A transport plane has a mass of 45,000 kg, a wing area of 160 m2, and an aspect ratio of 7. Assume all lift and drag due to the wing alone, with cd = 0.020 and CL, max =1.5. If the aircraft flies at 9,000 m standard altitude, make a plot of drag (in N) versus speed (from stall to 240 m/s) and determine the optimum cruise velocity (minimum drag per unit speed).

The answer to the question is

The optimum cruise velocity having minimum drag per unit speed is 130 m/s

Explanation:

Take the density of air from tables at 9000 m as =0.4661 kg/m³

W = weight = mass×acceleration due to gravity (9.81 m/s²)

We then plot our drag against speed using the formula drag as follows

For each speed V, we compute

(Each V)  ; ∞ + ; Drag =

Where AR = Aspect Ratio,   = Wing Area

For example when the speed = 60 m/s, = 3.288,   = 0.512, Drag = 68699.87 N The plot is attached

From the attached graph it is seen that speeds between 100 m/s and 200 m/s has the least drag therefore those speeds are more efficient. With the minimum occurring around 130 m/s

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