How can I calculate the drag coefficient for a given wing design? I am building an RC plane (for the first time. I am doing it for a competition) with a twin boom configuration like this:


My wing shape is like this:



I decided that the lift should be 0.8g and I need to use this equation to find the wing area (as per the instructions)

$$F_l=\frac{1}{2}\rho v^2 S C_d$$

$F_l=0.8$

$\rho=1.225$

$v=12m/s$

Can you help me in figuring out the value of $C_d$ considering that I am using Clark Y aerofoil design? 

After that, I will measure $b$ using the aspect ratio.

$$\frac{b^2}{S}=\text{Aspect Ratio}$$

My instructor asked me to obtain a wing span of 80-100cm. So I will have to choose Aspect ratio as well.
You may visit http://airfoiltools.com/airfoil/details?airfoil=clarky-il
You can estimate the value of Cd from the plots. For different angles of attack, the Cd and Cl varies. So, you will have to select one based on your requirement.