3241 Lecture 9

3241 Lecture 9 - MAE 3241: AERODYNAMICS AND FLIGHT...

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Unformatted text preview: MAE 3241: AERODYNAMICS AND FLIGHT MECHANICS Summary of Incompressible Flow Over Airfoils Summary of Thin Airfoil Theory Example Airfoil Calculation Mechanical and Aerospace Engineering Department Florida Institute of Technology D. R. Kirk KEY EQUATIONS FOR c l , L=0 , c m,c/4 , and x cp Within these expression we need to evaluate A , A 1 , A 2 , and dz/dx ( 29 ( 29 ( 29 ( 29 - + =- =-- = + = = 2 1 1 2 4 , 1 1 4 4 1 cos 1 2 A A c c x A A c d dx dz A A c l cp c m L l A , A 1 , and A 2 COEFFICIENTS =- = cos 2 1 d n dx dz A d dx dz A n = =- = 2 1 2 cos 2 cos 2 1 d dx dz A d dx dz A d dx dz A CENTER OF PRESSURE AND AERODYNAMIC CENTER Center of Pressure: It is that point on an airfoil (or body) about which the aerodynamic moment is zero Thin Airfoil Theory: Symmetric Airfoil: Cambered Airfoil: Aerodynamic Center: It is that point on an airfoil (or body) about which the aerodynamically generated moment is independent of angle of attack Thin Airfoil Theory: Symmetric Airfoil: Cambered Airfoil: ( 29 - + = = 2 1 1 4 4 A A c c x c x l cp cp 4 4 . . . . c x c x C A C A = = ACTUAL LOCATION OF AERODYNAMIC CENTER NACA 23012 x A.C. < 0.25c NACA 64212 x A.C. > 0.25 c x/c=0.25 x/c=0.25 EXAMPLE OF LEADING EDGE STALL NACA 4412 Airfoil (12% thickness) Linear increase in c l until stall At just below 15 streamlines are highly curved (large lift) and still attached to upper surface of airfoil At just above 15 massive flow-field separation occurs over top surface of airfoil significant loss of lift Called Leading Edge Stall Characteristic of relatively thin airfoils with thickness between about 10 and 16 percent chord EXAMPLE OF TRAILING EDGE STALL NACA 4421 (21% thickness) Progressive and gradual movement of separation from trailing edge toward leading edge as is increased Called Trailing Edge Stall THIN AIRFOIL STALL Example: Flat Plate with 2% thickness (like a NACA 0002)...
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3241 Lecture 9 - MAE 3241: AERODYNAMICS AND FLIGHT...

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