Answer:
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
[tex]V_{stall}=\sqrt{\frac{2W}{\rho A_{p}C_{L,max} } }=\sqrt{\frac{2(45000)(9.81N)}{0.4661(160)(1.5)} } = 89 m/s[/tex]
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) [tex]C_{L}=\frac{2W}{\rho V^{2}A_{p} }[/tex] ; [tex]C_{D} = C_{D}[/tex]∞ + [tex]\frac{C^{2} _{L} }{\pi AR}[/tex] ; Drag = [tex]C_{D\frac{\rho}{2}V^{2} A_{p} }[/tex]
Where AR = Aspect Ratio, [tex]A_{p}[/tex] = Wing Area
For example when the speed = 60 m/s, [tex]C_{L}[/tex] = 3.288, [tex]C_{D}[/tex] = 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
