This link will help you out: http://www.wattflyer.com/forums/showthread.php?t=17914

Now, like that Leo said, you don't want ducted fans. They are used in aircraft that travel at high speeds and suck for aircraft that like to hover or fly slowly. You need to turn a large prop at a slow rpm. Think about the Osprey. It has HUGE props. So big in fact that they can't turn the engines horizontal when the plane is on the ground because the props will hit the ground.

Lastly, I don't have much experience with VTOL aircraft, but my understanding is that they are difficult to design. Remember to take it slowly and test things a lot in order to get it right and keep yourself from getting pissed and quitting.