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Lecture # 3 Airfoil Aerodynamics

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Aerodynamic Coefficients C l = (Lift force/unit span)/(q c) C d = (Drag force/unit span)/(q c) C m = (Pitching moment/unit span)/(q c 2 ) where q is the dynamic pressure, q = 0.5 V 2, and c is the airfoil chord

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Some Questions What is an airfoil?

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Some Questions What is an airfoil? What aerodynamic characteristics are we interested in knowing?

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Some Questions What is an airfoil? What aerodynamic characteristics are we interested in knowing? What are the geometric parameters that describe an airfoil?

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Some Questions What is an airfoil? What aerodynamic characteristics are we interested in knowing? What are the geometric parameters that describe an airfoil? What are the factors that influence the aerodynamic characteristics?

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Airfoil Geometry

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Geometric Construction of an Airfoil From NASA Sp-367 by Taly

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Airfoil Camber line Variations From NASA Sp-367 by Taly

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Lift Coefficient versus angle of attack From Introduction to Flight by Anderson

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Drag Bucket

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Influence of Airfoil Geometry on airfoil aerodynamics What are some of the geometric factors that influence the aerodynamic performance of an airfoil? –Thickness to chord ratio, t/c Location of max t/c –Nose radius –Camber Maximum camber Location of max camber

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Aerofoil Thickness What is the influence of thickness?

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Aerofoil Thickness What is the influence of thickness? Influence of t/c on lift coefficient –C lmax increases with increasing t/c up to t/c in the order of 13-15% at t/c > 15% begins to C lmax decrease.

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Aerofoil Thickness What is the influence of thickness? Influence of t/c on lift coefficient –C lmax increases with increasing t/c up to t/c in the order of 13-15% at t/c > 15% begins to C lmax decrease. Influence of t/c on drag coefficient –C dmin increases with increasing t/c

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Leading edge nose radius What is the major effect of the leading edge radius on airfoil performance?

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Leading edge nose radius What is the major effect of the leading edge radius on airfoil performance? –Effects airfoil stall characteristics Small leading edge radius has a sharp stall break Large leading edge radius has a gentle stall break

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Camber What is the influence of camber on the aerodynamic characteristics?

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Camber What is the influence of camber on the aerodynamic characteristics? Increasing camber increases zero lift angle of attack.

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Camber What is the influence of camber on the aerodynamic characteristics? Increasing camber increases zero lift angle of attack. Camber can be used to get a low drag coefficient at the designed lift coefficient.

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Camber What is the influence of camber on the aerodynamic characteristics? Increasing camber increases zero lift angle of attack. Camber can be used to get a low drag coefficient at the designed lift coefficient. The maximum lift coefficient of moderately cambered airfoil sections increase with increasing camber.

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Camber What is the influence of camber on the aerodynamic characteristics? Increasing camber increases zero lift angle of attack. Camber can be used to get a low drag coefficient at the designed lift coefficient. The maximum lift coefficient of moderately cambered airfoil sections increase with increasing camber. Camber can effect the stall behavior. –For airfoil sections that have the maximum camber far forward the stall is very abrupt

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What other factors besides geometry influence the aerodynamic characteristics?

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Aerodynamic coefficients are a function of –Geometry –Angle of attack –Reynolds number –Mach Number

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Maximum Lift Coefficient

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Minimum Drag Coefficient

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