and must
take into consideration
drag and the lift
created.
Angles and Airfoils
Angle of Incidence
– The tilt of the wing with respect to its
attachment to the body of the airplane
(fuselage)
Angles and Airfoils
Angle of Attack
– The tilt of the airfoil with respect to the airflow
Angles and Airfoils
Tilt with
respect to
airflow
Airflow must remain
smooth
– Small angle of
attack; air flows
smooth on the
surface
Angles and Airfoils
Angle of attack
becomes too steep
– Airflow is disrupted
and the airplane
loses lift or stalls
– Critical Angle of
Attack is the point
where it stalls
Angles and Airfoils
Causes of stall
– Flying at too steep an angle
– Real-life flying situations
• Sudden gust of wind decreases the plane’s
forward speed, decreasing the airflow over the
wing
• Flying too slow (indicated airspeed)
– Wing icing
• Changes the shape of the airfoil
Amount of Lift
Amount of lift produced by an airfoil
depends on may factors
– Angle of attack
– Lift devices used (flaps, etc.)
– Density of the air
– Area of the wing
– Shape of the wing
– Speed at which the wing is traveling
Now follow along as we prove
Bernoulli’s Principle is True!
Image Resources
Aerospaceweb.org. (2009). Ask-Us – Parts of an airplane. Retrieved
June 26, 2009, from
http://www.aerospaceweb.org/question/design/q0101.shtml
Microsoft, Inc. (2008). Clip art. Retrieved June 26, 2009, from
http://office.microsoft.com/en-us/clipart/default.aspx
National Aeronautics and Space Administration (NASA). (n.d.). Virtual
skies: Aeronautics tutorial. Retrieved June 24, 2009, from
http://virtualskies.arc.nasa.gov/aeronautics/tutorial/intro.html
National Aeronautics and Space Administration (NASA). (n.d.).
FoilSimU beta version 1.5a. Retrieved June 19, 2009, from
http://www.lerc.nasa.gov/WWW/K-12/aerosim/applet/vj402.html