(Solution) - The total drag on an airfoil can be estimated by -(2025 Original AI-Free Solution)

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The total drag on an airfoil can be estimated by
D = 0.01?V2 + 0.95/? (W/V)2
Friction lift
Where D = drag, ? = ratio of air density between the flight altitude and sea level, W = weight, and V = velocity. As seen in Figure.

The two factors contributing to drag are affected differently as velocity increases. Where as friction drag increases with velocity, the drag due to lift decreases. The combination of the two factors leads to a minimum drag.
(a) If ? = 0.6 and W = 16,000, determine the minimum drag and the velocity at which it occurs.
(b) In addition, develop a sensitivity analysis to determine how this optimum varies in response to a range of W = 12,000 to 20,000 with ?0.06.