Question

An aircraft increases its speed by 2% in straight and level flight. If the total lift remains constant determine the revised CL as a percentage of its original value to three significant figure

Answer 1

Answer:

96.1%

Explanation:

We know that lift force

$F_L=\dfrac{1}{2}C_L\rho AV^2$

                                                                    ------------(1)

Where $C_L$ is the lift force coefficient .

          ρ is the density of fluid.

         A is the area.

        V is the velocity.

Now when speed is increased by 2 % and all other parameter remains constant except $C_L$ .

Let;s take new value of lift force coefficient is $C_L'$ .

$F_L=\dfrac{1}{2}C_L'\rho A(1.02V)^2$

                                                                         -----------(2)

Now from equation 1 and 2

$C_L\times V^2=C_L'\times1.0404 V^2$

⇒$C_L'=0.961C_L$

So we can say that revised value of  lift force coefficient is 96.1% of original value.