Question

Air is streaming past tye wings of an acroplane with a speed of $90m{s}^{-1}$ below and $120m{s}^{-1}$ above the surface. If the wing is $15m$ long and has an average width of $2m$, then: [Density of air $=1.2kg/m^2$]

• A. Pressure difference between the bottom the and top of he wing is $4090Pa$
• B. Up - lift on the wing is $81900N$
• C. Up - lift on the wings is $113.58kN$
• D. Pressure difference between the bottom the and top of he wing is $3780Pa$

Answer 1

Answer: (C)

Up - lift on the wings is $113.58kN$

Pressure above wing$=P_1$

Pressune below wing $=P_2$

So

$P_1+\frac{1}{2}\rho v_1^2=P_2+\frac{1}{2}\rho v_2^2$

$P_2-P_1=\frac{1}{2}\rho (v_1^2-v_2^2)$

$\Delta P=\frac{1}{2}\times 1.2\left(\right(120{)}^2-\left(90{)}^2\right)=0.6\cdot (14400-8100)$

$=37800$

$\text{Uplift}=37800\times 15\times 2$

$=113.58kN$

Answer: $\left(C\right)$