5 Introduction to Airfoil Theory EAS 4101 S11

5 Introduction to Airfoil Theory EAS 4101 S11 - EAS 4101...

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EAS 4101, S11 University of Florida 2/7/11 1/36 Section 5, Introduction to Airfoil Theory 5 Introduction to Airfoil Theory 5.1 Background In the period 1912-1918, Ludwig Prandtl showed that the aerodynamics of wings could be split into two parts: o The study of the section of a wing – an airfoil (infinite wing, no tips) o The modification of such airfoil properties to account for the complete, finite wing We begin our discussion with an introduction to airfoils. 5.1.1 Airfoil Nomenclature Basic Definitions: o Mean Camber Line (MCL) – locus of points halfway between the upper and lower surface of airfoil. o Leading Edge (LE) – forward most point on MCL. o Trailing Edge (TE) – rearward most point on MCL. o Chord Line (CL) – straight line connecting LE and TE. o Chord ( c ) – length of chord line. o Camber – maximum distance between MCL and CL. o Thickness ( t ) – distance between the upper and lower surface of airfoil measured perpendicular to the CL.
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EAS 4101, S11 University of Florida 2/7/11 2/36 Section 5, Introduction to Airfoil Theory 1. NACA four-digit series Airfoil Notation: o The first digit is the maximum camber in hundredths of chord. o The second digit is the location of maximum camber along the chord from the LE in tenths of chord. o The last two digits give the maximum thickness in hundredths of chord. Example: NACA 2412 – maximum camber is .02 c located at .40 c from the leading edge with a maximum thickness of .12 c . Example: NACA 0012 – symmetric airfoil with 12% thickness. 5.1.2 Airfoil Characteristics Airfoil Performance o Airfoil performance is described by its l c vs. curve, where ' l L c qc is the coefficient of lift (per unit span) and is the angle of attack which is defined as the angle between c and U . Note that this differs from Bertin who uses, ll Cc . I will use Anderson’s notation of all lowercase to avoid confusion. Figure 4.4 (Anderson 2001)
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EAS 4101, S11 University of Florida 2/7/11 3/36 Section 5, Introduction to Airfoil Theory o At low to moderate angles of attack, l c varies linearly with and has a lift-curve slope of 0 a . Note that this differs from Bertin who uses, ,0 l Ca . I will use Anderson’s notation to avoid confusion. o In this linear region, flow is smooth over airfoil and flow is attached. o As increases, the flow tends to separate from the top surface of the airfoil which results in a large decrease in lift and a large increase in drag. o The maximum values of l c which occurs just prior to stall is ,max l c . ,max l c is one of the most important indicators of airfoil performance. The higher ,max l c is, the lower the stall speed is. o In summary, l c increases linearly with until flow separation begins. The curve then becomes nonlinear, l c reaches a maximum value, then the airfoil stalls.
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This note was uploaded on 09/05/2011 for the course EAS 4101 taught by Professor Sheplak during the Spring '08 term at University of Florida.

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5 Introduction to Airfoil Theory EAS 4101 S11 - EAS 4101...

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