I built this last winter: The "Double D"

It's a cross between the tufflight 4D which is an EPP wing/spad design so it's very tough, and does insane waterfalls -- forward or back.

It has the throttles mixed into the rudder for better yaw control. Counter rotating props, twin Saito 72's. Under ideal conditions, it just sits there in a hover if the motors sync up perfectly.

Here's a vid from last January:

http://www.tufflight.com/double_d.wmv