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Airfoils, Lift and Bernoulli’s Principle

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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.

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Airfoil

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Trailing Edge Leading Edge Angle of Attack

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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.

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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.

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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.

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Bernoulli’s Principle Bernoulli proved that as fluids move faster, their pressure decreases. This principle explains why a plane rises.

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Factors that Affect Lift The Object: Shape and Size The Motion: Velocity and Angle of Attack The Air: Mass, Viscosity, Compressibility

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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

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Factors that Affect Lift Motion – Move the object –Velocity (speed) –Angle of attack (how the object is tipped toward the wind)

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Factors that Affect Lift Air – Mass –Viscosity Stickiness –Compressibility Springiness –Density Altitude Density of air molecules at a given altitude

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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.

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Angles and Airfoils Angle of Incidence –The tilt of the wing with respect to its attachment to the body of the airplane (fuselage)

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Angles and Airfoils Angle of Attack –The tilt of the airfoil with respect to the airflow

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Angles and Airfoils Airflow must remain smooth –Small angle of attack; air flows smooth on the surface Tilt with respect to airflow

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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

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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

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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

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Now follow along as we prove Bernoulli’s Principle is True!

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Image Resources Aerospaceweb.org. (2009). Ask-Us – Parts of an airplane. Retrieved June 26, 2009, from Microsoft, Inc. (2008). Clip art. Retrieved June 26, 2009, from National Aeronautics and Space Administration (NASA). (n.d.). Virtual skies: Aeronautics tutorial. Retrieved June 24, 2009, from National Aeronautics and Space Administration (NASA). (n.d.). FoilSimU beta version 1.5a. Retrieved June 19, 2009, from

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