Lecture on Aerodynamics

1. Lecture on Aerodynamics www.assignmentpoint.com

2. Airfoil Terminology This is some of the terminology typically associated with airfoils. Point out the listed features, and explain that the camber of an airfoil is the maximum distance between the mean or “camber line” and the chord line (in this diagram that is the horizontal line immediately below the camber line.) The amount of camber an airfoil has is important, and will be described in detail later. www.assignmentpoint.com

3. Angle of Attack The Angle of Attack is the angle that is formed between the chord line of an airfoil and the Relative Wind velocity vector. In this lab, the Relative Wind vector can be taken as being parallel to the ground (since the wind source is a fan set in a fixed position.) www.assignmentpoint.com

4. How is Lift Produced ? This is one of the most common theories about how airplanes fly – it is known as Bernoulli’s Principal. www.assignmentpoint.com

5. Air moving over the top of the wing has a higher velocity locally than the air on the bottom • The Bernoulli Principle prescribes: • Higher velocity locally = Lower pressure locally • Lower velocity locally = Higher pressure locally • The resulting pressure difference causes a force that pushes up on the wing (aka lift) www.assignmentpoint.com

6. Lift and Drag Lift is defined as a force normal to the relative wind Drag is a force parallel to the relative wind, and here is a "by-product" of producing lift www.assignmentpoint.com

7. How Angle of Attack and Camber Affect Lift Next slide….. www.assignmentpoint.com

8. This is a plot of the coefficient of lift versus the angle of attack. From the graph, it can be seen that the lift increases linearly until it reaches some maximum value, after which the airfoil “stalls” and the lift decreases drastically. This behavior is useful in determining the maximum angle at which a particular wing is capable of flying. • This plot also illustrates the behavior of a cambered airfoil. As you can see, this particular airfoil is capable of producing lift even at a zero degree angle of attack (and even at some negative angles of attack.) This is one of the main differences between cambered and un-cambered • Airfoils (other than the obvious difference in shape.) www.assignmentpoint.com

9. What About a Symmetric (no camber) Airfoil? This is a plot of a symmetric airfoil (i.e. one without camber.) As you can see, the airfoil does not produce any lift at a zero degree angle of attack. In other words, this airfoil must be set at some positive angle of attack to produce any lift. www.assignmentpoint.com

10. Bottom Line: Cambered Vs Symmetric • Cambered airfoils produced lift at zero angle of attack. • Symmetric (no camber) airfoils do not produce lift at zero angle of attack www.assignmentpoint.com

11. Sources of Drag on Airfoils • The drag that arises as a result of producing lift, called the "drag due to lift" or "induced drag" • The drag that results from friction between the air molecules and the surface of the airfoil, called "skin friction drag" • When flying near or faster than the speed of sound, the drag produced by shock waves in the flow, called "wave drag" www.assignmentpoint.com

12. What Happens to an Airfoil when it Stalls? Flow over the top surface separates from the airfoil, resulting in a high pressure wake region Next slide…. www.assignmentpoint.com

13. This is an illustration of a wing section that is operating at an angle of attack that is too high. You can see that the airflow on the top surface separates almost immediately, and begins to swirl – creating a region of relatively slow moving air. From the Bernoulli Principal, we know that this region of slow moving air corresponds to high pressure. • However, for a wing to produce lift, a low pressure region must exist on the top surface. As a result, once the airflow separates from the wing (or the wing becomes “stalled”), it will no produce any usable lift. www.assignmentpoint.com