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Midterm Exam

# Midterm Exam - Midterm Exam AEP 2640 Fall 2008 Open book...

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Midterm Exam, AEP 2640, Fall 2008 Open book and notes; time limit 90 minutes 1. (25 points) Fluid mechanics ( your numerical results are important for this problem ) In level flight an airplane is subject to 2 types of drag force. The first of these is called “parasitic drag”, which is the force required to move a solid object through a fluid. The parasitic drag accounts for viscous drag (skin friction) and form drag. The parasitic drag force is calculated with the relationship: Dp=Cd S (½ρV 2 ) (1) where Cd is the parasitic drag coefficient, S is the wing surface area, ρ is the air density, and V is the air speed. The airfoil deflects air downwards as it passes around the wing in order to produce lift. This deflection of air exerts a horizontal drag force on the wing called “induced drag”. Induced drag is given by the formula: Di=kL 2 /(½ρV 2 SπAR) (2) where k=1.1, L is the lift force, and AR is the aspect ratio: AR=b 2 /S, where b is the wing span. (3) The total drag force is the sum Dp+Di = Cd S (½ρV 2 ) + kL 2 /(½ρV 2

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