An aircraft is flying in level flight at a speed of 200 km/hr through air (density, $ρ = 1.2 k g / m^{3}$ , and viscosity $μ = 1.6 \times 10^{- 5} N s / m^{2}$ ). The lift coefficient at this speed is 0.4 and the drag coefficient is 0.0065. The mass of the aircraft is 800 kg. The effective lift area of the aircraft is

21.2 m^{2}

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10.6 m^{2}

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2.2 m^{2}

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1.1 m^{2}

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Solution

The correct option is B $10.6 m^{2}$
The lift force will be equal to self weight of the aircraft for equilibrium
$F_{L} = W$
$\Rightarrow C_{L} A_{L} \frac{ρ V^{2}}{2} = m g$
$\Rightarrow \frac{0.4 \times A_{L} \times 1.2 \times {(\frac{200 \times 10^{3}}{60 \times 60})}^{2}}{2} = 800 \times 9.81$
$\Rightarrow A_{L} = 10.6 m^{2}$

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