You know how much damage my 2 lb "drone" will do if it hits your thousand pound helicopter?
Yes, I do. And, even in the 4,000 pound helicopter I fly, a drone strike will absolutely take it out of the sky. The rotor wash will not move the drone out of the way. This is the second time I've heard this...
On this point, with a small to medium sized heli, BostonPilot is likely right. I know this, because I'm a responsible and experienced UAS operator, and actually did my best to figure out worst case scenarios to see what I absolutely must try to prevent happening.
My Inspire 1 can hit 60mph. The rotor wash wind velocity (in mph) for the Hughes 500 can be up to 46mph. While a Phantom 2 may be pushed out of the way by a copter that size at full wash potential (with no momentum into that direction), that does not account for a myriad of other scenarios where the P2/P3 (or as noted above, the Inspire 1) can push right into the copter or be sucked in.