Airfoils, Lift andBernoulli’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.

LiftBernoulli’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

Airflow must remain smooth– Small angle of

attack; air flows smooth on the surface

Tilt with respect to airflow

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 ResourcesAerospaceweb.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