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f10_sp - Fluids Lecture 10 Notes 1 Aircraft Performance...

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Fluids – Lecture 10 Notes 1. Aircraft Performance Analysis 2. Parasite Drag Estimation Reference: Hoerner,S.F., “Fluid-Dynamic Drag”, Ch 3. Aircraft Performance Analysis Drag breakdown The drag on a subsonic aircraft can be broken down as follows. D = D o + D p + D i where D o = “parasite” drag of fuselage + tail + landing gear + . . . D p = wing profile drag D i = induced drag We now use the wing airfoil drag polar c d ( c ; Re ) to give the wing profile drag, and use lifting line to give the induced drag. The nondimensional total drag coefficient is then D CDA o C 2 C D = + c d ( C L ; Re ) + L (1) 1 ρ V 2 S S π eAR 2 where the subscript on the flight speed V has been dropped. The parasite drag area CDA o will be considered later. Flight power The mechanical power P needed for constant-velocity flight is given by η p P = V ( D + W sin γ ) (2) where W is the weight, γ is the climb angle , and η p is the propulsive efficiency. If P is defined as the motor shaft power, then η p is the propeller efficiency. γ γ L D W W W sin L D V V γ In level flight, γ = 0, and the power is 1 η p P = V D = ρ V 3 S C D (3) 2 1
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The flight speed V is given by the Lift = Weight condition, together with the definition of the lift coefficient C L . 1 L = ρ V 2 S C L = W 2 2 W/S 1 / 2 V = ρ C L The ratio W/S is called the wing loading , and has the units of force/area, or pressure. The level-flight power
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