How to calculate lift and drag coeffecients for VTOL aircraft in the takeoff stage? How would I calculate CL and CD for a VTOL aircraft while it is in it's takeoff/landing stage? 

The particular aircraft is a fixed wing/quadcopter hybrid so I know that I can treat this as a thin rectangular plate problem. However, because the aircraft takes off vertically, I do not understand what formulas to use to calculate these coefficients.

If I use CL=2$\pi$$\alpha$, where $\alpha$=$\pi$/2, then I end up with CL=9.87, which just doesn't make sense.
At $\alpha$=$\pi$/2 the flat plate is perpendicular to the air stream.

CL is defined as the force perpendicular to airstream, CD as the force in direction of the air stream. When the craft takes off vertically, its CD is high and its CL is zero.

A graph and a most excellent explanation here